Particle charging and agglomeration in DC and AC electric fields

Experiments were carried out to investigate agglomeration characteristics of bipolarly charged particles under an AC electric field and to investigate charging characteristics of particles by using wire-to-plate type DC corona chargers. A laboratory-scale setup was built and experiments were conducted at laboratory conditions. The effects of DC and AC fields on the variation of particle size distribution are discussed. Bipolar voltages of + 8 and -8 kV DC were applied to the two corona chargers, respectively. The AC electric field applied to the agglomeration section was 3.9 kV/cm (rms), and the residence time in the agglomeration section was adjusted to 1 s. Particle size distributions were measured with a cascade impactor (MOUDI). The reduction ratio of submicron particles due to AC fields with 60-500 Hz was 25-29%. The average number of elementary charge per particle was measured when the polarities of two corona chargers were either positive or negative. Current/voltage characteristics of our corona chargers were obtained for high-mass loading condition and compared with those for the no mass loading. Seventy to ninety percent of corona-induced ions were intercepted by DOS particles in the negative corona charger. The results imply that the particle charges depend on the particle mass loading, i.e. higher mass loading will cause lower particle charges.