bluuebunny/crossref_metadata_2025 huggingface dataset:
Personality Testing and Industrial–Organizational Psychology: A Productive Exchange and Some Future Directions
Authors: Oswald Frederick L. , Hough Leaetta M.
Published: September 2008

The goal of our focal article was to provide a current perspective on personality testing and its use in organizational research and to elicit constructive discussion and suggestions for future research and practice. The present article caps off the discussion by integrating the main ideas presented in the commentaries within our original framework of questions and topics, with the immodest hope of advancing our understanding of personality and its measurement in the context of industrial–organizational psychology. In short, we recommend continuing to take advantage of the organizing framework of the Big Five while also pursuing more “bottom-up” approaches that examine facet-level relationships with multidimensional performance outcomes, in addition to developing process models that include more proximal motivational and situational variables. Work along these lines is valuable to both organizational science and practice.
Facts Are Stubborn Things
Authors: Highhouse Scott
Published: September 2008

In 1985, the U.S. Army commissioned prominent psychologists to investigate the possibility of extending human capabilities using parapsychological techniques (Swets & Bjork, 1990). Influential members of the army were frustrated by the slow pace of advancements in human performance and believed that large gains could be made using methods outside of the mainstream. They believed that things like mental concentration and guided imagery could allow soldiers to walk through walls, view things remotely, and even kill adversaries by staring at them (Ronson, 2005). Not surprisingly, the panel of psychologists concluded that these ideas were without merit. In reviewing the psychologists’ work, Morrison (1988) observed, “Among the most difficult lessons in science is how not to deceive yourself” (p. 109).
Low-Temperature Direct Propane Polymer Electrolyte Membrane Fuel Cell (DPFC)
Authors: Bharath Sudharsan
Published: September 2008

The low-temperature Direct Propane Polymer Electrolyte Membrane Fuel Cell (DPFC) based on low-cost modified membranes was demonstrated for the first time. The propane is fed into the fuel cell directly without the need for reforming. A PBI membrane doped with acid and a Nafion 117 membrane modified or non-modified with silicotungstic acid were used as the polymer membranes. The anode was based on Pt, Pt-Ru or Pt/CrO3 electro catalysts and the cathode was based on a Pt electro catalyst. For non-optimized fuel cells based on H2SO4 doped PBI membranes and Pt/CrO3 anode, the open circuit potential was 1.0 Volt and the current density at 0.40 Volt was 118 mA.cm-2 at 95°C. For fuel cells based on Nafion 117 membranes modified with silicotungstic acid and on Pt/CrO3, the open-circuit voltage was 0.98 Volt and the current density at 0.40 Volt was 108 mA.cm-2 while fuel cells based on non-modified Nafion 117 membranes exhibited an open-circuit voltage of 0.8 Volt and the current density at 0.40 Volt was 42 mA.cm-2. It was also shown that propane fuel cells using anodes based on Pt-Ru/C anode (42 mW.cm-2) exhibit a similar maximum power density to that exhibited by fuel cells based on Pt-CrO3/C-anode (46 mW.cm-2), while DPFC using a Pt/C-based anode exhibited lower maximum power density (18 mW.cm-2) than fuel cells based on the Pt-CrO3/C anode (46 mW.cm-2).
A Two-Fluid Mathematical Model for Gas-Liquid Flows in PEM Fuel Cells
Authors: Chan Shih-Hung , Tong Timothy W. , Abou-Ellail Mohsen , Beshay Karam R.
Published: September 2008

The present work considers a two-fluid mathematical model for the gas-liquid flow in PEM fuel cells. One fluid represents the continuous gas phase flow through the layers of the fuel cell. For this fluid, the governing equations of momentum, energy, mass continuity and species mass fractions, are considered with additional inter-fluid exchange source terms. The second fluid represents the dispersed liquid phase that is formed from the condensed water vapor inside the layers of the PEM fuel cell. For this fluid only the momentum and mass continuity equations need to be included, as no electrochemical reactions are essentially possible. The dispersed fluid is made up of small droplets in the gas channel. The mean droplet diameter can be computed from a balance equation of the forces acting on the emerging liquid water from the pores of the GDL into the gas channels. The droplet diameters are found to range between 150 and 170 microns for the present PEM fuel cell at 0.8 V. In the present work, the full momentum conservation equations are invoked, in the layers of the fuel cell, for the two fluids. The resulting governing equations for u, v, T and species mass fractions together with the electric potential and mass continuity equations are solved iteratively, using a modified SIMPLE algorithm, for the two fluids. One solution domain is superimposed over all the layers of the fuel cell. Special care is devoted to the electric potential, ‘Poisson-type’, equation boundary condition to prevent any escape of protons through the two gas diffusion layers and simultaneously insuring a non-singular matrix of finite-difference coefficients. The obtained two-fluid and single-phase numerical simulations are compared with the corresponding experimental and numerical data available in the literature. The 2-fluid model shows that the blocking effect of the liquid phase starts to dominate, for cell voltage less than 0.65 V; in this case, the flowing 2-phase flow produces faster drop in cell voltage as the loading electric current increases. This phenomenon was partially hindered by previous LHF model results and essentially completely bypassed by the single-phase simulations.
Modeling and Analysis Approaches for PEMFCs
Authors: Yuan Jinliang , Chen Jian , Sunde´n Bengt , Zhang Huamin
Published: September 2008

