Numerical simulation of thermal–hydraulic characteristics in a proton exchange membrane fuel cell

The thermal–hydraulic characteristics of a proton exchange membrane fuel cell (PEMFC) are numerically simulated by a simplified two‐phase, multi‐component flow model. This model consists of continuity, momentum, energy and concentration equations, and appropriate equations to consider the varying flow properties of the gas–liquid two‐phase region in a PEMFC. This gas–liquid two‐phase characteristic is not considered in most of the previous simulation works. The calculated thermal–hydraulic phenomena of a PEMFC are reasonably presented in this paper, which include the distributions of flow vector, temperature, oxygen concentration, liquid water saturation, and current density, etc. Coupled with the electrochemical reaction equations, current flow model can predict the cell voltage vs current density curves (i.e. performance curves), which are validated by the single‐cell tests. The predicted performance curves for a PEMFC agree well with the experimental data. In addition, the positive effect of temperature on the cell performance is also precisely captured by this model. The model presented herein is essentially developed from the thermal–hydraulic point of view and can be considered as a stepping‐stone towards a full complete PEMFC simulation model that can help the optima design for the PEMFC and the enhancement of cell efficiency. Copyright © 2003 John Wiley & Sons, Ltd.     

Constructal flow distributor as a bipolar plate for proton exchange membrane fuel cells

A plate-type constructal flow distributor is implemented as a gas distributor for a proton exchange membrane fuel cell. A 3D complete model is simulated using CFD techniques. The fuel cell model includes the gas flow channels, the gas diffusion layers and the membrane-electrode assembly (MEA). The governing equations for the mass and momentum transfer are solved including the pertinent source terms due to the electrochemical reactions in the different zones of the fuel cell. Three constructal flow configurations were studied; each pattern is a fractal expansion of the original design, therefore, the only difference between them is the number of branches in the geometry. It was found that the number of branches is the key parameter in the performance of a fuel cell when using the constructal distributors as flow channels. The performance of the fuel cell is reported in I-V curves, power curves, and overpotential curves in order to determine which irreversibility is the main cause of energy losses. In terms of flow analysis, it was found that the constructal flow distributor presents a low pressure drop for a wide range of Reynolds number conditions at the inlet, as well as an excellent uniformity of flow distribution. Regardless of the outstanding hydrodynamic performance of the constructal distributors and the large current density values obtained, the implementation of these designs as flow patterns for PEMFCs need further optimization; first, the manufacturing of the plates have to be addressed in an efficient way; and secondly, the application in stacks will require an elaborate design to accomplish this task.     

Optimization of PEM fuel cell flow channel dimensions—Mathematic modeling analysis and experimental verification

The objective of this work is to optimize the dimensions of gas flow channels and walls/ribs in a proton-exchange membrane (PEM) fuel cell. To achieve this goal conveniently, a relatively easy-to-approach mathematical model for PEM fuel cells has been developed. The model was used for the design optimization of fuel cells, which were fabricated and experimentally tested to compare the performance and examine these optimization effects. The model analyzes the average mass transfer and species' concentrations in flow channels, which allows the determination of an average concentration polarization, the humidity in anode and cathode gas channels, the proton conductivity of membranes, as well as the activation polarization. An electrical circuit for the current and ion conduction is applied to analyze the ohmic losses from anode current collector to cathode current collector. This model needs relatively less amount of computational time to find the V–I curve of the fuel cell, and thus it can be applied to compute a large amount of cases with different flow channel dimensions and operating parameters for optimization. Experimental tests of several PEM fuel cells agreed with the modeling results satisfactorily. Both simulation and experimental results showed that relatively small widths of flow channels and ribs, together with a small ratio of the rib's width versus channel's width, are preferred for obtaining high power densities. To further demonstrate the advantage of optimized fuel cell designs, two four-cell stacks, one with optimized channel/rib designs and the other without, were compared experimentally and a much better performance of the one with the optimized design was confirmed.     

