bluuebunny/crossref_metadata_2025 huggingface dataset:
Spray Penetration and Drop Size Analysis
Authors: Jawad Badih A. , Riedel Chris H. , Bazzari Ahmad
Published: October 2008

Understanding the disintegration mechanism, spray penetration, and spray motion is of great importance in the design of a high quality diesel engine. The atomization process that a liquid would undergo as it is injected into a high-temperature, high-pressure air, is investigated in this work. The purpose of this study is to gain further insight into the atomization mechanism, the variation over time in droplet size distribution and spray penetration. This is done based on the effects of chamber pressure, injection pressure, and type of fuel. A laser diffraction method is used to determine droplet mean diameters, single injection with synchronized time mechanism allowed the time dependent studies. Obscuration signals are obtained through a digital oscilloscope from which arrival time of spray can be measured. A spray penetration correlation is reported.
Large Eddy Simulation of Near-Field Dispersion Within and Above Forest Canopies
Authors: Edburg Steven , Stock David , Lamb Brian , Thistle Harold
Published: October 2008

Numerical simulations were conducted to investigate the feasibility of predicting near field concentrations of a tracer gas within and above forest canopies. The current research is geared towards providing forest managers with a tool for developing anti-aggregation techniques to control the bark beetle. Several field experiments have been conducted in different forest canopies linking tracer gas concentration fields with meteorological and canopy parameters. Field experiment results are site and situation specific. Numerical simulations are far less expensive and allow for variation in virtually all flow parameters such as atmospheric stability, wind speed and direction, and turbulence intensity. As a first step, a CFD simulation has been used to study dispersion in a generic lodgepole pine forest canopy based on leaf area index (LAI) and stem density. Steady Reynolds Averaged Navier Stokes (RANS) solutions were computed using the k-ε and Reynolds Stress Model (RSM) turbulence closure models. These solutions provide insight into in-canopy dispersion; however they do not fully capture the dynamics of the flow. The current work uses large eddy simulation (LES). LES resolves large flow dominated eddies while modeling smaller eddies using a sub grid scale model. Unsteady LES, can be used to capture the dynamics of flow within a canopy, including large rolling eddies above the canopy, bursting and sweeping within the canopy, multiple shear layers, and drainage flows.
Air Entrained Amount Measurement in the Two-Phase Flow Through Inlet Passage of Pump
Authors: Zhou Daqing , Xu Zhaofeng , Li Meng , Liu Shuhong , Wu Yulin , Nagahara Takahide
Published: October 2008

In the paper, we adopt Image method to perform entrained air amount measurement in the two-phase flow through inlet passage of pump. Furthermore, not only air entrained amount but also air bubble’s size are discussed and compared under different work conditions. Results show that under all the normal conditions, the maximum value of air entrained rate is 2.5 mL/s, and the maximum of volumetric ratio is 0.006%. The minimum measurable bubble volume is about 1 mm3, and the maximum bubble size is about 0.39 cm3. Analysis also shows that chest wall angle is a main factor that affects air entrained vortex occurrence.
Improvement of CO Tolerance of Proton Exchange Membrane Fuel Cell (PEMFC) by an Air-Bleeding Technique
Authors: Chung Chen-Chung , Chen Chiun-Hsun , Lin Hsiang-Hui , Yan Yi-Yie
Published: October 2008

The investigation studies improving PEMFC carbon monoxide by a periodic air dosing. The carbon monoxide in the fuel gas leads to a significant loss in power density due to CO poisoning in the anode. The method involves bleeding air into the anode fuel stream (H2-CO), which contains CO in various concentrations (20, 52.7, 100 ppm). In the transient CO poisoning test, air-bleeding is performed for four different periodic air dosing and cell voltage is fixed at 0.6 V. The result of a dosing of air during 10 sec in intervals of 10 sec is similar to that of continuous air-bleeding except 100 ppm CO. The CO tolerance of the fuel cell and cell performance recovery from poisoning can be improved by air-bleeding.
Conjugate Mass Transfer in Gas Channels and Diffusion Layers of Fuel Cells
Authors: Beale S. B.
Published: October 2008

