Decrease in Charge of Sharp-Edged Ellipsoidal Particles by Self-Discharge

The saturation charge of conductive sharp-edged ellipsoidal particles imparted by field charging is measured and found to be in agreement with the theoretical value. The saturation charge decreases, however, when the charging electric field exceeds a certain value. When the decrease in the saturation charge takes place, a corona discharge is observed from the particle at its one edge facing downstream in the ion flow. This discharge is referred to as the self-discharge. A theoretical initiation condition of the self-discharge is calculated, considering the field around the ellipsoidal particles. The theoretical initiation condition of the self-discharge is checked by an experiment to measure the electric field strength to initiate the decrease in the saturation charge of two conductive ellipsoidal particles with a = 3.5 mm focal length, ¿o = 0.068 eccentricity, and a = 1.87 mm, ¿o = 0.1. The theoretical initiation condition of the self-discharge for various sizes of ellipsoidal particles is also calculated to discuss the possibility of the self-discharge taking place with crushed or agglomerated particles.