Proton exchange membrane fuel cells (PEMFCs) are expected to play a significant role in the next generation of energy systems and road vehicles for transportation. To achieve high performance, low cost and high reliability, significant attention is needed on detailed modeling and simulation of various physical processes in PEMFC unit-cells. Substantial effort is also required to reach proper water and thermal balances for PEMFC stacks and integrated energy systems. For modeling and analysis at the unit-cell and component level, typically CFD-based approaches might be appropriate. On the stack and system levels, methods like lumped parameter analysis and overall energy/mass balances are more suitable. This paper discusses various kinds of methods for modeling and analysis, and how these can be used as well as their applicability and limitations. The focus is placed on water management/two-phase flow regimes and characteristics of relevant models.
Measurement of Water Production Behavior, Temperature, and Current Density Distributions in a Polymer Electrolyte Fuel Cell
Authors: Chikahisa Takemi , Tabe Yutaka , Kikuta Kazushige , Nohara Naofumi , Shinohara Hideki
Published: September 2008

This paper observes phenomena related to water production behavior inside a fuel cell and analyzes the effect on the current and temperature distribution across the reaction area. A fuel cell permitting direct observation of the phenomena in the cell, 2-D temperature measurements in the cathode channels, and local current density measurements on the anode side was manufactured. The experimental results showed the production and flow of liquid water in the cell, and there were good correlations among the distributions of current density, temperature, and water amounts in the channels. The behavior of current, voltage, water distribution, and pressure differences in the cathode channels were used to hypothesize about the possibility of gas paths deep in the gas diffusion layer in the flooded condition and a positive feedback mechanism in the drying-out condition.
Flow-Channel Shape Design of Stamped Bipolar Plate for PEM Fuel Cell by Micro-Forming Simulation
Authors: Peng Linfa , Lai Xinmin , Ni Jun , Lin Z. Q.
Published: September 2008

PEM fuel cells are promising candidate as most environmentally friendly power source for transport and stationary cogeneration applications due to its high efficiency, high power density, fast startup and system robustness. But the PEM fuel cell is still too expensive for widespread commercialization. Bipolar plate is one of the most important and costliest components of PEM fuel cells and accounts to more than 80% of the weight and 30% of the total cost in a fuel cell stack. To reduce the cost and weight of fuel cell stacks and at the same time meeting several technical requirements for mass production, a prototype of low-cost stamped bipolar plates made of stainless steel 316 sheets has been introduced in this paper. Base on micro sheet forming process simulation experiments, the influence of some key dimensions of the flow channel to the formability of the stamped polar plate is also detailedly studied. Micro-forming simulation results show that relative punch radius r/t (punch radius r, sheet thickness t) and the ration of the width of coolant channel to channel depth w/h (width of coolant channel w, channel depth h) are import factors that decide the final formability of the whole polar plate. Large r/t is recommended for compact flow channel design and larger w/t is recommended for safer forming process.
A Survey of PEM Fuel Cell System Control Models and Control Developments
Authors: Meyer Richard T. , Revankar Shripad
Published: September 2008

Proton Exchange Membrane (PEM) fuel cell system performance can be significantly improved with suitable control strategies. Control appropriate models of the fuel cell stack and balance of plant are presented along with current control research. Fuel cell stack models are zero dimensional and range from simple empirical stack polarization curves to complex dynamic models of mass flow rates, pressures, temperatures, and voltages. Balance of plant models are also zero dimensional and can be used individually to build a complete system around a stack. Models of this type are presented for the air compressor, air blower, manifolds, reactant humidification, fuel recirculation, air cooling, and stack cooling. Current control work is surveyed with regard to feedforward, feedback, observers, optimization, model prediction, rule based, neural networks, and fuzzy methods. The most promising fuel cell stack model is evaluated. Additionally, improvements to the balance of plant models are recommended. Finally, future control work is explored with a desire for system control that leads to greater output power.
Electrical Characterization of a Glucose-Fueled Alkaline Fuel Cell
Authors: Bubis Eugenia , Mor Lea , Sabag Nissim , Rubin Zeev , Vaysban Ury , Hemmes Kas , Schechner Pinchas
Published: September 2008

