Measurements of the Superfluid Joule–Thomson Refrigerator Using High Concentration 3He–4He Mixtures

THERMODYNAMIC PROPERTIES OF LIQUID [sup 3]He-[sup 4]He MIXTURES BETWEEN 0.15 K AND 1.5 K

“…Engineering interest in 3 He- 4 He mixtures is mainly due to their use in dilution refrigerators, one of the primary means to cool down to sub-Kelvin temperatures. As a result, thermodynamic property tables for these mixtures, developed from the late 1960s through to the early 1980s, are restricted to property regions where dilution refrigerators typically operate -low pressures and dilute solutions of 3 He in 4 He.…”

“…As a result, thermodynamic property tables for these mixtures, developed from the late 1960s through to the early 1980s, are restricted to property regions where dilution refrigerators typically operate -low pressures and dilute solutions of 3 He in 4 He. The most extensive set of thermodynamic property tables for 3 He- 4 He mixtures was developed by Radebaugh [1] in 1967. He calculated properties at saturated pressure, at temperatures below 1.5 K and 3 He mole fractions of only less than 30%.…”

“…The most extensive set of thermodynamic property tables for 3 He- 4 He mixtures was developed by Radebaugh [1] in 1967. He calculated properties at saturated pressure, at temperatures below 1.5 K and 3 He mole fractions of only less than 30%. The calculations were based on theoretical models whereby the 3 He component was assumed to behave like an ideal Fermi gas of quasiparticles.…”

“…The calculations were based on theoretical models whereby the 3 He component was assumed to behave like an ideal Fermi gas of quasiparticles. This assumption is reasonable at low temperatures and low 3 He concentrations but starts to break down at higher temperatures and 3 He concentrations.…”

“…They calculated properties for temperatures below 0.25 K and 3 He mole fractions below 8%; the ideal-Fermi-gas model becomes increasingly inappropriate beyond these limits.…”