Boling, Heat transfer, Low-pressure refrigerants, Smooth tube, Correlation
The flow boiling heat transfer of low-pressure refrigerants including R1224yd(Z), R1233zd(E), R1336mzz(Z), and R1336mzz(E) was experimentally investigated inside a horizontal smooth tube with outer and inner diameters of 9.52 and 8.40 mm, respectively. The experiments were conducted at a mass velocity range of 50–300 kgm−2s−1 and a saturation temperature of 40 °C. In the forced convection region, where the vapor shear force was dominant, the measured heat transfer coefficients were slightly larger than those of the conventional refrigerants were. A modified heat transfer correlation was developed based on a wettability separation angle to differentiate the stratified and annular flows. In addition, the heat transfer coefficient after the onset of dryout vapor quality was studied. Within the entire database, the mean deviation of the modified correlation was 1.0 %. The developed correlation agreed better with the experimental results compared to the conventional correlations.