A numerical study of flow crossover between adjacent flow channels in a proton exchange membrane fuel cell with serpentine flow field

The focus of this paper is to study the flow crossover between two adjacent flow channels in a proton exchange membrane (PEM) fuel cell with serpentine flow field design in bipolar plates. The effect of gas diffusion layer (GDL) deformation on the flow crossover due to the compression in a fuel cell assembly process is particularly investigated. A three-dimensional structural mechanics model is created to study the GDL deformation under the assembly compression. A three-dimensional PEM fuel cell numerical model is developed in the aforementioned deformed domain to study the flow crossover between the adjacent channels in the presence of the GDL intrusion. The models are solved in COMSOL Multiphysics—a finite element-based commercial software package. The pressure, velocity, oxygen mass fraction and local current density distribution are presented. A parametric study is conducted to quantitatively investigate the effect of the GDL’s transport related parameters such as porosity and permeability on the flow crossover between the adjacent flow channels. The polarization curves are also examined with and without the assembly compression considered. It is found that the compression effect is evident in the high current density region. Without considering the assembly compression, the fuel cell model tends to over-predict the fuel cell’s performance. The proposed method to simulate the crossover with the deformed computational domain is more accurate in predicting the overall performance.     

Effect of flow fields and humidification of reactant and oxidant on the performance of scaled‐up PEM‐FC using CFD code

The present study focuses on three‐dimensional two‐phase CFD investigation on scaled‐up proton exchange membrane fuel cell (PEM‐FC) for an active area of 100 cm² with different designs of serpentine and parallel flow configuration. The humidification of hydrogen and oxygen is varied from 10% to 100% to study the PEM‐FC performance. The numerical results of polarization curves predicted in this study have been numerically validated with that of the literature for both parallel and counter serpentine flow channels with active area of 24.8‐cm² PEM‐FC. Further upon validation, the numerical study is extended for scaled‐up PEM‐FC with active area of 100 cm² with different flow path designs to study its performance characteristics namely polarization curves, species concentration distribution, water content in the membrane electrolyte, and proton conductivity to evaluate the fuel cell performance. The three‐dimensional CAD models are created in SOLIDWORKS 10.0 and are discretised hexahedrally using finite volume method. The various governing equations namely conservation of mass, momentum, energy, species concentration, and electrochemical equations are solved numerically with the necessary boundary conditions using the CFD code. The novel design of straight zigzag flow path shows the better performance output over the other designs investigated which is having a higher power density of 0.3711 W/cm² for 100% relative humidity of reactant and oxidant.     

Mass transfer in proton exchange membrane fuel cells with baffled flow channels and a porous‐blocked baffled flow channel design

In proton exchange membrane fuel cells, baffled flow channels enhance the reactant transfer from flow channels to gas diffusion layers. However, the reactant transfer depends on both the diffusive transfer and convective transfer, and how the baffles in flow channels affect them is still unknown. Therefore, in this work, a two‐dimensional, two‐phase, nonisothermal, and steady‐state model of proton exchange membrane fuel cells is developed, and these two transfer processes from flow channels to gas diffusion layers are comparatively studied. Simulation results show that first of all, the reactant transfer from flow channels to gas diffusion layers mainly depends on the diffusive transfer. Therefore, if the desire is to enhance the mass transfer from flow channels to gas diffusion layers, the diffusive mass transfer should be enhanced firstly. Being guided by this goal, a porous‐blocked baffled flow channel is developed. This flow channel design can further enhance the reactant transfer from flow channels to gas diffusion layers, and the cell performance can be improved. Moreover, when the porosities of porous blocks at the front place of flow channels are lower, the cell power is also increased but the pumping power can be reduced a lot.     

Performance analysis of a proton exchange membrane fuel cell using tree-shaped designs for flow distribution

The performance of a proton exchange membrane (PEM) fuel cell is directly associated to the flow channels design embedded in the bipolar plates. The flow field within a fuel cell must provide efficient mass transport with a reduced pressure drop through the flow channels in order to obtain a uniform current distribution and a high power density. In this investigation, three-dimensional fuel cell models are analyzed using computational fluid dynamics (CFD). The proposed flow fields are radially designed tree-shaped geometries that connect the center flow inlet to the perimeter of the fuel cell plate. Three flow geometries having different levels of bifurcation were investigated as flow channels for PEM fuel cells. The performance of the fuel cells is reported in polarization and power curves, and compared with that of fuel cells using conventional flow patterns such as serpentine and parallel channels. Results from the flow analysis indicate that tree-shaped flow patterns can provide a relatively low pressure drop as well as a uniform flow distribution. It was found that as the number of bifurcation levels increases, a larger active area can be utilized in order to generate higher power and current densities from the fuel cell with a negligible increase in pumping power.     

