04). Performance optimization of a mK dilution refrigerator based on the first law of thermodynamics. Cryogenics 135 (2023) 103731, https://doi.org/10.1016/j.cryogenics.2023.103731.

[Abstract]
This paper analyzes and optimizes performance characteristics of the dilution refrigerator (DR) based on the first law of thermodynamics. The properties of the ³He/⁴He mixture below 0.7 K are analyzed and a simplified method to obtain the enthalpy of the working fluid in the whole dilution cycle is proposed. Then an enthalpy flow model is built, based on which the variations of the specific cooling capacity, specific still heating power and gross cooling capacity with the precooling temperature and upstream pressure are studied at the cooling temperature of 10 mK, and the effect of the first-stage heat exchanger efficiency on the gross cooling capacity is further analyzed. The results indicate that there exists an optimal upstream pressure which maximizes the gross cooling capacity for a given precooling temperature. The optimal upstream pressure and the maximum gross cooling capacity are investigated based on the fitting functions of precooling temperatures. Given a heat exchanger ef f iciency of 97%, it is found that the optimal upstream pressure and precooling temperature should be 1.41 *105 Pa and around 4 K, respectively, to achieve the maximum cooling capacity of 38.5 μW at 105 mK. This study provides a helpful theoretical guidance for the performance optimization of the DR.

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