采用非共沸混合工质机械过冷的跨临界CO_2制冷循环性能分析

Performance Analysis of Transcritical CO_2 Refrigeration Cycle with Mechanical Subcooling Employing Zeotropic Mixture as Working Fluid

本文提出了非共沸混合工质机械过冷跨临界CO_2制冷循环。在最优排气压力和最优过冷度下循环取得最大COP。最大COP、最优排气压力和过冷度与混合制冷剂的温度滑移密切相关。当选取合理温度滑移的混合工质作为机械过冷循环的制冷剂时,可明显提升CO_2制冷循环能效,降低排气压力。与基本CO_2制冷循环相比,在蒸发温度为-40℃、环境温度为35℃时,采用R32/R152a(40/60)循环总COP可提升46.53%,CO_2排气压力可降低2.758 MPa。总COP的提升程度受混合制冷剂的温度滑移影响显著,推荐机械过冷循环使用温度滑移合理的混合制冷剂。在温暖和炎热的气候地区及冷冻冷藏等低温应用领域,采用非共沸混合制冷剂机械过冷跨临界CO_2制冷循环整体性能的提升更加显著。

A novel transcritical CO2 refrigeration cycle by utilizing zeotropic mixture as working fluid for the mechanical subcooling （MS） cycle is proposed in the study, which can be utilized to subcool the CO2 fluid flowing from the gas cooler. A maximum overall COP is a- chieved at the optimum discharge pressure and optimum subcooling degree. The results indicate that the maximum overall COP, optimum subcooling degree, and discharge pressure are closely related to the temperature glide. Additionally, the energy efficiency of CO2 refrigera- tion cycle is improved efficiently and the high pressure is reduced significantly when mixtures with proper temperature glide are used as the refrigerant of MS cycle. When compared with the base CO2 refrigeration cycle, the overall COP is enhanced by 46. 53% , and discharge pressure is reduced by 2. 758 MPa at an evaporation temperature of -40 ℃ and ambient temperature of 35℃ when R32/R152a （40/60） is employed. The overall COP enhancement is significantly linked to the temperature glide. Furthermore, the thermal performance of the overall cycle is more significantly enhanced for hot or warm climate regions or relatively low evaporation temperature applications such as freezing and cold storage.