(122d) Granular Flow through an Orifice – Effect of Granule Size and Shape Distributions

This paper investigates jamming probabilities of vertical granular flow through an orifice, specifically the effects of granule size distribution, granule shape and the normal stress above the orifice. The jamming probability can be taken as a measure of differentiation between relatively free-flowing granules.

While shear cell systems are regarded as the most quantitative test measures of incipient flow of bulk cohesive powders and granules, these methods are relatively insensitive to differences in very free flowing materials. According to the continuum model, a ?cohesionless? material measured using a shear cell (i.e., a yield locus passing through the origin) implies flow through a hopper cone opening of infinitesimal diameter; at this limit, the continuum model fails because the orifice must be at least as large as the particle diameter. Further, local packing and jamming effects require that the opening be significantly larger than a single particle. A theoretical analysis of intrinsic cohesion suggests a boundary layer effect of 3-5 particle diameters. The current work presents experimental results on the effect of granule size distribution, and granule shape on jamming probability in 3-D flows.