机械过冷CO_2跨临界制冷循环性能理论分析

采用蒸气压缩制冷循环(辅助循环)对CO_2跨临界制冷循环气体冷却器出口的CO_2流体进行冷却,可减小节流不可逆损失,提高循环性能。本文对机械过冷CO_2跨临界制冷循环进行热力学循环分析,结果表明:当在最优排气压力和最优过冷度两个参数条件下,循环存在最大COP。环境温度越高、蒸发温度越低,采用机械过冷方法使循环性能提升越显著,相对传统CO_2制冷循环,通过辅助循环可显著提高循环COP,降低CO_2排气压力和温度。相对CO_2压缩机,辅助循环压缩机的功耗较少。分析了辅助循环中采用11种不同制冷剂的性能,可得除R41外,其它10种工质对循环整体COP的提升程度差异不明显。综上所述,机械过冷CO_2跨临界制冷循环更适用于环境温度较高、蒸发温度较低的场合。

Theoretical Performance Analysis of CO2 Transcritical Refrigeration Cycle with Mechanical Subcooling

The performance of the CO2 transcritical refrigeration cycle can be improved, and the throttling irreversibility loss can be reduced, by subcooling CO2 at the outlet of the gas cooler with a vapor compression refrigeration cycle (auxiliary cycle). A thermodynamical analysis is performed to study the operation characteristics of the CO2 transcritical refrigeration cycle with mechanical subcooling, and the results indicate that the maximum coefficient of performance (COP) is achieved at the optimum discharge pressure and optimum subcooling temperature. Compared with the traditional CO2 transcritical cycle, the improvement in COP is more significant at higher ambient temperatures and lower evaporation temperatures, and the discharge pressure and temperature can be notably reduced by the auxiliary cycle. The energy consumption of the auxiliary cycle compressor is much lower than that of the CO2 compressor. Among the 11 auxiliary cycle refrigerants, the differences between the COP improvements of the other 10 auxiliary working fluids are not obvious, except for R41. The CO2 transcritical cascade refrigeration cycle is more applicable to working conditions with higher ambient temperatures and lower evaporation temperatures.