117 - B316 Journal of The Electrochemical Society, 154 3...

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Prediction of Dry-Wet-Dry Transition in Polymer Electrolyte Fuel Cells Gang Luo, Hyunchul Ju, and Chao-Yang Wang * ,z Electrochemical Engine Center and Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 USA Condensation and evaporation fronts co-exist in present-day automotive polymer electrolyte fuel cells ~ PEFCs ! where low- humidity reactant gases are fed in counter±ow. Capturing of such a transition between a single- and a two-phase regime is not only of technological signi²cance, but also represents a great numerical challenge in PEFC modeling. In this work we demonstrate a computational capability to predict the dry-wet-dry transition in a PEFC based on the multiphase mixture s M 2 d framework. The M 2 model is a three-dimensional, two-phase, and multicomponent full-cell model featuring a detailed membrane-electrode assem- bly ~ MEA ! sub-model. Three-dimensional results on the dry-wet-dry transition under low-humidity operation and in counter±ow are presented. The dry-to-wet transition described in this work provides a benchmark problem to develop and test future generation PEFC models. © 2007 The Electrochemical Society. @ DOI: 10.1149/1.2429036 # All rights reserved. Manuscript submitted September 6, 2006; revised manuscript received October 31, 2006. Available electronically January 17, 2007. Low-humidity operation is ubiquitous in automotive polymer electrolyte fuel cells ~ PEFCs ! . Under low-humidity inlet conditions, reactant gases undergo a transition from the single-phase to two- phase ±ow inside the fuel cell when either anode or cathode gas becomes saturated with water vapor due to water production from oxygen reduction reaction. This transition, also called the condensa- tion front, is schematically sketched in Fig. 1. In the counter±ow of hydrogen and air gas streams at low humidity, the most common con²guration of automotive PEFCs, there may occur a second tran- sition from the two-phase zone back to the single-phase gas ±ow, or the evaporation front, also depicted in Fig. 1. The evaporation front results from the wet cathode outlet facing the dry anode inlet such that not only is product water from oxygen reduction reaction ~ ORR ! transported through the membrane to the dry anode gas, but liquid water accumulated in the cathode GDL also vanishes due to strong water diffusion through the membrane to the dry anode. Commonly, both fronts ~ i.e., the dry-wet-dry transition ! can exist simultaneously in the PEFC cathode and anode. Predicting the dry-wet-dry transition ~ DWT ! is of great impor- tance to PEFC performance and durability as the ultimate goal of water management is precisely met in the vicinity of a DWT. Here, the membrane is suf²ciently hydrated to exhibit excellent proton conductivity, and yet the electrodes have not been ±ooded. However, despite its technological importance and existence in virtually all automotive PEFC engines, the DWT has been scarcely studied due to the tremendous numerical dif²culty in capturing it. Falling into
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This note was uploaded on 10/28/2010 for the course EE 89 taught by Professor Asgarian during the Fall '10 term at Amirkabir University of Technology.

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117 - B316 Journal of The Electrochemical Society, 154 3...

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