An Analytical Solution to Predict the Inception of Two-Phase Flow in a Proton Exchange Membrane Fuel Cell
01 Dec 2010-Journal of Fuel Cell Science and Technology (American Society of Mechanical Engineers)-Vol. 7, Iss: 6, pp 064502
TL;DR: In this article, a pseudo-two-dimensional analytical model is developed to predict the inception of two-phase flow along the length of the cathode channel, where the diffusion of the water is considered to take place only across the gas diffusion layer (GDL).
Abstract: The presence of liquid water at the cathode of proton exchange membrane fuel cell hinders the reactant supply to the electrode and is known as electrode flooding. The flooding at the cathode due to the presence of two-phase flow of water is one of the major performance limiting conditions. A pseudo-two-dimensional analytical model is developed to predict the inception of two-phase flow along the length of the cathode channel. The diffusion of the water is considered to take place only across the gas diffusion layer (GDL). The current density corresponding to the inception of two-phase flow, called the threshold current density, is found to be a function of the channel length and height, GDL thickness, velocity, and relative humidity of the air at the inlet and cell temperature. Thus, for given design and operating conditions, the analytical model is capable of predicting the inception of two-phase flow, and therefore a flooding condition can be avoided in the first place.
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TL;DR: In this article, a Proton Exchange Membrane (PEM) fuel cell with three different types of flow distributors is modeled and numerically simulated to find out the water formation and distribution characteristics.
Abstract: Water management is one of the important factors which determine the performance of a Proton Exchange Membrane (PEM) fuel cell using hydrogen as fuel. For developing efficient water management systems, it is important to know the potential locations of formation and the nature of distribution of liquid water in the fuel cell. In the present study a PEM fuel cell with three different types of flow distributors are modeled and numerically simulated to find out the water formation and distribution characteristics. The model is validated by comparing the simulated polarization curve to experimental data. It is found that the type of flow distributor used plays a major role in determining the distribution of liquid water in the cell. A parallel flow distributor exhibits poor water removal capabilities whereas a serpentine flow distributor exhibits better water removal. A mixed flow distributor is found to give better water distribution characteristics compared to the parallel and serpentine distributors. Further the effect of liquid water formation and distribution on the species transport, temperature distribution and current generation are also investigated.
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TL;DR: In this paper, an isothermal, one-dimensional, steady-state model for a complete polymer electrolyte fuel cell (PEFC) with a 117 Nation | membrane is presented, which predicts an increase in membrane resistance with increased current density and demonstrates the great advantage of a thinner membrane in alleviating this resistance problem.
Abstract: We present here an isothermal, one-dimensional, steady-state model for a complete polymer electrolyte fuel cell (PEFC) with a 117 Nation | membrane. In this model we employ water diffusion coefficients electro-osmotic drag coefficients, water sorption isotherms, and membrane conductivities, all measured in our laboratory as functions of membrane water content. The model pre.dicts a net-water-per-proton flux ratio of 0.2 H20/H § under typical operating conditions, which is much less than the measured electro-osmotic drag coefficient for a fully hydrated membrane. It also predicts an increase in membrane resistance with increased current density and demonstrates the great advantage of a thinner membrane in alleviating this resistance problem. Both of these predictions were verified experimentally under certain conditions.
3,013 citations
TL;DR: In this article, a transient, multi-dimensional model has been developed to simulate proton exchange membrane (PEM) fuel cells, which accounts simultaneously for electrochemical kinetics, current distribution, hydrodynamics and multi-component transport.
