EVALUATION OF CONTINUUM REGIME THEORIES FOR BIPOLAR CHARGING OF PARTICLES IN THE 0.3-13-MU-M DIAMETER SIZE RANGE

Bipolar charging experiments were performed on particles in the 1–13-°m diameter size range, and the data were used to evaluate continuum regime models for predicting charge acquisition. In the experiments, particles were exposed to counter currents 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. Field-diffusion predictions were in excellent agreement with the data. The root mean square difference between theory and experiment was less than 10% for the large particle (1–13 µM) experiments and less than 17% for the earlier small particle (0.3–1.1 µm) experiments. Charge predictions based on classical diffusion theory approached the experimental results monotonically with decreasing electric field strength and were essentially equivalent to the measurements for dimensionless fields less than approximately 0.1. Classical field theory predictions approached the experimental results monotonically with increasing electric field strength and were within 20% of the data at a dimensionless field of 20. The field-plus-diffusion empiricism generally yielded good estimates of charge, although the calculations were 20–25% below the measurements for dimensionless fields between 0.5 and 5. © 1990 IEEE