An analysis is performed for mass transfer in a rectangular gas passage, porous diffusion layer, and the combination of the two. The results of detailed calculations are presented and correlated in terms of the mass transfer driving force as a function of the blowing parameter and geometry, as characterized by the aspect ratio and blockage factor. It is shown that a simple solution for the overall driving force may be obtained for the conjugate mass transfer problem. This solution is quite general in its nature. The mathematical foundations are presented together with the details of the computational procedure used to obtain the results.
A Technological Solution for Everywhere Energy Supply With Sun, Hydrogen and Fuel Cells
Authors: Orecchini F. , Santiangeli A. , Dell’Era A.
Published: October 2008

The hydrogen economy is still at the beginning but the society, innovation, and market push inexorably towards hydrogen, inspiring the idea to build an energy integrated system that can satisfy, in an independent way, the energy needs of small size consumers. The technologies used for the system design are already available in the market and, at least for the standard solutions, sufficiently mature. The innovation consists of an integration, optimization and industrialization of this modular system, which is an electric zero emissions generator, giving as output power 3,5 kWp. This is the only system able to produce its own fuel, guaranteeing renewable and clean energy, available where and when you want. This system is constituted of a polymer membrane electrolyser, a metal hydride tank, that absorbs and desorbs hydrogen, and a polymer fuel cell. The system modularity can satisfy also greater energy requirements and the hydrogen storage by metal hydride at low pressure guarantees the system safety.
Micro Fuel Cell Technologies, Advancements, and Challenges
Authors: Bonta Purnima V. S. , O’Neal Chad B. , Muthusami Sathiya
Published: October 2008

Compact fuel cells are gaining widespread recognition as the next generation power sources for portable and micro-scale electronics. Fuel cells are being implemented at the macro as well as microscale to provide pollution-free, high-density energy for various electronic applications. Micro fuel cells have been an innovative step in the direction of fuel cell miniaturization, and technologies are currently being developed for their commercialization. This paper is a review of micro fuel cell technologies based on an extensive study of the existing literature with the objective of identifying common components, designs, and fabrication methods for silicon based fuel cells, and compiling that information into a single location. This paper also evaluates the potential prospects for silicon micro fuel cells and various approaches employed to overcome several technical challenges.
Heat and Mass Balances of an Intercooler in PEM Fuel Cell Systems
Authors: Ito Takamasa , Yuan Jinliang , Sunde´n Bengt
Published: October 2008

In this paper, heat and mass balances of the intercooler in a 100 kW Proton Exchange Membrane Fuel Cell (PEMFC) system are analyzed by employing a commercial software IPSEpro. The compressor, ambient temperature, the humidification method and the PEMFCs cathode operating temperature were considered as the parameters influencing the heat and mass balances in the intercooler. Parametric studies of the heat and mass balances in the intercooler are carried out with various values of the parameters, such as operating pressure, air mass flow rate, compressor efficiency, ambient air temperature, cathode operating temperature and H2O injection temperature for the humidification, etc. As indicated in the paper, in the system with either high ambient temperature, high operating pressure, low cathode operating temperature or internal humidification, the required heat transfer rate in the intercooler is large. However, evaporation of H2O for the humidification contributes to reduction of the required heat transfer rate.
Pressure Drop on the Cathode Side of a PEM Fuel Cell as a Diagnostic Tool for Detection of Flooding and Drying Conditions
Authors: Barbir Frano , Wang Xinting , Gorgun Haluk
Published: October 2008

An increase in pressure drop on the cathode side of PEM fuel cell is a reliable indicator of PEM fuel cell flooding. Flooding, i.e., liquid water accumulation inside the cell causes a rather erratic cell potential behavior — steady voltage drops followed by sudden voltage increases. The pressure drop in this case behaves similarly, i.e., increases as the water accumulates, and drops as the water is expulsed from the cell, however with an obvious and detectable upward trend. In an opposite case of fuel cell drying, the cell potential steadily decreases as the ionic resistance increases, while the pressure drop initially decreases as the last of the liquid water is being expulsed, and thereafter remains constant. By monitoring both pressure drop and cell resistance in an operational fuel cell stack it was possible to reliably diagnose either flooding or drying conditions inside the stack, which were intentionally created by adjusting the humidification and stack temperatures. Pressure drop, therefore, may be used to define a control strategy, i.e. to make decisions on corrective actions. In most cases, the pressure drop is a linear function of flow rate when a single phase (gas) is flown through a fuel cell since the flow is well in the laminar regime. When the gas starts to carry water droplets, such as the case when the fuel cell operates with fully saturated gases, the pressure drop departs from linearity. In addition, slugs of water, possibly present inside the fuel cell passages, create unsteady conditions.
The Effect of Variable Catalyst Loading in Electrodes on PEM Fuel Cell Performance
Authors: Roshandel R. , Farhanieh B.
Published: October 2008

