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 (hav) and frictional pressure drop (ΔPF) 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 (Di) of 6.74 and 6.82 mm, respectively, are experimentally tested for various operating conditions such as saturation temperatures (Tsat = 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 (xav = 0.2 to 0.9). The influence of q", G, and Tsat on hav and ΔPF are discussed. First, a comparison between R-513A and R-134a in an ST showed maximum reductions of 16 and 20 % in hav and ΔPF, 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 hav and ΔPF, 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.