The fabrication of superhydrophobic surfaces and the studies on water flow characteristics therein are of great significance to many industrial areas as well as to science and technology development. Experiments were ...The fabrication of superhydrophobic surfaces and the studies on water flow characteristics therein are of great significance to many industrial areas as well as to science and technology development. Experiments were car- ried out to investigate slip characteristics of water flowing in circular superhydrophobic microtubes within lam- inar flow region. The superhydrophobic microtubes of stainless steel were fabricated with chemical etching- fluorination treatment. An experimental setup was designed to measure the pressure drop as function of water flow rate. For comparison, superhydrophilic tubes were also tested. Poiseuille number Po was found to be smaller for the superhydrophobic microtubes than that for superhydrophilic ones. The pressure drop reduc- tion ranges from 8% to 31%. It decreases with increasing Reynolds number when Re 〈 900, owing to the transition from Cassie state to Wenze] state. However, it is almost unchanged with further increasing Re after Re 〉 900. The slip length in superhydrophobic microtubes also exhibits a Reynolds number dependence similarly to the pressure drop reduction. The relation between slip length and Darcy friction factor is theoretically analyzed with consideration of surface roughness effect, which was testified with the experimental results.展开更多
基金the National Natural Science Foundation of China(20476014,51376030)
文摘The fabrication of superhydrophobic surfaces and the studies on water flow characteristics therein are of great significance to many industrial areas as well as to science and technology development. Experiments were car- ried out to investigate slip characteristics of water flowing in circular superhydrophobic microtubes within lam- inar flow region. The superhydrophobic microtubes of stainless steel were fabricated with chemical etching- fluorination treatment. An experimental setup was designed to measure the pressure drop as function of water flow rate. For comparison, superhydrophilic tubes were also tested. Poiseuille number Po was found to be smaller for the superhydrophobic microtubes than that for superhydrophilic ones. The pressure drop reduc- tion ranges from 8% to 31%. It decreases with increasing Reynolds number when Re 〈 900, owing to the transition from Cassie state to Wenze] state. However, it is almost unchanged with further increasing Re after Re 〉 900. The slip length in superhydrophobic microtubes also exhibits a Reynolds number dependence similarly to the pressure drop reduction. The relation between slip length and Darcy friction factor is theoretically analyzed with consideration of surface roughness effect, which was testified with the experimental results.
