Flow of Elastic Liquids

资助建议摘要聚合物有时被添加到液体中以增加材料的粘性-例如油漆和油墨-但聚合物也使液体具有弹性，这种额外的流体特性可能会影响流动。例如，在喷墨打印中，油墨的弹性可能会导致不需要的卫星液滴。有时，添加聚合物完全是为了改善弹性。两个成熟的应用是：农业喷洒，因为弹性改善了涂层的表面沉积；以及湍流管道流动，因为弹性应力降低了驱动压力。通常情况下，添加的聚合物数量很少，但效果可能是巨大的。例如，在湍急的管流中，添加百万分之十的聚合物可以将所需压力降低50%。虽然粘度是一种明显的流体属性--例如，液体通常被称为稠密或稀薄--但液体的弹性通常不那么明显。最明显的表现是粘稠，如唾液和蛋清。这项赠款申请集中在弹性效应显著的四个流动上。其中两项是添加聚合物的水射流微加工的新用途，以提高分辨率，并用于浓缩油砂尾矿，以改善流动特性。尾矿通常是水的，但当去除一些水以形成液态糊状物时，这些材料可以沉积在矿山周围的表面，而不是进入池塘，这是正常但对环境有害的做法。由于弹性改变了流动特性，沉积在地面上的尾矿需要更少的面积。另外两种流动也是试验性的：一种是流经一系列棒状物，另一种是流过单个圆柱体。这两个更基本，但实际上是相关的，因为前者与纤维增强塑料有关，后者与使用鞭毛的微生物游泳有关。这四个实验的总体目标是了解弹性在流动中的作用，即确定属性何时起作用，量化其影响，并确定弹性引起的应力如何改变流动。上述后两个实验将使用特殊的粘弹性流体--具有弹性但具有恒定粘性的液体--进行，这将使弹性效应与粘性效应明显分离。例如，杆阵列的初步结果表明，由弹性引起的流动阻力可能是由粘性引起的阻力的数倍，这表明了弹性在某些流动中的重要性。

Summary of Grant Proposal Polymers are sometimes added to liquids to make the material more viscous – paint and ink are examples – but the polymer also makes the liquid elastic, and this additional fluid property can affect a flow. In inkjet printing, for example, the ink’s elasticity can cause unwanted satellite droplets. Sometimes the polymer is added solely for the improvement provided by elasticity. Two well-developed applications are: to agricultural spraying, for elasticity improves surface deposition of the coating; and to turbulent pipe flow, because elastic stresses reduce the driving pressure. Often the amount of added polymer is minute but the effect can be dramatic. In turbulent pipe flow, for instance, the addition of 10 parts per million of polymer can reduce the required pressure by 50%. While viscosity is an obvious fluid property - liquids are often referred to as thick or thin, for example - elasticity in a liquid is generally less evident. The most visible manifestation is stringiness, as seen with saliva and egg whites. This grant application focusses on four flows in which the effect of elasticity is significant. Two of these are new uses of added polymer - to water jet micromachining for finer resolution, and to concentrated oil sand tailings for better flow characteristics. Tailings are normally watery, but when some water is removed to create a liquidy paste, the material can be deposited on the surface around a mine and not into a pond, which is the normal but environmentally dangerous practice. With flow behaviour modified by elasticity, tailings deposited on the ground require less area. The other two flows are also experimental: flow through an array of rods and flow past a single cylinder. These two are more fundamental but are practically relevant because the former pertains to fibre-reinforced plastics and the latter to the swimming of micro-organisms using flagella. The overall objective of the four experiments is to understand the role of elasticity in flows, that is, to identify when the property is operative, to quantify its effect, and to determine how the stresses caused by elasticity alter a flow. The latter two experiments above will be conducted with special viscoelastic fluids – liquids which are elastic but have constant viscosities – that will enable elastic effects to be clearly separated from viscous effects. Initial results with the rod arrays, for instance, have indicated that the resistance to flow caused by elasticity can be several times that caused by viscosity, demonstrating the importance of elasticity in some flows.