Saturated vapour condensation of R134a inside a 4 mm ID horizontal smooth tube: Comparison with the low GWP substitutes R152a, R1234yf and R1234ze(E)

This study performs the comparative analysis of R134a, R152a, R1234yf and R1234ze(E) condensation inside a 4 mm ID smooth tube. The experimental tests were carried out at three different saturation temperatures, 30, 35, and 40 °C, at different vapour qualities and mass velocities to evaluate the specific contribution of refrigerant mass flux, mean vapour quality, and condensation temperature (pressure). The frictional pressure drops exhibit great sensitivity to all the operating variables considered, while the condensation heat transfer coefficients show great sensitivity only to refrigerant mass flux and mean vapour quality. The transition between gravity dominated and forced convection condensation occurred in the range of the equivalent Reynolds number 10,000–20,000. The Friedel (1979) correlation was able to predict properly the whole set of frictional pressure drops data, while the Akers et al. (1959) model gave a very good estimation of the forced convection condensation heat transfer coefficients. R152a, R1234yf and R1234ze(E) show condensation heat transfer and pressure drop performances similar to those of R134a, therefore they seem valuable long-term low GWP substitutes for R134a.