DEM analysis of the effect of particle shape, cohesion and strain rate on powder rheometry

Discrete Element Method (DEM) is used to simulate the flow of particles addressing the influence of shear strain rate, particle shape and cohesion on the flow characteristics. For this purpose, the dynamics of particle motion in the Freeman Technology FT4 rheometer is analysed. The simulations are first validated by comparison with experiments with cohesive particles, i.e. silanised glass beads, from the literature. Particles with faceted shapes, sharp corners and edges are then simulated and found to require significantly higher energy to flow compared to spherical particles. The presence of truncated vertices, typical of active pharmaceutical ingredients, influences the flow behaviour drastically. The results of this analysis therefore reveal the importance of considering the actual particle shape in DEM simulations when faceted particles are considered. Finally, a rheological model describing the relationship between the dimensionless shear stress and the inertial number for several particle shapes, cohesion values and blade tip speeds is proposed. The outcome of this study may lead to a unified rheological description of powder flow, which incorporates the effect of cohesion, shape and shear strain rate.