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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-421-2

International Heat Transfer Conference 15
August, 10-15, 2014, Kyoto, Japan

Non-Similar Heat Transfer Characteristics Associated with Nanofluid Forced Convection Cooling and Heating

Get access (open in a dialog) DOI: 10.1615/IHTC15.hte.008562
pages 4137-4150

Sinopsis

Nanofluid forced convection cooling and heating in channels and tubes were investigated analytically using a modified version of the Buongiorno equations, which fully accounts for the effects of nanoparticle volume fraction distributions on the continuity, momentum and energy equations. Analytic solutions for the cases of alumina-water nanofluids were obtained for thermally fully developed flows in both channels and tubes under constant heat flux. It has been found that both Brownian diffusion and thermophoresis are equally important for controlling nanoparticles transport phenomena. Thermophoresis drives nanoparticles from hot to cold region while Brownian diffusion makes nanoparticles distribute evenly. On the walls, they balance each other to meet the impermeable boundary condition there. As a result, a low volume fraction layer is formed on the heated wall, leading to decrease in both effective viscosity and thermal conductivity. On the cooled wall, on the contrary, comparatively high volume fraction layer is built, increasing both effective viscosity and thermal conductivity. Thus, the velocity and temperature profiles for the case of heating differ substantially from those for the case of cooling. This non-similar heat transfer characteristics associated with nanofluid forced convection cooling and heating has been captured for the first time. Furthermore, a theoretical answer to the controversial issue on the anomalous heat transfer in nanofluids has been provided in this study. Both heated tube and cooled channel solutions do suggest the anomalous heat transfer, in which the heat transfer coefficient exceeds the level expected from the increase in the effective thermal conductivity of nanofluids.