Theoretical analysis of the heat exchanger of a dilution refrigerator for space applications

The closed cycle dilution refrigerator has been one of the competitive space cryogenic technologies for obtaining the sub-Kelvin temperature with the advantages of large cooling capacity, continuous refrigeration and the absence of magnetic field interference. The mass flow rate in the closed-cycle system is at least ten times larger than that in the open-cycle system to obtain greater cooling capacity. This results in different operating condi-tions for the dilution units of the two types of refrigerators. In order to study the thermal performance of the heat exchanger in a closed-cycle mode with large mass flow rate, this paper develops a thermodynamic model of the dilution unit with a finite volume method, based on the principles of the dilution refrigerators for space. Based on this model, the influences of the configuration, the 3He proportion, and the mass flow rates on the performance of the dilution unit are discussed.