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UBC Theses and Dissertations

Flow regimes and pressure histories during blowdown from a vertical tube Steeves, Alan 1983

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FLOW REGIMES AND PRESSURE HISTORIES DURING BLOWDOWN FROM A VERTICAL TUBE by ALAN STEEVES B.A.Sc, The U n i v e r s i t y of B r i t i s h Columbia, 1976 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n THE FACULTY OF GRADUATE STUDIES Department of Mechanical Engineering We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l 1983 © Alan Steeves, 1983 In presenting t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the l i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I f u r t h e r agree that permission f o r extensive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my department or by h i s or her r e p r e s e n t a t i v e s . I t i s understood that copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permission. ALAN STEEVES Department of Mechanical Engineering The U n i v e r s i t y of B r i t i s h Columbia Vancouver, Canada Date ABSTRACT A s e r i e s of blowdown e x p e r i m e n t s have been performed w h i l e d i s c h a r g i n g e i t h e r v e r t i c a l l y (upwards or downwards) or h o r i z o n t a l l y i n order to compare the e f f e c t of body forc e on t r a n s i e n t flow patterns and pressure h i s t o r i e s . Tests were done using Freon-114 i n a c l e a r polycarbonate pipe 4 m long with a 32 mm I.D. R e s u l t s , presented i n the form of flow regime maps, show that the b a s i c nature of the developing flow i n a v e r t i c a l pipe when d i s c h a r g i n g upward i s d i f f e r e n t than f o r the downward discharge case. Both cases are i n t u rn markedly d i f f e r e n t than f o r h o r i z o n t a l discharge. Pressure h i s t o r i e s were found to f a l l i n t o two c a t e g o r i e s : one i n which the pressure f e l l r a p i d l y to near the s a t u r a t i o n pressure, then s l o w l y to atmospheric; a second i n which t r a n s i e n t r e p r e s s u r i z a t i o n to n e a r l y the i n i t i a l pressure was observed f o l l o w i n g the i n i t i a l pressure drop. The second category occurred only i n the v e r t i c a l pipe and could not be s a t i s f a c t o r i l y e x plained. Rapid changes i n a x i a l pressure g r a d i e n t , and p o s s i b l e flow r e v e r s a l , were noted i n the r e p r e s s u r i z a t i o n case. - i i i -TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS i i i LIST OF FIGURES v ACKNOWLEDGEMENTS v i i i 1. INTRODUCTION 1 1.1 P r e l i m i n a r y Remarks 1 1.2 Previous Work 2 1.2.1 Experimental 2 1.2.2 T h e o r e t i c a l 6 1.3 Scope of This I n v e s t i g a t i o n 8 2. EXPERIMENTAL APPARATUS 10 2.1 General Concept of the Experimental Apparatus 10 2.2 D e t a i l s of the Apparatus Components 11 2.2.1 Test Section 11 2.2.2 Pressure Measurement 16 2.2.3 Temperature Measurement 18 2.2.4 Photographic Equipment 18 3. EXPERIMENTAL PROCEDURE 21 3.1 General 21 3.2 I n i t i a l P r e p a r a t i o n and C a l i b r a t i o n of the Apparatus 21 3.3 Procedure f o r Freon-114 Blowdown Measurements 23 - i v -Page 3.4 Data A n a l y s i s 26 4. EXPERIMENTAL RESULTS 27 4.1 General 27 4.2 Pressure H i s t o r i e s f o r Discharge H o r i z o n t a l l y 29 4.3 Flow H i s t o r i e s f o r Discharge H o r i z o n t a l l y 29 4.4 Pressure H i s t o r i e s f o r Discharge V e r t i c a l l y Down 32 4.5 Flow H i s t o r i e s f o r Discharge V e r t i c a l l y Down 58 4.6 Pressure H i s t o r i e s f o r Discharge V e r t i c a l l y Up 60 4.7 Flow H i s t o r i e s f o r Discharge V e r t i c a l l y Up 77 5. DISCUSSION OF THE RESULTS 80 5.1 Discharge H o r i z o n t a l l y 80 5.2 Discharge V e r t i c a l l y 81 6. CONCLUSIONS 88 6.1 General 88 6.2 Normal data 89 6.3 R e p r e s s u r i z a t i o n data 90 6.4 Suggestions f o r Further Study 91 REFERENCES 92 APPENDIX ONE 94 APPENDIX TWO 96 - v -LIST OF FIGURES Page FIGURE 1. Schematic diagram of the experimental apparatus 12 FIGURE 2. Pressure h i s t o r y showing the e f f e c t of a p a r t i a l l y blocked discharge end on the i n i t i a l stages of decompression of n i t r o g e n i n a h o r i z o n t a l pipe 14 FIGURE 3. D e t a i l s of the end-diaphragm mechanism, i n c l u d i n g a t y p i c a l transducer mounting arrangement 15 FIGURE 4. Block diagram of the data a c q u i s i t i o n system 20 FIGURE 5. Pressure h i s t o r i e s during decompression of n i t r o g e n from a h o r i z o n t a l tube 28 FIGURE 6. Pressure h i s t o r i e s during the blowdown f o r a h o r i z o n t a l pipe. Both present r e s u l t s as w e l l as those of Necmi and Hancox [4] are shown 30 FIGURE 7. Pressure h i s t o r i e s during the i n i t i a l stages of blowdown f o r a h o r i z o n t a l pipe. Both present r e s u l t s as w e l l as those of Necmi and Hancox [4] are shown 31 FIGURE 8. Flow regimes during blowdown of Freon-114 from a h o r i z o n t a l pipe, from Necmi and Hancox [4] 33 FIGURE 9. D e f i n i t i o n sketches of the flow regimes i d e n t i f i e d i n t h i s study. Time advances from l e f t to r i g h t f o r h o r i z o n t a l discharge; from top to bottom f o r di s c h a r g i n g e i t h e r upwards or downwards 34 FIGURE 10. Pressure h i s t o r i e s at two gauge s t a t i o n s f o r a v e r t i c a l pipe d i s c h a r g i n g down 36 FIGURE 11. Repeat of the discharge h i s t o r i e s of Figure 10 37 FIGURE 12. Pressure h i s t o r i e s at two gauge s t a t i o n s f o r a v e r t i c a l pipe d i s c h a r g i n g down 38 FIGURE 13. Repeat of one of the discharge h i s t o r i e s of Figure 12 ... 39 FIGURE 14. Pressure h i s t o r i e s at two gauge s t a t i o n s f o r a v e r t i c a l pipe d i s c h a r g i n g down 41 FIGURE 15. Long term pressure h i s t o r i e s f o r three gauge s t a t i o n s f o r a v e r t i c a l pipe d i s c h a r g i n g down 42 FIGURE 16. Long term pressure h i s t o r i e s f o r three gauge s t a t i o n s f o r a v e r t i c a l pipe d i s c h a r g i n g down 43 - v i -Page FIGURE 17. Repeat of the discharge h i s t o r i e s of Figure 15 44 FIGURE 18. Pressure h i s t o r i e s showing the r e p e a t a b l i t y of the data obtained f o r a v e r t i c a l pipe d i s c h a r g i n g downward 46 FIGURE 19. Pressure h i s t o r y showing r e p r e s s u r i z a t i o n during blowdown from a v e r t i c a l pipe d i s c h a r g i n g downward 47 FIGURE 20. Pressure h i s t o r y showing r e p r e s s u r i z a t i o n during blowdown from a v e r t i c a l pipe d i s c h a r g i n g downward 48 FIGURE 21. Repeat of the pressure h i s t o r y shown i n Figure 20 49 FIGURE 22. Pressure h i s t o r y showing r e p r e s s u r i z a t i o n during blowdown from a v e r t i c a l pipe d i s c h a r g i n g downward 51 FIGURE 23. Repeat of the pressure h i s t o r y shown i n Figure 22 52 FIGURE 24. Pressure h i s t o r y showing r e p r e s s u r i z a t i o n during blowdown from a v e r t i c a l pipe d i s c h a r g i n g downward 53 FIGURE 25. Long term pressure h i s t o r i e s f o r three gauge s t a t i o n s f o r a v e r t i c a l pipe d i s c h a r g i n g downward 55 FIGURE 26. Long term pressure h i s t o r i e s f o r three gauge s t a t i o n s f o r a v e r t i c a l pipe d i s c h a r g i n g downward 56 FIGURE 27. Pressure h i s t o r i e s showing the r e p e a t a b l i t y of the r e p r e s s u r i z a t i o n behaviour during blowdown from a v e r t i c a l pipe d i s c h a r g i n g downward 57 FIGURE 28. Flow regimes during blowdown of Freon-114 from a v e r t i c a l pipe d i s c h a r g i n g downward (see Figure 9) 61 FIGURE 29. Pressure h i s t o r y during the i n i t i a l stages of blowdown from a v e r t i c a l pipe d i s c h a r g i n g upward 62 FIGURE 30. Pressure h i s t o r y during the i n i t i a l stages of blowdown from a v e r t i c a l pipe d i s c h a r g i n g upward 63 FIGURE 31. Pressure h i s t o r y showing r e p r e s s u r i z a t i o n behaviour during blowdown from a v e r t i c a l pipe d i s c h a r g i n g upwards 64 FIGURE 32. Pressure h i s t o r y showing r e p r e s s u r i z a t i o n behaviour during blowdown from a v e r t i c a l pipe d i s c h a r g i n g upwards 66 - v i i -Page FIGURE 33. Repeat of the discharge h i s t o r y shown i n Figure 32 67 FIGURE 34. Pressure h i s t o r y during the i n i t i a l stages of blowdown from a v e r t i c a l pipe discharging upward 68 FIGURE 35. Pressure h i s t o r y during the i n i t i a l stages of blowdown from a v e r t i c a l pipe discharging upward 69 FIGURE 36. Repeat of the discharge h i s t o r y shown i n Figure 35 70 FIGURE 37. Pressure h i s t o r i e s showing the repeatablity of data taken at a gauge s t a t i o n that did not show repressurization during the blowdown from a v e r t i c a l pipe discharging upward 71 FIGURE 38. Pressure h i s t o r i e s showing the repeatablity of data taken at a gauge s t a t i o n that did not show repressurization during the blowdown from a v e r t i c a l pipe discharging upward 72 FIGURE 39. Pressure h i s t o r y showing the repeatablity of the repre s s u r i z a t i o n behaviour during blowdown from a v e r t i c a l pipe discharging upward 73 FIGURE 40. Long term pressure h i s t o r i e s for three gauge stations for a v e r t i c a l pipe discharging upward 74 FIGURE 41. Long term pressure h i s t o r i e s for three gauge stations for a v e r t i c a l pipe discharging upward 75 FIGURE 42. Repeat of the pressure h i s t o r i e s shown i n Figure 41 76 FIGURE 43. Flow regimes during blowdown of Freon-114 from a v e r t i c a l pipe discharging downward (see Figure 9) 79 FIGURE 44. Pressure p r o f i l e s along a pipe discharging downward when repressurization was noted ( I n i t i a l conditions as i n Figure 27) 84 FIGURE 45. Pressure p r o f i l e s along a pipe discharging upward when repres s u r i z a t i o n was noted ( i n i t i a l conditions as i n Figure 29) 85 - v i i i -ACKNOWLEDGEMENTS I would l i k e to express my sin c e r e thanks to my su p e r v i s o r , Dr. E. G. Hauptmann; without h i s help and encouragement t h i s work may never have been f i n i s h e d . A d d i t i o n a l thanks are due to Dr. P. G. H i l l f o r h i s i n v a l u a b l e comments and encouragement during our noon hour d i s c u s s i o n s . This work probably would never have been s t a r t e d i f i t was not f o r Dr. W. T. Hancox p r o v i d i n g us a very generous loan of much of the equipment he used f o r h i s o r i g i n a l experiments. I would a l s o l i k e to thank P h i l Hurren, John Richards, Fred Knowles, Len Drake and Ed Able of the Mechanical Engineering Department t e c h n i c a l s t a f f f o r t h e i r a s s i s t a n c e i n the c o n s t r u c t i o n and r e p a i r of the apparatus. I would e s p e c i a l l y l i k e to express my g r a t i t u d e to my Mom and Dad who have always supported any d e c i s i o n I have ever made. - 1 -CHAPTER ONE INTRODUCTION 1.1 P r e l i m i n a r y Remarks With the widespread use of nuclear power f o r the generation of e l e c t r i c i t y , many studies have been done to assure the sa f e t y of nuclear power p l a n t s . An area of great concern i s the problem of a l o s s - o f -coolant accident (LOCA), or blowdown. E s s e n t i a l l y the problem of blowdown i s one of r a p i d d e p r e s s u r i z a t i o n of the re a c t o r ' s c o o l i n g system. This could occur as the r e s u l t of a pipe f a i l u r e , a se a l break, a pump malfunction, or any conceivable accident that could cause the system to lose i t s p r e s s u r e - t i g h t s e a l . A l o s s of coolant can have serious consequences. The f u e l i n a CANDU re a c t o r i s co n s t a n t l y producing heat. Under normal operating c o n d i t i o n s the surface temperature of the f u e l i s over 300 degrees c e l s i u s . I f f o r any reason c o o l i n g of the f u e l i s In t e r r u p t e d , the heat that i s produced i n t e r n a l l y may cause the f u e l to melt. This would r e s u l t i n the f i s s i o n products contaminating the c o o l i n g water and producing r a d i o a c t i v e steam. Before a reac t o r can be l i c e n s e d f o r operation i n Canada, the manufacturer has to prove to the Atomic Energy Control Board (AECB) that the r e a c t o r w i l l be safe during a blowdown i n c i d e n t . To do t h i s , l a r g e s c a l e numerical c a l c u l a t i o n s are used to simulate accident c o n d i t i o n s . The v a l i d i t y of these simulations i s checked by using them to p r e d i c t what would happen during blowdown from a s t r a i g h t tube. Data f o r these - 2 -"benchmark" experiments can be obtained e i t h e r t h e o r e t i c a l l y or exp e r i m e n t a l l y . T h e o r e t i c a l data are obtained by using very s o p h i s t i c a t e d computer models. The theory involved i n these models i s such t h a t , while they can p r e d i c t what happens during blowdown i n a s t r a i g h t tube, they can not be a p p l i e d d i r e c t l y to an a c t u a l r e a c t o r s i t u a t i o n . This i s because i n t h e i r current s t a t e of development, these "benchmark" computer models can only be economically used f o r a s t r a i g h t tube. The cost of i n c l u d i n g v a l v e s , bends and other pieces associated w i t h a r e a l r e a c t o r becomes p r o h i b i t i v e l y h i g h. Experimental studies use blowdown of water or some other f l u i d to o b t a i n data on pressure, void f r a c t i o n , and other important parameters. Some studies use flow v i s u a l i z a t i o n to determine the flow regime h i s t o r i e s . This data can then be used to give some i n s i g h t i n t o model formation or be used to v e r i f y p r e d i c t i o n s of numerical s i m u l a t i o n s . These blowdown t e s t s can be done e i t h e r on s c a l e models or f u l l s c a l e t e s t setups. 