Hierarchical alveolate structures of micro-nano scale were prepared on stainless steel substrates with chemical etching.Fine papillae stand on protuberances are found.After fluorination treatments,the surfaces exhibit super-hydrophobic properties,with water contact angles of 163°.Stainless-steel micro-tubes with super-hydrophilic and super-hydrophobic surface were fabricated with chemical etching and chemical etching-fluorination treatment respectively.The effect of surface wettability on the fluid flow in micro-tubes was investigated with water as the working fluid.The experimental setup was designed in such a way that the investigation of the pressure drop and friction factor was possible.It is found that friction factor in super-hydrophilic micro-tube is in good agreement with Hagen-Poiseuille theory at low Reynolds number (Re<600),while higher than classical values at higher Reynolds number.The pressure drop of water flowing in super-hydrophobic micro-tube decreases compared with that in super-hydrophilic micro-tube,with the maximal decrease of 39%,which indicates the prospective utilization in process industry.
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