Percolation of a cohesive fine particle in a static bed

Percolation of fine particles (fines) in a static bed of larger particles is central to many industrial and natural processes. Fines either pass freely through the bed or become trapped depending on multiple factors including the particle sizes, friction and restitution coefficients, polydispersity, and cohesion. We use the discrete element method to simulate percolation of individual, non-interacting fine particles under gravity through a static bed of randomly packed large particles. A large-to-small particle diameter ratio of 7 geometrically permits fines to pass the narrowest pore throats formed by the large particles. However, sufficiently large cohesion and friction lead to non-geometric trapping. The coupled effects of cohesion, restitution coefficient, and impact velocity determine if a fine bounces or not following a collision with a bed particle. Fines are trapped when they fail to rebound after a collision due to large cohesion or low restitution and any subsequent rolling or sliding is insufficient to cause detachment. For non-rebounding collisions, frictional effects are enhanced by cohesion and, when large enough, prevent the fine from subsequently detaching.