水平圆管外降膜流动与传热过程研究

Study of Falling Film Flow and Heat Transfer Process outside Horizontal Circular Tubes

摘要: 对水平圆管管外降膜流动过程进行数值研究，分析了换热管径为19 mm时不同喷淋密度和壁面温差对管外液膜厚度、液膜表面速度、温度分布以及传热系数的影响。研究结果表明，液膜厚度及管外局部传热系数受轴向位置、周向角度、壁面温差和喷淋密度等因素影响较大。液膜干涸区域易出现在周向角度为130˚150˚附近；液膜厚度随着受热而减小，壁面温差的增加会加剧Marangoni效应，使局部液膜厚度有所增加。管外局部传热系数沿周向角度的分布呈递减趋势，在周轴向角度为130˚150˚时最低，而在管底部时略有回升；平均传热系数随喷淋密度和壁面温差的增加而增大;当喷淋密度为0.022 kg(ms)⁻¹时，壁面温差从10℃增加到20℃，平均换热系数增加了37%。

Abstract: A numerical study of the falling film flow process outside the horizontal circular tube was carried out to analyze the effects of different spray densities and wall temperature differences on the thickness of the liquid film outside the tube, the surface velocity of the liquid film, the temperature distribution, and the heat transfer coefficient for a heat exchanger tube diameter of 19 mm. The results show that the liquid film thickness and local heat transfer coefficient outside the tube are greatly affected by axial position, circumferential angle, wall temperature difference and spray density. The liquid film drying region is easy to appear near the circumferential angle of 130° 150°; the liquid film thickness decreases with the heat, and the increase of the wall temperature difference will exacerbate the Marangoni effect, which will increase the local liquid film thickness. The local heat transfer coefficient outside the pipe shows a decreasing trend along the distribution of circumferential angle, which is the lowest when the circumferential angle is 130°150°, and slightly recovered at the bottom of the pipe; the average heat transfer coefficient increases with the increase of the spray density and the wall temperature difference; when the spray density is 0.022 kg(ms)^-1, the wall temperature difference increased from 10°C to 20°C, and the average heat transfer coefficient increased by 37%.