Effect of Humidity on Discharge Characteristics of Air Positive Corona at Atmospheric Pressure

The occurrence and application scenarios of corona discharge are diverse, and most of them occur in scenarios where the background gas is air. The influence of different air relative humidity on the development of positive corona discharge is still unclear. In this article, a 2-D hydrodynamic plasma simulation model of axisymmetric needle-plate dc positive corona was established to study the effects of different air relative humidity on the electrical characteristics and plasma characteristics of positive corona discharge from the microscopic point of view. The results show that under the same other conditions, the higher the relative humidity of the air, the slower the development of the discharge. Specifically, the discharge development under high relative humidity condition lags behind that under low relative humidity condition, and the discharge current amplitude decreases with the increase in relative humidity. For the plasma in the discharge area, as the relative humidity of the air increases, the number of O-, H-, and OH- ions in the plasma area significantly increases, while the number of electrons decreases. In the initial stage of corona discharge, a large number of free electrons gather near the needle electrode. An increase in relative humidity will cause more free electrons to be adsorbed by water molecules to form negative ions, thereby weakening the electron collision ionization reaction near the needle electrode and increasing the initial corona voltage.