Air-cooled Fuel Cell Stack Research Articles

An experimental study on the hydrogen utilization in air-cooled proton exchange membrane fuel cell stack with a novel anode outlet design

In the realm of portable power system, air-cooled fuel cells stand out for their lightweight design and emission-free operation. Anode purging has emerged as an effective method to alleviate performance degradation in the dead-end anode stack. However, purging frequency can affect hydrogen utilization and output performance. This research aims to reduce the purging frequency and enhance hydrogen utilization of air-cooled fuel cell stacks by introducing a novel anodic outlet endplate. The novel outlet helps to remove liquid water and nitrogen from the stack, improve the output performance, and save the hydrogen usage in the air-cooled fuel cell stack. The peak power outputs of stacks equipped with the novel and conventional anodic outlets are recorded at 2313.95 W and 2213.35 W, respectively. Significantly, the novel anodic outlet configuration demonstrates a 4.54 % increase in peak power. Moreover, this configuration extends the purging interval, leading to a reduction in purging frequency. Under current load of 62 A, the novel anode outlet stack prolongs the purging interval of 134.73 s compare to its counterpart with a conventional anodic outlet than that of the conventional anode outlet. The findings presented in this study are poised to offer valuable insights into optimizing their efficiency and promoting sustainable solutions.

Experimental study and modelling of an air-cooled proton exchange membrane fuel cell stack in the static and dynamic performance

Research on Proton Exchange Membrane fuel cells is an important area in the field of modern energy sources. Such fuel cells are characterized by high efficiency and fast response times, making them a promising solution for sustainable energy production. Fuel cells operate under both static and dynamic conditions. Such varying operating conditions result in achieving different efficiency of fuel cell systems. This study attempts an experimental and modeled efficiency evaluation of a 1.2 kW open-cathode air-cooled fuel cell stack under static and dynamic conditions. A Sankey energy balance and an analysis of the balance components were determined for the fuel cell stack operating in these two operating states. Simultaneous modeling of the fuel cell under both static and dynamic conditions was carried out. The efficiency values of the fuel cell stack were found to be slightly higher under static conditions than under dynamic conditions. Modeling fuel cells in static and dynamic conditions results in slightly different parameters (better conformance was obtained for static models).

Experimental study on the endplate effect on the cold-start performance of an open-cathode air-cooled proton exchange membrane fuel cell stack

The temperature gradient inside an open-cathode air-cooled fuel cell is large because it uses air as its reaction and cooling media; moreover, the temperature of single cells near the endplates is low because of the high heat capacity of the endplate compared to single cells. Therefore, the cold start of open-cathode air-cooled fuel cells is difficult. In this work, the cold-start performance of an open-cathode air-cooled fuel cell stack, including the stack voltage, single-cell voltage and temperature distribution, are tested in a climatic chamber. The results show that the endplate effect has a significant adverse influence on the cold-start performance. Due to the existence of the endplate effect, the voltages of the single cells near the endplate decrease significantly. The stack can be successfully started at −5 °C without any external heating; however, when the temperature decreases below −10 °C, it cannot be started. At this time, if a certain power of endplate heating is adopted, successful cold-start can be achieved. However, if the temperature continues to decrease, the stack cannot be successfully started only through endplate heating because both the endplates and cold air affect the cold-start performance. Combining endplate and air heating may be a feasible cold-start method.

Experimental study on the thermal management of an open-cathode air-cooled proton exchange membrane fuel cell stack with ultra-thin metal bipolar plates

Reliable thermal management ensures stable and efficient operation of proton exchange membrane (PEM) fuel cells. An air-cooled fuel cell stack with metal bipolar plates was developed, and 32 micro-thermocouples were arranged for in situ measurement of the temperature distribution. The resistance characteristic of the stack was tested in a wind tunnel, and then the effects of hydrogen pressure and airflow rate were analyzed. The results show that the highest and average temperatures in the stack exhibit a “parabolic” distribution as well as the maximum temperature difference of each single cell on the inlet side of the cathode. However, the temperature difference on the outlet side shows an “anti-parabolic” distribution. With a decrease in the airflow rate, the temperature uniformity in the stack deteriorates gradually. When the maximum pulse width modulation (PWM) duty cycle of the fans was 70% and the current density was 500 mA/cm2, the temperature difference between different single cells and inside a single cell can reach 19.7 °C and 8.4 °C, respectively. The temperature uniformity in the stack at high current densities could be effectively improved by increasing the airflow rate. In addition, the hydrogen pressure and airflow rate have a certain effect on the voltage consistency.

