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Heat and mass transfer in external boundary layer flows using nanofluids.
Heat and Mass Transfer - Modeling and Simulation, Chapter 5, p. 95 – 116, Edited by : Monwar Hossain, Publisher : InTech, ISBN 978-953-307-604-1, 2011.

par   Catalin Viorel POPA , Guillaume POLIDORI , Ahlem ARFAOUI , Stéphane FOHANNO

Résumé :


In the present study, both free convection and forced convection problems of Newtonian CuO/water and alumina/water nanofluids over semi-infinite plates have been investigated from a theoretical viewpoint, for a range of nanoparticle volume fraction up to 5%. The analysis is based on a macroscopic modelling and under assumption of constant thermophysical nanofluid properties. Whatever the thermal convective regime is, namely free convection or forced convection, it seems that the viscosity, whose evolution is entirely due to the particle volume fraction value, plays a key role in the mass transfer. It is shown that using nanofluids strongly influences the boundary layer thickness by modifying the viscosity of the resulting mixture leading to variations in the mass transfer in the vicinity of walls in external boundary-layer flows. It has been shown that both viscous boundary layer and velocity profiles deduced from the Karman-Pohlhausen analysys, are highly viscosity dependent. Concerning the heat transfer, results are more contrasted. Whatever the nanofluid, increasing the nanoparticle volume fraction leads to a degradation in the external free convection heat transfer, compared to the base-fluid reference. This confirms previous conclusions about similar analyses and tends to prove that the use of nanofluids remains illusory in external free convection. A contrario, the external forced convection analyses shows that the use of nanofluids is a powerful mean to modify and enhance the heat transfer, and the thermal flow rate which are strongly dependent of the nanoparticle volume fraction.

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