Study of the distribution of air flow in a proton exchange membrane fuel cell stack

The flow of air to feed oxygen to the cathode of each plate in a proton exchange membrane fuel cell (PEMFC) is studied for a 300 W stack in a realistic 3D configuration. Two configurations for gas income are solved, a “U” shape, where both the inlet and outlet of the air collectors are at the same end plate, and a “Z” shape, where inlet and outlet are at opposite sides of the stack. Under a simplified assumption for the flow of oxygen entering the gas diffusion layer of each cell, detailed mass flow and pressure distributions are shown, including the possibility of a turbulent flow inside the main collectors.     

Experimental study on water transport coefficient in Proton Exchange Membrane Fuel Cell

Water transport within Proton Exchange Membrane Fuel Cell (PEMFC) is investigated by systematic measurements of the water transport coefficient, defined as the net water flux across the membrane divided by the water production. It is recorded for various operating conditions (current density, gas stoichiometry, air inlet relative humidity, temperature, pressure) in a fuel cell stack fed by dry hydrogen. The measurement of the water transport coefficient shows that a significant fraction of water is collected at the anode while water is produced or injected at the cathode. Moreover, in usual operating conditions, liquid water is present at the cell outlet not only in the cathode but also in the anode. Contrary to the electrical performances, ageing has no influence on the water transport coefficient, which allows the comparison between data collected at different periods of the fuel cell lifetime. From this comparison, it was found that the hydrogen flow rate, the amount of vapor injected at cathode inlet, and the temperature are the main parameters influencing the water transport coefficient. It is shown that air and hydrogen stoichiometry present significant effects on water transport but only through these parameters.     

车用PEMFC氢气系统建模及其排放特性研究

建立基于尾氢再循环的车用PEMFC氢气系统的集总参数模型和质子交换膜燃料电池堆的二维CFD模型,瞬态模拟研究额定功率工况下尾氢排放对系统及电堆工作特性的影响。结果表明：排放过程中,阳极进气压力和进气流量等参数出现显著的波动现象,且波动幅度和波动时间与排放持续时间存在直接关系;电堆性能在排放过程中有所下降,排放结束后能迅速恢复到排放前的水平;阳极内部的水气分布在排放过程中得到明显改善。     

Model-based decoupling control for the thermal management system of proton exchange membrane fuel cells

As one of the most promising sustainable energy technologies available today, proton exchange membrane fuel cell (PEMFC) engines are becoming more and more popular in various applications, especially in transportation vehicles. However, the complexity and the severity of the vehicle operating conditions present challenges to control the temperature distribution in single cells and stack, which is an important factor influencing the performance and durability of PEMFC engines. It has been found that regulating the input and output coolant water temperature can improve the temperature distribution. Therefore, the control objective in this paper is regulating the input and output temperature of coolant water at the same time. Firstly, a coupled model of the thermal management system is established based on the physical structure of PEMFC engines. Then, in order to realize the simultaneous control of the inlet and outlet cooling water temperature of the PEMFC stack, a decoupling controller is proposed and its closed-loop stability is proved. Finally, based on the actual PEMFC engine platform, the effectiveness, accuracy and reliability of the proposed decoupling controller are tested. The experimental results show that with the proposed decoupling controller, the inlet and outlet temperatures of the PEMFC stack cooling water can be accurately controlled on-line. The temperature error range is less than 0.2 °C even under the dynamic current load conditions.     

Air and H2 feed systems optimization for open-cathode proton exchange membrane fuel cells

