定热流加热下微管内部换热特征的实验研究

Study on Heat Transfer Characteristics in Microtube Under Heating of Constant Heat Flux

以蒸馏水为工质,流过内径分别为242 μm、315 μm 及520 μm石英管,石英管外部缠绕外径为80 μm的铜丝,通过给细铜丝通电来加热石英管以研究石英管内部的换热.根据细铜丝电阻值与温度的关系来确定石英管外壁的温度值,实现了定热流加热与温度测量的同步.实验得到了雷诺数Re在100～7000之间变化时的Nusselt数,并与经典的层流、过渡流及紊流换热准则方程式进行了对比.实验结果表明,在Re较低时,微石英管内部的Nu数低于常规经典的换热准则方程式的解,但随着Re数增加到1700～1900时,微石英管内Nu数已与过渡流准则方程式的解基本一致;当Re数增加到4000～5500左右时,微石英管内部换热Nu数达到常规尺度下的紊流换热方程式的解.

Experiments were carried out to investigate forced convective heat transfer of distilled water flowing through quartz microtubes with inner diameter of 242, 315 and 520 μm. The microtube was heated directly by electrifying a brass wire with diameter 80 tan,which was coiled evenly up around the microtube to keep a constant heat flux.The wall average temperature was obtained according to relationship between wire resistance and temperature and achieved the synchronization of heating and measuring temperature. As the Reynolds number varied in the range from 100 up to 7000, the Nusselt numbers were measured. The experimental results were compared with the classical convective heat transfer correlations in laminar, transitional and turbulent regimes for conventional tubes. The comparison results indicated that the Nusselt nmnber may be less than the classical laminar correlations when Reynolds number is lower. The Nusselt number quickly increases with the increase of Reynolds number. As Reynolds number is larger than 1700 - 1900 and 4000 - 5500, the corresponding Nusselt number will reach the value of the transitional correlations or that of the turbulent correlations.