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 carried out to investigate slip characteristics of water flowing in circular superhydrophobic microtubes within laminar 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 reduction ranges from 8% to 31%. It decreases with increasing Reynolds numberwhen Re 900

owing to the transition from Cassie state to Wenzel 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.