In this study, air and H₂ feed systems optimization for open-cathode proton exchange membrane fuel cells (PEMFCs) has been evaluated. For air feed system, a spoiler was introduced. The air velocity distribution, polarization curve, single-cell voltage distribution, and temperature distribution of the 11-cell open-cathode fuel cell stack with blowing, blowing-spoiler, and drawing air feed system were assessed. On this basis, the influences of the distance between the fan and stack with different air feed systems were investigated. The results show that the application of the spoiler could solve the problem of low air velocity in the middle of the stack and increase stack performance by 7.3%. And drawing air feed system could enhance the heat dissipation capacity of the stack and the uniformity of temperature distribution, resulting in the 7.9% stack performance increase. Optimization of the distance between the fan and stack enhances the full development of turbulence and the rate of heat transfer. In addition, the effects of four different H₂ feed systems and the flow direction between air and hydrogen on the fuel cell performance were also investigated. It is beneficial for open-cathode PEMFC to be operated with the location of the H₂ inlet and outlet staggered in two different endplates for better stack performance and single-cell voltage uniformity. Evidence also shows that the higher performance also could be obtained when the flow direction of air and hydrogen is vertical with lower ohmic resistance, charge and mass transfer resistance. The study contributes to the design of the open-cathode fuel cell stack to get better performance and reliability.     

Thermal analysis and management of proton exchange membrane fuel cell stacks for automotive vehicle

The thermal management of a proton exchange membrane fuel cell (PEMFC) is crucial for fuel cell vehicles. This paper presents a new simulation model for the water-cooled PEMFC stacks for automotive vehicles and cooling systems. The cooling system model considers both the cooling of the stack and cooling of the compressed air through the intercooler. Theoretical analysis was carried out to calculate the heat dissipation requirements for the cooling system. The case study results show that more than 99.0% of heat dissipation requirement is for thermal management of the PEMFC stack; more than 98.5% of cooling water will be distributed to the stack cooling loop. It is also demonstrated that controlling cooling water flow rate and stack inlet cooling water temperature could effectively satisfy thermal management constraints. These thermal management constraints are differences in stack inlet and outlet cooling water temperature, stack temperature, fan power consumption, and pump power consumption.     

Performance evaluation of an air breathing polymer electrolyte membrane (PEM) fuel cell in harsh environments – A case study under Saudi Arabia's ambient condition

A key parameter that determines the efficiency of proton exchange membrane fuel cells is their operating conditions. Optimization of various components in these fuel cells is pivotal in improving cell performance, as their performance is directly related to the operational conditions the cells are subjected to.This investigation examined the viability of an air breathing fuel cell subjected to ambient conditions in Riyadh in Saudi Arabia. A validated three-dimensional air breathing 5-cell stack, modelled in ANSYS was utilised to generate the results. Furthermore, the work also considered the feasibility of deploying a humidifier unit for the hydrogen inlet, so as to ascertain the physical behaviour of the PEMFC stack. It was observed that the performance of the stack reaches its peak during the summer time (June–August), and hydrogen humidification improves output performance by 40%.     

Effects of stack orientation and vibration on the performance of PEM fuel cell

An experimental study is carried out to investigate effects of stack orientation and vibration on the performance of Proton Exchange Membrane (PEM) fuel cell. A 25‐cm² single cell with serpentine anode and straight cathode flow channels is used. The hydrogen flow rate, cathode air temperature, and relative humidity are kept constant at 60 smL/min, 20 °C and 80%, respectively, whereas the cathode air flow rate values are 220, 440, and 660 smL/min as well as free breathing case. An orientation and vibration mechanisms are designed to facilitate different values orientation positions and vibration amplitude and frequency of the stack. The results show that stack orientation and vibration have significant effects on the performance of PEM fuel cell. Based on the results obtained from this study, it can be concluded that optimum positions of cell orientation are 30° and 90° at low and high values of cathode air flow rate, respectively. Also, an improvement in the performance of the fuel cell is achieved when the stack is vibrated with low values of amplitude and frequency. Each of cell maximum power density and maximum hydrogen utilization decreases with increasing each of amplitude and frequency of stack vibration. Copyright © 2014 John Wiley & Sons, Ltd.     

