Numerical study of simultaneous heat and mass transfer in Liquid Metal Batteries

Liquid metal batteries (LMBs) are promising candidates for electrical energy storage. An LMB is a concentration cell made of three liquid layers, stably stratified by density. A molten salt acts as an electrolyte between two liquid metal electrodes. The simple chemistry and geometry, the liquid nature of the active layers and the presence of multi-physics phenomena have made the LMB an intriguing candidate for continuum mechanics investigations. Simultaneous transport of charge, heat, mass and momentum takes place in each liquid layer together with chemical reactions. The interfaces between layers are the places in which electrochemical reactions occur along with interfacial transport phenomena.
In our work we investigate heat and mass transport in LMBs with openFOAM libraries using a multi-region approach. We assign to each layer a numerical region and we design a procedure able to ensure the physical coupling between the different transport mechanisms through an iterative procedure. The heat and mass transfer equations are solved on a global mesh and in the positive electrode region respectively. Then we solve the Navier-Stokes equations in each fluid region. Appropriate boundary conditions were designed to ensure a consistent transport at the interfaces between different regions. Thanks to this procedure we can compute temperature and concentration distributions and the corresponding thermal and compositional convection. Therefore, we can investigate the interaction of different mechanisms and can give a prediction of the fluid flow in the interior of an LMB. The numerical procedure is introduced as well as the first results. Furthermore, the modeling limitations and the future developments are discussed.