Charge Density, Electric Field, and Particle Charging in Electrostatic Precipitation with Back Ionization

A quantitative model is developed for the description of charge density and electric field structures and consequent particle charging characteristics of a cylindrical precipitator with back ionization at the collection electrode. Results are compared with the results of an experimental study done some time ago by Penney and Hewitt. Solution of the governing set of equations involves iterative numerical integration to produce an electric field at the inner electrode surface consistent with Peek's formula and a ratio of back ionization to corona wire charge density at the collection electrode consistent with experimentally measured current per unit length. A description of charging of spherical particles in a bipolar ion flux then permits a computation of particle charging as a function of position. Results are in substantive agreement with measured values of charge acquired by steel balls dropped through a cylindrical precipitator with back ionization. The maximum difference between theoretical and experimental values occurs at an intermediate voltage, where ion ``channeling'' may affect charge and field distributions.