Numerical simulation and analysis of mixing of polygonal particles in 2D rotating drums by SIPHPM method

- Effects of shape on mixing of noncircular polygonal particles are simulated by SIPHPM.
- Mixing index and entropy indicates that square, hexagon and triangle are best for mixing.
- Two mechanisms of static packing & dynamical reduction in concentration are explained.
- Area fraction of flowing layer indicates that triangle and square have movability thresholds.
- Less round particle (triangle and square) has larger dissipations in kinetic energy.

To study the non-circular effect, the mixing of polygonal particles in a rotating drum is simulated by the soft-sphere imbedded pseudo-hard-particle model (SIPHPM method). Eight particle shapes (Ns = 3-10) are filled in the drum at rotating speeds (ω = 0.5-3 π/s) respectively. The mixing process, quality, velocity and kinetic energy are analyzed by the mixing index and entropy. A cluster-like upcasting motion is found especially for square particles at the rapidest rotation. The mixing index and entropy show consistent variations of mixing degree. Two mechanisms can affect the mixing entropy, through either the static covering related to shapes or the concentration reduction in rolling/cascading/cataracting process related to the rolling capability. Only the first mechanism affects the mixing index. They are both used to explain the effects of particle shape on mixing from the points of view of overall dispersion uniformity and local concentration. The mixing index indicates higher mixing degree for the square, hexagonal and triangular shapes. Except the triangular and square shapes, other shapes play similar characteristics in the area fractions of the flowing core and static base, as well as the radial distributions of the mean and fluctuation velocities. Under the same rotating speed, the particle kinetic energy increases with Ns, which is caused by the reduction of energy dissipation with a better roundness of particle shapes.

Graphical Abstract421