Liquid convective heat transfer in microchannels exhibits high efficiency.However,the large pressure drop causes much concern for practical application.Water flowing in hydrophobic tubes shows low pressure drop owing to the slippage on the tube walls.Super-hydrophobic/hydrophilic micro aluminum tubes of 0.68mm inner diameter were fabricated with a two step procedure of chemical etching and then surface chemical modification.A kind of micro-nanometric hierarchical structure was formed on the surface,which could trap air serving as the slip agent.Heat transfer and fluid flow of deioned water flowing laminary in the super-hydrophobic/hydrophilic microchannels were studied experimentally.The results showed that the air-layer existing in the micro-nano hierarchical structures of the super-hydrophobic surface decreased flow resistance evidently but decreased heat transfer coefficient only a little,which was still higher than the superficial heat transfer coefficient while considering the heat conduction of stationary nanolayer of air.It was supposed that eddy flow was generated in the micro-nano bubbles by the slip flow of water on the tube wall,which enhanced the heat transfer.
