The present paper is devoted to experimental investigations of the flow and the associated heat transfer in two-dimensional microchannels. Scaling laws pertaining to the hydrodynamics and heat transfer in microchannels are not yet clearly established. The published results are affected by a significant scatter, owing to the various conditions used in the experiments, and, most likely, owing to the difficulty of measurements at micronic scales. The present facility was designed to modify easily the channel height e. It was then possible to investigate hydrodynamics and heat transfer in channels of height ranging from 1 mm, which corresponds to conventional size, up to 0.1 mm, where size effects are expected. Size effects were therefore tested in the same setup and with the same channel walls for all the experiments, which were carried out with demineralized water. Measurements of the overall friction coefficient and of local Nusselt numbers show that the classical laws of hydrodynamics and heat transfer are verified for e>0.4 mm. For lower values of e, a significant decrease of the Nusselt number is observed whereas the Poiseuille number keeps the conventional value of laminar developed flow. The transition to turbulence is not affected by the channel size.

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In this study, the effects of various vortex generator configurations on the heat transfer and flow Downloaded by [New York University] at 06:27 08 June 2015 ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 2 friction characteristics are investigated by numerical method. Compared with common-flow-down configuration, the Nusselt numbers of common-flow-up configuration increase by 2.7-2.9% in the range of studied Reynolds number, while the friction factors reduce by 7.8-10.0%. A comparative study of the effects of location of axial dimension, location of spanwise dimension, attack angle, length and height of vortex generator on fin performance is conducted. The results show that the intensity of heat transfer can be greatly increased with decreasing the location and attack angle of vortex generator, and with increasing height of vortex generator, accompanying with the increase of pressure drop. The Nusselt number and friction factors firstly increase and then decrease with increasing length of vortex generator. The parameters of vortex generator fin-and-tube heat exchanger are optimized by the Taguchi method. Sixteen kinds of models are made by compounding levels on each factor, and the heat transfer and flow friction characteristics of each model are analyzed. The results allow us toquantitatively estimate the various parameters affecting heat exchanger performance, and the main factors for optimal design of a heat exchanger are selected. The two optimal conditions are acquired, and the reproducibility of the results is verified by two analytical results.

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