Investigation of the flow patterns and mixing efficiency in a stirred tank through particle image velocimetry

Background: Fluid mixing is a complex process that can be significantly influenced by the impeller type and its geometry. Therefore, the selection of an appropriate impeller for effective mixing is crucial. Methods: A stirred tank setup incorporating various combinations of a lab-manufactured propulsion impeller, propeller boss cap fin (PBCF), and bottom impeller was proposed and experimentally investigated using particle image velocimetry (PIV). Significant findings: The installation of the PBCF onto the propulsion impeller led to an increase in the radial velocity component and shear rate, along with an enhancement in the flow circulation. Combining the bottom impeller with the propulsion impeller resulted in improved axial recirculation of the fluid. In all experiments involving the bottom impeller, the locations with the highest shear rate and maximum radial velocity components coincided, indicating the dominance of the radial velocity component in determining the shear rate. The mixing efficiency was found to be the highest for the propulsion impeller combined with the PBCF, followed by the propulsion impeller alone and the combination of all three impellers. The use of the bottom impeller alone yielded the lowest mixing efficiency. Additionally, the installation of the propulsion impeller improved the mixing efficiency while causing only a marginal increase in power consumption.