Experimental investigation on the condensation heat transfer coefficient and frictional pressure drop of R-513A and R-134a in commercial refrigeration tubes

An experimental investigation to determine the average heat transfer coefficient (h_av) and frictional pressure drop (ΔP_F) characteristic of R-513A and R-134a in a smooth tube (ST) and micro-fin tube (MFT) is carried out. A 2500 mm long counter-flow tube-in-tube heat exchanger made of copper is used for conducting experiments. The ST and MFT with inner diameters (D_i) of 6.74 and 6.82 mm, respectively, are experimentally tested for various operating conditions such as saturation temperatures (T_sat = 40 to 50 °C), heat fluxes (q" =9.8 to 19.6 kW/m²), mass fluxes (G = 575 to 770 kg/m²s) and average vapor qualities (x_av = 0.2 to 0.9). The influence of q", G, and T_sat on h_av and ΔP_F are discussed. First, a comparison between R-513A and R-134a in an ST showed maximum reductions of 16 and 20 % in h_av and ΔP_F, respectively for R-513A, when compared to R-134a. Second, the MFT, due to its higher heat transfer area, resulted in 69 % and 120 % enhancements in h_av and ΔP_F, respectively, compared to that of an ST. Hence, the findings of this research provide information that is currently useful to the thermal industries, affirming that R-513A can be a suitable long-term alternative refrigerant.