椭圆形针肋表面冷凝液滴分布特征的实验研究

Experimental study on condensate distribution on surface of ellipticalpin-fin plates

对6组不同几何参数的椭圆形针肋表面上的蒸汽冷凝过程进行了可视化实验研究,利用黑白二值化方法对针肋表面冷凝液滴的表面覆盖率进行了计算,分析了横向肋间距和肋高对冷凝液滞留、表面覆盖率和液滴脱落周期的影响.结果表明,当肋高较小时,随着横向肋间距的增加,针肋对冷凝液的滞留效应减弱;当肋高较大时,针肋对冷凝液的滞留作用变强,但是随着肋间距的增加,一些大液滴更难以脱落. 6组针肋板的表面覆盖率曲线均出现了大幅度下降,但发生大幅度下降的时间不同.随着横向肋间距和肋高的增大,表面覆盖率出现大幅度下降的时间均有所推迟.随着横向肋间距的增大,肋高对表面覆盖率平均值的影响逐渐减小.当横向肋间距较小时,肋高增大,液滴的脱落周期变短;当横向肋间距较大时,肋高的增大均使得脱落周期有所变长.实验结果可为针肋板的设计及实际工程应用提供参考.

The condensation process of steam on six groups of elliptical pin-fin surfaces with different geometric parameters was studied by visual experiments. The surface coverage of condensate droplets on the pin-fin surface was calculated by using the black-and-white binarization method. The effects of the horizontal pin spacing and the pin height on the condensate retention, the surface coverage and the droplet shedding period were analyzed. The results show that when the pin height was small, the retention effect of pin-fin on the condensate decreases with the increase of horizontal pin spacing. When the pin height is larger, the retention effect of the pin-fin on the condensate becomes stronger. However, with the increase of horizontal pin spacing, some large droplets are more difficult to fall off. The surface coverage curves of six pin-fin surfaces all show sharp declines, but the occurrence time of the sharp decline is different. With the increase of the horizontal pin spacing and the pin height, the occurrence time of the sharp decline is delayed. With the increase of horizontal pin spacing, the influence of pin height on average surface coverage decreases gradually. When the horizontal pin spacing is small, the shedding period becomes shorter. However, when the horizontal pin spacing is larger, the shedding period becomes longer with the increase of the pin height. Thus, experimental results can provide a reference for the design and practical engineering application of pin-fin plates.