Particle shape-induced radial segregation of binary mixtures in a rotating drum

Rotating drums are widely used in various processes such as mixing, coating and drying, where particle segregation remains one of the major concerns. In the past, most of the studies focus on the size or density induced segregation with the assumption that particles are spherical. The particle shape-induced segregation is still not well addressed and understood. In this work, DEM is used to study the radial segregation of binary mixtures of ellipsoidal particles in a rotating drum. The results show that for the binary mixture of ellipsoids (aspect ratio AR = 0.5 or AR = 2.0) and spheres, ellipsoids tend to distribute in the core of the bed, while spherical particles are more likely to accumulate in the periphery. When particle shape difference in the mixture increases, inverse segregation occurs with ellipsoids in the periphery and spheres in the centre. This is attributed to the increased flowability of ellipsoids and the formation of large voids in the free surface flowing layer. Spheres can percolate through the large voids and be trapped in the core section. For the mixture of oblate (AR = 0.5) and prolate (AR = 2.0) spheroids, no segregation is observed. The effect of rotating speed on the degree of segregation is also examined, showing that with the rotating speed increasing from 5 to 40 rpm, the segregation degree reduces for all mixtures.