Nucleate boiling of low GWP refrigerants on highly enhanced tube surface

This paper presents the experimental investigation of the heat transfer performance of alternative low GWP (Global Warming Potential) refrigerants during nucleate boiling. The fluids used in the study are R-1234ze, R-1233zd(E), and R-450A. The first two HFOs (hydro-fluoro-olefins) have a GWP index less than or equal to 1 while the zeotropic blend R-450a has a GWP index of 547. This study compared R-1234ze and R-450A to their targeted replacement, R-134a, and compared R-1233zd(E) to R-123 using a highly enhanced tube surface. Tests were conducted at a heat flux range of 10-110 kW/m2 and at a saturation temperature of 4.44 °C. Results show that the performance of R-1234ze is very similar to that of R-134a while R-450a shows performance degradation of 28% compared to R-134a. For the R-123 replacement, R-1233zd(E) demonstrates a noticeable 19% performance increase. The results section includes a power-law model to predict the refrigerant-side heat transfer coefficient for all five fluids. Meanwhile, the heat flux used in the model covers a range of 10-60 kW/m2, a typical range of interest for refrigerant evaporator design.