Mixing and segregation of granular materials in chute flows

Mixing of granular solids is invariably accompanied by segregation, however , the fundamentals of the process are not well understood. We analyze densi ty and size segregation in a chute flow of cohesionless spherical particles by means of computations and theory based on the transport equations for a mixture of nearly elastic particles. Computations for elastic particles (M onte Carlo simulations), nearly elastic particles, and inelastic, frictiona l particles (particle dynamics simulations) are carried out. General expres sions for the segregation fluxes due to pressure gradients and temperature gradients are derived. Simplified equations are obtained for the limiting c ases of low volume fractions (ideal gas limit) and equal sized particles. T heoretical predictions of equilibrium number density profiles are in good a greement with computations for mixtures of equal sized particles with diffe rent density for all solids volume fractions, and for mixtures of different sized particles at low volume fractions (nu < 0.2), when the particles are elastic or nearly elastic. In the case of inelastic, frictional particles the theory gives reasonable predictions if an appropriate effective granula r temperature is assumed. The relative importance of pressure diffusion and temperature diffusion for the cases considered is discussed. (C) 1999 Amer ican Institute of Physics. [S1054-1500(99)01603-1].