Flow of Elastic Liquids

该提案涉及含有溶解聚合物的液体，这种聚合物通常使液体既有弹性又有粘性。聚合物通常被添加到液体中，以增加材料的粘性--油漆和油墨就是一例--但聚合物也会使液体具有弹性，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。聚合物的加入量通常很小，但效果可能是戏剧性的。例如，在湍动的管流中，添加百万分之十就可以将所需压力降低50%。粘度是液体的一个明显性质--液体被称为稠度或稀度--但弹性通常不那么明显。最明显的表现可能是粘稠，如唾液和蛋清。

The proposal concerns liquids containing a dissolved polymer, which generally makes the liquid elastic as well as viscous. Polymers are often 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 because elasticity improves surface deposition of the coating; and to turbulent pipe flow because elastic stresses reduce the driving pressure. The amount of added polymer is often minute but the effect can be dramatic. In turbulent pipe flow, for instance, the addition of 10 parts per million can reduce the required pressure by 50%. Viscosity is an obvious property of a fluid - liquids are referred to as thick or thin - but elasticity is generally much less evident. The most visible manifestation is probably stringiness, as seen with saliva and egg whites.