DEM study of the effect of contact electrification on the flowability of pharmaceutical fine powders

Abstract

Electrostatic charge generated through contact electrification plays a key role in determining the flowability of pharmaceutical fine powders. This study investigated these electrostatic effects using a discrete element method (DEM) simulation that integrates a dynamic charge transfer model and an electrostatic interaction model. The model was validated by comparing its predictions with literature data and FT4 experimental results for charge accumulation and flowability. Simulations revealed that charge transfer predominantly occurs at particle–wall contacts due to differences in work function, leading to a higher charge level on particles near the walls, which then transfer charges to other particles upon contact. Repulsive electrostatic forces were found to reduce particle cohesion, thereby improving flowability, whereas strong attractive image forces between particles and walls caused significant adhesion. The study also explored the effects of work function differences between particles and walls, as well as operating conditions in FT4 tests. Results indicated that the specific charge of particles exhibited a linear relationship with the particle–wall work function difference and the blade penetration depth, but a non-linear relationship with blade tip speed and helix angle. Finally, a universal relation was proposed to predict specific charge and electrostatic forces under various conditions, offering a straightforward method for optimizing powder handling processes.