Theoretical helium liquefaction rate based on the temperature-distributed refrigeration method in regenerative refrigerators

Abstract

Helium liquefaction is important for applications of cryogenic engineering, helium recovery and purification, and so on. Regenerative refrigerators are generally applied for small-scale applications because of their relatively high efficiency, competitive compactness, etc. However, the liquefaction efficiency (the ratio of the input power of the ideal liquefaction cycle to that of the practical cycle) of helium is low. In this paper, a novel method called temperature-distributed refrigeration to improve the performance of helium liquefiers by utilizing distributed refrigeration power is proposed. The theoretical liquefaction efficiency by applying this method in the regenerative cycle is analyzed. The analysis assumes that there is no radial thermal resistance during the transmission of refrigeration power. The working pressure of helium in the refrigerator is in a wide reduced pressure range of 4.0–61.7, with the liquefied helium maintained at 0.1 MPa. The results indicate that the theoretical maximum liquefaction rate reaches 50.5 L/d (1.5 W at 4.2 K). This liquefaction rate is 2–3 times that of liquefying with only the cold ends. Meanwhile, the liquefaction efficiency increases with the working pressure, reaching a theoretical maximum of 44.5 % at a reduced pressure of 61.7. It is the highest possible efficiency for a two-stage regenerative refrigerator. This method should provide a reference for the optimization of small-scale helium liquefaction systems.