A mechanism for particle size segregation in three dimensions

Abstract

THE segregation of particles with different properties is important is many areas of science and technology, including materials science, engineering, agriculture and geophysics. In many segrega-tion processes the most important property of the particles is their size. Processes such as pouring, shaking, vibration, shear and fluidization lead to size segregation; in some cases it is found to occur even in processes developed for particle mixingM¹. Because of its practical importance, particle segregation has been studied extensively during the past few decades², and several two-dimensional models have been developed recently^3–6. Here we describe results obtained from a simple three-dimensional simula-tion in which spheres are added, one at a time, to a growing heap on an infinite planar surface or within a cylinder of finite radius. In this model, size segregation is a consequence of the ability of large spheres to roll over a random packing of smaller spheres. Our results show that the degree of segregation is sensitive to both the size ratio and the number ratio for the case of a binary mixture of spheres.