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

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.