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Comparison of alternative advanced experimental techniques for measurement of hydrodynamic characteristics of gas-fluidized beds

University of British Columbia

A novel travelling fluidized bed, designed to facilitate deployment at different research centres, was used to compare advanced measurement techniques for the study of key hydrodynamic properties of gas-fluidized beds. Fast X-ray imaging was employed to visualize the internal flow structures of the bubbling and turbulent fluidization flow regimes. Transition between flow regimes based on X-ray system images were compared with results from pressure fluctuations. Average Shannon entropy reached a maximum plateau at superficial gas velocities close to Uc derived from pressure fluctuations, whereas average kurtosis and skewness leveled off at lower Ug’s. The degree of interference of a 4-mm intrusive probe inserted in the fluidized bed was found to be small by comparing the time-average voidage in a region with and without the probe present. Voidage data obtained by different measurement techniques in a previous study were extended by new data based on fast X-ray imaging and borescopy. Fair, but imperfect agreement among voidage results from alternate techniques was observed and quantified in terms of deviations from the overall average results of all measurement techniques at each gas velocity. Radial profiles of time-average particle velocity in FCC (a Geldart A powder) and sand (a Geldart B powder) fluidized beds at different operating conditions, obtained by radioactive particle tracking (RPT – non-invasive, Ecole Polytechnique), positron emission particle tracking (PEPT – non-invasive, University of Birmingham), optical fibre probe (invasive, UBC) and borescopic high-speed particle image velocimetry (invasive, PSRI) were directly compared. For FCC, each of these techniques provided similar trends with respect to profiles of time-average particle velocity, but with significant differences in some cases. For sand, there were significant quantitative differences among the profiles in many cases. The reasons for the discrepancies included lack of matching of tracer particles, probe intrusiveness, unmatched sensitivities to the direction of motion and different analysis procedures. The RPT, PEPT and borescopy data were further analyzed to obtain solid mass and momentum flux for identical operating conditions. All three techniques provided broadly similar time-average flux profiles. The experimental results obtained in this study provide a unique hydrodynamic benchmark database for validation of CFD codes and other models.

Text

2015-05-27

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/53533

Chemical and Biological Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/