CFD simulation and verification of flow in mixing tanks

A novel approach was developed to simulate the velocity distribution in a mixing tank. Inlet boundary conditions were attributed to the moving impellers. Calculations were performed using FLUENT V 4.31 running on a HP-UNIX network platform. In the case of Rushton turbine impeller, the predicted velocity distribution in the turbulent flow regime was in favorable agreement with the reported laser doppler anemometer (LDA) data. In the case of pitched-blade impeller, the simulated three-directional velocity components in the laminar flow regime showed quantitative agreement with the reported LDA data.;Based on the angular momentum balance, the required torque in mixing tanks was calculated after the converged solution was obtained. The simulated power number in the turbulent regime was 5.6 for Rushton turbine impeller and 1.7 for pitched-blade impeller.;Three approaches to simulate mixing tanks were comparatively investigated with a Rushton turbine impeller in turbulent flow regime. Inlet boundary approach presented expected flow pattern with significant saving in computing effort. Sliding mesh approach showed more accurate and consistent agreement in velocity distribution with the limitation of incompatibility with RSM turbulence model.;The standard k-;The IDEAS software package was used to create an unstructured mesh for a mixing tank with a Rushton turbine impeller. The unstructured mesh was imported and modified in the FLUENT unstructured mesh module. The calculated data in unstructured mesh domain about velocity distribution and energy dissipation rate were in favorable agreement with the counterpart predicted in structured mesh domain. It was demonstrated that an unstructured mesh, created automatically and refined locally, could handle complicated geometry.