A new kinetic model for rapid granular flow

The fluid motion of an assemblage of cohesionless granules is governed by the balance laws of mass, momentum and energy and is special because due to the variability of the mean free path of the particles the density is not preserved and the particle fluctuation energy (= granular temperature) is determined together with the mean fields. Constitutive equations are postulated for the dispersive pressure, viscosity, thermal diffusivity and energy annihilation rate in terms of the mean free path length, the time of encounter between two collisions and geometric and dynamic quantities via dimensional arguments. The model defines the time of encounter to consist of the free flying time between collisions plus the contact duration. The inclusion of the latter brings in the elasticity of the particles and introduces a relaxation mechanism that explains the typical behaviour of shear and fluidized layers better than has been done by previous models.