S.E.C.R.E.T. : Shear Extension Combined Rheology Experimental Techniques

秘密。

• 批准号: EP/X028089/1
• 负责人: Richard Hodgkinson
• 金额: $ 52.58万
• 依托单位: University of Sheffield
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FX028089%2F1
• 关键词: S.E.C.R.E.T.; Shear; Extension; Combined; Rheology

Are you familiar with piping icing onto cakes? Would you be surprised to know that our understanding of many of the flow processes taking place whilst you lay down beads are not actually fully understood?Wherever a fluid is "strained" - slid, squashed, or changed in shape, it responds with a force, or "stress". Studying fluid response to straining is known as "rheology". These forces influence how the rest of the fluid nearby moves, making it vital information to computationally model fluid flow problems: models that inform processing molten plastic into everyday objects, or our understanding of how a spider spins it's silk. Colloquially, rheology describes how "thick" a fluid is, but fluids can have hugely varying behaviours, all dependent on microscopic interactions occurring in the fluid. The flow and straining occurring through a piping nozzle is quite complicated. Near the nozzle walls, icing is mainly undergoing a "shearing" flow, where fluid layers slide over one another - this flow type is well understood and measurable in a lab. Near the centre, the fluid is experiencing "extension", where fluid packets are stretched in the flow direction and squashed in other directions. The nozzle tapering causes this. This extensional flow is less well understood or measureable, but in the last 50 years our understanding has improved, mainly because of the plastics industry. Between the location of the wall and the centre of the flow, simultaneous shear and extension exists - we call this a "kinematically mixed" flow. Not stirred, but mixed as in more than one type of straining present. To date, our only approach to validate models in this region has been to measure fluid velocity (for example) and see if our mathematical model predictions agree - models based on data from pure shear or extensional flows. Until now there hasn't been a way to unambiguously isolate and measure separate stresses within the middle of such flows, something that depends, via microscopic interactions in the fluid, on both shear and extension together. Making the situation even more complex, icing is an example of a "suspension", a class of fluids that display what is called a "yield" stress - it only flows when an applied stress exceeds some threshold. This allows icing to flow when the piping bag is squeezed, but means it resists flow under gravity after being deposited on a cake.The behaviour of suspensions under extension is particularly poorly understood at this time, versus what we know for plastics, let alone their behaviour under kinematically mixed flows. Not just icing cakes is affected. 3D printing cement to build novel houses is conceptually the same process, scaled up, and must handle much more stress without flowing. Depositing solder paste in electronics manufacture has similarities, as does processing graphene fibres into next-gen high performance materials. Plastics processing, a mixed flow, is not perfectly understood, and even lubricant flow in engine bearings is mixed. In fact, few flows are purely shear or extensional, and lacking a method to directly see how fluid stresses are responding under these mixed flows is detrimental to being able to accurately model and predict them. This impacts our ability to design industrial processes around it, and perhaps in the future, to use it to engineer new materials with exacting flow responses for specific applications.This fellowship will develop a new experimental technique that allows us to measure what shearing stress is occurring throughout a kinematically mixed flow by using magnetic resonance imaging - the same technology used in hospitals - and critically, makes whether a fluid is clear or opaque unimportant. With members of the modelling community interested in the project and a "round table" planned, benchmark experiments will be conducted to inform new fluid model development, and thereby facilitate a wide range of next generation materials and manufacturing processes.

你熟悉蛋糕上的糖霜吗？当你知道我们对在你放下珠子时发生的许多流动过程的理解实际上并没有完全理解时，你会感到惊讶吗？无论流体在哪里受到“拉伸”——滑动、压扁或改变形状，它都会产生一种力或“应力”。研究流体对应变的反应被称为“流变学”。这些力会影响附近其他流体的运动方式，使其成为计算流体流动问题的重要信息：将熔融塑料加工成日常物品的模型，或者我们对蜘蛛如何吐丝的理解。通俗地说，流变学描述了流体的“厚度”，但流体可以有巨大变化的行为，所有这些都取决于流体中发生的微观相互作用。通过管道喷嘴的流动和拉伸是非常复杂的。在喷嘴壁附近，结冰主要经历“剪切”流动，流体层相互滑动-这种流动类型在实验室中很容易理解和测量。在中心附近，流体正在经历“延伸”，流体包在流动方向上被拉伸，在其他方向上被压扁。喷嘴变细导致了这一点。这种拉伸流动不太容易理解或测量，但在过去的50年里，我们的理解有所改善，主要是因为塑料工业。在壁面位置和流动中心之间，同时存在着剪切和伸展——我们称之为“运动混合”流动。不是搅拌的，而是混合的，在一种以上的过滤中存在。迄今为止，我们在该地区验证模型的唯一方法是测量流体速度（例如），看看我们的数学模型预测是否一致——基于纯剪切或拉伸流数据的模型。到目前为止，还没有一种方法可以明确地分离和测量这种流动中间的单独应力，这种应力取决于流体中的微观相互作用，同时取决于剪切和延伸。使情况更加复杂的是，结冰是“悬浮液”的一个例子，这是一类流体，显示出所谓的“屈服”应力——只有当施加的应力超过某个阈值时，它才会流动。这使得糖霜在挤压时可以流动，但这意味着糖霜在沉积在蛋糕上后会在重力作用下抵抗流动。与我们对塑料的了解相比，目前对悬浮液在延伸下的行为知之甚少，更不用说它们在运动混合流动下的行为了。受影响的不仅仅是糖霜蛋糕。3D打印水泥建造新房子在概念上是相同的过程，按比例扩大，必须处理更多的压力而不流动。电子制造业中焊膏的沉积与此类似，将石墨烯纤维加工成下一代高性能材料也是如此。塑料加工，一种混合流动，还没有完全理解，甚至发动机轴承中的润滑剂流动也是混合的。事实上，很少有纯剪切或拉伸流动，缺乏直接观察流体应力在这些混合流动下如何响应的方法，不利于准确建模和预测。这影响了我们围绕它设计工业流程的能力，也许在未来，用它来设计具有特定应用的严格流动响应的新材料。这项研究将开发一种新的实验技术，使我们能够通过使用磁共振成像（与医院使用的技术相同）来测量在运动混合流中发生的剪切应力，关键的是，使液体是透明还是不透明变得不重要。由于建模界的成员对该项目感兴趣，并计划举行“圆桌会议”，将进行基准实验，为新的流体模型开发提供信息，从而促进广泛的下一代材料和制造工艺。