Axial segregation in spherical and cylindrical rotating tumblers

Umberto D’Ortona,Richard M Lueptow,Nathalie Thomas,F Radjai,J.Y Delenne,S Nezamabadi,S Luding

doi:10.1051/epjconf/201714003011

Abstract

Monodisperse and bidisperse granular flows are studied in rotating tumblers using DEM. In spherical tumblers, flowing particles’ trajectories do not follow straight lines but are curved. At the same time particles near the surface drift toward the pole, inducing two global recirculation cells. Combined with radial segregation, drift and curvature compete to impose the axial segregation pattern: Small-Large-Small (SLS) or Large-Small-Large (LSL). Fill level, rotation speed and wall roughness influence drift and curvature, and modify the resulting segregation pattern. In cylindrical tumblers, equivalent recirculation cells occur next to the end walls. A second pair of recirculation cells with a weak drift in the opposite direction appears at the center for long enough tumblers. Unlike the sphere case, curvature and drift in the primary cells combine to push large particles toward the end walls, explaining why large particle bands appear at the end walls for axial segregation in cylinder.

Highlights

Mixtures of particles of equal density but different size segregate radially in rotating tumblers in only a few rotations
The choice of the pattern depends on fill level, particles size ratio, sphere-particles size ratio, rotation speed [1], and the wall roughness of the spherical tumbler [2]
This study of granular flow in spherical and cylindrical tumblers has demonstrated two competing processes responsible for the axial segregation in rotating tumblers: the drift leading to recirculation cells and the curvature of particle trajectories

Summary

Introduction

Mixtures of particles of equal density but different size segregate radially in rotating tumblers in only a few rotations. An axial segregation made of successive bands of small and large particles usually appears. Bands of small and large particles emerge with a wavelength of about one tumbler diameter. Large particles always accumulate near the end walls of the tumbler rapidly forming the first bands of segregation. In between them, alternating bands of small and large particles may appear subsequently. These results have been obtained experimentally [1]. Diameter spheres with smooth or rough (interior covered by a monolayer of 2 mm glue particles) walls [2]

Spherical tumbler

Segregation pattern

Recirculation cells

Conclusions