Effects of rotation axis on mixing behavior of dissimilar particles in rotating drums

Particle segregation is a common phenomenon observed in rotating drums. This study found that the mixing of dissimilar particles in a rotating drum depended on the orientation of the rotation axis. When the rotation axis of the drum was selected to be perpendicular to the drum's own axis, two species of particles of different sizes mixed together. Numerical simulation study revealed that four counter convection flows formed in the drum. The movements of the small and large particles were similar in the cores of the convection zones but different in the vicinity of the free surface. The convection flows carried particles from the inner cores to the free surface. The difference in velocities between small and large particles in the vicinity of the free surface caused the particles to mix together. The finding of this study provides an alternative approach for the design of devices for mixing dissimilar particles.