Abstract
A new unipolar charger was developed, in which the electric field was impressed to separate unipolar ions from bipolar ions generated by alpha irradiation from radioactive source. The shape of the unipolar charger and the electric field impressed in it was optimized by numerical trial and error method. The evaluation of the charging rate of a design was evaluated by solving the spatial distribution of charged particles numerically as follows: the flow field and electric field was solved, and then, 1) the transport of ions and particles by convection, diffusion, and electrical migration, 2) aerosol charging and neutralization by combination of ions and particles, and 3) recombination of positive and negative ion, simultaneously. Field charging by ions and charged particles was excluded to reduce the computational costs. Charging rate, so-called extrinsic charging efficiency of the unipolar charger and conventional bipolar charger was investigated by tandem-DMA method directory. The charging rate of unipolar charger on the aerosol particles of 4 nm in diameter was twice as high as that of conventional bipolar charger, and more for larger aerosol particles.
