壁面带微结构管道内Cassie状态稳定性的实验研究

保持液体在微结构表面处于Cassie状态,是流动减阻的关键。首先利用MicroPTV分别测量了带微结构侧壁处于Cassie和Wenzel状态下的流场速度,表明Cassie状态下近壁速度提高至光滑表面的1.6倍,而Wenzel状态下近壁速度将减小。通过精细控制微管道的驱动压强,观察了液体在近壁由Cassie向Wenzel状态的转变,并测出C/W转变的临界压强值Δpcr约10.9kPa,与Laplace理论预测值10.15kPa基本相符。考虑到Cassie状态失稳也会发生在液体进样过程中,实验还观察了微结构角点对液体进样的＂锚定＂作用,并初步分析了液体进样中自由液面在微结构表面保持Cassie状态的条件。

Experimental study of cassie state stability inside a microchannel with microstructured surface

Keeping liquid stay at Cassie state at the surface of microstructured wall in the microchannel is a key point of drag reduction. In this paper, MieroPTV was used to measure the flow velocity profiles under Cassie/Wenzel states near microstructured wall respectively. The results showed that the velocity near microstructured wall under Cassie state was 1.6 times as great as near a smooth wall, on the other hand, the velocity under Wenzel state decreased. By controlling precisely the driven pressure, we observed the transition process from Cassie state to Wenzel state of the liquid-solid surface near the microstructures in a microchannel. It is shown that the critical transition-pressure is about 10.9kPa, which is in good agreement with the theoretical value 10.15kPa based on Laplace equation. Considering the transition from Cassie state to Wenzel state could happen during liquid injection into the microchannel, the ＂anchor＂ effect of the corner point of microstructure is observed, and an analysis is given to explain how the interface near microstructures maintains Cassie state during injection.