Induction charging of granular materials in an electric field

It is well known that particles can be freely levitated in an electric field due to the charge induced on the particles by the external field. The charge depends upon the electric field strength and particle properties. This paper studies some of these factors to investigate the fundamentals of induction charging for granular materials. An experimental apparatus was set up to collect the levitated particles in a filter contained in a Faraday pail and the charge-to-mass (Q/M) ratio was obtained based on the charge and mass measurements for the samples in the filter. Furthermore, the particle size distribution was measured and analyzed by laser diffraction and microscopy and the surface mean diameter (D_s) and volume mean diameter (D_v) were obtained. In these experiments irregular shaped Al₂O₃ particles and spherical glass beads with a size range of 42-390 μm were used and tested at different electric field strengths. By combining the results of Q/M, D_s and D_v, the charge per particle was calculated and the results compared with theoretical values. It was confirmed that the particle charge is dependent upon the electric field strength and the particle properties of size, shape, density, resistivity, and adhesive force.