The hydrophobic coatings with different properties are coated on the surfaces of micro pin fins with different cross sections of circular

diamond and elliptical to obtain hydrophobic micro pin fins with contact angles of 99.5°

119.5° and 151.5°

respectively. The reduction coefficient of the pressure drop and the friction resistance are measured experimentally when water flows through the hydrophobic micro pin fins at different flow rates. Experimental results show that the change rate of pressure drop in ellipse and diamond micro pin fins increases gradually

however the change rate of pressure drop in circular micro pin fins increases at first and then decreases when the contact angle changes from 83° (the red copper smooth surface) to 151.5°. With the increase of the flow rate

the change rate of pressure drop in ellipse micro pin fins gradually decreases

while it decreases at first and then almost keeps constant in diamond and circular micro pin fins. The investigation also illustrates that the resistance reduction rates in all of test sections become large with the increase of the contact angle at the same Re. Under the same contact angle conditions

the resistance reduction rate gradually decreases in elliptical micro pin fins with the increase of Re

while it decreases at first and then keeps almost constant in diamond shaped and circular test sections. The minimal resistance reduction rates in diamond shaped and circular micro pin fins are 50.81% and 58.68% at contact angle of 151.5°

respectively.