Work

Two-dimensional Rayleigh-Bénard convection in molten salts affected by thermal radiation and magnetic field

Year: 2025

Type: article

Abstract: Direct numerical simulations of two-dimensional radiative magnetohydrodynamic Rayleigh-Bénard convection in an enclosed square cavity filled with radiatively participating and electrically conducting molten salts are performed. The study aims to investigate the effects of both thermal radiation and a vertical magnetic field on heat transfer and fluid dynamics under various forcing conditions. The present work is motivated by its relevance to the efficient design of thermal energy storage systems, particularly in concentrating solar power plants. To explore the underlying physics, the combined collocation spectral method and discrete ordinates method are developed to solve the governing equations, including the Navier-Stokes equations, energy equation, and radiative transfer equation. Numerical simulations are carried out for Rayleigh number within the range of 10 4 ≤ Ra ≤ 10 6 under different Hartmann number 0 ≤ Ha ≤ 150 , characterizing the effect of magnetic field, and radiative parameters such as Planck number 5 × 10 − 4 ≤ Pl ≤ 2 , optical thickness 0.2 ≤ τ ≤ 1 , and scattering albedo 0 ≤ ω ≤ 0.9 . First, in the case of Ha = 0 and fixed values of τ and ω , the numerical results of radiative Rayleigh-Bénard convection show that, depending on Ra , slight or moderate thermal radiation may enhance, suppress, or cause only slight changes on the global convective heat transfer and fluid flow. However, excessive radiation weakens the contribution of thermal convection to the overall heat transfer. Additionally, the increase of Ra diminishes this suppressing effect. For a fixed Ra , increasing ω while keeping τ constant also slows down this inhibition, whereas increasing τ at fixed ω speeds up this inhibitory process. For radiative magnetohydrodynamic Rayleigh-Bénard convection, i.e., Ha > 0 , we find that radiation imposes a similar influence on thermal convection as it does in the absence of magnetic field, while the magnetic field can weaken the positive effect of radiation on convection and enhance its negative impact.

Source: International Communications in Heat and Mass Transfer

DOI: 10.1016/j.icheatmasstransfer.2025.109688