Thermodynamic properties of liquid ³3He-⁴4He mixtures between 0.15 K and 1.8 K

Abstract

Thermodynamic property relations for liquid ³3He-⁴4He mixtures between temperatures of 0.15 K and 1.8 K are determined. The relations are valid over the entire concentration range. Thermodynamic properties are first calculated at saturated pressure (which is more or less equal to zero pressure) in the two-phase region, and then extended to the single-phase He-II (up to 1.8 K) and He-I (up to 1.5 K) regions. The calculations at saturated pressure are based on available specific heat data and previously determined sub- 0.15 K properties. The property relations are then extended to higher pressures (up to 10 bar) between 0.15 K and 1.5 K, using available molar volume data. The results are largely in good agreement with some other ³3He-⁴4He mixture property data, though the scarcity of experimental data in large parts of the region of interest precludes a more thorough comparison. Applications of the derived properties to components of sub-Kelvin refrigerators, specifically He-II mixture heat exchangers and He-II mixture throttles, are also discussed.