Influence of the initial charge on the charging and neutralization states of dielectric particles crossing a corona discharge

Abstract

This paper presents a detailed investigation into how the magnitude and polarity of an initial electrostatic charge influence the subsequent charging of dielectric particles as they pass through a coaxial corona electrode. High-density polyethylene (HDPE) particles with diameter 2.5 – 4 mm were pre-charged to various levels, using both positive and negative polarities, before being introduced into a DC corona discharge region. To encompass all relevant configurations, the corona discharge was operated with either the same or opposite polarity as the particles’ initial charge. The charging capability of the particle–corona system was assessed through the relationship between the charge acquired by the particles and the charge released by the corona discharge, while also considering the limitations imposed by particle saturation and self-discharge. The relationship between the corona charge released and the amount of charge captured by a single particle during its residence time in the ionized region is determined through analysis of the discharge current and particle charge measurements. The results reveal a strong dependence of the final particle charge on the ratio of the initial charge to the saturation charge. Two distinct behaviors were identified: (i) when the initial charge is below the saturation level or of opposite polarity, particles continue to accumulate charge until reaching saturation; (ii) when the initial charge has the same polarity but exceeds the saturation level, particles lose charge until converging to the saturation value. This latter, less frequently observed scenario is examined in depth. To further interpret these findings, the induced charge on the metallic components of the electrode—specifically the wire and the cylindrical collector—was analyzed in attempt to elucidate the mechanisms responsible for charge reduction when the initial charge substantially exceeds the saturation limit. Several mechanisms are considered, whose relative contributions may vary depending on the initial charge magnitude.