Interaction of convective modes with current-driven flow in a liquid metal battery experiment

Liquid metal batteries (LMBs) - a promising technology for grid-scale energy storage - are subject to a variety of flow forcings that may disrupt battery operation. In a typical model of the LMB anode, an adverse temperature gradient is established during operation due to Joule heating of the electrolyte layer. At the same time, the current tends to converge toward the negative current collector, inducing electrovortex flow (EVF). The specific interaction of these two forcings has seen little focus in laboratory studies. Here, we present a series of experiments in a cylindrical layer of gallium subject to the essential forcings of thermal convection and EVF. We scan through a range of temperature gradients and current strengths, using ultrasonic Doppler velocimetry to track the flow patterns. We find that at low currents, the jump-rope vortex (JRV) mode of convection tends to dominate. At the highest currents, the flow resembles canonical EVF. For a fairly broad range of intermediate currents, though, we observe flows that exhibit some properties of both EVF and JRVs, such as periodic oscillations resembling the JRV coinciding with a central jet descending from the electrode resembling EVF. Our results could have significant implications for the flows expected in industrial LMBs.