Flow boiling of zeotropic mixture R245fa/R141b inside horizontal smooth tube and microfin tube

Abstract

In this study, R245fa/R141b with mass ratio of 0/1, 0.25/0.75, 0.5/0.5, 0.75/0.25 and 1/0 is examined by focusing on the boiling heat transfer coefficients and fractional pressure drops inside a horizontal smooth tube and microfin tube. The inner diameter of smooth tube and equivalent diameter of microfin tube are 8.6 mm. In this experiment, mass flux, heat flux, saturation pressure and vapor quality are in the range of 100–300 kg m−2 s−1, 7–15 kW m−2, 0.15–0.25 MPa and 0–1.0, respectively. The results show that heat transfer coefficients of R245fa/R141b in smooth tube are lower than that of R245fa and R141b at low vapor quality, but higher than that of pure refrigerant at high vapor quality. While frictional pressure drop of the mixture is larger than that of the pure refrigerant. Among four empirical correlations, the Gungor-Winterton with Shah correlation and Müller-Steihagen and Heck correlation agree well with measured heat transfer coefficients and frictional pressure drops of R245fa/R141b, respectively. In the microfin tube, Yun et al. correlation, Newell and Shah correlation can well predict heat transfer coefficient and frictional pressure drop of R245fa/R141b, respectively. Compared with the smooth tube, the heat transfer coefficients of mixtures in the microfin tube increase by 60%–80%, while the frictional pressure drops of mixture in the microfin tube increase by 40%–60%. In addition, mixtures can achieve higher comprehensive performance inside microfin tube than that of pure refrigerants. Among these mixtures, R245fa/R141b (0.25/0.75) has the highest efficiency factor of 1.769.