Characterization and Modeling of Electrochemically Driven Natural Convection

Abstract

Natural convection arises in many types of fluid flow where a diffusive species causes a density change to the fluid. Electrochemical reactions are typically strong drivers of this flow given the combination of a large density change due to reaction and a relatively slow rate of species diffusion. Density stratification in lead-acid batteries is a well documented phenomenon, but the effect of density driven flow is not typically investigated in many electrochemical systems where it is a surprisingly important transport mode. Experiments and models show that a zinc-bromine cell's performance is dominated by this natural convection effect and results in a much higher utilization than would be expected based solely on a diffusive model. Finally we show how electrolyte composition can substantially modify the properties of this flow and how this can potentially benefit other systems.