Prediction of dielectric properties of N₂/O₂mixtures in the temperature range of 300–3500 K

A prediction method is proposed for dielectric strengths of hot N 2 /O 2 mixtures as well as hot air in the heavy particle temperature range of 300–3500 K. Electrical breakdown in hot gases by application of an electric field occurs more easily than that in cold gases. Such an electrical breakdown in hot gases can be seen in a circuit breaker after arc interruption. First, equilibrium compositions of hot N 2 /O 2 mixtures were calculated by means of Gibbs free energy minimization. Second, electron energy distribution functions (EEDF) for the hot mixtures to which electric fields were applied were computed using the derived composition by adoption of the two-term expansion approximation of Boltzmann equation. Third, the ionization coefficient α and the electron attachment coefficient η were calculated from the EEDF obtained. The reduced critical electric field strength ( E / N ) cr , which gives zero effective ionization coefficient , was derived for hot N 2 /O 2 mixtures as a function of heavy particle temperature. The result indicates that ( E / N ) cr decreases with increasing heavy particle temperature from 1500 to 3500 K, which results mainly from NO formations and O 2 dissociations. The predicted result for air was compared with experimental results, and they showed good agreement.