Investigation on Effective Ionization Coefficient and Critical Electric Field in Air in Temperature Range of 300-3500K by Solving Boltzmann Equation

Abstract

The present paper describes a prediction method of the dielectric strength of the air in gas temperature range of 300-3500K. First, the equilibrium composition of the air at gas temperatures of 300-3500K was calculated through Saha and Guldburg-Waage equations. Secondly, the electron energy distribution function (EEDF) was calculated by an adoption of the two-term expansion of Boltzmann equation. Finally, the effective ionization coefficient α was derived from the EEDF obtained. The critical reduced electric field strength (E/N)_cr, which gives zero effective ionization coefficient α=0, was obtained at gas temperatures of 300-3500K. The result indicates that (E/N)_cr decreases as the gas temperature increases from 1500K to 3500K, which is due mainly to an increase in the mole fraction of NO molecule which has a much lower ionization potential compared with N₂ and O₂. This calculated result fairly agrees with an experimental one.