G. Calvert

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

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...

A mechanistic analysis of bulk powder caking

Bulk powder transformations, such as caking, can lead to numerous problems within industry when storing or processing materials. In this paper a new Environmental Caking Rig (ECR) is introduced and has been used to evaluate the caking propensity of a hygroscopic powder as a function of temperature, Relative Humidity (RH), mechanical stress and also when RH is cycled. A linear relationship exists between cake strength and the extent of bulk deformation, here defined by the engineering strain. An empirical model has been used to predict the caking behaviour based on consolidation stress and environmental conditions.