Numerical Simulation Of The Influence Of Agitator Structure On The Gas-Liquid Dispersion In A Stirred Tank

Gas-liquid stirred tank have been widely used in industrial production. Study on the hydrodynamic behavior in such reactors can provide guidance in optimizing the existing reactors of developing and designing a novel reactor with high performance.The three-dimensional flow field, local void fraction distribution and average bubble diameter were numerically simulated in a gas-liquid baffled stirred tank using the commercial CFD code by a single CD-6 impeller, a dual CD-6 impeller and multi-impeller(HEDT+2WHu). The effects of gas flow rate and rotating speed on the fluid field, local void fraction distribution and bubble size distribution were investigated.The standard Euler-Euler formulation of the k-εturbulence model with multiple frames of reference (MFR) was used in this simulation.The way of FLUENT code deals with the bubble was a constant single average bubble diameter (SABD) not considering bubbles breakage and coalescence. The bubble coalescence and breakup were taken into account in the population balance model (PBM) combined with a multiple size group (MUSIG) model defining five group bubbles with commercial software CFX.Reasonable agreement is found between the simulation and experiment.The average error of local void fraction is 13.58%.The error in the upper part of the vessel near the liquid-free surface is larger.Bubble size decreases as the rotating speed increases, and increases as the gas flow rate increases. The bubble size is smaller in the impeller discharged region, and larger in the near wall and circulation regions.This was correctly predicted by the CFD-PBM model in good agreement with the experiment results. The results are of importance to the design and optimization of gas liquid stirred reactors.