Mixing characteristics and flow behaviors of different shaped tetrahedra in a rotary drum: A numerical study

Mixing of granular matter with irregular shapes is complicated and essential in many key industrial areas. In this case, the mixing process and flow behaviors of different shaped tetrahedra in a rotating drum with a filling level of 40.5% were numerically reproduced by using discrete element method (DEM). The effects of rotation speed and particle shape parameters (height ratio eta and eccentricity xi) on the mixing process, macroscopic charac-teristics (packing density, free surface profile, granular temperature), microscopic characteristics (coordination number, radial distribution function, contact force, total force), and transfer/dissipation of energy (total kinetic energy and power draw) were systematically investigated; meanwhile, corresponding mechanisms have been explored by analyzing the circulation time. The results show that the mixing rate increases with the sphericity when the flow regime is cascading; however, when the flow pattern is rolling or cataracting, the mixing rate decreases with the sphericity. The variations of macro-/microscopic flow properties and energy transfer/ dissipation of tetrahedra change with the rotation speed and shape parameters. The mechanism affecting the flow behavior of different-shaped tetrahedra lies in the fact that the larger circulation time allows more slippages to occur in the granular system, which enhances the convective mixing of tetrahedra in one circulation, thus increasing the mixing rate.