Condensation and Droplet Dynamics Under Shear at Superhydrophobic Surfaces

超疏水表面剪切下的凝结和液滴动力学

• 批准号: 1805805
• 负责人: Brian Iverson
• 金额: $ 36万
• 依托单位: Brigham Young University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-09-01 至 2023-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1805805&HistoricalAwards=false
• 关键词: Condensation; Droplet; Dynamics; Under; Shear

When a water droplet meets a surface, it can spread and wet the surface or bead up. This depends on the wetting property of the surface. When waxing a car, it is desirable to prepare the surface such that droplets bead up and roll off. Droplet spreading, however, is desirable if paint is sprayed on a surface. A surface that causes the droplets to bead up is called superhydrophobic. Such surfaces exist in nature (for example, the lotus leaf) and can be also engineered artificially. If a cold surface is in contact with hot vapor, water droplets will condense on it. This is the principle used in many industrial processes that use condensers, such as in power plants. These droplets can merge to form a thin film. If the condenser surface is designed to be superhydrophobic, the condensed droplets will roll off and do not form a film. This will enhance the efficiency of the condenser. This project investigates the condensation process on superhydrophobic surfaces. It explores droplet formation and growth, droplet detachment, and heat transfer on superhydrophobic surfaces. This award provides opportunities for graduate and undergraduate students to participate in research. The team of investigators will also prepare learning modules for teachers.This research focuses on an investigation to characterize convective thermal transport and fluid dynamics of condensed droplets at superhydrophobic (SH) surfaces in shear flow. The fundamental hydrodynamic and convective thermal transport physics for liquid in contact with SH walls exhibit radical departures from classical behavior due to distinct alterations to the boundary conditions at the surface. Previous work in the principal investigator's lab has shown dramatic departures from classical behavior for quiescent droplets and reduced pressure drop for adiabatic, two-phase flows with superhydrophobic boundaries. It is expected that two-phase condensing flows in contact with SH surfaces will experience significant departure from classical behavior for two reasons. First, superhydrophobicity exerts enormous influence on the liquid-solid surface tension, especially for thin films and droplets, which dominate large portions of two-phase flow systems. Second, when drop-wise condensation occurs, the condensing heat transfer coefficient experiences an order of magnitude increase compared to that associated with film-wise condensation. If SH walls are employed where condensation is occurring, the length of channel over which drop-wise condensation prevails may be significantly increased due to alteration of surface adhesion forces, reduction in nominal droplet size, and increased droplet mobility. These effects have the potential to provide transformative breakthroughs in next generation condenser technologies. No previous study has systematically explored the influence of SH channel walls on the droplet behavior under shear in condensing flows.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.

当一个水滴遇到一个表面时，它可以扩散并润湿表面或成珠。这取决于表面的润湿性。当给汽车打蜡时，最好准备好表面，使水滴成珠并滚落。然而，如果将油漆喷涂在表面上，则液滴扩散是期望的。使液滴聚集的表面称为超疏水表面。这样的表面存在于自然界中（例如荷叶），也可以人工设计。如果一个冷的表面与热蒸汽接触，水滴就会在上面凝结。这是许多使用冷凝器的工业过程（如发电厂）所使用的原理。这些液滴可以合并形成薄膜。如果冷凝器表面被设计成超疏水的，则冷凝的液滴将滚下并且不形成膜。这将提高冷凝器的效率。本计画研究超疏水表面上的凝聚过程。它探讨了液滴的形成和生长，液滴分离，以及超疏水表面上的传热。该奖项为研究生和本科生提供了参与研究的机会。本研究的重点是研究剪切流中超疏水表面上凝结液滴的对流热传输和流体动力学特性。与SH壁接触的液体的基本流体动力学和对流热输运物理表现出从经典的行为，由于在表面的边界条件的明显改变激进的偏离。首席研究员实验室先前的工作已经显示出与静态液滴的经典行为的显著偏离，以及具有超疏水边界的绝热两相流的压降降低。由于两个原因，预计与SH表面接触的两相冷凝流将经历与经典行为的显著偏离。首先，超疏水性对液-固表面张力产生巨大影响，特别是对于占两相流系统大部分的薄膜和液滴。第二，当滴状冷凝发生时，冷凝传热系数与膜状冷凝相比经历一个数量级的增加。如果在发生冷凝的地方采用SH壁，则由于表面粘附力的改变、标称液滴尺寸的减小和液滴流动性的增加，液滴冷凝占优势的通道的长度可能显著增加。这些效应有可能为下一代冷凝器技术提供变革性突破。以前没有研究系统地探讨了SH通道壁对冷凝流中剪切作用下液滴行为的影响。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。

项目成果

Retention Forces for Drops on Microstructured Superhydrophobic Surfaces

• DOI: 10.1021/acs.langmuir.2c02290
• 发表时间: 2022-12-14
• 期刊: LANGMUIR
• 影响因子: 3.9
• 作者: Humayun, Shaur;Maynes, R. Daniel;Iverson, Brian D.
• 通讯作者: Iverson, Brian D.

Superhydrophobic, carbon-infiltrated carbon nanotubes on Si and 316L stainless steel with tunable geometry

硅和 316L 不锈钢上的超疏水碳渗透碳纳米管，具有可调的几何形状

• DOI: 10.1063/1.5034471
• 发表时间: 2018
• 期刊: Applied Physics Letters
• 影响因子: 4
• 作者: Stevens, Kimberly A.;Esplin, Christian D.;Davis, Taylor M.;Butterfield, D. Jacob;Ng, Philip S.;Bowden, Anton E.;Jensen, Brian D.;Iverson, Brian D.
• 通讯作者: Iverson, Brian D.