Effect of near-wall blockage on the magnetohydrodynamics-based double-diffusive convection in rectangular cavities

Abstract

This research work reports the numerical investigation of magnetohydrodynamics (MHD) characteristics around the near-wall blockage $(\mathit{NWB})$ for various separation distances owing to double-diffusive convection (DDC) in a rectangular cavity. The distance between the bottom wall of the cavity and the lower wall of blockage is called separation distance $S_d,$ and it has varied from $(H/4\le S_d\le H/8),$ where H is the height of the cavity. The working fluid is considered as liquid metal - Sodium-Potassium alloy ($Pr=0.054$). The numerical computations are conducted by using an in-house developed lattice Boltzmann method $(\mathit{LBM})$ solver. The simulations are conducted for the steady-state, laminar, incompressible, and Newtonian fluid flow. The effect of NWB has been explored for a range of parameters, such as Rayleigh number $(Ra={10}^4$ and ${10}^5),$ Lewis number $(0.5\le Le\le 1.5),$ buoyancy ratio $(-1.5\le N\le 1)$ and Hartmann number $(0\le Ha\le 300).$ The variation and contour plots show the higher heat and mass transfer (HMT) rates for $S_d=H/4$ at constant Ra. As $S_d$ increases, HMT rates enhance. The increase in Ra, N, and Le induces multiple-cell formation inside the cavity for a given $S_d.$ As Ha augments HMT rates get decreased monotonically. For $Ha\ge 150,$ negligible or slight variation was observed in the rate of HMT. As the obstruction between the bottom wall of the blockage and the adiabatic bottom wall of the cavity increases, shear force occurs, and the buoyancy-driven flow decreases. The outcomes of the numerical investigation are summarized in the form of empirical correlation of $N{u}_{\mathit{Total}}$ for Ra = ${10}^4$ and ${10}^5$ at various separation distances, which might be utilized for probable design purposes.

Keywords:

• Double-diffusive convection
• lattice Boltzmann method
• magnetohydrodynamics
• near-wall blockage
• separation distance

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article.