Effect of filling degree on particle segregation in a rotating drum - an experimental and numerical study

Granular mixing, ubiquitous in industry, is difficult to observe. Ultrafast X-ray computed tomography is a relatively new technique that can be used to study rapid granular flows in opaque systems. A comparative study is here presented, where ultrafast X-ray computed tomography, camera and simulation with the Discrete Element Method are simultaneously used to investigate the radial segregation of 4-mm spherical polypropylene and glass beads in a rotating drum. The drum filling is varied from 20 to 50%. The granular flow and the associated segregation dynamics at the front-end wall and in the bulk are compared and good agreement among the three methods is found. Similar to unary systems, a transition from the rolling to the sliding regime, characterized by a critical dynamic angle of repose, is also reported.