Mechanistic Analysis and Computer Simulation of the Aerodynamic Dispersion of Loose Aggregates: Effect of Surface Energy

Abstract

Dispersion of bulk powders is important for a number of technological applications such as particle characterisation, and drug delivery through lungs using dry powder inhalers (DPIs). Over the last decade, the analysis of dynamics of particle‐fluid systems using the distinct element method (DEM), coupled with continuum models for the fluid phase, has received much attention. In this paper these computational techniques are used to investigate the aerodynamic dispersion of loose aggregates of cohesive powders in a uniform flow field. As intuitively expected, with an increase in particle surface energy, hence bond strength, it is progressively more difficult to disperse loose aggregates. However, once the relative particle‐fluid velocity goes beyond a threshold, dispersion occurs readily and approaches a completely dispersed state asymptotically. A mechanistic analysis, based on a balance between the external forces, including the fluid drag acting on a spherical aggregate and the bonding force given by the well‐established JKR model, leads to a dimensionless group which includes the Weber number. It is shown that the effect of surface energy on loose aggregate behaviour can be described by the above dimensionless group.