Concentration Dependence of the Thermal-Diffusion Factor for 3He–4He and H2—D2

The thermal-diffusion factors of 3He–4He and H2—D2 systems have been determined with high precision at several different compositions and at a fixed mean temperature, T̄ = 160°K, using a four-tube swing separator for 3He–4He mixtures, and a simple two-bulb apparatus in the case of H2—D2. The results indicate that the thermal-diffusion factor increases in magnitude with the increasing concentrations of the lighter component, as anticipated from theory. Detailed theoretical calculations on the Chapman—Cowling first approximation and the Kihara first and second approximations have been carried out, and comparisons made with the experimental results in both the cases. Good agreement between the Chapman—Cowling first approximation and the experimental results has been obtained, though Kihara approximations also could be fitted within the experimental uncertainty of the data in both the systems studied.