@prefix vivo: . @prefix edm: . @prefix ns0: . @prefix dcterms: . @prefix skos: . vivo:departmentOrSchool "Applied Science, Faculty of"@en, "Mechanical Engineering, Department of"@en ; edm:dataProvider "DSpace"@en ; ns0:degreeCampus "UBCV"@en ; dcterms:creator "Karakama, Keigo"@en ; dcterms:issued "2011-12-16T18:44:40Z"@en, "2011"@en ; vivo:relatedDegree "Master of Applied Science - MASc"@en ; ns0:degreeGrantor "University of British Columbia"@en ; dcterms:description "Generation IV CANDU Supercritical Water Reactor (SCWR) is being developed to use a light water coolant at high temperature and pressure beyond the critical point of water (374⁰C and 22.1 MPa). The dramatic decrease in the solubility of magnetite in supercritical water suggests that the precipitation of magnetite particles will occur in the reactor core which can deposit on the fuel cladding or be transported to the steam turbine. A once-through flow system was modified to develop experimental techniques for studying the deposition and transport of magnetite particles in supercritical water onto stainless steel 316L. Experiments were run with temperatures ranging from 200°C to 400°C and a pressure of 23.7 MPa. A hydrothermal method for synthesizing magnetite particles was adapted for producing simulated corrosion products in which a typical run had an iron concentration of 0.005 mol/L and lasted for 40 minutes. An online monitoring technique using thermal resistance to infer deposit loadings showed deposition and removal cycles of the corrosion product on the tube wall. Scanning electron microscope images of particles on the tube inner wall and those collected by the high temperature, high pressure filters revealed magnetite particles which were several hundred nanometers to several microns in diameter depending on the precursor and condition of the system. Ultrasound and acid wash cleaning methods were used to remove deposits from the test section for determining deposit thickness and adhesive strength. The strength of deposit adhesion was observed to increase along the tube, particularly under supercritical conditions suggesting precipitation of dissolved species may enhance the strength of the deposit. By comparing the results, a comprehensive approach was developed to study magnetite fouling in supercritical water conditions. Finally, comparison between a simulation model based on mass transport equations and experimental deposition suggests that mass transport alone can overestimate the deposition thickness when surface attachment and removal are significant as they were for many experiments in this study. The simulation predicted as an upper limit scenario that fouling in a CANDU SCWR could increase the fuel cladding temperature at certain locations by up to 23.9⁰C after one year of operation."@en ; edm:aggregatedCHO "https://circle.library.ubc.ca/rest/handle/2429/39772?expand=metadata"@en ; skos:note " Methods for the Characterization of Deposition and Transport of Magnetite Particles in Supercritical Water by Keigo Karakama B.A.Sc., The University of British Columbia, 2009 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES (Mechanical Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) December 2011 © Keigo Karakama, 2011 ii Abstract Generation IV CANDU Supercritical Water Reactor (SCWR) is being developed to use a light water coolant at high temperature and pressure beyond the critical point of water (374⁰C and 22.1 MPa). The dramatic decrease in the solubility of magnetite in supercritical water suggests that the precipitation of magnetite particles will occur in the reactor core which can deposit on the fuel cladding or be transported to the steam turbine. A once-through flow system was modified to develop experimental techniques for studying the deposition and transport of magnetite particles in supercritical water onto stainless steel 316L. Experiments were run with temperatures ranging from 200°C to 400°C and a pressure of 23.7 MPa. A hydrothermal method for synthesizing magnetite particles was adapted for producing simulated corrosion products in which a typical run had an iron concentration of 0.005 mol/L and lasted for 40 minutes. An online monitoring technique using thermal resistance to infer deposit loadings showed deposition and removal cycles of the corrosion product on the tube wall. Scanning electron microscope images of particles on the tube inner wall and those collected by the high temperature, high pressure filters revealed magnetite particles which were several hundred nanometers to several microns in diameter depending on the precursor and condition of the system. Ultrasound and acid wash cleaning methods were used to remove deposits from the test section for determining deposit thickness and adhesive strength. The strength of deposit adhesion was observed to increase along the tube, particularly under supercritical conditions suggesting precipitation of dissolved species may enhance the strength of the deposit. By iii comparing the results, a comprehensive approach was developed to study magnetite fouling in supercritical water conditions. Finally, comparison between a simulation model based on mass transport equations and experimental deposition suggests that mass transport alone can overestimate the deposition thickness when surface attachment and removal are significant as they were for many experiments in this study. The simulation predicted as an upper limit scenario that fouling in a CANDU SCWR could increase the fuel cladding temperature at certain locations by up to 23.9⁰C after one year of operation. iv Preface Chapter 5 is based on experimental work conducted at the mechanical engineering laboratories by the author, Keigo Karakama. Thermocouple temperature measurements and its analysis were done by the author. All Atomic absorption spectroscopy analysis, scanning electron microscopy images and energy dispersive x-ray analysis was completed by the author at the Materials Engineering Laboratories. X-ray diffraction data and analysis in Chapter 5 was produced by Anita Lam in the Chemistry Department. v Table of Contents Abstract ..................................................................................................................................... ii Preface...................................................................................................................................... iv Table of Contents ...................................................................................................................... v List of Tables ......................................................................................................................... viii List of Figures .......................................................................................................................... ix List of Symbols and Abbreviations......................................................................................... xv Acknowledgements ............................................................................................................... xvii 1 Introduction ....................................................................................................................... 1 1.1 Supercritical Water ..................................................................................................... 1 1.2 Systems using Supercritical Water Medium .............................................................. 3 1.3 Scope and Objectives ................................................................................................. 3 2 Literature Review.............................................................................................................. 6 2.1 Applications of Supercritical Water ........................................................................... 6 2.1.1 Supercritical Fossil-fueled Power Plants ............................................................ 6 2.1.2 Supercritical Water Oxidation ............................................................................ 8 2.1.3 Nuclear Energy and the Generation IV Nuclear Reactors .................................. 8 2.1.4 CANDU Supercritical Water Reactors ............................................................. 10 2.2 Materials for SCWR ................................................................................................. 11 2.3 Corrosion and Fouling in Subcritical and Supercritical Water ................................ 13 2.3.1 Properties of Magnetite ..................................................................................... 13 2.3.2 Magnetite and its Solubility in High Temperature and Pressure Water ........... 15 2.3.3 Corrosion........................................................................................................... 17 2.3.4 Fouling .............................................................................................................. 18 2.3.5 Corrosion Product Removal and Transport ...................................................... 22 3 Heat Transfer and Deposition Modeling ......................................................................... 25 3.1 Overview .................................................................................................................. 25 3.2 Heat Transfer Calculations of Water ........................................................................ 25 3.2.1 Enthalpy of Fluid in the Test Section ............................................................... 25 3.2.2 Heat Transfer Coefficient in Supercritical Water ............................................. 26 vi 3.2.3 Temperature of the Oxide Layer ....................................................................... 28 3.2.4 Temperature of the Outside Wall Temperature ................................................ 28 3.2.5 Buoyancy Calculations ..................................................................................... 29 3.3 Deposition Calculations ........................................................................................... 31 3.4 CANDU Supercritical Water Reactor Simulation ................................................... 38 4 Experiments .................................................................................................................... 41 4.1 Supercritical Water Once-through Flow Apparatus ................................................. 41 4.2 Flow and Temperature Control ................................................................................ 44 4.2.1 Safety ................................................................................................................ 44 4.2.2 Pressure Measurements ..................................................................................... 45 4.2.3 Flow Rate Measurements .................................................................................. 45 4.2.4 Fluid Conductivity Measurements .................................................................... 46 4.2.5 Dissolved Oxygen Concentration Measurements ............................................. 46 4.3 Particle Synthesis for Modeling Power Plant Fouling ............................................. 46 4.4 Experimental Procedure ........................................................................................... 48 4.4.1 Experiments with Precursor .............................................................................. 48 4.4.2 Experiments with Magnetite Particles .............................................................. 50 4.4.3 Post Experiment Cleaning................................................................................. 51 4.5 Analytical Methods .................................................................................................. 51 4.5.1 Online Thermal Resistance Monitoring ............................................................ 51 4.5.2 SEM Imaging for Filters and Tube Deposits .................................................... 59 4.5.3 Particulate Filtering System .............................................................................. 60 4.5.4 Deposit Thickness and Strength of Oxide Adhesion ........................................ 67 5 Results and Discussion of Experiments .......................................................................... 69 5.1 Reference Condition ................................................................................................. 70 5.1.1 Temperature Analysis ....................................................................................... 70 5.1.2 Filter Analysis ................................................................................................... 72 5.1.3 Deposit Analysis ............................................................................................... 73 5.2 Effect of Heat Flux ................................................................................................... 80 5.2.1 Temperature Analysis ....................................................................................... 80 5.2.2 Filter Analysis ................................................................................................... 80 vii 5.2.3 Deposit Analysis ............................................................................................... 84 5.3 High pH Conditions ................................................................................................. 87 5.3.1 Temperature Analysis ....................................................................................... 89 5.3.2 Filter Analysis ................................................................................................... 91 5.3.3 Deposit Analysis ............................................................................................... 93 5.4 Low Concentration and Blank Experiment .............................................................. 95 5.5 Overall Summary and Mass Balance ....................................................................... 95 6 Results and Discussion of Simulations ......................................................................... 100 6.1 Comparison between Simulation and Experimental .............................................. 100 6.2 Simulation for CANDU SCWR ............................................................................. 103 6.3 Limitations of the Simulation ................................................................................. 107 7 Conclusion .................................................................................................................... 109 8 Recommendations ......................................................................................................... 112 References ............................................................................................................................. 113 Appendix A: MATLAB Code .............................................................................................. 120 Appendix B: Filter Parts Drawings ....................................................................................... 131 Appendix C: Results of Experiments .................................................................................... 133 Reference Condition, Ferrous Chloride .............................................................. 133 C. 1. Reference Condition, Ferrous Sulfate ................................................................ 138 C. 2. Low Heat Flux, Ferrous Chloride ....................................................................... 143 C. 3. Low Heat Flux, Ferrous Sulfate ......................................................................... 148 C. 4. No Heat Flux, Ferrous Sulfate ............................................................................ 153 C. 5. High pH, Ferrous Sulfate .................................................................................... 158 C. 6. High pH & Subcritical, Ferrous Sulfate ............................................................. 163 C. 7. Low Concentration, Ferrous Chloride ................................................................ 166 C. 8. Blank Run ........................................................................................................... 169 C. 9. Appendix D: Filter Flow Rates ............................................................................................. 172 Appendix E: Atomic Absorption Spectroscopy .................................................................... 173 viii List of Tables Table 2-1: Generation IV systems and expected deployment year........................................... 9 Table 2-2: Stainless steel AISI 316L composition (American Society for Metals, 1985) ..... 12 Table 3-1: SCWR and fuel assembly design parameters ........................................................ 39 Table 4-1: Input power comparison ........................................................................................ 55 Table 4-2: Glass and silver membrane filter comparison ....................................................... 63 Table 5-1: Summary of experiments ....................................................................................... 69 Table 5-2: Results summary table - Part I .............................................................................. 96 Table 5-3: Results summary table - Part II ............................................................................. 97 Table 5-4: Mass balance of experiments #1 - 8 ...................................................................... 99 Table C-1: Summary table of experiment #1 ........................................................................ 133 Table C-2: Summary table of experiment #2 ........................................................................ 138 Table C-3: Summary table of experiment #3 ........................................................................ 143 Table C-4: Summary table of experiment #4 ........................................................................ 148 Table C-5: Summary table of experiment #5 ........................................................................ 153 Table C-6: Summary table of experiment #6 ........................................................................ 158 Table C-7: Summary table of experiment #7 ........................................................................ 163 Table C-8: Summary table of experiment #8 ........................................................................ 166 Table C-9: Summary table of blank run ............................................................................... 169 Table D-1: Flow rate through filter ....................................................................................... 172 ix List of Figures Figure 1-1: Pressure - temperature diagram for water, grey region indicating supercritical conditions. ............................................................................................................ 1 Figure 1-2: Density of water vs. temperature at various pressures, showing the effects of pressure on the pseudocritical temperature ......................................................... 2 Figure 2-1: Simplified drawing of a direct cycle coolant for Generation IV CANDU SCWR ........................................................................................................................... 11 Figure 2-2: Pourbaix diagram (a) Fe – H2O at 25ºC and 1 atm, (b) Fe – H2O at 374°C and 220 atm (c) Fe/Cr – H2O at 25°C and 1 atm, (d) Fe/Cr – H2O at 374ºC and 220 atm. Based on SUPCRT92 (Propp et al., 1996) ............................................... 14 Figure 2-3: Magnetite solubility adapted from Cook and Fatoux (2009) for neutral pH water at 25 MPa, Guzonas et al. (2009) for pH = 9.3 at 30 MPa, Burrill (2000) for neutral pH at 25 MPa, and Sweeton and Baes Jr. (1970) experimental results. 16 Figure 3-1: Calculation of Grq/Grth for determination of the effects of buoyancy along the test section using Bazargan et al. (2005) ........................................................... 31 Figure 3-2: Effect of particle diameter and fluid temperature on deposition velocity for experimental apparatus ...................................................................................... 38 Figure 3-3: Cross-sectional view of CANFLEX 43 rod fuel bundle and drawing of equivalent tube for simulation calculations (not to scale) ................................. 40 Figure 4-1: SCW system used in all experiments located in the Mechanical Engineering laboratories. ....................................................................................................... 41 Figure 4-2: Schematic of supercritical once-through flow apparatus................................... 42 Figure 4-3: Mounting block and test section inlet ................................................................ 54 Figure 4-4: Electrical wiring, heater controls and location of surface welded thermocouples and bulk fluid thermocouples ............................................................................ 57 Figure 4-5: Saturation temperature of 231.51ºC at 417psi, calibration for Experiment #1 . 58 Figure 4-6: Temperature of test section, calculated vs. calibrated thermocouples............... 58 Figure 4-7: Test section sample for SEM analysis ............................................................... 60 Figure 4-8: SS316L LTHP filter installed after the heat exchanger ..................................... 61 Figure 4-9: HTHP filter with silver membrane and SS304 back support ............................ 62 Figure 4-10: Glass fiber membrane and Swin-Lok LTLP filter holder .................................. 63 Figure 4-11: SEM photograph of clean silver membrane, 0.2µm pore size, using a Hitachi S3000N SEM ..................................................................................................... 65 Figure 4-12: EDX of silver membrane to determine elemental composition of background 65 Figure 4-13: SEM photograph of clean glass fiber filter, 0.7µm pore size, a Hitachi S2300 SEM ................................................................................................................... 66 Figure 4-14: EDX of glass fiber filter to determine elemental composition of background .. 66 Figure 5-1: Temperature measurements of test section vs. time for reference condition with ferrous chloride precursor (Experiment #1) ...................................................... 71 x Figure 5-2: SEM photograph of magnetite deposit on test section tube surface, 0.15 m location. Reference condition with ferrous chloride precursor (Experiment #1) ........................................................................................................................... 