  Liquid metal batteries are proposed for low-cost grid scale energy storage.
During their operation, solid intermetallic phases often form in the cathode
and are known to limit the capacity of the cell. Fluid flow in the liquid
electrodes can enhance mass transfer and reduce the formation of localized
intermetallics, and fluid flow can be promoted by careful choice of the
locations and topology of a battery's electrical connections. In this context
we study four phenomena that drive flow: Rayleigh-B\'enard convection,
internally heated convection, electro-vortex flow, and swirl flow, in both
experiment and simulation. In experiments, we use ultrasound Doppler
velocimetry (UDV) to measure the flow in a eutectic PbBi electrode at
160{\deg}C and subject to all four phenomena. In numerical simulations, we
isolate the phenomena and simulate each separately using OpenFOAM. Comparing
simulated velocities to experiments via a UDV beam model, we find that all four
phenomena can enhance mass transfer in LMBs. We explain the flow direction,
describe how the phenomena interact, and propose dimensionless numbers for
estimating their mutual relevance. A brief discussion of electrical connections
summarizes the engineering implications of our work.
