DEM-CFD simulation of particle comminution in jet-mill

Grinding systems are widely used in many industrial applications although they are operated at very low efficiency. A successful design of grinding/comminution systems has been the goal of many research groups. The spiral jet-mill is one of the most common comminution systems. In order to optimize the performance of the jet-mill, a 3D numerical model was developed to accurately predict the jet-mill's behavior. A discrete element model (DEM) was used to predict particle motion while subjected to fluid forces calculated by computational fluid dynamics (CFD). Discrete comminution functions were implemented into the DEM in order to simulate the fatigue and breakage of particles. Particle sizes decrease due to breakage in the simulation, just as in the actual process. The breakage forces acting on the particles are affected by both particle-particle and particle-wall interactions. As the forces increase, finer particles are formed and attraction forces, such as Van der Waals force (VdW) become dominant. The VdW forces cause the fine particles to agglomerate or stick (caking) to the jet-mill walls, eventually affecting the milling process. Since our aim is to understand the milling process in order to increase its efficiency, both breakage and attraction forces were considered. The effect of VdW forces on the milling process was investigated numerically, which cannot be done in an experimental unit, and the predictions of the numerical simulations with and without VdW force were compared with experimental data.