Condensation heat transfer characteristics of R1234yf and other Refrigerants inside small-scale tube: An experimental study and heat transfer correlation development

R1234yf is characterized by low global warming potential (GWP) and it is a very promising candidate to substitute traditional refrigerant in the near future. The condensation heat transfer of low GWP refrigerant R1234yf was experimentally studied in detailed in this study. The influence of tube diameter was also discussed. HTCs were measured in horizontal tubes with the inner diameter (ID) of 2 and 4 mm, and the flow patterns taken during experiment were used to analyze the results. Different effects including mass fluxes, vapor quality, thermophysical properties, flow pattern and tube diameter on the HTC were also analyzed. Under the same mass flux and vapor quality, the flow patterns within ID 4 mm and 2 mm are significantly different. The turbulence between the vapor and liquid interface become gentle within ID 2 mm compared that within ID 4 mm by observation. At high mass fluxes, the HTCs within ID 2 mm tube are close to or even higher than that within ID 4 mm tube. When reducing the tube diameter, the influence of thermophysical properties, especially the surface tension on heat transfer is more obvious. Based on the laminar liquid film analytical solution and single phase forced convective heat transfer correlation, also considering the influence of surface tension and gravity, a new heat transfer correlation is developed with the experimental data using R1234yf, R134a and R32 within tube inner diameter 2 mm. The comparison shows that the mean deviation is 13.5%.