Étude Numérique des écoulements thermoconvectifs d’un nanofluide à travers un espace cylindrique annulaire muni d’ailettes

Abstract

The doctoral project concerns a three-dimensional numerical study of the thermo-convective flows of a nanofluid through an annular cylindrical space without fin and equipped with fins. Newtonian, incompressible and laminar flow with temperature dependent physical properties. The single-phase approach is adopted. The outer cylinder is uniformly heated while the inner cylinder is adiabatic. The flow and thermal fields are modeled by the continuity equation, the three momentum equations and the energy equation of the nanofluid with appropriate initial and boundary conditions using a cylindrical coordinate system. The nonlinear differential equations with partial derivatives are solved numerically by the finite volume method with a spatio-temporal discretization of the second order. The SIMPLER algorithm was used to solve the speed-pressure coupling. A complete parametric analysis on the effect of the presence of nanoparticles dispersed in the fluid such as volume fraction, type and shape on the development of thermal and hydrodynamic fields. The dimensionless control parameters that control the problem under consideration are the Reynolds number, the Prandtl number and the Grashof number, a radius ratio set to 2. For the volume fraction ranging from 0 to 10%, six nanoparticles Types, two metallic types Cu and Ag, three ceramics Al2O3, TiO2 and CuO. Also four forms of the nanoparticles are the shape the spherical shape, Blade, Cylinder, Platelet and Bricks shape. The study of these effects on heat transfer in a annular cylinder without fins and with fins is the main objective of this study. The results concerning the different cases studied for the effect of the volume fraction of the different nanofluids shows that the increase in the volume fraction increases the heat transfer along the annular duct. The axial and mean Nusselt numbers obtained are also higher in the case of the nanofluid (Ag / water). They also show that the use of the Ag nanoparticle induces a better improvement of the heat transfer followed by Cu, Al2O3, CuO at the end TiO2. Regarding the effect of the shape of the nanoparticles Blade shape greatly improves the heat transfer compared to other shapes. A generating correlation expresses the average Nusselt number for the different shapes as a function of the volume fraction proposed: Nu moy = a + bϕ + cϕ2. Another correlation which expresses the average Nusselt number of the nanofluid (TiO2/water) and the hybrid nanofluid (Ag-TiO2 / water) as a function of the number of Grashof, Prandtl and the volume fraction:

The use of the heat-generating fins, attached longitudinally to the outer cylinder and immersed in the nanofluid, greatly improves the heat transfer compared to those of a nonfinned horizontal duct dû to the increase in the exchange area between The nanofluid and the fins in the annular space.