Performance improvement of proton exchange membrane fuel cell by using annular shaped geometry

A complete three-dimensional and single phase CFD model for a different geometry of proton exchange membrane (PEM) fuel cell is used to investigate the effect of using different connections between bipolar plate and gas diffusion layer on the performances, current density and gas concentration. The proposed model is a full cell model, which includes all the parts of the PEM fuel cell, flow channels, gas diffusion electrodes, catalyst layers and the membrane. Coupled transport and electrochemical kinetics equations are solved in a single domain; therefore no interfacial boundary condition is required at the internal boundaries between cell components.This computational fluid dynamics code is used as the direct problem solver, which is used to simulate the three-dimensional mass, momentum and species transport phenomena as well as the electron- and proton-transfer process taking place in a PEMFC that cannot be investigated experimentally. The results show that the predicted polarization curves by using this model are in good agreement with the experimental results. Also the results show that by increasing the number of connection between GDL and bipolar plate the performance of the fuel cell enhances.     

A two-phase flow and transport model for PEM fuel cells

A two-phase flow and multi-component mathematical model with a complete set of governing equations valid in different components of a PEM fuel cell is developed. The model couples the flows, species, electrical potential, and current density distributions in the cathode and anode fluid channels, gas diffusers, catalyst layers and membrane, respectively. The modeling results of typical concentration distributions are presented. The coupling of oxygen concentration, current density, overpotential and potential are shown in the membrane electrode assembly (MEA). The model predicted fuel cell polarization curves for different cathode pressures compared well with our experimental data.     

Design and simulation of a novel bipolar plate based on lung‐shaped bio‐inspired flow pattern for PEM fuel cell

Finding the optimal flow pattern in bipolar plates of a proton exchange membrane is a crucial step for enhancing the performance of the device. This design plays a critical role in fluid mass transport through microporous layers, charge transfer through conductive media, management of the liquid water produced in microchannels, and microporous layers and heat management in fuel cells. This article investigates different types of common flow patterns in bipolar plates while considering a uniform pressure and velocity distribution as well as a uniform distribution of reactants through all the surfaces of the catalyst layer as the design criteria so that there would be a consistent electron production by the catalyst layer. Then, by identifying the important parameters in achieving the best performance of a fuel cell, a microfluidic flow pattern is inspired from the lungs in the human body, and an innovative bipolar plate is suggested, which was not proposed before. Afterwards, numerical simulations were carried out using computational fluid dynamics methods, and the mentioned bipolar plate called lung‐shaped bipolar plate was modeled. Simulations in this research showed that the lung‐shaped microfluidic flow pattern is an appropriate flow pattern to gain maximum power and energy density. In other words, the best polarization curve and power density curve are obtained by using the lung‐shaped bipolar plate in a proton exchange membrane fuel cell compared with previously suggested patterns. Copyright © 2017 John Wiley & Sons, Ltd.     

Numerical investigation of innovative 3D cathode flow channel in proton exchange membrane fuel cell

Two kinds of innovative 3‐dimensional (3D) proton exchange membrane fuel cell (PEMFC) cathode flow channel designs were proposed to improve the water removal on the surface of gas diffusion layer and enhance mass transfer between flow channel and gas diffusion layer. A validated 2‐phase volume of fluid model was used to investigate different water removal behaviors in flow channel. The optimal length of water baffle and other parameters of the proposed designs were determined. A validated 3D PEMFC performance model was adopted to assess the new designs. The results suggest that these 2 designs can improve PEMFC performance as to 9% when operating at the high current density because of the significant enhancement of mass transfer induced by air baffles.     

CFD investigating the effects of different operating conditions on the performance and the characteristics of a high-temperature PEMFC

The effects of different operating conditions on the performance and the characteristics of a high-temperature proton exchange membrane fuel cell (PEMFC) are investigated using a three-dimensional (3-D) computational fluid dynamics (CFD) fuel-cell model. This model consists of the thermal-hydraulic equations and the electrochemical equations. Different operating conditions studied in this paper include the inlet gas temperature, system pressure, and inlet gas flow rate, respectively. Corresponding experiments are also carried out to assess the accuracy of this CFD model. Under the different operating conditions, the PEMFC performance curves predicted by the model correspond well with the experimentally measured ones. The performance of PEMFC is improved as the increase in the inlet temperature, system pressure or flow rate, which is precisely captured by the CFD fuel cell model. In addition, the concentration polarization caused by the insufficient supply of fuel gas can be also simulated as the high-temperature PEMFC is operated at the higher current density. Based on the calculation results, the localized thermal-hydraulic characteristics within a PEMFC can be reasonably captured. These characteristics include the fuel gas distribution, temperature variation, liquid water saturation distribution, and membrane conductivity, etc.     

