Experimental and computational fluid dynamic (CFD) studies on mixing characteristics of a modified helical ribbon impeller

Investigation on the Flow Field and Mixing Efficiency of a Stirred Tank Equipped with Improved Intermig Impellers

The flow field in a transparent stirred tank with a diameter of D = 0.42 m equipped with dual-layer improved Intermig impellers was numerically investigated using a multi-reference frame method based on the computational fluid dynamics (CFD) simulation code: Fluent. The simulation results were validated by experiments based on a stirred tank testing platform and a Particle Image Velocimetry (PIV) testing instrument. The effects on the flow field arising from the diameter of impellers, the installation height of impellers (C1), the rotational speed as well as the distance between two impellers (C2) were investigated. It was revealed that the distance between two impellers and the installation height has obvious influences on the local flow field around impellers. Appropriately increasing the two parameters can enhance the axial flow and achieve a better mass transfer effect. For the tank model rescaled for experiments, the optimized geometrical parameters are C1 = 0.36D and C2 = 0.49D that can result in full occupation of large eddies in the entire volume. The mixing process simulation indicates that the mixing efficiency is the best in the region near the impellers while it is the worst in the bottom of the tank. An appropriate increase in the diameter of the lower impellers and a reduction in the distance from the lower impellers to the tank bottom can improve the mixing efficiency in the central region near the tank bottom.