Numerical Investigations on the Flow Behaviors, Characteristics, and Mechanisms for Different Platonic Solids during Mixing in a Rotating Drum

Rotating drums have wide applications in engineering, but the mixing and flow behaviors of complex shaped particles in drums have not yet been fully understood. This work presents a systematic numerical study on the mixing characteristics and flow behaviors of five Platonic solids (tetrahedra, cubes, octahedra, dodecahedra, icosahedra) in the rotating drum using the discrete element method. The effects of rotation speed and shape of Platonic solids on the mixing characteristics (mixing pattern and rate), macroscopic properties (packing density and granular temperature), and microscopic properties (coordination number, radial distribution function, orientation, and forces) were investigated. Corresponding mechanisms have been also explored by analyzing the circulation time, radial distance, and kinetic energy. The results show that the mixing rate decreases to the minimum (for cubes) and then rises with the increase of the face number of Platonic solids. The larger is the sphericity of the Platonic solids, the higher is the average packing density at all rotation speeds. Microscopic analyses indicate that more face-face or quasi-face-face contacts are formed in the Platonic solids with large sphericity, which facilitates the force transmission. The power draw of cubes the smallest at different rotation speeds, and cubic particles have the largest radial displacements and kinetic energy in the drum, which is due to the fact that the interlocking effect of the cubes is not obvious, resulting in freer movement and stronger diffusive mixing in the drum.