Résumé:
The author presents here, a contribution to the study of two-dimensional laminar natural convection of Newtonian incompressible nanofluids confined in coaxial elliptical tubes heat exchanger. The external wall is maintained cold while the internal wall is subjected to different parietal thermal conditions. The effects of inclination angle and the injected nanoparticles type are examined for considered, Rayleigh number and volume fraction, values. A numerical code with finite volumes method based on Vorticity-Stream function formulation is developed to resolve the continuity, momentum, and energy equations written in elliptic coordinates considering Boussinesq approximation. The study consists of three parts, for different Rayleigh numbers (103<Ra<105) and volume fractions (0<<0.08). In the first part, the internal wall of the Cu/Water nanofluid filled annulus is partially heated while the external one is cold. Three different parietal thermal conditions are considered. In the first one, a constant temperature is imposed on the top and the bottom of the internal wall. Secondly, the same temperature is imposed on the right and left sides of this wall and finally, the right top and the left bottom of the wall are the heated areas. The areas kept cold in the three cases are at the same temperature as the external wall. For the second part, both walls of the Cu/Water filled annulus are kept at uniform temperatures, the internal hot and the external cold. The effect of the inclination angle α, for values 0°, 10°, 45°, 60° et 90°, is highlighted. A comparison of Cu/Water, Ag/Water and Al2O3/Water performances in our annular space when α=90°, has been established for the third part. The obtained numerical results, presented as mean and local Nusselt numbers profiles as well as isotherms and streamlines contours, show that adding nanoparticles to base fluid contribute to heat transfer enhancement.