基于人工神经网络的3 kW质子交换膜燃料电池电堆一致性优化

电堆工作过程中各个单体电压的一致性是提高其性能的关键,在3 kW电堆台架实验数据的基础上,利用人工神经网络（ANN）模型,对空气流量、氢气压力、过量空气系数等气体供给参数进行优化,并对优化前后电堆的功率特性、一致性特性进行对比分析。结果表明：当氢气入口压力为0.128 MPa、空气入口流量为11 g/s、过量空气系数为6.4时,电堆电压差异系数CV及功率参数可达到最佳。     

燃料电池空气系统增湿器建模与仿真

建立气-气增湿器的数学理论模型,并基于Amesim软件建立燃料电池增湿器及空气系统仿真模型,从燃料电池系统层面分析干湿侧不同温度、压力、水含量等输入条件下的干侧出口空气的湿度变化情况,并采用水转移率（water vapor transfer rate,WVTR）对增湿器增湿性能进行评价,结果表明此模型可进行前期验证,能较好地预测汽车运行过程中增湿器的动态响应特性。     

The effects of mine conditions on the performance of a PEM fuel cell

Proton exchange membrane fuel cells (PEMFC) have been selected to replace conventional underground power sources such as diesel engines, to improve underground air quality, to reduce green house gas emissions and operating costs and to facilitate equipment automation. The effects of underground mining conditions, gases, dust and shock and vibration on the performance of PEMFC’s were investigated during extensive testing in an operating underground metal mine. Neither the voltage–amperage nor the power–amperage curves showed significant damage effects, and a post-testing stack inspection showed minor pressure drop, at the higher current density and airflow rate. With the use of an air intake filter, little particle accumulation was registered in the stack, and effluent water testing revealed the presence of rock-derived particles, showing that the stack was able to purge itself of low particle concentrations. No physical damage was imposed to the stack, auxiliary system and hydrogen metal hydride storage unit. Fuel cell performance compared well to pre-test and initial construction power plant data generation. Further tests are recommended to study individual mine gas and particle mineralogy type effects.     

Effects of reformate on performance of PBI/H3PO4 proton exchange membrane fuel cell stack

The present study aims to examine the effect of nitrogen and carbon monoxide concentrations as well as the working temperature and the stoichiometry number on the performance of a self-made five-cell high-temperature Proton-exchange membrane fuel cell stack (PEMFC). The concentration of hydrogen in a reformed gas can be varied, and it may contain poisonous substances such as carbon monoxide. Hence, the composition of the fuel gas could affect the performance of the PEMFC. The polarization curve and the electrochemical impedance spectrogram are utilized to examine the behaviors of PEMFC. The cell temperature of 160 °C is found as an optimal working temperature in this study for high-temperature PEMFC. Measured results show that the stoichiometry of the anode gas has a minimal effect on the PEMFC performance. A high percentage of nitrogen makes hydrogen dilute and leads to poor cell performance. When carbon dioxide exceeds 3%, the pt-catalyst was covered with the CO and the cell performance significantly decreased. Finally, a raise of the PEMFC temperature boosted the catalyst energy and improved the detachment of the carbon monoxide and eventually enhanced carbon monoxide tolerance.     

Liquid water transport in parallel serpentine channels with manifolds on cathode side of a PEM fuel cell stack

Water management in a proton exchange membrane (PEM) fuel cell stack has been a challenging issue on the road to commercialization. This paper presents a numerical investigation of air–water flow in parallel serpentine channels on cathode side of a PEM fuel cell stack by use of the commercial Computational Fluid Dynamics (CFD) software package FLUENT. Different air–water flow behaviours inside the serpentine flow channels with inlet and outlet manifolds were discussed. The results showed that there were significant variations of water distribution and pressure drop in different cells at different times. The “collecting-and-separating effect” due to the serpentine shape of the gas flow channels, the pressure drop change due to the water distribution inside the inlet and outlet manifolds were observed. Several gas flow problems of this type of parallel serpentine channels were identified and useful suggestions were given through investigating the flow patterns inside the channels and manifolds.     

Numerical analysis on the effects of manifold design on flow uniformity in a large proton exchange membrane fuel cell stack

The size and configuration of manifold can affect the flow characteristics and uniformity in proton exchange membrane fuel cell (PEMFC) stack; then its efficiency and service life. Based on the simulation results of a single fuel cell considering electrochemical reaction, a stack model with 300 porous media is established to numerically investigate the performances of a large commercial PEMFC stack. The effects of manifold width and configuration type on the pressure drop and species concentration are studied by computational fluid dynamics (CFD). The results show that the uniformity for most cases of U-type configuration is better than those of Z-type configuration. For U-type configuration, a very good uniformity can be obtained by selecting anode inlet manifold width of 20 mm and anode outlet manifold in range from 25 to 30 mm; the uniformity is bad for all cathode inlet manifold width, relatively better uniformity can be achieved by adjusting cathode outlet manifold width. For Z-type configuration, bad uniformity is found for cathode inlet and outlet manifold with all width; a relatively good uniformity can be obtained with suitable anode manifold width of 35 mm. The research can provide some references to improve gas distribution uniformity in large PEMFC stacks.     

