An extension of the particle-based approach to simulating the sedimentation of polydisperse suspensions

We extend the particle-based approach to settling of polydisperse suspensions in which particles of at least one species move upward during all or part of the sedimentation process. The velocity of each downward-moving particle is governed by the solids concentration immediately below it; the velocity of each upward-moving particle by that immediately above it. This ensures that each particle remains in the rate-determining region in a small time-step. The robustness of the method is demonstrated by applying it to simulations in which the particles are initially distributed randomly. Despite the fluctuations that characterize these simulations, the essential features of the solids profile are maintained. The method was successfully applied to four hypothetical tridisperse suspensions. Simulations of two experiments produced settling curves that agreed closely with experimental values.