Experimental Study on Flow Boiling Heat Transfer Characteristics of R513A Inside Horizontal Tubes

Global warming has emerged as a world-wide concern; therefore, research on the fourth generation of new environmentally friendly refrigerants is an urgent requirement. The boiling heat transfer characteristics of a refrigerant in an evaporator are directly related to its application. Thus, the R513A refrigerant is a suitable alternative to R134a. The boiling heat transfer characteristics of R513A and R134A in a 12.7 mm horizontal smooth tube and microfin tube were experimentally studied. The effects of mass flow rate, evaporation temperature, heat flux, and internal thread structure on heat transfer coefficient and pressure drop were also analyzed. The experimental mass flow rate of refrigerant was 100-200 kg/（m²·s）and the evaporating temperature was 5 ℃-10 ℃. The results showed that the boiling heat transfer coefficient changed significantly with an increase in the heat flux. With an increase in mass flow rate, the boiling heat transfer coefficient increased by 15.06% to 42.33%, and the pressure drop increased by 26.16% to 61.83%. As the evaporating temperature increased, the boiling heat transfer coefficient increased by 13.27% to 38.25%, and the pressure drop decreased by 19.53% to 33.27%. The heat transfer coefficient of the microfin tube was significantly higher than that of the smooth tube, with a reinforcement multiplier of up to 2. Under the same conditions, the boiling heat transfer coefficient of R513A was 25.61%-30.74% higher than that of R134a. The pressure drop inside the microfin tube of R134a was approximately 12.33% higher than that of R513A. With an increase in the heat flux, the flow pattern transition of R513A occurred earlier than that of R134a, and the boiling heat transfer coefficient decreased sharply.