Investigations On The Fabrication Of Super-Hydrophobic Surface On Aluminum Micro-Tubes And Water Flow Characteristics In The Tubes

With acidic etching and fluorination treatment, super-hydrophobic surface is successfullymade on aluminous flake. The water contact angle on the surface is larger than 150°, as well ascontact angle hysteresis of about 4°(5-μL droplet).The resultant surfaces are examined by means of scanning electron microscopy (SEM). Itis shown that a "labyrinthic" structure with mass cuboid plateaus and caves of micro-and nanostructureforms on the super-hydrophobic surface of aluminous flake. Surface microstructures are thekey to the preparation of super-hydrophobic surfaces. Effects of different parameters oncontact angles are investigated. Based on above research, super-hydrophobic aluminousmicro-channels are successfully made by reasonable ameliorating preparation technology andexperiment condition.The flow characteristics of water in super-hydrophilic micro-channel are studied. Theexperiment results suggest that the critical Re for transition from laminar to turbulent flow insuper-hydrophilic micro-channels doesn't evidently change compared with that inmacro-channels. In laminar range, the roughness has a significant effect on the flowresistance.The flow characteristics of water in super-hydrophobic micro-channels are studied. It isfound that there is the later transition which may be induced by the characteristics ofsuper-hydrophobic surface compared with that in untreated channels. The pressure drop ofwater flowing in super-hydrophobic micro-channels evidently decreases compared with thatin super-hydrophilic micro-channels, with the maximal decrease of about 40%. The slipvelocity and the slip length are calculated at different flow velocity and the results show thatboth the slip velocity and the slip length increase along with water flow velocity. The reasonfor water slippage on super-hydrophobic surfaces is discussed.