Comparative investigation of R1270, R290, and R600a boiling in microfin and smooth tubes

This study investigates the comparative analysis performance of three environmentally friendly refrigerants, R1270, R290, and R600a, in the context of flow boiling heat transfer (FBHT) and pressure gradients. The experiments employ copper microfin and smooth tubes, operating under varying conditions, including saturation temperatures (T_sat) of 6 and 15 °C, heat fluxes (HF) ranging from 13 to 30 kW.m⁻², mass fluxes (MF) spanning 187 to 427 kg.m⁻².s⁻¹, and vapor quality from 0.1 to 1.0. Both tube types share identical dimensions - an outer diameter, inner diameter, and length of 7 mm, 6.14 mm, and 500 mm, respectively - facilitating a focused investigation into the impact of microfins on flow boiling characteristics. The results highlight noteworthy differences among the refrigerants, with the microfin tube exhibiting substantial enhancements in heat transfer coefficient (HTC), particularly pronounced with R1270 and R290. At the same time, the R600a demonstrates more HTC improvements than the smooth tube. Additionally, the microfin tube increases pressure gradients. The average enhancement factor (EF) for R600a, R290, and R1270 are 2.15, 1.95, and 1.9, respectively, while the average penalty factor (PF) for R600a, R290, and R1270 are 1.25, 1.3, and 1.35, respectively. Comparative analyses with established literature correlations validate the experimental findings.