Novel convergent-divergent serpentine flow fields effect on PEM fuel cell performance

A new design of convergent and divergent flow fields are being developed in single serpentine flow field pattern for proton exchange membrane (PEM) fuel cell. The channel depth is varied by means of inclination from inlet to outlet of the bipolar plate. By the varying inclined channel depth, it created convergent/divergent flow effect along the channel length in the single serpentine. Four different convergent flow fields are manufactured by the varying inclined channel depth from inlet to outlet as 1.5 mm–0.5 mm, 2.5 mm–1.5 mm, 3 mm～1 mm and 3.5 mm–0.5 mm, which are divergent flow fields as well by interchanging between inlet and outlet section. These convergent and divergent flow fields are compared with two conventional single serpentine having 1 mm and 2 mm constant channel depth for an active area of 4.7 cm². The experimental results showed that both convergent and divergent flow fields outperforms the conventional serpentine flow fields where maximum performance was achieved from convergent flow field C1 (1.5 mm–0.5 mm) improving 19–27% power than two conventional serpentine flow fields. Therefore this novel convergent serpentine flow field effect can improve PEM fuel cell performance by its suitable bipolar plate design.     

Experiment and simulation investigations for effects of flow channel patterns on the PEMFC performance

Experiments and simulations are presented in this paper to investigate the effects of flow channel patterns on the performance of proton exchange membrane fuel cell (PEMFC). The experiments are conducted in the Fuel Cell Center of Yuan Ze University and the simulations are performed by way of a three‐dimensional full‐cell computational fluid dynamics model. The flow channel patterns adopted in this study include the parallel and serpentine flow channels with the single path of uniform depth and four paths of step‐wise depth, respectively. Experimental measurements show that the performance (i.e. cell voltage) of PEMFC with the serpentine flow channel is superior to that with the parallel flow channel, which is precisely captured by the present simulation model. For the parallel flow channel, different depth patterns of flow channel have a strong influence on the PEMFC performance. However, this effect is insignificant for the serpentine flow channel. In addition, the calculated results obtained by the present model show satisfactory agreement with the experimental data for the PEMFC performance under different flow channel patterns. These validations reveal that this simulation model can supplement the useful and localized information for the PEMFC with confidence, which cannot be obtained from the experimental data. Copyright © 2007 John Wiley & Sons, Ltd.     

An inverse geometry design problem for optimization of single serpentine flow field of PEM fuel cell

The cathode flow-field design of a proton exchange membrane fuel cell (PEMFC) determines its reactant transport rates to the catalyst layer and removal rates of liquid water from the cell. This study optimizes the cathode flow field for a single serpentine PEM fuel cell with 5 channels using the heights of channels 2–5 as search parameters. This work describes an optimization approach that integrates the simplified conjugated-gradient scheme and a three-dimensional, two-phase, non-isothermal fuel cell model. The proposed optimal serpentine design, which is composed of three tapered channels (channels 2–4) and a final diverging channel (channel 5), increases cell output power by 11.9% over that of a cell with straight channels. These tapered channels enhance main channel flow and sub-rib convection, both increasing the local oxygen transport rate and, hence, local electrical current density. A diverging, final channel is preferred, conversely, to minimize reactant leakage to the outlet. The proposed combined approach is effective in optimizing the cathode flow-field design for a single serpentine PEMFC. The role of sub-rib convection on cell performance is demonstrated.     

Experimental investigation on scaling and stacking up of proton exchange membrane fuel cells

The performance of a proton exchange membrane fuel cell (PEMFC) with various flow channel design (serpentine and interdigitated) with different landing to channel ratios (L:C = 1:1; 2:2) for an active area of 25 cm² and 70 cm², for single cell and two cells stack is studied and compared. The effect of back pressure on the PEMFC performance is also investigated. This study establishes a strong relation between back pressure and power output from a PEMFC. It was concluded that the interdigitated flow channel gives better results than the serpentine flow channel configuration for various landing to channel ratios. It was also found that power outputs do not proportionally increase with active area of the membrane electrode assembly (MEA). Similarly, stacking up studies with single cell and two cell stack shows that the two cell stack has reduced power densities when compared to that of a single cell. The effect of cooling channels with natural and forced convection by using induced draught fan on the performance of a PEMFC stack is also studied. Fuel distribution and temperature management are found to be the significant factors which determine the performance of a PEMFC stack.     

