Analysis of the first and second laws of thermodynamics for MHD two-phase natural convection of water/Fe2O3 ferro-nanofluids in a 3D baffled enclosure

Abstract

The study of the flow of nanofluids (NFs) in the presence of external fields and the effect of these fields on the heat transfer rate of NFs is the subject of engineering and medical science. Magnetic fields are among the external fields applied to fluids. These fields receive a lot of attention in recent years due to their specific features and applications. This study conducts a numerical investigation of the natural convection of water/ Fe2O3 NFs in nanoparticle volume fractions of φ =0, 2, and 4% =0, 2, and 4% in a baffled l-shaped enclosure under a magnetic field. Calculations with different magnetic field intensities are examined. The natural convection is considered laminar and examined at different Rayleigh numbers. The effects of geometric shape changes (baffle displacement) on the heat transfer and entropy generation rates (S˙g) are also investigated. This study is mainly conducted to investigate the effect of the proposed parameters on the NF flow, heat transfer, average and local Nusselt numbers, the curves of velocity distribution and dimensionless temperature distribution, and S˙g. According to the results, increasing the Rayleigh number causes an increase in the temperature difference between hot and cold surfaces and intensification of the buoyancy currents. This increases local and average heat transfer and S˙g. Nuave increases by 59.20 and 38.168%, respectively, with an increase in the Rayleigh number from 104 to 105 and 106 in φ=4%. The results also showed that increasing the φ and magnetic field intensity decreases heat transfer and increases S˙g. So that in Ra=104 and 105, the S˙g increases from about 40 to 75 with increasing the φ and in Ra=106 the S˙g increases from about 8000 to 15,000. This can be attributed mainly to the reduction in the intensity of buoyancy currents. In general, any factor that increases heat transfer causes an increase in S˙g. The Nuave increases 4.64 and 9.29% 4.64 and 9.29% with increasing the φ from φ=0 to 2.4% in Ha= 40.