Effect of air pressure on particle charge saturation and charge dissipation under active charging

Electrostatic charging is a common issue during pneumatic conveying, leading to particle adhesion, pipeline blockage, and electrostatic discharge, posing significant safety risks. In this work, we propose an active charging method based on corona discharge to simulate particle charge saturation and charge dissipation processes. The mechanism of the interactions between gas molecules and charges during particle charging and charge dissipation is elucidated. To simulate different air pressure conditions, a 1 m diameter vacuum chamber is employed in the experiment, which can provide a pressure range from 0.1 Pa to 10⁵ Pa. The charge deposition rate of the active charging method is measured using a Faraday probe. At an applied voltage of −10 kV, the charge deposition rate reaches −49.21 nC/(s·mm²) at the center of the charging region and − 3.36 nC/(s·mm²) at the edge. These values are sufficient to ensure that the particles reached charge saturation. Notably, the saturated particle charge decreases from −82.17 nC to −3.20 nC as the air pressure decreases from 10⁵ Pa to 0.1 Pa, indicating a positive correlation between air pressure and saturated particle charge. It is also found that the air pressure significantly affects the charge dissipation process of the particles. The surface potential decay rate is used to characterize the charge dissipation behavior of the particles. At t = 10 s, the surface potential decay rate decreases from 8 V/s at an air pressure of 10⁵ Pa to a minimum of 0.13 V/s at 100 Pa. It then increases to 3.27 V/s as the air pressure decreases to 1 Pa, before decreasing again to 1.15 V/s at 0.1 Pa. The mechanism underlying charge dissipation is attributed to the collision frequency between gas molecules and particle surfaces. A higher collision frequency per unit volume and per unit time results in faster charge dissipation. The influence of air pressure on particle charge saturation and dissipation provides guidance for pressure regulation in industrial settings and offers valuable insights into reducing electrostatic effects in the pneumatic conveying of particulate materials.