A mixing study in a double-Rushton stirred tank

Computational and experimental methods have been used to investigate the flow field, power and mixing time in a fully baffled stirred vessel with two six-blade Rushton turbines. Flow in a stirred tank involves interactions between flow around rotating impeller blades and stationary baffles. In computational fluid dynamics (CFD), the flow field was developed using the sliding mesh (SM) approach. The large eddy simulation (LES) was used to model the turbulence. For validation of simulation results two series of experiments were performed: (i) velocity measurements of the liquid phase using particle image velocimetry (PIV) and (ii) concentration measurements of the determining tracer in the liquid phase using the planar laser-induced fluorescence (PLIF) technique. In each series three different rotational speeds of impellers: 225, 300 and 400 rpm were employed. The stirring power input was also calculated based on the PIV results. A considerable reduction in mixing time was achieved and stirring power input was increased by increasing the impeller speed. The satisfactory comparisons indicate the potential usefulness of this CFD approach as a computational tool for designing stirred reactors.