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 AijAji[gt-or-equal]λj/λi is fulfilled, where Aij and Aji 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.
