Kinematics of the flow of dry powders and bulk solids

摘要: Although qualitative pictures of the flow pattern in moving powders and bulk solids have been published, there is no quantitative evidence on velocity profiles. This was needed developing an energy theorem determining rates (Brown, Nature, 1961, 191, 458–461) experiments described here were undertaken to test various suppositions made at that time. It shown assumptions correct. The gravity dry through apertures cannot begin until powder has dilated. friction caused by motion then determines pattern. In this paper only those materials freely under are considered. such cohesive forces between grains inappreciable. results expected apply all do not contain large quantities finely-divided range sizes below 20 30 microns, closely graded with particles larger than about 100 microns. cases it assumed moisture content equilibrium ambient air. Measurements voidage a single layer ballbearings flowing down inclined plate show dilatant waves pass upward bed. Below aperture emergent stream forms vena contracta. At statistically empty space adjacent edges, which few balls pass. existence free-fall arch demonstrated, fall gravity. By fixing system wax just above radial, converging apex aperture, region bounded surfaces sliding separate from non-flowing material. observing transparent end face, angle vertical (β degrees) surface measured for (a) central slot (βc o), (b) edge wall (βE o). A different method used determine inclination circular (β3 o). found β3 o < βc o ⩽ βE o. steeper drained repose conical heap.