Contribution à l’etude théorique des fluides caloporteurs tel les nanofluides;

Abstract

The present work is concerned of numerical simulation of three-dimensional laminar forced and mixed convection of nanofluids. The effects of nanoparticle material, base fluid and volume concentration were highlighted. Al2O3-eau, Cu-eau and Al2O3-eau/ éthylène-glycol nanofluides were employed in this study at multiple volume fractions. The flow geometry is horizontal smooth pipe submitted to a constant and uniform heat flux. Based on single-phase approach, three dimensional conservation equations of mass, momentum and energy with the appropriate boundary conditions have been solved using finite volume method with the schemes of spatial and temporal discretization of second order precision and by using the SIMPLER. At a fixed Reynolds number Re = 300 and Grashof number varying from 0 to 5×105. The results show an increase in heat transfer ratio compared to pure water at several volume fractions for both alumina and copper based nanofluids. At a fixed volume fraction, the axial Nusselt number does not increase significantly in forced convection case. However, in mixed convection case the axial Nusselt number augments considerably especially with Cu-water nanofluid. Instead, the dispersion of the alumina nanoparticles in the water / ethylene glycol mixture with two volume concentrations 30 and 50% gives a better heat transfer ratio compared to pure water base fluid. On the other hand, secondary flow and axial velocity are slightly affected by nanoparticles volume fraction. It is proved in this study that nanofluids can also contributes to optimise pipes compactness, using 2% and 4% of alumina and copper respectively dispersed in water flowing through a pipe with given length gives higher axial Nusselt number ratio compared to pipes larger length but containing pure water.