Liquid metal Thermo-magnetic systems for space, nuclear and industrial applications

Abstract

Liquid alloy systems have a high degree of thermal conductivity far superior to ordinary non-metallic liquids and inherent high densities and electrical conductivities. This results in the use of these materials for specific heat conducting and dissipation applications. Typical applications for liquid metals include heat transfer systems, and thermal cooling and heating designs. Uniquely, they can be used to conduct heat and/or electricity between nonmetallic and metallic surfaces. The motion of liquid metals in strong magnetic fields generally induces electric currents, which, while interacting with the magnetic field, produce electromagnetic forces. Thermo-magnetic systems, such as electromagnetic pumps or electromagnetic flow meters, exploit the fact that liquid metals are conducting fluids capable of carrying currents source of electromagnetic fields useful for pumping and diagnostics. Liquid metal-cooled reactors are both moderated and cooled by a liquid metal solution. These reactors are typically very compact and they can be used in regular electric power production, for naval and space propulsion systems or in fission surface power systems for planetary exploration. Liquid metals in fusion reactors can be used in heat exchange, tritium breeder systems and in first wall protection, using a flowing liquid metal surface as a plasma facing component. Liquid metal targets and beam dumps for spallation and for heat removal will also be needed at many high power particle accelerator facilities where the severe constraints arising from a megawatt beam deposited on targets and absorbers will require complex procedures to dilute the beam, and liquid metals constitute an excellent working fluid due to its intrinsic characteristics. In the metal industry, thermo-magnetic systems are used to transport the molten metal in between processes. By developing methods to control the surface tension of liquid metals, applications can be developed in configurable electronics, microfluidic channels and MEMS. But the coupling between the electromagnetics and thermo-fluid mechanical phenomena observed in liquid metal thermo-magnetic systems, and the determination of its geometry and electrical configuration, gives rise to complex engineering magnetohydrodynamics and numerical problems were techniques for global optimization has to be used, MHD instabilities understood- or quantified- and multiphysics models analyzed. The environment of operation adds even further complexity, i.e. vacuum, high temperature gradients and radiation, whilst the presence of external factors, such as the presence of time and space varying magnetic fields, can lead to the need of developing active flow control systems. In this review paper we explore the different applications of liquid metal technology, we present the magnetohydrodynamics equations behind this technology and the research topics that should be addressed in the near future and currently under research by this author.