CFD Modeling of Gas-Liquid Hydrodynamics in a Stirred Tank Reactor

Multiphase impeller stirred tank reactors enhance mixing of reacting species used in a variety of chemical industries. These reactors have been studied based on Computational Fluid Dynamics (CFD) that can be used in the analysis, design and scale up of these reactors. Most of the researches done in this area are limited to single phase reactors, and a few remaining two phase flow investigations have been done based on MRF (Multi Reference Frame) and Snapshot approach. However, the MRF and snapshot approaches cannot be used in rigorous simulation of unsteady state problems. In order to simulate the unsteady state behavior of the multiphase stirred tank reactors we have used sliding mesh technique to solve the problem rigorously. In this work a 3D CFD model is used to investigate hydrodynamics of a fully baffled cylindrical stirred tank containing air-water in which air is sparged. The tank is equipped with a standard Rushton turbine impeller. This work has been done based on two fluid (Eulerian-Eulerian) model and finite volume method, along with standard k-e model to address turbulent behavior of both phases. The results obtained for velocity field show a good agreement with the corresponding data published by researchers in this field for the same case. The effect of gas inlet velocity on the gas holds up distribution has been studied. According to the obtained results, there should be an optimum value for gas inlet velocity in order to achieve appropriate gas distribution in the liquid. The most important parameter affecting the optimum value is impeller rotational speed.