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Experimental Characterization of Gas-Liquid Column: Effect of nozzle orientation and pressure

CHEMICAL REACTION ENGINEERING LABORATORY. Experimental Characterization of Gas-Liquid Column: Effect of nozzle orientation and pressure by Peter Spicka. October 30 th , Informal meeting. Objective.

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Experimental Characterization of Gas-Liquid Column: Effect of nozzle orientation and pressure

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  1. CHEMICAL REACTION ENGINEERING LABORATORY Experimental Characterization of Gas-Liquid Column: Effect of nozzle orientation and pressure by Peter Spicka October 30th, Informal meeting

  2. Objective • Study the sparger nozzle orientation effect on gas hold-up, liquid velocity and turbulence in gas-liquid column Motivation • Only few data, i.e. liquid velocity and gas holdup, available in the literature for churn-turbulent flow regime • CARPT and CT techniques allow relatively accurate acquisition of needed data • Different pressures and UGS can be covered • Additional experimental database for CFD simulations can be created

  3. 6.375” stainless steel column Cross-sparger, two nozzle orientations: facing upward and downward Air-water system Dynamic height maintained at 11 D Pressure: 1 bar and 4 bars UGS= 5 cm/s (only CT) and 20 cm/s CARPT setup Typical setup, 30 detectors Only photo peak acquisition 50 Hz sampling frequency CT setup 5 detectors, 7 projections per view 4 axial levels: 2.5D; 3.5D; 5.5D; and 9D 20 Hz sampling frequency Experiment

  4. Detector alignment and calibration CT CARPT Typical energy spectrum Typical calibration curve • CT • photopeak at 650 mV • acquisition threshold was set to 580 mV • CARPT calibration • relatively small number of counts compared to previous experiments Þ weak tracer particle • Calibration positions reconstructed with accuracy ±1 cm Reconstructed calibration positions Detector Alignment

  5. Accuracy of the experiments • Source of errors for CT data: • reconstruction algorithm disregards of the non-linear nature of the Lambert-Beer law • projection time t=17 s may be insufficient for reliable time averaging • CARPT data: • gas-holdup fluctuations • natural fluctuations in radiation intensity Mass balance for liquid phase Liquid net inflow, based on the exp. data, is calculated as: and its relative value (with respect to gas net inflow): Values of eL for different flow conditions

  6. Minimum count threshold Effect on instantaneous particle positions Threshold=25 Threshold=18 Threshold=11 • Strong influence of the minimum count threshold on particle occurrence Þ velocities computed in near the column walls can be less accurate • Present Data • Very high count threshold was used for the CARP data Þ more than 50% points rejected! Note: only 5% fraction of the total number of points is shown in the charts

  7. CT Results Effect of Nozzle Orientation- Global View • Configuration with nozzles facing upward provides increased hold-up Þ smaller bubbles? • Similar behavior was found for all the studied regimes Gas holdup at UGS= 20 cm/s and p = 1 bar nozzles facing downward nozzles facing upward Overall gas holdup

  8. CT Results Effect of Nozzle Orientation and Pressure Gas holdup profiles UGS=5 cm/s UGS=20 cm/s • Nozzle orientation • particularly pronounced at high pressure and high UGS in the sparger zone • diminishes with axial position • Pressure • Typical increase of gas holdup magnitude

  9. Axial velocity profiles Radial velocity profiles CARPT Results Liquid velocity • Steeper velocity profiles observed at high pressure Þ higher bubble momentum • However, effect of nozzle orientation on liquid velocity is visible only at near-sparger region

  10. CARPT Results Turbulent kinetic energy Nozzles facing down Nozzles facing up p = 4 bars • Turbulent kinetic energy is higher for nozzles pointing upward • Similarity with gas holdup maps Þ bubble-induced turbulence

  11. CARPT Results Reynolds stresses • u’xu’x are approximately 2.5 x higher than u’ru’r and they are weakly coupled • Magnitude of u’xu’x is comparable with the corresponding mean velocities • Highly anisotropic flow !

  12. Nozzle orientation Significant effect on gas holdup and turbulent kinetic energy mainly near the column bottom More pronounced at high UGS and high pressure Effect on liquid velocity profiles is less significant Uncertainty in magnitude of turbulent parameters due to gas holdup fluctuations Concluding Remarks Outlook for future • Experiment • Elimination of gas holdup fluctuations from CARPT data • CARPT reconstruction with improved parameters • Check for data reproducibility • CFD • Examination of nozzle orientation effect in churn-turbulent regime

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