Effect of a Periodic Magnetic Field on Natural Convection in a Hexagonal Cavity Containing a Nanohybrid Fluid

This article examines natural, laminar, and unsteady convective heat transfer in a hexagonal cavity filled with an Al2O3-Ag-water nanohybrid under the influence of a periodic magnetic field. The inclined walls of the cavity are maintained at a constant low temperature, the bottom wall is uniformly heated, and the top wall is considered adiabatic. The dimensionless equations governing the system were solved using the lattice Boltzmann method. The results illustrate the variation of the average Nusselt number (Num), streamlines, and isotherms. The study analyzes the effects of key parameters, including the Rayleigh number (Ra), Hartmann number (Ha), magnetic field period (λ), inclination angle of the cavity (γ) and nanoparticle volume fraction (ϕ), on the flow and heat transfer characteristics. The numerical results show a significant increase in the average Nusselt number with the increase in nanoparticle volume fraction and Rayleigh number. In contrast, the Hartmann number and the cavity inclination angle have opposing effects. Moreover, the numerical results have been proven that the period of the magnetic field significantly affects the heat transfer efficiency in the studied system. Finally, at high Rayleigh numbers (Ra = 106), the tilt angle γ significantly affects heat transfer, resulting in a reduction of more than 32% as γ varies from 0 to 3π/4.