This paper is part of an effort to establish design parameters for glucose-fueled room temperature membraneless alkaline fuel cells as possible electricity suppliers for portable devices. We report experimental results for three characteristics of glucose-fueled room temperature membraneless alkaline fuel cells: 1) polarization curve, 2) power density as a function of current density, and 3) internal resistance. The internal resistance of the cell was measured by two independent experimental methods: “Voltage Divider” and “Current Interrupt”. The three characteristics were measured as a function of glucose concentration while maintaining the electrolyte, KOH, constant at 0.35 M. The results were compared with those reported for other room temperature Alkaline Fuel Cells fuelled with glucose and methanol. We found that the maximum power density has a value of 0.36 mW/cm2 at a current density of 1.44 mA/cm2 when glucose concentration is 0.22M. The “Voltage Divider” and “Current Interrupt” methods for measuring the internal resistance produced practically the same results. The resistivity of the electrolyte/fuel solution was estimated from internal resistance measurements. Resistivity was found to be linearly dependent upon glucose concentration; at a constant KOH electrolyte concentration of 0.35 M, the specific resistivity of 1 M glucose is 2.56 Ω·m. The power density obtained with Alkaline Fuel Cells fuelled with glucose is an order of magnitude smaller than that obtained for cells fuelled with methanol. More efforts should be invested in order to develop a practical glucose-fuelled fuel cell.
Dynamic Simulation of a Stationary PEM Fuel Cell System
Authors: Min Kyoungdoug , Brouwer Jack , Auckland John , Mueller Fabian , Samuelsen Scott
Published: September 2008

A dynamic model of a stationary PEM fuel cell system has been developed in Matlab-Simulink®. The system model accounts for the fuel processing system, PEM stack with coolant, humidifier with anode tail-gas oxidizer (ATO), and an enthalpy wheel for cathode air. For the fuel processing system four reactors were modeled: (1) an auto thermal reactor (ATR) (2) a high temperature shift (HTS) reactor, (3) a low temperature shift (LTS) reactor, and (4) a preferential oxidation (PROX) reactor. Chemical kinetics for ATR that describe steam reformation of methane and partial oxidation of methane were simultaneously solved to accurately predict the reaction dynamics. Chemical equilibrium of CO with H2O was assumed at HTS and LTS reactor exits to calculate CO conversion corresponding to the temperature of each reactor. A quasi-two dimensional unit PEM cell was modeled with five control volumes for solving the dynamic species and mass conservation equations and seven control volumes to solve the dynamic energy balance and to capture the details of MEA behavior, such as water transport, which is critical to accurately determine polarization losses. The dynamic conservation equations, primary heat transfer equations and equations of state are solved in each bulk component and each component is linked together to represent the complete system. A comparison of steady-state model results to experimental data shows that the system model well predicts the actual system power and catalytic partial oxidation (CPO) temperature. Transient simulation of DC power is also well matched with the experimental results to within a few percent. The model predictions well characterized the observed dynamic CPO temperature, voltage, and temperature of stack coolant outlet observations that are representative of a generic PEM stationary fuel cell system performance. The model is shown to be a useful tool for investigating the effects of inlet conditions and for the development of control strategies for enhancing system performance.
Factors Impacting Liquid Droplet Instability in a PEFC Flow Channel
Authors: Kumbur Emin Caglan , Sharp Kendra Vail , Mench Matthew Michael
Published: September 2008

To achieve optimal performance with minimal parasitic losses and degradation, the relationship between water removal parameters such as flow rate and the diffusion media (DM) surface properties must be clearly identified. An extensive experimental study of the influence of controllable engineering parameters, including surface PTFE (Teflon™) coverage (ranging from 5% to 20% of wt.) and operational air flow rate, on liquid droplet deformation at the interface of the DM and the gas flow channel was performed. A new visualization technique was developed to better understand the droplet mechanisms with enhanced optical access of both side and top views of the flow channel of a simulated H2 PEFC. A telecentric lens and 5 mm by 5 mm prisms embedded in the flow channel side walls were used for the first time to measure droplet receding and advancing surface angles in an enclosed flow channel. The influence of channel air flow rate and emerging droplet size on droplet characteristics with varying PTFE content in the DM was investigated to identify the conditions under which the droplet tends toward an unstable state. The results indicate that operational conditions, droplet height, chord length, and level of surface hydrophobicity of the DM directly affect the droplet instability. At high flow rates, the surface hydrophobicity of the DM enhances the efficacy of droplet removal, and helps to avoid local channel flooding, however at low flow rates, regardless of the amount of PTFE content, droplet instability (and removal) is unaffected by the DM surface PTFE content.
Experimental Studies of the Performance of a Small Reformer for Hydrogen Generation
Authors: Huang Chih-Yung , Lin Chun-Hung , Chou Chung-Yang , Su Chin-Chia
Published: September 2008

