Measurements of charge imparted to fine particles by a corona discharge

IN electrostatic precipitation the diffusion mechanism of charging fine particles is extremely difficult to treat mathematically unless rather drastic simplifying assumptions are made. The size of these fine particles is comparable to the mean free path of the molecules of the gas. To treat this precisely one would have to include the effect of the field on the individual paths of the ions and consider the fact that the paths of the ions in the electric field are curves and not straight lines. If all of this is included in the differential equation it appears almost impossible to obtain any exact solution. White1 has given an excellent review of the solutions which have been obtained. In order to obtain reasonable mathematical equations all investigators have neglected the effect of the main electric field and have treated the problem by kinetic theory methods. Of course, since the field was neglected in deriving the equations, the calculated charge is independent of the field. In the past the Millikan oil-drop method has been the usual method for measuring the charge and with this method it was difficult to obtain sufficient experimental information to determine the agreement with calculations.