Abstract: A transient, multi-dimensional model has been developed to simulate proton exchange membrane (PEM) fuel cells. The model accounts simultaneously for electrochemical kinetics, current distribution, hydrodynamics and multi-component transport. A single set of conservation equations valid for flow channels, gas-diffusion electrodes, catalyst layers and the membrane region are developed and numerically solved using a finite-volume-based computational fluid dynamics (CFD) technique. The numerical model is validated against published experimental data with good agreement. Subsequently, the model is applied to explore hydrogen dilution effects in the anode feed. The predicted polarization cubes under hydrogen dilution conditions are found to be in qualitative agreement with recent experiments reported in the literature. The detailed two-dimensional electrochemical and flow/transport simulations further reveal that in the presence of hydrogen dilution in the fuel stream, hydrogen is depleted at the reaction surface resulting in substantial kinetic polarization and hence a lower current density that is limited by hydrogen transport from the fuel stream to the reaction site.
729 citations
TL;DR: In this paper, a one-dimensional non-isothermal model of a proton exchange membrane (PEM) fuel cell has been developed to investigate the effect of various design and operating conditions on the cell performance, thermal response and water management.
Abstract: A one-dimensional non-isothermal model of a proton exchange membrane (PEM) fuel cell has been developed to investigate the effect of various design and operating conditions on the cell performance, thermal response and water management, and to understand the underlying mechanism. The model includes variable membrane hydration, ternary gas mixtures for both reactant streams, phase change of water in the electrodes with unsaturated reactant gas streams, and the energy equation for the temperature distribution across the cell. It is found that temperature distribution within the PEM fuel cell is affected by water phase change in the electrodes, especially for unsaturated reactant streams. Larger peak temperatures occur within the cell at lower cell operating temperatures and for partially humidifed reactants as a result of increased membrane resistance arising from reduced membrane hydration. The non-uniform temperature rise can be significant for fuel cell stacks. Operation on reformed fuels results in a decrease in cell performance largely due to reduced membrane hydration, which is also responsible for reduced performance at high current densities for high cell operating pressures. Model predictions compare well with known experimental results.
528 citations
TL;DR: In this article, the authors used a steady-state multicomponent transport model to investigate the hydrodynamics of gases in the cathode of a proton exchange membrane fuel cell that is contacted to an interdigitated gas distributor.
Abstract: Hydrodynamics of gases in the cathode of a proton exchange membrane fuel cell that is contacted to an interdigitated gas distributor are investigated using a steady‐state multicomponent transport model. The model describes the two‐dimensional flow patterns and the distributions of the gaseous species in the porous electrode and predicts the current density generated at the electrode and membrane interface as a function of various operating conditions and design parameters. Results from the model show that, with the forced flow‐through condition created by the interdigitated gas distributor design, the diffusion layer is greatly reduced. However, even with a much thinner diffusion layer, diffusion still plays a significant role in the transport of oxygen to the reaction surface. The results also show that the average current density generated at an air cathode increases with higher gas flow‐through rates, thinner electrodes, and narrower shoulder widths between the inlet and outlet channels of the interdigitated gas distributor. © 1999 The Electrochemical Society. All rights reserved.
337 citations
TL;DR: In this paper, an integrated flow and current density model was developed to predict current density distributions in two dimensions on the membrane in a straight channel PEM fuel cell, which includes diffusion layers on both the anode and cathode sides and solved the same primary flow related variables in the main flow channel and the diffusion layer.
Abstract: The need to model three-dimensional flow in polymer electrolyte membrane (PEM) fuel cells is discussed by developing an integrated flow and current density model to predict current density distributions in two dimensions on the membrane in a straight channel PEM fuel cell. The geometrical model includes diffusion layers on both the anode and cathode sides and the numerical model solves the same primary flow related variables in the main flow channel and the diffusion layer. A control volume approach is used and source terms for transport equations are presented to facilitate their incorporation in commercial flow solvers. Predictions reveal that the inclusion of a diffusion layer creates a lower and more uniform current density compared to cases without diffusion layers. The results also show that the membrane thickness and cell voltage have a significant effect on the axial distribution of the current density and net rate of water transport. The predictions of the water transport between cathode and anode across the width of the flow channel show the delicate balance of diffusion and electroosmosis and their effect on the current distribution along channel.
329 citations