Dispersion of Rock- and Coal-Dust in Stratified Dust Layers*

Numerical simulations of a shock wave passing over layered rock and coal investigated whether and how the presence of rock effects the entrainment of coal in an explosion. We use a multifluid granular flow model based on the Kinetic Theory for Granular Flow (KTGF) and account for multiple particle types with a binning approach. More specifically, we consider the dispersal of coal and rock dust under the action of a Mach 1.4 shock wave.  The rock and coal particles have a density of 2680 kg/m³ and 1330 kg/m³, and a diameter of 15 μm and 30 μm, respectively.  When a thin layer of rock dust is initially placed on top of a thicker layer of coal particles, entrainment of the coal dust behind the shock wave is suppressed. Increasing the thickness of the rock dust shows that only the top 2-3 mm of the rock is entrained, and particles in the bottom layer remain stationary or become slightly compacted. We also performed simulations in which coal dust was initially placed on top of the rock dust. This configuration does not suppress entrainment of the coal particles, and particles in the dispersed region are primarily coal particles. The results are explained on the basis of the forces on the particles.