Natural convection of MHD flow in a long vertical closed duct with different wall conductance ratios

Jie Mao - Yang Cheng - Liming Xie

School of Mechanical Engineering, Hangzhou Dianzi University, Hangzhou 310018, China

Abstract
Buoyancy-driven magnetohydrodynamic (MHD) flow should be considered when studying the heat transfer mechanism of dual-cooled lead lithium blankets in thermonuclear fusion reactors. In this paper, an MHD heat transfer program considering the buoyancy effect has been developed and validated based on the OpenFOAM environment. Natural convection of MHD flow in a long vertical closed duct has been numerically simulated. The effect of the wall conductance ratio and applied magnetic field direction on the buoyancy-driven MHD flow has been studied. The applied magnetic field suppresses the MHD natural convection. The suppression effect is strengthened as the wall conductance ratio increases. The electric current induced both by the electric potential gradient and by the fluid motion of liquid metal in the magnetic field decreases with increasing wall conductance ratio. However, the induced electric current density increases with the wall conductance ratio increase. As a result, a stronger damping Lorentz force is applied to the liquid metal flow. The magnetic field direction has a significant effect on natural convection of MHD flow. The magnetic field parallel to the temperature gradient has a stronger suppression effect on natural convection than the magnetic field applied perpendicular to the temperature gradient. The average Nusselt number decreases with increasing wall conductance ratio, and it does not decrease noticeably when the magnetic field is parallel to the temperature gradient. The results can be referenced to when designing the dual-cooled lead lithium blankets. Tables 2, Figs 8, Refs 38.