73 Figure 5-3: SEM photograph of magnetite deposit on test section tube surface, 0.60 m location. Reference condition with ferrous chloride precursor (Experiment #1) ........................................................................................................................... 74 Figure 5-4: SEM photograph of magnetite deposit on test section tube surface, 1.20 m location. Reference condition with ferrous chloride precursor (Experiment #1) ........................................................................................................................... 74 Figure 5-5: SEM photograph of magnetite deposit on test section tube surface, 1.65 m location. Reference condition with ferrous chloride precursor (Experiment #1) ........................................................................................................................... 75 Figure 5-6: XRD of tube deposits of test section, reference condition ferrous chloride precursor (Experment #1) .................................................................................. 76 Figure 5-7: XRD of tube deposit of test section, reference condition ferrous sulfate precursor (Experiment #2) ................................................................................. 76 Figure 5-8: Deposit thickness on test section for reference condition with ferrous chloride precursor (Experiment #1) ................................................................................. 79 Figure 5-9: Deposit thickness on test section for reference condition with ferrous sulfate precursor (Experiment #2) ................................................................................. 79 Figure 5-10: SEM photograph of particles collected on HTHP filter, 5.0k magnification, for low heat flux with ferrous chloride precursor (Experiment #3) ........................ 81 Figure 5-11: EDX of HTHP filter for low heat flux with ferrous chloride precursor ............ 81 Figure 5-12: SEM photograph of particles collected on HTHP filter, 5.0k magnification, for low heat flux with ferrous sulfate precursor (Experiment #4) ........................... 82 Figure 5-13: SEM photograph of particles collected on HTHP filter, 5.0k magnification, for no heat flux with ferrous chloride (Experiment #5) .......................................... 82 Figure 5-14: XRD of deposit on HTHP filter for low heat flux with ferrous chloride precursor (Experiment #3) ................................................................................. 83 Figure 5-15: Deposit thickness on test section, low heat flux with ferrous sulfate precursor (Experiment #4) ................................................................................................. 84 Figure 5-16: Calibration of the conductivity meter for determining NaOH concentration in primary tank ....................................................................................................... 88 Figure 5-17: Predicted pH of the system using data from Arden (1950).............................. 89 Figure 5-18: Temperature measurements of test section vs. time for high pH with ferrous sulfate precursor (Experiment #6). Power turned off briefly at t = 48 minutes. 90 Figure 5-19: SEM photograph of particles collected on HTHP filter, 10.0k magnification, for high pH, ferrous sulfate (Experiment #6) .......................................................... 91 Figure 5-20: SEM photograph of particles collected on LTHP filter, 2.0k magnification, for high pH, ferrous sulfate (Experiment #6) .......................................................... 92 xi Figure 5-21: SEM photograph of particles collected on HTHP filter, 5.0k magnification, for high pH, subcritical, ferrous sulfate (Experiment #7) ....................................... 92 Figure 5-22: SEM photograph of particles collected on LTHP filter, 2.0k magnification, for high pH, subcritical, ferrous sulfate (Experiment #7) ....................................... 93 Figure 5-23: Deposit thickness on test section (Experiment #6) ............................................ 94 Figure 6-1: Comparison between simulation and experimental for reference conditions (a) Experiment #1, ferrous chloride with average particle size = 4 µm, magnetite concentration = 200 mg/L (b) Experiment #2, ferrous sulfate with average particle size = 1 µm, magnetite concentration = 299 mg/L. ............................ 100 Figure 6-2: Comparison between simulation and experimental for ferrous sulfate experiments with (a) Experiment #4, low heat flux with average particle size = 1 µm, magnetite concentration = 108 mg/L and (b) Experiment #5, no heat flux with average particle size = 2 µm, magnetite concentration = 89 mg/L. ........ 101 Figure 6-3: Comparison between simulation and experimental for Experiment #6, high pH, ferrous sulfate. Simulation was run with an average particle size = 0.15µm, magnetite concentration = 321 mg/L. .............................................................. 102 Figure 6-4: Bulk fluid and fuel cladding-surface temperature without particle deposition 104 Figure 6-5: Bulk fluid and fuel cladding-surface temperature after 1 year of operation with magnetite particles of 150 nm diameter .......................................................... 104 Figure 6-6: Magnetite deposition thickness on fuel cladding after 1 year of operation for 150 nm and 1 µm average particle diameters .................................................. 105 Figure C-1: Temperature measurements of test section vs. time for reference condition with ferrous chloride precursor. (Experiment #1) ................................................... 134 Figure C-2: SEM photograph of particles collected on HTHP filter, 2.0k magnification, for reference condition with ferrous chloride precursor. Low flow rate in secondary line resulting in very few particles collected. (Experiment #1) ....................... 134 Figure C-3: SEM photograph of particles collected on LTHP filter, 1.8k magnification, for reference condition with ferrous chloride precursor. (Experiment #1) ........... 135 Figure C-4: SEM photograph of particles collected on LTLP filter, 2.0k magnification, for reference condition with ferrous chloride precursor. Low flow rate in secondary line resulting in very few particles collected. (Experiment #1) ....................... 135 Figure C-5: SEM photograph of magnetite deposit on test section tube surface, (a) 0.15 m, (b) 0.60 m, (c) 1.20 m, and (d) 1.65 m location. (Experiment #1) .................. 136 Figure C-6: Deposit thickness on test section for reference condition with ferrous chloride precursor. (Experiment #1) .............................................................................. 137 Figure C-7: Comparison between simulation and experimental for reference condition ferrous chloride. Simulation was run with an average particle size = 4 µm, magnetite concentration = 200 mg/L. .............................................................. 137 xii Figure C-8: Temperature measurements of test section vs. time, temperature fluctuations were found in both the inlet and outlet bulk temperatures which may be attributed to the inconsistent flow. (Experiment #2) ....................................... 139 Figure C-9: SEM photograph of particles collected on HTHP filter, 2.0k magnification, for reference condition with ferrous sulfate. (Experiment #2) .............................. 139 Figure C-10: SEM photograph of particles collected on LTHP filter, 2.0k magnification, for reference condition with ferrous sulfate. (Experiment #2) .............................. 140 Figure C-11: SEM photograph of particles collected on LTLP filter, 2.0k magnification, for reference condition with ferrous sulfate. (Experiment #2) .............................. 140 Figure C-12: SEM photograph of magnetite deposit on test section tube surface, (a) 0.15 m, (b) 0.60 m, (c) 1.20 m, and (d) 1.65 m location. (Experiment #2) .................. 141 Figure C-13: Deposit thickness on test section for reference condition with ferrous sulfate precursor. (Experiment #2) .............................................................................. 142 Figure C-14: Comparison between simulation and experimental for reference condition ferrous sulfate. Simulation was run with an average particle size = 1 µm, magnetite concentration = 190 mg/L. .............................................................. 142 Figure C-15: Temperature measurements of test section vs. time for low heat flux ferrous chloride precursor. (Experiment #3) ................................................................ 144 Figure C-16: SEM photograph of particles collected on HTHP filter, 2.0k magnification, for low heat flux with ferrous chloride precursor. (Experiment #3) ..................... 144 Figure C-17: SEM photograph of particles collected on LTHP filter, 2.0k magnification, for low heat flux with ferrous chloride precursor. (Experiment #3) ..................... 145 Figure C-18: SEM photograph of particles collected on LTLP filter, - magnification, for low heat flux with ferrous chloride precursor. (Experiment #3) ............................ 145 Figure C-19: SEM photograph of magnetite deposit on test section tube surface, (a) 0.10 m, (b) 0.30 m, and (c) 0.90 m location. (Experiment #3) ..................................... 146 Figure C-20: Deposit thickness on test section for low heat flux ferrous chloride precursor. (Experiment #3) ............................................................................................... 147 Figure C-21: Temperature measurements of test section vs. time for low heat flux with ferrous sulfate precursor. (Experiment #4) ...................................................... 149 Figure C-22: SEM photograph of particles collected on HTHP filter, 2.0k magnification, for low heat flux ferrous sulfate precursor (Experiment #4) ................................. 149 Figure C-23: SEM photograph of particles collected on LTHP filter, 2.0k magnification, for low heat flux ferrous sulfate precursor. (Experiment #4) ................................ 150 Figure C-24: SEM photograph of particles collected on LTLP filter, 2.0k magnification, for low heat flux ferrous sulfate precursor. (Experiment #4) ................................ 150 Figure C-25: SEM photograph of magnetite deposit on test section tube surface, (a) 0.15 m, (b) 0.60 m, (c) 1.20 m, and (d) 1.65 m location. (Experiment #4) .................. 151 Figure C-26: Deposit thickness on test section for low heat flux ferrous sulfate precursor. (Experiment #4) ............................................................................................... 152 xiii Figure C-27: Comparison between simulation and experimental for low heat flux, ferrous sulfate. Simulation was run with an average particle size = 1 µm, magnetite concentration = 108 mg/L. ............................................................................... 152 Figure C-28: Temperature measurements of test section vs. time for no heat flux with ferrous sulfate precursor. (Experiment #5) .................................................................. 154 Figure C-29: SEM photograph of particles collected on HTHP filter, 2.0k magnification, for no heat flux with ferrous sulfate precursor. (Experiment #5) .......................... 154 Figure C-30: SEM photograph of particles collected on LTHP filter, 2.0k magnification, for no heat flux with ferrous sulfate precursor. (Experiment #5) .......................... 155 Figure C-31: SEM photograph of particles collected on LTLP filter, 2.0k magnification, for no heat flux with ferrous sulfate precursor. (Experiment #5) .......................... 155 Figure C-32: SEM photograph of magnetite deposit on test section tube surface, (a) 0.15 m, (b) 0.60 m, (c) 1.20 m, and (d) 1.65 m location. (Experiment #5) .................. 156 Figure C-33: Deposit thickness on test section for no heat flux with ferrous sulfate precursor. (Experiment #5) ............................................................................................... 157 Figure C-34: Comparison between simulation and experimental for no heat flux with ferrous sulfate precursor. Simulation was run with an average particle size = 2 µm, magnetite concentration = 89 mg/L. ................................................................ 157 Figure C-35: Temperature measurements of test section vs. time for high pH with ferrous sulfate precursor. (Experiment #6) .................................................................. 159 Figure C-36: SEM photograph of particles collected on HTHP filter, 2.0k magnification, for high pH with ferrous sulfate precursor. (Experiment #6) ................................ 159 Figure C-37: SEM photograph of particles collected on LTHP filter, 2.0k magnification, for high pH with ferrous sulfate precursor. (Experiment #6) ................................ 160 Figure C-38: SEM photograph of particles collected on LTLP filter, 2.0k magnification, for high pH with ferrous sulfate precursor. (Experiment #6) ................................ 160 Figure C-39: SEM photograph of magnetite deposit on test section tube surface, (a) 0.15 m, (b) 0.60 m, (c) 1.20 m, and (d) 1.65 m location. (Experiment #6) .................. 161 Figure C-40:Deposit thickness on test section for high pH with ferrous sulfate precursor. (Experiment #6) ............................................................................................... 162 Figure C-41: Comparison between simulation and experimental for high pH, ferrous sulfate. Simulation was run with an average particle size 0.15 µm, magnetite concentration = 321 mg/L. ............................................................................... 162 Figure C-42: Temperature measurements of test section vs. time for high pH & subcritical with ferrous sulfate precursor. (Experiment #7) .............................................. 164 Figure C-43: SEM photograph of particles collected on HTHP filter, 2.0k magnification, for high pH & subcritical with ferrous sulfate precursor. (Experiment #7) .......... 164 Figure C-44: SEM photograph of particles collected on LTHP filter, 2.0k magnification, for high pH & subcritical with ferrous sulfate precursor. (Experiment #7) .......... 165 xiv Figure C-45: SEM photograph of particles collected on LTLP filter, 2.0k magnification, for high pH & subcritical with ferrous sulfate precursor. (Experiment #7) .......... 165 Figure C-46: Temperature measurements of test section vs. time for low concentration with ferrous chloride precursor. (Experiment #8) ................................................... 167 Figure C-47: SEM photograph of particles collected on HTHP filter, 2.0k magnification, for low concentration with ferrous chloride precursor. (Experiment #8).............. 167 Figure C-48: SEM photograph of particles collected on LTHP filter, 2.0k magnification, for low concentration with ferrous chloride precursor. (Experiment #8).............. 168 Figure C-49: SEM photograph of particles collected on LTLP filter, 2.0k magnification, for low concentration with ferrous chloride precursor. (Experiment #8).............. 168 Figure C-50: Temperature measurements of test section vs. time for high pH & subcritical with ferrous sulfate precursor. (Experiment #9) .............................................. 170 Figure C-51: SEM photograph of particles collected on HTHP filter, 2.0k magnification, blank run. (Experiment #9) .............................................................................. 170 Figure C-52: SEM photograph of particles collected on LTHP filter, 5.0k magnification, blank run. (Experiment #9) .............................................................................. 171 Figure C-53: SEM photograph of particles collected on LTLP filter, 2.0k magnification, blank run. (Experiment #9) .............................................................................. 171 Figure E-1: Calibration curve for iron concentration using AAS, nitric acid matrix ......... 173 Figure E-2: Calibration curve for iron concentration using AAS, nitric acid and copper sulfate matrix ................................................................................................... 174 xv List of Symbols and Abbreviations AAS Atomic Absorption Spectroscopy AECL Atomic Energy of Canada Limited CANDU Canadian Deuterium Uranium Cb Concentration of magnetite in bulk fluid cp Heat capacity [kJ/kg·K] Csat Saturation concentration of magnetite dp Particle diameter [m] f Friction factor Gr Grashoff number H1 Enthalpy [kJ/kg] H2 Enthalpy [kJ/kg] HKF Helgeson-Kirkham-Flowers HTHP High temperature high pressure Ka Surface attachment deposition velocity [m/s] Kd Effective deposition velocity [m/s] Kt Mass transport deposition velocity [m/s] LTHP Low temperature high pressure LTLP Low temperature low pressure Nu Nusselt number ̇ Mass flow rate [kg/s] Pr Prandtl number q Heat input per meter [kW/m] Re Reynolds number Sc Schmidt number xvi SCWO Supercritical Water Oxidation SCWR Supercritical Water Reactor SEM Scanning Electron Microscope SPE Solid Particle Erosion Tb Bulk fluid temperature [ºC] Te Temperature of outer wall [ºC] tp + Dimensionless particle relaxation time Tw Wall temperature [ºC] U* Frictional velocity µ Dynamic viscosity [Pa·s] XRD X-ray Diffraction Δx Interval length [m] ε Tube roughness ρf Density of fluid [kg/m 3 ] ρp Density of particle [kg/m 3 ] τw Wall shear stress d Overall deposition velocity [m/s] xvii Acknowledgements First and foremost I would like to thank my supervisors, Dr. Steven Rogak and Dr. Akram Alfantazi for their invaluable insight and guidance into making this thesis possible. I would also like to express my gratitude to Dr. Edouard Asselin whose advice gave further direction to this thesis. Furthermore, I would like to thank NSERC and AECL for their financial support in this research. I would like to thank Andrej Boskovics for his help on the construction of the electrical heaters and flow loop. Additionally, I would like to thank my lab colleagues, Tirdad Nickchi, Hamid Zebardast, Hugo Tjong, Arka Soewono, Mohammad Taghavi, and Kamran Alba for their help, advice and support. Also, many thanks to the technicians who were incredibly helpful and patient in teaching me the operation and analysis of the equipment: Dr. Berend Wassink on atomic absorption spectroscopy, Jacob Kabel on the scanning electron microscope, Anita Lam for X-ray diffraction analysis, the mechanical machine shop for their assistance in machining components, the electronics shop for their advice on the electrical heater and controls, and Perry Yabuno for always making sure that parts were ordered and received as soon as possible. Finally, I would like to thank all my friends and family who provided moral support throughout the entire journey. 1 1 Introduction 1.1 Supercritical Water Supercritical water (SCW) refers to water above the critical point of 374⁰C and 22.1 MPa. Above this temperature and pressure, water exists only as a single phase fluid with very unique thermodynamic and fluid properties (Weingartner & Franck, 2005). Figure 1-1: Pressure - temperature diagram for water, grey region indicating supercritical conditions. Viscosity, density, and dissolution of non-polar and polar species can change dramatically from subcritical to supercritical conditions. At subcritical temperatures, water is highly polar and is an excellent solvent for other polar substances such as inorganic salts. On the other hand, organic species are generally non-polar and therefore are usually not soluble in subcritical water. In supercritical conditions, the characteristics described above are reversed Temperature P re s s u re Supercritical water 374ºC 22.1MPa Vapor Liquid Solid 2 and non-polar organic species and gases become significantly soluble, while ionic species become almost completely insoluble (Kritzer, 2004; Zhang et al., 2009). While the critical temperature gives the threshold temperature for achieving supercritical conditions, when describing the temperature at which thermodynamic changes occur, it is often times more useful to describe the transition using the “pseudocritical” temperature. The pseudocritical temperature is the temperature at which fluid thermal expansion is at its maximum for any given supercritical pressure. This temperature increases as the pressure increases as shown in Figure 1-2. Other parameters such as heat capacity and ionic product of water are also affected by pressure and its transition also shifts to higher temperature as pressure is increased (Kritzer, 2004). Figure 1-2: Density of water vs. temperature at various pressures, showing the effects of pressure on the pseudocritical temperature 3 1.2 Systems using Supercritical Water Medium Supercritical water has been a crucial medium in numerous industrial and research applications for its interesting properties. Large variations in fluid and thermal properties near the critical point offers an opportunity to fine tune fast chemical reactions with only small adjustments in pressure and temperature (Kritzer, 2004). The special properties of supercritical water as an excellent solvent for organic material have led to the technology of supercritical water oxidation systems (Shaw et al., 1991) while the excellent heat transport characteristics have led to power plants operating at higher temperature and pressure. Material degradation has been a major limiting factor, however, new technology in materials in the last few decades have allowed coal-fired power plants to operate in supercritical conditions (Viswanathan et al., 2005). Finally, the need for cleaner and more efficient energy has recently prompted research into supercritical water reactors (SCWR) for nuclear power plants. Despite the operational experience with supercritical water in various applications, corrosion and fouling in this medium remains a significant challenge. 1.3 Scope and Objectives Both the UBC Mechanical and Materials Engineering departments are collaborating with AECL in the development of monitoring techniques for corrosion and fouling in supercritical water. The primary application for the technology is for the CANDU supercritical water reactors, however, the scope of this research can be applied for many similar systems such as supercritical fossil-fueled and supercritical light water reactors. The purpose of this particular study is to explore the deposition and transport characteristics of magnetite formed in supercritical water with several experimental techniques and simulation models. 