Flow Characteristics of Deionized Water in Microtubes Absorbing Fluoro-Alkyl Silanes

In order to find the drag reduction mechanism of surface wettability, some experiments are carried out to research the flow of deionized water through microtubes. The flow rate of liquid through microtubes adsorbing Fluoro–Alkyl silanes (FAS) or not are compared. The inner diameters of the microtubes are 100 µm, 75 µm and 50 µm, respectively. The relations of shear rate and slip velocity, and shear rate and slip length are discussed. The inner surface wettability of the microtubes changes from hydrophilic at a contact angle of 23° to weak hydrophobic at a contact angle of 107° by adsorbing FAS. The results indicate that the flow rate in microtubes adsorbing FAS is larger than those without FAS, the efficiency of drag reduction if about 13%, the slip velocity near the wall is proportional to the shear rate and the slip length remains invariant for different shear rates in microtubes with different diameters.