Stabilizing the Advancing Front of Thermally Driven Climbing Films.
Stabilizing the Advancing Front of Thermally Driven Climbing Films.
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DOI：
10.1006/jcis.1998.5499
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发表时间：
1998-07
影响因子：
9.9
通讯作者：
Dawn E. Kataoka;S. Troian
中科院分区：
文献类型：
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作者：
Dawn E. Kataoka;S. Troian
从热力学原理可知，液体的表面张力随着温度的升高而降低。这种特性可以用来迫使液体膜爬上垂直的基底，其下端保持比顶部更温暖。表面张力的垂直梯度产生表面剪切应力，该表面剪切应力导致液膜在较高表面张力的方向上自发地向上扩展。实验研究表明，大的温度梯度的应用程序产生一个薄的攀爬膜，其前缘发展成一个明显的毛细边缘，分裂成垂直溪流。相反，较小的温度梯度产生较厚的膜，其轮廓朝向基板单调减小，没有边缘或随后的膜破裂的证据。我们以前在线性稳定性分析中已经表明，当膜足够薄或剪应力足够大，重力效应可以忽略不计时，爬升膜可以在前缘发生指进不稳定性。在这项工作中，我们表明，较厚的薄膜，经历显着排水不能形成一个毛细边缘和传播稳定的方式。重力排水有助于促进直线前进的前沿和完整的表面覆盖。我们对爬升膜的整个形状和稳定性的数值预测与Ludviksson和Lightfoot多年前发表的大量实验（AIChE J. 17，1166（1971））是一致的。我们建议，消除毛细管边缘的逆流的存在下，可以提供一个简单的和一般的技术，用于稳定在其他几何形状的热驱动膜。版权所有1998学术出版社。
As known from thermodynamic principles, the surface tension of a liquid decreases with increasing temperature. This property can be used to force a liquid film to climb a vertical substrate whose lower end is held warmer than the top. The vertical gradient in surface tension generates a surface shear stress that causes the liquid film to spread upward spontaneously in the direction of higher surface tension. Experimental investigations have shown that the application of a large temperature gradient produces a thin climbing film whose leading edge develops a pronounced capillary rim which breaks up into vertical rivulets. In contrast, smaller temperature gradients produce thicker films whose profiles decrease monotonically toward the substrate with no evidence of a rim or subsequent film breakup. We have previously shown within linear stability analysis that a climbing film can undergo a fingering instability at the leading edge when the film is sufficiently thin or the shear stress sufficiently large for gravitational effects to be negligible. In this work we show that thicker films which experience significant drainage cannot form a capillary rim and spread in stable fashion. Gravitational drainage helps promote a straight advancing front and complete surface coverage. Our numerical predictions for the entire shape and stability of the climbing film are in good agreement with extensive experiments published years ago by Ludviksson and Lightfoot (AIChE J. 17, 1166 (1971)). We propose that the presence of a counterflow which eliminates the capillary rim can provide a simple and general technique for stabilizing thermally driven films in other geometries. Copyright 1998 Academic Press.