A study of pool boiling and falling-film vaporization with R-245fa/oil mixtures on horizontal tubes
A study of pool boiling and falling-film vaporization with R-245fa/oil mixtures on horizontal tubes
复制标题
DOI：
10.1016/j.ijheatmasstransfer.2018.12.176
复制
发表时间：
2019-04
影响因子：
5.2
通讯作者：
L. Chien;Yue-Lin Tsai;Ching-Hung Chang
中科院分区：
文献类型：
--
作者：
L. Chien;Yue-Lin Tsai;Ching-Hung Chang
研究了润滑油质量分数为1%、2%和5%的油/R-245 fa混合物的池沸腾和降膜蒸发特性。饱和温度范围为5至20 °C，热通量在6 kW/m2和55 kW/m2之间变化。对两种外径为19 mm的管进行了测试：光滑管和翅片高度为0.4 mm、翅片间距为0.233 mm、翅片间距为60 FPI的翅片管。对于池沸腾和降膜蒸发试验，由折射率传感器测量的局部油浓度与从重量测量获得的平均油浓度良好一致。在池沸腾条件下，光管的换热系数随油浓度的增加而减小。相比之下，对于翅片管，它随着油浓度的增加而增加，因为更显著的气泡泡沫，这促进了气泡成核。对于降膜蒸发，光滑管和翅片管的传热系数随着油浓度的增加而增加，因为泡沫在高油浓度下增强了气泡成核。然而，第二翅片管的传热系数随着油浓度在高的热通量（>20 kW/m2）下降低，这是因为由保持在顶部管上的液体引起的部分干燥。
This paper presents the effect of oil concentration on the pool boiling and falling-film vaporization of oil/R-245fa mixtures with 1%, 2%, and 5% lubricant mass fraction. The saturation temperature ranges from 5 to 20 °C, and the heat flux varies between 6 kW/m2and 55 kW/m2. Two types of tubes with a 19-mm outer diameter are tested: a smooth tube and a fin tube with 0.4-mm fin height, 60 FPI (fins per inch), and a 0.233-mm fin gap. For both the pool boiling and falling-film vaporization tests, the local oil concentration measured by the refractive index sensors is in good agreement with the average oil concentration obtained from the weight measurement. In case of pool boiling, the heat transfer coefficient for the smooth tube decreases with increasing oil concentration. In contrast, it increases with increasing oil concentration for the fin tube because of a more significant bubbly foam, which facilitates bubble nucleation. For the falling-film evaporation, the heat transfer coefficient increases with increasing oil concentration for both the smooth and fin tubes because the bubble nucleation is enhanced by the foam at a high oil concentration. However, the heat transfer coefficient for the second fin tube decreases with the oil concentration at a high heat flux (>20 kW/m2) because of the partial dry out caused by the liquid held on the top tube.