Simulation of species transport and water management in PEM fuel cells

A single phase computational fuel cells model is presented to elucidate three-dimensional interactions between mass transport and electrochemical kinetics in proton exchange membrane (PEM) fuel cells with straight gas channels. The governing differential equations are solved over a single computational domain, which consists of a gas channel, gas diffusion layer, and catalyst layer for both the anode and cathode sides of the cell as well as the solid polymer membrane. Emphasis is placed on obtaining a basic understanding of how three-dimensional flow and transport phenomena in the air cathode impact the electrochemical process in the flow field. The complete cell model has been validated against experimentally measured polarization curve, showing good accuracy in reproducing cell performance over moderate current density interval. Fully three-dimensional results of the flow structure and species profiles are presented for cathode flow field. The effects of pressure on oxygen transport and water removal are illustrated through main axis of the flow structure. The model results indicate that oxygen concentration in reaction sites is significantly affected by pressure increase which leads to rising fuel cells power.     

Influence of local porosity and local permeability on the performances of a polymer electrolyte membrane fuel cell

In the literature, many models and studies focused on the steady-state aspect of fuel cell systems while their dynamic transient behavior is still a wide area of research. In the present paper, we study the effects of mechanical solicitations on the performance of a proton exchange membrane fuel cell as well as the coupling between the physico-chemical phenomena and the mechanical behavior. We first develop a finite element method to analyze the local porosity distribution and the local permeability distribution inside the gas diffusion layer induced by different pressures applied on deformable graphite or steel bipolar plates. Then, a multi-physical approach is carried out, taking into account the chemical phenomena and the effects of the mechanical compression of the fuel cell, more precisely the deformation of the gas diffusion layer, the changes in the physical properties and the mass transfer in the gas diffusion layer. The effects of this varying porosity and permeability fields on the polarization and on the power density curves are reported, and the local current density is also investigated. Unlike other studies, our model accounts for a porosity field that varies locally in order to correctly simulate the effect of an inhomogeneous compression in the cell.     

PEMFC翅脉流道传质及输出性能分析

为研究流道结构对质子交换膜燃料电池（PEMFC）反应气体质量传输及输出性能的影响,建立翅脉流道、叶脉流道及蛇形流道的三维PEMFC几何模型,并对比3种流道的反应气体浓度分布、压力分布及电流密度分布,最后对翅脉流道结构参数进行优化。结果表明,与蛇形流道、叶脉流道相比,翅脉流道能明显改善流道和扩散层内反应气体浓度分布的均匀性,有利于强化反应气体向催化层的质量传递;翅脉流道能减小气体压力分布梯度,使反应气体扩散更加充分;翅脉流道的平均膜电流密度更大,有利于促进电化学反应稳定进行;翅脉流道能改善PEMFC的输出性能,翅脉流道峰值功率密度比蛇形流道、叶脉流道分别提高7.72%和6.25%;减小翅脉流道的直流道长度或圆弧流道圆心角,可提升翅脉流道输出性能。     

Numerical evaluation of a PEM fuel cell with conventional flow fields adapted to tubular plates

In this research a 3D numerical study on a PEM fuel cell model with tubular plates is presented. The study is focused on the performance evaluation of three flow fields with cylindrical geometry (serpentine, interdigitated and straight channels) in a fuel cell. These designs are proposed not only with the aim to reduce the pressure losses that conventional designs exhibit with rectangular flow fields but also to improve the mass transport processes that take place in the fuel cell cathode. A commercial computational fluid dynamics (CFD) code was used to solve the numerical model. From the numerical solution of the fluid mechanics equations and the electrochemical model of Butler-Volmer different analysis of pressure losses, species concentration, current density, temperature and ionic conductivity were carried out. The results were obtained at the flow channels and the catalyst layers as well as in the gas diffusion layers and the membrane interfaces. Numerical results showed that cylindrical channel configurations reduced the pressure losses in the cell due to the gradual reduction of the angle at the flow path and the twist of the channel, thus facilitating the expulsion of liquid water from the gas diffusion layers and in turn promoting a high oxygen concentration at the triple phase boundary of the catalyst layers. Moreover, numerical results were compared to polarization curves and the literature data reported for similar designs. These results demonstrated that conventional flow field designs applied to conventional tubular plates have some advantages over the rectangular designs, such as uniform pressure and current density distributions among others, therefore they could be considered for fuel cell designs in portable applications.     

