Design of non-flammable mixed refrigerant Joule-Thomson refrigerator for precooling stage of high temperature superconducting power cable

Abstract

A cryogenic Joule-Thomson (JT) refrigerator has many advantages for large industrial applications, such as cooling power adjustability and high reliability. In this paper, single and dual-stage of non-flammable (NF) mixed refrigerant (MR) JT refrigeration cycles have been proposed for precooling process of high temperature superconductor (HTS) electric power cable below 100 K. The refrigeration target is a neon/nitrogen mixed refrigerant which requires a pre-cooling temperature which is approximately 105 K. The components of MR JT refrigerator for the 1st stage (low temperature cycle) of the cascade cycle or the single cycle are mixture of nitrogen (N2), argon (Ar), Tetrafluoromethane (R14) and Octafluoropropane (R218). R410A is selected as the refrigerant for the 2nd stage (high temperature cycle) of the cascade cycle, of which the cooling temperature is nearby 240 K. The design results of the whole precooling refrigeration cycle were modeled by a commercial software with Peng–Robinson equation of state (EOS). The optimal design is discussed with consideration of various parameters such as stage of refrigerator, the operating pressure of the compression system, and the mass flow rate of the working fluid. The maximum coefficient of performance (COP) and Carnot efficiency for the cascade MR JT cycle at 107 K is obtained as 0.24 and 44%, respectively. Exergy analysis is also carried out in this paper to reveal the irreversibility of the refrigeration cycle.