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ISSN Online: 2379-1748
8th Thermal and Fluids Engineering Conference (TFEC)
Fluid engineering issues in the design of industrial-scale flow batteries
Abstract
Vanadium redox flow batteries (VRFB) have independent scalability of energy and power and are best suited for grid-level energy storage applications. Conventional VRFB stacks have thick graphite plates on which channels are grooved to facilitate electrolyte flow uniformly distributed over the cell with minimal pressure drop, both of which are essential for large (industrial-scale) flow battery cells. However, the graphite plates are prone to sweating (leading to leakage issues) and also contribute to nearly 75 % of total stack weight. In the present work, we explore the use of thin graphite sheets as an alternative to thick graphite plates to serve as separator-cum-current collectors. We propose a two-frame cell concept in which the positive and the negative electrode felts are embedded in plastic frames, and are retained in compressed condition by the thin graphite sheet on one side and the proton-conducting membrane on the other side. The hydrodynamics and electrochemical performance of such a cell configuration is studied in the present work both experimentally and using computational fluid dynamics (CFD) simulations. Experimental results from cells of 132 and 440 cm2 active area shows excellent results with the smaller cells but not with the baseline case of the larger cell. Noting that CFD results do not indicate flow non-uniformity problems, an innovative serpentine bypass is created within the cell. This is shown to substantial improvement in the power density with a marginal pressure drop penalty. Optimization of this bypass approach may yield even better results and is under study.