Analysis and modelling of bead contacts in wet-operating stirred media and planetary ball mills with CFD-DEM simulations

Wet fine grinding is an important unit process in various industries. In the present work two different stirred media mills (one with a cylindrical stirrer; one with a disc stirrer) and a planetary ball mill are investigated using coupled CFD (computational fluid dynamics) and DEM (discrete element method) simulations. While the DEM takes the grinding media into account, the CFD is used for the calculation of the fluid flow. With these coupled simulations the grinding media movement and the resulting contacts per time unit as well as their kinetic energy at the start of the contact can be tracked. In a first step these values are compared to an analytical model that was originally developed for wet operating stirred media mills. To compare different types of mills the type of contact along the stress energy spectrum, which is based on the kinetic energy of the grinding media, is important. Therefore, in the present work an extended contact analysis was developed that enables the description of normal impact and torsion, shearing and rolling induced by rotational and translational velocities. The extended analysis enables the complete characterisation of the energy spectrum for different mill types and operating conditions.