Abstract:
Thermal conductivities of the four pure gases n-butane, iso-butane, iso-pentanc and nco-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 arc 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 ” arc greatest at 50nC and result in broad minima in each case. At 100 C minima arc less pronounced and arc confined to the n-butane, iso-pentane and neo-pcntanc 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 (Xj/X/) is not far from unity. The formal condition is AjjAji > where Ay and Aji arc coefficients of the Suthcrland-Wassiljcwa equation and subscript i denotes the component with the lower thermal conductivity.
The data arc used to test predictions of thermal conductivities of gas mixtures both by approximations to rigorous kinetic theory (Hirschfelder-Eucken, and Monchick, Pereira and Mason) and by the empirical relationship of Lindsay and Bromley. All three methods predict thermal conductivities which arc 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.
