Coarse grain model for DEM simulation of dense and dynamic particle flow with liquid bridge forces

In many powder handling processes, liquid is added and dispersed into bulk dry powder. To study these systems, simulations of wet particles with small amounts of liquid are often performed by incorporating liquid bridge forces consisting of capillary and viscous forces into Discrete Element Method (DEM) (Sakai and Koshizuka, 2009). One of the existing challenges in DEM is the high computational cost to perform industrial scale simulations with large number of particles. One of the strategies often employed to reduce computational cost is by scaling up particle size, also known as the coarse grain method, which have been applied in several studies for dry cohesionless or dry cohesive particles. In the present work, the “direct force scaling” coarse grain model (Sakai and Koshizuka, 2009; Sakai et al., 2012) is applied for a dense and dynamic system of wet particles with liquid bridge forces. A general scaling criteria is proposed for different types of DEM related forces based on force balances on a control volume: l3 scaling for body forces and l2 scaling for interaction forces, where l is the scaling factor of the coarse grain particle. The coarse grain model is validated for wet particles in a vertical mixer in terms of the bulk flow and mixing behaviour. It is shown that the coarse grain model with l2 scaling of the liquid bridge forces can accurately predict the flow and mixing behaviour of the original wet particles.