Comparative Study on Boiling Heat Transfer Characteristics and Performance of Low Temperature Heating System of R744 and its Azeotropic Refrigerant

R744 is the most competitive, and R744 is the most ideal when flammability and toxicity are strictly limited. There are some problems in the current R744 heating system, for example the pressure at the heat release side is often more than 10.0MPa. High operating pressure brings high cost. Therefore, mixing R744 and ethane (77.6/22.4) to form azeotropic refrigerant, which can effectively reduce the working pressure of R744 system and enhance the safety of the system. At the same time, R744 can inhibit the combustion of ethane and realize mutual complementarity. However, there is little research on R744 azeotropic refrigerant at present. Therefore, in this paper, through the establishment of CFD model and complie UDF program to focuses on the flow boiling heat transfer characteristics and performance of low temperature heating system of R744 and its azeotropic refrigerant, the result show that the heat transfer coefficient of R744 and its azeotropic refrigerant decreases with the increase of mass flux, increases with the increase of heat flux, and increases with the increase of saturation temperature, and the heat transfer coefficient of azeotropic refrigerant is greater than R744 under the same conditions. Under a given operating condition, there is a critical point which makes the performance of azeotropic refrigerant better than R744, and this critical point is related to the outlet temperature of gas cooler, and the system discharge temperature of azeotropic refrigerant is significantly lower than that of R744. In conclusion, azeotropic refrigerant has certain advantages in heat transfer and system performance compared with R744, which also plays an important role in promoting the replacement of refrigerant in the future