CFD-PBM Simulation Of Gas-Liquid Flow In Bubble Column Reactors Based On Moment Method

Bubble column reactors have been widely used in petrochemical,environmental,biological and energy industries in view of the simple structure and efficient heat and mass transfer.The study of hydrodynamics in bubble columns,in particularly,by the combination of computational fluid dynamics(CFD)and population balance modeling(PBM),is of great significance to reactor design and scaleup.In this study,CFD-PBM simulations are carried out to predict the hydrodynamic parameters and bubble size distribution.The first part,the classes method and QMOM for solving population balance equations are compared,and the accuracy of QMOM is validated with the experiments in literature.The computational efficiency of this method proves higher.Bubble size distribution is reconstructed based on the low-order moment by a priori distribution function.The second part,using QMOM in CFD-PBM,we then systematically evaluate the effects of drag,lift,and coalescence and breakup models on hydrodynamic parameters including gas holdup,axial liquid velocity,gas velocity and bubble size distribution.The research shows that:(1)The drag model plays an important role in gas holdup,gas velocity,and bubble size distribution,but has little effect on liquid velocity.(2)The lift model can improve the distribution of bubbles in the radial direction,intensify the gas-liquid interaction,and increase turbulent dissipation rate and breakup rate.It should not be neglected for the bubble columns operated at higher superficial gas velocities.The increase in gas holdup leads to an increase in bubbles collision frequency and promotes bubbles coalescence.(3)The prediction of Luo breakup model is affected by the local gas holdup.When gas holdup increases,the breakup rate decreases,which suppresses bubbles breakage.The Lehr and the Laakkonen breakup models are hardly affected by gas holdup.This study provides some useful clues on CFD-PBM,and deserves further investigation in future.