Investigations On Water Flow And Heat Transfer In The Super-Hydrophobic Micro-Channel

With acidic etching and fluorination treatment, super-hydrophobic surface is successfully fabricated on aluminous sheet. Water contact angle on the surface is larger than 150°and contact angle hysteresis is about 4°(5μL droplet) . The resultant surfaces are analyzed by means of scanning electron microscopy (SEM). It is shown that a "labyrinthic" structure with mass cuboid plateaus and caves is formed on the surface of aluminous sheet. Surface microstructures are the key to the preparation of super-hydrophobic surfaces.Water-repellency of the super-hydrophobic surface is studied in some aspects, such as the droplet's behaviors on the super-hydrophobic surface, the effects of the organic compound content in water on the wettability of the surface, the phase transformation process on the super-hydrophobic surface. It is shown that the super-hydrophobic surface has the characters of no-droplet adherence, oleophilic and dropwise condensation.Based on above research, super-hydrophobic aluminous micro-channels are successfully fabricated by reasonable ameliorating preparation techniques and experiment conditions. Heat transfer and fluid flow of deionized water flowing laminarly in the super-hydrophobic/hydrophilic microchannel are studied experimentally. The results show that the pressure drop and f·Re in super-hydrophobic micro-channels are lower than that of super-hydrophilic micro-channels, dimensionless pressure drop is fluctuating and the heat transfer coefficient and Nu in super-hydrophobic micro-channels are lower than that of super-hydrophilic micro-channels. The analysis result is that the air-layer existing in the micro - nano structures of the super-hydrophobic surface decreases flow resistance evidently and , in the same time, blocks heat transfer to a certain extent.The apparent heat transfer coefficient of super-hydrophobic micro-channels is computed in which the heat conduction of a stationary air-layer in no-slip boundary is considered. It is found that the apparent heat transfer coefficient is lower than experimental data and the difference increases with air-layer's thickness. It is supposed that eddy flow is generated in the micro-nano bubbles by the slip flow of water at the wall, which enhances the heat transfer.