Numerical simulations of the small bubble-big bubble-liquid three phase heterogeneous flowudin a square cross-sectioned bubble column were carried out with the commercial CFDudpackage CFX-4.4 to explore the effect of superficial velocity and inlet dispersed phaseudfractions on the flow patterns. The approach of Krishna et al. (2000) was adopted in theudEuler-Euler framework to numerically simulate the gas-liquid heterogeneous flow in bubbleudcolumns. On basis of an earlier study (Zhang et al. 2005), the extended multiphase k - εudturbulence model (Pfleger and Becker, 2001) was chosen to model the turbulent viscosity inudthe liquid phase and implicitly account for the bubble-induced turbulence. The obtainedudresults suggest that, first of all, the extended multiphase k - ε turbulence model of Pfleger andudBecker (2001) is capable of capturing the dynamics of the heterogeneous flow. Withudincreasing superficial velocity, the dynamics of the flow, as well as the total gas hold-upudincreases. It is observed that with increasing inlet phase fraction of the big bubbles, the totaludgas holdup decreases while the dynamic nature of the flow increases, which indicates that theudsmall bubble phase mainly determines the total gas holdup while the big bubble phaseudpredominantly agitates the liquid.
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