CAREER: A coupled multiscale study of phase change dynamics at curved liquid-vapor interfaces

液体-蒸汽表面在自然和工程设备中普遍存在。一杯咖啡、一棵树和一台空调，都有液体-蒸汽界面，并以某种形式进行“蒸发”。具有接触线的弯曲界面（例如液滴、微滴和薄膜）由于表面张力而表现出独特的性质，该表面张力显著地改变蒸发/冷凝。反过来，蒸发/冷凝移动液体-蒸气界面。当表面张力是主导力时，蒸发/冷凝和界面动力学之间的复杂耦合变得重要。然而，这种耦合仍然没有得到很好的理解。在该项目中，通过实验结合建模来研究液-气界面的动态稳定性。拟议的工作将推进对弯曲液体-蒸汽表面相变的基本理解，并使涉及薄膜和接触线的先进技术的发展成为可能。应用领域包括制造、沸腾、多孔介质输送、电子冷却、微型传热装置、脱碳、氢技术和食品-水-能源关系。PI还将在当地农贸市场建立一个“食用科学”推广计划，重点是厨房中的热流体科学。外联工作利用了辛辛那提大学的研究合作项目，以促进本科生的研究，同时鼓励国内少数民族学生的参与。此外，还将举办数据通信研讨会，为即将到来的数据驱动的就业市场培训学生“用数据讲故事”。蒸发薄膜对各种行业的设备开发至关重要。然而，仍然缺乏一个完整的理解，部分原因是由于相变和毛细作用/润湿动力学之间的复杂耦合。由于吸附膜的存在，弯曲界面呈现出不均匀的相变通量。该膜处于由对相变的热和机械贡献平衡的亚稳态条件。预计在纳米尺度下的热效应和机械效应的时空失配导致动态膜振荡，影响接触线运动、宏观稳定性和整体相变传热，并且是“粘滑”现象的主要贡献者。然而，由于涉及的长度尺度非常小，迄今为止还没有对热和机械因素进行直接测量。在这个项目中，动态相变驱动的稳定性的弯曲的液体-蒸汽界面是通过一个独特的实验和建模相结合的研究。新的实验将同时测量薄膜厚度/曲率和壁温与高时空分辨率在一个单一的双干涉设置。这是由一个瞬态多尺度计算模型组成的宏观尺度计算流体动力学子模型（10 μm），微观尺度薄膜子模型（10 μm）和纳米级分子动力学子模型（50 nm）的补充。使用一个耦合的方法，相变驱动（在）稳定性的影响，在微/纳米尺度上的宏观接触线运动将被调查。该项目将使人们对适当的边界条件有一个基本的了解，并使人们对多个长度尺度之间的复杂耦合有新的认识。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Liquid-vapor surfaces are ubiquitous in natural and engineered devices. A cup of coffee, a tree, and an air-conditioning unit, all have liquid-vapor interfaces and are undergoing “evaporation” in some form. Curved interfaces with contact lines (such as droplets, menisci, and thin films) exhibit unique properties due to surface tension that significantly alters evaporation/condensation. In turn, the evaporation/condensation moves the liquid-vapor interface. The intricate coupling between evaporation/condensation and interface dynamics becomes important when surface tension is the dominant force. However, this coupling is still not well understood. In the project, the dynamic stability of liquid-vapor interfaces is investigated using experiments coupled with modeling. The proposed work will advance fundamental understanding of phase change at curved liquid-vapor surfaces and enable the development of advanced technologies that involve thin films and contact lines. The application areas include manufacturing, boiling, porous media transport, electronics cooling, micro-scale heat transfer devices, decarbonization, hydrogen technology, and food-water-energy nexus. The PI will also establish an “edible science” outreach program at the local farmers market focused on thermo-fluid science in the kitchen. The outreach effort leverages the research co-op program at the University of Cincinnati to promote undergraduate research while encouraging domestic minority student involvement. In addition, data communication workshops will be developed to train students on “storytelling with data” for the upcoming data driven job market.Evaporating thin films are critical to the development of devices in a wide variety of industries. However, a complete understanding is still lacking, in part, due to the complex coupling between phase change and capillarity/wetting dynamics. A curved interface exhibits non-uniform phase change flux due to the existence of an adsorbed film. This film is in a metastable condition balanced by thermal and mechanical contributions to phase change. It is anticipated that a spatiotemporal mismatch of the thermal and mechanical effects at the nanoscale results in dynamic film oscillations, influences contact line motion, macroscale stability, and overall phase change heat transfer, and is a major contributor to the “stick-slip” phenomena. However, direct measurements of both the thermal and mechanical factors have not been made thus far due to the very small length scales involved. In this project, the dynamic phase change driven stability of the curved liquid-vapor interfaces is investigated through a unique combination of experiments and modeling. The novel experiment will simultaneously measure film thickness/curvature and wall temperature with high spatiotemporal resolution in a single dual-interferometry setup. This is complemented by a transient multiscale computational model consisting of a macroscale computational fluid dynamics submodel (10 μm), a microscale thin film submodel (10 μm) and a nanoscale molecular dynamics submodel (50 nm). Using a coupled approach, the influence of phase change driven (in)stability at the micro/nanoscale on macroscale contact line motion will be investigated. The project will enable a fundamental understanding of the appropriate boundary conditions and enable new insights into the complex coupling between multiple length scales.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.