Modelling of polymer electrolyte membrane fuel cell stacks based on a hydraulic network approach (original) (raw)
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Effect of flow and temperature distribution on the performance of a PEM fuel cell stack
Journal of Power Sources, 2006
A non-isothermal stack model has been developed to analyze the effects of flow variance and temperature distribution on the performance of a polymer electrolyte membrane (PEM) fuel cell stack. The stack model consists of the flow network solver for pressure and mass flow distributions for the reactant gas streams and cooling water, and the heat transfer solver for temperature distribution among the cells in the stack, as well as the fuel cell model for individual cell performance. Temperature, pressure and concentrations of fuel and oxidant are the most important conditions for the fuel cell operation. In this work, pressure, temperature and concentration distributions are determined incorporating the individual cell performance with the minor losses in stack flow network accounted for. The results indicate that the effect of temperature is dominant on the cell voltage variance when the flow variance is small for sufficiently uniform distribution of reactant flow among the cells in the stack. Sufficient flow uniformity can be achieved by a large manifold that reduces the cell active area, or a small flow channel diameter, the latter may result in excessive pumping power for the anode and cathode gas streams. The manifold and flow channel diameters were optimized considering stack performance and reactant stream pumping power requirement. It is further shown that the flow and temperature distribution have a different influence on the stack performance, and a judicial matching of their distribution can provide the ideal uniform cell voltage distribution. An optimal combination of the flow and temperature distribution along the stack yields the optimal stack performance.
Dynamic Systems and Control, Parts A and B, 2005
This paper describes a simple two-phase flow dynamic model that predicts the experimentally observed temporal behavior of a proton exchange membrane fuel cell stack and a methodology to experimentally identify tunable physical parameters. The model equations allow temporal calculation of the species concentrations across the gas diffusion layers, the vapor transport across the membrane, the degree of flooding in the electrodes, and then predict the resulting decay in cell voltage over time. A nonlinear optimization technique is used for the identification of two critical model parameters, namely the membrane water vapor diffusion coefficient and the thickness of the liquid water film covering the fuel cell active area. The calibrated model is validated for a 24 cell, 300 cm 2 stack with a supply of pressure regulated pure hydrogen. * cell voltage). The methodology used to experimentally identify tunable parameters is described. Finally, experimental data will be compared to the model predictions to provide a validation of the models presented. This is the first time to our knowledge that a two-phase flow, 1-D model predicts the experimentally observed temporal behavior of a multi-cell stack.
h i g h l i g h t s Experimental and computational study of PEM fuel cell stack with a dead-end anode. Investigation of the fuel cell performance, gas and water management. Gas and water management is better under low operating current conditions. Lower cathode stoichiometry is preferred to minimize nitrogen crossover. Anode purging is recommended to clear out the impurities for longer operations. a b s t r a c t The operation of polymer electrolyte membrane fuel cell (PEMFC) stack with a dead-end anode requires careful consideration on the gas and water management. Water accumulation at the anode and the nitrogen crossover from cathode to anode lead to performance deterioration over time. The accumulated water and nitrogen need to be removed properly by purging method to ensure good and stable stack performance. Thus, the careful selection of the operating parameters – inlet humidification, stoichiometry, and operating current – is the key factor for ensuring efficient water and gas management. This study aims at the experimental and numerical evaluation of the effect of the key operating parameters on the transient performance of a dead-end anode fuel cell stack. The experiments were carried out on a stack with 24 cells and a catalyst active area of 300 cm 2. By employing a validated transient two-phase mathematical model of a PEMFC with a dead-end anode, numerical simulations were performed which yield a better and deeper understanding of local distribution of water and species, i.e., hydrogen, oxygen, water vapor and nitrogen. The results suggest that the performance deterioration over time is closely related to the choice of the operating conditions. The study reveals that the anode and cathode inlet conditions become a limiting factor for the stack performance. Liquid accumulation at the anode is found to be strongly related to the inlet humidification as well as water transport across the membrane, whereas the cathode stoichiom-etry affects the nitrogen crossover.
New PEM Fuel Cell Stack Model Considering Reactants Diffsion Effects
ECS Proceedings Volumes, 2004
The focus of this paper is placed on research and development of a control-oriented dynamic PEM(polymer electrolyte membrane) fuel cell system model that includes a stack model and system models. Particularly, the stack model considers a single cell model composed of different layers. The framework models for the system are based upon inertia dynamics o f compressor, manifold filling dynamics and a simplified humidifier. The stack model is integrated into the system model under MATLAB/SIMULINK environment. Comparative simulation studies demonstrate different dynamics at a varying load than commonly employed semi-empirical models, which are mainly caused by the dynamics of the reactants in the GDL(Gas Diffusion Layer). One of possible applications will be for designing a fuel cell controller
Flow distribution in proton exchange membrane fuel cell stacks
Journal of Power Sources, 2006
A proton exchange membrane fuel cell (PEMFC) stack model which incorporates flow distribution effects and a reduced dimensional unit cell model is presented. The laws of Mass and Momentum Conservation are applied throughout the stack. Along the headers, flow splitting and recombination are applied at each tee junction, while along the unit cell channels, reactant consumption and byproduct production are accounted for. Cell performance is coupled to the channel conditions. Using this stack model, the sensitivity of stack performance to operating conditions (inlet velocity and pressure) and design parameters (manifold, flow configuration and friction factor) is investigated. In particular, performance under uniform, single anomaly, and random parameter distributions is investigated.
