Experimental study on forced convective heat transfer characteristics in quartz microtube

Experiments were carried out to investigate forced convective heat transfer of deionized water flowing through quartz microtubes with inner diameter of 242, 315 and 520 μm. The microtube was heated by directly electrifying a brass wire that was coiled evenly up around the microtube to keep a constant heat flux, or heated by steam to keep a constant temperature. As Reynolds number varied in the range from 100 up to 5000–7000 in the experiments, the corresponding Nusselt numbers were also measured. The experimental results were compared with those of the classical correlations for convective heat transfer in a laminar, transitional or turbulent regime for conventional tubes, and a difference was found. The comparisons indicated that the Nusselt number tends to be agreement with those of the classical laminar correlations at a lower Reynolds number, and increased sharply with the increasing of Reynolds number. If Reynolds number was larger than 1500, 1600 and 1900 for microtubes with inner diameter of 242, 315 and 520 μm, respectively, the corresponding Nusselt number was higher than the predictions by the classical transitional correlations. When Nusselt number reached the value from the classical turbulent correlations, Reynolds number was approximately equal to 4000, 4500 and 5500, respectively, for these types of microtubes.