Abstract: The fragmentation kernel function was applied to the population balance model（PBM）and coupled with computational fluid dynamics (CFD) method to simulate size distribution and liquid-liquid dispersion characteristics of droplets in the stirring tank under different types of impeller combinations. The results showed that the propeller (TXL) could promote the axial mixing of the fluid, while the turbine paddle was beneficial to the dispersion of the fluid. Meanwhile, there were significant differences in the flow field characteristics under different impeller combinations. At the same rotating speed, the suction (PM) + TXL combined oars had smaller power consumption, while the RT + RT combined oars had larger power consumption. The presence of baffles could effectively promote droplet breaking, and the stirring performance of the PM+RT combined oars was largely enhanced by the baffle. Moreover, simulation results showed that the dispersed phase was rapidly broken into small-sized droplets in the first few minutes, and then the droplet diameter became stable with the evolution of the operating time. Based on the results of this study, the application of baffle should be considered first in the commercial application of double impeller stirring tank. When the droplet dispersion performance was not required, the PM + TXL combined impeller with axial flow type should be preferred; when high droplet dispersion performance was required, the PM + RT combined impeller with baffle plate should be preferred.

Key words: population balance model, CFD, stirring tank, multi-impeller, liquid-liquid dispersion