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 ...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.展开更多
Based on the second law or the rmodynamics,the authors proposed the unit entropy generation analysis method for evaluation and analysis of the comprehensive thermal characteristics of different enhanced heat transfer ...Based on the second law or the rmodynamics,the authors proposed the unit entropy generation analysis method for evaluation and analysis of the comprehensive thermal characteristics of different enhanced heat transfer methods.The optimum operation condition of the enhanced heat transfer methods,such as fin type and swirl flow,is obtained through thermal characteristic analysis.This work provides a theoretical basis for engineering design.展开更多
文摘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.
文摘Based on the second law or the rmodynamics,the authors proposed the unit entropy generation analysis method for evaluation and analysis of the comprehensive thermal characteristics of different enhanced heat transfer methods.The optimum operation condition of the enhanced heat transfer methods,such as fin type and swirl flow,is obtained through thermal characteristic analysis.This work provides a theoretical basis for engineering design.
