Kinetics of mass transport in sheared particulate beds: Markov chains

Abstract

Mixing of cohesionless particulate solids is typically accompanied by various degrees of segregation. General conditions, which would result in asymmetric particle mobilities in dynamic multiparticulate systems, have been formulated and are postulated to be necessary and sufficient to produce segregation. This study examines the size segregation of binary mixtures of noncohesive spherical particles subjected to shear in a rotary cell. Particle migrations in the axial and radial directions were analyzed in terms of a stochastic model based on finite, time and space discrete, nonstationary Markov chains. Results were consistent with the proposed hypothesis and suggest that size segregation can arise from gradients in shear strain rate, simultaneously and independently from that induced by gravity. Segregation from both sources was found to be dependent principally on total shear strain, to a lesser extent on rate of shear, and to a negligible extent on pressure normal to the direction of a shear. These observations indicate that the micromechanics of particulate movements are insensitive to changes in conditions over the ranges investigated.