Platelet incubators are refrigerated laboratory storage devices aimed at preserving platelets in ... more Platelet incubators are refrigerated laboratory storage devices aimed at preserving platelets in liquid form at close to ambient temperature. Quality and shelf life of the stored platelets strongly depend on the storage temperature uniformity and continuous movement of the platelets provided by an agitator to avoid coagulation. Incubator manufacturers usually provide assurance that temperature uniformity will be within +/-1°C from the set point. Such strict requirement of uniformity is achieved by continuously running a forced convection vapor compression refrigeration system and by balancing excess cooling capacity with a controlled pulse heater located inside the cabinet. Dominant refrigerants currently employed in refrigerated laboratory equipment are HFCs with high GWP. In the future, HFCs will be gradually replaced mostly by flammable natural refrigerants of the ASHRAE A3 group such as R600a (isobutane), R290 (propane) and R170 (ethane) depending on the cooler size and applicat...
Effects of superficial liquid velocity (U l ), superficial gas velocity (U g ), and fiber mass fr... more Effects of superficial liquid velocity (U l ), superficial gas velocity (U g ), and fiber mass fraction (C) on gas holdup (ε) and flow regime transition are studied experimentally in well-mixed water-cellulose fiber suspensions in a cocurrent bubble column. Experimental results show that the gas holdup decreases with increasing U l when C and U g are constant. The gas holdup is not significantly affected by C in the range of C 0.4%, but decreases with increasing C in the range of 0.4% ≤ C < ≤ 1.5%. When C 1.5%, a significant amount of gas is trapped in the fiber network and recirculates with the water-fiber slurry in the system; as a result, the measured gas holdup is higher than that at C = 1.5%. The axial gas holdup distribution is shown to be a complex function of superficial gas and liquid velocities and fiber mass fraction. The drift-flux model is used to analyze the flow regime transitions at different conditions. Three distinct flow regimes are observed when C 0.4%, but on...
A gas holdup model is developed for cocurrent air–water–fiber bubble column flows using the drift... more A gas holdup model is developed for cocurrent air–water–fiber bubble column flows using the drift–flux model. The model coefficients are estimated using a nonlinear least square method and systematically acquired experimental data. The model correlates gas holdup with superficial gas and liquid velocity, and fiber type and mass fraction. The model reproduces most experimental data within ±10% error and all
International Journal of Multiphase Flow - INT J MULTIPHASE FLOW, 2006
Estimating gas holdup via pressure difference measurements is a simple and low-cost non-invasive ... more Estimating gas holdup via pressure difference measurements is a simple and low-cost non-invasive technique to study gas holdup in bubble columns. It is usually used in a manner where the wall shear stress effect is neglected, termed Method II in this paper. In cocurrent bubble columns, when the liquid velocity is high or the fluid is highly viscous, wall shear stress may be significant and Method II may result in substantial error. Directly including the wall shear stress term in the determination of gas holdup (Method I) requires knowledge of two-phase wall shear stress models and usually requires the solution of non-linear equations. A new gas holdup estimation method (Method III) via differential pressure measurements for cocurrent bubble columns is proposed in this paper. This method considers the wall shear stress influences on gas holdup values without calculating the wall shear stress. A detailed analysis shows that Method III always results in a smaller gas holdup error than...
Platelet incubators are refrigerated laboratory storage devices aimed at preserving platelets in ... more Platelet incubators are refrigerated laboratory storage devices aimed at preserving platelets in liquid form at close to ambient temperature. Quality and shelf life of the stored platelets strongly depend on the storage temperature uniformity and continuous movement of the platelets provided by an agitator to avoid coagulation. Incubator manufacturers usually provide assurance that temperature uniformity will be within +/-1°C from the set point. Such strict requirement of uniformity is achieved by continuously running a forced convection vapor compression refrigeration system and by balancing excess cooling capacity with a controlled pulse heater located inside the cabinet. Dominant refrigerants currently employed in refrigerated laboratory equipment are HFCs with high GWP. In the future, HFCs will be gradually replaced mostly by flammable natural refrigerants of the ASHRAE A3 group such as R600a (isobutane), R290 (propane) and R170 (ethane) depending on the cooler size and applicat...
Effects of superficial liquid velocity (U l ), superficial gas velocity (U g ), and fiber mass fr... more Effects of superficial liquid velocity (U l ), superficial gas velocity (U g ), and fiber mass fraction (C) on gas holdup (ε) and flow regime transition are studied experimentally in well-mixed water-cellulose fiber suspensions in a cocurrent bubble column. Experimental results show that the gas holdup decreases with increasing U l when C and U g are constant. The gas holdup is not significantly affected by C in the range of C 0.4%, but decreases with increasing C in the range of 0.4% ≤ C < ≤ 1.5%. When C 1.5%, a significant amount of gas is trapped in the fiber network and recirculates with the water-fiber slurry in the system; as a result, the measured gas holdup is higher than that at C = 1.5%. The axial gas holdup distribution is shown to be a complex function of superficial gas and liquid velocities and fiber mass fraction. The drift-flux model is used to analyze the flow regime transitions at different conditions. Three distinct flow regimes are observed when C 0.4%, but on...
A gas holdup model is developed for cocurrent air–water–fiber bubble column flows using the drift... more A gas holdup model is developed for cocurrent air–water–fiber bubble column flows using the drift–flux model. The model coefficients are estimated using a nonlinear least square method and systematically acquired experimental data. The model correlates gas holdup with superficial gas and liquid velocity, and fiber type and mass fraction. The model reproduces most experimental data within ±10% error and all
International Journal of Multiphase Flow - INT J MULTIPHASE FLOW, 2006
Estimating gas holdup via pressure difference measurements is a simple and low-cost non-invasive ... more Estimating gas holdup via pressure difference measurements is a simple and low-cost non-invasive technique to study gas holdup in bubble columns. It is usually used in a manner where the wall shear stress effect is neglected, termed Method II in this paper. In cocurrent bubble columns, when the liquid velocity is high or the fluid is highly viscous, wall shear stress may be significant and Method II may result in substantial error. Directly including the wall shear stress term in the determination of gas holdup (Method I) requires knowledge of two-phase wall shear stress models and usually requires the solution of non-linear equations. A new gas holdup estimation method (Method III) via differential pressure measurements for cocurrent bubble columns is proposed in this paper. This method considers the wall shear stress influences on gas holdup values without calculating the wall shear stress. A detailed analysis shows that Method III always results in a smaller gas holdup error than...
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Papers by Chengzhi Tang