On axial segregation in a tumbler: an experimental and numerical study

Abstract

We report experimental and discrete element method (DEM) simulation results on sizesegregation of granular materials in a rotating drum. We first define the degree ofsegregation which allows us to quantify the time evolution of the formation of axialsegregation bands. We then focus on the interplay between axial and radial segregation. Inexperiments, surface particle velocities are measured by particle tracking. There is nosignificant jump in velocity or velocity gradient at the interface between small to largegrains in the radial direction. On the other hand, there is a large difference inflow velocity between large and small particles along the axial direction of thedrum, and strong gradients at interfaces between large and small particle bands.Measurements of the diffusion of a localized axial band of small grains show theformation of a radial core from an axial band. This process is not sub-diffusive (norsuper-diffusive) in our simulation. The time evolution of the axial segregation patternis strongly affected by radial segregation. Coarsening and oscillatory motion ofaxial bands involve flows of small particles through the radial core, in particularwhen the band position or width oscillates. Coarsening of the axial segregationpattern is significantly retarded or eliminated in the absence of a radial core.