Ultrasound Velocity Measurement in a Liquid Metal Electrode

Abstract

A growing number of electrochemical technologies depend on fluid flow, and often that fluid is opaque. Measuring the flow of an opaque fluid is inherently more difficult than measuring the flow of a transparent fluid, since optical methods are not applicable. Ultrasound can be used to measure the velocity of an opaque fluid, not only at isolated points, but at hundreds or thousands of points arrayed along lines, with good temporal resolution. When applied to a liquid metal electrode, ultrasound velocimetry involves additional challenges: high temperature, chemical activity, and electrical conductivity. Here we describe the experimental apparatus and methods that overcome these challenges and allow the measurement of flow in a liquid metal electrode, as it conducts current, at operating temperature. Temperature is regulated within ±2 °C using a Proportional-Integral-Derivative (PID) controller that powers a custom-built furnace. Chemical activity is managed by choosing vessel materials carefully and enclosing the experimental setup in an argon-filled glovebox. Finally, unintended electrical paths are carefully prevented. An automated system logs control settings and experimental measurements, using hardware trigger signals to synchronize devices. This apparatus and these methods can produce measurements that are impossible with other techniques, and allow optimization and control of electrochemical technologies like liquid metal batteries. Video LinkThe video component of this article can be found at

Fluid Mechanics of Liquid Metal Batteries

“…If the sidewall is cylindrical, boundary conditions further encourage poloidal convection rolls. Such rolls have been observed in liquid metal battery experiments, and the characteristic mass transport time decreases as Ha increases [134,135]. Simulations have shown similar results, with the number of convection rolls decreasing as the current increases [136].…”

“…Also, no ultrasound measurements in a working, threelayer battery have been published. Instead, all measurements to date were made in a single liquid metal layer, without electrolyte or a second metal layer [134,135]. However, single-layer experimental models capture only a subset of the fluid mechanics of liquid metal batteries, including Joule heating but not heating via entropy change or heat of formation, which may have significant effects [22]; and including thermal convection but not compositional convection.…”

Competing forces in liquid metal electrodes and batteries

“…The temperature is chosen to match the operating conditions of a Na||PbBi battery [87]. The apparatus minimizes heat exchange by using ceramic insulation, which allows for the operating temperature to be maintained for the duration of the experiment [see 49,88].…”

Sloshing instability and electrolyte layer rupture in liquid metal batteries

“…Due to their completely liquid interior, LMBs have attracted the attention of fluid dynamists as well. A number of recent publications are devoted to the problem of the Tayler instability and its circumvention [19][20][21] , to temperature-driven convection [22][23][24] and electrovortex flows [25][26][27] in LMBs, and to a simplified model of sloshing in a three layer system 28 .…”