Étude des transferts thermo-convectifs tridimensionnels dans les jets impactant et canaux avec des nanofluides hybrides.

Abstract

The main objective of this thesis is to study three-dimensional thermoconvective transfers in impact and channel jets using single and hybrid nanofluids (binary and ternary hybrid nanofluids) of different types and shapes. The behavior of flow, heat transfer, pressure drop, friction factor, system performance, and entropy generation were evaluated using two models. The first is single phase-model, and the second is a two-phase mixture model under laminar and turbulent flow conditions with several turbulence models k-, k-, LES.... etc.). The governing equations were solved using the commercial software Ansys-Fluent 14.5 and, in some cases, with C++ code to program the thermophysical properties of the fluids used, except for the ninth part, which was executed using the Trio-CFD program, which is based on the C++ code. To assess the reliability of the simulation techniques and numerical methods used, the results were compared with several results available in the literature in numerical or experimental works; a good agreement was obtained. The results are divided into ten parts: The first part of this study focuses on the analysis of three-dimensional turbulent forced convection around a cubic block subjected to a horizontal flow and an impact jet. We compared our simulations with experimental data from the literature using different turbulence models. Then, we studied the impact of the position of the impacting jet axis and the Reynolds number ratio using the standard model k-, which gave us the best results compared to the experimental data. In the second part, we performed a numerical simulation of turbulent forced convection of the nanofluid k-, k-, LES.... etc.) to analyze the heat transfer and entropy generation in a channel containing heated blocks cooled by impacting jets. We evaluated the influence of the volume of the nanoparticle fraction, the distance between the heated blocks, and the location of the second jet concerning the first on the two-phase mixing model. In addition, we proposed correlations to facilitate the determination of important results related to this Al2O3 study. In the third part, we performed a numerical analysis of the entropy and generation of the waterTiO2 nanofluid in a corrugated channel subjected to a constant heat flux (q''). For this purpose, we used a two-phase mixing model. This allowed us to study the effect of using a corrugated wall versus a straight wall on flow behavior, heat transfer, and entropy production. In addition, we also examined the impact of the drift rate between the nanoparticles and the base liquid. In the fourth part, we numerically analyzed an impact jet cooling on a flat plate, subjected to a constant temperature, using the SST-kω turbulence model and extended jet holes covered with binary hybrid nanofluids. We were interested in the influence of the combination of two types of nanoparticles Al2O3 et MgO) with different shapes: spherical for Al2O3 and modified (spherical, brick, blade, cylindrical, or wafer) for MgO. Similarly, we evaluated the effect of extended jet holes. In the fifth part, we used hybrid ternary nanofluids to conduct a numerical study on the fluid behavior and heat transfer around a heated mass subjected to a crossflow and an impact jet. These nanofluids comprise particles dispersed in the base fluid, which are Al2O3 (aluminum oxide), Cu (copper) and Ag (silver) are spheres, cylinders, and platelets. We examined the influence of several variables, such as the Reynolds number ratio, the volume of the nanoparticle fraction, the length of the extended jet hole, and the angle of inclination of the impact jet inlet. In the sixth part, an extensive numerical evaluation was carried out on the heat transfer and entropy generation of a three-dimensional heat sink exposed to an impact jet, where the area between the fins of the heat sink was filled with a porous aluminum material saturated with hybrid water/Al2O3-Cu nanofluid.) The effects of various influential factors such as volumetric concentration, permeability, porosity, and nanoparticle diameter on fluid flow, heat transfer, pressure drop and entropy generation were investigated in depth. In the seventh part of our study, we focused on analyzing an impact jet's flow behavior and heat transfer, using hybrid nanoparticles as a working fluid for cooling a processor subjected to an external magnetic field. We used a two-phase mixing model under laminar forced convection flow to evaluate these phenomena. The working fluid was composed of SiO2and CuO nanoparticles with a diameter of 20 nm dispersed in water. We studied the influence of the magnetic field, determined by the Hartmann number, volumetric concentrations, and Reynolds number, on the flow field, heat exchange, thermal efficiency, and pressure drop. In the eighth part, we conducted a numerical study on the thermal analysis of turbulent forced convection flow inside a corrugated absorber tube filled with a porous material comprising molten salt-based hybrid nanofluids. We examined the effects of the porous medium's properties, the nanoparticles' volume fraction, and the type of molten salt on the fluid flow, heat transfer, pressure drop, pumping force, coefficient of friction, and working fluid efficiency. The nanoparticles used were Al2O3 and Gr, with a diameter of 20 nm. Concerning the molten salts,