DEM modelling and analysis of the mixing characteristics of sphere-cylinder granular mixture in a rotating drum

Mixing structures and characteristics are crucial to the mixing quality of spherical/cylindrical binary granular systems like the biomass-coal mixtures which can affect energy release and carbon emissions. In this work, the mixing of binary spheres/cylinders in a rotating drum was numerically reproduced by using discrete element method (DEM). Systematic parametric studies were conducted to identify the role of various parameters such as rotation speed (w) of the drum, aspect ratio (AR), mass fraction (wc) and volume fraction (wv) of cylindrical particles, and the density difference (w rho) between the binary particles; meanwhile, corresponding mechanisms were also explored by analyzing the kinetic energy. Results show that when the flow regime is rolling/cascading, the mixing quality can be effectively improved; however, when the flow regime is cataracting, the mixing quality becomes worse. With AR close to 1.0, the interlocking effect between particles becomes weaker and the porosity becomes smaller, which leads to the higher contact efficiency and thus improves the mixing quality. Binary mixtures with different wc are synergistically affected by energy input and interlocking structure. The volume of spherical particles is more conducive to improving the mixing quality than that of cylindrical particles when the volume of the granular system is at the same level. The w rho can cause segregation behavior of particles so as to make the mixing quality worse.

Automated summary

The mixing of binary spheres/cylinders in a rotating drum was numerically simulated using the discrete element method (DEM). The effects of various parameters on the mixing quality were studied, and the corresponding mechanisms were analyzed. Results showed that the mixing quality can be effectively improved under rolling/cascading flow regime, but becomes worse under cataracting flow regime. A higher aspect ratio leads to a weaker interlocking effect between particles, smaller porosity, and higher contact efficiency, thus improving the mixing quality. Spherical particles are more conducive to improving the mixing quality compared to cylindrical particles with the same volume.