A critique of methods for calculating the dielectric strength of gas mixtures

Three currently available methods for predicting the dielectric strength of gas mixtures are discussed and compared. All are based on the common principle of linear addition of some property of the individual gases in proportion to their concentration in the mixture. The simplest approach uses a weighted sum of the dielectric strengths of the separate gases. The other approaches are based on predicting the limiting reduced field (E/N)*m at which the net ionization coefficient of the mixture (ᾱ/N)m = 0. Wieland’s approximation for ᾱm involves a weighted sum of the ᾱ’s for the separate gases, and requires a knowledge of these over the range (E/N)*w<(E/N)<(E/N)*s, where w and s refer to the weakest and strongest gas involved. It is shown that this approach in general gives a mixture strength which varies monotonically with the fractional concentrations and lies within the above range of E/N. The simplest approach, using weighted linear addition of strengths, and the empirical rule proposed earlier by Takuma ...