This paper presents the experimental studies of the performance of a small reformer for hydrogen generation from water solution of methanol. An electric heater was built around the reactor unit to supply the energy for the endothermal reaction between methanol and steam. The parameters under studied were the temperature of the catalytic reaction (T), the mass flow rate of methanol solution (m˙), steam-to-methanol ratio (α), and the length (L) and number of cells (N) of the catalyst carrier, while the catalysts used were CuO-ZnO-Al2O3, CuO-ZnO-Al2O3-Pt-Rh, and Pt-Rh. The test results show that for all conditions both of the conversion and yield rates of hydrogen increase with increasing length and number of cells of the catalyst carrier. However, such increases become gradual in the high ranges of L and N. For the catalyst CuO-ZnO-Al2O3-Pt-Rh with N = 300 cells per square inch, L = 105mm, α = 1.9, and m˙ = 0.064 mole/min, the conversion rate may be as high as 99.9%. On the other hand, both of the conversion and yield rates decrease with increasing ratio of steam to methanol in the reactant. The decreases are more apparent at high temperature. When the mass flow rate of the methanol solution is increased, the conversion rate decreases. Such a decrease is more distinct in the medium range of methanol flow rate. On the other hand, the yield rate of hydrogen increases with the flow rate of methanol solution, especially at high temperature. For all of the three catalysts tested, both of the conversion and yield rates increase with reaction temperature, except for catalyst CuO-ZnO-Al2O3 at high temperature. Although catalyst CuO-ZnO-Al2O3-Pt-Rh shows no high-temperature deterioration, its performance is much poorer than that of catalyst CuO-ZnO-Al2O3 at low to medium temperatures. The difference in the performance between these two catalysts may be as high as 50%. By arranging a turbulence inducer located at the upstream side of the catalyst carrier, both of the conversion and yield rates can be increased significantly.
Reliability Analysis of the Cracked Ag-SU8 Interface on the Channel Wall in a Micro-PEMFC
Authors: Chien Chi-Hui , Shih Yi-San , Hsieh Shou-Shing , Tsai Huang-Hsiu , Lin Chih-Wei , Huang Yen-Lung , Yeh Chen-Hsiu
Published: September 2008

The efficiency of the fuel cell depends on both the kinetics of the electrochemical process and performance of the components. The main aim of this research is to analysis the reliability of the cracked Ag-SU8 interface on the channel wall in a micro-PEMFC. An existed surface crack on the channel wall subjected to the flow induced compressive stresses and shear stresses will propagate and lead to the spall formation. In this paper, at first, the flow induced compressive and shear stresses are obtained through simulation of stress state and flow-field in the micro-channel by commercial package software ANSYS® 8.0. Then, the stresses arising at the crack tip due to flow induced compressive and shear stresses can be calculated and characterized by the mode I and II stress intensity factors (SIF), KI and KII, respectively. Finally, the KI and KII stress intensity factors at the crack tip are computed for the different crack sizes and loadings. The results show that the inlet pressure and crack length affect the stress intensity factors more than the inlet velocity does. Also, the results show that as the crack length increases, the value of KI will increase, but the value of KII decreases slightly.
Molten Carbonate Fuel Cells: A High Temperature Fuel Cell on the Edge to Commercialization
Authors: Bischoff M. Manfred
Published: September 2008

The HotModule®, a collaborative effort utilizing the Direct FuelCell® technology of FuelCell Energy, Inc. and the Hot Module® balance of plant design of MTU CFC Solutions GmbH, is a stationary sub-megawatt carbonate fuel cell power plant in the power range of 250 kWel. Its function and reliability has been verified meanwhile in many field test applications within a test program started in 2001. Whereas the focal points of the early field test plants were the demonstration of function and reliability, some of the following projects are aiming at the demonstration of a variety of fuels, as for example methanol and digester gas. In total 14 of the highly integrated HotModule systems were installed so far within this European field trial program until July 2005.
Physical Simulator of Start-Up for Hybrid System Cathode Side
Authors: Traverso A. , Ferrari M. L. , Pascenti M. , Massardo A. F.
Published: September 2008

A start-up test rig at TPG laboratory at the University of Genoa, Italy, has been designed and built for two main purposes: physically simulating different early start-up layout and procedures of high temperature fuel cell hybrid systems, and validating time-dependent hybrid system models based on TRANSEO software. Since start-up is a critical operating phase for high temperature fuel cell hybrid systems, and it may require specific modifications to the hybrid system layout, the start-up test rig is meant to be very flexible for testing several start-up layouts as well as the coupling of different turbomachines and stacks. Results for cold test, 700°C and 950°C start-up combustor outlet temperature tests are reported. Such results show the pressure and temperature quick rise during the early phase of start-up, which could represent an issue for the mechanical and thermal stress to the stack. A dynamic model of the test rig was built up and validated showing good agreement with the experimental results. This achievement was very useful to increase the confidence with predictive dynamic simulation tools during the start-up phase, where experimental data are hardly available and where the fuel cell materials may undergo risky thermal shocks.
PtRuIr/C Catalyst With an Enhanced CO Tolerant Activity for PEM Fuel Cells
Authors: Liang Yongmin , Zhang Huamin
Published: September 2008

