Polymer electrolyte membrane fuel cells (PEMFCs) have been described as potential power systems for the future of the automotive sector. These devices combine hydrogen and oxygen to form water and to generate electricity. Benefits of the system include no tailpipe emissions, and the potential for higher efficiency than standard internal combustion engines. While these systems have improved over the years, there are still technical challenges that must be overcome before bringing them to the commercial vehicle market, including increasing the power output of these systems and reducing the total cost. One method of achieving this is to increase the power density of the individual fuel cells, allowing for smaller packs with higher power output, which saves on material costs, and improves power to the wheels. One potential way of improving power density is through improvements to the gas distributor design of the fuel cell, also known as the flow field, through the use of the interdigitated flow field. There has been simulation work exploring how design parameters affect the performance characteristics of the interdigitated flow field, but little in the way of experimental work to support these simulations. This dissertation provides experimental data on interdigitated flow field design choices, specifically how channel width, channel depth and channel length affect the performance and water removal characteristics. It further provides information on how gas diffusion layer (GDL) choices and cross flow velocity interact to affect the water removal characteristics of the fuel cell. This work is achieved using polarization curve based performance testing and neutron radiography to identify water in the flow field. This work found that for the interdigitated flow field, shorter channels result in improved performance, up to a 33% difference in the maximum net power for some conditions. The improved performance is due to improved water removal capabilities of the flow field. Flow field raw power and limiting current density both benefit from narrower, shallower channels, resulting in a 50% improvement in power density from standard 1x1mm to small 0.25x0.25mm channels. There does seem to be a point beyond which decreasing the channel dimensions will actually reduce net power density performance, due to high parasitic pumping power losses associated with the small dimensions. Finally, the choice of gas diffusion layer in these flow fields has a notable effect on the liquid water handling of the fuel cell, particularly at higher cross flow rates. All of these effects are taken into account when making a recommendation on design choices and the associated recommended operating conditions in interdigitated flow field fuel cells.
|Advisor:||Park, Jae Wan|
|Commitee:||Erickson, Paul A., Shaw, Benjamin D.|
|School:||University of California, Davis|
|Department:||Mechanical and Aerospace Engineering|
|School Location:||United States -- California|
|Source:||DAI-B 78/07(E), Dissertation Abstracts International|
|Keywords:||Cross flow, Flow field, Fuel cell, Interdigitated, Polarization curve, Polymer electrolyte membrane pem|
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