Exploring the mechanism of inter-particle charge diffusion

Abstract

Dispersed solid particles in wall-bounded flows may get electrified during particle-wall collisions due to triboelectric effects. Subsequently, the electrostatic charge migrates from the near-wall regions to the bulk of the flow through the dynamics of the particles (particle-bound charge transport) and charge transfer during collisions between particles (inter-particle charge diffusion). In this paper, we explore the physics underlying the mechanism of inter-particle charge diffusion, which remains not well understood, by means of numerical simulations. We investigated the efficiency of the charge transport within the particulate phase via this mechanism and propose a time-scale for its characterization for particular systems. The considered parameters of these systems included the particle number density and charge as well as their mechanical and electrical properties. It was found that both an increase of the material density of the particles or of their number density results in an enhanced inter-particle charge diffusion and, thus, a reduction of its time scale. Moreover, if only the number density is high but the material density is kept low, then inter-particle charge diffusion may even become the dominant wall-normal charge transport mechanism. Further, in case some particles carry a high charge they are accelerated towards uncharged particles through electrostatic forces which leads to an efficient charge redistribution.