CONTINUUM-REGIME FIELD CHARGING IN AN ELECTRON SWARM

The strong dependence of electrostatic precipitator collection efficiency on particle charge has innovated a number of investigations of charge enhancement techniques. Previous measurements of free electron charging of aerosols have confirmed early evidence that free electron charging yields substantially higher (two to five times) charges on 0.3- to 3-mu-m radius particles than ionic charging [1]. The previously available charging theories did not predict the observed dependence of particle charge on electric field, particle radius, charge density, and exposure time. A new continuum-regime field-diffusion model was proposed, and experiments were performed to verify the importance of electric field-enhanced electron temperatures in the model [2]. However, for the particle sizes studied (0.3 - 3-mu-m), both field and diffusion charging contributed to the particle charge. In this work, field charging by electrons is investigated separately by using very large particles (1500-9000-mu-m radius). The data are in good agreement with free-electron field-charging theory.