Thermal conductivities of ethene and its fluorocarbon analogues and of their binary mixtures with argon

Abstract

The thermal conductivities of the five pure gases CH₂CH₂, CHFCH₂, CF₂CH₂, CF₂CHF and CF₂CF₂ together with their binary mixtures with argon, have been measured at both 50 and 100°C.

At 50°C, negative deviations below the molar average value occur in the conductivity against composition curves for all five systems, and minima or signs of minima at intermediate compositions develop in the mixtures of CF₂CH₂, CF₂CHF and CF₂CF₂ with argon. At 100°C, the latter three systems again show negative deviations, and minima are once more displayed by the mixtures of CF₂CHF and CF₂CF₂ with argon. The system CHFCH₂ plus argon exhibits evidence for a point of inflexion in the curve.

This is the first time that minima have been observed in binary mixtures of a polar and a monatomic gas, though minima have been found with non-polar mixtures. Where minima develop, the formal condition A_ijA_jiλ_j/λ_i is fulfilled, where A_ij and A_ji are coefficients of the Sutherland–Wassil-jewa equation, subscript i denoting the component with the lower thermal conductivity.

The predictions of the empirical equation of Lindsay and Bronley are compared with experiment: the agreement is markedly less good than normally found, discrepancies being greatest in mixtures containing the most polar constituents. Outline comparisons with the Hirschfelder–Eucken approximation to rigorous theory are satisfactory.