Evaluation and Analysis from Pressure and Component in the Single-Stage Mixed-Refrigerant Joule-Thomson Cooler from 100 to 200 K

Mixed-refrigerant Joule-Thomson refrigeration (MJTR) technology has broad applications in cryogenic refrigerator. The operating pressure and components are key parameters in determining system efficiency. However, previous studies have not revealed the pattern of pressure's impact on system efficiency, nor have they clarified the intrinsic connection between pressure and components. This study optimized mixed refrigerants under different operating pressures through the optimization method based on the effective refrigeration effect of components. The results indicate that the influence of pressure cannot be ignored. Within the pressure range investigated in this study, the COP at the optimal pressure is more than twice that of the worst value. The selection of different components and refrigeration temperatures leads to different optimal pressures, which are essentially determined by the effective refrigeration temperature range of the components in the mixed refrigerant. The substitution of iC5H12 for iC4H10, C2H4 for C2H6, and N2 for Ar is proposed to improve the COP at various refrigeration temperatures. This study achieved higher exergy efficiency at all refrigeration temperatures compared to the references. Specifically, at the refrigeration temperature of 100 K, the exergy efficiency increased by 32 %. The lowest exergy efficiency is observed at the refrigeration temperature of 120 K, primarily attributed to the absence of suitable components between N2 and CH4. The increase in cooling capacity from the use of N2 is less than the increase in power consumption. Furthermore, within the refrigeration temperature range of 160 K–200 K, the exergy efficiency gradually decreases due to the absence of more suitable lowest-boiling-point components apart from CH4.