Lubricating Channel and Tube Flows - Fluid Sheathing using Textured Walls

很难想象有哪一天我们不能从管道运输的液体中受益。早上我们打开浴室的水龙头洗澡。早餐时，我们用的是保存在冰箱里的新鲜牛奶，冰箱里有一个复杂的冷却管道网络。去上班，我们使用的汽车或公共汽车的引擎依赖于从油箱中抽出的燃料。燃料本身通常以原油的形式通过管道进行远距离运输。我们不只运输一种液体。流动阻力是一项主要的工业成本，这一点并不令人惊讶，而且找到提高流速的方法可以在广泛的行业中带来更高的效率和新的应用。当水或其他液体沿通道或管道流下时，距离各壁等距离的中间位置的液体最容易流动。这是因为边界壁处产生的摩擦阻力。这个项目利用我们在流体力学和材料科学方面的研究成果，通过将流动的液体包裹在较低粘度的循环流体中来减少这种阻力，从而提高流量。在最近的工作中，我们表明，当一个实心球体被包裹在气泡中时，由于气泡中的“循环”流动，球体在液体中的运动受到润滑，这可以导致较低的摩擦阻力。在随后的模型中，我们证明了这个想法可以应用于核心液体通过管子或通道的流动，其中薄薄的护套边界层具有循环流动。这减少了边界处的摩擦阻力，并缓解了核心液体的流动(正如最近流体力学杂志的一篇文章，736(2013)卷1-4页所强调的那样)。在这个项目中，我们建议了两种在通道和管道中实验实现流动的方法，如上面模型中从理论上演示的那样。在这两种情况下，我们使用的边界墙具有坚固的纹理和自我修复的能力，因此应该是坚固的。在第一种情况下，适合于水(和类似的液体)的运输，我们使用一层薄薄的蒸汽层，最初是由疏水纹理表面造成的，但如果层局部坍塌，它可以自我愈合。这种自我修复可以通过两种方式实现：i)使用局部电解技术产生和更新气体层；ii)使用瞬时薄膜沸腾，也称为莱登弗罗斯特效应。在第二种情况下，适合于石油(和类似的液体)的运输，我们使用了一层薄的(不相容的)液层，保留在亲油的表面织构中；通过将织构设计为一个多孔的连接空间，注入的液体可以重新分布以自我愈合。该项目的工作涉及流体、材料科学和工程等多个学科。将使用一系列材料创新，从光刻产生的结构化通道到网格和缠绕膜。管道和管道将嵌入电极和加热器，或者注入液体，使它们能够自我修复边界。该项目将提供所需的理解，使未来能够开发新型的安全壁，以减少液体流动的摩擦阻力。这将在一系列工业和家庭背景下提供好处，并可能使我们还无法想象、但我们的工业合作伙伴可能有远见的应用受益。

It is difficult to imagine a day going by without us benefiting from liquids transported by tubes or pipes. In the morning we turn on the taps in the bathroom to wash. At breakfast we use milk kept fresh in a fridge that uses an intricate network of cooling tubes. To go to work we use cars or buses whose engines rely on fuel pumped from a tank. The fuel itself is often transported in its crude form over vast distances, in pipelines. We do not transport just one type of liquid. It is hardly surprising that resistance to flow is a major industrial cost, and that finding ways to improve the flow rate could lead to increased efficiencies and new applications in a wide range of industries. When water or other liquids flow down a channel or tube the liquid in the middle equidistant from each wall flows most easily. This is because of the frictional resistance that occurs at the boundary wall. This project uses insights from our research in fluid mechanics and materials science to reduce this resistance and therefore increase flow rate by sheathing the flowing liquid in a recirculating fluid of lower viscosity.In recent work we showed that when a solid sphere is encased in a gas bubble the motion of the sphere through a liquid is lubricated due to a 'recirculating' flow in the bubble, and this can lead to lower frictional resistance. In a subsequent model, we showed that this idea could apply to the flow of a core liquid through a tube or channel, with a thin sheathing boundary layer having a recirculating flow. This reduces frictional resistance at the boundary and eases the flow of the core liquid (as highlighted by a recent Journal of Fluid Mechanics "Focus on Fluids" article, vol. 736 (2013) pp. 1-4).In this project we suggest two ways of experimentally implementing flow in channels and tubes with recirculating boundary layer conditions as demonstrated theoretically in the models above. In both cases, we use boundary walls having a solid texture and the ability to self-repair and which should therefore be robust. In the first case, suitable for transport of water (and similar liquids), we use a thin vapour layer initially caused by a hydrophobic textured surface, but which can self-heal if the layer collapses locally. This self-healing can be achieved in two ways: i) by using a localised electrolysis technique to generate and refresh the layer of gas; ii) using instantaneous thin film boiling, also known as the 'Leidenfrost' effect. In the second case, suitable for transport of oils (and similar liquids), we use a thin (immiscible) liquid layer retained in an oleophilic surface texture; by designing the texture as a porous connected space the infused liquid can redistribute to self-heal. The work of this project is multidisciplinary across fluids, materials science and engineering. A range of materials innovations will be used from lithographically produced structured channels to meshes and wrapped membranes. Channels and tubes will have embedded electrodes and heaters, or be infused with liquids to enable them to self-repair their boundaries. The project will provide the understanding needed to allow future development of novel containment walls to reduce frictional resistance to the flow of liquids. This will provide benefits in a range of industrial and domestic contexts, and may benefit applications we cannot yet imagine, but ones that our industrial partners may have the vision to imagine.