Radial mixing and segregation of binary density ellipsoids in a rotating drum

Abstract

In this paper, the Discrete Element Method (DEM) is applied to investigate the radial mixing and segregation of a binary mixture of ellipsoids with different densities in a rotating drum. The ellipsoidal particles are constructed with multi-sphere model, and the periodic boundary condition is adopted. The influences of aspect ratio and density ratio on the mixing quality and final segregation extent are examined. Simulation results show that, light particles are inclined to occupy at the periphery of the granular bed, whereas heavy ones concentrate in the center area. As particle aspect ratio deviates from unity, i.e. oblate or prolate shape, the mixing index is increased and final segregation degree is decreased. It is discovered that convective mixing is predominant over diffusion for any given particle shape (oblate, spherical, prolate). The prolate particles (AR=4.0) reveal the highest compactness of a binary mixture system in the rotating drum. Particle translation is the main movement mode and ellipsoids are more easily to rotate. Particle shape affects collision probability and strength, and ellipsoidal particles need more energy to be driven. The reduction of density ratio of light to heavy particles does inevitably contribute to a greater segregation degree. The results also indicate that the initial states of binary mixtures do not affect the final segregation patterns.