Pressure drop and flow distribution in parallel-channel configurations of fuel cells: U-type arrangement (original) (raw)
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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.
Discrete approach for flow field designs of parallel channel configurations in fuel cells
International Journal of Hydrogen Energy, 2012
It is the major challenge to transform a laboratory scale production of fuel cells to an industrial scale one and to meet the requirements of throughput, operating life, low cost, reliability and high efficiency in R&D of fuel cells. Designs of uniform flow distribution are central to upscale fuel cells as well as to tackle critical issues of water, thermal and current management. However, in spite of our growing appreciation of designs of uniform flow distribution, there is little or no practical solution to ensure a uniform flow distribution across channels of a cell and cells of a stack in designs of flow fields. The purpose of this paper was to develop a discrete approach to find a design that met requirements of flow distribution uniformity and pressure drop in parallel channel configurations with Z-type arrangement through adjustments of configurations and normalised structural parameters. Variation of the frictional and the momentum coefficients with flow velocities was incorporated into the flow distribution equation to improve modelling accuracy. We also developed procedure, measures and guideline for the designs of flow distribution and pressure drop to bridge knowledge gap between the generalised theory and industrial applications. The results showed that the present approach could provide the practical guideline to evaluate quantitatively performance of different layout configurations, structures, and flow conditions.
Flow distribution in U-type layers or stacks of planar fuel cells
Journal of Power Sources, 2008
The flow distribution features in U-type layers or stacks with certain practical configurations have been investigated analytically. The formulations suggest general designing strategies to improve the flow uniformity, and narrowing some positions of the channels proves effective. The flow uniformity among the layers in a U-type stack is relatively easy to achieve in comparison with that among the channels in a U-type layer, due to the large stack headers and low-pressure loss in them. CFD simulations confirm the formulations, and the discrepancies between the analytical and CFD results have been attributed to the ignored factors during the analytical formulations.
Fluid dynamic study of fuel cell devices: simulation and experimental validation
Journal of Power Sources, 1994
The paper is concerned with the mass flow distribution in fuel cell stacks. In particular, the flow through the manifold system connected to the parallel arrangement of the cell channels is modelled and numerically treated. The numerical results are recognized to be more realistic than those obtained by means of an approximate analytical solution since more detailed effects could be accounted for. This evidence is confirmed by experiments carried out at a stack model device consisting of 100 cells. Pressure and velocity distributions were measured for various Reynolds numbers and geometrical shapes of the manifolds. The agreement between the experimental and numerical results is good. Keywordsr Fuel cell stacks; Fluid dynamic study 0378-7753/94/$07.00 0 1994 Elsevier Science S.A. All rights resewed SSDI 0378-7753(94)02014-T
Pressure and flow distribution in internal gas manifolds of a fuel-cell stack
Journal of Power Sources, 2003
Gas-flow dynamics in internal gas manifolds of a fuel-cell stack are analyzed to investigate overall pressure variation and flow distribution. Different gas-flow patterns are considered in this analysis. Gas-flow through gas channels of each cell is modeled by means of Darcy's law where permeability should be determined on an experimental basis. Gas-flow in manifolds is modeled from the macroscopic mechanical energy balance with pressure-loss by wall friction and geometrical effects. A systematic algorithm to solve the proposed flow model is suggested to calculate pressure and flow distribution in fuel-cell stacks. Calculation is done for a 100-cell molten carbonate fuel-cell stack with internal manifolds. The results show that the pressure-loss by wall friction is negligible compared with the pressure recovery in inlet manifolds or loss in outlet manifolds due to mass dividing or combining flow at manifold-cell junctions. A more significant effect on manifold pressure possibly arises from the geometrical manifold structure which depends on the manifold size and shape. The geometrical effect is approximated from pressure-loss coefficients of several types of fittings and valves. The overall pressure and flow distribution is significantly affected by the value of the geometrical pressure-loss coefficient. It is also found that the flow in manifolds is mostly turbulent in the 100-cell stack and this way result in an uneven flow distribution when the stack manifold is incorrectly, designed.
Heat and Mass Transfer, 2007
A 3D numerical study was carried out to analyze flow, heat and mass transfer first in a single half-cell cathode channel of proton exchange membrane (PEM) fuel cell. From practical point of view, it is necessary to put the appropriate number of cells in a stack. Hence, the above study on a single half-cell is extended to a stack of channels. Due to stacking, the assumption of uniform flow distribution would no longer hold true. Therefore, the channel flow-maldistribution is considered. The water formed at the active surface due to the electrochemical reaction diffuses through the porous layer and eventually enters the gas flow duct. The higher gas velocities in the duct result in faster water vapour removal which leads to a lower value of water vapour into the duct and hence a lower Nusselt number.
Modeling Flow Distribution for Internally Manifolded Direct Methanol Fuel Cell Stacks
Chemical Engineering & Technology, 2000
A model is presented for the liquid feed direct methanol fuel cell, which describes the hydraulic behavior of an internally manifolded cell stack. The model is based on the homogeneous two-phase flow theory and mass conservation equation. The model predicts the pressure drop behavior of an individual fuel cell, and is used to calculate flow distribution through fuel cell stack internal manifolds. The flow distribution of the two-phase fluids in the anode and the cathode chambers is predicted as a function of cell operating parameters. An iterative numerical scheme is used to solve the differential equations for longitudinal momentum and continuity.
Applied Thermal Engineering, 2005
The air flow in a simplified model of the flow plate and adjacent diffusion layer of a PEM fuel cell has been numerically studied. The flow plate has been assumed to have serpentine flow channels with a square cross-section. It has been assumed that the flow in the porous diffusion layer can be modelled by using DarcyÕs law. It has also been assumed that there is a uniform rate of heat generation at the base of this diffusion layer. The three-dimensional flow and temperature distribution in the flow plate-diffusion layer combination has been numerically studied by writing the governing equations in dimensionless form and solving the resultant equations using a commercial software package. As a result of the pressure drop along the flow channel, there can be crossover of air through the porous diffusion layer from one part of the channel to another. The conditions under which this crossover becomes important and the effect this crossover on the pressure distribution in the channel and the temperature distribution in the flow plate has been examined in this study. Attention has been given to flow plates having a single serpentine channel. Various numbers of flow passes through the plates have been considered these flow passes leading to what are effectively a series of parallel serpentine channels in the plate. The effects of Reynolds number, relative flow plate material thermal conductivity, dimensionless permeability of the diffusion layer and of flow channel geometry on the channel flow and the plate temperature distribution have been numerically examined and related to air crossover.
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.
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.