Direct measurement of through-plane thermal conductivity of partially saturated fuel cell diffusion media

Direct measurement of through-plane thermal conductivity of partially saturated fuel cell diffusion media. " Master's Thesis, I am submitting herewith a thesis written by Guoqing Xu entitled "Direct measurement of through-plane thermal conductivity of partially saturated fuel cell diffusion media." I have examined the final electronic copy of this thesis for form and content and recommend that it be accepted in partial fulfillment of the requirements for the degree of Master of Science, with a major in Mechanical Engineering. We have read this thesis and recommend its acceptance: (Original signatures are on file with official student records.) ACKNOWLEDGEMENTS To my advisor, Dr. Matthew M. Mench, for giving me the opportunity to work in the lab collaborating with an amazing group of graduate students, postdocs, research professors and administrative staff, and for passing on to me his research, career and cultural experience. To the members of the Navigators at University of Tennessee, Knoxville for their help, friendship and support. To General Motors for their insight and support. ABSTRACT Polymer electrolyte fuel cells (PEFCs) are predicted by many as the most feasible alternative to heat engines and for battery replacement in automotive, portable, and stationary power applications. Fuel cell performance and durability are inseparably related to the presence of liquid water throughout the fuel cell system. To better understand the mechanical and thermal characterization of diffusion media (DM) is essential to PEFC DM design, optimization and production to improve water and thermal managements. Diffusion media are one of the important components in PEFCs in terms of the reactant permeability, the product permeability, the electronic conductivity, the heat conductivity, and the mechanical strength. Thermal conductivity is a particularly important parameter due to the interplay between heat and water management. The thickness of DM is one of the components that are highly dependable on compression. In this study, optical microscope was used to investigate the stress strain relationship. Nonlinear sharp increase in strain at initial compressive loading was observed. Thermal conductivity of all dry DM was found to increase with compression. Measured and predicted maximum thermal conductivity as a function of saturation for DM at 2MPa compression was performed. There was a significant increase in thermal conductivity with an increase in saturation. Thermal conductivity as a function of both compression and saturation was developed. Figure 2. SEM of nonwoven fiber paper and woven carbon cloth DM structure: (a) nonwoven fiber; (b) woven carbon cloth. …