Catalyst layers are one the important parts of the PEM fuel cells as they are the main place for electrochemical reaction taking place in anode and cathode of the cells. The amount of catalyst loading of this layer has a large effect on PEM fuel cell performance. Non-uniformity of reactant concentration could lead to a variation of current density in anode and cathode catalyst layer. The main reason for this phenomenon is porosity variation due to two effects: 1. compression of electrode on the solid landing area and 2. Water produced at the cathode side of diffusion layer. In this study the effect of variable current density in anode and cathode electrode on cell performance is investigated. It has shown that better cell performance could be achieved by adding a certain amount of catalyst loading to each electrode, with respect to the reactant concentration.
Nonlinear Thermal Modelling and Control of a PEM Fuel Cell Stack
Authors: Kolodziej Jason R.
Published: October 2008

The purpose of this paper is to present a nonlinear control method for accurately maintaining coolant temperature within a proton exchange membrane (PEM) fuel cell stack by controlling coolant flow rate. Due to the current sensitive nature of the membrane and a strict relative humidity requirement it is critical to precisely control the internal temperature of the fuel cell. First, an optimization-based parameter identification is applied to determine unknown coefficients to the nonlinear thermal model of the fuel cell stack. The stack is modelled according to a lumped parameter Continuous-flow Stirred Tank Reactor (CSTR) form. The paper then presents a nonlinear disturbance rejection control technique to accomplish the necessary temperature control. Experimental data from a 17-cell fuel cell stack is used for both the modelling and control portions of this work.
Numerical Simulations of Gaseous Mixture Flow in Porous Electrodes for PEM Fuel Cells by the Lattice Boltzmann Method
Authors: Asinari Pietro , Coppo Marco , von Spakovsky Michael R. , Kasula Bhavani V.
Published: October 2008

Throughout the last decade, a considerable amount of work has been carried out in order to obtain ever more refined models of proton exchange membrane (PEM) fuel cells. While many of the phenomena occurring in a fuel cell have been described with ever more complex models, the flow of gaseous mixtures in the porous electrodes has continued to be modeled with Darcy’s law in order to take into account interactions with the solid structure and with Fick’s law in order to take into account interactions among species. Both of these laws derive from the macroscopic continuum approach, which essentially consists of applying some sort of homogenization technique which properly averages the underlying microscopic phenomena for producing measurable quantities. Unfortunately, these quantities in the porous electrodes of fuel cells are sometimes measurable only in principle. For this reason, this type of approach introduces uncertain macroscopic parameters which can significantly affect the numerical results. This paper is part of an ongoing effort to address the problem following an alternative approach. The key idea is to numerically simulate the underlying microscopic phenomena in an effort to bring the mathematical description nearer to actual reality. In order to reach this goal, some recently developed mesoscopic tools appear to be very promising since the microscopic approach is in this particularly case partially included in the numerical method itself. In particular, the lattice Boltzmann models treat the problem by reproducing the collisions among particles of the same type, among particles belonging to different species, and finally among the species and the solid obstructions. Recently, a procedure based on a lattice Boltzmann model for calculating the hydraulic constant as a function of material structure and applied pressure gradient was defined and applied. This model has since been extended in order to include gaseous mixtures with different methods being considered in order to simulate the coupling strength among the species. The present paper reports the results of this extended model for PEM fuel cell applications and in particular for the analysis of the fluid flow of gaseous mixtures through porous electrodes. Because of the increasing computational needs due to both three–dimensional descriptions and multi-physics models, the need for large parallel computing is indicated and some features of this improvement are reported.
Preparation, Coating and Patterning of Cu-Based Catalyst for Methanol Steam Reforming by Micro Fuel Reformer
Authors: Kim Taegyu , Lee Dae Hoon , Yoon Cheonho , Park Dae-Eun , Kwon Sejin , Yoon Euisik
Published: October 2008

