Effect of surface tension on deformation of free falling drops

doi:10.11949/j.issn.0438-1157.20151867

Abstract

Abstract:

The deformation of moving drop plays an important role in its evaporation and combustion. Surface tension is one of the factors which influence the deformation. For investigating the effect of surface tension on the deformation, the low concentration SDBS surfactant water based solutions with surface tension in the range of 30 to 72 mN·m^-1 are used as the experimental liquid. The different sizes of needles are employed to get drops with diameter at 3-5 mm. The image processing is utilized to analyze the drop shape by using a high speed camera (Phantom V211, 1000 pps,800×600 pixel). The complete drop falling image process is assembled by 9 sections at different position with different drops. A stable drop formation time of (2.4±0.1) s makes the dispersion of size and initial velocity of these drops meet the experimental accuracy. Analyzing the experimental data by Image-pro plus obtains the semi-empirical correlations of Eötvös number (Eo). The results show that the period and amplitude of drop deformation decrease with increasing surface tension. Furthermore, the momentum transfer inside the drop causes initial transient impulse, which makes the drop periodic deformation when it falls down.

Key words: evaporation, surfactants, surface tension, momentum transfer, drop, deformation, Eötvös number

摘要：

液滴运动过程中的形状变化对液滴的蒸发、燃烧等过程有重要影响,表面张力是影响其形状变化的因素之一。为研究表面张力对液滴形变的影响规律,采用低浓度的表面活性剂(十二烷基苯磺酸钠SDBS)配制表面张力为30~72mN·m^-1的水溶液。利用不同外径的针管得到3~5mm粒径的液滴。高速摄像机(PhantomV211,1000pps,800×600pixel)对这些液滴在自由落体过程中的形变规律进行了可视化实验研究,得到了关于Eötvös数(Eo)的半经验关系式。实验结果表明,液滴在自由落体过程中会形成周期性振动形变,振动周期和振幅随表面张力增大而减小。进一步研究发现,初始时液滴形成并断裂所引起的瞬态冲量使液滴内部动量传递进而表现出周期性振动形变。

关键词: 蒸发, 表面活性剂, 表面张力, 动量传递, 液滴, 形变, Eötvös数

CLC Number:

O353.1

DING Siyuan, WANG Ruixiang, XU Rongji, ZHANG Yihao, CAI Jichi. Effect of surface tension on deformation of free falling drops[J]. CIESC Journal, 2016, 67(6): 2495-2502.

丁思源, 王瑞祥, 徐荣吉, 张一灏, 蔡骥驰. 表面张力对自由落体液滴形变的影响[J]. 化工学报, 2016, 67(6): 2495-2502.

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