4 Experimental investigations were conducted to examine four techniques for measuring and monitoring fouling and transport of magnetite in supercritical water. These experiments were focused on determining the effects of heat flux, temperature and pH on the particle size, deposition rate, and adhesive strength of particle to the wall. A once-through flow loop was modified to conduct experiments of magnetite deposition in conditions which attempted to replicate SCWR conditions. A hydrothermal method for synthesizing iron oxide particles in supercritical water was adapted for producing simulated magnetite corrosion particles. Experimental procedures and description of the apparatus can be found in Chapter 4. A high-current, electrically-heated test section with temperature control and tube-wall temperature measurements was constructed by the author for this study to measure fouling and removal rates. High and low temperature filters were also fabricated and installed after the test section to collect particles in each experiment. These filters were analyzed using Scanning Electron Microscopy (SEM) to provide insight into the effects of pH on the magnetite particle size and structure produced in supercritical water. In addition, deposition morphology and thickness was determined using SEM and Atomic Absorption Spectroscopy (AAS). A novel, two-step cleaning procedure was developed for qualitatively determining the bond strength of the magnetite deposit. A heat and mass transfer model was created to compare simulations with experimental deposition thicknesses to determine if a mass transport limited model can accurately predict deposition of magnetite particles in supercritical water. Due to the lack of experimental data on the deposition mechanism of magnetite particles in supercritical water, deposition was 5 assumed to be mass transport limited. Simulations were also run to quantify the deposition of magnetite onto a CANDU nuclear reactor for one year. The results and its implications on a SCWR are presented in Chapter 6. Finally the conclusions and recommendations for future work are summarized in Chapters 7 and 8 respectively. 6 2 Literature Review 2.1 Applications of Supercritical Water 2.1.1 Supercritical Fossil-fueled Power Plants The thermal efficiency of fossil-fueled power plants has increased over the past century by operating steam at higher pressure and temperature, and thereby increasing the thermodynamic efficiency (Masuyama, 2001). In the 1920’s, the pressure and temperature was limited to 4 MPa and 370°C due to the mechanical properties of carbon steel. However, technological improvements in materials such as the development of nickel-based alloys and high temperature resistant steels have allowed coal-fired power plants to operate as high as 24 MPa and 600°C. With nearly two dozen power plants worldwide currently operating at 580 – 600°C and 24 – 25 MPa, there is considerable operational experience with supercritical water in power generation (Viswanathan et al., 2005). These experiences with supercritical fossil-fueled power plants can provide invaluable insight into possible operational issues for a nuclear SCWR. Studies on the scaling of austenitic steels in supercritical fossil-fueled power plants show a duplex oxide structure in which the outer layer is likely to exfoliate compared to an inner layer of chromium and nickel oxide which almost never exfoliates. Once the scale thickness reaches approximately 100 – 200 µm, oxides on austenitic steel begin to exfoliate due to the differences in thermal expansion between the tube surface and the outer oxide layer, especially during startup and stop time of the boiler (Masuyama, 2001). It was also found that fine-grained steels and high-Cr steels had very slow oxide growth with very little 7 exfoliation. In general, chromium content above 20% was effective at preventing steam oxide buildup. Tube plugging due to exfoliated material buildup can cause overheating in the portion of the tube, resulting in creep rupture of the piping when the pressure due to the fouling buildup exceeds the creep strength of the tubing (Masuyama, 2001). In addition, exfoliated material has also been found to erode turbine components in a supercritical fossil- fueled power plant if solid particles are found in the fluid stream. Therefore, scale build-up and its resistance to exfoliation is a major concern for any system running SCW. There are several key differences between a supercritical fossil-fueled power plant and nuclear SCWR design requirements which make it particularly challenging for SCWR (Was et al., 2007). First, compared to supercritical fossil-fueled power plants which usually can have fire tubes with wall thickness of up to 10 mm, the fuel cladding in a nuclear reactor core is restricted to 0.5 - 0.6 mm due to thermal and neutron efficiency (Zhang et al., 2009). Larger amount of corrosion product deposits are often found on superheater tubes operating above the critical point in a supercritical fossil-fueled power plant and it is not unusual to find oxide films of several hundred micrometer thickness on these tubes (Cook & Fatoux, 2009). Such high fouling rates and deposit thickness would be unacceptable for a fuel cladding in a SCWR. Second, the cooling water in the boiler tubes sees a geometrically smooth surface along the boiler while the core of a SCWR will have a fuel assembly of intricate geometry (Was et al., 2007). 8 2.1.2 Supercritical Water Oxidation The high solubility of organic species in supercritical water has led to the research in “supercritical water oxidation” (SCWO), technology which was developed for destroying hazardous organic waste (Helling & Tester, 1988). Despite its initial success, problems with fouling and corrosion resulted in high operating costs which has forced the majority of commercial SCWO plants constructed and operated in the late 90’s and early 2000’s to permanently shut down (Marrone et al., 2005). There was extensive experimental work conducted on fouling and corrosion in supercritical conditions for SCWO applications, however, the environment is often highly oxidizing and in some cases highly acidic which are significantly different from the water chemistry which will likely be used for a CANDU SCWR (Kritzer, 2004). It has been well observed from SCWO research that acidic water chemistry promotes rapid corrosion, especially slightly below the pseudocritical temperature. With inorganic salts in supercritical conditions, very high fouling rates are observed and the deposit can completely plug flow of a system resulting in increased system pressure and the need for immediate shut down and cleaning (Teshima, 1997). 2.1.3 Nuclear Energy and the Generation IV Nuclear Reactors As energy demand continues to increase and the effects of energy production on the global environment escalates, the need for cleaner and more efficient technology grows ever more important. Nuclear energy provides approximately 13.8% of the world’s energy demand and its fuel provides energy with low greenhouse gas emissions making it an ideal candidate for future energy production (International Atomic Energy Agency, 2010). These facilities require some of the most advanced technology available and the Generation III++ is the most 9 recent design incorporating the technology developed for the industry over the last half century. Generation IV nuclear technology is to succeed the current Generation III++ nuclear reactors with state-of-the-art technology to improve on safety, lower byproduct waste, and higher efficiency (Cook & Fatoux, 2009; Khartabil, 2009). There are currently six emerging technologies for Generation IV nuclear reactors, one of these systems being SCWR in which the coolant will operate above the critical point of water. The first of the Generation IV nuclear reactors utilizing SCWR technology are expected to go online in 2025 as presented in Table 2-1 (Generation IV International forum SCWR Committee, 2002) . Table 2-1: Generation IV systems and expected deployment year Generation IV R&D Systems Year Gas-Cooled Fast Reactor System 2025 Lead-Cooled Fast Reactor System 2025 Molten-Salt Reactor System 2025 Sodium-Cooled Fast Reactor System 2015 Supercritical-Water-Cooled Reactor System 2025 Very-High Temperature Reactor System 2020 The higher operating temperature and pressure of a SCWR is expected to increase the thermodynamic efficiency of nuclear power plants to 45 - 50% in comparison to the 33% - 35% for conventional nuclear power plants (Naidin et al., 2009). This is due to the single phase coolant which improves heat transfer and simplifies the overall design by reducing the number of equipment and flow loops. In addition, the higher enthalpy of the coolant at higher temperatures especially near the critical point offers an opportunity to decrease the mass flow of the coolant for the same thermal output, resulting in smaller pumps, piping and housing (Generation IV International forum SCWR Committee, 2002). 10 2.1.4 CANDU Supercritical Water Reactors The CANDU (Canadian Deuterium Uranium) nuclear reactor is a Canadian-designed nuclear reactor developed by Atomic Energy of Canada Limited (AECL). The CANDU nuclear design is unique in that it uses heavy water as a moderator versus light water, which allows the reactors to use non-enriched uranium as fuel. In addition, the CANDU reactors use pressure tubes rather than a pressure vessel in the reactor core, simplifying high pressure designs and making the movement towards a supercritical coolant the next logical step (Torgerson et al., 2006). The coolant would enter the reactor core at 350⁰C and leave the core at above 600⁰C and 25MPa, finally leading to a high pressure turbine in the case of a direct cycle system (Naidin et al., 2009). A simplified drawing of the proposed CANDU SCWR is provided in Figure 2-1. The low solubility of inorganic salts in supercritical water suggest that there is greater possibility for higher fouling rates of metal oxides in a SCWR core than previously seen in a subcritical CANDU reactor. Metal oxides may nucleate from solution to form nano to micrometer sized particles which may foul onto various heat transfer surfaces, leading to higher than expected temperatures and accelerating material degradation. Particles which do not deposit may be carried in the bulk fluid to the steam turbines which can lead to solid particle erosion and out-of-core radiation (Guzonas et al., 2009). 11 Condenser GeneratorTurbine Pump Reactor Core Preheater Figure 2-1: Simplified drawing of a direct cycle coolant for Generation IV CANDU SCWR 2.2 Materials for SCWR There are currently five materials that are under evaluation as potential materials to be used in SCWR for various components such as the fuel cladding, pressure tubes, etc. (Zhang et al., 2009).  Nickel Alloys: 690, 625, 718  Austenitic Stainless Steels: 304NG, 316L, D9, AL-6XN  Ferretic / Martensitic Steels: P92, P112  Oxide Dispersed Steels (ODS): 9Cr-ODS, 12Cr-ODS, MA956  Modified zircaloys 12 Experiments presented in this study are constructed from mainly SS316L material. Austenitic Stainless Steels such as AISI 304 and AISI 316 are part of a family of stainless steels with nickel content which preserve the austenite crystal structure during cooling. Compared to martenitic and ferritic stainless steels, austenitic stainless steel enjoys the advantages of being easily formable, weldable, and ductile. The ‘L’ of 316L indicates that the particular stainless steel has lower carbon content than that of unstabilized austenitic steels such as 316 and 304. When types 316 and 304, are subject to high temperatures in the range of 550°C to 880ºC, chromium carbide tend to precipitate along the grain boundaries, forming areas depleted of chromium below the minimum 12%. These areas become susceptible to corrosion in and near these boundaries where the material has become sensitized (Sinha, 1989). In operational power plants, these sensitized austenitic steels have been found to fail by intergranular stress corrosion cracking (IGSCC) in the tubing of boiler water reactors (R. L. Jones et al., 1993). By lowering the carbon content to below 0.03%, the amount of M23C6 that forms is minimized. Furthermore, the addition of molybdenum (Mo) in 316L SS as opposed to 304L SS which does not have Mo, improves corrosion resistance of stainless steel in chloride aggressive environments by forming a uniform passive layer (Bastidas et al., 2002). Table 2-2: Stainless steel AISI 316L composition (American Society for Metals, 1985) C Mn Si Cr Ni P S Mo N 0.03 2.00 1.00 16.0 - 18.0 10.0 - 14.0 0.045 0.03 2.0 - 3.0 0.10 13 2.3 Corrosion and Fouling in Subcritical and Supercritical Water 2.3.1 Properties of Magnetite Magnetite is an iron oxide mineral with the chemical composition of Fe3O4. It is also known as a ferric-ferrous oxide as it is one part wüstite (FeO) and one part hematite (Fe2O3). It is part of the spinel group which is a group of minerals that have a chemical composition of A 2+ B2 3+ O4 2- . It typically forms as an octahedral, less commonly as dodecahedral and rarely as a cubic (Anthony et al., 1997). Magnetite, which is the stable form of iron oxide in SCWR conditions, is expected to be the dominant metal oxide formed in the core due to the presence of iron in many high temperature alloys. It is a common corrosion product found on the tubes of fossil-fueled and nuclear power plants (Propp et al., 1996). Pourbaix diagrams, also known as Eh-pH diagrams indicate the stable regions for metal species. Solid lines indicate the border between two species while the diagonal dashed lines indicate the stable region for water. Above the upper dashed line, water is oxidized to oxygen while below the lower line, water is reduced to hydrogen (D. A. Jones, 1996). The equilibrium equations of water in neutral or alkaline solutions are shown below: 2-1 2-2 Figure 2-2 is a Pourbaix diagram for iron and iron-chromium created from SUPCRT92. Because of its dependence on temperature and pH, the borders for stable species will vary 14 from one temperature to another and change dramatically in supercritical conditions (Propp et al., 1996). Fe Cr CrO Cr2O3 Fe2O3 CrO4 2- CrO2 Cr3+ Fe2+ Cr2+ Cr2O7 2- FeO4 2- Fe Cr CrO3 3- Cr2O3 Fe2O3 CrO4 2-CrO2 Cr3+ Cr2O7 2- FeO4 2- Fe Fe Fe2+ Fe2+ Fe2O3 Fe3+ Fe3O4 FeO4 2- Fe2O3 Fe3O4 HFeO2 FeO4 2- -1.55 -0.88 -0.05 0.70 1.45 2.20 -1.55 -0.88 -0.05 0.70 1.45 2.20 -2 2 6 10 14 -2 2 6 10 14 pH E h (V ) Figure 2-2: Pourbaix diagram (a) Fe – H2O at 25ºC and 1 atm, (b) Fe – H2O at 374°C and 220 atm (c) Fe/Cr – H2O at 25°C and 1 atm, (d) Fe/Cr – H2O at 374ºC and 220 atm. Based on SUPCRT92 (Propp et al., 1996) 15 2.3.2 Magnetite and its Solubility in High Temperature and Pressure Water The solubility of corrosion products play a primary role in corrosion and fouling in aqueous systems (Kritzer, 2004). In particular, the solubility of magnetite, an iron oxide of the form Fe3O4, in high temperature and pressure water is a crucial information to operators in the power industry due to the prevalence of the mineral found on heated tube surfaces. Solubility of magnetite in alkaline and acidic water conditions has been measured up to 300⁰C by several groups. Sweeton and Baes Jr. (1970) tested magnetite solubility with varying pH using potassium hydroxide and hydrochloric acid while Tremaine and LeBlanc (1980) adjusted pH with sodium hydroxide and hydrochloric acid. The dissolution of magnetite requires the reduction of Fe III to Fe II . The equilibrium equation is provided in equation 2-3 (Tremaine & LeBlanc, 1980). ( ) ( ) ( ) 2-3 In order to predict the magnitude of super-saturation and potential fouling rates in supercritical water, the solubility of magnetite under these conditions is required. Unfortunately, the experimental solubility data for magnetite in supercritical water is currently unavailable. There are several major problems which make measuring solubility of magnetite extremely difficult. First, the low solubility of iron means that measurements must be done in parts per billion and parts per trillion ranges. Preventing iron contamination of the solution from tubing, pumps, valves, etc. becomes increasingly difficult as materials that withstand supercritical conditions are limited to high temperature alloys which often have iron content eg. 316L, Inconel 625, Alloy 800. 16 To overcome the deficiency in experimental solubility data for magnetite, thermodynamic studies utilizing the Helgeson-Kirkham-Flowers (HKF) extrapolation for the Gibbs free energy at high temperature and pressure have been used to predict the solubility of magnetite in supercritical conditions (Cook & Fatoux, 2009; Guzonas et al., 2009). In another study by Burrill (2000), magnetite solubility data from Bohnsack was extrapolated from subcritical to supercritical conditions, assuming a direct dependence of magnetite solubility with water density. The simulation results are provided for comparison in Figure 2-3. Figure 2-3: Magnetite solubility adapted from Cook and Fatoux (2009) for neutral pH water at 25 MPa, Guzonas et al. (2009) for pH = 9.3 at 30 MPa, Burrill (2000) for neutral pH at 25 MPa, and Sweeton and Baes Jr. (1970) experimental results. 17 All three solubility simulations show a drop in solubility between 350ºC to 400ºC as the density of water drops and the water transitions from polar to non-polar solvent. For models based on HKF, the solubility increases once again as the temperature increases even higher after the initial drop. The HKF model has been successful in correlating equilibrium constants for hundreds of inorganic aqueous species in high temperature and high pressure water including supercritical water (Sue et al., 2002). Cook and Fatoux model was adopted for the simulation in this study for this reason as well as because it used pressure closer to those expected in a CANDU SCWR of 25 MPa. Under this model, minimum solubility is reached at 400°C and 25 MPa under neutral pH conditions with an iron concentration of approximately 0.2µg/L. At supercritical conditions, neutral species such as Fe(OH)2 and Fe(OH)3 are expected to be the dominant dissolved species in the solution (Cook & Fatoux, 2009). 2.3.3 Corrosion Due to significant changes in the thermal and chemical properties of water from subcritical to supercritical conditions, corrosion rates and mechanisms can be substantially different in supercritical water environment (Was et al., 2006). In supercritical water systems, general corrosion and stress corrosion cracking are found to be one of the dominant corrosion mechanisms (Was et al., 2007; Zhang et al., 2009). For general corrosion, the surface of the alloy undergoes oxidation and forms metal oxide corrosion product. This can be of particular concern since SCW can be an aggressively oxidizing environment if certain species or dissolved oxygen are present, resulting in very high corrosion rates (Lister, 1980). It has been 18 found experimentally that at high temperatures, oxides are preferentially formed over hydroxides as the primary form of corrosion product (Kritzer, 2004). However, not all corrosion products are undesirable and the corrosion products can produce a protective film that reduce the rate of corrosion of the underlying metal (Lister, 1980). Corrosion of austenitic stainless steel and nickel alloys subject to supercritical water is observed to form a multilayer oxide on the surface. These are found to be tens to hundreds of nanometers thick after several hundred hours in a deaerated supercritical condition (Was et al., 2007). In high temperature aqueous systems, iron ions diffuse to the outer surface while oxygen from the solution diffuses into the metal alloy. This produces a duplex oxide structure: a dense inner chromium-iron rich layer and a porous magnetite outer layer. The inner chromium rich layer has a spinel structure and provides protection to the alloy while the porous outer layer provides no further protection (Gao et al., 2007; Was et al., 2006). Therefore, the corrosion rate is dependent on the oxygen diffusion through the inner layer following an Arrhenius behavior in which the high temperature provides the activation energy for diffusion to occur (Zhang et al., 2009) 2.3.4 Fouling Another method for corrosion products to form on the surface is the deposition of corrosion products from the bulk solution through “ex-situ” fouling. Ex-situ fouling can be further divided into two subcategories of crystallization and particulate fouling. In crystallization fouling, the bulk fluid is super-saturated with, for example, iron species which may have come from other parts of the power plant where corrosion had occurred and been transported 19 to the surface of interest. Once these iron species reach the wall, super-saturation causes particles to nucleate and deposit onto the wall. In particulate fouling, nucleation happens in the bulk fluid and the corrosion products are carried to the wall as solid particles. Lister (1980) hypothesized that the deposits of these ex-situ corrosion products may be the same form as the outer layer oxide formed from the alloy. As the iron species diffuse from the alloy to the surface, the iron first dissolves into the solution. Then, due to local super- saturation, it re-deposits as porous outer layer resembling ex-situ fouling. Ex-situ fouling of oxides onto heat transfer surfaces can be detrimental to power systems as they can decrease thermal efficiency and increase the temperature of the heat transfer material promoting earlier degradation (Lister, 1980). To track thermal efficiency issues due to deposition, heat transfer performance is regularly monitored on steam generators in pressurized water reactors (PWR) (Schwarz, 2001). The steam generator of a PWR is a heat exchanger where the reactor coolant transfers the heat to the feed water / steam cycle. The accumulation of deposits, mainly iron hydroxides and oxides was found to impair heat transfer between the two systems. Schwarz (2001) compiled data from twelve Siemens steam generators, many spanning over a decade and one for 27 years. Fouling was determined using energy balance and heat exchanger equation shown below. 2-4 where Q is the thermal energy into the system, ΔTlog is the mean logarithmic temperature and U is the overall heat transfer coefficient for the heat exchanger, calculated by equation 2.3. 