Nanoparticle charging efficiencies and related charging conditions in a wire-tube ESP at DC energization

This study addresses the lack of unipolar charging data for aerosol particles below 100 nm at high charging intensities (Nt>1013s/m3, ion concentration N, particle residence time t). Average particle charges of a narrow distributed 60 nm DEHS aerosol acquired in a wire-tube ESP with DC corona were measured. In order to vary particle residence times in the charging zone, experiments with different carrier gas velocities and with different active corona wire lengths were carried out. On the basis of FEM solutions of the electrostatic equations the measured charging results are compared with diffusion charging theory. For negative polarity the measured charges surpass the predicted values strongly up to factor 1.6, which cannot be explained by theory (here, the established Fuchs model is applied). However, for positive charging low deviations compared to theory are found. It is shown that the Nt-product is the essential charging parameter, also in the high-intensity charging regime.