Contribution à l’étude théorique des transferts thermiques convectifs dans un nanofluide

Abstract

This research is a 3D computer simulation of fluid flows, combined to heat transfer in a forced and mixed convection mode, for a permanent and steady laminar flow through an annular duct made up of two horizontal and concentric cylinders. While the inner cylinder is adiabatic, the outer cylinder is subjected to a constant parietal heating. The annulus duct is traversed by a nanofluid laminar flow composed of a fluid base (water) and nanoparticles of aluminum oxide Al2O3 with constant physical properties regarded as incompressible and Newtonian. This physical problem is modeled by mass conservation equations, by movement and energy amounts in a cylindrical coordinate system accompanied by appropriate boundary conditions. Different approaches were developed, such as the monophasic and the biphasic approaches, to which belong the fluid volume models, the mixing model and the Eulerian model. These equation systems were solved as to the single-phase model by means of the finite volume method with a second-order spatial and temporal precision and the SIMPLER algorithm for the sequential solution of equations. The dynamic and thermal fields are obtained for various Reynolds number values, ranging from 500 to 2000, reaching (1%, 4%,8%) for different concentrations of nanoparticles, and between (0, 104 and 105) for different numbers of Grashof. The results show that the nanofluid behavior, whether in a forced convection mode or in mixed convection mode are, from both a hydrodynamic and a thermal points of view, characteristics of a trend similar to the behavior of a conventional fluid. In a forced convection, dynamic and thermal fields reflect radial velocity and temperature gradients, as well as a Nusselt number with asymptotic behavior at the output. In a mixed convection, the cell structure and the lamination temperatures through a straight section appear with an increasing number of Grashof, giving rise therefore to an increase in the Nusselt number, and thus to a better heat transfer.