A Critical Review of Real Gas Effects on the Regenerative Refrigerators

The regenerative refrigeration is an important reverse work-heat conversion cycle with a theoretical coefficient of performance (COP) identical to the Carnot efficiency. Practical regenerative refrigerators are capable of working down to 4 K and largely fulfill the refrigeration requirement of modern technologies in many fields, especially for space applications. However, the enthalpy flow associated with the pressure dependence, abbreviated as pressure-induced enthalpy flow, brought about by real gas effects degrades the theoretical COP of the refrigerator to below about 30% of the Carnot efficiency at the temperatures of below the critical point. This paper reviews the long history of exploring the real gas effects which dates back to the 1970s and continues to now. Important explorations of uncovering the loss mechanism and reducing such losses are summarized. The theories that are in accordance with experimental results and simulation results are expounded. We further carry out analyses on the expansion components, including the pulse tube and the clearance gap. Several inferences are made in order to explore the long-lasting puzzles about real gas effects. It is emphasized that the underlying cause of the loss in the regenerator is an indirect effect of the real gas properties. Further study about carrying out a direct verification of the theory is proposed.