(379e) Granular Flow through An Orifice – Effect of Granule Size and Shape Distributions

Authors: 
Geiger, D. - Presenter, Procter & Gamble Company
Wandstrat, M. - Presenter, Procter & Gamble Company


This paper investigates jamming probabilities of vertical granular flow through an orifice, specifically the effects of granule size and shape distributions on jamming at 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, these methods are relatively insensitive to differences in very free flowing materials [1]. 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 [2]. A theoretical analysis of intrinsic cohesion suggests a boundary layer effect of 3-5 particle diameters [3]. Experimental work has investigated jamming probabilities in a 2-D hopper with monosized discs [4]. The current work presents experimental results on the effect of granule size distribution, and granule shape on jamming probability in 3-D flows.

[1] de Jong, J.A.H., Hoffmann, A.C. and Finkers, H.J., Properly determine powder flowability to maximize plant output, Chemical Engineering Progress, 95, No. 4, 25-34, (1999). [2] Birks, A. H., Bradley, M.S.A. and Rarnish, R., The conversion of the analytical simple shear model for the Jenike failure locus into principle stress space and implication of the model for hopper design, in Handbook of Conveying and Handling of Particulate Solids, A. Levy, H. Kalman, Eds., Elsevier Science, 95-105, (2001). [3] Weir, G. J., The intrinsic cohesion of granular materials, Powder Technology, 104, 29-36, (1999). [4] K. Lo, P-K Lai, H.K. Pak, Jamming of Granular Flow in a Two-Dimensional Hopper, Phys. Rev. Lett., 86, 71-4, (2001).

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