Natural convection and anisotropic heat transfer of shear-thinning ferro-nanofluid in partially heated rectangular enclosures under magnetic field

This paper studies the anisotropic natural convective heat transfer of ferro-nanofluids with shear-thinning property in a partially heated square enclosure for revealing the influence of the anisotropic thermal conductivity. The viscosity model of water-based Fe2O3 nanofluids that depends on both shear rate and the volume fraction is fitted with experimental data. The constitutive model of the anisotropic thermal conductivity is derived based on the principle of material frame indifference of Continuum Mechanics, and the numerical solver is built based on the library of OpenFOAM. The parametric study shows that the shear-thinning property can enhance the heat transfer rate, and the effect is related to the intensity of the shear thinning. Furthermore, the analysis of the influence of the magnetic field reveals that the existence of the magnetic field enhances the heat transfer, and the heat always transfer faster along the magnetic field, which implies the possibility of controlling the heat transfer of the ferro-nanofluids by changing the distribution of the external magnetic field. In addition, the anisotropy of thermal conductivity will be strengthened by the increase of the Hartmann number and nanoparticle concentration, and the Nusselt number is larger with higher Rayleigh number and lower Hartmann number.