Hydrophobic solution was prepared by adding 2% perfluorinated octyl fluorine silane and micro-nano particles to modified silicone dilute solution. This hydrophobic solution could be solidified to obtain hydrophobic surfaces

and the contact angle of water on these surfaces could be adjusted by changing the content of micro-nano particles in hydrophobic solution. Using the method above

different micro cylinders groups with contact angles of 99.5°

119.5° and 151.5° (de-ionized water) were prepared

respectively. Using de-ionized water as working fluid

the flow resistance and pressure drops in micro cylinders groups with different contact angles were measured. The value of friction factor of test section with hydrophobic layer was apparently lower than that without the layer at the same Reynolds number

and this was because the surface tension on hydrophobic interaction interface led to a reduction of friction resistance. The larger the contact angle

the smaller the distance between the micro/nano bumps on the double structure of hydrophobic layer at the same Re

meanwhile the ratio of liquid-air contact area to the total flow area became higher

thus flow resistance decreased. The drag reduction rates attributed to the three kinds of hydrophobic coatings on surfaces of micro pin fins decreased continuously with the increase of Re.