20 2-5 where Rf is the fouling factor representing the additional thermal resistance due to the iron oxide deposit. The thermal power Q was determined from the change in enthalpy of the feedwater, derived by the inlet and outlet temperatures at constant pressure. Accuracy of the fouling measurements was found to be highly sensitive on the accuracy of the steam generator outlet temperature and pressure measurements. Using the heat exchanger and the calculations described above, it was possible to observe the fouling rates on the steam generator over its operational time. It was found that switching from phosphate-treatment to an all-volatile treatment (AVT) with hydrazine to ensure high pH, significantly reduced the fouling rate on the SG. The fouling factor increased gradually over time under phosphate- treatment which occasionally would encounter a sharp drop after undergoing chemical cleaning (Schwarz, 2001). Experimental, simulations and theoretical studies of magnetite deposition in aqueous systems has been the subject of many previous studies. A classic study of particle deposition was conducted by Thomas and Grigull (1974) using magnetite powder in high temperature and pressure system. Their experiment used an electrical heater in a flow loop system and is one of the few studies which reached supercritical conditions of 24.6 MPa and 471°C. They observed that the deposition of magnetite in both subcritical and supercritical single phase flow was approximately linear to Reynolds number and concentration which is an indication that the deposition was mass transport limited (Thomas & Grigull, 1974). More recent studies by Turner and Klimas (2000) and Basset et al. (2000) used sol-gel methods to form 21 narrow size-distribution magnetite particles for deposition experiments. Deposition experiments have shown the effects and differences of deposition of single phase, boiling, and non-boiling two phase flow. Under single-phase flow, removal was not found to be a significant factor and only significant in sub-cooled boiling (Basset et al., 2000). Since the proposal of the CANDU SCWR reactor design, deposition of corrosion products in the reactor core has been identified as a problem by a number of researchers prompting simulations for deposition to be developed. Using the solubility mentioned in section 2.2, Burrill (2000) created a simulation with a CANDU 6 fuel channel design and the temperature went from 350°C to 384°C at 25 MPa. Ferrous ions were assumed to diffuse towards the wall and crystallize as magnetite deposits. Deposition was assumed to be mass transport limited and the diffusivity coefficient of ferrous species was calculated using empirical formulations by Miller (1982). Burrill (2000) determined that after one year of operation the peak deposit was 108mg Fe/cm 2 occurring 4m from the channel inlet. The effect of dissolved iron concentration on deposition was also investigated by setting the concentration at the inlet of the reactor core to 18.22 µg/L and 5 µg/L. The higher inlet concentration led to deposition nearly six times higher than the lower concentration, suggesting that the uncertainty in magnetite solubility can have a significant impact on the simulation results (Burrill, 2000). In a similar study, Cook and Fatoux (2009) proposed the use of steam generator such as the one used in a PWR for the CANDU SCWR to prevent corrosion products from travelling to the steam turbine. A simulation using the HKF model for saturation of iron was used and the kinetics of mass transport was arbitrarily assumed to be described by constant deposition 22 velocities of 0.01 cm/s and 0.001 cm/s. The peak deposition thickness in the steam generator was calculated to be up to 300µm or 50µm depending on the kinetic constant assumed. The deposit decreased the efficiency of the steam generator by 4% after five years of operation (Cook & Fatoux, 2009). 2.3.5 Corrosion Product Removal and Transport Once attached to the tube surface, adhesive forces prevent the particle from flowing back into the fluid stream. Adhesive forces are generally classified into three categories; The first class of adhesive forces is intermolecular forces which can include van der Waals, the second are chemical bonds including hydrogen bonds, and the third is sintering effects such as diffusion. (Cooper et al., 2001). As particles deposit, they are located in the viscous sub-layer, a very thin layer near the wall where viscous effects are dominant and the flow is laminar (Cengel & Cimbala, 2006). Detailed investigations of particulate removal by Cleaver and Yates (1973) have shown that the viscous sub-layer is unsteady in turbulent flows, and that there are turbulent “bursts” that can cause particle removal when the shear flow generate lift forces exceeding adhesive forces of the particle and surface. In contrast, if the viscous sub-layer thickness is much greater than the particle deposited, the viscous forces can rapidly dissipate the turbulent bursts (Cengel & Cimbala, 2006; Turner et al., 1990). Previous studies for calculating removal rates have used an exponential relationship (equation 2-6) and incorporated the frictional velocity U* (equation 2-7). 23 ̇ ̇ 2-6 The value ̇ is found experimentally, t is time [s] and λ is removal rate constant [1/s] calculated using equation 2-7. 2-7 where f is the friction factor and ν is the kinematic viscosity. While fouling of corrosion product on heated surfaces is of concern, the transport of particulates outside the reactor core is also of great importance to the reliability and safe operation on a power system. Solid particle erosion (SPE) can be problematic in power generating systems where the protective oxide layer of piping and other components are eroded by particles suspended in the fluid stream (Crockett & Horowitz, 2010). SPE can contribute to increased maintenance costs and the decrease in the thermal efficiency of a turbine which can be expensive (Dai et al., 2007). For a SCWR, a direct cycle from the reactor core to the steam turbine is expected and the problem of SPE may be enhanced due to lower solubility of oxides in supercritical water and the formation of particulates. Another issue with corrosion products being transported in a nuclear reactor is the transport of radioactive material. Corrosion products can form in the reactor core, attaching to fuel cladding and pressure tubes which are then irradiated (Burrill, 1977). Once the particle exfoliates, it can travel to other parts of the 24 system outside the core and become a source of hazardous radiation to its operators and maintainers (Lister, 1980). The need for in-situ particulate sampling systems can be significant for power plant applications. Information about the properties of the particle such as size, shape, hardness and strength can lead to information about potential damage that particulates can have on system components surfaces (McCabe et al., 1985). The composition of the particles give an indication as to where they may be coming from (eg. fuel cladding, piping, etc.) as well as a predicted hardness and strength of the particles. Furthermore, sampling at high temperature has been shown to provide better representation of the particulates in the system. Turner and Klimas (2000) made measurements of particulates before and after a filter and found that by placing the filter before the heat exchanger, the concentration of iron was twice as large as when the filter was sampled cold. Turner argued that such difference is likely due to thermophoresis where the particles diffuse down a temperature gradient, therefore transported to the colder surface and attaching to the heat exchanger wall. In addition, sampling ports in real power-generating systems are often far away from the sampling line which can cause losses in the particulates found at the ports. In PWR, it was found that 50-75% of particles were lost or dissolved in the solution due to long sampling lines (Srisukvatananan et al., 2007) 25 3 Heat Transfer and Deposition Modeling 3.1 Overview A heat transfer and deposition model was created in MATLAB to aid in the design of the experiments and to predict the effects of magnetite deposition on a CANDU SCWR fuel cladding. Only particle deposition was considered in this model due to the lack of data on the deposition rate constant for ferrous species in supercritical water. Simulation models were also used to compare expected deposition thicknesses with those found in the experiments. The heat transfer and deposition model for the CANDU SCWR and the experimental simulation are based from the same code. However, due to different geometry and flow characteristics, adjustments to the code were made where necessary. The MATLAB program source code can be found in Appendix A. 3.2 Heat Transfer Calculations of Water 3.2.1 Enthalpy of Fluid in the Test Section The test section in the once-through flow loop is electrically heated and the heat flux is assumed to be constant throughout the test section. As a result, the enthalpy of the bulk fluid is a linear function of the distance along the tube, and at any point, the enthalpy can be determined from equation 3-1: ̇ 3-1 26 where H1 and H2 is the enthalpy [kJ/kg] at a distance Δx [m] away, ̇ is the mass flow rate [kg/s], and q is the heat input per meter [kW/m]. The enthalpy of the inlet and outlet of the test section is determined by using the inlet and outlet bulk fluid temperatures [⁰C] at the specified pressure P [bar]. The bulk fluid temperatures were measured experimentally using in-situ thermocouples before and after the test section, as described in detail in Chapter 4. 3.2.2 Heat Transfer Coefficient in Supercritical Water Heat transfer correlations developed for subcritical conditions are not applicable for supercritical conditions due to the dramatic changes in the thermodynamic and transport properties near the critical region. Therefore, a number of correlations have been developed for supercritical conditions in previous studies. Calculating non-dimensional numbers for heat transfer generally require the use of either bulk or wall temperatures, however, there can be dramatic changes in the heat transfer properties if bulk and wall temperatures are near the pseudocritical region. Correlations such as those developed by Swenson et al. (1965) and Yamagata et al. (1971) attempt to reflect these changes in the properties by using both wall and bulk temperature to determine a suitable average. The equations provided by Swenson are a relatively straightforward method for calculating the Nusselt number and has been shown to predict heat transfer well, demonstrated by Teshima (1997). ( ) 3-2 27 By using equation 3-2, one can determine the Nusselt number for finding the heat transfer of the tube to fluid. This requires the Reynolds number as well as the Prandtl number found in equation 3-3. ̅ 3-3 where ̅ is the integrated average heat capacity. ̅ ∫ 3-4 A recent study by Bazargan and Fraser (2009) on the heat transfer correlation in supercritical water in a horizontal pipe showed that many previous correlation used were insufficient in predicting the Nusselt number accurately. Bazargan concluded that large variations in fluid properties near the pseudocritical zone dramatically enhanced heat transfer. A comprehensive explanation and discussion of the approach is described by Bazargan and Fraser (2009). Both the correlation of (Swenson et al., 1965) and (Bazargan & Fraser, 2009) were programmed in MATLAB for comparison between the empirical models and experimental results. These results are presented in section 4.5.1. The Nusselt number calculated from the correlations is then used to calculate the wall temperature using equation 3-5. 3-5 To determine the fluid properties at the wall, the wall temperature is required in the previous calculation. Since this is the parameter which is currently unknown, a wall temperature must 28 first be predicted by the software. The program runs through an iterative loop, first calculating the wall temperature with the initial guess, calculating the new wall temperature and modifying the initial guess until the two temperature converges to within 0.1ºC. 3.2.3 Temperature of the Oxide Layer As the particles begin to foul the inner wall of the tube, the deposits create a heat transfer resistance between the fluid and tubing wall interface. The temperature at the wall calculated from section 3.2.2 is therefore the temperature of the oxide/fluid layer as deposition occurs. The temperature of the oxide/tube layer can be calculated as follows: 3-6 where koxide is the thermal conductivity of the fouling oxide (Holman, 2002). Magnetite thermal conductivity was calculated using the following empirical formula 3-7 where T is the temperature of magnetite (Electric Power Research Institute Inc., 2003). 3.2.4 Temperature of the Outside Wall Temperature Calculating the outside wall temperature of the tube was necessary because the thermocouples on the test section are measuring outside wall temperature. The tube has internally generated heat from the low AC voltage and high current applied to the tube. The 29 equation for determining the external wall temperature with internally generated heat assuming a perfectly insulated outside wall is shown in equation 3-8. ( ) 3-8 where A is the ratio of the inner and outer radius found by equation 3-9. 3-9 3.2.5 Buoyancy Calculations Buoyancy effects were calculated for the experimental conditions to determine if it would have an effect on the temperature profile of the tubing wall. Buoyancy effects can be significant for fluids near the pseudocritical point due to large variations in the fluid density at the bulk and wall temperatures (Bazargan et al., 2005). This can cause the low density supercritical water to flow at the top of the tube while the denser subcritical water flows at the bottom of the tube. Since the heat transfer coefficient varies dramatically from supercritical to subcritical, this means that a difference in top and bottom surface temperatures can have significant implications for a horizontal flow in tube. Buoyancy effects were calculated according to Petukhov et al. by a threshold value for the Grashof number, which below the threshold the buoyancy can be neglected. The threshold is defined as follows: 30 ̅̅ ̅ ̅̅ ̅ 3-10 where ̅̅ ̅ 3-11 The Grashof number is calculated using a heat-flux-related definition of equation 3-12. ̅ 3-12 where ̅ 3-13 Evaluation is done by determining if Grq < Grth or that the Grq/Grth is less than one. 31 Figure 3-1: Calculation of Grq/Grth for determination of the effects of buoyancy along the test section using Bazargan et al. (2005) Since Grq 98% Fe3O4). The use of prepared magnetite powder for the experiments offered several advantages over using a precursor; the amount of magnetite particles in the system could be accurately known without the need to determine yield rates and the size of the particles could also be externally controlled. The magnetite powder had a diameter of 50 nm or less and was suspended in deaerated solution in the injection tank. The solution was continually mixed with an electrically powered mixer to prevent particle settlement. The magnetite particles were observed to agglomerate and stick to the glass flask and tubing, lowering the overall concentration of magnetite powder in the solution. To mitigate this problem, the pH of the solution was increased to 10 using sodium 51 hydroxide where the zeta potential of the solution/magnetite favored dispersion. However, the HPLC injection pump continued to experience difficulty pumping at consistent concentration of magnetite nano-particles, therefore further experiment with magnetite slurry was not pursued. 4.4.3 Post Experiment Cleaning After each experiment with the exception of experiments 7 and 8, the test section was removed and replaced with a temporary tube and the system was chemically cleaned. For experiments 7 and 8, both the test section tube and the rest of the system underwent chemical cleaning. The system was cleaned using 1N hydrochloric acid at 80⁰C for one hour before each test to ensure that magnetite deposits were removed from the system. After cleaning with hydrochloric acid, the entire system was flushed out with de-ionized water for several hours. When required, mechanical cleaning of tubes and fittings was also conducted by disassembling the sections and cleaning the section with an ultrasonic cleaner and/or a mechanical brush. 4.5 Analytical Methods 4.5.1 Online Thermal Resistance Monitoring The electrical heater was designed and constructed to serve several purposes. First, the heaters increase the temperature from subcritical to supercritical temperatures, allowing for a wide range of temperatures and heat flux conditions which can be tested. Second, it offered an online monitoring of fouling in the system. Deposits on the heat transfer surface would increase thermal resistance which would be detected by an increase in temperature of the tube outer wall. By modeling magnetite deposits and heat transfer characteristics, the deposition and removal rates 52 can be calculated. Calculated values can be compared to the deposition found in SEM images and cleaning methods. The test section is electrically wired with current running directly through the tube causing the electrical resistance of the 1/8” tube to dissipate power in the form of heat. It is assumed that the electrical resistivity remains constant along the tube and therefore the heat flux into the water will also remain constant along the tube. This method for heating the tube was chosen over heating tapes and ceramic heaters for its uniform heat flux demonstrated by Teshima (1997) and Khan (2005). The test section tube is connected to a 2400VA transformer with its primary coil wired in series and secondary coil wired in parallel using 6V center taps. Power input was provided by two of three legs of a three-phase delta-configured power supply, which supply a voltage of 208V RMS to the transformer. Fuzzy Pro logic controllers monitored the temperatures for both the preheaters and test section. These have PID control which read temperatures from the thermocouples and send a signal for optimal power level to the solid-state rectifiers (SSR) which act as a gate for the electrical current. Metal oxide varistors (MOVs) were installed both at the inlet before and after the SSR to prevent voltage spikes from damaging the SSR and transformer. The transformer connects to the tube with one connection to the center and two ground wires to each of the ends. This is to prevent any ground loops from forming within the system, which may create safety hazards. The resistance of the 1/8” SS316L tube was measured to be on average ~0.13 Ω per meter, however the effective resistance is reduced to a quarter of its value due to the parallel connection. 53 Thermal expansion of the tubing was also considered which can be as high as a few millimeters from room temperature to experimental temperatures. The heat exchanger is free to move axially a short distance, allowing thermal expansion to occur without introducing significant stress on the test section. For both safety and protection of the equipment from voltage on the tube, secondary grounding wires were attached at the inlet of the injection line and after the heat exchanger. Three tube mounting blocks were constructed from SS303 for clamping the tube and the electrical conductor together. These mounting blocks were specially designed and optimized to offer high thermal resistance to decrease heat loss from the test section yet maintain high electrical conductivity for the electrical path. Aluminum heat sinks were attached to the mounting blocks to dissipate any excess thermal heat. The configuration of the test section and mounting blocks are provided in Figure 4-3. 54 Figure 4-3: Mounting block and test section inlet Temperature along the tube was measured using K-type Chromel/Alumel thermocouples with twisted shield for protection against electrical noise. Although not as accurate as RTD, they are very robust even at high temperature and can be calibrated to be accurate within less than 1⁰C. Six thermocouples were connected to the control panel for input power control and safety reasons. Eleven thermocouples were spot welded to the 1/8” test section tubing on the outside wall. These thermocouples were placed on the top of the tube, however, since buoyancy is negligible in these conditions, the location around the circumference of the tubing should not have a significant impact on the temperature reading. Thermocouples were clamped onto the Wall temperature thermocouple Mounting blocks Tee with inlet bulk thermocouple Test section Heat exchanger From main pump From injection pump 55 outside wall of the outlet of heaters 1 and 2 and the tube downstream of the heat exchanger of the main line. Bulk fluid temperatures were measured using Inconel sheathed, ungrounded probes which were inserted at the Tees with the probe end approximately at the center of fluid flow. The outlet bulk temperatures were fed into the control panel and were used to control the temperature of the electrically heated section. A wiring and thermocouple placement diagram is shown in Figure 4-4. AC voltage and current into the heated tube sections were measured for calculating power input. Although these measurements are not used for determining the enthalpy of the water, it provided a secondary confirmation for ensuring temperature rise corresponding to the electrical power provided by the system. A fluke clamp meter was used to measure AC current with resolution of ±0.1A. Measurements of the voltage across each half-section were performed with a Mastercraft multimeter with a resolution of ±0.01V. Input power calculations derived from current/voltage measurements closely matched input power calculations using bulk temperature measurements, shown in the table below as the electrical and thermal power respectively. The small discrepancy between the two values is likely due to thermal loss to the mounting blocks and surrounding insulation, hence the electrical power is slightly higher than the actual heat gained by the fluid. Table 4-1: Input power comparison Experiment First half of tube Second half of tube Power [W] (electrical) Power [W] (thermal) Current [A] Voltage [V] Current [A] Voltage [V] 1 54.3 10.00 51.5 9.93 1054 1025 56 Calibration of the thermocouples was conducted by measuring the outside wall temperatures with the bulk inlet and outlet temperature of the test section set at a saturation temperature and pressure, and the section was thermally insulated with no input power. This process was completed before the experiment each time a new test section was installed. Temperature was recorded for thermocouples and any significant temperature differences were noted. For the thermocouples, the temperature measured usually fell within one or two degrees of expected wall temperature. These were used to correct the temperature readings for any future measurements for each experiment. Subsequently, the accuracy of the temperature profile calculated by the MATLAB simulation fluidproperties.m was checked by comparing the simulation to experimental temperature profile with inlet and outlet temperatures at 350⁰C and 400⁰C respectively. The measured and calculated temperatures using correlations of Swenson and Bazargan are shown in Figure 4-6. 