Particle-shape induced radial segregation in rotating cylinders

Abstract

In this work we assess whether particle shape can induce radial segregation in a rotating cylinder. To this end, mixtures of spheres and non-spherical particles of equal-volume were modelled in a discrete element modelling framework. We could observe that particle-shape (alone) can induce radial segregation with the non-spherical particles accumulating in the centre of the cylinder. To probe the underlying segregation mechanism, a large number of particle trajectories and orientations were analysed. We observed that non-spherical particles, when segregating towards the centre of the bed, did not necessarily orientate themselves such that their projected area (in the sinking direction) was smaller than that of spheres. Instead, we found that there was a high probability that the avalanching, non-spherical particles are orientated such that their projected area in the direction perpendicular to the bed surface is maximal. Hence, particle-shape induced segregation cannot be explained by the conventional percolation mechanism. Instead, we propose that shape-induced segregation originates from the lower mobility of the non-spherical particles than spheres. We explain the lower mobility of non-spherical particles by their larger radius of gyration than equal-volume spheres, leading to an increased number of collisions and thus a higher rate of kinetic energy dissipation.