An easy-to-approach and comprehensive model for planar type SOFCs

An easy-to-approach and comprehensive mathematical model for planar type solid oxide fuel cells is presented in the current work. It provides a tool for researchers to conduct parametric studies with less-intensive computation in order to grasp the fundamentals of coupled mass transfer, electrochemical reaction, and current conduction in a fuel cell. In the model, the analysis for the mass transfer polarization at a known average fuel cell operating temperature is based on an average mass transfer model analogous to an average heat transfer process in a duct flow. The effect of the species' partial pressure at electrode/electrolyte interfaces is therefore included in the exchange current density for activation polarizations. An electrical circuit for the current and ion conduction is used to analyze the ohmic losses from anode current collector to cathode current collector. The three types of over-potentials caused by different polarizations in a planar type solid oxide fuel cell can be identified and compared. The effects of species concentrations, properties of fuel cell components to the voltage–current performance of a fuel cell at different operating conditions are studied. Optimization of the dimensions of flow channels and current-collecting ribs is also presented. The model is of significance to the design and optimization of solid oxide fuel cells for industrial application.     

Performance of a polymer electrolyte fuel cell for automotive applications

The objectives of this study were to fabricate a self‐humidifying fuel cell stack of 10 cells with 104 cm² cell areas humidified with water recovered at cathodes, and to measure and simulate the performance of the stack. This involves the simulation of a three‐dimensional model of the heat and mass transfer of the water and the gaseous reactants in the fuel cell components with a water‐cooling system. The results of the stack experiments indicated a maximum power of 250 kW at a current density of 0.5 A/cm². The simulation showed good agreement with the actual performance of the stack. The performance of the self‐humidifying stack with a vapor‐permeating membrane is comparable to a conventional stack with external humidifiers, and it appears very effective in simplifying stack systems. The modeling analysis indicated that for the gas flow directions, at anode and cathode, a parallel flow is superior to a cross flow, and that one cooling cell is necessary for two to three generating cells in order to maintain the fuel cell temperature below 100 °C. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(6): 421–429, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10041     

质子交换膜燃料电池参数敏感性分析

为分析质子交换膜燃料电池（PEMFC）的参数敏感性,采用COMSOL建立三维、两相、等温燃料电池单体模型,对其进行模拟计算。通过分析物质浓度分布、极化曲线及功率密度曲线得到不同的离聚物体积分数、背压对传质及电池性能的影响。计算结果表明：随着离聚物体积分数的增大,欧姆极化损失减小,从而使电池性能得到提升,且随着工作电压的减小,电流密度增幅增大;背压的增加使电流密度增大,改变阴极背压比改变阳极背压造成的影响更大。     

Dynamic tank in series modeling of direct internal reforming SOFC

A dynamic tank in series reactor model of a direct internally reforming solid oxide fuel cell is presented and validated using experimental data as well as a computational fluid dynamics (CFD) model for the spatial profiles. The effect of the flow distribution pattern at the inlet manifold on the cell performance is studied with this model. The tank in series reactor model provides a reasonable understanding of the spatio‐temporal distribution of the key parameters at a much lesser computational cost when compared to CFD methods. The predicted V–I curves agree well with the experimental data at different inlet flows and temperatures, with a difference of less than ±1.5%. In addition, comparison of the steady‐state results with two‐dimensional contours from a CFD model demonstrates the success of the adopted approach of adjusting the flow distribution pattern at the inlet boundaries of different continuous stirred tank reactor compartments. The spatial variation of the temperature of the PEN structure is captured along with the distributions of the current density and the anode activation over‐potential that strongly related to the temperature as well as the species molar fractions. It is found that, under the influence of the flow distribution pattern and reaction rates, the dynamic responses to step changes in voltage (from 0.819 to 0.84 V), fuel flow (15%) and temperature changes (30 °C), on anode side and on cathode side, highly depend on the spatial locations in the cell. In general, the inlet points attain steady state rapidly compared to other regions. Copyright © 2017 John Wiley & Sons, Ltd.