Modelling of conductive particle behaviour in insulating fluids affected by DC electric fields

Several electrostatic technologies, such as separation of granular mixtures, flocking, printing, biological cells manipulation, are based on the accurate control of conductive particle motion in insulating gases or liquids, by means of relatively high DC electric fields. The present work is aimed at characterizing the behaviour of such particles by numerical modelling of two aspects: (1) particle motion under the action of electric field forces; and (2) insulation breakdown triggered by mobile particles. The equations of particle motion were written by taking into account both gravitational and drag forces, as well as the rebound at particle impact with the electrodes. If the particles move in ionized air, their charge varies in time. In that case, the equation of particle charge should be added to the mathematical model. The output data of the programs for numerical simulation of particle behaviour are in good agreement with the available experimental results. Particle movements were shown to be influenced by the intensity of the electric field, by the density of the space charge, by size and mass density of the particles, as well as by their coefficient of restitution at impart with the electrodes. The conclusions regarding the behaviour of conductive particles in insulating fluids are useful for the development of improved electrostatic separation technologies; they are of particular interest to all manufacturers of high-voltage equipment.