Thermal conductivities of binary mixtures of organic vapours and inert diluents

Abstract

Thermal conductivities of the six sets of binary mixtures of n-pentane, diethyl ether, n-hexane and diethyl peroxide (5- and 6-membered chain species) with one another, and of their sixteen sets of binary mixtures with helium, neon or argon (monatomic species), or nitrogen (diatomic species), have been measured at 50 and 100°C. Marked similarities between all the polyatomic molecules (chain species) are shown by their individual thermal conductivities and by their behaviour in mixtures with monatomic and diatomic molecules.

Thermal conductivities of mixtures of chain and monatomic species have less than molar average values, deviations being numerically greatest for mixtures with helium and least for mixtures with argon. At both 50 and 100°C, pronounced minima have been found for mixtures with argon of either n-pentane or diethyl ether; and at 100°C, each of these systems also shows a point of inflexion in the conductivity-composition diagram. At 100°C, mixtures with argon of either hexane or diethyl peroxide show broad minima, but at 50°C the thermal conductivities of these mixtures vary monotonically with composition.

In every case, the variation of thermal conductivity with composition can be accommodated by expressions of the Sutherland-Wassiljewa form, and “best experimental” values for the coefficients A_ij are derived. The results are discussed in terms of the obstruction of heat transport in collisions between like and unlike molecules, and are used as a test of predictions based as closely as possible on rigorous theory (Hirschfelder-Mason and Monchick). Of all approximations, the simple Hirschfelder-Eucken approach is most successful in describing the thermal conductivities of the present systems (mean absolute deviation, 1.16 %). In an appendix, the physical significance of the occurrence of maxima, minima and points of inflexion in thermal conductivity-composition curves is examined.