Computational fluid dynamics (CFD) has been successfully used for many years for simulations of stirred tanks. When the tank contains a multiphase mixture, a number of models are traditionally used. For example, the mixture model treats the multiphase system as a single fluid and tracks the local volume fraction and slip velocity between the phases. The Eulerian multiphase model uses separate sets of fluid equations for the phases and is popular for gas-liquid or liquid-liquid mixtures. A special granular form of this model, which takes into account the unique properties of a granular phase, such as viscosity and packing, is typically used for solid-liquid mixtures. Despite the special treatment used for the solids, however, the Eulerian granular model treats the solid phase as a continuum without regard to individual particle motions.

With recent increases in computational power and speed, the possibility of modeling thousands or even millions of individual particles in a multiphase system has now become a reality. The macroscopic particle model (MPM) in FLUENT has been developed for this purpose, and to date it has been used for applications ranging from hoppers to separators, in industries ranging from pharmaceutical to oil & gas. This novel approach for simulating granular mixtures has now been applied to a stirred tank. Using a dilute suspension, the results are compared with the Eulerian granular model both in terms of the solution predictions and computation time.