水在不同管径超疏水性微管内的流动特性

Flow characteristics of water in super-hydrophobic micro-tubes with different diameters

在改性有机硅稀溶液中加入2%全氟辛基氟硅烷以及添加剂配制成超疏水液,采用滴定法在内径分别为0.447、0.728和0.873 mm的3种微铜管内壁实现微米级超疏水性涂层涂覆,其水滴表观接触角超过150°。建立微管内流动特性实验系统对超疏水性处理的减阻规律进行了实验研究,分别测量了雷诺数为100~3 000时去离子水流过处理前后微铜管时的内部摩擦阻力系数f。研究发现,内壁面的超疏水性处理显著降低了微管内的流动阻力,且该影响随微管内径的增加而增大,实验范围内流动阻力系数最大降幅达29.08%。超疏水涂层使得微管内的流动转捩现象出现滞后,且转捩Re随微管管径增加而略有增大。

We prepared super-hydrophobic solutionby adding 2% perfluorinatedoctyltriethoxysilane and additiveto modified-organosilicone dilute solution. We implemented micron order super-hydrophobic coating on inner-walls of three micro-tubes with diameters of 0.447 mm, 0. 728 mm and 0.873 mm to form super-hydrophobic micro-tubes. The contact angles of water on their inner surfacesare all larger than 150°. We further constructed aninnermicro-tube fluid characteristicexperimental system and exploredsuper-hydrophobic resistance reduction law. We measured frictional resistance coefficients f of de-ionized water flowing micro-tubes with super-hydrophobic layer and without super- hydrophobic layer for Re changing from 100 - 3000. Experimental results show flowing resistance in a micro-tube is significantly reduced through super-hydrophobic processing. Moreover, such resistance gradually reduces with the increase of the innerdiameter of a micro-tube. The maximum decreasing amplitude canreach 29.08%. Super-hydrophobic coating can make the transition of flow from laminar to turbulenceinobviously delayed and the transitional Re in micro-tubes increases with the increase of the diameter.