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

摘要

The present paper describes a prediction method of the dielectric strength of the air in gas temperature range of 300–3500 K. First, the equilibrium composition of the air at gas temperatures of 300–3500 K 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 ᾱ was derived from the EEDF obtained. The critical reduced electric field strength (E/N)cr, which gives zero effective ionization coefficient ᾱ= 0, was obtained at gas temperatures of 300–3500 K. The result indicates that (E/N)cr decreases as the gas temperature increases from 1500 K to 3500 K, 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. © 2004, The Institute of Electrical Engineers of Japan. All rights reserved.