Etude des améliorations des nombres de nusselt par l’utilisation de nanofluides ou changement de la géométrie

Abstract

This Ph. D. thesis work reports the results of the study of the laminar forced convective heat transfer flow in two different geometries: A geometry made with two coaxial discs and a micro-channels heat sink. This study is numerical and is based on a finite volume single-phase approach and was achieved using the mixture (water- /γ-Al2O3 ) as nonofluid. The flows are modeled using the Navier Stokes equations along with the energy conservation equation in the fluid domain and the heat conduction equation in the solid domain. The thermophysical properties used (thermal conductivity and dynamic viscosity) were assumed constant or temperature dependent. The thermal and dynamic fields resulting from our calculations show an increase in the local and average Nusselt number, in the average radial heat transfer coefficient, in the relative radial heat transfer coefficient and in the average shear stress at the contact interfaces with increasing Reynolds number. We also noted that the increase in heat flux, the addition of nanoparticles in the base fluid, the assumption of temperature dependent properties and the change in the entry cross section of the channels significantly affect these fields. This improvement of heat transfer using nanofluids may therefore give birth to a promising new technology which manufactures very compact heat exchangers to be used particularly in the domain of power electronics.