The energy performance improvement of a PEM fuel cell with various chaotic flowing channels

To improve the energy performance of a proton exchange membrane fuel cell (PEMFC), novel chaotic structures are proposed and numerically evaluated for replacing straight types in the serpentine gas diffusion flow channels. The numerical model is verified by the available experimental data. Nine cases (chaotic channels, Cases A2, B1, B2, C1, C2, D1, D2, E1, and E2) and a baseline case (straight flow channel, Case A1) are evaluated, and the detailed temperature and the flow characteristics are presented and analyzed. The influences of the main design parameters including the corner angle, bends number, and datum surface number are also analyzed and concluded. It is found that the newly proposed chaotic structures can improve not only the temperature uniformity, but also the maximum output power and the energy efficiency of the PEMFC. Compared with a traditional PEMFC, the power output of the new PEMFCs with chaotic flowing channels can be improved by 6.26% and the efficiency of PEMFC can be promoted by 8.40%.     

Detailed analysis of polymer electrolyte membrane fuel cell with enhanced cross‐flow split serpentine flow field design

Most generally used flow channel designs in polymer electrolyte membrane fuel cells (PEMFCs) are serpentine flow designs as single channels or as multiple channels due to their advantages over parallel flow field designs. But these flow fields have inherent problems of high pressure drop, improper reactant distribution, and poor water management, especially near the U‐bends. The problem of inadequate water evacuation and improper reactant distribution become more severe and these designs become worse at higher current loads (low voltages). In the current work, a detailed performance study of enhanced cross‐flow split serpentine flow field (ECSSFF) design for PEMFC has been conducted using a three‐dimensional (3‐D) multiphase computational fluid dynamic (CFD) model. ECSSFF design is used for cathode part of the cell and parallel flow field on anode part of the cell. The performance of PEMFC with ECSSFF has been compared with the performance of triple serpentine flow design on cathode side by keeping all other parameters and anode side flow field design similar. The performance is evaluated in terms of their polarization curves. A parametric study is carried out by varying operating conditions, viz, cell temperature and inlet humidity on air and fuel side. The ECSSFF has shown superior performance over the triple serpentine design under all these conditions.     

Comparison of PEMFC performance with parallel serpentine and parallel serpentine-baffled flow fields under various operating and geometrical conditions; a parametric study

Optimal flow channel design of a fuel cell is crucial to further improve the performance of polymer electrolyte membrane fuel cell (PEMFC). In this work, a comprehensive parametric study was conducted to analyze the performance of a PEMFC with conventional parallel serpentine flow fields (PSFF) and parallel serpentine-baffled flow fields (PSBFF). A three-dimensional two-phase computational fluid dynamics model was used to numerically simulate the fuel cell performance. The effects of operating parameters such as pressure, temperature, and stoichiometric ratio, as well as the geometric parameters of channel height to channel width ratio and rib width to channel width ratio for both flow fields on fuel cell performance were investigated. The results show that as pressure, temperature, and stoichiometric ratio increase, cell performance increases for both flow fields, with a more substantial rate of improvement for the PSBFF design. A 16.1% improvement in cell performance at an operating pressure of 1 atm, a 19.9% improvement at a cell temperature of 70 °C, and a 16.1% improvement at a stoichiometric ratio of 2 were obtained when PSBFF was used instead of PSFF. By increasing the channel height and rib width, the cell performance for PSBFF remains almost constant due to the improved forced convection of the gas mixture and the reduction in concentration loss, while the cell performance for PSFF decreases significantly. At the largest channel height to channel width ratio of 1.5 and rib width to channel width ratio of 1.315 studied in this work, an improvement in cell performance of 53.3% and 58.5%, respectively, was achieved when PSBFF was used instead of PSFF. In addition, PSBFF was more effective in removing water from the porous zones than PSFF under all conditions.     

