非圆管管外降膜流动和换热特性分析

Analysis on falling-film flow and heat transfer characteristics outside non-circular tube

利用VOF方法，对圆管、椭圆管和扁管进行水平管外降膜流动二维数值模拟分析，研究Re数在1278-3406范围内3种管形对管外降膜传热和流动的影响。计算结果表明：在顶部冲击区和尾流区，管的曲率及其变化对流动和换热的影响很复杂，曲率较小会导致顶部冲击区的扰动面积增加和液膜厚度增加；相比圆管，椭圆管和扁管平均液膜厚度更小，传热性能更优；从平均液膜厚度上看，椭圆管最小，扁管次之；从平均传热系数上看，扁管最大，椭圆管次之。之所以椭圆管和扁管的平均液膜厚度和平均传热系数存在不一致，本文认为是由顶部冲击区对扁管的扰动影响要远大于椭圆管，且Re数取值较大，椭圆管的平均液膜厚度较小的优势无法凸显导致的。

Using the method of VOF, two-dimensional numerical simulation analysis on the horizontal tube falling film flow of circular tube, elliptical tube and flat tube is car- ried out. The effect of these three kinds of tube type on the heat transfer and flow of the falling-film outside the tubes is studied under the Re range of 1 278 to 3 406. The results show that the influence of the curvature and its change of the tube on the flow and heat transfer is very complicated in the top impact zone and the wake region. The smaller cur- vature will lead to the top of the impact zone at the disturbed area and the film thickness increase. Compared with the eireular tube, liquid film thickness of elliptical tube and flat tube are smaller and the heat transfer performance are better. From the perspective of av- erage liquid film thickness, the elliptical tube is the smallest and the flat tube is the sec- ond. As for average heat transfer coefficient, the flat tube is the biggest, the elliptical tube is the second. The reason why the average film thickness and the average heat trans- fer coefficient are inconsistent between the elliptical tube and flat tube, it ~s considered that the impact of the top impact zone on the flat tube is much larger than that of the ellip- tical tube. Besides that, when values of Re is larger, the advantages of the average liquid film thiekness of the elliptical tube is not prominent.