2025 年 20 巻 2 号 p. 25-00277
This work evaluates the evaporation heat transfer of R455A, a low Global Warming Potential (GWP) refrigerant, in a horizontal tube. As high-GWP refrigerants like R410A and R404A are being phased down under stricter environmental regulations, R455A has gained attention as a potential alternative. With a GWP of around 146, it not only meets regulatory requirements but also offers thermodynamic properties comparable to R404A. However, experimental data for small-diameter tubes under low saturation temperature (pressure) and low heat flux conditions remain limited. Therefore, this work investigates the evaporation heat transfer coefficient (HTC) of R455A under conditions representative of compact systems and low-temperature operation. Experiments were carried out in a 1 m long smooth horizontal tube with an inner diameter of 4.6 mm. In the experiments, the parameters covered were mass flux (200–400 kg/m2·s), heat flux (10–20 kW/m2), and saturation temperature (–10 °C to 10 °C), while the vapor quality (x) varied from 0.1 to 0.9 for HTC measurement. It was observed that HTC decreased with increasing saturation temperature but increased with both mass flux and vapor quality. The pressure drop decreased with higher saturation temperature and increased with higher mass flux. Relative to other correlations, the Kim and Mudawar (2013) model showed superior prediction accuracy. These findings provide experimental evidence supporting the practical applicability of R455A as an alternative refrigerant.
