Investigations on thermodynamic characteristics of the novel still with combustion chamber used in a closed-cycle cryogen-free dilution refrigerator

Abstract The closed-cycle cryogen-free dilution refrigerator (DR) is one of the most promising cryocooler candidates for achieving continuous cooling below 100 mK. As a key component of DR, the still is used to control the circulation rate and the ratio of 3 He- 4 He gas in the cycle, pre-cool the throttled fluid, and provide the power for the dilution cycle. The 3 He- 4 He gas ratio is a key parameter directly affecting the cycle efficiency. The film burner (FB) is a key component for controlling the gas ratio in the still. Therefore, a novel still is proposed, the annular pore is used to guide the superfluid helium, and an FB is set to connect with a 4 He shelter. The comprehensive relationship between several parameters such as 3 He molar concentration, still cooling power, still heat exchanger initial parameters and the still temperature is determined. FBs can improve the still cooling power by 5.61% (0.39 mW) compared with orifices when the still is 700 mK. The research results provide a reference for the performance optimization and structural design of the still of DR. It will also provide a guidance for increasing the overall cooling capacity of DRs.