Bipolar Charging of Near-Micrometer Sized Aerosol

Experimental data are presented on the electrical charge acquired by near-micrometer sized aerosol particles exposed to bipolar ions. Aerosols ranging in size from 0.31 to 1.09 itm in diameter were atomized from monodisperse polystyrene latex hydrosols and exposed to bipolar air ions in a laminar flow charging apparatus. Particle charge was determined by an integral mobility analysis technique. Results demonstrating the charging time dependence (expressed through the parameter μ+ N+ t), the particle size dependence, and the charging electric field strength dependence are presented for ratios of positive to negative ion conductivity between one and infinity (unipolar positive). The range of &3x003BC;+ N+ t for the time dependent data was from approximately 4.0 x 10
¹⁰
to 6.0 x 10
¹²
kV
^-I
m
^-1
, with the charging field strength at 50 kV m
^-1
. The μ+ N+t product was maintained at 6.08 x 10" kV
^-1
-m
^-1
for the particle size dependent and field strength dependent tests, where for the latter, the electric field strength was varied from 25 to 300 kV m
^-1
. The charging electric field strength for the size dependent data was 300 kV m-1. Charge measurements are compared to predictions ofclassical continuum field theory and to an empirical superposition calculation in which the prediction of charge from continuum diffusion theory is simply added to that from field theory. Field theory predictions fall significantly below measurements; however, the empirical superposition calculations show good agreement with experiment.