MHD Natural Convection of Fe3O4-Water Nanofluid in a Cubic Cavity

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Sumy State University
The effect of the three main directions of a uniform external magnetic field on the free convection in a cubic cavity differentially heated and filled with the Fe3O4-H2O nanofluid is numerically studied. The finite volume method is chosen for the discretization of the system of partial differential equations governing the MHD phenomenon and the numerical resolution is made using the Ansys-Fluent 14.5 software. In this work, the problem was studied for pure water (∅ = 0), then for water with the addition of small proportions of nanoparticles (∅ = 1%,2%,3% and 4%). The effect of the three main magnetic field directions, the Hartmann number (𝐻𝑎 = 0,5,10,15 and 20) and the Rayleigh number (𝑅𝑎 = 103, 104, 105 and 106), on the thermo-hydrodynamic nanofluid behavior is examined. The thermal conductivity and the dynamic viscosity are determined by correlations specifically elaborated for Fe3O4-H2O nanofluid from anterior experimental works. Results of this numerical simulation show that, the more the value of Rayleigh number increases, the more the slope of the decrease of the Nusselt number with the increase of the intensity of the magnetic field becomes stronger. The horizontal application of the magnetic field, i.e. parallel to the temperature gradient, reduces the heat transfer more than the other two directions. In the second position, the greatest decrease in the rate of convective heat transfer is recorded when the direction of the magnetic field is vertical, i.e. in the direction of gravity.