Flow of Elastic Liquids

有时候，聚合物会被加入到液体中，使材料变得更粘稠，例如油漆和墨水，但聚合物也会使液体具有弹性，这种额外的流体特性会影响流动。例如，在喷墨打印中，墨水的弹性会导致不需要的卫星液滴。有时添加聚合物仅仅是为了弹性提供的改进。两个发展良好的应用是：农业喷雾，因为弹性改善了涂层的表面沉积;以及湍流管流，因为弹性应力降低了驱动压力。通常，添加的聚合物的量是微小的，但效果可以是戏剧性的。例如，在湍流管流中，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性质-例如，液体通常被称为稠或稀-但液体中的弹性通常不太明显。最明显的表现是粘稠，如唾液和蛋清。这项拨款申请集中在四个流动，其中弹性的影响是显着的。其中两个是添加聚合物的新用途-用于水射流微加工以获得更高的分辨率，以及用于浓缩油砂尾矿以获得更好的流动特性。尾矿通常是含水的，但是当一些水被去除以产生液体糊状物时，材料可以沉积在矿山周围的表面上，而不是进入池塘，这是正常但对环境有害的做法。由于弹性改变了尾矿的流动特性，因此沉积在地面上的尾矿所需的面积更小。另外两种流动也是实验性的：流过一排杆和流过单个圆柱。这两个是更基本的，但实际上是相关的，因为前者涉及纤维增强塑料，后者涉及微生物利用鞭毛游动。这四个实验的总体目标是了解弹性在流动中的作用，也就是说，确定何时该属性起作用，量化其效果，并确定弹性引起的应力如何改变流动。上面的后两个实验将用特殊的粘弹性流体--具有弹性但粘度恒定的液体--进行，这将使弹性效应与粘性效应清楚地分开。例如，杆阵列的初步结果表明，弹性引起的流动阻力可能是粘性引起的阻力的几倍，这表明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.