An experimental study of the aerodynamic dispersion of loose aggregates in an accelerating flow

Abstract

The dispersion of powders in gas flows is relevant in some powder processing techniques, in dry powder inhalers and in particle size analysers, among others. When using small particle sizes, the powder tends to form stronger aggregates and the dispersion becomes more difficult. There are many approaches to the dispersion process but most include collisions as one of the possible agglomerate break-up mechanisms. This is not always a satisfactory solution as particles may get contaminated or reduced. In the present work we explore the dispersion of powder aggregates in an accelerating flow with no particle-wall collisions. We built a fluid-dynamic device with a simple geometry consisting of a sharp slit, producing a rapidly converging flow at the entrance and a planar jet at the exit. A powder feeder exited with an ultrasonic actuator was used to generate single powder aggregates. The stationary flow field was calculated numerically and the velocity and degree of aggregate dispersion were assessed based on imaging results. In all the cases tested, erosion of the aggregates could be observed. In the case with the highest suction pressure, a different mechanism arises, which leads to the disintegration of the aggregate and a significantly better dispersion of the powder.