Discrete element method study of the impact of vessel wall friction on the mixing dynamics of a resonant acoustic mixer

Resonant acoustic mixing (RAM) has shown promise processing materials within the pharmaceutical and energetics industries. One of RAM’s strengths is the freedom to attach a wide variety of mixing vessels to the vibrating plate to induce mixing. This flexibility introduces the vessel material properties as a tuneable parameter for optimising mixing performance within RAM. In addition to material changes, understanding the impact of vessel wear, polishing, or adding a liner to the RAM vessel is key to ensuring optimal RAM operation. Assessing the impact of vessel material changes on RAM performance therefore requires insight into how container frictional properties influence mixing behaviour and internal flow patterns. The effect of particle-wall sliding friction on mixing performance was analysed using the discrete element method (DEM), for powder fill levels ranging from 10% to 90% and RAM operating accelerations between 20 and 100 times the acceleration due to gravity. Wall friction was found to significantly impact RAM’s performance. Transverse mixing performance was consistently poorer than the vertical and radial mixing performance, highlighting the sensitivity of RAM to the initial loading configuration. Furthermore, the frictional properties of the RAM vessel for optimal transverse mixing differed from those that optimised radial and vertical mixing performance.