The anisotropic mass transport issues inside a fuel cell membrane have been studied in this thesis using computer modelling. The polymer electrolyte membrane (PEM) conductivity of a PEM fuel cell (PEMFC) depends on the hydration state of the hydrophilic charged sites distributed in the pores of the membrane. Water humidification of these charged sites is crucial for sustaining the membrane conductivity and reducing concerning voltage losses of the cell. During the operation of a PEMFC, the transport of humidified inlet gases (fuel/oxidant) is influenced by external design factors such as flow field plate geometry of the gas circulating channels. As a result, there arises a distribution in the mass transport of water inside the membrane electrode assembly. A two-dimensional, cross-the-channel, fuel cell membrane layer mass transport model, developed in this work, helps the study of the impact of factors causing the distribution in the membrane ionic conductivity on ohmic losses.<p>The governing equations of the membrane mathematical model stem from the multicomponent framework of concentrated solution theory. All mass transport driving forces within the vapour and/or liquid equilibrated phases have been accounted in this research. A computational model, based on the finite control volume method, has been implemented using a line-by-line approach for solving the dependent variables of the mass transport equations in the two-dimensional membrane domain. The required boundary conditions for performing the anisotropic mass transport analysis have been obtained from a detailed agglomerate model of the cathode catalyst layer available in the literature.<p>The results obtained using boundary conditions with various flow field plate channel-land configurations revealed that the anisotropic water transport in the cathode half-cell severely affects the ohmic losses within the membrane. A partially humidified vapour equilibrated membrane simulation results show that a smaller channel-land ratio (1:1) sustains a better membrane performance compared to that with a larger one (2:1 or 4:1). Resistance calculations using the computer model revealed that ohmic losses across the membrane also depend on its physical parameters such as thickness. It was observed that the resistance offered by a thinner membrane towards vapour phase mass transport is comparatively lower than that offered by a thicker membrane. A further analysis accounting the practical aspects such as membrane swelling constraints, imposed by design limitations of a fuel cell, revealed that the membrane water content and ionic conductivity are altered with an increase in the compression constraint effects acting upon a free swelling membrane.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:SSU.etd-08282006-122548 |
| Date | 29 August 2006 |
| Creators | Devulapalli, Venkateshwar Rao |
| Contributors | Phoenix, Aaron, Nemati, Mehdi, Evitts, Richard W., Baranski, Andrzej S. |
| Publisher | University of Saskatchewan |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-08282006-122548/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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