Experimental and numerical study of a condensation-driven dilution refrigerator

Abstract

Dilution refrigerators are widely used in the fields of condensed-matter physics and quantum technology. For small cooling power applications, condensation-driven dilution refrigerator utilizes a condensation pump to achieve 3He cryogenic circulation and has advantages of compact structure, small 3He usage, and convenient operation. Related published research mainly focused on the overall system performances, and in-depth thermodynamics and fluid dynamics analyses are lacking. In this paper, a condensation-driven dilution refrigerator was experimentally studied and corresponding numerical simulations were performed. The results of experiments and simulations were compared and analyzed. In the experiments, lowest no-load temperature was 84.4 mK. The experimental cooling power was 1.91 μW @100 mK with a still heating power of 280 μW and the corresponding COP and second-law efficiency of the dilution cold cycle at 100 mK reached 0.0068 and 2.4% with the high temperature of 452 mK, respectively. The experiments also revealed that the charged mixture amount had a certain influence on the performance. With the help of simulations, the heat leak to the mixing chamber was estimated and certain intrinsic features of the cycle were enlightened. The heat leak and Kapitza resistance in the mixing chamber are possibly the main reasons for the differences between experimental and simulation results. Extended study based on the simulation also showed how flowrate variation changed the liquid column height difference and how the requirement of gas circulation and liquefaction set the limit on the minimum still temperature.