Performance of Small Plate and Tube Unipolar Particle Chargers at Low Corona Current

Two small chargers, a plate and a tube particle charger, were compared in terms of their performance at low DC-corona current. Both chargers are designed for compact/miniature electrical-mobility-based particle sizers and were operated at a corona current of 0.3 µA for simultaneous low energy consumption and high charging efficiency. A thin wire was utilized in the plate charger for the ion generation via the DC-corona discharge, while a sharp-tipped needle was used in the tube charger. The intrinsic and extrinsic charging efficiencies of particles in various electrical mobility sizes were measured for both chargers at aerosol flow rates of 0.3 and 0.6 L min–1. In general, the plate charger exhibited a lower intrinsic charging efficiency than the tube charger. Also, its extrinsic charging efficiency was slightly higher at 0.3 L min–1 than 0.6 L min–1 and reached approximately 80% for particles larger than 40 nm. On the other hand, the extrinsic charging efficiency of the tube charger was higher at 0.6 L min–1 than 0.3 L min–1 for particles larger than 60 nm, with the reverse being true for smaller particles. The extrinsic charge distributions of particles with mobility sizes smaller than 300 nm were also characterized. It was found that a multiple-charge status occurred on particles larger than 20 nm for both chargers. At the same particle size, more charges attached to particles in the tube charger than the plate charger. The birth-and-death charging model was proposed for calculating the extrinsic charge distributions of particles measured in this study. In addition, the Gaussian distribution function was also suggested for best fitting the measured extrinsic charge distributions of particles.