Flow Patterns of Granular Materials in Flat-Bottom Bins

Bins with flat bottoms and multiple openings are commonly used in industry to store granular solids because of their lower cost and because they occupy smaller vertical space than bins with a singular hopper outlet. However, in many flat-bottom bins the live capacity is much smaller than the bin volume because the spacing of openings does not permit the flow patterns above the openings to intersect. A theory has been developed to predict the boundary of the flow patterns that occur in these bins when circular openings are used, and experimental results in a small-scale bin have been found to agree closely with the theory. Boundaries of flow patterns are a function of the effective angle of friction of the material, the diameter of the opening, and the head of material in the bin. In general, the flow patterns expand outward from the edge of the opening, and become almost vertical near the top of the bin. Results of this study make it possible to determine which materials can be satisfactorily stored and which opening designs must be used to achieve adequate live-storage capacity in flat-bottom bins.