Coupled CFD-DEM simulation of hydrodynamic bridging at constrictions

This paper presents a coupled CFD-DEM approach to simulate the flow of particulate suspensions in the intermediate concentration regime where solid volume concentration is 1% < phi < 50%. In particular, hydrodynamic multi-particle bridging during flow through a single constriction in a rectangular channel is studied. It is shown that for neutrally buoyant, monodispersed particulate suspensions, the probability of jamming increases with the particle concentration. There also exists a critical particle concentration (phi*) for spontaneous bridging, which depends on the ratio of pore size to particle size, the flow velocity, the particle-fluid density contrast, and the flow geometry leading to the constriction. The phi* has a strong dependence on the outlet-to-particle relative size (R-0). For 1.5 <= R-0 <= 2.5, a direct transition from a flowing state to a jammed state was observed. For R-0 <= 3, the flowing state typically transitioned to a dense state characterized by the accumulation of particles near the constriction before jamming. Increasing the inlet-to-particle relative size (R-ip) lowers phi* by increasing the number of particles arriving at the constriction simultaneously. The effect of changing R-ip is more pronounced at high R-0 when the probability of bridging is lower. A high fluid velocity increases particle interactions near the constriction and accelerates the onset of bridging. However, no distinct effect of velocity on phi* was observed in this study. A higher particle-to-fluid density ratio (rho(p)/rho(f)) increases the probability of bridging and leads to a lower phi* in a given constriction geometry. The effect saturates at higher rho(p)/rho(f) when gravitational forces completely dominate over viscous drag forces. phi* is also found to decrease with increasing angle of constriction convergence (theta) for theta < 30 degrees, but increases beyond that at theta = 60 degrees. (C) 2016 Elsevier Ltd. All rights reserved.