Experimental study on the dynamic performance of an air-cooled proton exchange membrane fuel cell stack with ultra-thin metal bipolar plate

In this paper, a compact 3 kW air-cooled fuel cell stack consists of 95 single cells with metallic bipolar plate is designed. Compared with graphite bipolar plates, metal stamping bipolar plates are lighter in weight, smaller in size and faster in heat conduction, therefore the transient behaviors of the voltage and temperature of each cell are analyzed. The results show that the heat distribution of the air-cooled fuel cell is very uniform, and the temperature difference between the inlet and outlet of cathode air of the fuel cell is lower than 15 °C. The individual cell voltage uniformity percentage variation value reaches 7% when the drop in the loading current is over 25 A. Moreover, the voltage uniformity variation value is higher than 4% when the loading current output exceeds 35A. Thus, a large drop in loading and a high loading current easily increase the voltage uniformity variation value. Long-term continuous operation has a negative influence on the performance of the stack, especially the last fuel cell near the anode outlet. Anode purging can effectively alleviate the uniformity percentage variation in the voltages. The designed air-cooled fuel cell exhibits good performance and strong environmental adaptability.

A Feasibility Study of Placing a Heated Turbulence Grid in Front of an Air-Cooled Fuel Cell Stack in Freezing Conditions

The telecommunications industry is growing fast, and the air-cooled fuel cell is a promising alternative to the diesel-gensets as a backup power system. These systems are required to operate in freezing conditions where temperatures can be as low as -40°C, and they are usually located in remote areas where they can not be easily accessed. Berning proposed the placement of a turbulence grid in front of an air-cooled fuel cell stack to improve the heat transfer and thereby the performance, since the performance of the fuel cells was restricted due to the membrane overheating[1]. In an experimental study, Al Shakhshir et al. measured a performance increase of over 30% by placing a turbulence grid before an air-coiled fuel cell stack [2]. Then, Berning and Knudsen studied how the performance of the fuel cell would be affected while operating in different climate regions [3]. Additionally, previous studies allocated a turbulence inducing grid in front of the cathode inlet of the fuel cell where the main goal was to improve the heat transfer between the air and the components to achieve higher performances of the fuel cell while keeping the operating temperature in a good range [4] and how the design of this turbulence inducing grid would affect the cell [5]. Besides the use of a turbulence grid, this paper aims to analyze how the effect of the freezing ambient temperature can be reduced by pre-heating the incoming fuel cell air. A feasibility study is developed where different temperature differences and four different grid designs where the number of grid pores and its thickness are varied. The aims of this project were to identify feasible surface temperatures of the grid while having a reasonable consumption of fuel cell power to be provided to the grid and heated it up. A three-dimensional, steady state numerical analysis has been conducted on these grid dimensions where the computational domain considered was a single cathode channel where the gas diffusion layer would be the bottom surface, and the bipolar plate is to remain walls. Four different grid dimensions, namely grids with one and two millimeters of thickness and six 1 mm2 pores and grids with one and two millimeters of thickness and twenty-four 0.17 mm2 pores, have been considered. The outside temperature has been varied from -20 °C to 0 °C and heated up to 5 °C before air flow enters the cathode. The goal of this study is to better understand the temperature of the turbulence grid that is required to pre-heat the incoming air and thus conclude, which materials are suited. A parametric study was conducted, and with the last designed grid the best result was achieved. Preheating the air by 10°C, a surface temperature around 236°C was predicted. The fuel cell power usage would be approximately 30% of the total provided by fuel cell. It is possible to conclude the surface area of a single grid is not sufficient, leading to too high temperatures. A possibility could be having two staggered grids. Finally, an energy storage system could be used to provide this additional power required, avoiding such consumption of hydrogen and its slow dynamic response. [1] Berning T. A Numerical Investigation of Heat and Mass Transfer in Air-Cooled Proton Exchange Membrane Fuel Cells. InFluids Engineering Division Summer Meeting 2019 Jul 28 (Vol. 59032, p. V002T02A030). American Society of Mechanical Engineers.[2] Shakhshir SA, Gao X, Berning T. An experimental study of the effect of a turbulence grid on the stack performance of an air-cooled proton exchange membrane fuel cell. Journal of Electrochemical Energy Conversion and Storage. 2020 Feb 1;17(1):011006.[3] Berning T, Knudsen Kær S. A thermodynamic analysis of an air-cooled proton exchange membrane fuel cell operated in different climate regions. Energies. 2020 Jan;13(10):2611.[4] Lind A, Yin C, Berning T. A Computational Fluid Dynamics Analysis of Heat Transfer in an Air-Cooled Proton Exchange Membrane Fuel Cell with Transient Boundary Conditions. ECS Transactions. 2020 Sep 8;98(9):255.[5] Pløger LJ, Fallah R, Al Shakhshir S, Berning T, Gao X. Improving the Performance of an Air-Cooled Fuel Cell Stack by a Turbulence Inducing Grid. ECS Transactions. 2018 Jul 23;86(13):77. Figure 1