1.2 PREVIOUS WORK 1.2.1 Experimental Blowdown st u d i e s demand an understanding of the e f f e c t s of many wide l y v a r y i n g parameters. This understanding i s gained by a combination of experimental and a n a l y t i c a l work. Several i n v e s t i g a t i o n s have been done on the blowdown of high enthalpy water from h o r i z o n t a l pipes; these i n c l u d e Edwards and O'Brien [ 1 ] , Edwards and Mather [ 2 ] , and the recent - 3 -work of Alamgir, Kan and Lienhard [ 3 ] . Necmi and Hancox [4] d i d s i m i l a r s t u d i e s but w i t h high enthalpy Freon-114. Edwards and O'Brien ran experimental t e s t s which c o n s i s t e d of heating a w a t e r - f i l l e d pipe to the required temperature w i t h the pressure maintained above s a t u r a t i o n c o n d i t i o n s , then a d j u s t i n g to the required pressure before r u p t u r i n g a glass d i s c at the end of the pipe. They recorded the t r a n s i e n t pressure, temperature and d e n s i t y changes along the pipe during the blowdown phase. A l l t r a n s i e n t measurements were recorded on a FM tape recorder w i t h a frequency response of DC to 80 KHZ. The d e p r e s s u r i z a t i o n t e s t s were performed using a s t e e l pipe 13.44 f t long and 2.88 inches i n i n t e r n a l diameter. The range of pressure was 500 to 2500 p s i . The i n i t i a l temperature v a r i e d from 467°F to 636°F. From t h i s work Edwards and O'Brien were able to draw the f o l l o w i n g c o n c l u s i o n s : 1. the pressure i n i t i a l l y f a l l s below, then recovers s l i g h t l y , but never reaches that corresponding to the i n i t i a l s a t u r a t i o n value; 2. the observed propagation v e l o c i t y of the i n i t i a l decompression wave f r o n t i s i n good agreement w i t h the i s e n t r o p i c speed of sound i n the compressed l i q u i d phase, deduced from the steam t a b l e s ; 3. t h e i r c a l c u l a t i o n method, based on conduction c o n t r o l l e d heat t r a n s f e r to a cloud of bubbles, i s capable of reproducing very c l o s e l y the e a r l y stages of the d e p r e s s u r i z a t i o n of a s i n g l e pipe system; - 4 -4. both pressure and void f r a c t i o n time h i s t o r i e s i n d i c a t e that t h e i r t h e o r e t i c a l c a l c u l a t i o n gave a higher than a c t u a l mass discharge. Edwards and Mather [2] performed a s e r i e s of experiments i n the same manner. They studied the blowdown of water from three d i f f e r e n t pipes. The pipes were a l l 13 feet long w i t h 1.25 i n c h , 3 inc h and 8 inch nominal i n t e r n a l diameters. The t e s t s covered values of s a t u r a t i o n pressure of 500, 1000 and 2000 p s i a , w i t h most of the t e s t s s t a r t i n g from a sub-cooled c o n d i t i o n of 500 p s i over-pressure. Their experimental work i n d i c a t e d that an assumption of thermal e q u i l i b r i u m i s not always a p p r o p r i a t e . When there i s a change from subcooled to saturated pressure c o n d i t i o n s , non-equilibrium e f f e c t s can u s u a l l y be observed u n t i l the system has had time to nucleate and grow vapour bubbles. S o z z i and Fe d r i c k [5] ran t e s t s on the discharge of a pressure v e s s e l through a h o r i z o n t a l pipe. Their t e s t s e c t i o n consisted of a 110 inch h o r i z o n t a l length of 2 inch schedule 80 pipe, closed at one end by two rupture d i s k s and attached at the other end to the bottom o u t l e t nozzle of a one foot outside diameter by 14 foot t a l l pressure v e s s e l . Water i n the v e s s e l was heated by means of submersible e l e c t r i c heaters to provide 1000 p s i saturated water and steam. Before the i n i t i a t i o n of blowdown, the d e s i r e d amount of subcooling was achieved by i n j e c t i n g cold water i n t o the lower plenum of the v e s s e l and h o r i z o n t a l pipe through a sparger. Pressure and temperatures were monitored at s e v e r a l l o c a t i o n s i n the v e s s e l and along the h o r i z o n t a l pipe. The pressure h i s t o r i e s f o r the h o r i z o n t a l pipe showed the usual r a p i d drop to below the s a t u r a t i o n pressure due to a delay i n n u c l e a t i o n . - 5 -However, r a t h e r than the pressure recovering to approximately the s a t u r a t i o n pressure i t was observed to recompress to approximately 50 p s i below the i n i t i a l pressure. S o z z i and Fedric k b e l i e v e d that the pressure recovery was caused i n part by the growth of vapour bubbles In the l o c a l l y decompressed l i q u i d and a l s o by choking and flow f r i c t i o n i n the t e s t s e c t i o n . They speculated that l o c a l f r i c t i o n and choking l i m i t the flow, f u r t h e r i n c r e a s i n g the back pressure i n the t e s t s e c t i o n , r e s u l t i n g i n the f l u i d pressure recovering to above the s a t u r a t i o n pressure. No attempt was made i n any of these s t u d i e s to determine the flow regime h i s t o r y . Necmi and Hancox [4] were the f i r s t to i n v e s t i g a t e flow regime h i s t o r y during blowdown. Their experimental data on flow regime, pressure and void f r a c t i o n was obtained f o r the blowdown of Freon-114 from a h o r i z o n t a l transparent tube. The flow regime and void f r a c t i o n were determined from high speed photography. Necmi and Hancox drew the f o l l o w i n g conclusions: (1) b o i l i n g occurs f i r s t at the gauge s t a t i o n s as the i n i t i a l expansion wave passes, and i t i s suppressed between the s t a t i o n s . (2) a f t e r 100 m i l l i s e c o n d s , the flow at the discharge plane c o n s i s t s of small l i q u i d d r o p l e t s uniformly dispersed i n vapour while bubbly flow i s s t i l l present i n the i n t e r i o r . Dispersed flow remains at the discharge plane u n t i l the end of blowdown and g r a d u a l l y propagates inwards about one metre as the l o c a l v e l o c i t y reaches about 6 to 10 metres per second. The cine f i l m s show that dispersed flow f o l l o w s a b r i e f period of s t r a t i f i e d f l o w . - 6 -(3) a f t e r 400 m i l l i s e c o n d s the bubbly flow regime i s no longer present and the l i q u i d and vapour phases s t r a t i f y . As noted above, w i t h i n one metre of the discharge plane there i s a t r a n s i t i o n between s t r a t i f i e d and dispersed flow; l i q u i d occupies the bottom p o r t i o n of the pipe w h i l e vapour-droplet mixture occupies the upper p o r t i o n . For the remainder of the pipe the flow was s t r a t i f i e d u n t i l the end of the blowdown. 1.2.2 T h e o r e t i c a l A two-phase mixture behaves, i n many resp e c t s , l i k e a single-phase compressible f l u i d . I t w i l l only a l l o w the propagation of pressure disturbances at l i m i t e d v e l o c i t i e s , s i m i l a r to sonic speed l i m i t a t i o n s , and e x h i b i t s l i m i t e d discharge or choked flow e f f e c t s . Measurements have shown that sonic speed i n two-phase mixtures i s dependent on the d i s t r i b u t i o n of the phases, the r e f o r e d i f f e r e n t r e l a t i o n s h i p s apply to d i f f e r e n t flow regimes. Due to t h i s , no s i n g l e theory w i l l describe a l l aspects of t r a n s i e n t two-phase flow [ 2 ] . The complexity of the r e l a t i o n s h i p s between the phases u s u a l l y r e s u l t s i n only one-dimensional flow s i t u a t i o n s being considered t h e o r e t i c a l l y . The general treatment i s an extension of the w e l l -documented case of single-phase compressible f l u i d dynamics using a d d i t i o n a l r e l a t i o n s h i p s to describe the interchange of mass, momentum and energy between the two phases [ 2 ] . The simplest approach i s based on the assumption of thermal and v e l o c i t y e q u i l i b r i u m between the two phases. This i s c a l l e d the Equal V e l o c i t y Equal Temperature model (EVET). By use of these assumptions and an equation of s t a t e which describes the v a r i a t i o n of den s i t y w i t h pressure and temperature, i t i s p o s s i b l e to o b t a i n a set of equations - 7 -i d e n t i c a l i n form to those f o r single-phase flow. These equations may be evaluated i n a s i m i l a r manner to the single-phase equations. U s u a l l y the d i f f e r e n t i a l equations are solved d i r e c t l y by numerical methods, with the method of c h a r a c t e r i s t i c s being the most popular. The use of the equal v e l o c i t y and e q u a l temperature a s s u m p t i o n l e a d s to t h e o r e t i c a l p r e d i c t i o n s which do not f i t a l l the observed f a c t s . The two major d i s c r e p a n c i e s are too low a p r e d i c t e d sonic speed i n low void f r a c t i o n mixtures, and too low a value f o r the choked discharge flow i n steady s t a t e s i t u a t i o n s [2]. Improved agreement f o r steady-state choked flow can be obtained by the i n t r o d u c t i o n of r e l a t i v e motion between the phases [2]. This i s an Unequal V e l o c i t y Equal Temperature model (UVET). C o r r e l a t i o n s are a v a i l a b l e to f i t a wide range of data from small diameter p i p i n g . This i s done by making the b a s i c assumption that an annular flow p a t t e r n e x i s t s , w i t h a f a s t moving c e n t r a l core of vapour. Such c o r r e l a t i o n s are unable to p r e d i c t the flow from short pipes ( l / d l e s s than 20) where there i s i n s u f f i c i e n t time f o r an annular flow p a t t e r n to become e s t a b l i s h e d . Thus the c o r r e l a t i o n s are of l i t t l e use i n the f a s t -changing c o n d i t i o n s of t r a n s i e n t decompression from a constant diameter pipe [2]. Necmi and Hancox [4] abandoned the assumption of thermal e q u i l i b r i u m , r e p l a c i n g i t w i t h a statement of the rate at which heat and mass may be t r a n s f e r r e d between the two phases. Their Equal V e l o c i t y Unequal Temperature model (EVUT) gives equations that are h y b e r b o l i c , and e x i s t i n g s o l u t i o n procedures can be used. They used the method of c h a r a c t e r i s t i c s s o l u t i o n procedure to give r e s u l t s that c l o s e l y match t h e i r experimental observations. - 8 -At present there i s some work being done on Unequal V e l o c i t y Unequal Temperature (UVUT) models. These assumptions give equations that are e l l i p t i c a l , l e a d i n g to some problems i n t h e i r s o l u t i o n . Lyczkowski [6] was able to apply the method of c h a r a c t e r i s t i c s to an UVUT model. The r e s u l t s he obtained when using h i s method f o r blowdown of steam from a h o r i z o n t a l pipe showed good agreement with h i s experimental observations. Most of the work to date has been performed f o r h o r i z o n t a l pipes. M o z a f f a r i [7] performed a t h e o r e t i c a l i n v e s t i g a t i o n of the e f f e c t of pipe o r i e n t a t i o n on the blowdown of water. He used an EVET model to compare the pressure and void f r a c t i o n h i s t o r i e s . This i n v e s t i g a t i o n showed that the r a t i o of g r a v i t y f o r c e to pressure f o r c e (GP) was an important measure of the e f f e c t of g r a v i t y . When GP was low (high pressure d i f f e r e n t i a l ) there was n e g l i g i b l e d i f f e r e n c e between the pressure h i s t o r i e s f o r the upflow and downflow cases. However, as GP was increased the d i f f e r e n c e between the upflow and the downflow cases became more d i s t i n c t . 1.3 SCOPE OF THIS INVESTIGATION From the work of Necmi and Hancox [4] i t i s evident that flow regimes p l a y an important part i n the blowdown of a l i q u i d from h o r i z o n t a l pipes. Their observations of the flow h i s t o r y during blowdown showed a large d i s p a r i t y between the observed regimes and the simple flow assumed f o r most c a l c u l a t i o n models. Body forces are a major f a c t o r i n determining the flow regime h i s t o r y ; therefore i t was decided to design a set of experiments that would examine the e f f e c t s of body forces on blowdown. To do t h i s i t would be necessary to make measurements of both pressure and f l o w regime h i s t o r i e s , so i t was d e c i d e d t h a t t h i s s t u d y - 9 -should follow the l i n e s of Necmi and Hancox. In fact much of the equipment used i n the present experiments was the same as that used by Necmi. Accordingly the present experimental study was designed with the idea of using the blowdown of Freon-114 from a st r a i g h t pipe at d i f f e r e n t angles to show the e f f e c t s of pipe o r i e n t a t i o n and hence the e f f e c t s of body forces on the blowdown. The objective was to experimentally determine pressure and flow regime h i s t o r i e s and to develop a flow regime map for d i f f e r e n t pipe o r i e n t a t i o n s . Experimental data are presented here for the blowdown of Freon-114 discharging h o r i z o n t a l l y , v e r t i c a l l y upwards and v e r t i c a l l y downwards. - 10 -CHAPTER TWO EXPERIMENTAL APPARATUS 2.1 General Concept of the Experimental Apparatus The present study was concerned w i t h the blowdown of Freon-114 from a s t r a i g h t tube. In p a r t i c u l a r i t was desired that measurements be made of pressure and flow regime h i s t o r y during the blowdown. As a general plan i t was envisaged that a transparent tube be f i l l e d w i t h a subcooled l i q u i d , then by some means a r a p i d break would be made at one end a l l o w i n g the f l u i d to discharge. As t h i s was happening, measurements of the pressure and flow regime h i s t o r i e s would be made at various l o c a t i o n s along the tube. One c o n d i t i o n f o r choosing a working f l u i d was that i t have a low s a t u r a t i o n pressure at room temperature. This would enable use of a p l a s t i c tube making p o s s i b l e the flow v i s u a l i z a t i o n . U n t i l the work of Necmi and Hancox [ 4 ] , no e f f o r t had been made to v i s u a l i z e or otherwise determine the a c t u a l flow patterns during blowdown. Their experiments were conducted w i t h Freon-114, i n a h o r i z o n t a l tube. The same working f l u i d was used here because i t was f e l t that i t s continued use would give some base f o r comparing r e s u l t s . The i n i t i a l pressure of 1500 kPa was chosen because at t h i s pressure the reduced pressure (Pr) of the Freon-114 i s equal to the reduced pressure of water under the operating c o n d i t i o n s found i n a CANDU r e a c t o r . I t should be noted that blowdown i n a r e a c t o r would have the f l u i d blowing down to atmospheric pressure. To match t h i s i n a Freon-114 experiment the f l u i d would have to blow down to 15.0 kPa, r e q u i r i n g a l a r g e evacuated storage tank to c o l l e c t the Freon - 11 -gas. This was not p r a c t i c a l f o r t h i s set of experiments so a l l the t e s t s were performed with the f l u i d blowing down to atmospheric pressure. I t was planned that the system pressure be c o n t r o l l e d by a simple nitrogen-over-Freon system. No plans were made f o r c o n t r o l l i n g the system temperature. A schematic diagram of the experimental apparatus i s shown i n Figure 1. 