Recent increase in need for a portable power source drives research on micro fuel cell and micro fuel reformer as a key component of micro power generation system. Various concept of reforming system is proposed and has been studied. As an attempt to develop wafer based micro reforming system, preparation, coating, and patterning of Cu-based catalysts for methanol steam reforming for micro fuel reformer are presented. Preliminary step to develop MEMS based micro fuel reformer is carried. As a first step, Cu-based catalysts are prepared by co-precipitation method. The effect of precipitation condition on physical characteristics and catalytic activity of the catalyst such as particle size, conversion rate and quality of coating on substrate are reported. And then coating processes of prepared catalysts on glass and silicon wafer are developed. A uniform and robust catalyst layer is obtained. The amount of coated catalyst on unit area of wafer is measured to be 5∼8 mg/cm2, and the thickness of catalyst layer is about 50μm. By multiple coating processes, catalyst thickness can be controlled and up to 15mg/cm2 is obtained that has good reactivity. After then, patterning of coated catalyst layer is reported. Deposited catalyst layer is patterned by way of lift-off process of PVA (Poly-Vinyl Alcohol), organic sacrificial layer, by heating the substrate instead of etching a sacrificial layer. With the results aforementioned on catalyst preparation, coating, and patterning, a prototype micro catalytic reactor for micro fuel reformer is fabricated with MEMS technology. The fabrication process includes wet anisotropic etching of photosensitive glass wafer, coating/patterning of catalyst and bonding of layers. Next step that is challenging part of development of micro reformer is to find a way to overcome the effect of heat loss that lowers the conversion rate of reforming process and to achieve fast kinetics for reduction of the device scale. We are pursuing further optimization of structural design to improve conversion efficiency and to obtain fast kinetics.
An Improved Design of Microchannel Fuel Processors
Authors: Jung Hye-Mi , Yim Sung-Dae , Um Sukkee , Yoon Young-Gi , Park Gu-Gon , Sohn Young-Jun , Yang Tae-Hyun , Lee Won-Yong , Kim Chang-Soo
Published: October 2008

This paper focuses on a new systematic configuration of micro-channel fuel processors, particularly designed for portable applications. An alternative integration method of the micro-channel fuel processors is attempted to overcome the serious thermal unbalance and to minimize the system volume by introducing the direct contact method of the sub-components. An integrated micro-channel methanol processor was developed by assembling unit reactors, which were fabricated by stacking and bounding micro-channel patterned stainless steel plates, including fuel vaporizer, catalytic combustor and steam reformer. Commercially available Cu/ZnO/Al2O3 catalyst (ICI Synetix 33-5) was coated inside micro-channel of the unit reactor for steam reforming. The steam reforming reaction was conducted in the temperature range of 200°C to 260°C in the basis of reformer side end-plate and the temperature was controlled by varying methanol feeding into the combustor. More than 99% of methanol was converted at 240°C of reformer side temperature. A mechanism-based numerical model aimed at enhancing physical understanding and optimizing designs has been developed for improved micro-channel fuel processors. A two-dimensional numerical model in the reformer section created to model the phenomena of species transport and reaction occurring at the catalyst surface. The mass, momentum, and species equations were employed with kinetic equations that describe the chemical reaction characteristics to solve flow-field, methanol conversion rate, and species concentration variations along the micro-channel. This mechanism-based model was validated against the experimental data from the literature and then applied to various layouts of the micro-channel fuel processors targeted for the optimal catalyst loading and fuel reforming purpose. The computer-aided models developed in this study can be greatly utilized for the design of advanced fast-paced micro-channel fuel processors research.
Autothermal Reforming of Natural Gas for High-Temperature Fuel Cells
Authors: Leem Sungkwang , Bae Joongmyeon
Published: October 2008

Hydrogen production using current fueling facilities is essential for near- term applications of fuel cells. A preliminary process for developing natural gas autothermal reforming (ATR) reactor for solid oxide fuel cell (SOFC) was performed in this study. Catalyst scanning was performed for three catalysts and Pt based catalyst selected for further study. Using Pt catalyst we determined feeding conditions for the thermal neutrality by varying O2/CH4 with selected temperatures and feeding conditions. Temperature profiles of a reactor were observed and reformed gas composition was analyzed to evaluate efficiency, conversion and heat of reaction. O2/CH4 showed strong effects on reactor temperature, efficiency and conversion. Thermal neutral conditions were determined for two cases of ATR system on the basis of yields of products of experimental results. These conditions could be used as a guideline for reformer design and operation parameter for self-sustaining ATR.
Inconel Coating on Stainless Steel Plate for Metal-Supported SOFC
Authors: Lee Chang Bo , Jee Hyunjin , Bae Joongmyeon
Published: October 2008