Design,manufacturing, assembling and testing of a transparent PEM fuel cell for investigation of water management and contact resistance at dead-end mode

PEM fuel cell can operate at two different modes. At first mode the outlet of gas flow field is open and at the second mode the outlet of flow field is closed. The second mode is known as dead-end PEMFC. Proton exchange membrane fuel cells (PEMFCs) with dead-ended anode and cathode can obtain high hydrogen and oxygen utilization by a comparatively simple system. Nevertheless, the accumulation of the water in anode and cathode channels can lead to a local fuel starvation degrading the performance and durability of PEMFCs. There are different methods for investigation of water management such as: neutron radiography, gas chromatography, capturing by use of X-ray and capturing by use of infrared ray. Due to high cost and many hazards these methods at most cases cannot be used. According to the above mentioned problem we recommend a transparent PEMFC as a simplest, cheapest and the most suitable method for investigation of water management. Designing and manufacturing this type of PEMFC require special techniques. In this paper at first an optimal flow field is numerically designed and according to numerical results a transparent PEMFC is designed, manufactured and tested. Furthermore the performance of PEMFC at dead-end mode and open-end mode is studied. The applied design with a higher efficiency could have a same polarization curve as open-end mode. The results showed that by setting the purge interval time on 5 s and then opening purge valve for 1 s, there isn't any degradation on PEMFC performance but for purge interval of 10 s gradual performance degradation is recorded.     

Experimental study on dual recirculation of polymer electrolyte membrane fuel cell

Durability and start-up ability in sub-zero environment are two technical bottlenecks of vehicular polymer electrolyte membrane (PEM) fuel cell systems. With exhaust gas recirculation on the anode and cathode side, the cell voltage at low current density can be reduced, and the membrane can be humidified without external humidifier. They may be helpful to prolong the working lifetime and to promote the start-up ability. This paper presents an experimental study on a PEM fuel cell system with anodic and cathodic recirculation. The system is built up based on a 10 kW fuel cell stack, which consists of 50 cells and has an active area of 261 cm². A cathodic recirculation pump and a hydrogen recirculation pump are utilized on the cathode and anode side, respectively. Key parameters, e.g., stack current, stack voltage, cell voltage, air flow, relative humidity on the cathode side, oxygen concentration at the inlet and outlet of the cathode side, are measured. Results show that: 1) with a cathodic recirculation the system gets good self-humidification effect, which is similar to that with an external humidifier; 2) with a cathodic recirculation and a reduction of fresh air flux, the cell voltage can be obviously reduced; 3) with an anodic recirculation the cell voltage can also be reduced due to a reduction in the hydrogen partial pressure, the relative humidity on the cathode side is a little smaller than the case with only cathode recirculation. It indicates that, for our stack the cathodic recirculation is effective to clamp cell voltage at low current density, and a self-humidification system is possible with cathodic recirculation. Further study will focus on the dynamic model and control of the dual recirculation fuel cell system.     

Simulation analysis of hydrogen recirculation rates of fuel cells and the efficiency of combined heat and power

