A Critical Review of Real Gas Effects on the Regenerative Refrigerators
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https://doi.org/10.1007/s11630-020-1381-4
Article ID: 1003-2169(2020)00-0000-00
A Critical Review of Real Gas Effects on the Regenerative Refrigerators CAO Qiang1,2, LUAN Mingkai1, LI Peng1, WEI Li3, WU Yan1* 1. Institute of Refrigeration and Cryogenics, School of Mechanical Engineering, Tongji University, Shanghai 201804, China 2. Shanghai Key Laboratory of Vehicle Aerodynamics and Vehicle Thermal Management Systems, Tongji University, Shanghai 201804, China 3. Department of Electrical Engineering, School of Electronics and Information Engineering, Tongji University, Shanghai 201804, China © Science Press, Institute of Engineering Thermophysics, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract: 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.
Keywords: real gas effects, regenerative refrigerators, loss mechanism, reduction methods
1. Introduction The refrigerator is one kind of reverse work-heat conversion machine that removes heat from a low-temperature reservoir. Regenerative refrigerators are widely used for cryogenic applications because of the advantages of high reliability [1], compactness [1], high efficiency [2] and low temperature oscillation [3], which make them very appealing for small-scale and mid-scale Received: Jul 20, 2020
Article type: Invited Review
applications [4], especially for space applications [5]. In principle, the regenerative refrigerator is possible to achieve a low temperature even close to absolute zero with the highest possible efficiency, i.e. Carnot coefficient of performance (COP) [6]. The precondition is a set of lossless hardware as well as working with an ideal gas. However, there will be some losses if working with a real gas because
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