Department of Chemical and Materials Engineering and ‡Department of Mechanical Engineering, University of Alberta , Edmonton, Alberta, Canada T6G 1H9.
Langmuir. 2017 May 9;33(18):4578-4591. doi: 10.1021/acs.langmuir.7b00616. Epub 2017 Apr 26.
Although evaporation is considered to be a surface phenomenon, the rate of molecular transport across a liquid-vapor boundary is strongly dependent on the coupled fluid dynamics and heat transfer in the bulk fluids. Recent experimental thermocouple measurements of the temperature field near the interface of evaporating water into its vapor have begun to show the role of heat transfer in evaporation. However, the role of fluid dynamics has not been explored sufficiently. Here, we have developed a mathematical model to describe the coupling of the heat, mass, and momentum transfer in the fluids with the transport phenomena at the interface. The model was used to understand the experimentally obtained velocity field in the liquid and temperature profiles in the liquid and vapor, in evaporation from a concave meniscus for various vacuum pressures. By using the model, we have shown that an opposing buoyancy flow suppressed the thermocapillary flow in the liquid during evaporation at low pressures in our experiments. As such, in the absence of thermocapillary convection, the evaporation is controlled by heat transfer to the interface, and the predicted behavior of the system is independent of choosing between the existing theoretical expressions for evaporation flux. Furthermore, we investigated the temperature discontinuity at the interface and confirmed that the discontinuity strongly depends on the heat flux from the vapor side, which depends on the geometrical shape of the interface.
虽然蒸发被认为是一种表面现象，但分子在液-气边界的传输速率强烈依赖于体相中的流场和传热的耦合。最近对蒸发水进入蒸汽时界面附近温度场的热电偶实验测量开始显示传热在蒸发中的作用。然而，流场的作用尚未得到充分的探索。在这里，我们开发了一个数学模型来描述流体中的热、质量和动量传递与界面处传输现象的耦合。该模型用于理解在各种真空压力下从凹月面蒸发时从实验中获得的液体中的速度场和液体及蒸汽中的温度分布。通过使用该模型，我们表明，在我们的实验中，在低压下，一个相反的浮力流抑制了蒸发过程中液体中的热毛细流。因此，在不存在热毛细对流的情况下，蒸发由向界面的传热控制，并且系统的预测行为与在现有的蒸发通量理论表达式之间进行选择无关。此外，我们研究了界面处的温度不连续性，并证实该不连续性强烈依赖于来自蒸汽侧的热通量，而热通量又取决于界面的几何形状。