A Feasibility Study of Placing a Heated Turbulence Grid in Front of an Air-Cooled Fuel Cell Stack in Freezing Conditions

This paper aims to better understand the temperature profile of a turbulence inducing grid if pre-heating of the incoming air in the cathode channel is required when the stack is operating under freezing conditions. The goal of this study is to design the grid by changing its thickness and the number of pores. A three-dimensional, steady-state computational fluid dynamic model was developed and validated for a baseline case of a single cathode channel of an air-cooled cell. The computational domain consists of the cathode flow channel, a gas diffusion layer, and the turbulence inducing grid. Four different grid designs were analyzed and compared, and in the best case heating of the turbulence grid was achieved where the temperature of the grid will be 236 °C and the power consumption will be around 30 % of the total power produced by the fuel cell stack. It is concluded that 2 mm thickness is not sufficient, leading to too high temperatures, and a multitude of staggered grids might be required.

A Feasiblity Study of the Placement of a Heated Turbulence Grid in Front of an Air-Cooled Fuel Cell Stack in Subzero Conditions

Within telecom back-up applications, the air-cooled fuel cell is a promising alternative to diesel generators as a backup powersystem. Additionally, these fuel cell systems are required to operate in a subzero environment with temperaturesas low as -40C. In this study, a numerical analysis of a heated turbulence-inducing grid to preheat the air before the cathode channel, has been conducted. The turbulence model used is the comprehensive Reynolds Stress Model. Four different grid dimensions, namely grid with 1mm in depth and six 1 mm2 holes, grid with 2mm in depth and six 1 mm2 holes, grid with 1mm in depth and twenty-four 0.17 mm2 holes, grid with 2mm in depth and twenty-four 0.17 mm2 holes have been considered. The outside temperature has been varied from -20C and -10C and heated up to 5C before air flow enters the cathode. A three-dimensional, steady state numerical analysis has been conducted on these grid dimensions using the finite volume method. First results indicate very high grid surface temperatures. Additionally, it can be concluded that the grid surfacetemperature decreases as the turbulence grid thickens. Figure 1

Improving Water Management and Performance of an Air-Cooled Fuel Cell System Using Pressurized Air for Aviation Applications

Air-cooled fuel cell systems feature a light-weight and simple design and are thus recognized as a suitable technology for drone and aviation applications. As compared to liquid-cooled fuel cell systems, however, they suffer from low specific power per unit volume and unstable performance due to severe electrolyte dehydration and nonuniform profiles of current density and temperature inside a fuel cell stack. Here, we present a high-pressure air-cooled fuel cell system in which atmospheric air is pre-compressed by a compressor and then fed into the fuel cell stack. To minimize the compressor power consumption, the system is designed to recirculate the exhaust air from the fuel cell stack. A three-dimensional two-phase fuel cell model is implemented with a high-pressure air-cooled fuel cell system mainly consisting of an air-cooled fuel cell stack, compressor, air chamber and duct, and heat exchanger and is used to predict superior fuel cell performances under various high-pressure conditions. Simulation results show that the fuel cell operation at 2 atm allows an increase of up to two times the stack power and 1.5 times the net system power compared to a 1-atm fuel cell operation.

