Effect of curvature and undercooling degree of surface on behavior of droplet spreading

doi:10.11949/j.issn.0438-1157.20160224

Abstract

Abstract:

To considerate the harmness and the icing type of the power transmission line, the glaze was the most deadly harmness to the power transmission line than the other icing types. Dynamic characteristics of droplets impacting on the solid surface has a significant effect on the mechanism of heat and mass transfer during the phase transformation as well as the mechanism of the conductor ice coating. The evolution behaviors of droplets impacting on the different temperature curved surfaces were investigated by the visional experiments. It showed that the effects of the different undercooling degree and the surface curvature on the law of droplet spreading behavior. The results indicated that the circumferential liquid film spread out better and the axial one did worse with the increase of cylindrical surface curvature. Increasing the surface undercooling degree, the droplet spread worse and oscillation time became shorter and the upper film freeze faster on the undercooling surface. However, the droplet impacting on undercooling surface spread better than that at ambient temperature. It was speculated that there was an ice film formed rapidly at the bottom of the droplet when it spread on the cold solid surface by analyzing the effects of the surface tension and viscosity of water droplet on the spread behavior. The ice film, which obviously altered the interface energy between the solid phase and liquid phase, made the droplet spread easily. The ice film was distinctly observed at the droplet recoiling stage. The conclusion can provide theoretical reference for glaze ice on the conductors.

Key words: icing, droplet, impact, curved surface, viscosity, phase change, condensation

摘要：

从覆冰类型及危害来看，雨凇对于导线产生的危害是最为严重和致命的。液滴撞击壁面的动力学特性对于相变凝固过程中的热质传递有重要影响，进而影响导线覆冰的特性。通过对比液滴撞击常温及过冷弯曲壁面过程中的液滴行为演变的异同，获得了表面过冷度和曲率大小对液滴铺展行为的影响规律。实验结果表明，随着圆柱曲面曲率的增加，周向上液膜铺展更好，轴向上液膜铺展更差。对于低温壁面上液滴的铺展过程，增加表面的过冷度，液滴的铺展更差，液滴振荡弛豫时间更短，表层液膜结冰速率加快。然而，低温壁面上液滴的铺展好于常温壁面上液滴的铺展，通过分析温度对液滴表面张力和黏性的影响规律，推论在铺展过程中，较低的壁面温度使得液滴底层快速形成了一层冰膜，改变了液固之间的界面能，使得液滴更易于铺展。在液滴回缩阶段，可明显观察到底层结冰的现象。该结论可为导线雨凇结冰提供理论参考。

关键词: 覆冰, 液滴, 碰撞, 曲面, 黏度, 相变, 凝固

CLC Number:

TQ028.8

FAN Yao, WANG Hong, ZHU Xun, HUANG Geyong, DING Yudong, LIAO Qiang. Effect of curvature and undercooling degree of surface on behavior of droplet spreading[J]. CIESC Journal, 2016, 67(7): 2709-2717.

范瑶, 王宏, 朱恂, 黄格永, 丁玉栋, 廖强. 壁面曲率及过冷度对液滴铺展特性的影响[J]. 化工学报, 2016, 67(7): 2709-2717.

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