Powder flowability and density ratios: the impact of granules packing

The propensity of powders to ow under given circumstances (flowability) affects a large number of industrial applications. A single, reliable and widely applicable flowability test does not exist, because of the variety of both granular materials and in uence of handling on the measurements results. Here we critically examined the results provided by Hausner’s method, based on apparent densities ratio, with several granular materials. Major limitations appeared to be the achievement and measurement of a dense packing condition, provided by the tapped density in the Hausner’s ratio. After a detailed discussion of standard and modified techniques to measure bulk density, we eventually suggest a new flowability criterion based on a novel technique to determine a high packing density. The proposed criterion is more sensitive to differences in owability, as quantified by the repose angle. In order to investigate also the domain of cohesive powders, we developed a novel procedure to measure the repose angle of such powders. Eventually, the new criterion was able to account consistently for free-flowing and cohesive powders. It also stimulates the discussion on subtle issues involved in the determination and use of elementary powder’s properties.