Numerical Modeling of Triboelectric Charging of Granular Materials in Vibrated Beds

The triboelectric charging of granular materials is a complex physical phenomenon, the outcome of which is difficult to predict. The aim of this paper is to validate a numerical model of the tribocharging process taking place in vertically-vibrated beds of granular plastics. The granular dynamics is modeled with the Distinct Element Method that is commonly employed to design pneumatic conveyors or predict hopper emptying. The charge exchanged in granule-to-granule and granule-to-wall collisions is computed by taking into account the physical properties of the respective materials, their area of contact, as well as the effect of the electric field created by a system of high-voltage electrodes and by the charges of the granules themselves. The numerical model simulates also the free-fall motion of the charged granules in the electrostatic field created between two vertical plate electrodes. The outcome of the simulation, i.e. the charge of the particles collected at the two electrodes in a definite laps of time, is in good agreement with the results of an experiment carried out with mixtures of mm-size polyamide and polycarbonate granules in a laboratory vibrated bed.