The present work is to examine the coating characteristic in oxidation environment. Inconel was deposited on SUS430 plate with size of 1 mm thickness and 28 mm diameter. The resistances of each alloy — uncoated and coated SUS430 — were measured at the condition of 973 K and air environment. Also, after pre-oxidized treatment for 24 hours at 973 K, the resistance characteristic was investigated. In all cases, the ASR of inconel-coated SUS430 is superior to that of the uncoated SUS430. Consequently, the cause of resistance reduction was grasped with the microstructure analysis of SEM images with EDX data.
Mixed-Fuels Fuel Cell Running on Methane-Air Mixture
Authors: Yoon Sung Pil , Kim Hyun Jae , Park Byung-Tak , Nam Suk Woo , Han Jonghee , Lim Tae-Hoon , Hong Seong-Ahn
Published: October 2008

In order to develop SOFC running on hydrocarbon fuels, we have focused on a new method of improving electrode performance and reducing carbon deposition by coating thin films of samaria-doped ceria (SDC) within the pores of electrode by a sol-gel coating technique. The SDC coating on the pores of anode made it possible to have a good stability for long-term operation due to low carbon deposition and nickel sintering. In this study, we demonstrated a new method of improving electrode performance and reducing carbon deposition by coating thin films of samaria-doped ceria (SDC) and applied the modification technique to two different types of fuel cell structures, anode-supported SOFC and comb-shaped SOFC. From our results, the maximum power density of an anode-supported cell (electrolyte; 8 mol% YSZ and thickness of 30 μm, and cathode; La0.85Sr0.15MnO3) with the modified anode was about 300 mW/cm2 at 700 °C in the mixture of methane (25%) and air (75%) as the fuel and air as the oxidant. The cell was operated for 500 h without significant degradation of cell performance. For the comb-shaped SOFCs operated in the mixed-fuels fuel cell (MFFC) conditions, the cell performance was 40 mW/cm2 at 700 °C in the CH4/O2 ratio of 1.
PEM Fuel Cell Models Validation and Accuracy Analysis
Authors: Liu Qingyun , Yan Qiangu , Wu Junxiao
Published: October 2008

A multi-resolution method is developed for the polymer electrolyte membrane (PEM) fuel cell simulation. A full 3D modeling is employed for membrane and diffusion layer, 1D+2D model is applied to the catalyst layer, that is, at each location of the fuel cell plate, the governing equations are integrated only in the direction perpendicular to the fuel cell plate; and a quasi-1D method with high numerical efficiency and reasonable accuracy is employed for the flow channels. The simulation accuracy was assessed in terms of fuel cell polarization curves and membrane ohmic overpotential. Overall, the agreements between simulated results and experimental data are good. However, at large current densities, when high relative humidity reactant inputs are employed, the simulation under predicts the fuel cell performance due to a single-phase assumption. The method slightly over predicts the fuel cell performance for a dry cathode input, possibly due to the nonlinearity of the membrane properties in dehydration case. Further, a parameter study was performed for a fully humidified cell and a relative dry cell. These parameters include porosity and permeability of gas diffusion layer; porosity, effective oxygen permeability, ratio of thickness of surrounding Nafion layer to exposed agglomerate area density and cathodic transfer coefficient of catalyst layer. Some insight can be obtained by examining their effects on the cell performances in order to further improve the model accuracy.
Development of High Performance Micro DMFCs and a DMFC Stack
Authors: Lu Guoqiang , Wang Chao-Yang
Published: October 2008

A silicon-based micro direct methanol fuel cell (μDMFC) for portable applications has been fabricated and its electrochemical characterization carried out. A membrane-electrode assembly (MEA) was specially fabricated to mitigate methanol crossover. The cell with the active area of 1.625 cm2 demonstrated a maximum power density of 50 mW/cm2 at 60°C. Since silicon wafer is too fragile to compress for sealing, and a thicker layer of gold has to be coated on the silicon wafer to reduce contact resistance, further development of micro DMFCs for high power application was carried out using stainless steel plate as bipolar plate in which flow channels were fabricated by photochemical etching technology. The maximum power density of the micro DMFC reaches 62.5 mW/cm2 at 40 °C and 100 mW/cm2 at 60°C with atmospheric pressure. An 8-cell air-breathing DMFC stack has been developed. Mass transport phenomena such as water transport, and oxygen transport were investigated. By using a water management technique, cathode flooding was avoided in our air-breathing DMFC stack. Furthermore, it was found that oxygen transport in the air-breathing cathode is still very efficient. The DMFC stack produced a maximum output power of 1.33 W at 2.21 V at room temperature, corresponding to a power density of 33.3 mW/cm2. A passive DMFC using pure methanol was demonstrated with steady-state output power of 20–25 mW/cm2 over more than 10 hours without heat management.
Modeling and Control of an Ejector Based Anode Recirculation System for Fuel Cells
Authors: Karnik Amey Y. , Sun Jing
Published: October 2008

