Search

In this work, the pseudo-3D multiphysics model introduced in Part 1 of this two-part series of papers is used to investigate heat and water transport in a Proton Exchange Membrane Fuel Cell designed for an automotive application. The main advantage of the model is the consideration of the bipolar plate design and the detailed description of the studied geometrical domain while maintaining an acceptable computational time. When applied on an automotive cycle, the simulation results highlight the impact of the bipolar plate design on temperature and humidity heterogeneities. The operating conditions induce a non-uniform cycling of temperature and humidity over the cell active area. In addition, at a more local scale, the increase in fuel cell load leads to larger heterogeneities between channel and rib, for temperature as well as for humidity. The results of the simulation of liquid water distribution are in good agreement with the experimental results, demonstrating the reliability and robustness of the model which can be used for the design of new bipolar plates or to understand the degradation phenomena.

Neutron radiography and tomography were used to study the transient and steady-state distributions, respectively, of hydrogen within a prototypical, LaNi 4.78 Sn 0.22 -based hydrogen-storage bed during and after various absorption and desorption steps. It was shown that using deuterium instead of hydrogen enabled the imaging of thicker beds. These measurements serve to demonstrate the unique utility of neutron imaging as an important diagnostic tool for in situ , real-time characterization of hydrogen-concentration profiles in practical hydrogen-storage systems.

In this study neutron radiography is applied to investigate the performance of a polymer electrolyte membrane (PEM) fuel cell based on the effect of liquid water accumulation in the cell. Dynamic performance tests have been carried out on a PEM fuel cell with a specially designed serpentine flow channel under various operating conditions and simultaneous measurements of accumulated liquid water with neutron imaging. Liquid water tends to accumulate in the gas diffusion layer (GDL) adjacent to the flow channel area while the liquid water formed in the GDL next to the channel land area seems to be effectively removed by the cross leakage flow through the porous GDL between the adjacent flow channels. The amount of liquid water accumulation in the cell is dependant on the cell operating temperature, the pressure drop in the flow channel and the current density under the present test conditions of fixed stoichiometry. It is shown that the cell performance is strongly affected by the presence and accumulation of liquid water, especially at high current densities. This phenomenon results in performance hysteresis for load variations. The rate of liquid water production is also mathematically modeled to analyze the effect of the cell operating temperature and pressure drop on the liquid water formation in a cell. The model result shows good agreement with experimental measurements. The history of liquid water accumulation is also analyzed.

Water is the main product of the electrochemical reaction in a proton exchange membrane (PEM) fuel cell. Where the water is produced over the active area of the cell and how it accumulates within the flow fields and gas diffusion layers, strongly affects the performance of the device and influences operational considerations such as freeze and durability. In this work, the neutron radiography method was used to obtain two-dimensional distributions of liquid water in operating 50 cm 2 fuel cells. Variations were made of flow field channel and diffusion media properties to assess the effects on the overall volume and spatial distribution of accumulated water. Flow field channels with hydrophobic coating retain more water, but the distribution of a greater number of smaller slugs in the channel area improves fuel cell performance at high current density. Channels with triangular geometry retain less water than rectangular channels of the same cross-sectional area, and the water is mostly trapped in the two corners adjacent to the diffusion media. It was also found that cells constructed using diffusion media with lower in-plane gas permeability tended to retain less water. In some cases, large differences in fuel cell performance were observed with very small changes in accumulated water volume, suggesting that flooding within the electrode layer or at the electrode-diffusion media interface is the primary cause of the significant mass transport voltage loss. 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.