R513A condensation heat transfer inside tubes: Microfin tube vs. smooth tube

The imminent phase-down of the common refrigerant R134a is calling for lower GWP alternatives. Real alternatives must have a lower global warming impact and they should be not flammable. In this context, R513A (azeotropic mixture made of R1234yf and R134a at 56% and 44% by mass) has been proposed as alternative to R134a due to its similar thermodynamic and transport properties and due to its lower GWP. This paper proposes a direct comparison between the thermal performances of a 3.5 mm ID smooth tube and those of a 3.4 mm ID microfin tube, during R513A condensation under the same working conditions of vapor quality (from 0.10 to 0.99), of mass velocity (from 100 to 1000 kg m−2 s−1), and of saturation temperature (30 °C and 40 °C). The comparison permits to highlight in which working conditions the microfin tube leads to a real heat transfer augmentation which is higher than the mere increase of heat transfer area. In the end, the experimental heat transfer coefficients, both for the smooth tube and for the microfin tube, are compared against values calculated with empirical correlations from the open literature.