Comparison of heat transfer coefficient during evaporation of natural refrigerants and R-1234yf in horizontal small tube

• The convective boiling HTC for the flow of CO2, NH3, C3H8 and R-1234yf is studied.
• The effects of mass and heat flux, saturation temperature and ID on HTC are reported.
• A new HTC correlation with 3114 data points is developed with MD of 12.28%.

An experimental data comparison of evaporation heat transfer coefficient of R-744(CO2), R-717(NH3), R-290(C3H8) and R-1234yf in horizontal small tubes was conducted under some various flow conditions. The experimental data were obtained over a heat flux range of 5–60 kW m−2, mass fluxes from 50 to 600 kg m−2 s−1, saturation temperatures from 0 to 10 °C, and quality up to 1.0. The test section made of stainless steel tubes with inner diameters of 1.5 mm and 3.0 mm, and a length of 1000 and 2000 mm, respectively, was heated uniformly by applying an electric power to the tubes directly. Effects of mass flux, heat flux, saturation temperature and inner tube diameter on heat transfer coefficient are reported in the present study. Among the present working refrigerants, R-744 has a highest heat transfer coefficient. Laminar flow was observed in the evaporative small tubes and considered in the modification of evaporation heat transfer coefficient correlations.