1K Heat Exchangers for 3He/4He Dilution Refrigerator

Abstract

For the condensation of 3He into 3He/4He dilution refrigerator, two types of 1K heat exchanger operated by 4He evaporation were designed. One is a disk type and the other is a coaxial counter-flow type heat exchanger. Each exchanger consists of a flow limiting impedance, a sintered copper heat exchanger, and a buffer volume for pumped liquid 4He. No moving part is included in the system. The exchanger is continuously supplied with liquid 4He through the impedance. Sufficient thermal exchange areas for 3He and 4He were obtained in a space of a few cubic centimeters by the use of sintered copper sponges. The small buffer volume for pumped liquid 4He, which forms the 4He-outlet of the exchanger, is useful to stabilize the temperature of the exchanger for an abrupt injection of heat load.The exchanger can absorb approximately 10mW for molar flow rate of 2×10-4 moles/sec of 4He. Therefore it is suitable as a 1K heat exchanger for a dilution refrigerator which has a maximum 3He circulation rate of 10-4 moles/sec. As the exchanger requires a small spacing in the vacuum jacket of the dilution refrigerator, it will be useful for shortening the vertical length of the refrigerator.