2.2 D e t a i l s of the Apparatus Components 2.2.1 Test S e c t i o n The blowdown v e s s e l was made from a 4 m l o n g t r a n s p a r e n t polycarbonate tube ( i n s i d e diameter = 32 mm). Flanges were welded onto each end of the tube. The vent l i n e , the Freon supply l i n e and a thermocouple were held by an aluminum block which was attached to the flange at the closed end of the tube. The supply l i n e was connected to a Freon-114 storage tank through an i s o l a t i o n valve f o r f i l l i n g and p r e s s u r i z i n g . To begin the experiment i t was necessary to be able to cause a very r a p i d opening at the discharge end of the tube. No commercially a v a i l a b l e f a s t opening valve was capable of opening as r a p i d l y as was re q u i r e d . T r a d i t i o n a l l y a f a s t opening has been achieved by using an impact to break a hardened glass d i s c . The problem w i t h t h i s method i s that the shock of breaking the d i s c i s transmitted i n t o the f l u i d r e s u l t i n g i n erroneous pressure readings. In an attempt to solve t h i s problem a t h i n metal diaphragm was used to s e a l the discharge end. The plan was that a small hole be punched i n t o the diaphragm and that i t explode outward, much l i k e a b a l l o o n would when pr i c k e d by a needle. This method d i d give a very r a p i d break but i n some p r e l i m i n a r y t e s t s i t - 12 -FREON-114 STORAGE TANKS ^BOURDON PRESSURE GAUGE |VPRY N2 CYLINDER THERMOCOUPLE SOLENOID VALVE ALUMINUM CHANNEL THERMOCOUPLE SOLENOID VALVE DIAPHRAGM CAVITY ELECTRICALLY OPERATED PLUNGER CHANNEL SUPPORT Figure 1. Schematic diagram of the experimental apparatus. - 13 -was found that the break was not as clean as was necessary. This can be seen from the graph of pressure vs time i n Figure 2. The p l o t shows the pressure wave caused by the r e f l e c t i o n from the s e c t i o n of the diaphragm s t i l l b l o c k i n g the pipe. The f i n a l s o l u t i o n , shown i n Figure 3, i s a combination of these two methods. The discharge end was sealed by a 0.5 mm t h i c k g l a s s diaphragm separated from a commercial Inconel diaphragm by a 12 mm long c a v i t y . This c a v i t y was p r e s s u r i z e d by n i t r o g e n gas to match the pressure of the Freon-114 i n the pipe. To begin blowdown, the pipe and c a v i t y were i s o l a t e d by s o lenoid valves and an e l e c t r i c a l l y operated plunger was f i r e d to break the Inconel diaphragm. This caused the c a v i t y to drop to atmospheric pressure r e s u l t i n g i n a pressure imbalance of 1500 kPa across the 0.5 mm t h i c k g l a s s diaphragm, causing i t to s h a t t e r . This arrangement provided a clean break to the f u l l pipe c r o s s - s e c t i o n i n l e s s than 0.5 m i l l i s e c o n d s . In using t h i s method, the pressure i n the pipe caused the g l a s s diaphragm to break outwards; because of t h i s there i s no impact shock tr a n s m i t t e d i n t o the Freon. In e f f e c t the use of two diaphragms i s o l a t e s the f l u i d from the shock of breaking the f i r s t diaphragm. Another advantage was that the Inconel diaphragm can only withstand pressures of up to 1930 kPa. Once t h i s diaphragm breaks the whole system loses pressure, stopping the system pressure from a c c i d e n t a l l y exceeding a safe l i m i t . The blowdown tube was held by four pipe supports, which were fastened to a ten i n c h aluminum channel. This channel was mounted between two 1.6m tubular s t e e l t r i p o d s as shown i n Figure 1. This arrangement allowed f o r t e s t i n g at any i n c l i n a t i o n of the pipe, although t e s t s were - 14 -2 000 o Q_ LU rr to CO LU or o. 1000 800 600 -400 -200 h 100 1 1 1 1 1 1 NITROGEN HORIZONTAL DISCHARGE Pi = 750 kPa — Z = 2.38 m — V W V V V V — — V V V V 1 V V V V 1 1 V v V V v V V 1 1 1 0 6 12 18 24 30 36 42 TIME ms Figure 2. Pressure h i s t o r y showing the e f f e c t of a p a r t i a l l y blocked discharge end on the I n i t i a l stages of decompression of nitrogen i n a hori z o n t a l pipe. - 15 -THERMOCOUPLE NEOPRENE ^N 2 GAS LINE HOLE \ vGASKET ^ 2 INCONEL H/DIAPHRAGM GLASS DIAPHRAGM T R A N S D U C E R DIAPHRAGM CAVITY P R E S S U R E ' T R A N S D U C E R S C A L E IN mm O 20 40 I I I I—i Figure 3. D e t a i l s of the end-diaphragm mechanism, including a t y p i c a l transducer mounting arrangement. - 16 -only conducted w i t h the discharge end h o r z o n t a l , v e r t i c a l l y up and v e r t i c a l l y down. Pressure was c o n t r o l l e d by using regulated n i t r o g e n gas as shown i n Figure 1. The Freon-114 that f i l l e d the tube was held i n a s e r i e s of two tanks. Nitrogen was supplied to the top of these tanks and to the discharge assembly v i a a 2100 kPa. r e g u l a t o r . This arrangement allowed the pressure across the glass diaphragm to always be balanced. The n i t r o g e n supply l i n e could be vented to a l l o w the system pressure to be lowered. ^ The system pressure was measured by a 0 to 1500 p s i Heise-Bourdon tube pressure gauge, f a c t o r y c e r t i f i e d against a dead weight t e s t e r to be accurate to .1% of the f u l l s c a l e reading. 2.2.2 Pressure Measurement Seven pressure gauge s t a t i o n s were lo c a t e d at 40 mm, 180 mm, 860 mm, 1.62 m, 2.38 m, 3.14 m and 3.9 m from the discharge end of the tube. Each of these gauge s t a t i o n s c onsisted of a P r e c i s e Sensor model 211-3 s t r a i n gauge type pressure transducer mounted i n a p l e x i g l a s s block as shown i n Figure 3. These pressure transducers use a four-arm bridge c i r c u i t to give a s e n s i t i v i t y of 3.0 mV/V nominal. For the maximum pressure of 1500 kPa and w i t h the 10 v o l t power supply used f o r e x c i t a t i o n , the pressure transducers produced 30 mV output. The p l e x i g l a s s mounting blocks served as a support f o r the pressure transducers and as reinforcement f o r the polycarbonate tube. The blocks had t h e i r I.D. machined to be s l i g h t l y l a r g e r than the tube O.D. A pressure t i g h t s e a l was formed by 0-rings on e i t h e r side of the 0.5 i n c h pressure tap i n the polycarbonate tube. - 17 -The pressure transducers were c a l i b r a t e d i n place against a s t a t i c pressure over the range of 100 to 1500 kPa. The accuracy of the c a l i b r a t i o n was one part i n 1024 or ± 1.4 kPa. Output from the pressure transducers was increased to f i v e v o l t s by d i f f e r e n t i a l a m p l i f i e r s made by the Mechanical Engineering E l e c t r i c a l s t a f f . The transducer response time i n c l u d i n g s i g n a l t ransmission and a m p l i f i c a t i o n e f f e c t s was determined to be 0.3 m i l l i s e c o n d s . The a m p l i f i e d pressure s i g n a l was fed i n t o a D i g i t a l Equipment AR11 analog-t o - d i g i t a l converter. The AR11 i s 10-bit a n a l o g - t o - d i g i t a l converter made by D i g i t a l Equipment Li m i t e d f o r use w i t h t h e i r PDP 11 s e r i e s d i g i t a l computers. Each pressure transducer s i g n a l was scanned, d i g i t i z e d and stored i n core memory every 0.5 m i l l i s e c o n d s by a PDP 11/10 d i g i t a l computer. The d i g i t i z e d pressure s i g n a l s were then t r a n s f e r r e d to floppy d i s c f o r permanent storage. Due to the l i m i t e d amount of core storage a v a i l a b l e the maximum number of samples that could be taken on any run was 9688. Therefore, i t was necessary to be as e f f i c i e n t as p o s s i b l e i n the sampling method used. To avoid wasting samples by s t a r t i n g too e a r l y a TTL e l e c t r i c switch was used. This switch placed the ground side on the Inconel diaphragm and the f i v e v o l t side on the e l e c t r i c plunger. When the plunger contacted the Inconel diaphragm the voltage across the switch dropped to zero. The PDP 11/10 was set-up i n such a way that i t would s t a r t sampling as soon as the voltage s t a r t e d to drop. This meant that the sampling s t a r t e d w i t h the breaking of the Inconel diaphragm. - 18 -2.2.3 Temperature Measurement The i n i t i a l s t a t e of the Freon-114 was determined by temperature measurement at both ends of the pipe. These temperatures were measured by copper-constantan thermocouples, set i n s t a i n l e s s s t e e l sheaths. The thermocouple sheaths were 1/16 inch O.D. which enabled them to be sealed by f i t t i n g s made by the Mechanical Engineering machine shop. Output from the thermocouples were measured by a Newport Laboratory Inc. model 267A-TC1 d i g i t a l thermometer. The thermocouples were c a l i b r a t e d i n a Calora constant temperature bath f i l l e d with d i s t i l l e d water. C a l i b r a t i o n was by comparison w i t h two P r e c i s i o n 18 inch mercury-in-glass thermometers p r e v i o u s l y c a l i b r a t e d against a Dymec model 2801 q u a r t z - c r y s t a l d i g i t a l thermometer accurate to 0.0001 degrees c e l s i u s . A f t e r two c a l i b r a t i o n s , one before and one a f t e r the experiments, the readings d i d not vary by more than 1%. The thermocouples were only used to f i n d the i n i t i a l s t a t e of the Freon-114. They were not used to make any dynamic measurements and a c c o r d i n g l y no measure of t h e i r dynamic response was made. 2.2.4 Photographic Equipment Measurements of flow regime h i s t o r y at various l o c a t i o n s along the pipe were made by using a "Redlake Hycam" high speed movie camera framing at 2000 p i c t u r e s per second. The Hycam i s a 16 mm camera that uses an e i g h t - s i d e d prism and an eight-bladed segmented shutter to achieve very hig h framing r a t e s . The camera i s d r i v e n by an AC motor with the camera speed being a d i r e c t f u n c t i o n of the a p p l i e d v o l t a g e . The camera has a b u i l t - i n timing l i g h t which marks a pulse on the f i l m margin. The ti m i n g l i g h t was t r i g g e r e d by an e x t e r n a l s i g n a l generator and f o r the - 19 -present study timing marks were put on the f i l m every 0.001 seconds. These timing marks enabled the c a l c u l a t i o n of the exact framing r a t e . The p i c t u r e s were taken on Kodak type 7224 4-X negative f i l m , an ASA 400 f i l m intended f o r use with high speed cameras. The Hycam had an a c c e l e r a t i o n l a g between the time the camera s t a r t e d and the time the f i l m was up to i t s operating speed. Due to the short d u r a t i o n of the blowdown i t was necessary to have some way of s y c h r o n i z i n g the beginning of the experiment to the f i l m reaching i t s proper speed. To do t h i s a l i g h t e m i t t i n g diode and r e c e i v e r were mounted across the Hycam s h u t t e r , g i v i n g a pulse f o r each frame of f i l m . These pulses were counted by an e l e c t r o n i c c i r c u i t and when the required number of frames had elapsed a pulse was emitted that s t a r t e d the experiment. Figure 4 shows a block diagram of the photographic and data a c q u i s i t i o n systems. - 20 -Camera reaches operating speed I Plunger triggered Plunger contacts metal diaphragm I Computer starts sampling Samples written into core memory I I Floppy disc I Teletype Pressure transducers 3 0 m Volts Amplif iers 5 Volts A n a l o g - t o digital converter 1 Oscil loscope Figure 4. Block diagram of the data acquisition system. - 21 -CHAPTER THREE EXPERIMENTAL PROCEDURE 3.1 General Experiments were run to get blowdown data f o r the tube oriented w i t h the open end f a c i n g h o r i z o n t a l l y , v e r t i c a l l y down and v e r t i c a l l y up. Pressure measurements and high speed movies were taken at s e v e r a l a x i a l l o c a t i o n s during the blowdown. The movies were analyzed to give the flow regimes. The method f o r taking and analyz i n g the data i s described below. 3.2 I n i t i a l P r e p a r a t i o n and C a l i b r a t i o n of the Apparatus Due to i t s high c o s t , Freon-114 was replaced by n i t r o g e n f o r the i n i t i a l p r eparation and c a l i b r a t i o n of the apparatus. A l s o , to conserve the Inconel diaphragms, the i n i t i a l t e s t s were done with diaphragms made from 0.002 inch s t e e l shim stock. Although the s t e e l diaphragms d i d not break as c l e a n l y as the Inconel diaphragms they were s u i t a b l e f o r use i n s e t t i n g up the experiment. A f t e r the components of the system were assembled i t was pres s u r i z e d to 1500 kPa, and the blowdown v e s s e l and f i l l i n g l i n e s were checked f o r l e a k s . Several l e a k i n g f i t t i n g s were found and tightened. One of the gauge s t a t i o n blocks was found to be l e a k i n g through the 0-rings that sealed the gap between the block and the tube. This was f i x e d by remachining the block and f i t t i n g i t with l a r g e r 0-rings. During shipping the blowdown tube was cracked near the discharge end at gauge s t a t i o n two. During the i n i t i a l t e s t s i t was noticed that t h i s - 22 -crack was getting l a r g e r . In an attempt to f i x this problem a clamp was made to keep t h i s section of the tube i n compression. As a precaution a s i m i l a r clamp was attached to the closed end of the tube. Coarse adjustment i n the gain of the amplifiers was made by changing one of the r e s i s t o r s i n th e i r c i r c u i t s . The system was brought up to i t s operating pressure of 1500 kPa and the resistances adjusted to give approximately 5 v o l t s output. Fine adjustment was then made by means of trim potentiometers to bring the output to 5 v o l t s , plus or minus 0.005 v o l t s . The data a c q u i s i t i o n system was checked by pressurizing the tube with nitrogen gas and breaking one of the s t e e l diaphragms. It was found that the sampling was s t a r t i n g too soon, r e s u l t i n g i n a l l the data buffers measuring only the system i n i t i a l pressure. This problem was traced to a voltage spike i n the solenoid used to f i r e the plunger that broke the diaphragm. The problem was corrected by changing