PtRuIr/C catalyst was prepared via a microwave-irradiated polyol plus annealing (MIPA) synthesis strategy. Tests by CO stripping voltammetry and in the single PEM fuel cells showed a greatly high CO-tolerant performance of the catalyst. The catalyst was characterized by a series of techniques, such as TEM, XRD, EDS, XPS and gas chromatography, etc., and the data were discussed with respect to the PtRu/C catalyst prepared following the same procedure. On the basis of the characterizations, the performance-structure relationship was explored and a speculative mechanism was supposed.
Numerical Modeling of the Proton Exchange Membrane Fuel Cell for Thermal Management
Authors: Yu Sangseok , Jung Dohoy , Assanis Dennis N.
Published: September 2008

A thermal model of the Proton Exchange Membrane Fuel Cell (PEMFC) was developed to investigate the performance of a large active area fuel cell with the water cooling thermal management system. The model includes three sub-models: water transport model, electrochemical reaction model and heat transfer model. The water transport model calculates water distribution and the electric resistance of the membrane electrolyte. The electrochemical reaction model for the agglomerate structure cathode catalyst layer predicts the cathode overpotentials including mass transport limitation effect at high current density region. Two-dimensional heat transfer model incorporated with coolant and gas channels predicts the temperature distribution within the fuel cell. By integrating those sub-models, local electric resistance and overpotentials depending on the water and temperature distribution can be predicted. The model was calibrated with published experimental data and sensitivity studies were performed. The effects of the inlet gas temperature and humidity on the fuel cell performance were explored. In addition, the effect of the temperature distribution, and accordingly the electric resistance distribution within the fuel cell depending on the coolant temperature and flowrate was investigated. The results shows that the change in the local electric resistance due to temperature distribution eventually causes fuel cell power decrease and it is also concluded that the coolant temperature and flowrate should be controlled properly depending on the operating conditions in order to minimize the temperature distribution while maximizing power output of the fuel cell.
Optimization of Gas Delivery and Current Collecting System in Fuel Cells
Authors: Chen S. P. , Li P. W. , Chyu M. K.
Published: September 2008

The over-potentials in a fuel cell due to ohmic losses and concentration polarization can be reduced if the gas delivery field and the current collection system are well designed. To obtain such a substantial understanding for designing the gas delivery and current collection system, this study proposed a model to theoretically analyze the current collection process, and finally a method and tool of optimization for scales of gas channels and current collection ribs is presented. The analysis found that small current collectors and collection area is advantageous for getting high power density in both PEMFCs and SOFCs.
Modeling and Simulation of a Modern PEM Fuel Cell System
Authors: Meyer Richard T. , Yao Bin
Published: September 2008

Recent trends and advances in hydrogen/air Proton Exchange Membrane Fuel Cells (PEMFC) are incorporated into a dynamic control oriented model. This type of model is important for development of control systems for PEMFC powered transportation where unpredictable and widely varying changes in power demand can be expected. Self humidification and low pressure operation are the two major changes to past systems. As a result, a high pressure air compressor, air cooler, and inlet gas humidifiers are no longer required. Also, the likelihood of cathode flooding is reduced. The overall fuel cell model consists of four basic sub-models: anode, cathode, fuel cell body, and cooling. Additionally, the oxidant supply blower, cooling pump, and cooling fan are explicitly incorporated. Mass and energy conservation are applied to each using a lumped parameter control volume approach. Empirical modeling is minimized as much as possible, however it is necessary for model manageability in a control context. Interactions between each subsystem and balance of plant components are clearly defined. The overall model is capable of capturing the transient behavior of the flows, pressures, and temperatures as well as net output power. The influence of the charge double layer effect on transient performance is also explored. Numerical simulations of the system are presented which illustrate the usefulness of the model. Finally, future control work is described.
Velocity Measurements in a PEM Fuel Cell Manifold and Individual Cells Using Particle Image Velocimetry
Authors: Grega Lisa M. , McGarry Matthew , Begum Mahfuja
Published: September 2008

Detailed measurements of flow through a model of a PEM fuel cell stack were made using Particle Image Velocimetry. The objective was to obtain high caliber sets of velocity fields in both the inlet manifold and within the cells over a range of Reynolds numbers in order to demonstrate relationships between flow distributions in the manifold and those along the cells of the stack. A scaled up model was built and placed in a wind tunnel under uniform inlet flow conditions. Using the PIV technique, instantaneous flowfields were captured and ensemble averaged to obtain mean and fluctuating velocity statistics. Reynolds numbers associated with operating conditions in the range of three to nine stoichs were studied in the experiments. Examination of instantaneous velocity distributions in the manifold demonstrated the existence of complex fluid motions towards the aft, resulting in increased velocity fluctuations in this region. Velocity fluctuations within the cells were also found to increase towards the aft of the stack. The inlet to the cells was characterized by a relatively large region of flow separation, which was strongest towards the front of the stack, but still persisted in cells towards the aft of the stack.
Order Reduction for a Control-Oriented Model of the Water Dynamics in Fuel Cells
Authors: McCain B. A. , Stefanopoulou A. G.
Published: September 2008

