Numerical simulation of small bubble-big bubble-liquid three-phase flows

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