Impact of Equipment Material and Surface Finish on the Flowability of dry Cohesive Powders – an Important Consideration in Calibration of Discrete Element Models

Abstract

Discrete Element Method (DEM) simulations of cohesive particles are of great importance in understanding powder flows in processing equipment. Calibration of the particle–particle or particle–wall interaction parameters is important, and although there are many studies on DEM simulations of cohesive powders, most of them do not differentiate between particle–particle cohesive and particle–wall adhesive forces. In this work, a bench-top experimental setup was designed to demonstrate the effect of particle–wall adhesive forces. A simulation-based sensitivity analysis was also performed using a commercial scale tablet press feeder (TPF) and hopper screw feeder (HSF), by independently varying the particle–particle and particle–wall cohesive energy density values to illustrate their effect on powder flowability. Both the feeders experienced blockages for highly cohesive particles whose cohesive energy density exceeds 80 kJ/m³ in case of TPF and 110 kJ/m³ for HSF. The occurrence of such blockages was eliminated by reducing the particle–wall adhesion to 30 kJ/m³ in case of TPF and 50 kJ/m³ for HSF while keeping the particle–particle cohesion at the same high value. Thus, this work demonstrates that the particle–particle cohesion and particle wall adhesion should be considered as separate entities and must be calibrated separately in DEM so that the materials interaction effects of both powder and equipment can be captured adequately.