Improving the Performance of an Air-Cooled Fuel Cell Stack by a Turbulence Inducing Grid

Air-cooled proton exchange membrane fuel cells (ACPEMFC’s) are gaining popularity as an alternative power source for their simplicity and quick startup. They’re commercialized for large number of applications in the power range up to a few kWs. One of the problems regarding these fuel cells is the thermal management of the electrochemical reaction resulting in overheating of the air-cooled fuel cell stack (ACS) at low current densities, often around 0.4 Acm-2. This study aims to solve the problem by placing turbulence grids before the cathode inlet. The purpose of the turbulence grids is to induce turbulences in the cathode channels and thereby induce a mixing effect and improve the heat transfer. A CFD model is build and assisted by experiments. The CFD results showed improvement of the mixing effect in the cathode channels and reduction of the channel wall temperature. The experiments resulted in 10.42% improved performance.

Aalborg team use grid to achieve 30% higher fuel cell efficiency

Researchers at Aalborg University in Denmark have demonstrated that a small plastic grid, which costs less than a dollar to produce, can increase the efficiency of an air-cooled fuel cell stack by more than 30%.

Stack Cooling Profile of an Air-Cooled 3-Cell Polymer Electrolyte Membrane Fuel Cell Stack

A locally designed, 3-cell closed cathode PEM fuel cell stack was developed as a platform for thermal engineering studies. Stack polarization behavior is combined with thermal behavior analysis to identify the cooling profiles of an air-cooled fuel cell stack under variable load and cooling settings. The objective of the study is to identify the bulk thermal effects of the stack under cooling for further consideration in fuel cell system control development. The stack is designed with 40 cooling channels and tests were conducted with airflows in the range between 200 and 400 Reynolds number. Different fan settings are applied to analyze the response of the design to negative and positive pressure airflows. The temperature measurements are translated into an averaged stack temperature and a subsequent second order thermal analysis showed that an exponential cooling trend is obtained. Analytical evaluation on the dynamic cooling rates relative to response time and cooling trend is also performed and reported.

Performance evaluation of a polymer electrolyte membrane fuel cell system for powering portable freezer

A polymer electrolyte membrane fuel cell (PEMFC) powered portable freezer has been developed. The PEMFC system is composed of an air-cooled fuel cell stack module with combined oxidant and coolant flow, a fuel supply subsystem with two metal hydride canisters, a power management subsystem with a DC–DC converter and a lead acid battery, and a control electronics subsystem. The vapor compression refrigeration cycle has been adopted for refrigerating. The control logic for fuel cell stack operation, cabinet temperature maintenance and fuel canister replacement has been designed for a stable system operation. To estimate PEMFC system performance, the stack power output, parasitic loss and battery charging power are measured for various external loads. The PEMFC system provides a rated power output of 200.5W at 13.4V with balance-of-plant (BOP) efficiency of 72%. The maximum system efficiency based on lower heating value (LHV) is 37% at 120.7W. The PEMFC powered freezer stably operates with the continuous replacement of hydrogen canisters, and the cabinet temperature drops to −21.8°C when the ambient temperature is 26.6°C.

200 W급 휴대용 고분자 전해질막 연료전지 시스템 개발

A 200 W portable polymer electrolyte membrane fuel cell (PEMFC) system is developed. The PEMFC system consists of an air-cooled fuel cell stack module, a fuel supply subsystem, a power management subsystem, and a control electronics subsystem. The control logic is designed for the stable system operation. The system-level performance evaluation discloses that the present PEMFC system provides a rated power output of 200.5 W at 13.4 V with the maximum balance-of-plant (BOP) efficiency of 72%, and maximum system efficiency based on lower heating value (LHV) is 37% at 120.7 W system power output.

5518828 Thermal integration of an air-cooled fuel cell stack

5518828 Thermal integration of an air-cooled fuel cell stack