Dynamics of wet particles in rotating drums: Effect of liquid surface tension

Abstract

A numerical model based on the discrete element method was developed to simulate the wet particle flow in a rotating drum. The model explicitly considered the capillary force between particles and liquid distribution within the packed bed. Physical experiments under similar conditions were carried out to validate the model, showing that the simulation and experiment results were quite comparable in terms of the flow patterns, maximum flow repose angle, and the frequency of avalanching. Flow properties in two different states were investigated with the focus on the effect of liquid surface tension. In the quasistatic state with the drum rotating at very low speeds, discrete avalanches were observed after the flow reached the maximum repose angle. However, flow properties had changed well before avalanches occurred. The microscopic analysis indicated that the strength caused by the capillary force reached a minimal when avalanches started. The maximum repose angle increased with increasing capillary force and their relationship was compared with the theoretical models based on the Mohr–Coulomb criterion and force balance. In the dynamic state, the bed showed continuous surface flow at weak surface tensions but transited into discrete avalanches characterized by the plough flow as the surface tension further increased. The flow became more dilated at high surface tensions with increased particle contacts and more uniform stress distribution. The energy and frequency of collisions between particles also decreased as the liquid surface tension increased and more collisions were observed in the region 4–5 particle diameters below the flow surface. The results would be useful to the development of a comprehensive understanding of the mechanisms of particle mixing and segregation.