Doctoral Dissertations

Date of Award

12-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Mechanical Engineering

Major Professor

Matthew M. Mench

Committee Members

Douglas S. Aaron, Robert M. Counce, Kenneth D. Kihm, Feng-Yuan Zhang

Abstract

Redox flow batteries (RFBs) are a promising grid energy storage technology with the potential to solve numerous problems arising from anticipated increases in renewable energy integration. These systems involve a number of key design tradeoffs, many involving the movement of liquid electrolyte through the system, which impact the overall system efficiency.This work examines the design of the fluid network throughout RFB systems and how design tradeoffs impact the system efficiency. Insights are gained that inform future research and design decisions. Initially, this work focuses on single cell concerns, primarily flow field design. Two common designs from the literature, serpentine and interdigitated, are analyzed to uncover underlying transport characteristics. These findings are used to develop and evaluate two new flow field designs, the Equal Path Length (EPL) and aspect ratio designs. All four designs are evaluated with regard to a number of metrics including viability to be scaled up to larger sizes.To assess the viability of these conclusions on a commercial system, a short four cell stack was developed and evaluated for efficiency and mass transport performance. Additional efficiency concerns specific to stack design such as shunt current were explored using a novel in-situ shunt current measurement technique. The relative impact of this self-discharge phenomenon is investigated and its relationship to operating conditions is evaluated.Finally, a cost model taking into account earlier findings of this dissertation is presented. This model provides context for these findings in terms of real world applications and financial metrics. This model allows for the exploration of which design factors are key cost drivers and provides a guideline for where future research should focus to reduce cost.The primary outcome of this dissertation is a new framework for the design of RFBs rooted in the principle that there may not be one panacea solution for every design problem. Unique solutions dependent upon operating conditions and applications are necessary to maximize performance and minimize cost. Using the conclusions presented in this work will guide researchers and system engineers alike, allowing for improved efficiency and minimized costs as RFBs become a viable grid energy storage solution.

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