The metal pad roll, or sloshing instability is a long-wave deformation of an interface (fig. 1). It is well known from aluminium reduction cells, where it limits the possible minimal thickness of the electrolyte layer. The instability is caused by an interaction of a vertical magnetic field with horizontal cell currents. The latter result directly from the deformed interface (fig. 2). A vertical magnetic field may originate from external feeding lines or may just be the Earth magnetic field.
|Fig. 1: Metal pad roll instability in a liquid metal battery.||FIg. 2: Compensation current due to the interface inclination.|
The metal pad roll instability may potentially short-circut a liquid metal battery. It must therefore be avoided. Especially shallow cells with large cell currents and large vertical stray fields are susceptible to the sloshing instability. The density jumps between the single phases should be as large as possible to avoid sloshing. At HZDR we use potential theory, numerical simulation and experiments in order to better understand the onset and relevance of metal pad rolling for large scale liquid metal batteries. We further study the coupling of both interfaces in the battery. Depending on the density ratios and the surface tension, very different wave shapes can appear (fig. 3).
|Fig. 3: Different instabilites of the two interfaces in a liquid metal battery.|
- Horstmann, G.M.; Weber, N.; Weier, T.
Coupling and stability of interfacial waves in liquid metal batteries
- Weier, T.; Bund, A.; El-Mofid, W.; Horstmann, G.M.; Lalau, C.-C.; Landgraf, S.; Nimtz, M.; Starace, M.; Stefani, F.; Weber, N.
Liquid metal batteries - materials selection and fluid dynamics
IOP Conference Series: Materials Science and Engineering 228(2017), 012013
- Weber, N.; Beckstein, P.; Herreman, W.; Horstmann, G.M.; Nore, C.; Stefani, F.; Weier, T.
Sloshing instability and electrolyte layer rupture in liquid metal batteries
Physics of Fluids 29(2017), 044101
- Weber, N.; Beckstein, P.; Galindo, V.; Herreman, W.; Nore, C.; Stefani, F.; Weier, T.
Metal pad roll instability in liquid metal batteries
Magnetohydrodynamics 53(2017), 129-140