The mixing of powder layers on a chute: The effect of particle size and shape

Superimposed layers of sand have been allowed to flow down a chute, and the amount of mixing occurring between the layers has been measured. Particle size and particle shape have both been varied in the layers. At constant particle size, the amount of mixing, assessed as an effective diffusion coefficient, decreases with decreasing sphericity. Reducing the particle size of the upper layer increases the mixing rate, and even at a size ratio as close as 0.65 it was possible to pass beyond the maximum degree of mixedness and into a zone of segregation of the smaller particles.