Anti-agglomeration of spark discharge-generated aerosols via unipolar air ions

This paper reports the effect of air ions on the reduction of the agglomeration of metal aerosol particles generated from a homogeneous spark discharge. A carbon fiber ionizer was used to generate air ions near the spark channel formed between two metal electrodes. Once the air ions were generated, particles mixed with ions from the ionizer became charged by random collisions resulting from Brownian motion of the ions. Under the experimental conditions, the particle size right after the spark generation was about 4 nm. Then, the size increased to 50 nm, 1 m downstream (residence time of 1.76 s) of the spark channel due to Brownian agglomeration when there were no air ions injected. However, with the injection of air ions (ion concentration: particle concentration=10:1), the size of the particles was reduced to be around 10 nm due to the repulsive force between unipolar charged particles with an average charge number of 0.39. In this study, the classical Brownian agglomeration theory for unipolar charged particles was combined with the moment method to predict the particle size distribution as a function of time. The theoretically determined particle size distribution was in good agreement with the size distribution measured using a scanning mobility particle sizer (SMPS) system.