Study of Turbulent Drag Reduction Mechanisms in Dilute Polymer Solution by Using Micro Opto-imaging Technique

采用微观可视化技术对稀链聚合物溶液中的湍流减阻机理进行了实验研究。它是基于暗场显微镜。该系统采用市售显微镜配备干物镜（x40,NA0.75,WD0.51mm）或油浸物镜（x100,NA0.50-1.35,WD0.10mm）。照明由频闪灯或脉冲激光器（25mJ输出能量）与光纤光导一起提供。采用ICCD相机进行图像采集。该成像系统已成功用于直径800 ~ 10nm的标准乳胶颗粒的可视化；悬浮在滑动玻璃和覆盖玻璃之间形成的液体层中的。将聚乙烯氧化物（PEO, Alcox E-160）添加到重量为50- 500ppm的纯净水中制备稀链聚合物溶液。当溶液被玻璃板夹在中间并施加适当的力时，溶液就会受到剪切应力。这使得在液体中拉伸的长度约为20 μm的单体链聚合物成功地可视化。在50 ppm溶液中存在孤立的单个聚合物分子，而在500 ppm溶液中存在缠结的链状聚合物结构。构建了由两个平行玻璃板组成的毫米大小的矩形通道，以可视化PEO在静压差驱动下10m/s湍流中的行为。用脉冲Nd:YAG激光进行照明，以便在显微镜的放大视图中冻结PEO的行为。结果表明，该方法可以在湍流中显示直径为150nm的乳胶颗粒。然而，在湍流中PEO行为的可视化中获得的图像质量还不够高，建议进一步优化现有通道和暗场显微镜，以便更好地微观显示导致湍流减阻机制的分子行为。少

Experimental studies have been carried out to clarify turbulent drag reduction mechanisms in dilute chain polymer solution by using a micro visualization technique. It is based on the dark-field microscopy. The system employs a commercially available microscope equipped with a dry objective (x40,NA0.75,WD0.51mm) or an oil immersion objective (x100,NA0.50-1.35,WD0.10mm). Illumination is given by a strobe or a pulsed laser (25mJ output energy) together with fiber light guide. An ICCD camera is used for image acquisition. The present imaging system has successfully been used for visualization of standard latex particles, 800-10nm in diameter ; suspended in a liquid layer formed between a slide glass and a cover glass.Dilute chain polymer solutions are prepared by adding polyethyleneoxide (PEO, Alcox E-160) to purified water at 50-500 ppm at weight. Shear stress is given to the solutions when they are sandwiched by glass plates that are pressed by an appropriate force. This has resulted in … More a successful visualization of individual chain polymer, about 20 μm in length, stretched in the liquid. The 50 ppm solution shows the existence of isolated individual polymer molecule while the 500 ppm solution shows the existence of tangled structures of chain polymers.A millimeter-size rectangular channel formed by two parallel glass plates is constructed to visualize PEO's behaviors in a turbulent flow of 10m/s driven by a static pressure difference. Illumination is given by a pulsed Nd:YAG laser in order to freeze PEO'S behaviors in a magnified view of the microscope. It is shown that the present method permits visualization of latex particles, 150nm in diameter, in the turbulent flow. However, the image quality obtained in the visualization of PEO's behaviors in the turbulent flow is not sufficiently high, suggesting further optimization of the present channel and the dark-field microscope for better micro visualization of molecular behaviors responsible for the turbulent drag reduction mechanisms. Less