Effect of textured hydrophobic surfaces on laminar drag reduction

We studied the mechanism of drag reduction due to the textured hydrophobic surfaces in Newtonian laminar flow through a rectangular channel. Fine fabrication was given to the test wall surface so that the groove pattern and the groove area ratio may be changed methodically, and the surface was coated with PTFE for hydrophobic processing. Drag reduction was estimated by pressure loss measurement in a 12 × 12 mm channel. Visualization experiment was carried out using a 0.5X5 mm microchannel. Shear rate is changed with the result of pressure loss measurement and the form of the air-liquid interface was visualized. A series of experiments showed that the air-water contact area ratio and the air layer thickness influence the drag reduction, and the maximum drag reduction ratio is 3.7%.