High Temperature Thermal Conductivity of Rare Gases and Gas Mixtures

The thermal conductivities of pure argon, pure xenon, and of three helium-argon mixtures have been determined in the temperature range 650–5000 deg K by measuring heat transfer rates from shock heated gases to the end wall of a shock tube. The heat transfer rate was measured by monitoring the time dependence of the voltage drop across a thin-film gage mounted in the end cap of the shock tube. During the course of the experiments, the pressure of the test gas behind the reflected shock wave ranged from approximately 1/3 to 2 atmospheres. In all cases, the temperature dependence (T) of the thermal conductivity (K) was assumed to follow a power law relationship of the form K/Kw = (T/Tw)b where Kw is the established value of the gas conductivity at the reference temperature (Tw) which was chosen near room temperature. The parameter b was evaluated by applying a least squares fit to the experimental data. Theoretical values of the conductivity of all of the gases studied were computed utilizing the Lennard-Jones (6–12) potential. In the case of the gas mixtures, an empirical combining rule was used to relate the force constants between unlike atoms to the known constants between like atoms. The experimental and theoretical results for the pure gases are in good agreement. The experimental and theoretical values of the mixture conductivities are within 10–20 percent, and as expected the theoretical predictions are least accurate for equimolar mixtures.