A three-dimensional full-cell CFD model used to investigate the effects of different flow channel designs on PEMFC performance

A three-dimensional “full-cell” computational fluid dynamics (CFD) model is proposed in this paper to investigate the effects of different flow channel designs on the performance of proton exchange membrane fuel cells (PEMFC). The flow channel designs selected in this work include the parallel and serpentine flow channels, single-path and multi-path flow channels, and uniform depth and step-wise depth flow channels. This model is validated by the experiments conducted in the fuel cell center of Yuan Ze University, showing that the present model can investigate the characteristics of flow channel for the PEMFC and assist in the optima designs of flow channels. The effects of different flow channel designs on the PEMFC performance obtained by the model predictions agree well with those obtained by experiments. Based on the simulation results, which are also confirmed by the experimental data, the parallel flow channel with the step-wise depth design significantly promotes the PEMFC performance. However, the performance of PEMFC with the serpentine flow channel is insensitive to these different depth designs. In addition, the distribution characteristics of fuel gases and current density for the PEMFC with different flow channels can be also reasonably captured by the present model.     

Estimation of crack propagation in polymer electrolyte membrane fuel cell under vibration conditions

In transportation applications, the main reasons of mechanical damage in polymer electrolyte membrane fuel cell (PEMFC) are road-induced vibrations and impact loads. The most vulnerable place of these cells is the interface between membrane and catalyst layer in the membrane electrode assembly (MEA). Hence, studies on mechanical strength of PEMFC should focus on that interface. The objective of present study lies in the fact that employing a prediction method to investigate the damage propagation behavior of vibration applied PEMFC using artificial neural network (ANN). The data available in the literature are used to constitute an ANN model. Three-layer model; input, hidden and output, are used for construction of ANN structure. Initial delamination length (a), amplitude (A), frequency (ω) and time (t) are used as input neurons whereas delamination length is output. Levenberg–Marquardt algorithm is selected as learning algorithm. On the other hand, number of hidden layer neuron is decided with the use of different neuron numbers by trial and error method. It is concluded that prediction capability of ANN model is in allowable limits and model can be suggested as efficient way of delamination length estimation.     

Comparison of current distributions in proton exchange membrane fuel cells with interdigitated and serpentine flow fields

Current distributions in a proton exchange membrane fuel cell (PEMFC) with interdigitated and serpentine flow fields under various operating conditions are measured and compared. The measurement results show that current distributions in PEMFC with interdigitated flow fields are more uniform than those observed in PEMFC with serpentine flow fields at low reactant gas flow rates. Current distributions in PEMFC with interdigitated flow fields are rather uniform under any operating conditions, even with very low gas flow rates, dry gas feeding or over-humidification of reactant gases. Measurement results also show that current distributions for both interdigitated and serpentine flow fields are significantly affected by reactant gas humidification, but their characteristics are different under various humidification conditions, and the results show that interdigitated flow fields have stronger water removal capability than serpentine flow fields. The optimum reactant gas humidification temperature for interdigitated flow fields is higher than that for serpentine flow fields. The performance for interdigitated flow fields is better with over-humidification of reactant gases but it is lower when air is dry or insufficiently humidified than that for serpentine flow fields.     

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。     

Performance improvement of proton exchange membrane fuel cells with compressed nickel foam as flow field structure

In order to improve the performance of proton exchange membrane fuel cell (PEMFC), the compressed nickel foam as flow field structure was applied to the fuel cell. The fuel cell test system was built and the performance of fuel cells with nickel foam flow field with different thicknesses were tested and analyzed by electrochemical active surface area (EASA), electrochemical impedance and polarization curve. And its operating parameters were optimized to improve the performance of PEMFC. Our results show that the membrane electrode assembly (MEA) can show a larger catalytic active area and uniformity of gas diffusion can be improved by using the nickel foam flow field instead of the conventional graphite serpentine flow field, and the impedance characteristic of 110PPI nickel foam can be improved by increasing the compression ratio of the original material. What's more, the polarization characteristic and power output performance of PEMFC with nickel foam flow field were improved by optimizing the operating parameters. Using the optimized operating parameters (cell temperature = 80 °C; humidification temperature = 75 °C; stoichiometric ratio = 2; back pressure = 0.23 Map), a peak power density of 1.89 W cm⁻² was obtained with an output voltage of 0.46 V.     

