Electromagnetically excited flows and instabilities in liquid metal batteries

We will provide an overview of the liquid metal battery (LMB) related activities at the Helmholtz-Zentrum Dresden - Rossendorf (HZDR) with a focus on magnetohydrodynamic aspects of future large scale LMBs. High current densities together with a large cross section will result in substantial currents accompanied by considerable magnetic fields. Thus electromagnetically driven flows and instabilities should be taken into account for large enough installations. While beneficial effects of mild electromagnetically driven flows are to be expected for the cathodes, the thin electrolyte layers have to be protected against violent motion.

The Tayler instability (TI) can be understood as a generic case of a current driven instability under perfectly uniform current, i.e., ideal conditions. In this sense it constitutes sort of an upper bound for a current bearing fluid to remain at rest. Modifying the magnetic field distribution in the cell is an effective means to suppress the TI.
Different field configurations to achieve TI suppression and their relative merits will be discussed and related to TI saturation mechanisms.
Non-uniform current distributions are more typical for real settings. They give rise to rotational Lorentz force distributions and will thereby also generate electro-vortex flows (EVFs). In terms of LMBs the concrete shape of the current collectors plays a crucial role in whether EVFs exist and how they might interact with the TI. We will conclude with electromagnetically exited interface instabilities and discuss similarities to and differences from sloshing modes known from aluminium reduction cells.