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Section 9.1 Summary Chapter 9 Summary and Outlook Summary and Outlook 9.1 Summary This work consists of three parts. In the first part, a comprehensive, multi-physical lumped-parameter model is developed on the basis of numerous publications. The model is then validated using experimental data from three different manufacturers. However, because models typically found in the literature do not accurately reflect the behavior of the three real-life systems, an adaption method is introduced. Using the experimental data, the surface area for calculating the current density in the diffusion layer around the fibers of the graphite felt electrode is approximated. After its adaption, the model simulates the behavior of two systems very well; the simulation of the third system, although not ideal, is still more accurate than with the non-adapted literature approach. In the second part of this work, the validated model is applied to the most comprehensive design study of a VRFB published to date. Twenty-four cell designs are evaluated for their eligibility for a single-stack system and a three-stack string system. In each system, 40-cell stacks are assembled virtually using the twenty-four designs. The design study presents a straightforward approach that uses the desired operational limits for cell voltage, SoC and flow rate to obtain a realistic system design. A unique feature of this design study is its simultaneous consideration of design and operational parameters. For each design, of both the single-stack and the three-stack string systems, the flow rate is optimized, to maximize the comparability of the designs. The design study produced the following four key results: Increasing the electrode area and using a longer and narrower channel limit the impact of the shunt currents equally well. However, both measures face a strong saturation effect. For a given flow factor and aspect ratio, a larger electrode yields a larger electrolyte fluid velocity and thus a larger mass transfer coefficient. Hence, a larger electrode requires a lower flow factor for optimal operation. The large electrolyte demand of a large electrode causes an over-proportionally high pressure drop in the inlet and outlet channels. The electric series connection of three stacks facilitates the grid connection of the battery but reduces system efficiency by 1.6 to 3.3 %-points, depending on the applied current density. Only for higher current densities, however, it appears that the more efficient PCS resulting from higher input DC voltage might more than compensate for these efficiency losses. For a single-stack system operating under variable load, a 2000-cm2 cell with a long, medium-width channel is the best design. However, VRFB systems having comparable efficiencies can be built using electrode areas between 1000 and 4000 cm2. 143PDF Image | Model-based Design Vanadium Redox Flow Batteries
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