Abstract:

During the condensation of certain mixed vapors, the temperature gradient of the heat transfer surface causes an imbalance in the concentration of the condensate and the surface tension, thereby driving the condensed droplets to spontaneously move. The necessary condition for this kind of phenomenon is the evident bulk temperature gradient on the heat transfer surface. However, in this study, the spontaneous movement of condensate drop was initially observed on the heat transfer surface with uniform temperature distribution, during the condensation of water-ethanol binary vapor mixture. The comparison and analyzation were performed on the characteristics of drop movement between the condensate drops with and without evident initial velocity on uniform temperature surface. It was confirmed that the spontaneous movement occurred when the condensate drops have evident initial velocity, while the random movement occurred when the drops didn t have evident initial velocity (no spontaneous movement). Finally, it was verified the inference that the driven force for the spontaneous movement of condensate drops on uniform temperature surface was, the local temperature distribution and the resulting local imbalance of surface tension around the drops.

Key words: Marangoni condensation, water-ethanol binary mixture, temperature gradient, surface tension gradient, spontaneous drop movement

摘要：

在某些混合蒸气的冷凝过程中，传热面温度梯度导致冷凝液浓度及表面张力不平衡，从而驱动冷凝液滴产生自发移动现象。此现象产生的前提为传热面具有整体温度分布，即传热面从一侧表面的相对低温状态，随着表面位置变化逐渐过渡到另一侧的相对高温状态，而本论文在水-酒精混合蒸气的冷凝过程中，观测到在均匀温度传热面上也会发生冷凝液滴自发移动现象。通过对具有和不具有初速度的冷凝液滴在均匀传热面上的不同移动特性进行比较分析，确认了具有明显初速度的冷凝液滴在均匀温度领域产生自发移动现象，而无初速度液滴则产生无序运动（非自发移动）。从而验证了在均匀温度传热面，冷凝液滴自发移动的驱动力为液滴移动同时其周围形成的局部温度分布和局部表面张力不平衡的推测。

关键词: Marangoni凝结, 水-酒精二元混合物, 温度梯度, 表面张力梯度, 液滴自发移动