Experimental investigations of fine particle charging by unipolar ions — A review

Abstract

Many theories have been offered in attempts to describe accurately the rate of charge accumulation of fine particles in a unipolar ion field. There has been little experimental data, however, for comparison with these new theories. In this study, the existing experimental data are reviewed and compiled, and additional particle charging experiments done to extend the quantity of data. Before this study was performed the majority of the experimental data which was available for comparison with particle charging theories was contained in a paper by G. Hewitt, published in 1957. Hewitt's experiments were carefully done, but the range of experimental variables was limited and his work was never independently verified. The experiments reported here followed Hewitt's procedures closely and were designed to extend the quantity of experimental data. There is some overlap between this and Hewitt's data, and in these instances, the agreement is good. Experimental results are presented in this paper for the charging rate of particles of 0.109–7 μm dia. at various values of electric field strength, ion density and charging time. A limited amount of data is also given which shows the important effects on the charging rate of variations in the particle dielectric constant and the polarity of the corona ion source.