Abstract: Carbon dioxide is increasingly attracting attention as a natural refrigerant due to its environmental friendliness(ODP=0,GWP=1),large unit volume refrigerating capacity and good heat transfer performance,etc. However,it is mainly used in transcritical refrigeration cycle due to limitation of its physical properties and working conditions. The operating pressure in the high pressure side of the transcritical CO₂ cycle may exceed 12MPa,which results in high requirements for safety and manufacturing costs. In this paper,we summarized current CO₂ refrigerant systems using CO₂ mixture refrigerant to effectively improve the problem of its high operating pressure,reviewed the research progress of refrigeration systems using CO₂ mixture refrigerant to reduce its cycle pressure,and analyzed the characteristics of the CO₂ mixture refrigeration systems,including the transcritical refrigeration cycle system,auto-cascade refrigeration system and compression-absorption coupled cycle system. Furthermore,we pointed out the development prospect of the refrigeration systems using CO₂ mixture refrigerant for depressurization,and discussed the main research directions of the CO₂ refrigeration systems in the future.

Key words: carbon dioxide, refrigeration cycle, mixture refrigerant, mixture, thermodynamics, depressurization

摘要： 自然工质CO₂ 因其具有良好的环境友好特性（ODP=0，GWP=1）、单位容积制冷量高、良好的传热性能等优点而得到制冷行业的再次关注。然而，由于其自身物性及工况条件的限制，在实际应用中CO₂制冷系统大多采用跨临界循环，高压侧压力高达12MPa左右，这对系统各部件的安全性和制造成本提出非常高的要求。本文总结了目前采用CO₂混合工质来有效改善纯CO₂制冷系统运行压力较高问题的制冷循环系统，综述了国内外以降压为目的的CO₂混合工质制冷系统研究进展，分析了CO₂混合工质的跨临界制冷循环系统、自复叠式制冷系统以及压缩-吸收耦合循环系统各自的特点，指出了以降压为目的的CO₂混合工质制冷系统的发展前景，并对今后的CO₂混合工质制冷系统的主要研究方向进行了讨论。

关键词: 二氧化碳, 制冷循环, 混合工质, 混合物, 热力学, 降压