Thermodynamic analysis of a high cooling capacity dilution refrigerator in the critical velocity limitation of the dilute phase

Abstract With the rapid progress of superconducting quantum technology, the demand for cooling capacity from dilution refrigerators (DRs) is growing. The approach of increasing the mass flow rate to obtain a high cooling capacity is limited by the critical velocity of the dilute phase. In this paper, the critical velocity limitation of the dilute phase is considered, and the effects of the dilution unit structures on the performance of a high cooling capacity DR are studied. Furthermore, leveraging the physical properties of 3 He and 3 He- 4 He mixtures, a comprehensive analysis is conducted on the viscous heating in the heat exchanger, particularly in the critical velocity conditions. The structural dimensions of the heat exchangers at 0-5000 μW@100 mK and 0-50 μW@10 mK are obtained theoretically. This thermodynamic model provides strong support to design and optimize DRs with high cooling capacity.