Operation of polymer electrolyte membrane fuel cells with dry feeds: Design and operating strategies

The operation of polymer electrolyte membrane fuel cells (PEMFCs) with dry feeds has been examined with different fuel cell flow channel designs as functions of pressure, temperature and flow rate. Auto-humidified (or self-humidifying) PEMFC operation is improved at higher pressures and low gas velocities where axial dispersion enhances “back-mixing” of the product water with the dry feed. We demonstrate auto-humidified operation of the channel-less, self-draining fuel cell, based on a stirred tank reactor; data is presented showing auto-humidified operation from 25 to 115 °C at 1 and 3 atm. Design and operating requirements are derived for the auto-humidified operation of the channel-less, self-draining fuel cell. The auto-humidified self-draining fuel cell outperforms a fully humidified serpentine flow channel fuel cell at high current densities. The new design offers substantial benefits for simplicity of operation and control including: the ability to self-drain reducing flooding, the ability to uniformly disperse water removing current gradients and the ability to operate on dry feeds eliminating the need for humidifiers. Additionally, the design lends itself well to a modular design concept.     

Three-dimensional numerical study on cell performance and transport phenomena of PEM fuel cells with conventional flow fields

In this paper, a three-dimensional numerical model of the proton exchange membrane fuel cells (PEMFCs) with conventional flow field designs (parallel flow field, Z-type flow field, and serpentine flow field) has been established to investigate the performance and transport phenomena in the PEMFCs. The influences of the flow field designs on the fuel utilization, the water removal, and the cell performance of the PEMFC are studied. The distributions of velocity, oxygen mass fraction, current density, liquid water, and pressure with the convention flow fields are presented. For the conventional flow fields, the cell performance can be enhanced by adding the corner number, increasing the flow channel length, and decreasing the flow channel number. The cell performance of the serpentine flow field is the best, followed by the Z-type flow field and then the parallel flow field.     

Measurements of serpentine channel flow characteristics for a proton exchange membrane fuel cell

Flow characteristics at Re = 660–3000 in a serpentine channel are measured. A scale-up model whose channel hydraulic diameter is 50 times as large as that for a proton exchange membrane fuel cell (PEMFC) is used for the measurements. The flow conditions correspond to operating conditions for PEMFCs of 25–40 cm² at current density of 1–3 A/cm² when the fuel utilisation ratio is 0.75 and air is used for the O₂ supply. Two different porous media are used to simulate the gas diffusion layer (GDL). The results suggest that although the leakage flow rate is rather insensitive to the total flow rate, it increases significantly depending on the increase of the GDL permeability. Increasing the flow rate or the permeability enhances the sectional secondary flows and is expected to enhance mass transfer on the GDL. It is confirmed that the flow becomes turbulent around the bend even at Re = 660.     

Neural network model of 100 W portable PEM fuel cell and experimental verification

The inherent properties of artificial neural networks (ANNs) such as low sensitivity to noise and incomplete information make the ANN a promising candidate to model the fuel cell system. In this paper, an ANN-based model of 100 W portable direct hydrogen fed proton exchange membrane fuel cell (PEMFC) is presented. The model is built based on experimentally collected data from a portable 100 W direct hydrogen fed PEMFC in the authors’ laboratory. A multilayer feedforward ANN with back-propagation training algorithm is used to model the portable PEMFC. The ANN consists of fully connected four layers network with two hidden layers. The PEMFC ANN model is trained using extracted data from experimentally measured and calculated parameters. To validate the model, the outputs of the PEMFC ANN are compared against experimental data and results from a dynamic model of portable direct hydrogen fed PEMFC. In addition, three statistical indices to measure variations, unbiasedness (precision), and accuracy in voltage, power, and hydrogen flow are used to evaluate the PEMFC ANN model performance. The indices indicate that the maximum variations, unbiasedness, and accuracy of the voltage, power, and hydrogen flow are 1.45%, 2.04%, and 1.90%, respectively, which shows a close agreement between the outputs of the PEMFC ANN and the experimental results.     