Predicting the water dynamics and estimating humidity and flooding conditions in a low-temperature fuel cell are critical for robust operation and long life. Previous work by McKay et al [1] shows that the fuel cell anode, cathode, and membrane water dynamics and gaseous species concentrations can be accurately modeled by discretizing the partial differential equations that describe mass transport into three segments. Avoiding sensitivities associated with over-parameterization, and allowing for the real-time computations necessary for embedded controllers, requires in-depth investigation of the model order. In this paper the model from [1] is formulated into a bond graph representation. The objective is to establish the necessary model order for the fuel cell model using the Model Order Reduction Algorithm (MORA) [2], where an energy-based metric termed the Activity is used to quantify the contribution of each element of the model. Activity is a scalar quantity that is determined from the generalized effort and flow through each element of the model. We show the degree of model order reduction and provide a guideline for appropriate discretization.
A Dynamic Model of an Atmospheric Solid Oxide Fuel Cell System for Stationary Power Generation
Authors: Kemm Miriam , Selimovic Azra , Assadi Mohsen
Published: September 2008

This paper focuses on the transient behavior of a solid oxide fuel cell system used for stationary power production. Dynamic modelling is applied to identify the characteristic time scales of the system components when introducing a disturbance in operational parameters of the system. The information on the response of the system may be used to specify the control loops needed to manage the changes with respect to safe component operation. The commercial process modelling tool gPROMS is used to perform the system simulations. The component library of the tool is completed with dynamic models of a fuel cell stack and a prereformer. The other components are modelled for steady state operation. For the fuel cell a detailed dynamic model is obtained by writing the constitutive laws for heat transfer in the solid part of the cell and conservation of heat and mass in the air and fuel channels. Comprehensive representation of resistive cell losses, reaction kinetics for the reforming and heat conduction through the solid part of the cell is also included in the model. The prereformer is described as a dynamic pseudo-homogeneous one-dimensional tubular reactor accounting for methane steam reforming and water-gas shift reaction. The differences in the transient behavior of the system components and their interaction are investigated under load changes and feed disturbances.
Optimizing the Performance of a PEM Fuel Cell Using the Powell Algorithm
Authors: Zhang Zhuqian , Wang Xia , Zhang Xinxin , Yu Fan
Published: September 2008

A three-dimensional steady-state electrochemical mathematic model is established where the mass, fluid and thermal transport processes are considered as well as the electrochemical reaction. The influences of the parameters of interest, which include the porosity, the permeability, and the thickness of the gas diffusion layer and the inlet gas stoichiometric flow rate, on the performance of fuel cells are identified. By applying the Powell algorithm, multiple optimum parameters are obtained from the optimization solution with respect to the objective function, which is defined as the maximum potential of the electrolyte fluid phase at the membrane/cathode interface with a typical value of the cell voltage. By comparing the optimized oxygen mole fraction and the local current density distribution with the reference case, the results shown in the paper provide useful tools for a better design of fuel cells.
Air Supply System for the Fuel Cell of a Mobile Robot
Authors: Kim Choong Hyun , Lee Yong-Bok
Published: September 2008

An air supply system has been developed for the fuel cell of a mobile robot, named ROBHAZ, using a rotary vane pump with a muffler. Research is concentrated on the design of the system, not only decreases the sound pressure level to an affordable range but also provides appropriate air flow rate for the fuel cell with the maximum output of 500W. At the same time, it has small volume; outer diameter of 80mm and total length of less than 150mm; which enables its installation into the limited space of the robot system. The muffler was designed to have concentric pipes to form a dual muffler which corresponds to the intake and outlet of the pump, respectively. DC motor was assembled inside the inner muffler to save the space. Developed device is thought be a satisfactory air supply system for a fuel cell.
Designing Solid Oxide Fuel Cell Gas Turbine Hybrid Systems Using Exergy Analysis
Authors: Bosch K. J. , Woudstra N. , van der Nat K. V.
Published: September 2008

In conventional gas turbine systems combustion results in high exergy losses (∼30%) of fuel exergy input. Replacing the combustor with a high temperature fuel cell, like the Solid Oxide Fuel Cell (SOFC), will significantly reduce these exergy losses. As the SOFC electrochemically converts the natural gas, exergy losses are far lower (∼10%) compared to combustion. Natural gas entering a SOFC system has to be reformed first to hydrogen and carbon monoxide by steam reforming. Here it is chosen to use the heat generated by the fuel cell to drive the endothermic reforming reactions: internal reforming. The SOFC-GT system has the advantage that both fuel cell and gas turbine technology contribute to power production. In earlier work [1] several fuel cell system configurations with PEMFC, MCFC or SOFC, were analyzed studying the exergy flows. Here is focused on the SOFC-GT configuration, to get a detailed understanding of the exergy flows and losses through all individual components. Several configurations, combining the SOFC with the GT are possible. The selected operating conditions should prevent carbon deposition. Systems studies are performed to get more insight in the exergy losses in these combined systems. Exergy analysis facilitates the search for the high efficient SOFC-GT hybrid systems. Using exergy analysis, several useful configurations are found. Exergy losses are minimized by varying pressure ratio and turbine inlet temperature. Sensitivity studies, of equivalent cell resistance and fuel cell temperature, show that total system exergy efficiencies of more than 80% are conceivable, without using a bottoming cycle.
Hybrid Solid Oxide Fuel Cell/Gas Turbine System for High Altitude Long Endurance Aerospace Missions
Authors: Himansu Ananda , Freeh Joshua E. , Steffen Christopher J. , Tornabene Robert T. , Wang Xiao-Yen J.
Published: September 2008

