Sharif Digital Repository

In this paper, a two-dimensional, two-phase, isothermal model is presented to investigate the water transport characteristic and water distribution in a direct methanol fuel cell (DMFC) with emphasis on exploring the water distribution in different layers of DMFC. The liquid-gas two-phase mass transport in the porous anode and cathode is formulated based on multi-fluid model in porous media and water and methanol crossover through the membrane are considered with the effect of diffusion, electro-osmotic drag, and convection. The modeling results agree well with the three different experimental data in an extensive range of operation conditions. A parametric study is also performed to examine... 

The catalyst layers are the most important part of the polymer electrolyte membrane (PEM) fuel cells, and the cell performance is highly related to its structure. The gas diffusion layers (GDLs) are also the essential components of the PEM fuel cell since the reactants should pass through these layers. Model prediction shows that electrical current in catalyst layer is non-uniform, influenced by the channel-land geometry. In addition, the compression effect of GDLs and water generation due to the electrochemical reaction may cause non-uniformity in porosity and, therefore, increases the non-uniformity in reactant concentration in GDL/catalyst layer interface. Simulation results suggest that... 

Gas diffusion layers (GDL) are one of the important parts of the PEM fuel cell as they serve to transport the reactant gases to the catalyst layer. Porosity of this layer has a large effect on the PEM fuel cell performance. The spatial variation in porosity arises due to two effects: (1) compression of the electrode on the solid landing areas and (2) water produced at the cathode side of gas diffusion layers. Both of these factors change the porosity of gas diffusion layers and affect the fuel cell performance. To implement this performance analysis, a mathematical model which considers oxygen and hydrogen mass fraction in gas diffusion layer and the electrical current density in the... 

Gas diffusion layers are essential components of proton exchange membrane fuel cell since the reactants should pass through these layers. Mass transport in these layers is highly dependent on porosity. Many of simulations have assumed, for simplicity, the porosity of GDL is constant, but in practice, there is a considerable variation in porosity along gas diffusion layers. In the present study the porosity variation in GDL is calculated by considering the applied pressure and the amount of water generated in the cell. A two dimensional mathematical model is developed to investigate the effect of stack compression and water generation on porosity of GDL and cell performance. The validity of... 

In this paper, numerical and analytical approaches are presented to evaluate the effect of catalyst loading gradient in the catalyst layer (CL) of a polymer electrolyte membrane (PEM) fuel cell. The model is developed based on agglomerate catalyst and accounts for reactant spices and charge (ion and electron) transport in the cathode side of a PEM fuel cell. The special variation of catalyst loading is considered in two direction, "across the layer" from membrane/CL interface to gas diffusion layer (GDL) and "in catalyst plane" under the channels and land areas in the channel direction. A fuel cell test stand is designed and built to facilitate experimental validation of the model. The... 

In this research, it is investigated to numerically evaluate the performance of a polymer electrolyte membrane fuel cell (PEMFC). The performance is investigated through the nonuniformity gradient loading at the catalyst layer (CL) of the considered PEMFC. Computational fluid dynamics is used to simulate a 2D domain in which a steady-state laminar compressible flow in two-phase for the PEMFC has been considered. In this case, a particular nonuniform variation inside the CL along the channel is assumed. The nonuniform gradient is created using a nonisothermal domain to predict the flooding effects on the performance of the PEMFC. The computational domain is considered as the cathode of PEMFC,...