Numerical and experimental investigations of the flow of powder into a confined space

In this paper, the flow behaviour of a powder as it is delivered into a confined space from a moving shoe is investigated. An experimental system has been developed to model the filling process. Two-dimensional discrete element models (DEMs) have also been constructed to simulate the flow process. Through a combination of experimental and numerical studies, qualitative and quantitative results are obtained, which provide new insights into the complicated filling process. DEM and experimental results have demonstrated that the flowability of powders can be characterised by a novel concept-the critical velocity. The flowability of powders with different shaped particles is assessed in terms of its influence on the critical velocity. It is shown that two groups of particle shapes can be distinguished. The first group consists of particle shapes that can tessellate, so that in principle they could completely fill the die (such as monosized rectangular and hexagonal particles). The second group includes those particle shapes that cannot tessellate. It is found that the former generally has a lower flowability than the latter. The powder behaviour during the filling of a stepped die is also analysed. Two major features have been observed: the formation of a forward concave shrink zone and a merge surface, where two different flow regimes meet, which are both filled with a low intensity. A low packing density is likely to be found in these two regions. A more chaotic filling process is induced by the presence of air. The built-up of air pressure can significantly slow down the filling process. Comparison of experimental and simulation results indicates that DEM simulations can capture the major features observed during the flow of powder into a confined space. (C) 2005 Elsevier Ltd. All rights reserved.