57 15 cm Omega 1200 High Speed Isolated Measurement System Transformer Parallel Series Mounting blocks SSR Fuzzy Pro logic controller Fuzzy Pro logic controller Flow Figure 4-4: Electrical wiring, heater controls and location of surface welded thermocouples and bulk fluid thermocouples 58 Figure 4-5: Saturation temperature of 231.51ºC at 417psi, calibration for Experiment #1 Figure 4-6: Temperature of test section, calculated vs. calibrated thermocouples 59 It was observed from the comparison that Swenson’s correlation predicted temperatures well both in subcritical and supercritical conditions. Bazargan’s correlation over-predicted heat transfer enhancement at bulk fluid temperatures above 380°C. Therefore, all subsequent simulations presented in this study use Swenson’s correlation for determining the heat transfer coefficient. The temperatures read were quite stable (std = 0.7⁰C for experiment #1) and therefore, any temperature differences due to fouling can be measured with an accuracy to 1⁰C. Temperature measurements of the test section thermocouples were recorded using a data acquisition hardware and computer. The Omega Multiscan 1200 has 24 electrically isolated channels and two internal channels which are used for cold junction compensation. The 16-bit temperature measurements offer 3.12 uV or 0.1⁰C resolution. Electrically isolated channels were needed for the temperature measurements since the thermocouples were welded and electrically connected to parts of the test section which are at various voltage potentials. AC line rejection and averaging helped to reduce noise caused by the AC voltage applied to the test section in the measurement. Temperature data is sampled at 20kHz frequency and the data was sent to “TempView” software, displaying real-time temperature measurements. The measurements were automatically averaged over a 5 second period and then outputted to the text file which was later analyzed in MATLAB. 4.5.2 SEM Imaging for Filters and Tube Deposits A Hitachi S-3000N in the Frank Forward Materials Engineering building at UBC was used for SEM imaging, with the exception of those photographs which are labeled as Hitachi 2300 SEM, also located in the Frank Forward building. 60 To observe the morphology of the deposit on the tube inner-wall surface, the test section was cut into 1.5cm long samples using a 1/8” tube cutter. The sample was then carefully cut in the middle of the tube by grinding halfway through the tube until there was exposure to the other inner wall. Then the tube was bent slightly to open the section and the sample was placed into a mounting clamp for SEM imaging. Figure 4-7: Test section sample for SEM analysis 4.5.3 Particulate Filtering System Three filters were constructed and installed at various locations in the system to collect particles formed in supercritical water. After each experiment, the filters were removed and analyzed with SEM/EDX with the objective of determining particle size, shape, and composition. The main body for the low temperature, high pressure (LTHP) filter holder shown in Figure 4-8 was constructed from stainless steel 316L. The filter was designed and constructed with the 61 intention of allowing future filter holders to be constructed from any material and allow for easy assembly and reassembly after each experiment (see Appendix B for details). The metal spiral wound sealant allows the filter to reach high temperature and pressure applications and compensates for uneven or scratched surfaces of the mating parts. Glass fiber filters were inserted into the LTHP filter to collect particles in the primary line after the heat exchanger as well as to protect the back pressure regulator which was sensitive to particulate fouling. After each experiment, the glass filter was carefully removed, left to dry overnight, and was gold coated using a gold sputtering machine for SEM/EDX analysis. Figure 4-8: SS316L LTHP filter installed after the heat exchanger 62 A high temperature, high pressure (HTHP) holder was made from Swagelok 316L fittings shown in Figure 4-9. A stainless steel 304 perforated metal with a porosity of 22% and a hole diameter of 0.02” was fitted into the holder to provide back support for the filter. Glass fiber filters were initially tested in supercritical water, however, the filters were destroyed when exposed to supercritical water. It is thought that at high temperature and pressure, the glass fiber mechanical properties degrade significantly and the pressure drop across the filter may have caused it to break down. It was decided that the glass fiber filters would be used to collect particles only at low temperatures. In replacement of glass fiber filters, sintered silver membranes from SPI supplies with absolute retention pore size of 0.2 µm and thickness of 50 µm were used for high temperature applications. The thin filter makes it ideal for higher flow rates and the conductive properties of the silver membrane make it excellent for SEM/EDX and XRD analysis. The filter holder and its components are shown in Figure 4-9. Figure 4-9: HTHP filter with silver membrane and SS304 back support 63 Finally, a polypropylene 25mm Swin-Lok filter holder was used for the low temperature, low pressure (LTLP) filter shown in Figure 4-10. The same glass fiber filters used in the LTHP filters were also used for the LTLP filter. A summary of the properties of the glass and sintered silver filters are described in Table 4-2. Figure 4-10: Glass fiber membrane and Swin-Lok LTLP filter holder Table 4-2: Glass and silver membrane filter comparison Commercial Supplier Effective Pore size [µm] Thickness [µm] Water Flow [mL/min/cm2] Temp Max Sintered Silver SPI Supplies 0.2 50 17 550 Glass Fiber Millipore 0.7 380 1.4 500 SEM and EDX analysis were taken of clean filters to determine its composition, and therefore providing information about the background of the filters. This helps to identify which elements 64 found on the filter are coming from the particle and which are the background of the filter. The silver membrane was found to be composed of only silver and oxygen. The glass fiber filter had Si, O, Ca, K, Ti and Zn. 65 Figure 4-11: SEM photograph of clean silver membrane, 0.2µm pore size, using a Hitachi S3000N SEM Figure 4-12: EDX of silver membrane to determine elemental composition of background 66 Figure 4-13: SEM photograph of clean glass fiber filter, 0.7µm pore size, a Hitachi S2300 SEM Figure 4-14: EDX of glass fiber filter to determine elemental composition of background 67 4.5.4 Deposit Thickness and Strength of Oxide Adhesion To quantify the mass of magnetite deposited on the tube, two techniques for magnetite removal was used; mechanically using an ultrasonic cleaner and chemically using acid wash procedures. 5.0 cm sample tubes were cut at 30.0cm intervals along the test section for magnetite deposition quantification. For ultrasonic cleaning, the sample tube was immersed in 25.0mL of 1N hydrochloric acid at room temperature and cleaned in a Cole-Parmer ultrasonic cleaner for 20 minutes. The sample tube was then removed and the solution was heated on a bunsen burner with a watch plate and evaporated in a fume hood. Once the beaker was completely dry, it was washed with 25.0mL of 1% nitric acid solution. 2.0mL was taken from the sample and diluted in another sample container of 25.0mL, 1% nitric acid. This was repeated once more to achieve three sets of sample solutions which have of 1×, 13.5× and 182.25× dilution ratios. For acid wash, the sample tube was immersed in 15.0mL of 1N preheated hydrochloric solution (≈75°C) for 2 minutes. The sample tube is then removed from the solution and the solution is further heated to evaporate it completely. The beaker was then washed using the same procedure as the ultrasonic cleaning method. A Varian AA240 Atomic Absorption Spectroscopy (AAS) was used to analyze iron concentrations in the samples. AAS uses measured absorbance to determine analyte concentrations according to the Beer-Lambert law. Calibration of the AAS was conducted by first measuring the absorbance using standards of known concentration. For these experiments, the calibration was done with 0.0, 1.0, 2.0, 5.0, and 7.5mg/L of iron standards in 1% nitric acid 68 matrix. All sample solutions were also digested in a 1% nitric acid matrix. The detection limit of atomic absorption spectroscopy for iron is approximately 0.1 mg/L (Willard et al., 1969). Since stainless steel 316L also contains iron, there would be dissolution of iron from the tubing itself and not just the deposited magnetite. To account for this, clean tubes without deposits were exposed to the same conditions as those of the sample tubes and its iron content was measured using AAS. This was done for both the ultrasonic cleaning and acid wash procedures and the resulting iron concentration from the clean samples were subtracted from the raw sample tube concentration. A mass balance of the entire system was pursued by measuring the concentration of ferrous species in the effluent, filters and test section. Effluent concentrations were determined by taking 20.0mL samples and analyzing them using Atomic Absorption Spectroscopy in a similar manner to the test section; first by dissolving any possible magnetite that might have passed through the filter, evaporating the solution, and re-dissolving in 1% nitric acid matrix. For experiments with ferrous chloride, the effluent samples were taken during the experiment directly from the system effluent. It was determined that due to changing deposition/exfoliation rates over time, an averaged effluent concentration would be more representative for mass balance purposes. Therefore for all ferrous sulfate experiments, the effluent was stored in the high-density- polyethylene (HDPE) tank until the experiment was completed and a sample was taken of the total effluent. In addition, for all ferrous sulfate experiments, sulfate was known to interfere with the AAS in measuring iron, therefore as a way of mitigating this, a copper sulfate of 0.1 mol/L and 1% nitric acid matrix was used for these standards and sample solutions. 69 5 Results and Discussion of Experiments A total of eight experiments and one blank were conducted using the SCW once-through flow apparatus. After each experiment, filters, effluent, and tube samples were analyzed using SEM and AAS to determine significant findings. A brief summary of the results is provided in Table 5-1 while a more detailed overview and collection of all results can be found in Appendix C. The two precursors used were ferrous chloride tetrahydrate (FeCl2·4H2O) from Fisher Scientific and ferrous sulfate heptahydrate (FeSO4·7H2O) from BDH. The experiments are broken down into the following categories: reference condition, effect of heat flux, high pH, low concentration and blank run with no precursor. Table 5-1: Summary of experiments Run Category Pressure [MPa] Tube length [m] Bulk Temperature Heat Flux [kW/m2] pH Concentration [mmol Fe2+/L] Inlet [⁰C] Outlet [⁰C] Dissolved Fe2+ Precursor 1 Reference 23.7 1.8 350 400 102 3 5.48 FeCl2·4H2O 2 Reference 23.9 1.8 350 397 97 3.5 4.97 FeSO4·7H2O 3 Heat Flux 22.4 1.0 372 376 24 3 5.31 FeCl2·4H2O 4 Heat Flux 23.0 1.8 371 376 13 3.5 5.04 FeSO4·7H2O 5 Heat Flux 23.3 1.8 384 383 - 3.5 5.32 FeSO4·7H2O 6 High pH 23.8 1.8 350 396 97 9 5.11 FeSO4·7H2O 7 High pH 23.7 1.8 200 370 92 9 5.17 FeSO4·7H2O 8 Concentration 23.7 1.8 350 395 96 3 0.56 FeCl2·4H2O - Blank 23.7 1.8 351 399 99 Neutral 0.00 - 70 5.1 Reference Condition Experiments were run with ferrous chloride and ferrous sulfate precursors with the test section at maximum heat flux of approximately 100 kW/m 2 . These were considered to be reference experiments that all other experiments could be compared to. Temperatures of the bulk fluid inlet and outlet were 350°C and 400°C respectively at 23.7MPa. The injection tank consisted of 1L of precursor in deaerated, deionized water while the primary tank had deaerated, deionized water, producing an acidic solution (pH≈3) once both fluids were mixed. The injection method is similar to those described by Adschiri et al. (1992) in hydrothermal synthesis. 5.1.1 Temperature Analysis The transient temperature of the test section outer wall for reference condition with ferrous chloride precursor is shown in Figure 5-1. As mentioned in Chapter 4, the large spike and subsequent fall in the temperature at 15-20 minutes is due to the momentary shutoff/on of the injection pump for switching the supply line from deionized water to ferrous chloride solution. At subcritical temperatures, the temperature remain constant throughout the experiment. At supercritical temperature (1.65m from the inlet), the wall temperatures increase rapidly at the start and reaches an asymptotic temperature after 10 minutes of injection. 71 Figure 5-1: Temperature measurements of test section vs. time for reference condition with ferrous chloride precursor (Experiment #1) Fouling was observed by the sharp rise in temperature as well as an increase in system pressure to 26.2 MPa during the injection period as a result of restricted flow. The temperature profile at the 1.65m location has an asymptotic fouling behavior similar to those found in several studies of iron oxide fouling (Müller-Steinhagen et al., 1988; Newson et al., 1983; Thomas & Grigull, 1974). It was speculated that the removal rate increases as the deposition thickness increases, since the bond at the top layer of the surface weakens as the deposit grows higher and is more likely to be removed by the shear force of the fluid (Newson et al., 1983). Another explanation presented by Thomas and Grigull (1974) suggested that the initial high deposition rate was due to the particles adhering to the troughs in an initially rough tube. As deposition continued, the Injection 72 troughs would be filled and the tube surface would become effectively smooth and more difficult for the particles to adhere to. High fouling rates observed at the 1.65m location from the inlet was converted to an equivalent magnetite deposition thickness at the asymptotic temperature. This was found to be 0.47 mm or 1.5g of magnetite in a 15 cm long section of the tube. Such high fouling rates are unlikely with only magnetite fouling, and therefore the high increase in temperature may be a product of mixed recrystallization of ferrous chloride as well as magnetite particles. Such a scenario should be considered as the solubility of any salt, including ferrous chloride would be very low in supercritical conditions. Temperature measurements for ferrous sulfate precursor showed variations in the test section temperature but also in the bulk fluid temperatures (Appendix C. 2). This may be due to inconsistent flow rate of the injection pump for this experiment. Once this was taken into consideration, it was concluded that no significant fouling was observed from the temperature measurements. 5.1.2 Filter Analysis In the experiment with a ferrous chloride precursor, it was determined after the experiment that the secondary line was at a significantly lower flow rate than initially set. The HTHP and LTLP filter was visibly unchanged and showed very few particles collected through SEM images. On the other hand, the HTHP filter for the ferrous sulfate precursor had a very fine but visible black film on the silver membrane after the experiment. SEM analysis of the HTHP filter revealed 73 significant amount of particles collected, with particle diameters ranging from less than a micron to several microns in diameter. These particles are much larger than those seen by Adschiri et al. (2000) in hydrothermal synthesis of iron oxide particles which observed the formation of ~50nm diameter particles. However, there is a possibility that the larger particles were captured by their system filter which had not been analyzed. 5.1.3 Deposit Analysis SEM images of the test section revealed that the ferrous chloride precursor produced magnetite particles early in the test section. The particles which deposited near the inlet were smaller with few larger micron-sized particles. Further down the test section at higher temperatures, the particles deposited grew in size to several microns in which deposition was dense and compact. Figure 5-2: SEM photograph of magnetite deposit on test section tube surface, 0.15 m location. Reference condition with ferrous chloride precursor (Experiment #1) 74 Figure 5-3: SEM photograph of magnetite deposit on test section tube surface, 0.60 m location. Reference condition with ferrous chloride precursor (Experiment #1) Figure 5-4: SEM photograph of magnetite deposit on test section tube surface, 1.20 m location. Reference condition with ferrous chloride precursor (Experiment #1) 75 Figure 5-5: SEM photograph of magnetite deposit on test section tube surface, 1.65 m location. Reference condition with ferrous chloride precursor (Experiment #1) X-ray diffraction (XRD) was conducted on the oxide deposits found in the test section tube by mechanically removing the deposit. Figure 5-6 and Figure 5-7 show XRD results for ferrous chloride and ferrous sulfate precursors respectively. For ferrous chloride, a General Area Detector Diffraction System (GADDS) using a copper radiation operated at 40kV and 40mA scanned the deposit from 21.4⁰ to 71.8⁰ at 0.050⁰ increments. A diffracted beam graphite monochromator and Hi-Start detector was used for producing and detecting the signal. Signals were relatively weak and the peaks were broad due to the small quantity of deposit that was available from the tube (see Figure 5-6). 76 Figure 5-6: XRD of tube deposits of test section, reference condition ferrous chloride precursor (Experment #1) Figure 5-7: XRD of tube deposit of test section, reference condition ferrous sulfate precursor (Experiment #2) 77 For ferrous sulfate reference experiment, a D-8 Advance X-ray Diffractometer using a copper anode tube operated at 40kV and 40mA, scanned the filter from 5.0⁰ to 70.0⁰ at 0.040⁰ increments. A diffracted beam graphite monochromator and NaI scintillation detector was used for producing and detecting the signal. XRD of the deposit indicated a mixture of magnetite and hematite which may have formed due to oxygen contamination during the experiment (see Figure 5-7). To determine the deposition thickness along the test section, cleaning methods described in section 4.5.4 were applied to the sample tubes. This is similar to chemical analysis methods for deposition determination used in previous studies by dissolving magnetite layers from experimental tubes using hydrochloric acid (Newson et al., 1983). Between ferrous chloride and ferrous sulfate precursors, the amount and location of the deposit was relatively similar. At lower temperatures near the inlet, the deposit was found to be less and the deposit thickness grew as the temperature increased towards the outlet of the test section. Ultrasonic cleaning was able to remove the majority of the deposit, however, some of the deposit remained intact to the tube and was only removed after the acid wash procedure. It was observed that for tube sections which were subject to supercritical temperatures, depositions remained intact and were much more difficult to remove than those exposed to subcritical temperatures. This suggests an increase in the oxide adhesive strength to the surface at supercritical conditions, shown by the increased amount of magnetite which was removed only after an “aggressive” cleaning method, regardless of the precursor injected. 78 In a study conducted by Yeon et al. (2006), the deposition characteristic of hematite particles onto a heated zircaloy tubing was found to change by adding ferrous species to the solution. Under single phase flow conditions, there was almost no deposition of hematite particles onto a zircaloy surface unless the particles were mixed with ferrous ions. The deposit was found to form two layers on the surface; a top layer which was easily removed with ultrasonic cleaning using distilled water and an inner layer which was only removed after ultrasonic cleaning with concentrated acid. Yeon et al. (2006) concluded that the top layer was formed from particle deposition while the inner layer was formed from the precipitation of ferrous ions. Therefore, the crystallization of dissolved ferrous species formed a stronger bond to the surface which then allowed the loosely attached particles to stick to the wall. In the case of the ferrous precursors in supercritical water, the higher strength of the oxide in supercritical conditions is believed to be due to small amounts of crystallization occurring at the interface between particles and the tube surface due to the solubility drop of magnetite in supercritical water. 79 Figure 5-8: Deposit thickness on test section for reference condition with ferrous chloride precursor (Experiment #1) Figure 5-9: Deposit thickness on test section for reference condition with ferrous sulfate precursor (Experiment #2) 80 5.2 Effect of Heat Flux Experiments were run with low heat flux and no heat flux conditions and are compared with the reference condition. Low heat flux of approximately 20 kW/m 2 in the test section was conducted for both ferrous chloride and ferrous sulfate precursor, with temperature ranging from 371°C to 376°C. A third experiment under no heat flux condition had ferrous sulfate precursor solution and the temperature was at 384°C. 5.2.1 Temperature Analysis Temperature measurements were taken for the low heat flux conditions, however, no significant differences in temperature were found in these cases. 5.2.2 Filter Analysis SEM analysis showed sub-micron to several micron-sized particles scattered along the membrane similar to those seen in the reference conditions for ferrous sulfate (see Figure 5-10). The filter shows particles of various shapes and sizes, some which appear to be crystalline. 20.0keV area EDX was applied on the filter which confirmed the presence of iron oxide along with silver from the background as shown in Figure 5-11. The absence of other metal oxides such as nickel, chromium, or molybdenum oxides support the assumption that corrosion of the stainless steel 316L test section under experimental conditions is negligible. The HTHP filter for ferrous sulfate at low heat flux was fairly uniform magnetite particles of 1 µm size with agglomerates of smaller particles on HTHP filter suggesting that the type of precursor has some influence on the particles formed under the same conditions. 