Abstract:

The hydrophobic coatings with different properties are coated on the surfaces of micro pin fins with different cross section of circular, diamond and elliptical, respectively, and hydrophobic micro pin fins are formed. The contact angle of the deionized water on the surface of hydrophobic micro pin fins is 99.5°, 119.5° and 151.5°, respectively. The pressure drop and the friction resistance coefficient are measured experimentally when water flow through the hydrophobic micro pin fins at different flow rates. Experimental results show that the pressure drop in the circular micro pin fins is highest and the ellipse is minimum at the same contact angle and flow rate, and the frictional resistance coefficient in ellipse micro pin fins is higher than that in diamond and circular micro pin fins when the contact angle is 99.5 degrees and Reynolds numberRe is less than 600; however, the former is lower than that of the latter two whenRe>600. The resistance reduction rate of circular micro pin fins is higher than that of the diamond and ellipse micro pin fins with the increase of the contact angle and those of the diamond and the ellipse is close at lowRe, but the diamond is higher than the ellipse at highRe. The surface hydrophobic treatment can significantly reduce the friction resistance, at the same time it delay flow separation and the transition from laminar flow to turbulent flow at the wake, so the resistance reduction effect of micro pin fins is more obvious for the earlier separation and the lager differential pressure resistance.

Key words: contact angle, friction resistance coefficient, pressure drop, resistance reduction rate, hydrophobic micro pin fins