| Summary: | 碩士 === 國立成功大學 === 機械工程學系碩博士班 === 95 === In this study, the problem of turbulent forced convection flow of nanofluids has been investigated numerically for two particular geometrical configurations, namely a uniformly heated tube and radial flow. Both water-Cu and water-Al2O3 nanofluids are discussed. The numerical simulations are undertaken for the parameters：the Reynolds number Re, the volume concentration , the constant heat flux and the particle diameter. The turbulent governing equations are solved with the Low Reynolds number turbulence model for tube flow and the Standard turbulence model for radial flow, respectively. The theoretical model developed for tube flow is validated by comparing the numerical predictions with available experimental data in the literature, and the numerical results show that the averaged Nusselt numbers are reasonably predicted with a maximum discrepancy within 10%.
The present study indicates that in the tube flow, with the use of volume fraction 1% and 2% water/Cu nanofluids, the thermal enhancement can achieve 15%、30% compared with pure fluid. As for the radial flow, volume fraction 0.5% and 1% water/alumina nanofluids can result in 16%、40% thermal enhancement, respectively. The heat transfer coefficient increases with the increase of the particle concentration and Reynolds number. Besides, the inclusion of smaller particles into water can produce a more considerable augmentation of the heat transfer coefficient at the fixed particle volume concentration. Among the mixtures studied, the water/Cu nanofluid appears to offer a better heat transfer enhancement than water/Al2O3. On the other hand, the friction factor of the nanofluids is discussed, and it seems that no significant augmentation in pressure drop for the dilute nanofluid is found. Compared with the use of water, it will not cost more input power to make the dilute nanofluids flow.
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