Large Eddy Simulation of Turbulent Flow and Mixing Time in a Gas-Liquid Stirred Tank

Mixing time is a key parameter relevant to the scale-up and design of agitated reactors. Although there have been many published papers on mixing times in stirred tanks predicted by computational fluid dynamics (CFD), there are few reports on the large eddy simulation (LES) based prediction of the mixing time in a gas liquid stirred tank. In this work, an LES method based on an Eulerian-Eulerian model is presented for predicting the mixing time in a gas liquid stirred tank agitated by a Rushton turbine. In order to verify the simulated results, mixing time experiments were carried out using a conductivity technique. In the present LES, the Smagorinsky subgrid scale model was used to model the effect of subgrid scale on the resolved scales. The concentration distributions and operating parameters such as feed positions, impeller speeds, and gas flow rates on the mixing time were examined. It is shown that the predicted concentration distributions of tracers are more irregular and realistic by using LES. Also, the mixing time decreases with the increase of impeller speed. However, with increasing gas flow rate, the mixing time first increases and then levels off. The predicted mixing time by the LES method shows good agreement with the measured values.