941 Prediction of hygro–thermal stress distribution in proton exchange membranes using a three-dimensional multi-phase computational fluid dynamics model M A R Sadiq Al-Baghdadi ∗† and H A K Shahad Al-Janabi Department of Mechanical Engineering, International Technological University, London, UK The manuscript was received on 10 September 2006 and was accepted after revision for publication on 25 June 2007. DOI: 10.1243/09576509JPE368 Abstract: A three-dimensional, multi-phase, non-isothermal computational fluid dynamics model of a proton exchange membrane fuel cell has been developed to simulate the hygro and thermal stresses in polymer membrane, which developed during the cell operation. The behaviour of the membrane during the operation of a unit cell has been studied and inves- tigated. The model accounts for both gas and liquid phase in the same computational domain, and thus allows for the implementation of phase change inside the gas diffusion layers. The model includes the transport of gaseous species, liquid water, protons, energy, and water dissolved in the ion-conducting polymer. The new feature of the present model is to incorporate the effect of hygro and thermal stresses into actual three-dimensional, multi-phase, non-isothermal fuel cell model. In addition to hygro–thermal stresses, the model features an algorithm that allows for a more realistic representation of the local activation overpotentials, which leads to improved prediction of the local current density distribution in high accuracy, and therefore, high accuracy prediction of temperature distribution in the cell and then thermal stresses. This model also takes into account convection and diffusion of different species in the channels as well as in the porous gas diffusion layer, heat transfer in the solids as well as in the gases, and electrochemical reactions. Keywords: proton exchange membrane, Nafion, hygro–thermal loading, multi-phase, water transport, computational fluid dynamics, modelling 1 INTRODUCTION The durability of proton exchange membranes used in fuel cells is a major factor in the operating life- time of fuel cell systems. Durability is a complicated phenomenon, linked to the chemical and mechanical interactions of the fuel cell components, i.e. electro- catalysts, membranes, gas diffusion layers, and bipolar plates, under severe environmental conditions, such as elevated temperature and low humidity. In fuel cell systems, failure may occur in several ways such as chemical degradation of the ionomer membrane or mechanical failure in the PEM that results in gradual ∗ Corresponding author: Department of Mechanical Engineer- ing, International Technological University, London, UK. email: maherars@hotmail.com † Currently at Department of Mechanics and Energy, Higher Institute of Mechanical Engineering,Yefren, PO Box 65943, Libya. reduction of ionic conductivity, increase in the total cell resistance, and the reduction of voltage and loss of output power. Mechanical damage in the PEM can appear as through-the-thickness flaws or pinholes in the membrane, or delaminating between the polymer membrane and gas diffusion layers [1]. An operating fuel cell has varying local conditions of temperature and humidity. As a result of the changes in temperature and moisture, the PEM, gas diffusion layer (GDL), and bipolar plates will all experience expansion and contraction. Because of the different thermal expansion and swelling coefficients between these materials, hygro–thermal stresses are expected to be introduced into the unit cell during operation. In addition, the non-uniform current and reactant flow distributions in the cell can result in non-uniform temperature and moisture content of the cell, which could in turn, potentially causing localized increases in the stress magnitudes, and this leads to mechanical damage, which can appear as through-the-thickness JPE368 © IMechE 2007 Proc. IMechE Vol. 221 Part A: J. Power and Energy