Composition dependence of the thermal conductivity of low-density polyatomic gas mixtures

Abstract

We present a predictive scheme for the composition dependence of the thermal conductivity of mixtures containing polyatomic gases at zero density. This supplements earlier work which developed a method to interpolate for the composition dependence of dense gas mixtures, as well as an earlier procedure to calculate the thermal conductivity of mixtures of monatomic gases. In all cases, the algorithm makes use of accurately measured values of the thermal conductivity of pure gases and is validated with the aid of almost equal accurately measured values of selected binary mixtures. Such accurate data have been obtained mostly in transient hot-wire instruments. The formulae proposed for the calculations use the Monchick-Pereira-Mason kinetic-theory analysis as a starting point but contain a number of detailed improvements. The present algorithm is tested by comparison with measurements on 22 mixtures, which show absolute average deviations from the predictions ranging from 0.7 to 2.7%, with one unexplained case, that of CF4-He mixtures, which show deviations reaching as much as 7%. We estimate that the algorithm predicts the zerodensity thermal conductivity of binary mixtures, containing at least one polyatomic component, with a probable error in the order of 2%.