Spatiotemporal Distribution of Granular Kinetic Energy in Rotating Tumblers with Axial Segregation

Axial bands of particles having different sizes often occur in long rotating tumblers. However, the mechanisms of the formation and evolution of the axial bands is not yet clear. Here, axial segregation of granular mixtures in a long tumbler is investigated through DEM (Discrete Element Method) simulations. We find that the spatiotemporal distribution of the granular kinetic energy in the tumbler is nonuniform as the axial segregation appears. Small particle bands have lower kinetic energy than large particle bands. Furthermore, the time-averaged kinetic energy of all particles increases as the number of bands increases. This suggests that more mixed particles at the interfaces between bands result in a lower overall kinetic energy of particles. Thus, it appears that the kinetic energy related to the purity of the bands and interfaces plays a role in the formation and evolution (coarsening) of the axial bands in long tumblers.