Solução numérica da convecção natural laminar de nanofluido em cavidade fechada preenchida com meio heterogêneo

Abstract

In the past decades, as technology developed, several numerical studies have been performed with nanofluids due to its beneficial properties offered, especially on heat transfer enhancement. Nanofluids have been used in different applications, such as electronic circuit cooling systems, aiming for higher efficiencies and costs reduction. In the present study, it is carried a numerical investigation of the laminar natural convection of nanofluids in an enclosure filled with disconnected conductive solid blocks. The enclosure is laterally heated and the horizontal walls are adiabatic. The mathematical formulation is given by the mass, momentum and energy equations. The numerical analysis is performed through the CFD Ansys Fluent Software. It is evaluated different parameters on the heat transfer magnitude, such as the Rayleigh number, nanoparticle diameter and volume fraction, type of nanofluid and number of blocks inside the enclosure. The Rayleigh numbers employed are 104, 105, 106 and 107. The cavity has constant porosity of 0,64 and the number of blocks are 9, 16 and 36. The nanoparticle diameters are 25, 50 and 100nm. Alumina and copper nanoparticles are used with water as base fluid. The nanoparticle volume concentrations are 0, 1, 2, 3, 4 and 5%. For the calculation of effective thermal conductivity and dynamic viscosity, it is employed correlations from the literature. The flow is assumed as laminar, single-phase, steady state, bi-dimensional and with constant thermophysical properties and incompressible with Boussinesq-Oberbeck for the buoyancy term. The solution methods are verified numerically by reproducing and comparing results with scientific studies. The results are presented with the mean, minimum and maximum Nusselt number, streamlines and isothermals. It was noticed that as the Rayleigh number increases the heat transfer increases. The same effects are observed, in general, with the reduction of the nanoparticle diameter and with the increase of the nanoparticle volume fraction, in some cases reaching 27%. However, by increasing the number of blocks inside the enclosure, the heat transfer decreases. The alumina, Al2O3, nanoparticles achieved better results on the heat transfer enhancement than the copper nanoparticles, Cu.