A system level analysis, inclusive of mass, is carried out for a cryogenic hydrogen fueled hybrid solid oxide fuel cell and bottoming gas turbine (SOFC/GT) power system. The system is designed to provide primary or secondary electrical power for an unmanned aerial vehicle (UAV) over a high altitude, long endurance mission. The net power level and altitude are parametrically varied to examine their effect on total system mass. Some of the more important technology parameters, including turbomachinery efficiencies and the SOFC area specific resistance, are also studied for their effect on total system mass. Finally, two different solid oxide cell designs are compared to show the importance of the individual solid oxide cell design on the overall system. We show that for long mission durations of 10 days or more, the fuel mass savings resulting from the high efficiency of an SOFC/GT system more than offset the larger powerplant mass resulting from the low specific power of the SOFC/GT system. These missions therefore favor high efficiency, low power density systems, characteristics typical of fuel cell systems in general.
Evaluation of Cathodic Air Flow Transients in a Hybrid System Using Hardware Simulation
Authors: Tucker David , Lawson Larry , Smith Thomas P. , Haynes Comas
Published: September 2008

Effective control of cathode airflow in a direct fired solid oxide fuel cell gas turbine (SOFC/GT) hybrid power system is critical to thermal management of a fuel cell stack. Hybrid fuel cell turbine designs often incorporate the use of a valved hot air bypass in parallel with the cathode flow to divert a portion of the compressor effluent around the fuel cell system. The primary objective of this valve in the early development of hybrid power systems was to facilitate system startup. From a system controls perspective, the hot air bypass offers the means to balance and manipulate the level of airflow supplied to the fuel cell stack at a minimal efficiency penalty. Manipulation of this valve has a significant impact on stack performance and reliability, as well as cathodic exhaust airflow conditions. Since the turbine is directly coupled to the fuel cell subsystem through the cathode airflow, non-linear effects are propagated through the system components in response to any hot air bypass valve change. The effect of cathode flow transients on hybrid system performance has been evaluated though the manipulation of a hot air bypass valve on a hardware-based simulation facility designed and built by the U.S. Department of Energy, National Energy Technology Laboratory (NETL). A brief overview of this experimental facility is provided and has been described in more detail previously. Open loop experiments were conducted using the facility, where a perturbation was made to the hot air bypass flow and turbine speed was allowed to change in response. The impact of the transients to both fuel cell and turbine performance are discussed.
Heat Transfer Limitations in Hydrogen Production via Steam Reformation: The Effect of Reactor Geometry
Authors: Vernon David R. , Davieau David D. , Dudgeon Bryce A. , Erickson Paul A.
Published: September 2008

Hydrogen can be produced in a variety of methods including steam-reformation of hydrocarbon fuels. In past studies the quasi non-dimensional space velocity parameter (inverse residence time) has been shown to be insufficient in accurately predicting fuel conversion in hydrocarbon-steam reformation. Heat transfer limitations have been manifest with reactors of different geometries. In order to achieve ideal fuel conversion, the heat transfer limitations and the changes of these limitations with respect to geometry must be considered in the reactor design. In this investigation, axial and radial temperature profiles are presented from reactors of different aspect ratios while holding space velocity constant. Using both the temperature profile information as well as the traditional space velocity limitations one may be able to develop an optimal reactor design.
Numerical Analysis of Heat/Mass Transfer and Electrochemical Reaction in an Anode-Supported Flat-Tube Solid Oxide Fuel Cell
Authors: Suzuki Masayuki , Shikazono Naoki , Fukagata Koji , Kasagi Nobuhide
Published: September 2008

Three-dimensional heat and mass transfer and electrochemical reaction in an anode-supported flat-tube solid oxide fuel cell (FT-SOFC) are studied. Transport and reaction phenomena mainly change in the streamwise direction. Exceptionally, hydrogen and water vapor have large concentration gradients also in the cross section perpendicular to the flow direction, because of the insufficient mass diffusion in the porous anode. Based on these results, we develop a simplified one-dimensional cell model. The distributions of temperature, current, and overpotential predicted by this model show good agreement with those obtained by the full three-dimensional simulation. We also investigate the effects of pore size, porosity and configuration of the anode on the cell performance. Extensive parametric studies reveal that, for a fixed three-phase boundary (TPB) length, rough material grains are preferable to obtain higher output voltage. In addition, when the cell has a thin anode with narrow ribs, drastic increase in the volumetric power density can be achieved with small voltage drop.
Water Recovery Schemes and Effects on the Water/Thermal Balances for a 100 kW PEMFC System
Authors: Ito Takamasa , Yuan Jinliang , Sunde´n Bengt
Published: September 2008

