Tribocharging of bidisperse particles in fluidized beds

Tribocharging refers to the phenomenon that materials pick up static charges upon contact with other materials [1]. In fluidized beds, granular particles undergo tribocharging due to repeated particle-wall and particle-particle collisions, resulting in complex charge distributions. Particle size distribution brings in additional complexities [2-4]. In this study, we seek to investigate the effect of particle size distribution on tribocharging in fluidized beds by using a bidisperse system as a model problem.

The system is simulated using Computational Fluid Dynamics coupled with Discrete Element Method (CFD-DEM) where the tribocharging model is coupled with hydrodynamics [5]. The rate of charge transfer between two surfaces that come into contact depends on the effective work function difference between the surfaces and the local electric field [6]. We first assign different combinations of effective work functions to the two particle sizes and vary their size and volume ratio. The relation between these factors and the resultant charge distribution is examined.

We then simulate the system by assigning the same effective work function to both particle sizes. When the effective work function of the wall is different from that of the particles, a counter-intuitive bipolar charge distribution is found to develop. The source of opposite charges in the system is investigated based on the macroscopic electric field and particle-particle and particle-wall collisions.