Numerical analysis of contact electrification using DEM-CFD

Contact electrification occurs in many powder handling processes and involves electrostatic charges that are transferred between contacting particles during collisions. In the current paper, a successive condenser model was developed and implemented into a discrete element method coupled with computational fluid dynamics (DEM-CFD) to analyse the charge transfer during powder processing. The numerical results for the contact electrification between a dielectric particle and a neutral conductive surface were in excellent agreement with experimental data reported in the literature. It was also shown that, during single collisions, the transferred charge is proportional to the maximum contact area but decreases linearly as the initial charge of the particle increases. In a successive impact process, charge accumulation on a particle increases exponentially with the number of collisions and eventually reaches an equilibrium state. During these processes, larger particles gain higher steady state charge but the charge-to-mass ratio is smaller. Nevertheless, particles of different sizes have identical surface charge density and charging coefficient when the impact velocity is identical. In the case of gas fluidization, the electrostatic charge gradually accumulates on particles and eventually reaches an equilibrium state. Non-uniform charge distribution is generally induced. A higher superficial gas velocity results in a faster charge accumulation due to increased collision frequency and impact velocity.