the soleniod from AC to DC and adding a f i l t e r to stop the voltage spike that remained. The system was run again and found to be more than capable of taking the 2000 samples per second per channel that was necessary. C a l c u l a t i o n of the l i g h t i n t e n s i t y necessary for 2000 pictures per second with the camera used showed that i t was necessary to have 16 equivalent units of l i g h t . A 1000 watt spo t l i g h t was used with a d i f f u s i n g screen to give this i n t e n s i t y . Focusing i s very important in high speed photography. To set the focus an ink l i n e was placed on some cle a r f i l m and t h i s f i l m loaded in the camera. The focusing ring on the lens was then adjusted u n t i l both the l i n e on the f i l m and the object to be photographed were i n focus. - 23 -As a f i n a l check that the data a c q u i s i t i o n system was working p r o p e r l y a run was made under the same c o n d i t i o n s as the f i n a l c o n f i g u r a t i o n w i t h the exception that n i t r o g e n , not Freon, was used i n the blowdown tube. A l s o , to give a b e t t e r i n d i c a t i o n of the q u a l i t y of the photographs some c o n f e t t i was placed i n the tube. The r e s u l t s of t h i s run showed that the data a c q u i s i t i o n system was working as expected. P r i o r to beginning the a c t u a l experiments the tube had to be cleaned. F i r s t i t was vacuumed to remove most of the c o n f e t t i . I t was then washed w i t h water and blown dry w i t h n i t r o g e n gas. The tube was not de-greased because the Freon that was to be used as the working f l u i d i s a very good de-greasing agent. I t was f e l t that any contamination i n the form of grease would be removed by the f i r s t t e s t run. The system was pressure tested and found to be l e a k i n g through one of the s o l e n oid valves used to i s o l a t e the tube before the blowdown was s t a r t e d . This v a l v e was disassembled and found to contai n s e v e r a l pieces of c o n f e t t i that were preventing i t from c l o s i n g p r o p e r l y . To ensure proper o p e r a t i o n , both solenoid valves were disassembled and cleaned. The components were reassembled and found to be working pr o p e r l y . 3.3 Procedure f o r Freon-114 Blowdown Measurements The i n i t i a l Freon-114 t e s t s were made i n the h o r i z o n t a l p o s i t i o n to a l l o w d i r e c t comparison w i t h Necmi and Hancox [ 4 ] . The f o l l o w i n g procedure was used to f i l l the tube. Freon-114 was supplied from the storage tanks and the tube allowed to f i l l w i t h the vent open. The tube was i n c l i n e d s l i g h t l y with the vent end up, a l l o w i n g any trapped a i r to escape. While the tube was f i l l i n g preparations were made to enable the - 24 -computer to do the pressure sampling. Once these preparations were complete a s a f e t y s w i tch was set that stopped the computer from t r i g g e r i n g a c c i d e n t a l l y . The tube was allowed to f i l l u n t i l l i q u i d Freon-114 was observed at the vent. The vent was then closed as was the va l v e that i s o l a t e s the Freon storage tank. The tube was then l e v e l e d w i t h the use of a Wilde s p l i t - b u b b l e l e v e l . Nitrogen gas was then used to p r e s s u r i z e the system. As the pressure was being r a i s e d readings were taken at 200 kPa i n t e r v a l s from 100 kPa to 1500 kPa. These would l a t e r be used f o r c a l i b r a t i n g the pressure transducers. When the s t a r t i n g pressure of 1500 kPa was reached the solenoid valves that i s o l a t e the tube were c l o s e d . The thermocouples were then read to give the i n i t i a l temperature of the Freon. The saf e t y switch on the computer was r e l e a s e d , then the camera l i g h t was turned on. The reason f o r not t u r n i n g the l i g h t on e a r l i e r was to avoid any unnecessary heat a d d i t i o n to the tube. The camera was then s t a r t e d ; when i t reached i t s operating speed i t t r i g g e r e d the plunger which i n turn t r i g g e r e d the computer. The computer then took readings from each of the s i x pressure transducers every 0.5 m i l l i s e c o n d s . The data from the experiment was held i n the core memory of the PDP 11/10. Before the experiment could be repeated i t was necessary to save the data. This was done by copying the contents of the core memory to a 128K byte storage d i s c . This o r g i n a l d i s c was then copied to another storage d i s c to provide a backup. F i n a l l y a p r i n t o u t of the data was obtained on the LA36 terminal attached to the PDP 11/10. On examining the t e s t r i g i t was noticed that the crack near gauge s t a t i o n two had propagated completely around the tube. This probably occurred during the blowdown as the r e s u l t of the tube f l e x i n g . To f i x - 25 -t h i s problem the discharge end of the tube was disassembled. The crack i n the tube was r e p a i r e d by using solvent to cement the two pieces together. The support block was remachined to provide a b e t t e r f i t and l a r g e r 0-rings were i n s t a l l e d . The discharge assembly was reassembled and the pipe support was moved so that one support was on e i t h e r side of the gauge s t a t i o n . This stopped the leak and prevented the tube from f l e x i n g . Once the tube was r e p a i r e d one more run was made i n the h o r i z o n t a l p o s i t i o n . The experimental procedure f o r the v e r t i c a l tube d i s c h a r g i n g downward i s b a s i c a l l y the same as f o r the h o r i z o n t a l tube. To a i d i n s e t t i n g the tube to v e r t i c a l , a plumb-line was attached to the top pipe support. This plumb-line was then a l i g n e d w i t h the bottom pipe support to set the tube to v e r t i c a l . The data was taken and stored by the same method as i n the h o r i z o n t a l case. To use the apparatus f o r d i s c h a r g i n g v e r t i c a l l y upwards I t was necessary to remove the tube from i t s supports and turn i t so the discharge end could point up. This required that some of the plumbing be redone and that the cable that t r i g g e r s the computer be lengthened. A f t e r reassembling the piece i t was found that the computer was t r i g g e r i n g too soon. This problem was f i x e d by r e p l a c i n g the c o a x i a l cable that was being used by the a u t o t r i g g e r with a s h i e l d e d twisted p a i r c a b l e . Once t h i s problem was f i x e d the procedure f o r t a k i n g and s t o r i n g the data was the same as f o r the other two cases. - 26 -3.4 Data Analysis The bulk of the work i n reducing the pressure data was done by the PDP-11/10 minicomputer. A program was written that takes the eight c a l i b r a t i o n samples for each channel and uses them to compute the pressure during the blowdown (see Appendix). To obtain the flow regime data i t was necessary to repeatedly view the movies. This was o r i g i n a l l y done by using a 16 mm projector that was capable of framing forwards or backwards at a rate as low as 1 frame per second. However the f i l m was very b r i t t l e and some of the sprocket holes had been torn during the f i l m i n g , r e s u l t i n g i n the f i l m s l i p p i n g i n the projector and tearing. This problem was corrected by using a manual f i l m editor to view the movies. - 27 -CHAPTER FOUR EXPERIMENTAL RESULTS 4.1 General The i n i t i a l t e s t s on the apparatus were performed using n i t r o g e n gas as a s u b s t i t u t e f o r the more expensive Freon-114. These p r e l i m i n a r y t e s t s were done to debug the data a c q u i s i t i o n system and to decide on the f i n a l c o n f i g u r a t i o n of the diaphragms i n the discharge assembly. Figure 2 shows a graph of pressure versus time f o r one gauge s t a t i o n and i s t y p i c a l of the r e s u l t s obtained f o r the e a r l y t e s t s . The pressure o s c i l l a t i o n s are present because of the metal diaphragm not breaking c l e a n l y and b l o c k i n g the end of the tube. Because of t h i s blockage, the pressure wave was r e f l e c t e d and caused the pressure at the gauge s t a t i o n s to o s c i l l a t e . Several d i f f e r e n t c o n f i g u r a t i o n s of diaphragm were t e s t e d , most of which gave s i m i l a r r e s u l t s . The arrangement f i n a l l y decided on was the same as that used by Necmi and Hancox [ 4 ] . Figure 5 shows t y p i c a l r e s u l t s from two gauge s t a t i o n s f o r t h i s discharge assembly. As can be seen from t h i s graph the o s c i l l a t i o n s have disappeared and the pressure wave appears to be t r a v e l l i n g at the speed of sound i n n i t r o g e n f o r that temperature and pressure. During these experiments the high speed camera was a l s o being used at another l o c a t i o n . This required the camera being p e r i o d i c a l l y moved to another b u i l d i n g . Apparently during one of these moves the camera was dropped, knocking the i n t e r n a l prisms out of alignment. The r e s u l t of t h i s was p i c t u r e s of l e s s than i d e a l q u a l i t y . The movies s t i l l showed - 28 -2000 o CL UJ rr CO CO UJ c r Q_ 1000 800 600 400 200 100 1 l i i i t I O O O O O O O O O Q o - • o — • NITROGEN HORIZONTAL DISCHARGE Pj = 1500 kPa o Z = 3.14 m • Z = 180 mm • o DD D D ° d D ° AoDo°o88e i 0oeegaBBB8B88So i I I i i u i 12 18 24 TIME ms 30 36 42 Figure 5. Pressure h i s t o r i e s during decompression of nitrogen from a horizontal tube. - 29 -how the flow patterns developed, but i t was d i f f i c u l t to see d e t a i l on i n d i v i d u a l frames. It was f e l t that the q u a l i t y of enlargements of i n d i v i d u a l frames was so poor that there was no reason to include them i n t h i s work. Instead flow regime maps have been developed and sketches of the various flow patterns that were observed have been included to explain these maps. 4.2 Pressure H i s t o r i e s f o r Discharge H o r i z o n t a l l y Two tests were made with the tube discharging h o r i z o n t a l l y . Both tests had an i n i t i a l pressure of 1500 kPa, while the temperatures ranged from 18.4 to 18.9 degrees C e l s i u s . The r e s u l t s for these tests are g r a p h i c a l l y summarized i n Figures 6 and 7. Figure 6 compares the pressure h i s t o r y for the i n i t i a l Freon-114 run of the apparatus for one gauge s t a t i o n and data from work done by Necmi and Hancox [4]. During this run the tube broke at gauge s t a t i o n two, which probably explains why there i s not better agreement between the two sets of data. After the tube was repaired the experiment was repeated for the h o r i z o n t a l p o s i t i o n . The r e s u l t s from this run are compared to the r e s u l t s obtained by Necmi and Hancox [4] i n Figure 7. As can be seen from these graphs the data compares very well and therefore i t appears that the experimental set-up was working properly. 4.3 Flow Hi s t o r y for Discharge H o r i z o n t a l l y In t h i s case as in the ones that follow the pictures were taken at 2000 frames per second and as a r e s u l t the flow v i s u a l i z a t i o n s show only the gross flow patterns. No attempt was made to look for very short 250 o CL LU rr ZD CO CO LU rr CL 200 h 150 L 8 100 50 HORIZONTAL DISCHARGE Pi * I 500 kPa PRESENT WORK i o NECMI DISTANCE FROM CLOSED END Z = 40 mm L_ 0.4 0.8 1.2 CO o 1.6 2.0 TIME s Figure 6. Pressure h i s t o r i e s during the blowdown for a h o r i z o n t a l pipe. Both present r e s u l t s as well as those of Necmi and Hancox [4] are shown. The dashed l i n e i ndicates the saturation pressure at the i n i t i a l temperature. - 31 -2000 1000 800 o ^ 600 LU cr CO CO LU rr CL 400 200 100 HORIZONTAL DISCHARGE Pj = I 500 kPa v , x NECMI PRESENT WORK DISTANCE FROM DISCHARGE END v , • Z = 40 mm Z = 3.14 m v xx x x xxx I I 1 1 12 18 24 30 TIME ms 36 42 7. Pressure h i s t o r i e s during the i n i t i a l stages of blowdown for a horizontal pipe. Both present r e s u l t s as well as those of Necmi and Hancox [4] are shown. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 32 -time period flow p a t t e r n s . This would have required f i l m i n g i n the order of 10,000 frames per seconds which was i m p r a c t i c a l f o r these experiments. At 2.92 m (91.25 tube diameters) from the discharge end, n u c l e a t i o n s t a r t e d 13 m i l l i s e c o n d s a f t e r the diaphragm was broken. I t was b e l i e v e d that the pressure transducers, which were mounted on the top of the tube, might act as p r e f e r e n t i a l n u c l e a t i o n s i t e s . However, contrary to what was expected, the bubbles were formed on the bottom of the tube. This bubbly flow continued u n t i l 230 m i l l i s e c o n d s Into the experiment. Near t h i s time organized slugs of l i q u i d were noticed moving down the tube. The waves i n t h i s s l u g flow g r a d u a l l y become smaller and l e s s d i s t i n c t . At approximately 410 m i l l i s e c o n d s the flow was d e f i n i t e l y s t r a t i f i e d , w i t h l i q u i d on the bottom and bubbles on the top. The bubbles seemed to c o l l a p s e onto the l i q u i d and by 550 m i l l i s e c o n d s the flow was completely s t r a t i f i e d w i t h vapour on the top and l i q u i d on the bottom. The flow remained s t r a t i f i e d f o r the r e s t of the experiment. This flow regime could be observed by watching the pipe as the blowdown was o c c u r r i n g . Necmi and Hancox [4] have done a d e t a i l e d i n v e s t i g a t i o n of the flow regime h i s t o r y f o r the blowdown of Freon-114 from a h o r i z o n t a l pipe. T h e i r r e s u l t s are shown i n Figure 8. Figure 9 shows sketches of the flow regimes observed during the present i n v e s t i g a t i o n . The r e s u l t s of t h i s i n v e s t i g a t i o n are superimposed on the flow regime map of Necmi and Hancox [4] i n Figure 8. As can be seen from t h i s f i g u r e , once again, the two sets of r e s u l t s are i n good agreement. 