Proton exchange membrane fuel cell (PEMFC) systems have been investigated as alternative power sources for the stationary and automotive applications. However, they do not appear on the market yet. One of the main reasons is the difficulty of the water/thermal management in the system. Several water recovery schemes have been proposed to overcome this difficulty and to simplify the system configuration. In this paper, the influence of the water recovery schemes on the water/thermal balances in the PEMFC system is investigated. One is a scheme without water phase change at the condenser and the humidifier. The other is a scheme with water phase change. As a result, at low operating pressure, the scheme with water phase change has a large heat dissipation from the system. This is because large water recovery is required in the condenser. With increasing operating pressure, the influence of the difference in the water recovery scheme is diminished from the thermal balance point of view. This is because the requirement of the water recovery becomes small. In the favorable operating range for the stack, the water/thermal balances in the system with water phase change is quite difficult because the heat loads in the intercooler and condenser are very large. However, the water recovery scheme without phase change can solve this difficulty. This scheme makes the component design simpler in this operating range.
Proton Exchange Membrane Fuel Cell System Identification and Control: Part I — System Dynamics, Modeling and Identification
Authors: Yang Yee-Pien , Wang Fu-Cheng , Chang Hsin-Ping , Ma Ying-Wei , Huang Chih-Wei , Weng Biing-Jyh
Published: September 2008

This paper consists of two parts to address a systematic method of system identification and control of a proton exchange membrane (PEM) fuel cell. This fuel cell is used for communication devices of small power, involving complex electrochemical reactions of nonlinear and time-varying dynamic properties. From a system point of view, the dynamic model of PEM fuel cell is reduced to a configuration of two inputs, hydrogen and air flow rates, and two outputs, cell voltage and current. The corresponding transfer functions describe linearized subsystem dynamics with finite orders and time-varying parameters, which are expressed as discrete-time auto-regression moving-average with auxiliary input models for system identification by the recursive least square algorithm. In experiments, a pseudo random binary sequence of hydrogen or air flow rate is fed to a single fuel cell device to excite its dynamics. By measuring the corresponding output signals, each subsystem transfer function of reduced order is identified, while the unmodeled, higher-order dynamics and disturbances are described by the auxiliary input term. This provides a basis of adaptive control strategy to improve the fuel cell performance in terms of efficiency, transient and steady state specifications. Simulation shows the adaptive controller is robust to the variation of fuel cell system dynamics.
Dynamic Behavior and In-Situ Diagnostics of PEFCs
Authors: Friedrich Kaspar Andreas , Kaz Till , Scho¨nbauer Stefan , Sander Heinz
Published: September 2008

During fuel cell operation the electrochemical activity often is not homogenous over the electrode area. This may be caused by an non-uniform water content in the membrane, an inhomogeneous temperature distribution, and reactant gradients in the cell. Consequently a variation of the current density over the cell area occurs which tends to result in inferior performance. For in situ measurements of the current density distribution in fuel cell stacks a segmented bipolar plate was developed. The segmented bipolar plate was first tested in single cells with stack endplates to verify the function of all components. The tests showed that the measurement tool works very reliable and accurate. The insight in an operating fuel cell stack via current density distribution measurement is very helpful to investigate interactions between cells. Results can be used to validate models and to optimise stack components, e.g. flow field and manifold design, as well as to detect the best stack operating conditions. By applying segmented bipolar plates as sensor plates for stack system controls an improved performance, safe operation and longer life cycles can be achieved. The developed segmented bipolar plates with integrated current sensors were used to assemble a short stack consisting of 3 cells; each of them having an active area of 25cm2 divided into 49 segments. The design of the bipolar plate proofed very suitable for easy assembling of single cells and stacks. First measurement results show that different current distributions can appear in the cells and these can vary from cell to cell, depending on the operating conditions of the stack. Electrical coupling between the cells was investigated and found to be only marginal for the assembly used.
Gas Flow Analysis of Bi-Polar Plate Designs for Fuel Cells
Authors: Boddu Rajesh , Majumdar Pradip
Published: September 2008

A tri-layer fuel cell includes separate flow channels for hydrogen and oxygen. One potential alternative flow channel design is the use of a Bi-polar plate that connects cathode of a tri-layer fuel cell to anode of the next tri-layer fuel cell in order to provide an efficient flow of current through the cells with reduced voltage loss. The design of the bipolar plates provides considerable engineering challenges. It requires being thin with good contact surfaces for the purpose reduced electrical resistances as well as efficient transport processes for the reactant gasses in micro-channels with reduced pressure drops. Fluid flow and heat and mass transport in gas flow channels plays an important role in the effective performance of the fuel cell. A bi-polar plate design with straight parallel channels is considered and flow field in gas flow channels are analyzed using computational fluid dynamic model. Results for pressure drop coefficient and heat transfer coefficients with varying flow Reynolds number are presented.