Viscoplastic fluid mixing in a rotating tank

The laminar 2D mixing of viscoplastic fluids with an anchor impeller in a stirring tank is studied numerically. The flow structures, and particularly the static and moving rigid zones induced by the plasticity such as the presence of vortices, are examined in detail. Calculations are made for a wide range of yield and inertia values. It is shown that the application of a small yield stress can eliminate vortices. On the other hand, the increase in rotation velocity, i.e. the inertia, is not generally sufficient to reduce the size of the rigid zones. Power consumption is calculated and the mixing quality is determined by particle tracking. The calculations are made for different types of impeller configurations and an optimum configuration is proposed.