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

• Experimental velocity fields were used to evaluate the computational model.
• Flow properties are described for different blade angles of axial flow impellers.
• Segregated regions arise at the boundary of the discharge flow.
• The shape of the active zone varies as the viscous forces change.

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 327 rpm to 684 rpm, and yield stresses and viscosity levels provided by three carbopol solutions (0.075, 0.09 and 0.1 w/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.