Equivalent Stiffness Model of a PEM Fuel Cell Stack including hygrothermal effects and dimensional tolerances

[+] Author and Article Information
Ashley Fly

Department of Aeronautical and Automotive Engineering, Loughborough University, United Kingdom

Rui Chen

Department of Aeronautical and Automotive Engineering, Loughborough University, United Kingdom

Xiao-Dong Wang

Research Center of Engineering Thermophysics, North China Electric Power University, China

1Corresponding author.

ASME doi:10.1115/1.4039141 History: Received June 29, 2017; Revised December 24, 2017


Proton exchange membrane fuel cells (PEMFCs) require mechanical compression to ensure structural integrity, prevent leakage and minimise electrical contact resistance. The mechanical properties and dimensions of the fuel cell vary during assembly due to manufacturing tolerances and during operation due to both temperature and humidity; variation in stack compression effects the interfacial contact pressures between components and hence fuel cell performance.

This paper presents a one-dimensional equivalent stiffness model of a PEMFC stack capable of predicting independent membrane and gasket contact pressures for an applied external load. The model accounts for non-linear component compression behaviour, thickness variation due to manufacturing tolerances, thermal expansion, membrane expansion due to water uptake and stack dimensional change due to clamping mechanism stiffness. The equivalent stiffness model is compared to a three dimensional finite element model, showing good agreement for multi-cell stacks.

Results demonstrate that the correct specification of gasket thickness and stiffness is essential in ensuring a predictable membrane contact pressure, adequate sealing and avoiding excessive stresses in the bi-polar plate. Increase in membrane contact pressure due to membrane water uptake is shown to be significantly greater than the increase due to component thermal expansion in the typical PEMFC operating temperature range. The predicted increase in membrane contact pressure due to thermal and hydration effects is 14% for a stack containing fully hydrated Nafion® 117 membranes at 80 °C, 90% relative humidity using an eight bolt clamping design and a nominal 1.2 MPa assembly pressure.

Copyright (c) 2018 by ASME; use license CC-BY 4.0
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