81 Figure 5-10: SEM photograph of particles collected on HTHP filter, 5.0k magnification, for low heat flux with ferrous chloride precursor (Experiment #3) Figure 5-11: EDX of HTHP filter for low heat flux with ferrous chloride precursor 82 Figure 5-12: SEM photograph of particles collected on HTHP filter, 5.0k magnification, for low heat flux with ferrous sulfate precursor (Experiment #4) Figure 5-13: SEM photograph of particles collected on HTHP filter, 5.0k magnification, for no heat flux with ferrous chloride (Experiment #5) 83 For the experiment run with ferrous sulfate with no heat flux and supercritical temperature, the particles on the HTHP filter were of larger diameter than in low heat flux experiments and some of these larger particles also appear to have an octahedral structure as seen in Figure 5-13, which is a common crystal structure for magnetite (Anthony et al., 1997). XRD was carried out on the HTHP silver membrane filter of Experiment #3 to determine the crystal structure of the deposited particles. Results show that the peaks match very well with those of magnetite and comparison of these peaks to other iron oxide such as hematite indicated that these were not present in the sample. Carbon graphite is also present in the sample and is believed to have been detected due to the carbon tape used on the filter for SEM. Figure 5-14: XRD of deposit on HTHP filter for low heat flux with ferrous chloride precursor (Experiment #3) 84 5.2.3 Deposit Analysis Deposition thickness of the test section for ferrous sulfate precursor under low and no heat flux conditions were examined and the results are found in Appendix C. SEM images of the tubes show very little deposition and these findings are confirmed using cleaning methods. Figure 5-15: Deposit thickness on test section, low heat flux with ferrous sulfate precursor (Experiment #4) The effect of heat flux compared to reference condition suggests that lower heat flux results in lower deposition. This compares to previous models which showed that deposition had a direct influence from heat flux (Electric Power Research Institute Inc., 2003). In previous studies, experiments showed that deposition of magnetite particles in bulk concentration of 0.16mg to 5.04mg of Fe kg/L was 30% lower on an unheated surface than one with heat flux of 400kW/m 2 (Newson et al., 1983). 85 Although the original Kern and Seaton model does not account for the influence of heat flux on particle deposition, there have been several attempts in later studies to include heat flux by incorporating thermophoresis and an Arrhenius term with an activation temperature (Müller- Steinhagen et al., 1988). Thermophoresis has been shown to create a measurable change in the deposition of a particle onto a heated surface for particles as large as 11 µm (Epstein, 1997), although it primarily observed to influence smaller submicron particles. The thermophoretic velocity is dependent on the fluid properties and temperature gradient and can be calculated using the equation below: 5-1 where is a coefficient determined by: 5-2 The constant k is 1.8 for gases and 0.26 for liquids, λp and λl represent the conductivity of the particle and liquid respectively (Epstein, 1997). The overall deposition velocity accounting for thermophoresis is described in equation 5-3: ( ) 5-3 The equation resulted in values for the thermophoretic velocity of Kth in the range of 10 -10 m/s, much smaller than the mass transport velocity of 10 -4 m/s for these experiments, suggesting that thermophoresis should have an insignificant impact on deposition. 86 In addition to thermophoresis, high heat flux conditions usually result in higher surface temperature given constant flow rates, which provide the activation energy required for the particle to stick to the wall. In an experiment with alumina particles depositing on a heated surface, Müller-Steinhagen et al. (1988) observed that an asymptotic fouling resistance had a maximum at any given heat flux for a fixed flow rate, concentration and bulk temperature. To model the data, Müller-Steinhagen included both thermophoresis and activation energy into the Kern and Seaton model. The model showed that the increase in heat flux initially resulted in the increase of surface temperature resulting in higher deposition rates. However, as Tw increasingly exceeds Tb, deposition is counteracted and eventually overtaken by thermophoresis thereby decreasing deposition with increasing heat flux. In general, the correlation over-predicted deposition velocities and a correction factor had to be introduced to give a reasonable fit to the experimental data. Such a procedure demonstrates the difficulty in accurately modeling the complex nature of particles in heat transfer flow. Although the Arrhenius term predicts lower deposition rates for lower heat flux conditions, it fails to adequately explain the extent to which deposition rate decreased in these experiments compared to reference conditions. Müller-Steinhagen et al. (1988) postulated that surface/fluid temperature may also affect the structure of the deposit, making it more porous and loosely packed in certain conditions. It is not known if this is affected by absolute wall temperature or by the wall-liquid temperature difference. If it is assumed that the lower heat flux results in loosely packed deposits which can easily be subject to removal, this may explain the lower deposition of the low heat flux condition observed in this study. However, further research would be required 87 in order to make any conclusions regarding if heat flux has a direct influence on the deposit structure. 5.3 High pH Conditions Current CANDU reactors normally operate with a pH of 9 ~ 10 using a simple water chemistry of lithium hydroxide for pH control (Burrill, 2000). Two experiments were conducted with ferrous sulfate as a precursor but at a higher pH of 9 (at room temperature). The experiments were run with temperatures running at 350°C to 400°C and 200°C to 370ºC. The pH of the system was increased by adding sodium hydroxide salt to the feedwater. At first, ferrous sulfate and sodium hydroxide was mixed in the injection tank and the pH was measured directly. However, the introduction of sodium hydroxide to a ferrous sulfate solution immediately produced particles in the system which would cause problems with the injection pump. As an alternative approach, sodium hydroxide solution was introduced in the primary tank and allowed to mix with the ferrous sulfate in-situ of the system. Due to size limitations of the main tank, sodium hydroxide was added to the first tank after heating the entire system. The sodium hydroxide was weighed and mixed into a deaerated tank and a sample was drawn from the tank. The conductivity was measured and compared to the amount of sodium hydroxide required using a calibration curve shown in Figure 5-16. A linear regression gave the equation 5- 3 for the concentration as a function of conductivity. 5-4 where C is the concentration [mmol/L] and σ is the conductivity [mS/cm]. 88 Figure 5-16: Calibration of the conductivity meter for determining NaOH concentration in primary tank The pH could not be measured directly in the system due to the high temperature and pressure of the solution at the mixing tee. Instead, the pH of the ferrous sulfate solution was determined by using data from Arden (1950) for ferrous sulfate and sodium hydroxide solution. Conditions in Arden’s experiment are similar to the conditions in this study. The solution was deaerated to eliminate the presence of oxygen and ferric ions which have been found to create large errors in the pH measurements. Oxygen in the system promotes the formation of ferrosic hydroxide, a ferric ion compound instead of the desired ferrous hydroxide (Arden, 1950). The conductivity of the primary tank after dissolving sodium hydroxide was 2.02 and 2.10 mS/cm which correspond to a concentration of 10.49 and 10.91 mmol/L for experiments #6 and 89 #7 respectively. The ratio of Na to Fe was calculated with equation 5-4 taking into consideration the dilution of the primary stream with the injection stream. ̇ ̇ ̇ ̇ 5-5 The molar ratio of Na to Fe was compared to data with Arden (1950) and the pH was determined to be approximately 9 in both experiments, as shown below. Figure 5-17: Predicted pH of the system using data from Arden (1950) 5.3.1 Temperature Analysis For the experiment with the test section heated from subcritical to supercritical, large temperature changes were found at locations 0.15 m and 1.20 m while a steady temperature rise was found near the outlet at 1.65m. The temperature at the 1.20 m location approached 500°C 90 after 30 minutes which was considered too high and the power to the test section was momentarily turned off to cool the section. Once the temperature dropped to below 400°C, the test section was turned on once more to continue the injection at the original temperatures until the end of 40 minutes. Figure 5-18: Temperature measurements of test section vs. time for high pH with ferrous sulfate precursor (Experiment #6). Power turned off briefly at t = 48 minutes. Temperature measurements at 0.15 m from the inlet suggest that deposits exfoliated from the tube surface relatively easily and quickly. These deposition-removal cycles found in the temperature was also observed by Khan (2005) with the injection of sodium carbonate in supercritical water. These occurred with combined particle and crystallization deposition and signaled a weaker adhesion to the tube wall than pure crystalline deposit. Injection 91 5.3.2 Filter Analysis Observing the particles captured on the HTHP and LTHP filters under an SEM, revealed that the particle sizes are consistently much smaller than in the reference case, falling in the 100-200nm diameter range. Formation of smaller particles in higher pH solution are confirmed by literature studies using sol-gels. Sugimoto and Matijevic (1980) displayed that under excess OH - ions, the magnetite particles formed were small, tens of nanometer in diameter and had a cubic morphology. On the other hand, large magnetite particles of 1.1 µm formed under 0.03M excess Fe 2+ conditions. The LTHP filter for both experiments had a significant amount of small particles deposited on the glass fiber. In experiment #7, it can be seen that the deposit was enough to completely cover all signs of the glass fiber matrix. Figure 5-19: SEM photograph of particles collected on HTHP filter, 10.0k magnification, for high pH, ferrous sulfate (Experiment #6) 92 Figure 5-20: SEM photograph of particles collected on LTHP filter, 2.0k magnification, for high pH, ferrous sulfate (Experiment #6) Figure 5-21: SEM photograph of particles collected on HTHP filter, 5.0k magnification, for high pH, subcritical, ferrous sulfate (Experiment #7) 93 Figure 5-22: SEM photograph of particles collected on LTHP filter, 2.0k magnification, for high pH, subcritical, ferrous sulfate (Experiment #7) 5.3.3 Deposit Analysis SEM images of the tube surface after the test section was disassembled confirm that there was very few particles attached to the surface. Furthermore, deposit thickness determination using cleaning methods indicate that the deposit is less than 1 µm shown by Figure 5-23. 94 Figure 5-23: Deposit thickness on test section (Experiment #6) As mentioned in Section 2.3.3, the particles that deposit on the tube are submerged in the viscous sub-layer which dissipates turbulent bursts responsible for particle removal. The viscous sub- layer thickness was calculated for the high pH at supercritical experiment using equation 5.5 below (Cengel & Cimbala, 2006). 5-6 The calculations showed that this distance was approximately 25 µm at 200°C, 14 µm at 350°C, and 6 µm at 400ºC under the experimental conditions. In the case of Experiment #6 at 0.15m location, the deposition-removal cycles had an average temperature change of 12°C from the initially clean state. This corresponded to a calculated thickness of the deposit right before the removal of 42 µm. 95 The cool down procedure was repeated in a similar manner for all experiments for direct comparison between the experiments. Significant amount of particles were found in the effluent of the system during the cooling/depressurization for both high pH experiments, indicating that removal rates post-injection were much higher for this deposit. This may be attributed to the increase in flow rate during depressurization. Turner et al. (1990) suggested that the change in flow rates are a larger factor in removal rates compared to steady state conditions. 5.4 Low Concentration and Blank Experiment The experiment with lower concentration of 0.5 mmol/L and proportionally longer duration of 400 minutes was conducted to determine the effects of concentration on deposition without changing the total amount of ferrous species injected. All three filters showed ferrous-chromium exfoliation occurring in the system indicating corrosion of the tube. Hence, the results from this experiment were not analyzed any further. A blank test was also run with reference conditions but without a precursor. SEM analysis of the HTHP and LTLP filters showed almost no particles collected as expected. The LTHP filter had few particles which likely exfoliated from the heat exchanger, but the amount was insignificant compared to the experiments with a precursor. 5.5 Overall Summary and Mass Balance A summary of the significant results from each of the experiments are provided in Table 5-2. 96 Table 5-2: Results summary table - Part I Parameter Precursor Filters Tube Samples SEM HTHP LTHP LTLP 1 Reference case for ferrous chloride FeCl2 Almost no particles Large amount of submicron and some micron sized particles Almost no particles Small particles at inlet, large micron sized particles at high temperatures 2 Reference case for ferrous sulfate FeSO4 Nanometer to several micron Very Small particles of unknown size Almost no particles found Small and few deposits at inlet, large deposits at center of test section 3 Low heat flux FeCl2 Several micron size Very Small particles of unknown size N/A consistent micron sized particles found at inlet and outlet of test section 4 Low heat flux FeSO4 Consistent ≈ 1 micron size Very Small particles of unknown size Almost no particles found Very few deposits 5 No heat flux, all supercritical FeSO4 Hundred nanometer to several micron size Approximately 500nm consistent size Almost no particles found Combination of submicron and micron sized particles 6 High pH FeSO4 Approximately 100-200nm consistent sizes Approximately 100-200nm consistent sizes Small amount of particles, hundred- nanometer sized particles Very few deposits 7 High pH, all subcritical FeSO4 Approximately 100-200nm consistent sizes Approximately 100-200nm consistent sizes Almost no particles found N/A 8 Low Concentration FeCl2 Nanometer to several micron Large amount of particles and flakes Large amount of very small particles N/A Blank - Almost no particles Few particles of sub-micron size Almost no particles N/A 97 Table 5-3: Results summary table - Part II Temperature Measurements Deposit Thickness Deposit Strength Mass Balance XRD Comments 1 Temperature rise at supercritical temperatures, no temperature difference for subcritical 10µm maximum More depost strength in supercritical conditions Recovery of 79% Analyzed tube deposits, found magnetite Secondary line flow rate was much lower resulting in very few particles on secondary line filters 2 No difference found 12µm maximum More deposit strength in supercritical conditions Recovery of 82% Analyzed tube deposits, found magnetite and some hematite 3 No difference found N/A N/A Recovery of 52% Analyzed HTHP Filter, found magnetite Test section is 1.0m long, test section not examined using cleaning method 4 No difference found Less than 1µm thickness No difference Recovery of 72% N/A 5 N/A Less than 1µm thickness No difference Recovery of 77% N/A 6 Temperature rise at supercritical temperatures, oxide deposition and exfoliation found at subcritical Less than 1µm thickness No difference Recovery of 53% N/A Large amount of black particles found in the effluent after cooling the system 7 No difference found N/A N/A Recovery of 39% N/A Did not dissassemble test section for this experiment 8 No difference found N/A N/A Recovery of 83% N/A Did not dissassemble test section for this experiment No difference found N/A N/A N/A N/A Did not dissassemble test section for this experiment 98 A mass balance calculation was completed for all experiments, however, not all sections for each experiment were analyzed and therefore, are presented to provide an approximation only. The majority of the experiments had good recovery of the ferrous species injected into the system with the exception of experiment #7 which was below 50%. To determine the yield of magnetite for input into the simulation, the iron content found in the effluent was subtracted from the total injected amount. Hence, it was assumed that the iron mass which was not recovered had deposited as magnetite particles onto other surfaces within the system not analyzed, such as the heat exchanger or the tube fittings between the mixing tee and test section. Mass balance for future experiments may be improved by cleaning the heat exchanger after each experiment and analyzing the iron concentration in the cleaning solution. The equation for recovery and yield are given in equations 5-7 and 5-8 respectively. 5-7 5-8 In experiment #6 and #7, it was found that the effluent contained significant amount of oxide particles which passed through the LTHP filter, perhaps due to overloading. The experiment produced a higher yield of iron oxide particles indicated by the relative number of particles collected on the HTHP filter. To gain insight into the yield in the high pH experiments, the effluent from experiment #7 was first filtered using a Fisherbrand filter (Grade - P2) to separate the residue from the filtrate. The residue and filtrate were independently analyzed using AAS. It was found that the effluent was 57% particulate matter. Therefore, for experiments #6 and #7, 99 the same percentage of particulate matter in the effluent was assumed and the amount was added to the total yield of particles in the system. Table 5-4: Mass balance of experiments #1 - 8 Experiment # Fe 2+ [mmol/L] Flow Rate [L/hr] Run Time [min] Effluent [mg] Test Section [mg] Total Filter Deposit [mg] Total Iron Expected [mg] Total Iron Measured [mg] Recovery [%] Estimated Yield 1 5.48 3.54 42 353 244 0.69 758 598 79% 52% 2 4.97 3.54 39 141 380 1.28 639 522 82% 78% 3 5.31 3.60 44 404 NM NM 783 404 52% 48% 4 5.04 3.54 40 478 11.5 NM 664 478 72% 28% 5 5.32 3.50 40 536 26.1 NM 692 536 77% 23% 6 5.11 3.50 37 310 12.0 2.53 615 324 53% 78% 7 5.17 3.47 40 260 NM NM 667 260 39% 83% 8 0.56 3.50 400 605 NM NM 729 605 83% 17% 100 6 Results and Discussion of Simulations 6.1 Comparison between Simulation and Experimental Simulations were run with parameters from experiments and these were compared to experimental deposition thickness obtained from the cleaning method. The magnetite concentration used for the simulation was obtained from the yield estimated from mass balance in Table 5-4, while the average particle size was estimated from the SEM images of the tube deposit and filters. For the reference conditions, the average particle size was estimated to be 4 µm and 1 µm for ferrous chloride and ferrous sulfate precursors respectively. For these reference condition experiments, the simulation results predicted magnetite deposition reasonably well. The simulation predicted similar deposition thickness for each case, however, with larger particles the peak deposit shifted closer towards the inlet of the test section. (a) (b) Figure 6-1: Comparison between simulation and experimental for reference conditions (a) Experiment #1, ferrous chloride with average particle size = 4 µm, magnetite concentration = 200 mg/L (b) Experiment #2, ferrous sulfate with average particle size = 1µm, magnetite concentration = 299 mg/L. 101 For low heat flux conditions, the deposition thickness was overestimated by nearly a factor of four. However, the simulation did predict a lower deposition rate compared to the other experiments and a uniform deposition rate along the test section compared well to experimental results, as shown in Figure 6-2. (a) (b) Figure 6-2: Comparison between simulation and experimental for ferrous sulfate experiments with (a) Experiment #4, low heat flux with average particle size = 1 µm, magnetite concentration = 108 mg/L and (b) Experiment #5, no heat flux with average particle size = 2 µm, magnetite concentration = 89 mg/L. Finally, for the experiments at high pH, the simulation greatly overestimated the deposition thickness. This is likely due to the removal that occurred during and after the deposition process described in section 5.3.3. Higher removal rates in the high pH conditions suggest that the deposit had a weaker adhesion to the tube. As discussed in section 5.1.3, the strength of oxide adhesion was enhanced with the precipitation of ferrous species, and one explanation is that the 102 reduced amount of dissolved ferrous ions in the solution resulting from the high yield of particles formed under high pH condition may have caused the formation of a weak deposit. A second possibility is that the formation of molten sodium hydroxide salts had formed and deposited along with the magnetite particles in supercritical conditions. During cool down, the molten salt would have re-dissolved in the water, possibly carrying the magnetite particles along with it. Figure 6-3: Comparison between simulation and experimental for Experiment #6, high pH, ferrous sulfate. Simulation was run with an average particle size = 0.15µm, magnetite concentration = 321 mg/L. In all cases, the simulation overestimated the deposition of magnetite suggesting that surface attachment and/or removal rates cannot be neglected in magnetite particle deposition in supercritical water. 