Determination of Eucken Factor from Relative Change in Thermal Conductivity of Gas Mixtures. Ortho–Parahydrogen Mixtures at 77°K

Abstract

At 77°K the measured change in thermal conductivity of hydrogen caused by a change in the relative proportions of ortho- and parahydrogen can be used to determine the dimensionless parameter δ (introduced by Hirschfelder in his formula for the “modified Eucken correction”) which is a measure of the contribution of rotational energy to the thermal conductivity of a polyatomic gas. The present method, which is very reproducible and is not sensitive to systematic errors in the measurement of absolute thermal conductivity, yields δ = 0.73 ± 0.04. An analogous method, using the variation of thermal conductivity at 311°K of a H2–Ar mixture as the proportion of H2 is increased, yields δ = 0.76, which is in excellent agreement with values previously obtained by other investigators from absolute measurements of thermal conductivity and Prandtl number. These experimental values of δ are lower than Hirschfelder's theoretical values. Possible reasons for this discrepancy are discussed.