Composition and Temperature Dependence of the Thermal Diffusion Factor in H2–He Gas Mixtures

A Swing separator has been used to measure the composition and temperature dependence of the thermal‐diffusion factor ${\alpha }_T$ in the H₂–He system. This work was initiated following reports of abnormal behavior of this gas mixture in thermal conductivity measurements. We have measured ${\alpha }_T$ values as a function of composition at three average temperatures: 129.3°, 239.8°, and 320.5°K. At each of these temperatures both a minimum and a maximum occur in the α_T‐composition curve. The position of the minimum shifts towards the higher percentages of H₂ in the mixture as the temperature decreases, and the minimum tends to smooth out at higher temperatures. We have also measured ${\alpha }_T$ as a function of temperature in the range 130°–600°K for H₂ percentages 4.84, 14.5, 49.59, and 62.89 in the H₂–He mixtures. As the temperature increases ${\alpha }_T$ passes through a broad maximum and then slowly decreases. An approximate semitheoretical explanation is presented.