An experimental investigation of single-phase heat transfer in 0.045mm to 0.141mm microtubes

Deioned water, used as the working fluid, flowed through the quartz glass microtubes with inner diameters of 45, 92, and 14-1 mu m, respectively, which was heated by a directly electrifying brass wire coiled evenly up around them. As the Reynolds number varied in the range from 100 up to 3000 in the experiments the corresponding Nussult number was obtained. The experimental results showed that the experimental Nussult numbers were less than predictions of the classical laminar correlations at a lower Reynolds number, which resulted from the effects of the variation of the thermophysical properties with temperature and nonlinear temperature variation of the working fluid along the wall. With the increase of the Reynolds number, the experimental data sharply increased and they were higher than the predictions by the classical transitional correlations due to the conjugate effects of the thinner conductive liquid layer, the entrance length, the viscous dissipation, and the wall roughness when the Reynolds number exceeded 1000.