Modeling of conducting particle charging on plate electrodes affected by non-uniform electric fields

Analytical formulae are available for the estimation of the charge acquired by conductive bodies of regular shape (spherical, hemi-spherical, hemi-ellipsoidal, cylindrical) in contact with a plate electrode affected by a uniform electric field. The electrode arrangements employed for charging the particles in some electrostatic processes generate nonuniform electric fields for which no such formulae can be derived. The authors employed a computer program based on the boundary element method for the numerical analysis of the electric field and the computation of the charge carried by cylindrical bodies in contact with a plate electrode. The study was carried out for an electrode arrangement that simulates the charging conditions in plate-type electrostatic separators. It enabled the evaluation of the effect of field nonuniformity on the amount of charge acquired by single particles, in various positions on the surface of the plate electrode. In most of the actual applications, several particles are simultaneously in contact with the charging electrode. Therefore, the study was extended to the situation of several equally-spaced cylindrical bodies in contact with the plate electrode. Several simple experiments confirmed the theoretical predictions. From a practical point of view, the results reported in this paper will serve as a basis for the development of a computer program for the numerical simulation of particle behavior in plate-type electrostatic separators.