Characterization of flooding and two-phase flow in polymer electrolyte membrane fuel cell stacks
2009
A partially flooded gas diffusion layer (GDL) model is proposed and solved simultaneously with a stack flow network model to estimate the operating conditions under which water flooding could be initiated in a polymer electrolyte membrane (PEM) fuel cell stack. The models were applied to the cathode side of a stack, which is more sensitive to the inception of GDL flooding and/or flow channel two-phase flow. The model can predict the stack performance in terms of pressure, species concentrations, GDL flooding and quality distributions in the flow fields as well as the geometrical specifications of the PEM fuel cell stack. The simulation results have revealed that under certain operating conditions, the GDL is fully flooded and the quality is lower than one for parts of the stack flow fields. Effects of current density, operating pressure, and level of inlet humidity on flooding are investigated.
Flow distribution in the manifold of PEM fuel cell stack
Journal of Power Sources, 2007
In this study, the pressure variation and the flow distribution in the manifold of a fuel-cell stack are simulated by a computational fluid dynamics (CFD) approach. Two dimensional stack model composed of 72 cells filled with porous media is constructed to evaluate pressure drop caused by channel flow resistance. In order to simplify this model, electrochemical reactions, heat and mass transport phenomena are ignored and air is treated as working fluid to investigate flow distribution in stacks. Design parameters such as the permeability of the porous media, the manifold width and the air feeding rate were changed to estimate uniformity of the flow distribution in the manifold. A momentum-balance theory and a pressure-drop model are presented to explain the physical mechanism of flow distribution. Modeling results indicate that both the channel resistance and the manifold width can enhance the uniformity of the flow distribution. In addition, a lower air feeding rate can also enhance the uniformity of flow distribution. However, excessive pressure drop is not beneficial for realistic applications of a fuel-cell stack and hence enhanced manifold width is a better solution for flow distribution.
Hydrogen, Fuel Cell & Energy Storage, 2016
In order to present a new and high performance structure of PEM fuel cell and study the influence of the flow direction and distribution on the rate of reactants diffusion, three novel models of vertical reactant flow injection into the anode and cathode reaction area field have been introduced. They consist of one inlet and two inlets and also a continuous channel. The governing equations on the steady, three dimensional non-isothermal flow have been discretized using finite volume method. These 3D simulations are going to evaluate the effectiveness of flow direction on the transportation and chemical phenomena inside the PEM fuel cell by applying computational fluid dynamics (CFD) method to the transportation and conservation equations with the suppositions of steady state and one phase flow. The numerical results are validated with experimental ones for available common fuel cells. The results show that the presented geometries have several mechanical and chemical benefits such as extra diffusion of reactants because of flow direction, improvement of species distributions, enhancement in temperature management and more effective water removal due to the number of outlets and uniform current distribution. Furthermore, the continuous channel inlet due to cover more reaction area and high rate of reactants diffusion presents substantial higher performance than others. With regard to the polarization curve along with other advantages, the so-called design can be strongly recommended for obtaining high operating efficiency and can be considered for the manufacturing of new generation of PEM fuel cells in the form of high performance stacks.
International Journal of Hydrogen Energy, 2009
The research activity in polymer electrolyte fuel cell (PEFC) is oriented to the evolution of components and devices for the temperature range from 20 to 130 1C, and covers all the aspects of this matter: membranes and electrodes, fuel cell stack engineering (design and manufacturing) and characterization, computational modelling and small demonstration systems prototyping. Particular attention is devoted to portable and automotive application. Membranes research is focused on thermostable polymers (polyetheretherketone, polysulphone, etc.) and composite membranes able to operate at higher temperature ð4100 CÞ and lower humidification than the commercial Nafion s , while Pt load reduction and gas diffusion layer improvement are the main goals for the electrode development. PEFC stack engineering and characterization activity involve different aspects such as the investigation of new materials for stack components, fuel cell modelling and performance optimization by computational techniques, single cell and stack electrochemical characterization, development of investigation tools for stack monitoring and data acquisition. A lot of work has been focused to the fuel cell stack architecture, assembling, gas leakage and cross-over reduction (gasketing), flow field and manifold design. Computational fluid dynamics studies have been performed to investigate and improve reactants distribution inside the cell. A flow field design methodology, developed in this framework and related to serpentine like flow field, is actually under investigation. All of these aspects of PEFC stack research are realized in the framework of National and European research projects, or in collaboration with industries and other research centres. In the present work our stack research activity is reported and the most important results are also considered.