Basic evaluation of separator type specific phenomena of polymer electrolyte membrane fuel cell by the measurement of water condensation characteristics and current density distribution

This paper investigates phenomena related to water condensation behavior inside a polymer electrolyte membrane fuel cell (PEMFC), and analyzes the effects of liquid water and gas flow on the performance of the fuel cell. A method for simultaneous measurements of the local current density across the reaction area and direct observation of the phenomena in the cell are developed. Experimental results comparing separator types indicate the effect of shortcut flow in the gas diffusion layer (GDL) under the land areas of serpentine separators, and also show the potential of straight channel separators to achieve a relatively uniform current density distribution. To evaluate shortcut flows under the land areas of serpentine separators, a simple circuit model of the gas flow is presented. The analysis shows that slight variations in oxygen concentration caused by the shortcut flows under the land areas affect the local and overall current density distributions. It is also shown that the establishment of gas paths under the water in channels filled with condensed water is effective for stable operation at low flow rates of air in the straight channels.     

A parametric comparison of temperature uniformity and energy performance of a PEMFC having serpentine wavy channels

Proton exchange membrane fuel cells (PEMFCs) are regarded as alternative energy sources because they are environment friendly and deliver no harmful emission. As its reliability and power generating efficiency is largely influenced by the temperature distribution, it is necessary to improve the temperature uniformity which is crucial in PEMFCs. To this end, this numerical study presents an attempt to optimize the flow channels via introducing wavy shape flow channels at the ribs. The numerical model is validated by experimental data available in the open literature. Two kinds of wavy shape flow channels are designed while straight flow channel is set as a reference. In the PEMFCs with wavy shape flow channels, the effects of the amplitude and wavelength on the thermal performance are simulated and analyzed. Results show that wavy shape flow channels provide better performance not only for thermal uniformity but also for PEMFC output power and efficiency. With lower amplitude and wavelength of wavy shape flow channels, the power can be promoted up to 3.69% and 7.26% for two kinds of wavy shaped flow channels compared with straight flow channel, respectively. The influences of amplitude and wavelength on the thermal uniformity and the output power are also analyzed. This paper provides a new insight to PEMFC flow channel designers.     

Effects of cathode channel configurations on the performance of an air-breathing PEMFC

A mathematical model is developed for evaluating the effects of various channel dimensions on the performance of an air-breathing polymer electrolytes membrane fuel cell (PEMFC). The model, which is based on Nguyen's model, has been extended to include the natural convection to consider buoyancy effect in the channels, electro-chemical reaction in the catalyst layer, and concentration overpotential due to mass transportation limitation. Results from the model indicate that the concentration loss is more serious in natural convection than in forced convection, especially at small channel width, and the performance of air-breathing PEMFC could be improved by increasing the channel width to some extend. Results also show that the temperature, channel size, and air flow rate influence each other, and the performance cannot be improved infinitely by increasing the channel size, and thus the cathode flow field should be optimized. This model provides insights into many design issues of air-breathing fuel cell, and can be easily used as an optimal design tool for air-breathing PEMFC.     

Dynamic characteristics of local current densities and temperatures in proton exchange membrane fuel cells during reactant starvations

Reactant starvation during proton exchange membrane fuel cell (PEMFC) operation can cause serious irreversible damages. In order to study the detailed local characteristics of starvations, simultaneous measurements of the dynamic variation of local current densities and temperatures in an experimental PEMFC with single serpentine flow field have been performed during both air and hydrogen starvations. These studies have been performed under both current controlled and cell voltage controlled operations. It is found that under current controlled operations cell voltage can decrease very quickly during reactant starvation. Besides, even though the average current is kept constant, local current densities as well as local temperatures can change dramatically. Furthermore, the variation characteristics of local current density and temperature strongly depend on the locations along the flow channel. Local current densities and temperatures near the channel inlet can become very high, especially during hydrogen starvation, posing serious threats for the membrane and catalyst layers near the inlet. When operating in a constant voltage mode, no obvious damaging phenomena were observed except very low and unstable current densities and unstable temperatures near the channel outlet during hydrogen starvation. It is demonstrated that measuring local temperatures can be effective in exploring local dynamic performance of PEMFC and the thermal failure mechanism of MEA during reactants starvations.