(1) It has excellent thermodynamic properties so that it can have a higher cycle efficiency when operating in a given temperature region. The specific requirements are: the critical temperature is higher than the condensing temperature, the saturation pressure corresponding to the condensing temperature should not be too high, the standard boiling point is low, the specific heat capacity of the fluid is small, and the refrigerant

　　Low adiabatic index, large heating capacity per unit volume, etc.

　　(2) It has excellent thermophysical properties. The specific requirements are higher heat transfer coefficient, lower viscosity, and lower density.

　　(3) Good chemical stability The working fluid is required to have good chemical stability at high temperatures to ensure that the working fluid does not decompose at the highest working temperature.

　　(4) Good miscibility with lubricating oil

　　(5) Safety The working fluid should be non-toxic, non-irritating, non-flammable, and explosive.

　　(6) Good electrical insulation

　　(7) Economy. The working quality is low and easy to obtain.

　　(8) Environmental protection The ozone depletion potential (ODP) and global warming potential (GWP) of the working fluid are required to be as small as possible to reduce the damage to the atmospheric ozone layer and cause global warming.

　　Refrigerant, also known as refrigeration working fluid, is commonly known as a refrigerant in some areas in the south. It is a working substance that continuously circulates in the refrigeration system and changes its state to achieve refrigeration.

　　The refrigerant absorbs the heat of the cooling medium (water or air, etc.) in the evaporator and vaporizes, and transfers the heat to the surrounding air or water in the condenser to condense.

　　The application of single-stage compression of the non-azeotropic mixed working fluid can obtain very low evaporation temperature and can increase the refrigeration capacity and reduce the power consumption. Its nature is directly related to the refrigeration effect, economy, safety, and operation management of the refrigeration device, so the understanding of the nature of the refrigerant cannot be ignored.