Mixed solids distribution in stirred vessels: Experiments and computational fluid dynamics simulations

The distribution of dilute, mixed solids in Newtonian fluids in a baffled vessel stirred with multiple impellers has been studied experimentally and simulated by means of Computational Fluid Dynamics. For the sake of experimental simplicity, fractions of two solids of different density and equal size have been used. The experimental part, which was primarily meant to provide data for the validation of the simulation procedure, showed that the two phases act independently and that simple distribution superposition holds true. The computational approach is an extension of that already used for the calculation of monodisperse particle distribution in stirred vessels and is based on the solution of sets of RANS equations, one for each of the phases involved in the process coupled with the ‘homogenous’ k- model for closure. The Sliding Grid method is selected for the simulation of the baffled vessel. As in the case of a single solid fraction, the momentum transfer between each solid phase and the liquid is modelled only through the drag force – with the influence of turbulence being accounted for. As shown by comparison with experimental data, the simulation results are very realistic predictions of the solids distribution along the vessel vertical coordinate.