Intra-particle coating variability: Analysis and Monte-Carlo simulations

An analytical model is presented that describes the intra-particle coating variability of a single particle by a uniform spray. For uniformly random orientations, the film thickness coefficient of variation is proportional to the number of coating trials raised to the −1/2 power, and thus the coefficient of variation asymptotes to zero as the number of coating trials increases. However, if the particle has a preferred orientation while in the spray zone, the limiting value of the coefficient of variation is non-zero. Monte-Carlo simulations of a single particle subject to a coating spray are also presented and verify the theoretical model. Finally, analysis of discrete element method (DEM) computer simulations of spheres in a rotating, circular drum without baffles show that a sphere passing through the “spray zone” has an orientation corresponding to a preferred rotation from the sphere's orientation during its last past through the spray zone. Although the intra-particle coefficient of variation for orientations exhibiting this effect still asymptote to zero over time, the rate at which this occurs is smaller than that for uniformly random orientations.