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1. Numerical study of the effect of eddy-bubble interaction model onthe turbulent dispersed flow of gas bubbles in stirred tanks1 | |||
HAN Luchang,LIU Yuejin,Luo Hean,Cao Yang,Bai Ge | |||
Chemical Engineering 12 January 2009 | |||
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Abstract:In gas-liquid bubbly flow, due to marked density difference between gas and liquid phases, some no-drag forces, such as virtual mass force, pressure gradient force, etc., may become important. In this case, the effect of these no-drag forces on the turbulent dispersion of gas bubble should be considered. Buwa et al.[1] have used an eddy lifetime (EL) model to simulate the turbulent dispersion in bubble column and neglected the effect of these forces on the renew time scale of turbulent fluctuations, but our simulations showed the EL model wasn’t fully applicable to stirred tank because of high non-homogeneous turbulence. In this work, based on the analysis of forces exerted on gas bubble, we obtained an eddy-bubble interaction (EBI) model, which coupled the neglected the effect of these forces on the renew time scale of turbulent fluctuations, but our simulations showed the EL model wasn’t fully applicable to stirred tank because of high non-homogeneous turbulence. In this work, based on the analysis of forces exerted on gas bubble, we obtained an eddy-bubble interaction (EBI) model, which coupled the effect of no-drag forces and used the eddy-bubble interaction time as the renew time scale. The relationship of crossing time and eddy lifetime was discussed, and the radial, axial velocities and gas holdup distribution predicted by the EBI and EL models were also compared with the experimental data, we found that the crossing time showed obviously different from the eddy lifetime, the crossing time may be much smaller than the eddy lifetime in some positions and the EBI model predicted much bigger slip velocity in the discharge flow region and lower circulation region near the tank wall, and somewhat smaller axial velocity in the upper circulation part, the predicted gas holdup distribution showed a better agreement with the experiment data than that predicted by the EL model. | |||
TO cite this article:HAN Luchang,LIU Yuejin,Luo Hean, et al. Numerical study of the effect of eddy-bubble interaction model onthe turbulent dispersed flow of gas bubbles in stirred tanks1[OL].[12 January 2009] http://en.paper.edu.cn/en_releasepaper/content/27673 |
2. Measurement and Comparison of Gas Holdup Distributions in a Stirred Rushton Tank with γ-CT1 | |||
LIU Yuejin,HAN Luchang,LUO Hean,BAI Ge | |||
Chemical Engineering 08 January 2009 | |||
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Abstract:Three gas dispersion states in liquid — cup dispersion, critical dispersion and full dispersion in a standard gas-liquid stirred Rushton tank (20cm i.d.) were divided based on experimentally based on experimentally observed phenomena. Only those gas dispersion states that were over their corresponding critical gas dispersion states were of signification in industrial applications. Detailed cross-section CT scan images were obtained using a Cs-137 γ-CT scan setup in CREL for the tank at 3/4 dimensionless static liquid height at larger gas rates and higher impeller rotating speeds, when gas dispersion states were over the corresponding critical dispersion states, and their corresponding relationships of gas holdup distribution with dimension radius were established based on the CT images. The comparsions and analyses of the distributions of gas holdup at 3/4 dimensionless static liquid height were investigated based on the CT images and their corresponding digital distribution curves of gas hold up with dimension radius. The work done in this paper is of great significance in measurement and comparison of gas holdup distributions for gas-liquid stirred Rushton tanks. | |||
TO cite this article:LIU Yuejin,HAN Luchang,LUO Hean, et al. Measurement and Comparison of Gas Holdup Distributions in a Stirred Rushton Tank with γ-CT1[OL].[ 8 January 2009] http://en.paper.edu.cn/en_releasepaper/content/27502 |
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