SIMPLE-MODELS FOR 2 AND 3-DIMENSIONAL PARTICLE-SIZE SEGREGATION

The segregation of binary particle mixtures has been investigated using simple two and three dimensional models in which particles are deposited one at a time with the same lateral position on a growing heap of particles. After deposition the particles follow a path of steepest descent on the heap until they reach a local minimum, contact the substrate or reach the walls of a containing vessel. For large values of the diameter ratio, r(r = d(t)/d(s) where d(s) is the small particle diameter and d is the large particle diameter) the width of the large particle depletion region near the center of the heap is directly proportional to the area ratio-phi (phi = dx2Nx/d2NL where Nx and N are the number of small and large particles respectively) for two dimensional heaps. A qualitatively similar structure has been found for the deposition of a binary mixture of spheres into a vertical cylinder but we have not been able to carry out large enough simulations to measure the dependence of the core depletion width on r and phi. Other measures of the degree of segregation do show that the degree of segregation increases with increasing r and phi for three dimensional cases. For example, the three dimensional simulations indicate that (R1(2)BAR)1/2-(R5(7)BAR) approximately r(2) phi(1/2) where R is the distance from the cylinder axis.