External natural convection heat transfer of liquid metal under the influence of the magnetic field

Abstract

Liquid metal is an important heat exchange media in high-power industrial installations. In the fusion reactor, large temperature difference generating in the liquid metal of facing high temperature plasma leads to external natural convection on the first wall. The heat load on the first wall is carried away by the liquid metal which covers on the first wall. The cooling process of unforced liquid metal on large-sized plate is regarded as the external natural convection. A numerical simulation is employed to investigate the external natural convection heat transfer of liquid metal on the vertical plate under the different horizontal magnetic field which is perpendicular to the temperature gradient. The heated plate is placed on one side of the cavity, and two horizontal walls adjacent to it are thermally insulating. The remaining walls are stationary temperature. The results derived from velocity boundary layer and temperature boundary layer analysis are presented as the important investigation subject at different Grashof numbers under the influence of magnetic field. It can be observed that magnetic field will promote or inhibit the liquid metal flow and heat transfer, and the thickness of boundary layer different from internal natural convection, it presents diverse results at different magnetic field intensities and vertical height positions of the heated plate. Under the influence of magnetic field, the thickness of velocity boundary layer increases first and then decreases, while the thickness of thermal boundary layer generally increases. Three modes are found when there is a magnetic field exerting effects on the liquid metal external natural convection. When there is a weak magnetic field and small Grashof number, the magnetic field will enhance natural convection heat transfer, when increasing the Grashof number, magnetic field will inhibit convection heat transfer but will not suppress the flow, the flow changes from three-dimensional to quasi-two-dimensional in a moderate magnetic field. A strong magnetic field restrains convection heat transfer and flow significantly.