Flow boiling heat transfer and pressure drop data of non-azeotropic mixture R455A in a horizontal 6.0 mm stainless-steel tube

This paper carries out an experimental investigation on R455A, a low GWP (148) non azeotropic mixture, to determine its performance in terms of flow boiling heat transfer coefficient and pressure drop in a smooth circular horizontal stainless-steel tube, with an internal diameter of 6 mm. The effect of the operating parameters, such as mass flux (from 300 to 500 kg‧m−2‧s−1), bubble saturation temperature (from 10 to 40 °C), heat flux (from 5 to 40 kW‧m−2) and vapor quality (between 0 and 1) is analyzed. Results show an increase of the heat transfer coefficient with mass and heat flux, while it decreases with saturation temperature. On the other hand, pressure drop increases with mass flux, and decreases with bubble saturation temperature. An assessment of several predictive methods from literature is finally conducted. Two-phase heat transfer methods based on an exclusive convective contribution can predict quite well the experimental results, while all other methods improve their statistics once a glide-related modification on the nucleate boiling contribution is assumed. The fictional pressure gradient results are well fitted with the separated flow model of Müller Steinhagen and Heck and with the Cicchitti two-phase viscosity expression considering a homogeneous flow approach.