103 6.2 Simulation for CANDU SCWR As one of the design criteria in the proposed SCWR, the maximum fuel cladding temperature cannot exceed 850⁰C (Naidin et al., 2009). This is to ensure that the material’s mechanical and chemical properties can withstand the aggressive environment of supercritical water. Li et al. (2009) developed a 3-dimensional heat transfer simulation for a CANFLEX fuel bundle in a SCWR which showed that the maximum temperature of the cladding can reach as high as 802.2⁰C at certain locations of the fuel bundle. The CANDU SCWR deposition simulation developed in this study does not account for oxide growth from the fuel cladding. This is due to the fact that the alloy for the fuel cladding has not been decided and the rate of oxide growth from the alloy varies dramatically depending on the material (Was et al., 2006). Additionally, only the surface temperature of the fuel cladding exposed to supercritical water is calculated since the design criteria of maximum fuel cladding is concerned with the surface temperature (Li et al., 2009). Figure 6-4 shows the expected fuel cladding-surface temperature with a heat flux of 1000 kW/m 2 with no deposition (see Table 3-1 for simulation parameters). The fluid enters the test section at 350ºC and 25MPa, saturated with 11µg/L of ferrous ions. As the temperature increases beyond the pseudocritical temperature, the solubility drops in accordance with Figure 2-3 and particles form in the bulk fluid. Figure 6-5 shows the temperature profile of the fuel bundle after one year of operation assuming a particle diameter of 150 nm. 104 Figure 6-4: Bulk fluid and fuel cladding-surface temperature without particle deposition Figure 6-5: Bulk fluid and fuel cladding-surface temperature after 1 year of operation with magnetite particles of 150 nm diameter 105 Figure 6-6: Magnetite deposition thickness on fuel cladding after 1 year of operation for 150 nm and 1 µm average particle diameters In Figure 6-6, the effects of particle diameter is compared between 150 nm and 1 µm. The experimental results from section 5.3 suggest that at a pH ≈ 9-10 where a typical CANDU reactor operates (Burrill, 2000), the formation of small, ~100 nm particles are likely. For the 1 µm scenario where 0.279 ≤ tp + ≤ 8.284, inertial coasting is the dominant mechanism for deposition and the deposition velocity is approaching maximum rate. On the other hand, for the particle diameter of 150 nm where 0.006 ≤ tp + ≤ 0.215, the deposition mechanism changes from diffusion to inertial coasting inside the reactor core and the deposition velocity remains closer to the minimum of the deposition velocity curve. Maximum temperature difference between fouled and un-fouled cladding-surface temperatures was found to be 23.9⁰C occurring approximately 3 m downstream of the inlet. 106 Since the simulation was based from 1 fuel element, the cladding temperature represents an average among all 43 actual elements. The Li et al. (2009) simulation which looked at all 43 elements, found that cladding-surface temperatures can vary by several hundred degrees depending on the fuel element. The highest fuel cladding temperature of 802.2⁰C occurred at the 4 m location where an increase of 19.6⁰C due to fouling was found by this study. Therefore after several years of operation, fouling on the fuel cladding may cause temperatures to exceed the design criteria of 850⁰C if magnetite deposition considerations are not taken into account. Calculation of the deposit thickness found in the simulation by Burrill (2000) discussed in section 2.3.4 suggest a peak deposit of 297 µm assuming mass transport of ferrous ions in a CANDU SCWR after one year of operation. This is in relatively good agreement to the results presented in this study considering several key differences in the parameters and assumptions in the model; a slightly higher saturation concentration of 18µg/L (Burrill, 2000) compared to 11 µg/L, temperature of core outlet of 384°C (Burrill, 2000) compared to 625°C, and the use of an ionic diffusion model. Similarly, the transport and deposition model of Cook and Fatoux (2009) concluded a deposit thickness of 22.8 µm near the outlet of a CANDU SCWR reactor. The arbitrary deposition velocity assumed by Cook and Fatoux of 10 -5 m/s which is slightly lower than the 4.2×10 -5 – 28.7×10 -5 m/s range for the deposition velocity calculated here using mass transport for 150 nm sized particles. Despite these differences, the maximum deposition thickness of 50 µm found from this study fits reasonably well with the model by Cook and Fatoux. 107 6.3 Limitations of the Simulation In Chapter 5, surface attachment resistance and removal rates were found to be important factors in the deposition of magnetite particles in supercritical water. However, these were neglected in the simulation as further experimental work is required to properly include a surface attachment and removal term. Therefore, for the situation where surface attachment and removal terms are unknown, mass transport models provide a relatively good estimate on the upper limit for deposition rate. Similar results were found by Turner and Klimas (2000) who examined magnetite particle deposition onto Alloy 600 under single-phase forced convection at high temperature and pressure water. Significant deviations were found between calculated and measured deposition velocities, all of which the mass transport model overestimated deposition rates. Surface attachment was determined to be the main limitation in this experiment while removal was found to be insignificant. Turner measured the isoelectric point for both magnetite and Alloy 600 and determined that they have the same sign of charge in high temperature alkaline water resulting in a repulsive force between the particle and surface, thereby significantly limiting deposition (Turner & Klimas, 2000). Therefore, it is possible that the magnetite particles formed in these experiments in subcritical water experienced repulsion due to the electric double layer repulsion. On the other hand, surface attachment behaviour can be significantly different in supercritical water. The electric double layer force was calculated by Ghosh et al. (2006) as a function of temperature in subcritical and supercritical water at 25MPa. These forces were found to decrease significantly in supercritical water due to its low dielectric constant. On the other hand, Van der Waals attraction potential was shown to increase as temperature increased in 108 subcritical water, and further increase in supercritical water (Ghosh et al., 2006). This would suggest that in supercritical water, double layer and Van der Waals forces should not limit deposit growth. Instead, the lower deposition would most likely be the result of the removal process. This may be particularly important for particulate fouling which has a weaker bond to the surface than crystallization fouling. Another limitation to the model is that the nucleation and growth of the particles was assumed to be uniform and instantaneous. Agglomeration of particles was also not considered as it is difficult to model the interactions of particles in a complex system (Bott, 1995). Although the formation of nanometer sized particles can be very fast (Adschiri et al., 1992), SEM images along the test section has shown that micron-sized particles require time to grow. Therefore, better models could be produced by including crystal growth along the test section. 109 7 Conclusion In this study, fouling and transport of magnetite particles in supercritical water were examined experimentally and through computer simulation models. Experimental work was conducted with the objective of utilizing several online and offline techniques for characterizing the deposition and transport phenomena under different heat flux, temperature ranges, and pH conditions. To form simulated corrosion products, a hydrothermal synthesis technique was adapted for producing magnetite particles in deaerated supercritical water using ferrous chloride and ferrous sulfate as precursors. EDX analysis of the particles collected on the filter clearly show an iron oxide composition and XRD of the tube and filter deposits confirm the formation of magnetite. An online monitoring method utilizing thermal resistance properties of magnetite was implemented in the test section to infer the deposition thickness on the tube wall. Deposits led to an increase in outer wall temperature under supercritical conditions during the injection of ferrous chloride with no pH adjustment and ferrous sulfate at high pH. It is speculated that the mixed deposition of magnetite and precipitated ferrous precursor was the source of very high fouling rates in supercritical water. For high pH ferrous sulfate condition, deposition-removal cycles were observed at subcritical temperatures which are believed to be only magnetite particulate fouling. These cycles continued throughout the injection with complete removal occurring when deposit thickness approached 42 µm. It was observed that removal during cool down was particularly important for high pH experiments where sub-micron sized particles of 100 - 200 nm diameter were observed. 110 Using ultrasound and acid wash cleaning procedures, a qualitative method for determining deposit strength was developed. Results suggest that under supercritical conditions, the particulate deposit had a stronger adhesion to the tube and required an aggressive cleaning procedure to completely remove the deposit. It is possible that the precipitation of ferrous species between the depositing particle and surface was responsible for the stronger bond. In addition, SEM imaging of the test section showed the morphology of the deposit varied along the tube length and corresponded to the particles found on the filters. All four techniques individually provide unique data on the particles while the combination of the techniques give an overall understanding of deposition/transport in the system. The online thermal resistance monitoring provided valuable information about deposition and removal cycles, while particle size and adhesive strength could only be determined from offline methods. In the future, high temperature high pressure filters could be implemented in full scale SCW systems which could provide valuable information on the effects of water chemistry on corrosion product transport. On the other hand, destructive testing techniques such as surface SEM and cleaning methods would likely be useful for small test setup experiments such as the one demonstrated in this study. Simulation using heat and mass transport equations produced comparable predictions to experiments for the deposition thickness in the test section. In all cases, the simulation overestimated the deposit thickness, particularly for the high pH experiment where high removal was observed experimentally. The results suggest that both surface attachment and removal rates should be included in the simulation model which would effectively reduce the deposition 111 thickness. In supercritical conditions, the effects of surface attachment forces become less significant and removal is likely to be the dominant limitation to deposition. However, difficulty in modeling both removal and surface attachment stems from the lack of fundamental theory for predicting their coefficients, can vary significantly depending on environmental conditions. Finally, the simulation was adapted to predict fouling rates in a hypothetical CANDU SCWR. The design parameters of a current ACR-700 fuel bundle along with proposed SCWR parameters provided a baseline for the simulation. Thermodynamic solubility predictions using HKF models from literature were used to predict the concentration of magnetite particles which would form in the reactor core. These simulations (assuming mass-transfer limited deposition) suggested that fouling may lead to an increase of fuel cladding-surface temperatures of up to 23.9⁰C after one year of operation assuming the formation of submicron particles. At 4 m down from the inlet, the temperature rise is expected to be 19.6ºC, raising the peak temperature of one section from 802.2ºC to 823.7ºC. This temperature increase in the fuel cladding can potentially be a significant problem for long term operation of a CANDU SCWR, and therefore requires further research. 112 8 Recommendations This study showed that fouling and transport of corrosion products can be a significant issue for the development of a Generation IV CANDU SCWR. Therefore there is a need for developing new techniques and instruments for monitoring and characterizing deposition and transport, particularly for magnetite particles. It remains a challenging task to produce these instruments which can withstand the high temperature and pressure of supercritical water. The following provide recommendations for further development for the techniques presented in this study.  Use nickel alloys for test section tube material which will provide better resistance to hydrochloric acid and are immune to sulfuric acid, both a byproduct of the hydrolysis of ferrous chloride and sulfate respectively, making it more suitable for hydrothermal synthesis of magnetite and cleaning method analysis (Kritzer, 2004).  Experiments of longer duration would be useful for validating the online thermal resistance measurements in more realistic deposition rates. Thermocouple drift may become an issue when the thermocouples are exposed to high temperature for extended period of time.  Experiments of very long durations (>1000 hrs) could simulate deposition and transport of corrosion products without the need for artificially introduced ferrous species. 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Materials Letters, 63, 307-309. 120 Appendices Appendix A: MATLAB Code %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % main.m % % This is the main program to run to calculate heat transfer and deposition % Written by Keigo Karakama % Date created: September 25, 2010 % Last modified: October , 2011 % Clear everything from previous programs clc clear all %------------------------------------------------------------------------- % Section 1: User defined inputs flowrate = 3.50; % Total flow rate (Pump 1 and 2) Ti = 350; % Temp. of bulk fluid going in [deg C] To = 400; % Temp. of bulk fluid going out [deg C] P = 237; % Pressure [bar] di = 0.069*0.0254; % Inside tube dia. of test section [m] do = 0.125*0.0254; % Outside tube dia. of test section [m] tlength = 1.75; % Length of tube [m] runtime_min = 40; % Run time of injection [min] Cb(1) = 500*10^-6; % Initial concentration of suspended... % magnetite in solution [kg/L] dp = 0.1 *10^-6; % Diameter of particle [m] corr = 2; % Correlation to use for heat transfer flowrate_pump2 = 0.5; % Injection pump flow rate [L/hr] %--------------------------------------------------------------------------- % Section 2: Runtime Variables m = flowrate/3600; % Flow rate in [kg/s] Nlength = 100; % Number of length steps dt = runtime_min*60 % Time step [s] dx = tlength/Nlength; % Increment [m] x = 0:dx:tlength; % Array h_upstream = XSteam('h_pT',P,Ti); h_downstream = XSteam('h_pT',P,To); delta_h = (h_downstream - h_upstream)/Nlength; Q = (h_downstream - h_upstream)*m; % [kW] q = Q*1000/(pi * di); % [W/m] hflux = Q*1000/(pi * di * tlength); % [W/m^2] %-------------------------------------------------------------------------- % Section 3: Constants rho_oxide = 5200; % Density of magnetite [kg/m^3] K316L = 20.2; % Thermal conductivity of 316L [W/mK] 121 % Other Variables % KFe3O4 Thermal conductivity of Fe3O4 [W/mK] % Tw1 Temperature at the bulk/surface interface % Tw2 Temperature at the point between the oxide and alloy % Tw3 Outside wall temperature and is measured experimentally %-------------------------------------------------------------------------- % Section 4: Set Initial Values count = 0; % Set initial count of loop to zero Tb(1) = Ti; % Temperature of bulk fluid dmdt(1) = 0; % Deposition mass flux dm(1) = 0; % Deposition mass thickness = zeros(1,Nlength+1); [buo(1),Re(1),rhoB(1),Tw1(1),hconv(1)] ... = fluidproperties(m,Tb(1),di,P,hflux,corr); Tw2(1) = Tw1(1); % Temperature inside wall Tw3(1) = twecalc(Tw2(1),hflux,K316L,di,do); h(1) = h_upstream; %-------------------------------------------------------------------------- % Section 5: Main part of the code for j = 2:Nlength+1, % Track and print to display count = 1 + count % Calculate fluid properties of next step h(j)=h(j-1) + delta_h; % Enthalpy at position x Tb(j) = XSteam('T_ph',P,h(j)); % Bulk temperature at position x [buo(j),Re(j),rhoB(j),Tw1(j),hconv(j)]... = fluidproperties(m,Tb(j),di,P,hflux,corr); % For preformed particle transport, saturation is negligible Csat(j) = 0; % Calculate bulk concentration calculated from previous deposition Cb(j) = Cb(j-1) - dmdt(j-1)/m; % If bulk concentration is not zero, then particles are in the fluid if (Cb(j) > Csat(j)) [Kt(j),TP(j), LN(j),viscouslayer(j)] = depositionvelocity(m,... rho_oxide,P,Tb(j),dp,di,thickness(j)); dmdt(j) = depositionfun(Kt(j),dx,di,rho_oxide,Cb(j),... Csat(j)); dm(j) = dmdt(j)*dt; rfoul(j) = thicknessfun(dmdt(j),rho_oxide,di/2,dx,dt); % If bulk concentration is zero, set values to default value of 0 else Kt(j) = 0; TP(j) = 0; LN(j) = 0; viscouslayer(j) = 0; dmdt(j) = 0; 122 dm(j) = 0; rfoul(j) = 0; end % Calculate the cumulative thickness of the deposit thickness(j) = rfoul(j) + thickness(j); % Calculate the thermal conductivity of magnetite at the temperature KFe3O4(j) = 4.133 - 0.852*10^-2*Tw1(j) + 0.757*10^-5*Tw1(j); % Calculate the temperature at the surface interfaces Tw2(j) = twocalc(Tw1(j),hflux,KFe3O4(j),... (di-2*thickness(j)),di); Tw3(j) = twecalc(Tw2(j),hflux,K316L,di,do); end %-------------------------------------------------------------------------- % Section 6: Plotting xnew = dx:dx:tlength; %For graphs which does not need value at x=0 for k=1:Nlength, yfoul(k) = thickness(k+1)*1000000; end % Plot of result summary figure(1) subplot(2,2,1) plot(xnew,yfoul) xlabel('Length [m]') ylabel('Thickness [\\mum]') title('Thickness vs Length') subplot(2,2,2) semilogy(x,TP,x,0.2,x,20) xlabel('Length [m]') ylabel('tp*') title('tp* vs Length') subplot(2,2,3) plot(x,Tb) xlabel('Length [m]') ylabel('Temperature [(Khan)C]') title('Bulk Temperature vs Length') subplot(2,2,4) plot(x,Cb*1000000) xlabel('Length [m]') ylabel('Concentration [mg/kg]') title('Concentration vs Length') % Plot of temperature profile figure(2) plot(x,Tb,'k.-',x,Tw1,'k:',x,Tw2,'k--',x,Tw3,'k') legend('Bulk fluid temperature','Oxide temperature', ... 'Tube inside wall temperature','Tube outside wall temperature'); xlabel('Length (m)') 123 ylabel('Temperature (C)') % Plot of fouling thickness vs. distance figure(3) plot(xnew,yfoul) xlabel('Distance [m]') ylabel('Magnetite thickness [\\mum]') % Plot of Reynolds vs. distance figure(4) plot(x,Re) xlabel('Distance [m]') ylabel('Re') % Plot of heat transfer coefficient vs. distance figure(5) plot(x,hconv) xlabel('Distance [m]') ylabel('Heat transfer coefficient') % Plot of Gr/Grth vs. distance for buoyancy figure(6) plot(x,buo,'k') xlabel('Distance [m]') ylabel('Gr/Grth') %-------------------------------------------------------------------------- % Section 6: Reporting to MATLAB display thickp = thickness'*1000000; xp = x'; Bulkfluid = Cb(Nlength+1); section_mass = zeros(10,1); count1 = 1; count2 = 1; for p=1:Nlength, section_mass(count1) = section_mass(count1)+dm(p); if count2 == (Nlength/10) count1 = count1+1; count2 = 1; else count2 = count2+1; end end section_mass_mg = section_mass*1000000 total_mass_mg = Cb(1)*flowrate*runtime_min*1000000/60 deposited_mass_mg = sum(section_mass_mg) mass_to_filter_mg = total_mass_mg - deposited_mass_mg deposited_percentage = deposited_mass_mg*100/total_mass_mg concentration_tank2_mgL = Cb(1)*(flowrate/flowrate_pump2)*1000000 total_mass_g = Cb(1)*flowrate*runtime_min*1000/60 transpose(thickness); hflux 124 Functions %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % Buoyancy Effects Calculation % Bouyancy Calculations based from Petukhov, evaluated by Bazargan % Written by Keigo Karakama % Date created: April 18, 2011 % Last modified: July 19, 2011 function [A,Grth,Grq] = bouyancy(Tw,Tb,Reb,d,P,m,hflux) % Grth = Grashof number threshold % Grq = Grashof number heat-flux-related % Pr = Prandtl number % Hw,Hb = Enthalpy at wall and bulk respectively % Tw,Tb = Temperature at wall and bulk respectively % mu = bulk dynamic viscosity % k = bulk thermal conductivity % hflux = heat flux g = 9.81; Tf = (Tw + Tb)/2; rhoF = XSteam('rho_pT' ,P,Tf); rhoB = XSteam('rho_pT' ,P,Tb); rhoW = XSteam('rho_pT' ,P,Tw); Hw = XSteam('h_pT' ,P,Tw); Hb = XSteam('h_pT' ,P,Tb); k = XSteam('tc_pT' ,P,Tb); mu = XSteam('my_pT' ,P,Tb); Pr = (Hw-Hb)*1000*(mu/k)/(Tw-Tb); Refun_pipe(m,d,mu); B = (1/rhoF)*(rhoB - rhoW)/(Tw-Tb); Grth = (3*10^-5)*(Reb^2.75)*(Pr^0.5)*(1+2.4*(Reb^-0.125)*(Pr^(2/3)-1)); Grq = g*B*hflux*d^4/((mu/rhoB)^2*k); A = Grq/Grth; end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % Deposition Velocity % Written by Keigo Karakama % Date created: January 9, 2011 % Last modified: January 20, 2011 function dmdt = depositionfun(Kt,dx,di,rho_oxide,Cb,Csat); % Kt = mass transport deposition velocity [m/s] % di = inner diameter of tube [m] % dx = step size [m] % rhoB = bulk fluid density [kg/m^3] % Cb = bulk concentration [kg Fe3O4/kg H2O] % Csat = Saturation concentration [kg Fe3O4/kg H2O] 125 dmdt = rho_oxide*Kt*(Cb-Csat)*pi*di*dx; end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % Deposition Velocity % Written by Keigo Karakama % Date created: January 9, 2011 % Last modified: January 10, 2011 function [Kd TP LN delta] = depositionvelocity(m,rhop,P,Tb,dp,di,thickness) % m = mass flow rate [kg/s] % rhop = density of particle [kg/m3] % P = pressure [bar] % Tb = temperature of bulk fluid [C] % dp = diameter of particle [m] % di = diameter of inner wall of tube [m] rhof= XSteam('rho_pT',P,Tb); mu = XSteam('my_pT',P,Tb); Re = Refun_pipe(m,di,mu); eps = 0.000002 + thickness; f = frictionfun(eps,di,Re); u = 4*m/(rhof*pi*di^2); U = u*sqrt(f/8); D = diffusioncoefficient(Tb,mu,dp); TP = rhop*(rhof*U*dp/mu)^2/(18*rhof); Sc = Scfun(mu,rhof,D); % Wood, Fan and Ahmadi Equation if TP < 0.2 KD = (4.5*10^-4)*TP^2+0.057*Sc^(-2/3); LN = 1; elseif (((TP > 0.2)||(TP == 0.2))&&((TP < 20)||(TP == 20))) KD = (3.5*10^-4)*TP^2; LN = 2; elseif TP > 20 KD = 0.18; LN = 3; end % Calculate the deposition velocity [m/s] Kd = KD*U; % Calculate the viscous sublayer distance [m] delta = 5*mu/(rhof*U); end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % Diffusion Coefficient % Written by Keigo Karakama % Date created: January 9, 2011 126 % Last modified: January 9, 2011 function D = diffussioncoefficient(T,mu,dp) % kB = Boltzmann constant [J/K] % T = temperature [K] % mu = dynamic viscosity [Pa.s] % dp = diameter of particle [m] kB = 1.38065*10^-23; Tk = T + 273; D = kB*Tk/(3*pi*mu*dp); end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % Fluid/thermal Properties Function % Written by Keigo Karakama % Date created: August 23, 2010 % Last modified: October 9, 2011 function [A,Reb,rhoB,Tw,hconv] = ... fluidproperties(m,Tb,di,P,hflux,select) % m = mass flow rate [kg/s] % Tw = wall temperature [C] % Tb = bulk fluid temperature [C] % di = inside diameter [m] % P = pressure [bar] % hflux = heat flux [W/m^2] % k = thermal conductivity of fluid [W/m.K] % Calculate bulk fluid properties rhoB = XSteam('rho_pT' ,P,Tb); % First estimate to Tw Tw = Tb + 1; Tw_old = Tb + 2; % Determine pseudocritical temperature Tpc = pseudocritical(P); % Correlation by Swenson et al. if select == 1 while (abs(Tw-Tw_old) > 0.2) % Calculate fluid properties Hw = XSteam('h_pT' ,P,Tw)*1000;% [J/kg] Hb = XSteam('h_pT' ,P,Tb)*1000;% [J/kg] k = XSteam('tc_pT' ,P,Tw); % [W/m.K] rhoW = XSteam('rho_pT' ,P,Tw); % [kg/m^3] viscosity = XSteam('my_pT' ,P,Tw); % [Pa.s] cp = (Hw - Hb)/(Tw-Tb); % [J/kgK] % Calculate non-dimensional numbers Re = Refun_pipe(m,di,viscosity); 127 Pr = Prfun(viscosity,cp,k); Nu = Nufun(Re,Pr,rhoB,rhoW,Tb,P); hconv = Nu*k/di; % Store the old