Computational simulation of mixing flow of shear thinning non-Newtonian fluids with various impellers in a stirred tank

Abstract

The main features of the flow generated by three axial flow impellers installed on the side of cylindrical tanks filled with pseudoplastic solutions exhibiting yield stress were exposed using computational fluid dynamics (CFD). The numerical results were evaluated using velocity vector maps obtained from particle image velocimetry (PIV) experiments. The models were able to predict macroscale flow structures and global mixing parameters under different operating conditions. However, limitations of the model to predict the symmetric flow observed during the experiments were identified at high rotational speeds. The operating conditions included angular speeds from 327rpm to 684rpm, and yield stresses and viscosity levels provided by three carbopol solutions (0.075, 0.09 and 0.1w/w%). These conditions create mainly laminar flow inside the mixing domain. The results indicated that the operating conditions and the blade angle establish the structure of the impeller discharge, which in turn defines the shear rate distribution, some physical cavern properties, and the formation of segregated regions.