The mechanism of polymer thread drag reduction
The mechanism of polymer thread drag reduction
复制标题
聚合物丝减阻机理
DOI：
10.1007/bf01134599
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发表时间：
1991
期刊：
影响因子：
2.3
通讯作者：
W. G. Tiederman
中科院分区：
文献类型：
--
作者：
R. Smith;W. G. Tiederman
减少湍流流体流动的阻力的一种非常有效的方法是通过使用可溶的、粘弹性的、长链的、高分子量聚合物添加剂。这些添加剂在管流中产生高达80%的减阻。聚合物通常通过将高浓度溶液注入到已建立的Newtonian flow.This研究调查减阻的机制时发生的长链，高分子量的聚合物沿着管的中心线与浓度足够高，形成一个单一的，连贯的，完整的线程。在目前的实验中，完整的螺纹存在超过200管直径下游的喷射器，并产生约40%的阻力减少。以前的作者认为这种类型的阻力减小是由螺纹与外部流动的相互作用引起的。然而，已经证明，在聚合物在整个流动中混合的情况下，减阻需要在近壁区域中存在聚合物。本研究的目的是测试的假设，从聚合物线程的阻力减少是由运输的聚合物分子从线程到近壁区域的管道。通过测量减阻率、螺纹径向位置和近壁区聚合物浓度来实现这一目标。利用荧光素染料作为示踪剂，通过激光诱导荧光测量浓度。这项研究提供了强有力的证据表明，从聚合物线程的阻力减少是由非常低浓度的聚合物从线程到近壁区域的运输。
One very effective method of reducing the drag of a turbulent fluid flow is through the use of soluble, viscoelastic, long-chain, high-molecular-weight polymer additives. These additives have produced drag reduction of up to 80% in pipe flows. Polymers are typically added by injecting high concentration solutions into an established Newtonian flow.This study investigated the mechanism of drag reduction that occurs when a long-chain, high-molecular-weight polymer is injected along the centerline of a pipe with a concentration high enough to form a single, coherent, unbroken thread. In the present experiments, the unbroken threads existed for more than 200 pipe diameters downstream of the injector and produced drag reductions on the order of 40%. Previous authors have contended that this type of drag reduction is caused by the interaction of the thread with the outer flow. However, it has been proven in cases where the polymer is mixed throughout the flow that drag reduction requires the existence of polymer in the near-wall region. The objective of this study was to test the hypothesis that drag reduction from a polymer thread is caused by transport of polymer molecules from the thread into the near-wall region of the pipe. The objective was realized through the measurement of the drag reduction, the radial location of the thread, and the polymer concentration in the near-wall region. The concentration was measured by laser-induced fluorescence utilizing fluorescein dye as the tracer. This study provides strong evidence that the drag reduction from a polymer thread is caused by the transport of very low concentrations of polymer from the thread into the near-wall region.