wall temperature and calculate a new one Tw_old = Tw; Tw = Twfun(hflux,Nu,k,Tb,di); Tw = (Tw+Tw_old)/2; end % Correlation by Bazargan and Fraser elseif select == 2; % Calculate enthalpy of pseudocritical and bulk temperatures Hpc = XSteam('h_pT' ,P,Tpc); Hb = XSteam('h_pT' ,P,Tb); % Initial guess of Tw Tw = Tb + 1; Tw_old = Tb + 2; while (abs(Tw-Tw_old) > 0.2) Hw = XSteam('h_pT' ,P,Tw); Izone = (Hpc - Hb) / (Hpc - Hw); if ((Izone > -0.9)&&(Izone < 1)) Hfac = (1-Izone)*(Hpc)/(1.9*Hw); LM = 1; else Hfac = 0; LM = 2; end Href = Hb + Hfac*(Hw - Hb); Tref = XSteam('T_ph' ,P,Href); cp = XSteam('Cp_pT' ,P,Tref) * 1000; %J/kg.K k = XSteam('tc_pT' ,P,Tref); % W/mK rhoW = XSteam('rho_pT' ,P,Tref); % kg/m3 viscosity = XSteam('my_pT' ,P,Tref); % Pa.s Re = Refun_pipe(m,di,viscosity); Pr = Prfun(viscosity,cp,k); % Dittus Boelter Correlation Nu = 0.023*Re^0.8*Pr^0.4; hconv = Nu*k/di; Tw_old = Tw; Tw = Twfun(hflux,Nu,k,Tb,di); Tw = (Tw+Tw_old)/2; end end end % Calculate bouyancy effects for this temperature and pressure viscB = XSteam('my_pT' ,P,Tb); % Pa.s Reb = Refun_pipe(m,di,viscB); 128 [A,Grth,Grq] = bouyancy(Tw,Tb,Reb,di,P,m,hflux); end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % Friction Factor Calculation % Written by Keigo Karakama % Date created: January 12, 2011 % Last modified: January 12, 2011 % % Note: Uses explicit relation developed by S.E.Haaland function f = frictionfun(eps,di,Re) % Re = Reynolds number % di = diameter of inside of tube [m] % eps = roughness value of tube [m] f = (-1.8*log10((6.9/Re)+(eps/(3.7*di))^1.11))^-2; end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % Nusselt number function % Written by Keigo Karakama % Created: November 28, 2010 % Modified: December 9, 2010 function Nu = Nufun(Re,Pr,rhoW,rhoB,Tb,P) % Re = Reynolds number % Pr = Prandtl number % rhoW, rhoB = fluid density at wall and bulk respectively [kg/m^3] % Tb = Bulk fluid temperature [C] % P = Pressure [bar] Tcritical = 374; Pcritical = 221; if ((Tb > Tcritical)&&(P > Pcritical)) % Swenson et al. equation Nu = 0.00459*Re^0.923*Pr^0.613*(rhoW/rhoB)^.231; else % Dittus and Boelter equation Nu = 0.023*Re^0.8*Pr^0.4; end end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % Prandtl Function % Written by Keigo Karakama % Date created: August 23, 2010 % Last modified: August 23, 2010 129 function prandtl = Prfun(viscosity,cp,k) % viscosity = viscosity [Pa.s] % cp = specific isobaric heat capacity [J/kg.K] % k = thermal conductivity [W/mK] prandtl = cp*viscosity/k; end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % Reynolds Pipe Function % Written by Keigo Karakama % Date created: August 23, 2010 % Last modified: December 9, 2010 function reynolds = Refun_pipe(m,D,viscosity) % D = inner tube diameter [m] % m = mass [kg/s] % viscosity = viscosity [Pa.s] % Laminar Re ~< 2300 % Transitional 2300 < Re < 4000 % Turbulent Re > 4000 reynolds = 4*m/(pi*D*viscosity); end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % Schmidt Number = viscous diffusion rate / mass diffusion rate % Written by Keigo Karakama % Date created: January 9, 2011 % Last modified: January 9, 2011 function Sc = Scfun(mu,rho,D) % mu = dynamic viscosity [Pa.s] % rho = density [kg/m^3] % D = diffusion coefficient [m^2/s] Sc = mu/(rho*D); end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % Thickness of deposit calculation % Written by Keigo Karakama % Date created: December 1, 2010 % Last modified: January 24, 2011 % Equation from Holman (see reference) function t = thicknessfun(m_oxide,rho_oxide,r2,dx,dt) 130 % m_oxide = mass of deposit [kg] % rho_oxide = density of oxide [kg] % r2 = radius [m] t = r2 - sqrt(r2^2 - m_oxide*dt/(rho_oxide*pi*dx)); end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % External Wall Temperature % Program to calculate the outside wall temperature with internal heat % Written by Keigo Karakama % Date created: December 1, 2010 % Last modified: December 1, 2010 function To = twecalc(Ti,hflux,k,di,do) % Ti = Inside wall temperature [deg C] % To = Outside wall temperature [deg C] % hflux = Heat flux [W/m2] % k = Thermal conductivity of solid [W/mK] % di = Inside diameter [m] % do = Outside diamter [m] A = di/do; To = Ti + hflux*(di/2)/(2*k)*((A^2-log(A^2)-1)/(1-A^2)); end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % Oxide/Wall temperature % Written by Keigo Karakama % Date created: December 1, 2010 % Last modified: January 24, 2011 % Equation from Holman (see reference) function To = twocalc(Ti,hflux,k,di,do) % Ti = Inside wall temperature [C] % To = Outside wall temperature [C] % hflux = Heat flux [W/m2] % k = Thermal Conductivity of solid [W/mK] % di = Inside diameter [m] % do = Outside diamter [m] To = Ti + hflux*do*log(do/di)/(2*k); end %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 131 Appendix B: Filter Parts Drawings 132 133 Appendix C: Results of Experiments Reference Condition, Ferrous Chloride C. 1. Table C-1: Summary table of experiment #1 Summary Units Values Comments Main Parameters Date of Experiment 19-Apr-11 Precursor FeCl2∙4H2O Average Pressure [MPa] 23.7 Concentration [mmol/L] 5.48 Pump 1 Flow Rate [L/hr] 3.00 Pump 2 Flow Rate [L/hr] 0.54 Total Flow Rate [L/hr] 3.54 Secondary Line Flow Rate [L/hr] 0.03 pH 3 pH Base - Injection Time [min] 42 Test Section Length of Test Section [m] 1.8 Thermocouple Spacing [cm] 15 Bulk Fluid Temperature Inlet [°C] 350 Bulk Fluid Temperature Outlet [°C] 400 Heat Flux In (based on enthalpy) [kW/m2] 102 # of Thermocouples (test section) 11 Analysis Thermal Resistance Yes Filters Yes (1) Deposit with SEM Yes Deposit with Cleaning Methods Yes XRD Yes Effluent Yes Comments: (1) Flow rates of the secondary line were found to be significantly lower than originally set and therefore there was very little filter deposits. 134 Figure C-1: Temperature measurements of test section vs. time for reference condition with ferrous chloride precursor. (Experiment #1) Figure C-2: SEM photograph of particles collected on HTHP filter, 2.0k magnification, for reference condition with ferrous chloride precursor. Low flow rate in secondary line resulting in very few particles collected. (Experiment #1) Injection 135 Figure C-3: SEM photograph of particles collected on LTHP filter, 1.8k magnification, for reference condition with ferrous chloride precursor. (Experiment #1) Figure C-4: SEM photograph of particles collected on LTLP filter, 2.0k magnification, for reference condition with ferrous chloride precursor. Low flow rate in secondary line resulting in very few particles collected. (Experiment #1) 136 (a) (b) (c) (d) Figure C-5: SEM photograph of magnetite deposit on test section tube surface, (a) 0.15 m, (b) 0.60 m, (c) 1.20 m, and (d) 1.65 m location. (Experiment #1) 137 Figure C-6: Deposit thickness on test section for reference condition with ferrous chloride precursor. (Experiment #1) Figure C-7: Comparison between simulation and experimental for reference condition ferrous chloride. Simulation was run with an average particle size = 4 µm, magnetite concentration = 200 mg/L. 138 Reference Condition, Ferrous Sulfate C. 2. Table C-2: Summary table of experiment #2 Summary Units Values Comments Main Parameters Date of Experiment 24-Jun-11 Precursor FeSO4·7H2O Average Pressure [MPa] 23.9 Concentration [mmol/L] 4.97 Pump 1 Flow Rate [L/hr] 3.05 Pump 2 Flow Rate [L/hr] 0.49 Total Flow Rate [L/hr] 3.54 Secondary Line Flow Rate [L/hr] 0.21 pH 3.5 pH Base - Injection Time [min] 39 Test Section Length of Test Section [m] 1.8 Thermocouple Spacing [cm] 15 Bulk Fluid Temperature Inlet [°C] 350 Bulk Fluid Temperature Outlet [°C] 397 Heat Flux In (based on enthalpy) [kW/m2] 97 # of Thermocouples (test section) 11 Analysis Thermal Resistance Yes Filters Yes Deposit with SEM Yes Deposit with Cleaning Methods Yes XRD Yes Effluent Yes 139 Figure C-8: Temperature measurements of test section vs. time, temperature fluctuations were found in both the inlet and outlet bulk temperatures which may be attributed to the inconsistent flow. (Experiment #2) Figure C-9: SEM photograph of particles collected on HTHP filter, 2.0k magnification, for reference condition with ferrous sulfate. (Experiment #2) Injection 140 Figure C-10: SEM photograph of particles collected on LTHP filter, 2.0k magnification, for reference condition with ferrous sulfate. (Experiment #2) Figure C-11: SEM photograph of particles collected on LTLP filter, 2.0k magnification, for reference condition with ferrous sulfate. (Experiment #2) 141 Figure C-12: SEM photograph of magnetite deposit on test section tube surface, (a) 0.15 m, (b) 0.60 m, (c) 1.20 m, and (d) 1.65 m location. (Experiment #2) 142 Figure C-13: Deposit thickness on test section for reference condition with ferrous sulfate precursor. (Experiment #2) Figure C-14: Comparison between simulation and experimental for reference condition ferrous sulfate. Simulation was run with an average particle size = 1 µm, magnetite concentration = 190 mg/L. 143 Low Heat Flux, Ferrous Chloride C. 3. Table C-3: Summary table of experiment #3 Summary Units Values Comments Main Parameters Date of Experiment 30-Mar-11 Precursor FeCl2∙4H2O Average Pressure [MPa] 22.4 Concentration [mmol/L] 5.31 Pump 1 Flow Rate [L/hr] 3.06 Pump 2 Flow Rate [L/hr] 0.54 Total Flow Rate [L/hr] 3.60 Secondary Line Flow Rate [L/hr] 0.21 pH 3 pH Base - Injection Time [min] 44 Test Section Length of Test Section [m] 1 (1) Thermocouple Spacing [cm] 10 Bulk Fluid Temperature Inlet [°C] 372 Bulk Fluid Temperature Outlet [°C] 376 Heat Flux In (based on enthalpy) [kW/m2] 24 # of Thermocouples (test section) 10 Analysis Thermal Resistance Yes Filters Yes (2) Deposit with SEM Yes Deposit with Cleaning Methods No XRD Yes Effluent Yes Comments: (1) Experiment used a 1 m long test section and lower line voltage. (2) LTLP filter had not been added yet to the system for this experiment. 144 Figure C-15: Temperature measurements of test section vs. time for low heat flux ferrous chloride precursor. (Experiment #3) Figure C-16: SEM photograph of particles collected on HTHP filter, 2.0k magnification, for low heat flux with ferrous chloride precursor. (Experiment #3) Injection 145 Figure C-17: SEM photograph of particles collected on LTHP filter, 2.0k magnification, for low heat flux with ferrous chloride precursor. (Experiment #3) Figure C-18: SEM photograph of particles collected on LTLP filter, - magnification, for low heat flux with ferrous chloride precursor. (Experiment #3) Image Not Available (See comments in Summary) 146 (a) (b) (c) Figure C-19: SEM photograph of magnetite deposit on test section tube surface, (a) 0.10 m, (b) 0.30 m, and (c) 0.90 m location. (Experiment #3) 147 Figure C-20: Deposit thickness on test section for low heat flux ferrous chloride precursor. (Experiment #3) Data Not Available (See comments in Summary) 148 Low Heat Flux, Ferrous Sulfate C. 4. Table C-4: Summary table of experiment #4 Summary Units Values Comments Main Parameters Date of Experiment 31-Aug-11 Precursor FeSO4·7H2O Average Pressure [MPa] 23.0 Concentration [mmol/L] 5.04 Pump 1 Flow Rate [L/hr] 3.03 Pump 2 Flow Rate [L/hr] 0.51 Total Flow Rate [L/hr] 3.54 Secondary Line Flow Rate [L/hr] 0.20 pH 3.5 pH Base - Injection Time [min] 40 Test Section Length of Test Section [m] 1.8 Thermocouple Spacing [cm] 15 Bulk Fluid Temperature Inlet [°C] 372 Bulk Fluid Temperature Outlet [°C] 376 Heat Flux In (based on enthalpy) [kW/m2] 13 # of Thermocouples (test section) 11 Analysis Thermal Resistance Yes Filters Yes Deposit with SEM Yes Deposit with Cleaning Methods Yes XRD No Effluent Yes 149 Figure C-21: Temperature measurements of test section vs. time for low heat flux with ferrous sulfate precursor. (Experiment #4) Figure C-22: SEM photograph of particles collected on HTHP filter, 2.0k magnification, for low heat flux ferrous sulfate precursor (Experiment #4) Injection 150 Figure C-23: SEM photograph of particles collected on LTHP filter, 2.0k magnification, for low heat flux ferrous sulfate precursor. (Experiment #4) Figure C-24: SEM photograph of particles collected on LTLP filter, 2.0k magnification, for low heat flux ferrous sulfate precursor. (Experiment #4) 151 (a) (b) (c) (d) Figure C-25: SEM photograph of magnetite deposit on test section tube surface, (a) 0.15 m, (b) 0.60 m, (c) 1.20 m, and (d) 1.65 m location. (Experiment #4) 152 Figure C-26: Deposit thickness on test section for low heat flux ferrous sulfate precursor. (Experiment #4) Figure C-27: Comparison between simulation and experimental for low heat flux, ferrous sulfate. Simulation was run with an average particle size = 1 µm, magnetite concentration = 108 mg/L. 153 No Heat Flux, Ferrous Sulfate C. 5. Table C-5: Summary table of experiment #5 Summary Units Values Comments Main Parameters Date of Experiment 20-Sept-11 Precursor FeSO4·7H2O Average Pressure [MPa] 23.3 Concentration [mmol/L] 5.32 Pump 1 Flow Rate [L/hr] 2.97 Pump 2 Flow Rate [L/hr] 0.53 Total Flow Rate [L/hr] 3.50 Secondary Line Flow Rate [L/hr] 0.21 pH 3.5 pH Base - Injection Time [min] 40 Test Section Length of Test Section [m] 1.8 Thermocouple Spacing [cm] 15 Bulk Fluid Temperature Inlet [°C] 384 Bulk Fluid Temperature Outlet [°C] 383 Heat Flux In (based on enthalpy) [kW/m2] - # of Thermocouples (test section) 11 Analysis Thermal Resistance No (1) Filters Yes Deposit with SEM Yes Deposit with Cleaning Methods Yes XRD No Effluent Yes Comments: (1) Because there was no net heat flux in this experiment, thermal resistance measurements on the test section were not taken. 154 Figure C-28: Temperature measurements of test section vs. time for no heat flux with ferrous sulfate precursor. (Experiment #5) Figure C-29: SEM photograph of particles collected on HTHP filter, 2.0k magnification, for no heat flux with ferrous sulfate precursor. (Experiment #5) Image Not Available (See comments in Summary) 155 Figure C-30: SEM photograph of particles collected on LTHP filter, 2.0k magnification, for no heat flux with ferrous sulfate precursor. (Experiment #5) Figure C-31: SEM photograph of particles collected on LTLP filter, 2.0k magnification, for no heat flux with ferrous sulfate precursor. (Experiment #5) 156 (a) (b) (c) (d) Figure C-32: SEM photograph of magnetite deposit on test section tube surface, (a) 0.15 m, (b) 0.60 m, (c) 1.20 m, and (d) 1.65 m location. (Experiment #5) 157 Figure C-33: Deposit thickness on test section for no heat flux with ferrous sulfate precursor. (Experiment #5) Figure C-34: Comparison between simulation and experimental for no heat flux with ferrous sulfate precursor. Simulation was run with an average particle size = 2 µm, magnetite concentration = 89 mg/L. 158 High pH, Ferrous Sulfate C. 6. Table C-6: Summary table of experiment #6 Summary Units Values Comments Main Parameters Date of Experiment 03-Aug-11 Precursor FeSO4·7H2O Average Pressure [MPa] 23.8 Concentration [mmol/L] 5.11 Pump 1 Flow Rate [L/hr] 2.99 Pump 2 Flow Rate [L/hr] 0.51 Total Flow Rate [L/hr] 3.50 Secondary Line Flow Rate [L/hr] 0.23 pH 9 pH Base NaOH Injection Time [min] 37 Test Section Length of Test Section [m] 1.8 Thermocouple Spacing [cm] 15 Bulk Fluid Temperature Inlet [°C] 350 Bulk Fluid Temperature Outlet [°C] 396 Heat Flux In (based on enthalpy) [kW/m2] 97 # of Thermocouples (test section) 11 Analysis Thermal Resistance Yes Filters Yes Deposit with SEM Yes Deposit with Cleaning Methods Yes XRD No Effluent Yes 159 Figure C-35: Temperature measurements of test section vs. time for high pH with ferrous sulfate precursor. (Experiment #6) Figure C-36: SEM photograph of particles collected on HTHP filter, 2.0k magnification, for high pH with ferrous sulfate precursor. (Experiment #6) Injection 160 Figure C-37: SEM photograph of particles collected on LTHP filter, 2.0k magnification, for high pH with ferrous sulfate precursor. (Experiment #6) Figure C-38: SEM photograph of particles collected on LTLP filter, 2.0k magnification, for high pH with ferrous sulfate precursor. (Experiment #6) 161 (a) (b) (c) (d) Figure C-39: SEM photograph of magnetite deposit on test section tube surface, (a) 0.15 m, (b) 0.60 m, (c) 1.20 m, and (d) 1.65 m location. (Experiment #6) 162 Figure C-40: Deposit thickness on test section for high pH with ferrous sulfate precursor. (Experiment #6) Figure C-41: Comparison between simulation and experimental for high pH, ferrous sulfate. Simulation was run with an average particle size 0.15 µm, magnetite concentration = 321 mg/L. 163 High pH & Subcritical, Ferrous Sulfate C. 7. Table C-7: Summary table of experiment #7 Summary Units Values Comments Main Parameters Date of Experiment 22-Aug-11 Precursor FeSO4·7H2O Average Pressure [MPa] 23.7 Concentration [mmol/L] 5.17 Pump 1 Flow Rate [L/hr] 2.95 Pump 2 Flow Rate [L/hr] 0.51 Total Flow Rate [L/hr] 3.47 Secondary Line Flow Rate [L/hr] 0.27 pH 9 pH Base NaOH Injection Time [min] 40 Test Section Length of Test Section [m] 1.8 Thermocouple Spacing [cm] 15 Bulk Fluid Temperature Inlet [°C] 200 Bulk Fluid Temperature Outlet [°C] 370 Heat Flux In (based on enthalpy) [kW/m2] 92 # of Thermocouples (test section) 11 Analysis Thermal Resistance Yes Filters Yes Deposit with SEM No (1) Deposit with Cleaning Methods No (1) XRD No Effluent Yes Comments: (1) Test section was not disassembled after experiment. 164 Figure C-42: Temperature measurements of test section vs. time for high pH & subcritical with ferrous sulfate precursor. (Experiment #7) Figure C-43: SEM photograph of particles collected on HTHP filter, 2.0k magnification, for high pH & subcritical with ferrous sulfate precursor. (Experiment #7) Injection 165 Figure C-44: SEM photograph of particles collected on LTHP filter, 2.0k magnification, for high pH & subcritical with ferrous sulfate precursor. (Experiment #7) Figure C-45: SEM photograph of particles collected on LTLP filter, 2.0k magnification, for high pH & subcritical with ferrous sulfate precursor. (Experiment #7) 166 Low Concentration, Ferrous Chloride C. 8. Table C-8: Summary table of experiment #8 Summary Units Values Comments Main Parameters Date of Experiment 26-May-11 Precursor FeCl2∙4H2O Average Pressure [MPa] 23.7 Concentration [mmol/L] 0.56 Pump 1 Flow Rate [L/hr] 2.95 Pump 2 Flow Rate [L/hr] 0.54 Total Flow Rate [L/hr] 3.50 Secondary Line Flow Rate [L/hr] 0.24 pH 3 pH Base - Injection Time [min] 400 Test Section Length of Test Section [m] 1.8 Thermocouple Spacing [cm] 15 Bulk Fluid Temperature Inlet [°C] 350 Bulk Fluid Temperature Outlet [°C] 400 Heat Flux In (based on enthalpy) [kW/m2] 96 # of Thermocouples (test section) 11 Analysis Thermal Resistance Yes Filters Yes Deposit with SEM No (1) Deposit with Cleaning Methods No (1) XRD No Effluent No Comments (1) Test section was not disassembled after experiment. 167 Figure C-46: Temperature measurements of test section vs. time for low concentration with ferrous chloride precursor. (Experiment #8) Figure C-47: SEM photograph of particles collected on HTHP filter, 2.0k magnification, for low concentration with ferrous chloride precursor. (Experiment #8) Injection 168 Figure C-48: SEM photograph of particles collected on LTHP filter, 2.0k magnification, for low concentration with ferrous chloride precursor. (Experiment #8) Figure C-49: SEM photograph of particles collected on LTLP filter, 2.0k magnification, for low concentration with ferrous chloride precursor. (Experiment #8) 169 Blank Run C. 9. Table C-9: Summary table of blank run Summary Units Values Comments Main Parameters Date of Experiment 23-Jun-11 Precursor None Average Pressure [MPa] 23.7 Concentration [mmol/L] 0.00 Pump 1 Flow Rate [L/hr] 2.98 Pump 2 Flow Rate [L/hr] 0.50 Total Flow Rate [L/hr] 3.48 Secondary Line Flow Rate [L/hr] 0.21 pH Neutral pH Base - Injection Time [min] 40 Test Section Length of Test Section [m] 1.8 Thermocouple Spacing [cm] 15 Bulk Fluid Temperature Inlet [°C] 351 Bulk Fluid Temperature Outlet [°C] 399 Heat Flux In (based on enthalpy) [kW/m2] 99 # of Thermocouples (test section) 11 Analysis Thermal Resistance Yes Filters Yes Deposit with SEM No (1) Deposit with Cleaning Methods No (1) XRD No Effluent No Comments (1) Test section was not disassembled after experiment. 170 Figure C-50: Temperature measurements of test section vs. time for high pH & subcritical with ferrous sulfate precursor. (Experiment #9) Figure C-51: SEM photograph of particles collected on HTHP filter, 2.0k magnification, blank run. (Experiment #9) 171 Figure C-52: SEM photograph of particles collected on LTHP filter, 5.0k magnification, blank run. (Experiment #9) Figure C-53: SEM photograph of particles collected on LTLP filter, 2.0k magnification, blank run. (Experiment #9) 172 Appendix D: Filter Flow Rates Table D-1: Flow rate through filter Filter 1 2 3 4 5 6 7 8 Flow Rate [L/hr] HTHP 0.034 0.21 0.21 0.20 0.21 0.23 0.27 0.24 LTHP 3.506 3.33 3.39 3.339 3.285 3.265 3.195 3.255 LTLP 0.034 0.21 - 0.201 0.21 0.23 0.27 0.24 Area of Filter Sample [cm 2 ] HTHP 0.71 0.71 0.71 0.71 0.71 0.71 0.71 0.71 LTHP 2.85 2.85 2.85 2.85 2.85 2.85 2.85 2.85 LTLP 4.91 4.91 4.91 4.91 4.91 4.91 4.91 4.91 Time of Injection [min] 42 39 44 40 40 37 40 400 Volume per Area [L/cm 2 ] HTHP 0.033 0.191 0.216 0.188 0.196 0.199 0.252 2.244 LTHP 0.861 0.759 0.872 0.781 0.768 0.706 0.747 7.614 LTLP 0.005 0.028 - 0.027 0.029 0.029 0.037 0.326 Ratio LTHP/HTHP 25.8 4.0 4.0 4.2 3.9 3.6 3.0 3.4 173 Appendix E: Atomic Absorption Spectroscopy The concentration of iron in each sample using AAS was determined from the calibration curve found in Figure E-1and Figure E-2 which produced equations E-1 and E-2 respectively. Figure E-1: Calibration curve for iron concentration using AAS, nitric acid matrix E-1 where C is the concentration [mg/L] and A is the absorbance. 174 Figure E-2: Calibration curve for iron concentration using AAS, nitric acid and copper sulfate matrix E-2 The uncertainty in the thickness of the deposit was estimated from the uncertainty of several sources in the calculation including tube length, calibration curve, background concentration, and volume error. Uncertainty from calibration curve: ±0.3 mg/L Uncertainty from background iron concentration = ±0.1 mg/L Uncertainty in volume = 5% Uncertainty in timing, heating, loss of iron in transfer = 10% "@en ; edm:hasType "Thesis/Dissertation"@en ; vivo:dateIssued "2012-05"@en ; edm:isShownAt "10.14288/1.0072444"@en ; dcterms:language "eng"@en ; ns0:degreeDiscipline "Mechanical Engineering"@en ; edm:provider "Vancouver : University of British Columbia Library"@en ; dcterms:publisher "University of British Columbia"@en ; dcterms:rights "Attribution-NonCommercial-NoDerivatives 4.0 International"@en ; ns0:rightsURI "http://creativecommons.org/licenses/by-nc-nd/4.0/"@en ; ns0:scholarLevel "Graduate"@en ; dcterms:title "Methods for the characterization of deposition and transport of magnetite particles in supercritical water"@en ; dcterms:type "Text"@en ; ns0:identifierURI "http://hdl.handle.net/2429/39772"@en .