Evaluation of continuum regime theories for bipolar charging of particles in the 0.3-13 μm diameter size range

Bipolar charging experiments were performed on particles in the 1-13 μm 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 charging times from approximately 1 to 40, dimensionless electric fields from 1 to 20, and positive-to-negative ion conductivity ratios of 3, 10 and ∞. 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. Comparisons were also performed using data obtained previously for particles in the 0.3-1.1 μm diameter size range. Predictions were found to be in excellent agreement with the data