The flow and the heat transfer characteristics in quartz microtube with inner diameter of 0.0196mm are investigated experimentally. By measuring the pressure drop between the inlet and outlet of microtube with different working fluid and the average temperature of microtube wall heated by steam, the corresponding friction factors and Nusselt number are obtained. The experimental results show the friction factors in microtubes exceeds the prediction of Hagen-Poiseulle due to the predominance of the electrical double layer effect (EDL effect) when the working fluid is distilled water, and the experimental Nusselt number is less than the classical laminar at Reynolds number<500 due to the effects of the variation of the thermophysical properties with temperature and the conjugate heat transfer. However, the effect of viscous dissipation results in temperature rise of the working fluid, due to which the friction factors are less than the prediction of Hagen-Poiseulle with the working fluid of tetrachloromethane. Using nitrogen gas as the working fluid, the rarefaction effect still brings on that the friction factor is less than the classical laminar solution, though gas density and viscosity increases resulted from the stagnant velocity between gas and inner wall and the viscous heating lead to the increase of friction factor.

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