水在不同接触角微柱群内的流动特征

采用向改性有机硅稀溶液中加入2%全氟辛基氟硅烷以及微纳米粒子的方法制备疏水液,通过改变微纳米粒子添加量调控疏水液固化成涂层后的表观接触角,紫铜叉排排列微柱群表面经不同疏水液处理后接触角分别为99.5°、119.5°和151.5°(水为工质),并测试流道内流动阻力和压力降。实验结果表明,相同Reynolds数(Re)下流道内摩擦因子(f)比疏水处理前有明显下降,主要是由于疏水性界面的张力作用所致;相同Re下,接触角越大,疏水涂层双重结构中微纳米凸起间距越小,去离子水与空气接触面增大,使得摩擦因子减小;随Re增加,3种涂层实验段内的减阻率均不断降低。

Flow characteristics of water in hydrophobic micro cylinders group with different contact angles

Hydrophobic solution was prepared by adding 2% perfluorinated octyl fluorine silane and micro-nano particles to modified silicone dilute solution. This hydrophobic solution could be solidified to obtain hydrophobic surfaces, and the contact angle of water on these surfaces could be adjusted by changing the content of micro-nano particles in hydrophobic solution. Using the method above, different micro cylinders groups with contact angles of 99.5°, 119.5° and 151.5° (de-ionized water) were prepared, respectively. Using de-ionized water as working fluid, the flow resistance and pressure drops in micro cylinders groups with different contact angles were measured. The value of friction factor of test section with hydrophobic layer was apparently lower than that without the layer at the same Reynolds number, and this was because the surface tension on hydrophobic interaction interface led to a reduction of friction resistance. The larger the contact angle, the smaller the distance between the micro/nano bumps on the double structure of hydrophobic layer at the same Re, meanwhile the ratio of liquid-air contact area to the total flow area became higher, thus flow resistance decreased. The drag reduction rates attributed to the three kinds of hydrophobic coatings on surfaces of micro pin fins decreased continuously with the increase of Re.