Title: Natural convection in shallow cavity filled with nanofluids taking into account the Soret effect

Authors: Fakhreddine S. Oueslati; R. Bennacer; Habib Sammouda

Addresses: LETTM, Department de Physique, FST Campus Universitaire, 2092 El Manar Tunis, Tunisia. ' ENS-Cachan Dpt GC/LMT, 61, Av du Président Wilson, 94235 Cachan Cedex, France. ' LabEM, LR11ES34, Sousse University, ESSTHS, Rue Lamine Abbassi, 4011 H. Sousse, Tunisia

Abstract: Natural convection, in a shallow horizontal cavity filled with nanofluids, is studied both numerically and analytically. The horizontal surface of the enclosure are submitted to heat on the bottom and cooled on the upper. The vertical walls are subject to variable heat fluxes. The nanofluids are treated as heterogeneous mixtures with weak solutal diffusivity and possible Soret separation. Owing to the pronounced Soret effect of these materials in combination with a considerable solutal expansion, the resulting solutal buoyancy forces could be significant and interact with the initial thermal convection. A modified formulation taking into account the thermal conductivity, viscosity versus nanofluids type and concentration and the spatial heterogeneous concentration induced by the Soret effect is presented. The induced nanofluid heterogeneity showed a significant heat transfer modification. The heat transfer in natural convection increases with nanoparticle concentration. The analytical solution, based on the parallel flow approximation, is found to be in good agreement with a numerical solution. The existence of both natural and antinatural flows is demonstrated. Indeed, the critical Rayleigh number for the onset of motion is dependent on the concentration of nanoparticles and their nature.

Keywords: natural convection; nanofluids; Soret effect; natural flows; antinatural flows; shallow cavities; nanotechnology; thermal conductivity; viscosity; heat transfer; nanoparticles; parallel flow approximation.

DOI: 10.1504/PCFD.2012.048255

Progress in Computational Fluid Dynamics, An International Journal, 2012 Vol.12 No.4, pp.260 - 269

Published online: 30 Jul 2012 *

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