4.4 Pressure H i s t o r i e s f o r Discharge V e r t i c a l l y Down The pressure data f o r discharge v e r t i c a l l y down were observed to f a l l i n t o two d i s t i n c t c l a s s e s which have been c a l l e d r e g u l a r and - 33 -5 0 0 0 l O O O h tn E uj 100 0 1 2 3 DISTANCE FROM O P E N E N D Z m Figure 8. Flow regimes during blowdown of Freon-114 from a horizontal pipe, from Necmi and Hancox [4]. - 34 -horizontol dischorg"e| l o g o ' bubbly slug stratified bubbly stratified discharging down t m & 2 discharging up annular (liquid core) slug S i ; o j o o ' bubbly (large and well defined) bubbly slug 'O'O;O;O'D. A Wo bubbly annular (vapor core) slug annular Figure 9 . D e f i n i t i o n sketches of the flow regimes i d e n t i f i e d i n th i s study. Time advances from l e f t to right f o r horizontal discharge; from top to bottom for discharging either upwards or downwards. - 35 -r e p r e s s u r i z a t i o n data. The re g u l a r data are summarized g r a p h i c a l l y i n Figures 10 to 17. The pressure h i s t o r i e s during the i n i t i a l stages of blowdown are shown i n Figures 10 to 14. Figure 10 shows the pressure h i s t o r i e s measured at the two gauge s t a t i o n s c l o s e s t to the discharge end of the pipe. As can be seen from t h i s graph the pressure dropped very r a p i d l y to the s a t u r a t i o n pressure of Freon-114. Figure 11 i s a repeat of Figure 10 but i t i s f o r a d i f f e r e n t run of the experiment. The data f o r these two runs compare very w e l l . However on run 2 (Figure 11) at 5 m i l l i s e c o n d s f o r Z = 40 mm there i s some evidence of the pressure undershoot caused by delayed n u c l e a t i o n not seen f o r run 1 (Figure 10). The pressure h i s t o r i e s measured at the middle two gauge s t a t i o n s are shown i n Figure 12. As before there i s a very r a p i d drop i n the pressure to near the s a t u r a t i o n pressure of Freon-114. The pressure f o r Z = 1.62 metres shows a pressure spike beginning at 6.5 m i l l i s e c o n d s , probably caused by delayed n u c l e a t i o n . From t h i s graph we can get some idea of the speed of sound i n Freon-114. The data was recorded at 2000 samples per second g i v i n g a time i n t e r v a l of 0.5 m i l l i s e c o n d s . This w i l l give a l a r g e range to the c a l c u l a t e d speed of speed of sound but should s t i l l g i v e some b a s i s f o r comparision. The a c o u s t i c wave passes the f i r s t pressure transducer (Z = 860 mm) at between 2 and 2.5 m i l l i s e c o n d s . This gives a speed of sound between 340 and 430 metres per second. S i m i l a r l y f o r the pressure transducer at Z = 1.62 metres the speed of sound i s between 360 and 405 metres per second. The pressure h i s t o r y at the gauge s t a t i o n 860 mm from the discharge end of the pipe i s repeated f o r a d i f f e r e n t run i n Figure 13. The pressure h i s t o r y shown here i s very s i m i l a r to the one shown f o r run 1 (Figure 12). As f o r the previous run the speed of sound from t h i s graph i s between 340 to 430 metres per second. - 36 -2 0 0 0 o CL *c LU rr Z> CO CO LU rr C L 'fJ00|E 8 0 0 6 0 0 4 0 0 2 0 0 100 • ICO °_Rrrxxrq VERTICAL .DISCHARGE DOWN RUN 1 Pi = 1500 kPa Tj = 18.9 °C DISTANCE FROM OPEN END o Z = 40 mm • Z = 180 mm 12 18 2 4 TIME ms 3 0 36 4 2 Figure 10. Pressure h i s t o r i e s at two gauge stations for a v e r t i c a l pipe discharging down. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 37 -2 0 0 0 Co o CL LU rr 1000 8 0 0 6 0 0 CO 4 0 0 CO LU rr C L 2 0 0 100 VERTICAL, DISCHARGE DOWN RUN 2 P: i = I 500 kPa = 189 °C DISTANCE FROM OPEN END o Z = 4 0 mm • Z = 180 mm co • 12 18 24 TIME ms 3 0 36 4 2 Figure 11. Repeat of the discharge h i s t o r i e s of Figure 10. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 38 -2 0 0 0 o CL LU rr co CO LU rr 1 0 0 0 8 0 0 6 0 0 4 0 0 100 1 1 1 1 1 I "V VERTICAL, DISCHARGE DOWN V RUN 1 — Pj * 1500 kPa — — A T = 18.9 °C DISTANCE FROM OPEN END — • Z = 1.62 m — A Z = 860 mm A V — — A . .JUAA. ^TTT O^AAAAAAAAAAAAAAAA AAAAA ... 1 1 1 1 1 1 12 18 24 TIME ms 3 0 36 4 2 Figure 12. Pressure h i s t o r i e s at two gauge stations for a v e r t i c a l pipe discharging down. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 39 -2 0 0 0 LU rr ZD CO CO LU rr 1 0 0 0 8 0 0 6 0 0 4 0 0 2 0 0 100 ' i A A A i 1 1 i A VERTICAL , DISCHARGE DOWN RUN 2 — Pj = 1 500 kPa Tj = 18.9 °C — - A DISTANCE FROM OPEN END Z =860 mm -A -^ A A A . _ 1 L 1 1 1 l 12 18 2 4 TIME ms 3 0 36 42 Figure 13. Repeat of one of the discharge h i s t o r i e s of Figure 12. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 40 -Figure 14 shows the pressure h i s t o r i e s at the two gauge s t a t i o n s nearest the closed end of the pipe. The pressure here a l s o showed a r a p i d drop to near the s a t u r a t i o n pressure of Freon-114. For Z = 3.14 metres there was a long dip i n the pressure beginning at 11.5 m i l l i s e c o n d s and l a s t i n g u n t i l 19 m i l l i s e c o n d s . The speed of sound c a l c u l a t e d from the data are i n the range of 340 to 390 metres per second. Long-term pressure h i s t o r i e s f o r the r e g u l a r data are shown i n Figures 15 to 17. Figures 15 and 16 shows the long-term pressure h i s t o r y measured during run 1. These two graphs show that i t took approximately 100 m i l l i s e c o n d s f o r the pressure to s t a b i l i z e at the s a t u r a t i o n pressure, then at approximately 0.6 seconds the pressure s t a r t s to drop below s a t u r a t i o n . The reason the graphs do not extend past 0.8 seconds i s , because of l i m i t a t i o n s i n computer memory, only 9688 samples could be taken. I f pressure readings were taken f o r a l l s i x gauge s t a t i o n s the sampling could only l a s t f o r 0.8 seconds. Figure 17 i s a repeat of Figure 15 except that the data was recorded f o r j u s t three gauge s t a t i o n s r e s u l t i n g i n data being stored f o r 1.6 seconds. The data f o r t h i s run compares very w e l l w i t h that f o r run 1 (Figure 15). This data shows the pressure going to atmospheric at 1.3 seconds i n t o the t e s t . To summarize the r e g u l a r data i t can be s a i d that the pressure behaved as would be expected. The pressure at each gauge s t a t i o n drops very r a p i d l y to the s a t u r a t i o n pressure of Freon-114, then g r a d u a l l y drops to atmospheric pressure. The pressure wave appears to be t r a v e l l i n g between the pressure transducers at the speed of sound i n - 41 -2 0 0 0 o CL 1000 8 0 0 6 0 0 rr CO 400 CO LU cr C L VERTICAL .DISCHARGE DOWN RUN I P I = I 500 kPa Tj = 189 °C DISTANCE FROM OPEN END o Z * 3.14 m O Z = 2.38 m 2 0 0 100 12 18 TIME 24 ms 3 0 36 42 Figure 14. Pressure h i s t o r i e s at two gauge stations for a v e r t i c a l pipe discharging down. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. 3 0 0 2 0 0 100 Q o VERTICAL , DISCHARGE DOWN RUN 1 Pj = 1500 kPa Tj = 18.9 °C DISTANCE FROM OPEN END • Z = 180 mm A Z = 860 mm o Z = 40 mm 0.25 0.50 TIME sec 0.75 1.0 Figure 15. Long term pressure h i s t o r i e s for three gauge stations for a v e r t i c a l pipe discharging down. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. 275 o CL 225 LU rr ZD CO CO LU rr 175 125 9 _ o o I o o o i VERTICAL.DISCHARGE DOWN RUN I Pj = 1500 kPa Tj = 18.9 °C DISTANCE FROM OPEN END * Z = 1.62 m o Z * 3.14 m O Z = 2.38 m g9 ooo 0<>0 o 0 v V v , 0 0 o o I * v v * „ ^ o o o o o o o ^ T o o 0 o o 0 o o o o v y 7 o o o 0 v oo V 'OoooAo 0.25 0 .50 TIME sec 0.75 OJ 1.0 Figure 16. Long term pressure h i s t o r i e s for three gauge stations for a v e r t i c a l pipe discharging down. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. 300 a CL 2 0 0 LU rr ZD CO CO LU rr C L o o 100 _ ^o_°-°-o o o .. ° g a o n a VERTICAL,DISCHARGE DOWN RUN 2 1 * 1500 kPa Tj * 18.9 °C DISTANCE FROM OPEN END o Z 8 40 mm A Z ' 860 mm • Z = 180 mm §4 4> a aa a. 0.5 1.0 TIME sec 1.5 2.0 Figure 17. Repeat of the discharge h i s t o r i e s of Figure 15. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 45 -Freon-114. Figure 18 shows an example of the agreement that can be obtained w i t h i n t h i s set of data. The r e p r e s s u r i z a t i o n set of data are summarized i n Figures 19 to 26. The pressure h i s t o r i e s f o r the i n i t i a l stages of the blowdown are shown i n Figures 19 to 24. Figure 19 i s a graph of the pressure h i s t o r y measured at the gauge s t a t i o n 860 mm from the discharge end of the pipe. During the i n i t i a l stage of the t e s t the data compares very w e l l w i t h the data f o r runs 1 (Figure 12) and 2 (Figure 13). At 2.5 m i l l i s e c o n d s the pressure dropped to near the s a t u r a t i o n pressure, however at 21 m i l l i s e c o n d s the f l u i d pressure increased r a p i d l y , reached a peak of approximately 1000 kPa at 24 m i l l i s e c o n d s and then f e l l r a p i d l y back to 200 kPa at 28 m i l l i s e c o n d s . Figure 20 shows the pressure h i s t o r y at the gauge s t a t i o n 1.62m from the discharge end of the pipe. Again there i s good agreement with the i n i t i a l stage of the data f o r run 1 (Figure 12). At 4 m i l l i s e c o n d s the pressure drops r a p i d l y to the s a t u r a t i o n pressure of Freon-114. At 7 m i l l i s e c o n d s there i s some pressure recovery, a l s o seen f o r run 1 (Figure 12 ). From 12 m i l l i s e c o n d s on the pressure h i s t o r y f o r t h i s run deviates from that of run 1. As can be seen from the graph the r e p r e s s u r i z a t i o n here was i n the form of two peaks; the f i r s t began at 17.5 m i l l i s e c o n d s , reached a maximum pressure of 1120 kPa at 20 m i l l i s e c o n d s , then f e l l to 400 kPa by 23.5 m i l l i s e c o n d s ; the second began at 23.5 m i l l i s e c o n d s , reached a maximum pressure of 800 kPa at 24.5 m i l l i s e c o n d s , then f e l l to 200 kPa by 28 m i l l i s e c o n d s . Figure 21 i s a repeat of Figure 20 f o r a d i f f e r e n t run of the experiment. I t i s i n t e r e s t i n g to note the s i m i l a r i t y i n these two graphs. The times f o r the beginning and end of the pressure peaks are di s p l a c e d by approximately 1 m i l l i s e c o n d , but the - 46 -2 0 0 0 s. L U rr 3 C O C O L U rr Q_ 2 0 0 100 VERTICAL , DISCHARGE DOWN 1000 Pj * 1500 kPa — 8 0 0 Tj * 18.9 °C • RUN 1 • RUN 2 -6 0 0 _ • DISTANCE FROM OPEN END Z = 180 mm 4 0 0 • U agio 12 18 24 TIME ms 3 0 36 4 2 Figure 18. Pressure h i s t o r i e s showing the repeatablity of the obtained f o r a v e r t i c a l pipe discharging downward. - 47 -2 0 0 0 VERTICAL, DISCHARGE DOWN RUN 4 Pj = 1500 kPa Tj = 20.7 °C DISTANCE FROM OPEN END Z s 860 mm o CL 1 0 0 0 LU rr CO CO LU rr 8 0 0 6 0 0 4 0 0 2 0 0 100 12 18 TIME 2 4 ms 3 0 36 42 Figure 19. Pressure h i s t o r y showing repressurization during blowdown from a v e r t i c a l pipe discharging downward. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 48 -2000 £ 1000 LU rr co co LU rr 8 0 0 6 0 0 4 0 0 200 100 1 -1 1 I . 1 VERTICAL,DISCHARGE DOWN RUN 3 Pj = 1 500 kPa Tj = 20.8 °C DISTANCE FROM OPEN END Z = 1.62 m v w V - -— v V — V V V -V v v V V V v W V - v v ^ -1 1 1 1 1 1 0 6 12 18 24 30 TIME ms 36 4 Figure 20. Pressure h i s t o r y showing rep r e s s u r i z a t i o n during blowdown from a v e r t i c a l pipe discharging downward. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 49 -2 0 0 0 o ^ 1 0 0 0 LU 8 0 0 or S 6 0 0 CO LU CL 4 0 0 2 0 0 100 1 1 1 1 1 1 «* VERTICAL t DISCHARGE DOWN RUN 4 Pj = 1500 kPa Tj = 20.7 °C DISTANCE FROM OPEN END Z = 1.62 m — V — V V V V — v v ^ v v * — v V — 1 1 1 1 I I 12 18 24 TIME ms 3 0 36 4 2 Figure 2 1 . Repeat of the pressure h i s t o r y shown i n Figure 2 0 . The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 50 -shape and d u r a t i o n of the peaks are almost i d e n t i c a l . The maximum pressure reached i n the peaks of Figure 21 are approximately 150 to 200 kPa lower then those of Figure 20. Figure 22 shows the pressure h i s t o r y at the gauge s t a t i o n 2.38m from the discharge end of the pipe. Again the pressure h i s t o r y compares w i l l w i t h the normal run shown i n Figure 14. The data d i s p l a y e d here shows four occurrences of pressure recovery. The f i r s t began at 15.5 m i l l i s e c o n d s , reached a peak pressure of 1120 kPa at 18 m i l l i s e c o n d s , then f e l l to 300 kPa by 25.5 m i l l i s e c o n d s . The second r e p r e s s u r i z a t i o n began at 25.5 m i l l i s e c o n d s , reached a peak pressure of 800 kPa at 26.5 m i l l i s e c o n d s , then f e l l to 180 kPa by 30 m i l l i s e c o n d s . The t h i r d r e p r e s s u r i z a t i o n began at 33 m i l l i s e c o n d s , the peak pressure of 500 kPa was reached at 34 m i l l i s e c o n d s and then the pressure f e l l to 200 kPa by 35.5 m i l l i s e c o n d s . The f i n a l r e p r e s s u r i z a t i o n shown on t h i s graph began at 37.5 m i l l i s e c o n d s and reached a peak of 500 kPa at 39.5 m i l l i s e c o n d s . Figure 23 i s a repeat of the pressure h i s t o r y shown i n Figure 22. Again there i s very good agreement between these two graphs. The pressure peaks are di s p l a c e d s l i g h t l y on the time a x i s , but the shape and du r a t i o n of the peaks are very s i m i l a r i n both cases. Figure 24 shows the pressure h i s t o r y f o r run 3 at the gauge s t a t i o n 3.14 m from the discharge end of the pipe. This set of data compares very w e l l w i t h the i n i t i a l stage of the normal run shown i n Figure 14. The pressure h i s t o r y f o r run 3 shows three occurrences of pressure recovery. The f i r s t began at 13 m i l l i s e c o n d s , reached i t s peak of 1260 kPa at 15 m i l l i s e c o n d s , then decreased to 300 kPa by 28.5 m i l l i s e c o n d s . The second pressure recovery s t a r t e d at 28.5 m i l l i s e c o n d s , reached a peak - 51 -2 0 0 0 1 -LU rr CO CO LU rr CL CL IOOO 8 0 0 6 0 0 4 0 0 2 0 0 100 VERTICAL, DISCHARGE DOWN RUN 3 Pj * 1 500 kPa Tj = 20.8 °C DISTANCE FROM OPEN END Z = 2.38 m o o o oo o o o o o o o o 12 18 24 TIME ms 3 0 36 4 2 Figure 22. Pressure h i s t o r y showing repressurization during blowdown from a v e r t i c a l pipe discharging downward. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 52 -2 0 0 0 k o 1000 8 0 0 LU £ 6 0 0 CO CO LU rr CL 4 0 0 2 0 0 100 1 1 1 1 1 1 VERTICAL, DISCHARGE DOWN RUN 4 Pj * 1500 kPa Tj = 207 °C — DISTANCE FROM OPEN END Z = 2.38 m — o o <>o ° V — — ' \ — o o o o o o o o 1 & o A oof ° A <*>° 1 o 1 1 1 1 1 12 18 24 TIME ms 3 0 36 42 Figure 23. Repeat of the pressure h i s t o r y shown i n Figure 22. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 53 -2 0 0 0 h o ^ 1 0 0 0 LU rr to to LU rr 8 0 0 6 0 0 4 0 0 h 2 0 0 h 100 1 1 1 1 1 1 VERTICAL, DISCHARGE DOWN RUN 3 Pj * 1500 kPa Tj = 20.8 °C DISTANCE FROM OPEN END Z = 3.14 m r i f r n p >"y> w > — O — ° — O ^ « » v $ > 0 ° o % " o o O \J o -O o °o ° o 1 o -( t i l l 12 18 2 4 TIME ms 3 0 36 4 2 Figure 24. Pressure h i s t o r y showing repressurization during blowdown from a v e r t i c a l pipe discharging downward. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 54 -of 800 kPa at 32 m i l l i s e c o n d s , then f e l l to 200 kPa by 33.5 m i l l i s e c o n d s . The l a s t r e p r e s s u r i z a t i o n shown on t h i s graph began at 36 m i l l i s e c o n d s , and reached i t s peak of 700 kPa at 37 m i l l i s e c o n d s . Figures 25 and 26 show the long-term pressure h i s t o r i e s f o r three gauge s t a t i o n s during two of the runs that showed r e p r e s s u r i z a t i o n behavior. The long-term pressure h i s t o r i e s f o r the r e p r e s s u r i z a t i o n runs show a much greater time was necessary f o r the pressure to s t a b a l i z e at the s t a t u r a t i o n pressure, 500 m i l l i s e c o n d s f o r the r e p r e s s u r i z a t i o n data as compared to 100 m i l l i s e c o n d s f o r the normal data. For both groups of data the time to reach atmospheric pressure are approximately the same. In summary the r e p r e s s u r i z a t i o n data appears to be much l i k e the r e g u l a r data f o r the i n i t i a l stage of decompression. As with the r e g u l a r data the r e p r e s s u r i z a t i o n data shows a r a p i d drop to near the s a t u r a t i o n pressure of Freon-114, however, 10 to 15 m i l l i s e c o n d s l a t e r (depending on the gauge s t a t i o n ) the pressure jumps to w i t h i n 500 kPa of the i n i t i a l pressure. I t i s i n t e r e s t i n g to note that as the d i s t a n c e from the discharge end increased the pressure recovery occurred sooner and the width of the f i r s t peak increased. Figure 27 shows an example of the agreement w i t h i n t h i s group of data. R e p r e s s u r i z a t i o n occurred during runs three and four of the f i v e runs made w i t h the discharge end down. As shown by the pressure h i s t o r i e s there was good agreement among the data i n t h i s group, however the data was not reproducible on demand. At present we do not have a d e f i n i t i v e cause f o r what was t r i g g e r i n g the r e p r e s s u r i z a t i o n . A more d e t a i l e d explanation and p o s s i b l e causes f o r these unusual r e s u l t s can be found i n the next chapter on the d i s c u s s i o n of the r e s u l t s . 3 0 0 2 2 0 0 LU rr co co LU rr 100 o o O^ S* 8 VERTICAL , DISCHARGE DOWN RUN 3 I 500 kPa 208 °C DISTANCE FROM OPEN END V z s 162 m O z = 2.38 m o Z = 3.14 m tt«nO°0onOO 0.5 1.0 TIME 1.5 2.0 Figure 25. Long term pressure h i s t o r i e s for three gauge stations for a v e r t i c a l pipe discharging downward. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. 3 0 0 I VERTICAL, DISCHARGE DOWN RUN 4 i I 500 kPa 20.7 °C DISTANCE FROM OPEN END A Z =860 mm v Z = 1.62 m O Z = 2.38 m 0.5 1.0 TIME sec 1.5 2.0 Figure 26. Long term pressure h i s t o r i e s for three gauge stations for a v e r t i c a l pipe discharging downward. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 57 -2 0 0 0 o IOOO LU rr z> CO CO LU rr Q_ 8 0 0 6 0 0 4 0 0 2 0 0 100 1 i r i i 1 VERTICAL, DISCHARGE DOWN Pi = 1500 kPo v Tj = 20.7 °C (RUN 3) • Tj = 20.8 °C (RUN 4) DISTANCE FROM OPEN END -***** • Z = 1.62 m — • -V V -— • -1 • 1 1 1 1 1 ' 12 18 24 TIME ms 3 0 36 4 2 Figure 27. Pressure h i s t o r i e s showing the repeatablity of the re p r e s s u r i z a t i o n behaviour during blowdown from a v e r t i c a l pipe discharging downward. - 58 -4.5 Flow H i s t o r y f o r Discharge V e r t i c a l l y Down Flow v i s u a l i z a t i o n d i d not shed any l i g h t on the reasons f o r the r e p r e s s u r i z a t i o n . The r e p r e s s u r i z a t i o n only covered 2 to 15 frames of the f i l m and t h i s was i n s u f f i c i e n t to make any s i g n i f i c a n t observations as to what was causing the r e p r e s s u r i z a t i o n . However, i t was p o s s i b l e to observe how the gross flow patterns changed with time. Sketches of the various flow regimes observed f o r the present work are show i n Figure 9. The f i r s t camera p o s i t i o n was 460 mm (1.44 tube diameters) from the discharge end of the tube. N u c l e a t i o n s t a r t e d at the w a l l s one m i l l i s e c o n d a f t e r the diaphram broke. By 40 m i l l i s e c o n d s the amount of bubbles had grown u n t i l only a small l i q u i d core remained at the center of the tube. The t r a n s i t i o n from t h i s annular flow p a t t e r n to bubbly f l o w was i n d i s t i n c t but occurred around 460 m i l l i s e c o n d s . Around 640 m i l l i s e c o n d s i n t o the blowdown there was some evidence of organized slugs of bubbles moving down the pipe. The l a s t flow regime observed at t h i s l o c a t i o n was a vapour-core annular flow p a t t e r n , beginning around 970 m i l l i s e c o n d s i n t o the blowdown. The next movies were taken 1.22 m (38.13 tube diameters) from the discharge end. Three m i l l i s e c o n d s a f t e r the blowdown s t a r t e d there was a small amount of n u c l e a t i o n on the pressure transducer side of the tube but the flo w regime returned to a l l - l i q u i d . At 25 m i l l i s e c o n d s there were bubbles a l l around the w a l l s of the tube. This l i q u i d - c o r e annular f l o w regime remained u n t i l around 200 m i l l i s e c o n d s i n t o the blowdown. By t h i s time the l i q u i d core had disappeared and the flow was bubbly. Organized slugs of f l u i d where seen around 560 m i l l i s e c o n d s , but t h i s f l o w regime was very i n d i s t i n c t . - 59 -The t h i r d camera l o c a t i o n was 2.03 m (63.44 tube diameters) from the discharge end. There was some nucleation at the tube center s i x milliseconds into the flow, however the flow regime returned to a l l -l i q u i d . At 89 milliseconds a great deal of bubbles were formed on the pressure transducer side of the tube with only a s l i g h t amount of bubbles formed on the opposite side. This annular flow remained u n t i l around 225 milliseconds by which time the tube was f u l l of bubbles. There was some vapour-core annular flow beginning at around 590 milliseconds. By 930 milliseconds there was just a thin f i l m of l i q u i d draining down the walls of the tube. The next movies were taken 2.92 m (91.25 tube diameters) from the discharge end of the tube. Nucleation began at the pressure transducer side of the tube at eight milliseconds. A l i q u i d - c o r e annular flow pattern was r a p i d l y formed and continued u n t i l around 135 milliseconds, by which time the l i q u i d core was being broken by the bubbles and a pattern of slugs of l i q u i d and bubbles was formed. By 190 milliseconds the slugs of l i q u i d had disappeared and the flow was bubbly. The amount and size of the bubbles at the center l i n e seemed to grow u n t i l by around 350 milliseconds the flow was vapour-core annular. This flow regime continued u n t i l the f i l m ended at 960 milliseconds. The l a s t series of pictures were taken at 3.56 m (111.25 tube diameters) from the discharge end. Nucleation began at the tube ce n t e r l i n e 10 milliseconds into the flow. There was a l i q u i d - c o r e annular flow pattern u n t i l around 72 milliseconds, when some slug flow was observed. By 210 milliseconds the tube was f u l l of bubbles, which seemed to coalesce into a vapour-core annular flow regime by 320 - 60 -m i l l i s e c o n d s . The amount of f l u i d at the w a l l s decreased u n t i l at 670 m i l l i s e c o n d s there was j u s t a f i l m of l i q u i d d r a i n i n g down the tube. The r e s u l t s of these flow v i s u a l i z a t i o n s have been used to make the flow regime map shown i n Figure 28. 4.6 Pressure H i s t o r i e s f o r Discharge V e r t i c a l l y Up Pressure data i s a v a i l a b l e f o r only two t e s t s w i t h the tube d i s c h a r g i n g v e r t i c a l l y up. During the f i r s t t e s t d i s c h a r g i n g up the pressure data was l o s t because of a problem w i t h the experimental apparatus. This problem was corrected but only two a d d i t i o n a l runs were made before our supply of Freon was exhausted. This pressure data i s summarized g r a p h i c a l l y i n Figures 29 to 42. The f i r s t few m i l l i s e c o n d s of the blowdown are shown i n Figures 29 to 39. Figure 29 shows the pressure h i s t o r y f o r the gauge s t a t i o n nearest the discharge end (Z = 40 mm). The pressure h i s t o r y f o r t h i s discharge up run i s very s i m i l a r to those f o r the "normal" discharge down runs (Figures 10 and 11). Figure 30 shows the pressure h i s t o r y at 180 mm from the discharge end. Again t h i s pressure h i s t o r y i s s i m i l a r to those f o r the "normal" runs d i s c h a r g i n g down (Figures 10 and 11). Figure 31 shows the pressure h i s t o r y 860 mm from the discharge end. The i n i t i a l stage of t h i s pressure h i s t o r y was very s i m i l a r to those f o r the discharge down runs (Figures 12, 13 and 19). However on t h i s graph there are two pressure peaks, one i s centered at 17 m i l l i s e c o n d s and reaches a peak of 500 kPa and the other i s centered at 28 m i l l i s e c o n d s and reaches a maximum of 280 kPa. I t should be noted that during the time shown on t h i s graph the pressure i s always above the s a t u r a t i o n pressure of Freon-114. - 61 -5 0 0 0 DISTANCE FROM O P E N END Z m Figure 28. Flow regimes during blowdown of Freon-114 from a v e r t i c a l pipe discharging downward (see Figure 9). - 62 -2 0 0 0 o CL 1000 8 0 0 6 0 0 LU §5 4 0 0 CO CO LU rr C L 2 0 0 100 VERTICAL, DISCHARGE UP RUN 7 Pj = 1500 kPa • — Tj = 20.8 °C — DISTANCE FROM OPEN END Z = 40 mm b& 12 18 24 TIME ms 3 0 36 42 Figure 29. Pressure h i s t o r y during the i n i t i a l stages of blowdown from a v e r t i c a l pipe discharging upward. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 63 -2 0 0 0 t o CL LU rr co CO LU rr C L 1000 8 0 0 6 0 0 4 0 0 VERTICAL, DISCHARGE UP RUN 7 i = 1500 kPa Tj = 20.8 °C DISTANCE FROM OPEN END Z s 180 mm 2 0 0 100 12 18 24 TIME ms 4 2 Figure 30. Pressure h i s t o r y during the i n i t i a l stages of blowdown f a v e r t i c a l pipe discharging upward. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 64 -2 0 0 0 CL LU rr ZD co co LU rr a. 1 0 0 0 8 0 0 6 0 0 4 0 0 2 0 0 100 1 1 1— i i 1 VERTICAL, DISCHARGE UP RUN 7 A Pj = 1500 kPa Tj = 20.8 °C DISTANCE FROM OPEN END Z = 860 mm A 1 A A — A A A * A r f ^ 1 1 A . A M \ 1 1 1 1 12 18 TIME 24 ms 3 0 36 42 Figure 31. Pressure h i s t o r y showing repr e s s u r i z a t i o n behaviour during blowdown from a v e r t i c a l pipe discharging upwards. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 65 -Figure 32 shows the pressure measured at 1.62 m from the discharge end of the pipe. Again the time f o r the i n t i a l decompression to s t a r t compares very w e l l w i t h that f o r the discharge down runs. However beginning at 7 m i l l i s e c o n d s there were a s e r i e s of recompressions of d i m i n i s h i n g amplitude. Figure 33 i s a repeat of Figure 32 except that i t i s f o r a d i f f e r e n t run. As can be seen, the pressure f o r t h i s run d i d not show any signs of recovery. Instead there was a r a p i d drop to 900 kPa, then the slope of the pressure d e c l i n e became much more g e n t l e . Figure 34 shows the pressure h i s t o r y f o r the gauge s t a t i o n at 2.38 meters. The data here showed a r a p i d drop to 600 kPa at 6 m i l l i s e c o n d s . The slope of the pressure decrease then became much more g e n t l e . Figure 35 shows the pressure h i s t o r y f o r the gauge s t a t i o n at 3.14 meters, during run 7. The data showed a r a p i d drop i n pressure to 700 kPa beginning at 9 m i l l i s e c o n d s . The pressure then d e c l i n e d at a slower r a t e l e v e l i n g o f f at 400 kPa. Figure 36 i s a repeat of Figure 35 but f o r run 8. The pressure drop seen here begins at the same time as that of run 7 but the pressure d e c l i n e i s at a much slower r a t e . Figures 37 to 39 show the r e p r o d u c i b i l i t y among these sets of data f o r the i n i t i a l stages of the t e s t s . Figures 40 and 41 show the long-term pressure h i s t o r i e s f o r run 7. A l l the pressure h i s t o r i e s show a dip at approximately 0.1 seconds and a pressure peak at between 0.25 and 0.35 seconds i n t o the flow. Figure 42 shows the long-term pressure h i s t o r i e s f o r run 8. The data i s very d i f f e r e n t from the data f o r run 7 (Figure 42). Run 8 d i d not show the pressure dip seen i n run 7, but instead showed a gradual d e c l i n e i n pressure, l e v e l i n g o f f at approximately 0.25 seconds, then s t a r t i n g to f a l l again at 0.5 seconds, reaching atmospheric pressure at 1.0 seconds. - 66 -2 0 0 0 h o CL LU rr z> CO CO LU rr C L 1 0 0 0 8 0 0 6 0 0 4 0 0 2 0 0 VERTICAL, DISCHARGE UP RUN 7 Pj = 1500 kPa Tj = 20.8 °C DISTANCE FROM OPEN END Z = 1.62 m V V V V V V V w 100 12 -I I 18 24 TIME ms 3 0 36 42 Figure 32. Pressure h i s t o r y showing repressurization behaviour during blowdown from a v e r t i c a l pipe discharging upwards. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 67 -2 0 0 0 o CL LU rr co co LU rr C L 1000 8 0 0 6 0 0 4 0 0 2 0 0 100 1 I I 1 I 1 V V - V ^ ^ ^ ^ ^ — VERTICAL , DISCHARGE UP -RUN 6 Pj = 1500 kPa Tj = 22.6 °C DISTANCE FROM OPEN END Z = 1.62 m 1 1 1 i i i 12 18 24 TIME ms 3 0 36 42 Figure 33. Repeat of the discharge h i s t o r y shown i n Figure 32. The dashed l i n e indicates the saturation pressure at the I n i t i a l temperature. - 68 -O CL LU rr co co LU rr 2 0 0 0 h 1 0 0 0 -8 0 0 -6 0 0 h 4 0 0 2 0 0 100 T T T VERTICAL , DISCHARGE UP RUN 7 Pj = 1500 kPa T| = 20.8 °C DISTANCE FROM OPEN END Z = 2.38 m 12 18 24 TIME ms 3 0 36 4 2 Figure 34. Pressure h i s t o r y during the i n i t i a l stages of blowdown from a v e r t i c a l pipe discharging upward. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 69 -O CL LU rr co co LU rr C L VERTICAL , DISCHARGE UP 2 OCX) RUN 7 Pj * 1500 kPa Tj = 20.8 °C o DISTANCE FROM OPEN END 1000 o Z =3.14 m 8 0 0 6 0 0 4 0 0 2 0 0 100 o 12 18 2 4 TIME ms 3 0 36 4 2 Figure 35. Pressure h i s t o r y during the i n i t i a l stages of blowdown from a v e r t i c a l pipe discharging upward. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 70 -2 0 0 0 l O O O h o LU rr co co LU rr Q_ 18 24 TIME ms Figure 36. Repeat of the discharge h i s t o r y shown i n Figure 33. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 71 -2 0 0 0 o CL LU rr ZD CO CO LU rr C L 6 0 0 4 0 0 h 2 0 0 100 1 > 1 1 1 1 1 VERTICAL , DISCHARGE UP — Pj = 1500 kPa o Tj = 20.8 °C (RUN 7) • Tj = 22.6 °C (RUN 8) DISTANCE FROM OPEN END o Z = 40 mm % . « 8 S S S S H 8 o - 8 S 8 8 * 8 8 8 M 8 8 8 8 8 8 8 S S 8 S 8 8 " 1 1 1 1 I I 12 18 24 TIME ms 3 0 36 42 Figure 37. Pressure h i s t o r i e s showing the repeatablity of data taken at a gauge s t a t i o n that did not show repressurization during the blowdown from a v e r t i c a l pipe discharging upward. - 72 -2 0 0 0 o CL UJ rr co co UJ rr C L i ooo F 8 0 0 6 0 0 4 0 0 2 0 0 100 1 p 1 1 1 1 1 • VERTICAL , DISCHARGE UP • Pj = 1 500 kPa • Tj = 20.8 °C (RUN 7) • Tj = 22.6 °C (RUN 8) DISTANCE FROM OPEN END Z = 180 mm — • • -o i i i i i 1 12 18 24 TIME ms 3 0 36 4 2 Figure 38. Pressure h i s t o r i e s showing the repeatablity of data taken at a gauge s t a t i o n that did not show repre s s u r i z a t i o n during the blowdown from a v e r t i c a l pipe discharging upward. - 73 -2 0 0 0 h A A I 0 0 0 8 0 0 6 0 0 4 0 0 2 0 0 100 VERTICAL , DISCHARGE UP Pj = 1 500 kPa A Tj = 20.8 °C (RUN 7) A Tj s 22.6 °C (RUN 8) DISTANCE FROM OPEN END — Z = 860 mm A* A A A A A A A — *** A A A A A A * A AA A A A A A A A A A A ^ A A A A A 12 18 24 TIME ms 3 0 3 6 4 2 Figure 39. Pressure h i s t o r y showing the repeatablity of the repressurization behaviour during blowdown from a v e r t i c a l pipe discharging upward-7 0 0 5 0 0 o Q_ LU cn co co LU or 3 0 0 CL A A VERTICAL , DISCHARGE UP RUN 7 Pj « 1500 kPa T: = 20.8 °C 1 DISTANCE FROM OPEN END o Z 8 40 mm • Z = 180 mm A Z = 860 mm 100 A A . 8 2 ° a • o o 9 D 0 0 n O A D D D ° ° 0 • 0.25 0.50 TIME s 0.75 1.0 Figure 40. Long term pressure h i s t o r i e s for three gauge stations for a v e r t i c a l pipe discharging upward. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. 7 0 0 o 5 0 0 LU rr ZD CO CO LU rr Q. 3 0 0 100 o o oo o oo oo oo0o<>Ooo T I VERTICAL .DISCHARGE UP RUN 7 Pj = I 500 kPa Tj = 20.8 °C DISTANCE FROM OPEN END v Z = 1.62 m O Z * 2.38 m o Z =3.14 m — o — 0 % * 0 S 0.25 0.50 TIME S 0.75 1.00 Figure 41. Long term pressure h i s t o r i e s for three gauge stations for a v e r t i c a l pipe discharging upward. The dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. 7 0 0 2 5 0 0 LU rr ZD CO CO LU rr C L 3 0 0 100 o o V o -0. o VERTICAL , DISCHARGE UP RUN 8 1 3j = 1500 kPa T| = 22.6 °C DISTANCE FROM OPEN END v Z = 1.62 m 0 Z = 2.38 m o Z = 3.14 m ON Figure 42. Repeat of the pressure h i s t o r i e s shown in Figure 41. dashed l i n e indicates the saturation pressure at the i n i t i a l temperature. - 77 -To summarize the discharge up data, repressurization was seen on both runs. However the repressurization was only seen at the middle two gauge statio n s (Figures 31, 32 and 39). The two gauge stations closest to the open end showed a rapid drop to approximately the saturation pressure of Freon-114 (Figures 29, 30, 37 and 38). At the two gauge stations nearest the closed end the pressure dropped r a p i d l y , but the slope of the graphs became much more shallow at a pressure well above the saturation pressure. 4.7 Flow H i s t o r i e s for Discharge V e r t i c a l l y Up The f i r s t camera po s i t i o n was 460 mm (1.44 tube diameters) from the open end of the tube. Nucleation started approximately 1 millisecond a f t e r the diaphragm was broken, and was followed by a period of bubbly flow. During t h i s flow regime the size of the bubbles appeared to be increasing. Around 20 milliseconds into the blowdown the flow was i n the form of a slug of large bubbles followed by a slug of smaller bubbles. This bubbly-slug flow continued u n t i l around 53 milliseconds a f t e r the blowdown, at which time the flow became a mass of very t i g h t l y packed bubbles. A period of annular flow, having l i q u i d at the edges and with a vapour core, could be seen around 256 milliseconds into the flow. This flow regime continued u n t i l the camera ran out of f i l m at 1106 milliseconds a f t e r the blowdown. The second camera positon was 2.56 m (80 tube diameters) from the discharge end. The flow regimes at t h i s l o c a t i o n are very s i m i l a r to those described previously. Nucleation started 6 milliseconds a f t e r the - 78 -blowdown. It was followed by a period of bubbly flow which lasted u n t i l 37 m illiseconds. The bubbly-slug flow described e a r l i e r i s evident u n t i l 72 milliseconds, when the flow regime returned to bubbly flow. This lasted u n t i l 529 milliseconds at which time the flow h i s t o r y at this l o c a t i o n deviated from that described e a r l i e r by showing some slug flow. This flow pattern changed to an annular flow regime around 630 milliseconds into the flow which continued for the rest of the t e s t . However, at 1132 milliseconds the flow can be seen to reverse d i r e c t i o n and s t a r t to flow back down the tube. The l a s t camera po s i t i o n was 3.56 m (111.25 tube diameters) from the discharge end of the tube. The flow patterns were considerably d i f f e r e n t from those at the previous two lo c a t i o n s . Nucleation started 10 milliseconds a f t e r the blowdown. This was followed by a period of bubble growth with very l i t t l e movement i n the f l u i d . This continued u n t i l around 590 milliseconds when the tube was f u l l of bubbles and the f l u i d began moving very r a p i d l y . There was some evidence of slug flow around t h i s time. By 837 milliseconds the bubbles had migrated to the walls and there was an annular flow pattern. This flow regime was v i s i b l e for the remainder of the test with the flow reversing d i r e c t i o n around 1273 milliseconds. The data from the movies taken for discharge v e r t i c a l l y up have been summarized i n Figure 43. - 79 -5 0 0 0 1 0 0 0 in E UJ 100 10 Flow Reversal Annular Bubbly Flow K B u b b l y - S l u g Flow o-Bubbly Flow L iquid •o 0 1 2 3 4 DISTANCE FROM O P E N END Z m Figure 43. Flow regimes during blowdown of Freon-114 from a v e r t i c a l pipe discharging upward (see Figure 9). - 80 -CHAPTER FIVE DISCUSSION OF THE RESULTS 5.1 Discharge H o r i z o n t a l l y The primary reason f o r conducting experiments w i t h the tube d i s c h a r g i n g h o r i z o n t a l l y was to o b t a i n data f o r comparison with that of Necmi and Hancox [ 4 ] . Figure 7 compares the present pressure h i s t o r i e s to those of Necmi. For both cases the data showed a r a p i d decrease i n pressure to a pressure near the s a t u r a t i o n pressure of the Freon-114 f o r the i n i t i a l temperature. The pressure wave appears to be t r a v e l l i n g along the tube at 360 metres per second which i s approximately the speed of sound i n l i q u i d Freon-114. Figure 8 compares the flow regimes observed during the present work at one l o c a t i o n along the pipe w i t h the flow regime map compiled by Necmi. Once again there i s good agreement between the two r e s u l t s . I t should be noted that some sl u g flow not seen by Necmi was observed. Another i n t e r e s t i n g point i s that the complete s t r a t i f i c a t i o n of the l i q u i d and vapour phases of the flow that Necmi reported was a l s o seen during these t e s t s . The r e s u l t s obtained from the h o r i z o n t a l experiments were very encouraging. The data was much as i t was expected to be. I t should be noted that although the blowdown apparatus was the same f o r both these i n v e s t i g a t i o n s , the method of a c q u i r i n g the data was completely d i f f e r e n t . From the clo s e agreement between our data and the r e s u l t s obtained by Necmi we i n f e r r e d that the data a c q u i s i t i o n system was working p r o p e r l y . - 81 -5.2 Discharge V e r t i c a l l y The pressure data f o r d i s c h a r g i n g v e r t i c a l l y up and f o r d i s c h a r g i n g v e r t i c a l l y down can be d i v i d e d i n t o two d i s t i n c t groups. There i s a "normal" group which c o n s i s t s of pressure readings that conformed to our expe c t a t i o n s . This group shows a ra p i d pressure drop to near the s a t u r a t i o n pressure at the i n i t i a l temperature. The pressure wave appears to be t r a v e l l i n g between the pressure transducers at the speed of sound i n Freon-114. For a short time i n t e r v a l a f t e r the blowdown t h i s group i s i n f a c t much l i k e the pressure data f o r the h o r i z o n t a l discharge. The second or "unusual" group of data shows pressure h i s t o r i e s that resemble the "normal" data f o r the f i r s t few m i l l i s e c o n d s of the blowdown. However, a f t e r the i n i t i a l decompression to the s a t u r a t i o n pressure had occurred, a recompression to a pressure s l i g h t l y under the i n i t i a l pressure of the f l u i d was observed. Both groups of data were reproduced (although not on demand) and agreement w i t h i n the groups i s very good. The primary o b j e c t i v e of t h i s i n v e s t i g a t i o n was to examine the e f f e c t of body forces on the blowdown of a tube. Body forces were not expected to have much i n f l u e n c e on the time f o r the i n i t i a l decompression wave to pass, because the f i r s t passage i s s t r i c t l y a c o u s t i c . The times f o r the pressure to drop to s a t u r a t i o n i n both the "normal" and the "unusual" data confirm t h i s . For example, at the gauge s t a t i o n 3.14 metres (98.13 tube diameters) from the discharge end, the i n i t i a l decompression s t a r t s at 10.0 m i l l i s e c o n d s f o r the h o r i z o n t a l discharge, at 9.0 m i l l i s e c o n d s f o r the v e r t i c a l down discharge and at 9.5 m i l l i s e c o n d s f o r the v e r t i c a l up discharge. - 82 -The e f f e c t s of g r a v i t y are more evident i n the flow regime h i s t o r i e s . The time scales here are much longer and with i n c r e a s i n g time the r a t i o of pressure to body forces becomes s m a l l e r , meaning we should expect to see the body forces having more i n f l u e n c e . The most obvious e f f e c t of body forces i s that f o r discharge up the tube never empties. In f a c t about 90% of the Freon i s discharged during the blowdown. The other 10% remains b o i l i n g i n the tube. From the flow regime map f o r discharge up (Figure 43) i t can be seen that the flow reverses d i r e c t i o n and s t a r t s to run down the tube at about one second Into the blowdown. At t h i s time the pressure i n the tube i s approximately atmospheric (Figures 40, 41 and 42). Another and h o p e f u l l y more obvious e f f e c t of body force i s that f o r discharge down the tube does empty completely! A great deal of time has been spent i n attempting to e x p l a i n the occurrence of the recompression phenomenon In some of the v e r t i c a l discharge data. As of yet no d e f i n i t i v e answer has been obtained, although a number of p o s s i b i l i t i e s have been proposed. When the recompression was f i r s t observed i t was thought to be the r e s u l t of a pressure undershoot as observed by a number of experimenters i n c l u d i n g Alamgir and Lienhard [ 8 ] , Alamgir, Kan and Lienhard [ 3 ] , Necmi and Hancox [4] and Edwards and O'Brien [ 1 ] . T y p i c a l l y what was observed during these studies was a r a p i d drop i n the f l u i d pressure and a delay i n n u c l e a t i o n u n t i l the f l u i d pressure had dropped below the s a t u r a t i o n pressure. With the onset of n u c l e a t i o n the pressure would recover to s l i g h t l y above the s a t u r a t i o n pressure and then the f l u i d pressure would g r a d u a l l y drop as the l i q u i d continued to b o i l . U s u a l l y the pressure recovery i s to a point near the s a t u r a t i o n pressure of the f l u i d at the - 83 -i n i t i a l temperature [ 8 ] , The r e s u l t s of delayed n u c l e a t i o n can be seen a number of times i n t h i s work (see Figure 7 f o r the case of h o r i z o n t a l d i s c h a r g e ) . Pressure recovery was seen f o r both groups of data w i t h the tube d i s c h a r g i n g v e r t i c a l l y down. Figure 12 shows some pressure recovery 10 m i l l i s e c o n d s i n t o the discharge during one of the "normal" runs at the gauge s t a t i o n 1.62 metres (50.63 tube diameters) from the discharge end. Fig u r e 20 shows the same pressure recovery f o r the same gauge s t a t i o n during one of the " r e p r e s s u r i z a t i o n " runs. Pressure undershoot and recovery can al s o be seen f o r the discharge v e r t i c a l l y up data (Figures 29, 30 and 31). Delayed n u c l e a t i o n was r e j e c t e d as a p o s s i b l e e x p l a n a t i o n f o r the l a r g e pressure recovery seen i n the "unusual" data i n the present work, since i t was f e l t that delayed n u c l e a t i o n could not e x p l a i n a pressure recovery of such a l a r g e magnitude. The next p o s s i b i l i t y that was considered was that the recompression was caused by a flow r e v e r s a l . As noted e a r l i e r no evidence of flow r e v e r s a l was seen on the movies at times c o r r e s p o n d i n g to the r e p r e s s u r i z a t i o n . Figure 44 shows the pressure p r o f i l e s along the pipe at various times f o r a r e p r e s s u r i z a t i o n run with the discharge v e r t i c a l l y down and Figure 45 shows s i m i l a r pressure p r o f i l e s f o r discharge v e r t i c a l l y up. As can be seen from t h i s f i g u r e the a x i a l pressure gr a d i e n t along the pipe reversed r a p i d l y during the r e p r e s s u r i z a t i o n . This would i n d i c a t e a r a p i d d e c e l e r a t i o n of the flow, i f not a complete r e v e r s a l , must have occurred along the pipe. The l a s t e xplanation considered f o r the recompression was that i t could be the r e s u l t of some type of experimental f a i l u r e . There are a number of p o s s i b l e experimental shortcomings that could p o t e n t i a l l y lead to r e s u l t s of the kind observed. The f i r s t one considered was the e f f e c t - 84 -2 000 100 _L TIME o 3 ms • 9 ms 15 ms o 21 ms X 27 ms 33 ms I 2 3 DISTANCE FROM OPEN END m Figure 44. Pressure profiles along a pipe discharging downward when repressurization was noted ( i n i t i a l conditions as in Figure 27). - 