Bipolar charging of particles in the 1 to 10 mu m diameter size range

Bipolar charging experiments were performed for particles in the 1 to 10 mu m diameter size range, and the data were used to evaluate continuum regime models for predicting charge acquisition. Particles were exposed to countercurrents of positive and negative ions in the presence of an external electric field. Particle charge was determined from observations of particle trajectories in a uniform electric field. Data were obtained for dimensionless electric fields from 1 to 13, and ion conductivity ratios of 3, 10, and infinity . The data were compared to predictions of field-diffusion theory, classical field theory, classical diffusion theory, and an empiricism formed by adding the field and diffusion approximations. Field-diffusion theory and the field plus diffusion empiricism were in excellent agreement with the measurements. Field theory was in good agreement for dimensionless fields greater than 10, and diffusion theory significantly underestimated charge for the range of dimensionless fields that were studied.<>