Abstract:

An experimental investigation on the boiling heat transfer of a new mixture R245fa/R141 in a 10 mm horizontal smooth tube was conducted. The boiling heat transfer performances of R245fa, R141b and their mixture were investigated, and the prediction accuracy of four commonly used correlations was compared. The results show that the boiling heat transfer coefficients of pure and mixture increase with the increase of mass flow rate and heat flux, and decrease with the increase of saturation pressure. Besides, the boiling heat transfer coefficient of working fluids increases first and then decreases with the increase of vapor quality, which indicates that there is transitional vapor quality. What s more, the value of transitional vapor quality of R245fa/R141b is greater than that of R245fa and R141b. When the vapor quality is less than 0.55, the heat transfer coefficient of the mixture is lower than that of the pure working fluid. On the contrary, when the vapor quality is greater than 0.55, R245fa/R141b can achieve a higher heat transfer coefficient. The boiling heat transfer coefficient of R245fa/R141b increases with the increase of R245fa mass fraction. Among several selected correlations, the Gungor-Winterton correlation can predict the boiling heat transfer coefficient more accurately, and the average absolute error is 16.67%.

Key words: horizontal smooth tube, binary mixture, phase change, prediction correlation, heat transfer

摘要：

针对新型混合工质R245fa/R141b，开展水平光滑管(外径10 mm)内工质沸腾换热特性的实验研究，对比纯工质与混合工质的换热性能及4种常用关联式的预测精度。结果表明：纯工质与混合工质的沸腾传热系数均随质量流速和热通量的增加而增大，随饱和压力的增加而减小；随干度的增加，沸腾传热系数均先增大后减小，即存在“过渡干度”，且混合工质的过渡干度大于纯工质；干度小于0.55时，混合工质传热系数小于纯工质；干度大于0.55后，混合工质的传热系数更高；随R245fa质量分数的增加，混合工质的沸腾传热系数增大。在所选关联式中，Gungor-Winterton关联式能准确地预测工质在光滑管内的沸腾换热特性，平均相对误差为16.67%。

关键词: 水平光滑管, 二元混合物, 相变, 关联式, 传热