Liquid metal batteries are discussed today as an economic grid-scale energy storage, as required for the deployment of fluctuating renewable energies. These batteries consist of three stably stratified liquid layers: two liquid metal electrodes are separated by a thin molten salt electrolyte, this way forming an electrochemical concentration cell. The completely liquid interior, which is on the one hand very beneficial for the energy efficiency, also poses some major challenges on the other hand. Strong cell currents in combination with electromagnetic fields make liquid metal batteries highly susceptible to various kinds of magnetohydrodynamic instabilities. In particular, the so-called metal pad roll instability, which can drive uncontrollable wave motions in both interfaces, was identified as a key limiting factor for the operational safety. The metal pad roll instability is well known from conceptually similar aluminum reduction cells, but still poorly understood in the framework of liquid metal batteries. Mainly by developing analytical wave models, but also by employing numerical simulations and by setting up a newly designed wave experiment, the present thesis pursues the goal of providing a better understanding of interfacial wave dynamics and the manifestation of the metal pad roll instability in liquid metal batteries. As a main result, a three-layer formulation of standing gravity-capillary waves reveals that the pressure coupling between the two interfaces plays a crucial role in the cell stability. Three different coupling regimes, which partially involve novel types of interfacial wave instabilities, are identified and classified by two dimensionless parameters. Building on this theoretical work, the wave experiment is exploited to further investigate different metal pad roll-related wave properties. The crucial importance of the contact line dynamics is emphasized and viscous damping, which is important for the estimation of instability onsets, is discussed as a function of the layer heights. Finally, a hybrid interfacial sloshing model is formulated and equipped with recently derived two-layer damping rates to account for viscous dissipation. The model allows to study and interpret the forced wave mechanics in the wave experiment as a function of eight dimensionless parameters and can, as an additional application, be exploited to optimize mixing in orbitally shaken bioreactors. As a further key result, the sloshing model reveals the formation of novel spiral wave patterns under the effect of strong damping.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:76390 |
| Date | 08 November 2021 |
| Creators | Horstmann, Gerrit Maik |
| Contributors | Eckert, Kerstin, Kelley, Douglas H., Herreman, Wietze, Technische Universität Dresden, Helmholtz-Zentrum Dresden-Rossendorf |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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