The Role of Interface Shape on Drag Reduction and Filtration using Superhydrophobic Surfaces

界面形状对超疏水表面减阻和过滤的作用

• 批准号: 1334962
• 负责人: Jonathan Rothstein
• 金额: $ 27.5万
• 依托单位: University of Massachusetts Amherst
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1334962&HistoricalAwards=false
• 关键词: Role; Interface; Shape; Drag; Reduction

1334962RothsteinIn the research outlined within this proposal, a new superhydrophobic surface design will be developed that is capable of actively controlling both the slip length and overall drag reduction under environmental conditions inaccessible to current superhydrophobic surfaces. Superhydrophobic surfaces are engineered by taking materials with micron or nanoscale surfaces roughness and chemically treating them to make them hydrophobic. Because of the hydrophobicity of these microscale and nanoscale protrusions, when water is brought in contact with a superhydrophobic surface, it does not fully wet the surface. Instead, it remains in contact with only the peaks of the surface topology resulting in a shear-free air-water interface. In this proposal, the focus will be on how the interface shape and deformation affects drag reduction, slip length and the potential of these surfaces to be used as novel filters.Intellectual Merit :One of the challenges of implementation of superhydrophobic surfaces in real-world applications is that the air-water interface is not robust. Under even modest static or dynamic pressures, the air-water interface can collapse, fully wetting the superhydrophobic surface and eliminating the desired drag reduction. In this proposal, a new microfluidic design is presented that will allow to extend the range and lifetime of superhydrophobic surface. This is achieved through an active back pressurization scheme that will stabilize the air-water interface even under large static pressures. The proposed microfluidic design will allow the investigation of the role of interface curvature on drag reduction, slip velocity and slip length. Access to the air trapped within the superhydrophobic surface will allow the probing of the stability and dynamics of the air water interface under unsteady flow conditions akin to those experienced in turbulent flows through the imposition of a periodic pressure pulse of variable amplitude and frequency. The design will also make it possible to replace the air with incompressible oil that is immiscible in water. With this liquid infused superhydrophobic surfaces the importance of the viscosity ratio between the two liquid phases can be studied on drag reduction while simultaneously maintaining the desired interface shape at arbitrary pressures without the need for back pressurization. Finally, the principles and strategy of back pressurization will be used to develop a series of low-porosity, high-permeability microfluidic filters from a regular array of posts, where the posts are uniquely designed such that their sides are superhydrophobic and support a shear-free air-water interface. The effect of post design and air interface shape will be studied on the permeability of the filter and its effectiveness at removing large and small contaminants from the flow.Broader Impacts:The proposed research program bridges fundamental experimental wetting phenomena and fluid dynamics with commercial and industrial applications where drag reduction could significantly reduce costs. Investigating paths towards back pressurized superhydrophobic surfaces will allow them to be adapted for high-pressure applications such as pumping and commercial shipping where the large static pressures make implementation a significant challenge. Finally, the proposal will develop a new class of high permeability, low porosity filters that can be quickly and broadly implemented in a number of commercial, biomedical and academic applications. The project has several educational components including involvement of undergraduates in the research through the hiring of three REU students who will work closely with the PI and graduate students on the grant. Additionally, we propose the continuation and further development of an ongoing multifaceted K-12 outreach program. This program will include the development of instructional modules, presentations and videos on fluid dynamics, surface tension and superhydrophobicity that will be presented and distributed to both middle and high school teachers and students through a series of weekend and weeklong outreach activities organized through the UMASS STEM program.

1334962Rothstein在这项提案中概述的研究中，将开发一种新的超疏水表面设计，该设计能够在当前超疏水表面无法达到的环境条件下主动控制滑移长度和总体减阻。超疏水表面是通过获取微米或纳米级表面粗糙度的材料，并对其进行化学处理使其疏水而设计的。由于这些微米和纳米级突起的疏水性，当水接触到超疏水表面时，它不会完全湿润表面。相反，它只与表面拓扑的峰部接触，从而形成无剪切的空气-水界面。在这项建议中，重点将放在界面形状和变形如何影响减阻、滑移长度以及这些表面作为新型过滤器的潜力。智能优点：在现实世界应用中实现超疏水表面的挑战之一是空气-水界面不牢固。即使在适度的静态或动态压力下，空气-水界面也会坍塌，完全润湿超疏水表面，从而消除所需的减阻效果。在这个方案中，提出了一种新的微流控设计，它将允许延长超疏水表面的范围和寿命。这是通过主动背压方案实现的，该方案即使在很大的静压下也能稳定空气-水界面。所提出的微流控设计将允许研究界面曲率对减阻、滑移速度和滑移长度的作用。进入被困在超疏水表面内的空气将允许在非稳定流动条件下通过施加可变幅度和频率的周期性压力脉冲来探测气水界面的稳定性和动力学，类似于在湍流中所经历的那样。该设计还将使人们有可能用不可压缩的、在水中不相容的油来取代空气。利用这种液体注入的超疏水表面，可以研究两液相之间粘度比对减阻的重要性，同时在任意压力下保持所需的界面形状，而不需要背压。最后，背压的原理和策略将被用于从规则的柱子阵列开发一系列低孔隙率、高渗透率的微流控过滤器，其中柱子的独特设计使得其侧面是超疏水的，并支持无剪切的空气-水界面。后期设计和空气界面形状将研究过滤器的渗透性及其去除气流中大小污染物的有效性。广泛的影响：拟议的研究计划将基本的实验润湿现象和流体动力学与商业和工业应用联系起来，在商业和工业应用中，减阻可以显著降低成本。研究背压超疏水表面的路径将使它们能够适应高压应用，如泵和商业航运，在这些应用中，巨大的静压使实施成为一个巨大的挑战。最后，该提案将开发一种新型的高渗透性、低孔隙率过滤器，可以在许多商业、生物医学和学术应用中快速和广泛地实施。该项目有几个教育部分，包括通过雇用三名REU学生让本科生参与研究，这些学生将在补助金问题上与私营部门和研究生密切合作。此外，我们建议继续并进一步发展正在进行的多方面的K-12外展计划。该计划将包括开发有关流体动力学、表面张力和超疏水行为的教学模块、演示文稿和视频，并通过UMassSTEM计划组织的一系列周末和一周的外展活动向初中和高中教师和学生展示和分发。