Electrostatic characterisation of corona-wire aerosol chargers

This paper investigates the electrostatic properties of aerosol corona-wire diffusion chargers. The most important parameters that determine charging levels of particles at the outlet of such devices are the ion concentration, N-i, and the mean residence time of the aerosol in the charging zone, t. A method to determine the exact N(i)t product is presented and used for the characterization of a Hewitt-type corona charger. It is shown that ignoring the space charge effect leads to significant errors when the ion concentration is greater than 5 x 10(13) ions/m(3). A numerical model developed to describe the performance of the device in more detail is used to predict the behavior of the charger when some geometric characteristics are changed. Estimations of ion penetration levels through the inner electrode based on the numerical model show better agreement with the experimental results at sub-atmospheric pressures. Finally, calculations of the average Nit product appear to increase with pressure despite the fact that the ionic concentration is significantly lower. (C) 2004 Elsevier B.V. All rights reserved.