Unipolar field charging of particles by electrical discharge: effect of particle shape

In order to control the properties of the pollutant particles (diameter, charge, concentration, aerosol flow rate) to be collected in a coagulation device, a corona charger (negative wire cylinder discharge) has been designed and tested. This paper presents results of di ethyl hexyl sebacat (DEHS) and NaCl particle charging in a corona discharge. The aerosol particles are charged in a high electric field (>106 V m−1) so as to check the validity of the field charging law. A special care is taken to characterise accurately the discharge, to calculate, for each experimental condition, the gaseous ion density and electric field in which particles get charged. The first point is that the field charging law fits well with experimental charging data for spherical particles in the intermediate size range (0.44–1.13 μm). Nevertheless, for cubic NaCl particles in the same charging conditions (i.e. ion density and transit time), the experimental charge level appears to be greater than predicted by classical field charging law. The only difference between DEHS and NaCl particles seems to be the particle shape, that could lead to an increase of saturation charge in the case of cubic particles, due to local electric field enhancement.