Flow of Elastic Liquids

该提议涉及含有溶解聚合物的液体，这种聚合物通常使液体具有弹性和粘性。聚合物通常被添加到液体中，以使材料更粘稠——油漆和墨水就是例子——但聚合物也使液体具有弹性，这种额外的流体特性会影响流动。例如，在喷墨印刷中，油墨的弹性会产生不必要的卫星液滴。有时加入聚合物仅仅是为了提高弹性。两种发展良好的应用是：农业喷洒，因为弹性改善涂层的表面沉积；而对于紊流管道，由于弹性应力降低了驱动压力。添加聚合物的量通常很小，但效果却很显著。例如，在紊流的管道中，加入百万分之十的气体可以将所需的压力降低50%。粘度是流体的一个明显的特性——液体被称为厚或薄——但弹性通常不那么明显。最明显的表现可能是粘稠，就像在唾液和蛋清中看到的那样。

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.