Aerosol Charger Using Sinusoidally Driven Ion Current from a Corona Discharge

Abstract

Construction and testing of an aerosol charger capable of charging initially neutral 0.913–μm diameter plastic spheres to 200 elementary charge units in 20 ms is described. The charger utilizes a continuous corona discharge from fine wires located in cylindrical cavities in opposite walls of a rectangular aerosol flow channel of dimensions 1.00 × 5.56 × 2.54 cm. A 3000-Hz AC voltage with maximum amplitude of 10 kV is applied across the 1.00-cm channel gap to produce an ion current which reverses direction with the cycling of the electric field. Aerosol particles moving through the channel are impacted by unipolar ions from first one side and then the other. Lateral motion of charged particles is oscillatory at the frequency of the applied electric field. This serves to minimize loss of charged particles due to wall deposition. A method for calculating the acquired particle charge based on field charging theory is presented. Particle charge levels calculated are in satisfactory agreement with measured particle charges.