CFD Modelling of Liquid Homogenization in Stirred Tanks with One and Two Impellers Using Large Eddy Simulation

Abstract

A prediction of liquid homogenization in stirred tanks using a CFD code FLUENT is presented. The study was performed for tanks agitated by one and two impellers on a centrally-located shaft. Two types of impellers were used: a six-blade 45° pitched blade turbine and a standard Rushton turbine. Different methods were employed for simulations of fluid flow in the stirred tanks—the multiple reference frames technique together with the standard k– ɛ turbulence model, the sliding mesh technique with the standard k– ɛ turbulence model, and the sliding mesh technique with the large eddy simulation (LES) model and a non-iterative time-advancement algorithm. The dynamic Smagorinsky–Lilly model using a locally calculated subgrid scale dynamic viscosity constant was used in the LES calculations. Tracer mass fractions in the tanks were recorded during time-dependent species transport simulations. The calculated flow field results—velocity profiles, power and pumping numbers were compared with the experimental results from literature. Time traces of normalized concentrations obtained from the simulations were compared with our experiments and the resulting mixing times were compared to literature correlations. The LES approach was the most time-consuming method; however, it described the real flow in stirred tanks better and we obtained more realistic courses of the liquid homogenization and the best agreement of the computed and experimental homogenization times of all the used models.