Coarse-grained discrete element method of particle behavior and heat transfer in a rotary kiln

• Coarse-grained model of a discrete element method (DEM) was studied. • Modified Coarse-grained method for a Granular Shear Flow (M−CGSF) was developed. • The scaling laws for the rolling friction and heat transfer were derived. • M−CGSF was applied to a coarse-grained DEM simulation of a rotary kiln. • The simulations with M−CGSF showed the very similar results to the original case. Recent improvements in computational capabilities have made numerical simulation of the particle behavior and heat transfer in a rotary kiln reactor possible via the discrete element method (DEM). However, even with current computational capabilities, it is still difficult to simulate particle behavior and heat transfer in a rotary kiln reactor on the manufacturing scale because an enormous number of particles would be required. To address this issue, here, we propose for the first time a coarse-graining method for the Hertz–Mindlin contact force, the rolling friction, and conductive heat transfer between particles called the modified coarse-grained method for granular shear flow (M-CGSF). In M-CGSF, the scaling laws and governing equations for motion and conductive heat transfer of coarse-grained particles were derived according to matching centroid motions, elastic and rotational energy, and the overall heat transfer rate between the cluster of original particles and coarse-grained particles. Verification tests showed that coarse-graining of the particle dynamics, particle mixing, and particle heating behaviors in a rotary kiln were successfully performed by applying M-CGSF, demonstrating the effectiveness of M-CGSF for coarse-grained DEM simulations with conductive heat transfer in a rotary kiln reactor.