The objective of this study was to simulate a proton-electrolyte membrane fuel cell (PEMFC) system, namely a PEMFC stack, an anode gas supply subsystem, an anode gas-recovery subsystem, a cathode gas supply subsystem, and a tail gas exhaustion subsystem. In addition, this paper presents an analysis of the efficiency of combined heat and power (CHP) systems. MATLAB and Simulink were employed for dynamic simulation and statistical analysis. The rates of active and the passive anode hydrogen recirculation were considered to elucidate the mechanism of hydrogen circulation. When recovery involved diverse recovery mechanisms, the recirculation rate was affected by the pressure at the hydrogen outlet of the PEMFC system. The greater the pressure was at that outlet, the higher the recovery rate was. In the hydrogen recovery system, when the temperature of the hydrogen supply end remained the same, increasing the temperature of the gas supply end increased the efficiency of the fuel cells; fixing the flow of the hydrogen supply end and increasing the temperature of the hydrogen supply end increased the efficiency of the PEMFC system. A calculation of the efficiency of the recovery system indicated that the thermal efficiency of the fuel cells exceeded 35%, the power generation efficiency exceeded 45%, and the efficiency of the CHP system exceeded 80%.     

Experimental investigation of the effect of hydrogen recirculation on the performance of a proton exchange membrane fuel cell

The hydrogen recirculation in proton exchange membrane fuel cell (PEMFC) is recommended for the hydrogen supply of PEMFC, and hydrogen ejectors are gradually being used in fuel cell vehicles due to low noise and low energy consumption. However, there is a lack of discussion about the influence of recirculation rate on the stack. Due to passive regulating mechanism of the ejectors, a miniature speed-adjustable peristaltic pump is used to simulate the hydrogen ejector in this study to investigate the effect of hydrogen recirculation on the performance of PEMFC stack. Experiments are conducted under different pump flow rates. The stack with hydrogen recirculation is proven to have better performance, but over high pump flow rate can lead to hydrogen shortage. It is interesting to find that the flow rate fluctuation of hydrogen inlet affects the stability of stack performance, and pressure drop and recovery time during purge process are proposed as effective indicators for performance analysis. Finally, pump flow rates between 60 ml/min and 105 ml/min are defined as “effective area”. Based on the analysis of effective indicators, keeping at “effective area” is further proved to improve the performance of the stack, which is also useful to design hydrogen recirculation.     

Study on voltage clamping and self-humidification effects of pem fuel cell system with dual recirculation based on orthogonal test method

Durability and reliability are still major challenges of vehicular polymer electrolyte membrane fuel cell (PEMFC) systems. With exhaust gas recirculation on both the anode and cathode sides, two important functions can be achieved: the voltage clamping in low current density, and the self-humidification without any external humidifiers. The former restrains catalyst decay in small load working conditions, and the latter is beneficial for improving the cold-start ability. In this study, dynamic performances and stable characteristics of a fuel cell system with dual exhaust gas recirculation are firstly experimentally studied using an orthogonal test method. System parameters, including humidification temperature of cathode external humidifier, fresh air stoichiometric ratio (SR), current density, cathode and anode recirculation pump speeds, are regarded as key factors in the experiments based on the testing conditions of the test-bench. Two four-factor and three-level orthogonal tables are designed, and the effects of key factors on system performance indices (average cell voltage, relative humidity (RH) at cathode inlet, high frequency resistance (HFR), oxygen concentrations at cathode inlet and outlet, and the concentration difference between these two positions) are investigated. Results show that: (1) with the cathode recirculation, the cell voltage can be reduced in low current densities by coordinately adjusting the recycled gas flow and reducing fresh air SR; (2) with the dual recirculation, the fuel cell membrane can be well hydrated, and system performance only shows 3% reduction compared with a system with an external humidifier; (3) the difference between the oxygen molar concentration at the inlet and outlet of cathode gas channels becomes small using dual recirculation.     

The use of on-line hydrogen sensor for studying inert gas effects and nitrogen crossover in PEMFC system

The design and construction of a polymer electrolyte membrane fuel cell (PEMFC) system test bench suitable for investigating the effects of inert gas build-up and hydrogen quality on the performance of PEMFC systems is reported. Moreover, a new methodology to measure the inert gas crossover rate using an on-line hydrogen concentration sensor is introduced, and preliminary results are presented for an aged 8 kW PEMFC stack. The system test bench was also characterized using the same stack, whereupon its performance was observed to be close to commercial systems. The effect of inert gas accumulation and hence the quality of hydrogen on the performance of the system was studied by diluting hydrogen gas in the anode supply pipeline with nitrogen. During these experiments, uneven performance between cells was observed for the aged stack.