Thermal conductivities of gaseous mixtures containing hydrocarbons. Part 1.—n-Butane, iso-butane, iso-pentane and neo-pentane, and their binary mixtures with argon

Thermal conductivities of the four pure gases n-butane, iso-butane, iso-pentane and neo-pentane and of their binary mixtures with argon have been measured at 50 and 100°C. The thermal conductivities of all four polyatomic gases lie close together and there are marked similarities in the conductivity against composition curves for their binary mixtures with argon.Thermal conductivities less than molar average values are found at both 50 and 100°C for each mixture. These “negative deviations” are greatest at 50°C and result in broad minima in each case. At 100°C minima are less pronounced and are confined to the n-butane, iso-pentane and neo-pentane mixtures. Points of inflexion develop in all the conductivity against composition curves at this temperature. We believe that negative deviations are generally to be associated with binary mixtures of a monatomic with a non-polar polyatomic gas, and minima can be manifested when the ratio of thermal conductivities for the pure components (λj/λi) is not far from unity. The formal condition is AijAjiλj/λi where Aij and Aji are coefficients of the Sutherland-Wassiljewa equation and subscript i denotes the component with the lower thermal conductivity.The data are used to test predictions of thermal conductivities of gas mixtures both by approximations to rigorous kinetic theory (Hirschfelder-Eucken, and Monchik, Pereira and Mason) and by the empirical relationship of Lindsay and Bromley. All three methods predict thermal conductivities which are in reasonable agreement with experimental measurements, but the Hirschfelder-Eucken approximation is found to be most satisfactory (mean deviation 1.27 % from 74 compositions) for these mixtures.