Segregation of granular materials in rotating cylinders

Mixtures of flowing granular materials containing particles of different sizes or different densities have a tendency to segregate. We focus here on the segregation that occurs in the cross-section of the cylinder using short cylinders (axial length is much smaller than the diameter) ensuring small variation along the cylinder axis. The typical structure formed in these systems is a radial core of the smaller or more dense particles. Coupling of composition with flow can lead to instability causing a pattern of radial streaks. The predictions of hard sphere mixture theories are briefly discussed first. Results of experimental and modelling studies of segregation are reviewed for density-induced radial segregation of equal sized particles, and size-induced radial streak formation. Experimental results for size-induced radial segregation are presented. (C) 2002 Published by Elsevier Science B.V.