85 -2 000 LU rr 1000 eoo 600 CO 400 CO LU rr CL 200 100 TIME o 3 ms • 9 ms 15 ms o 21 ms X 27 ms * 33 ms 1 2 3 DISTANCE FROM OPEN END m Figure 45. Pressure p r o f i l e s along a pipe discharging downward when repressurization was noted ( i n i t i a l conditions as i n Figure 29). - 86 -of gas i n so l u t i o n . Sozzi and Fedrick [5] showed i n t h e i r work with water that gas i n solution had l i t t l e e f f e c t on the pressure measurements during blowdown. However, this may not be the case when Freon i s used as the test f l u i d . In fact i t has been suggested by some unpublished work of Sozzi that f o r Freon, i n e r t gases i n so l u t i o n can have a s i g n i f i c a n t e f f e c t on experimental measurements. It should be noted that i n the present study the Freon was allowed to b o i l i n an attempt to eliminate the gas i n solu t i o n and that no evidence of gas forming a s h i e l d around the pressure transducers was observed i n any of the photographs. Another p o t e n t i a l problem area i s a flow r e s t r i c t i o n caused by the diaphragms not breaking cleanly. The e f f e c t of such a flow r e s t r i c t i o n was observed during the i n i t i a l nitrogen tests of the apparatus. As mentioned e a r l i e r the r e s u l t i n g pressure o s c i l l a t i o n s were the r e s u l t of the diaphragms not breaking cleanly. It i s possible the recompression observed during the Freon tests was caused by a s i m i l a r mechanism. However, at the end of each test there was no evidence of the diaphragms blocking the end of the tube. Sozzi and Fedrick [5] saw a si m i l a r recompression i n t h e i r work with the discharge of a reservior through a pipe. Their explanation of the pressure recovery was that i t was caused i n part by growth of the vapour bubbles i n the l o c a l l y decompressed l i q u i d and also by choking and flow f r i c t i o n i n the test section. They believe that l o c a l f r i c t i o n and choking l i m i t the flow, further increasing back pressure i n the test section, r e s u l t i n g i n the pressure recovering to above the saturation pressure. - 87 -Lienhard, Kan and Alamgir [3] i n r e f e r r i n g to the repressurization observed by Sozzi and Fedrick [5], state that they suspect the behaviour "to be the combined r e s u l t of the presence of the reservoir and the r e f l e c t e d r a r e f a c t i o n wave i n t e r a c t i n g with the recovering pressure." This gives r i s e to the question how would i t be possible for the present experiment to recreate the conditions of the Sozzi and Fedrick [5] experiment. One possible answer i s , i f for some reason the solenoid valve at the closed end of the tube remained open i t would have b a s i c a l l y duplicated the experimental conditions of a reservoir discharging through a tube as was the case i n the Sozzi and Fedrick experiment. This would adequately explain the repressurization seen i n the discharge down case. From the pressure p r o f i l e s of Figure 44 i t appears as though there was a slug of high pressure moving down the tube. However th i s theory would not explain the repressurization seen i n the discharge up case. From the p r o f i l e s of Figure 45 i t can be seen that the pressure recovery only occurred at the middle two gauge s t a t i o n s . There was no i n d i c a t i o n of a slug of high pressure passing the two gauge stations nearest the closed end of the tube, which would had to have occurred i f the recovery was the r e s u l t of a reservoir discharging. A f i n a l experimental e f f e c t considered as a source of the spurious pressure readings was the e l a s t i c v i b r a t i o n of the tube wall due to a sudden release of load. While t h i s possibly could have been a contributing factor i t i s f e l t that i t was not the primary cause of the large repressurization seen i n some of the present r e s u l t s . During the ho r i z o n t a l tests the tube was subjected to the same sudden release of pressure, but during these experiments no repr e s s u r i z a t i o n was seen. For t h i s reason e l a s t i c v i b r a t i o n of the tube wall has been ruled out as the p r i n c i p l e cause of the rep r e s s u r i z a t i o n . - 88 -CHAPTER SIX CONCLUSIONS 6.1 General The objective of the present study was to experimentally investigate the e f f e c t of pipe o r i e n t a t i o n on the flow regimes and pressure h i s t o r i e s during blowdown from a pipe. The reason for a i n v e s t i g a t i o n of th i s type i s to gain some insig h t into the mechanism of blowdown that could ult i m a t e l y be used i n the formation of an an a l y t i c model. As explained previously the pressure data for discharging v e r t i c a l l y has been divided into two d i s t i n c t groups. There was a "normal" group that showed pressure h i s t o r i e s that were very s i m i l a r to those for ho r i z o n t a l discharge and an "unusual" group that showed an anomolous re p r e s s u r i z a t i o n e f f e c t that could not be s a t i s f a c t o r i l y explained. Despite these anomalies i n the pressure h i s t o r i e s , i t i s f e l t that v a l i d conclusions can s t i l l be drawn from the present r e s u l t s . The anomalies i n the data do not appear to have affected either the i n i t i a l decompression time or the long-term flow h i s t o r i e s . Conclusions about the short- and long-term e f f e c t s of body forces on the blowdown of a tube discharging v e r t i c a l l y up and discharging v e r t i c a l l y down have been drawn on the basis of the experimentally measured pressure h i s t o r i e s and the study of the flow regime h i s t o r i e s r e s u l t i n g from viewing the high speed photographs. S t r i c t l y speaking, the conclusions drawn are v a l i d only - 89 -for discharge v e r t i c a l l y up or v e r t i c a l l y down, however, i t i s f e l t that the conclusions can be q u a l i t a t i v e l y extended to include pipes at d i f f e r e n t o r i e n t a t i o n s . 6.2 Normal data The present r e s u l t s show that body forces have a s i g n i f i c a n t e f f e c t on flow regimes, pressure gradients and discharge rates during sudden blowdown from a pipe. In the early stages of the transient while discharging upward (or h o r i z o n t a l l y ) a bubbly flow develops f i r s t , whereas a l i q u i d - c o r e annular flow develops f i r s t while discharging downward. For l a t e r times ( a f t e r 400 ms) a bubbly-slug flow develops when discharging either upward or downward, while a horizontal pipe becomes s t r a t i f i e d . For times approaching one second af t e r the transient the v e r t i c a l pipe discharging downward i s nearly empty, while the upward discharge case reverses flow d i r e c t i o n and leaves some f r a c t i o n of l i q u i d i n the pipe (around 10% in the present t e s t s ) . Despite the greatly varying flow regimes, pressure h i s t o r i e s during the early portion of the transient did not change s i g n i f i c a n t l y f o r the d i f f e r e n t d i r e c t i o n s of discharge, although a tendency for the pressures to be s l i g h t l y higher during upward discharge was noted. The time for the i n i t i a l decompression i s approximately equal f o r d i s c h a r g e h o r i z o n t a l l y , upward and downward. This i s because the the i n i t i a l decompression i s s t r i c t l y acoustic and pipe o r i e n t a t i o n should not - 90 -e f f e c t the pressure h i s t o r y during the i n i t i a l stages. This hypothesis has been shown to be c o r r e c t by the present study. 6.3 R e p r e s s u r i z a t i o n Results I t i s d i f f i c u l t t o draw any c o n c l u s i o n s r e g a r d i n g t h e r e p r e s s u r i z a t i o n observed i n some of the data because at present no d e f i n i t i v e e xplanation f o r the r e p r e s s u r i z a t i o n has been found. L i k e l y causes such as f l u i d i m p u r i t i e s , outgassing, w a l l n u c l e a t i o n e f f e c t s , l eaks and end-diaphragm p a r t i a l r e s t r i c t i o n s have been s y s t e m a t i c a l l y examined and r e j e c t e d as p o s s i b l e causes i n t h i s case. T h i s g i v e s r i s e to the o b v i o u s q u e s t i o n , why s h o u l d the r e p r e s s u r i z a t i o n data be believed? A number of d i f f e r e n t f a c t s support the r e s u l t s that were observed. The r e p r e s s u r i z a t i o n data was repeatable, although not on demand, and agreement w i t h i n t h i s group of data was very good. This would i n d i c a t e that the r e p r e s s u r i z a t i o n observed was not the r e s u l t of some unusual set of circumstances. Also the r e s u l t s f o r the h o r i z o n t a l case, none of which showed any signs of r e p r e s s u r i z a t i o n , compared very w e l l with the r e s u l t s observed by Necmi and Hancox [4]. This shows that the data a c q u i s t i o n and handling systems were working c o r r e c t l y . Indeed the f a c t that r e p r e s s u r i z a t i o n was noted i n the v e r t i c a l , but not the h o r i z o n t a l case suggests i t i s not apparatus-generated. In f a c t i t i s d i f f i c u l t to come to any c o n c l u s i o n - 91 -other than that the r e p r e s s u r i z a t i o n i s somehow l i n k e d to the pipe o r i e n t a t i o n . 6.4 Suggestions f o r Further Study Further experiments are necessary to determine the cause of the r e p r e s s u r i z a t i o n seen during some of the t e s t s . Of a l l the p o s s i b l e explanations put f o r t h i n Chapter Five i t i s f e l t that the f i r s t one that should be i n v e s t i g a t e d i s the discharge of a r e s e r v o i r through a pipe. This could be accomplished by a l t e r n a t e l y running the experiment with the valve on the i n l e t side open and c l o s e d . Another area that should be i n v e s t i g a t e d more thoughly i s the e f f e c t of i n e r t gases such as a i r or carbon d i o x i d e on both the flow and pressure h i s t o r i e s . Other p o s s i b i l i t i e s f o r f u r t h e r study are the e f f e c t of i n i t i a l c o n d i t i o n s on the r e s u l t s , e s p e c i a l l y pressure and the amount of subcooling. I t would a l s o be i n t e r e s t i n g to repeat the experiments with d i f f e r e n t pipe s i z e s and d i f f e r e n t pipe o r i e n t a t i o n s . - 92 -REFERENCES 1. Edwards, A.R. and O'Brien, T.P., Journal of BNES, V o l . 9, pages 125-135, 1970. 2. Edwards, A.R. and Mather, D.J. "Some UK Studies Related to the Loss of Coolant Accident", Safety and R e l i a b l i t y D i r e c t o r a t e , UKAEA Culcheth, Warrington, Lanes (1973). 3. Alamgir, Md., Kan, C.Y. and Lienhard, J.H. " E a r l y Response of P r e s s u r i z e d Hot Water i n a Pipe to a Sudden Break", E l e c t r i c Power Research I n s t i t u t e Report NP-1867, June 1981. 4. Necmi, S. and Hancox, W.T., "An Experimental and T h e o r e t i c a l I n v e s t i g a t i o n of Blowdown From a H o r i z o n t a l Pipe", S i x t h I n t e r n a t i o n a l Heat Transfer Conference Toronto, Canada, August 7-11, 1978, Volume 5 pages 83-88. 5. S o z z i , G.L. and F e d r i c k , N.A., "Decompression Waves i n a Pipe and V e s s e l Containing Subcooled Water at 1000 PSI." NEDE-13333, General E l e c t r i c Company, March 1973. 6. Lyczkowski ,Robert W., "Transient Propagation Behavior of Two-Phase Flow Equations", A paper submitted to the session "Two Phase Flow" at the 15th N a t i o n a l Heat Transfer Conference, San F r a n c i s c o , August 10-13, 1975. - 93 -7. M o z a f f a r i H., " P r e d i c t i n g the E f f e c t s of V e r t i c a l Pipe O r i e n t a t i o n by the Method of C h a r a c t e r i s t i c s During Sudden Discharge of a Two-Phase F l u i d " , M.A.Sc. Thesis, U n i v e r s i t y of B r i t i s h Columbia, 1979. 8. Alamgir Md. and Lienhard J.H., " C o r r e l a t i o n of Pressure Undershoot During Hot-Water D e p r e s s u r i z a t i o n . " , Journal of Heat Trans f e r , Volume 102, November, 1980. 9. Massey B.S., "Mechanics of F l u i d s " , Van Nostrand Reinhold Company, 1970, pages 414 to 417. - 94 -APPENDIX ONE CALCULATIONS AND ERROR ANALYSIS A. Pressure Measurements As the pipe was being pressurized c a l i b r a t i o n samples were taken by the PDP 11/10 for each of the s i x pressure transducers. An example of one of these tables i s give below Pressure (kPa) D i g i t a l Reading 100 0 300 144 500 291 700 435 900 582 1100 728 1300 871 1500 1017 The computer program that did the data reduction used these tables to c a l c u l a t e the f l u i d pressure from the d i g i t a l readings. For example the d i g i t a l reading 410 would be converted to a pressure i n the following manner: 1. The program would find the d i g i t a l range, which i n this case i s 291 to 435 which corresponds to a pressure of 500 to 700 kPa. - 95 -2. The r a t i o of the d i g i t a l readings to the pressure range would then give the pressure increase above the base pressure, i n t h i s case 500 kPa. The d i g i t a l reading of 410 would be converted as f o l l o w s : 410 (±1) - 291 (±1) X 700 kPa (±0.7 kPa) - 500 kPa (±0.5 kPa) 435 (±1) - 291 (±1) 119 (±2) X 200 kPa (±1.2 kPa) 144 (±2) = 119 (±1.7%) X 200 kPa (±0.6%) 114 (±1.4%) 165 kPa (±3.7%) 165 kPa (± 6.1 kPa) above the base pressure of 500 kPa (±0.5 kPa) Pressure = 165 kPa (±6.1 kPa) + 500 kPa (±0.5 kPa) = 665 kPa (±6.6 kPa) B. Bulk Temperature Bulk Temperature was measured by a Newport Laboratory Inc. model 267A-TC1 d i g i t a l thermometer. The thermocouples were c a l i b r a t e d by d i r e c t immersion i n a heated bath. From c a l i b r a t i o n s before and a f t e r the experiments i t was estimated that the e r r o r i n the temperature measurements Is l e s s than 1%. - 96 -APPENDIX TWO PROPERTIES OF FREON-114 A. Speed of Sound From Massey [9] the speed of sound i n a pipe i s given by the formula: C = /(K'/p) Where: C = the speed of sound 1/K' = 1/K + D/(t)(E) K = the bulk modulus of Freon-114 = 225,000 l b / ( i n ) 2 D = the diameter of the pipe = 1.35 i n t = the thickness of the pipe = .1875 i n E = the e l a s t i c modulus of the pipe = 320,000 i b / ( i n ) 2 p = the d e n s i t y of Freon-114 = 92 l b / ( f t ) 3 Using t h i s formula g i v e s : C - 1367 f t / s = 416 m/s - 97 -B. Saturation Pressure at Various Temperatures Temperature(°C) Pressure(kPa) 4 104 10 128 16 156 21 188 27 225 32 268 

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