Flow boiling heat transfer coefficient and pressure drop of R448A inside various multiport tubes: An experimental investigation and correlation assessment

Abstract

R448A, a safety class A1 a-zeotropic refrigerant blend with a GWP of 1390, is considered an efficient and environmentally friendly substitute for R404A in direct-expansion commercial refrigeration systems. Herein, we experimentally investigate the flow boiling heat transfer and pressure drop of R448A inside a multiport mini-channel tube. The experimental ranges of mass flux and heat flux are 100–500 kg/m2s and 3–15 kW/m2, respectively, and they cover the entire quality range at three different saturation temperatures of 3, 6, and 10°C. Three different test tubes are utilized in this study to evaluate the effect of tube geometry on the heat transfer, and their diameters range from 0.831 to 1.14 mm. The results show that mass flux has favorable effects on the heat transfer coefficient and pressure drop, while heat flux has a favorable effect on the heat transfer coefficient at low mass fluxes. As the saturation temperature decreases when the mass flux is high, the heat transfer coefficient and pressure drop increase. The tube with largest perimeter but the smallest hydraulic diameter has the highest heat transfer coefficient under the low mass flux condition. Heat transfer coefficient and pressure drop experimental data were compared with the models in literature, and the results of our statistical assessment indicate that the pure fluid model modified to account for the mixture effect produces the best results. Meanwhile, most pressure drop models produce reasonably good predictions. Additionally, a new correlation is proposed to predict the heat transfer coefficient in practical applications.