Étude théorique et expérimentale de l'écoulement et du transfert de chaleur des nanofluides

Nanofluids are considered to offer important advantages over conventional heat transfer fluids. However, at this early stage of their development, their thermophysical properties are not known precisely. As a result, the assessment of their true potential is difficult. A first study was conducted and concerned the effects of uncertainties in physical properties on laminar and turbulent convection heat transfer with nanofluids. On the third hand, an exact analytical solution has been derived for the fully-developed mixed convection using a nanofluid in a vertical tube with uniform heat flux at the wall, uniform internal volumetric heat source and viscous dissipation. Explicit expressions have been obtained for the temperature and velocity profiles as well as for the axial pressure gradient. They were satisfactorily validated for the case of forced convection with both heat source and dissipation, and also for cases of mixed convection with heat source and with or without dissipation. The explicit solution has been used to study the effect of viscous dissipation and the particle fraction on thermal and velocity fields. This analytical solution has been also used in order to identify the sources of the irreversible losses encountered in such flows. Furthermore, an experimental investigation was carried out to study a laminar mixed convection flow and heat transfer of Al[subscript 2]O[subscript 3]-water nanofluid inside inclined tubes submitted to a uniform wall heat flux at their outer surface. Measured data were collected for different the governing parameters such as the Reynolds number the Grashof number and particle volume concentration. Results have shown that the experimental heat transfer coefficient remains nearly constant with an increase of particle volume concentration from 0 to 4%. In contrast, numerical results have shown that the presence of nanoparticles slightly intensifies the secondary flow due to buoyancy, in particular in the developing region. It also increases the average Nusselt number and decreases slightly the product ReC[subscript f] with respect to those of water