A Study on the Surface Tension Effect on Condensation Phenomena on the Thin Vertical Tubes

对垂直布置的细管湿润外表面的蒸汽凝结现象进行了观察和测量。凝析液的表面张力影响凝析液的模式，由于薄管表面张力的不稳定，凝析液表面出现波浪状。对于外径1.0 mm的管道，可以观察到均匀厚度的光滑冷凝水表面，而对于直径0.5 mm的管道，则可以观察到厚度不均匀的波浪形状。随着管径的减小，波纹形状变得明显。低凝结速率下的不稳定性波长与Rayleigh自由液体射流分析的波长几乎一致，但随着凝结速率的增加和从顶部开始的轴向长度的增加，不稳定性波长也随之增加。此外，还利用运动图像分析技术对浓液峰间形成的冷凝膜厚度进行了精确测量。利用VOF方法对液体厚度的测量结果与数值分析结果进行了比较。在此基础上，研究了细管外表面凝结物的特性。

Observation and measurement of steam condensation phenomena on the wetted outer surface of thin tubes arranged vertically were conducted. The condensate modes were affected by surface tension of the condensate, and the wavy shape of the condensate surface appeared due to surface tension instability on the thin tubes. While smooth condensate surface of uniform thickness was observed for tubes having an outer diameter of 1.0 mm, a wavy shape with non-uniform thickness was observed for tubes of 0.5 mm in diameter. The wavy shape became distinct with a decrease in tube diameter. Although the wavelengths of the instability at low condensation rates almost coincided with those obtained from analysis on free liquid jet by Rayleigh, they increased with increases in the condensation rate and axial length from the top.Furthermore, the precise measurement of thin condensate film thickness formed between the thick liquid humps by using the motion picture analysis. Also, the measuring results of liquid thickness were compared with the numerical analysis by using VOF method.On the basis of those results, the characteristics of condensate formed on the outer surface of thin tubes were investigated.