A control oriented analysis of an anode recirculation system that uses an ejector with a variable throat area is presented for a PEMFC system. Two control issues addressed in this paper are (a) achieving desired recirculated flow to meet humidity control requirements, and (b) regulating anode pressure to protect the polymer membrane from deformation. To meet these objectives, a static feedforward controller using the variable throat area is applied to control the recirculation flow rate, while a proportional-integral controller is designed for anode pressure regulation. A dynamic system model comprising of a nonlinear static characterization of the ejector and dynamic representation of the anode recirculation flow path is developed for controller design and evaluation. Linear analysis is used to derive design guidelines for tuning the feedback controller and to analyze the interactions between the feedback and the feedforward controllers. Our analysis shows that the system characteristics are dependent on the operating condition of throat area of ejector. To meet the control objectives for different operating conditions, a gain scheduling scheme is proposed to adjust the feedback controller parameters and the performance is evaluated through simulations. Results for two representative conditions are included.
Dynamic Numerical Modeling and Experimental Validation of a Molten Carbonate Fuel Cell
Authors: Leal Elisaˆngela Martins , Jabbari Faryar , Brouwer Jacob
Published: October 2008

In this paper, a detailed model incorporating simplified geometric resolution of a molten carbonate fuel cell (MCFC) with detailed and dynamic simulation of all physical, chemical, and electrochemical processes in the stream-wise direction is presented. The model was developed using mass and momentum conservation, electrochemical and chemical reaction mechanisms, and heat-transfer. Results from the model are compared with data from an experimental MCFC unit. Furthermore, the model was applied to predict dynamic variations of voltage, current and temperature in an MCFC as it responds to varying load demands. The voltage was evaluated by applying a model developed by Yuh and Selman [1, 2]. The results show that the model can be used to predict voltage and dynamic response characteristics of an MCFC accurately and consistently for a variety of temperatures and pressures.
Experimental Investigation of the Propagation of Local Current Density Variations to Adjacent Cells in PEFC Stacks
Authors: Santis Marco , Freunberger Stefan A. , Papra Matthias , Bu¨chi Felix N.
Published: October 2008

The propagation of single cell performance losses to adjacent cells in a polymer electrolyte fuel cell stack is studied by means of local current density measurements in a two cell stack. In this stack, the working conditions of adjacent cells can be controlled independently in order to deliberately change the performance of one cell (inducing cell) and study the coupling effects to the adjacent cell (response cell), while keeping the working conditions of the later one unchanged. The experiments have shown that changes in the current density distribution caused by lowering of the air stoichiometry in the inducing cell cause changes in the current density distribution of the response cell in the order of 60% of the change of the inducing cell, even when the air stoichiometry of the response cell is kept constant. The losses in cell voltage of the inducing cell cause losses in cell voltage of the response cell in a magnitude between 30 and 50%.
Viscoelastic Stress Model and Mechanical Characterization of Perfluorosulfonic Acid (PFSA) Polymer Electrolyte Membranes
Authors: Lai Yeh-Hung , Mittelsteadt Cortney K. , Gittleman Craig S. , Dillard David A.
Published: October 2008

Many of the premature failures in the PEM fuel cells are attributed to crossover of the reactant gas from pinholes or through-the-thickness flaws in the membranes. The formation of these pinholes is not fully understood, although mechanical stress is often considered one of the major factors in their initiation and/or propagation. This paper reports evidence of pinhole failure from mechanical stress by cycling between wet and dry conditions in a normally built single 50cm2 fuel cell. In an effort to understand the source of the mechanical stress, to quantify the magnitude, and to correlate its role in membrane failure, a membrane stress model based on linear viscoelastic theory was developed. The effects of temperature, water content, and time are accounted for in the membrane stress model. To satisfy the inputs for the membrane model and to characterize the mechanical behavior of the polymer electrolyte membrane, a series of experiments was performed. Using commercially available Nafion® NR111 membrane as a model material, swelling of 15% and shrinkage of 4% were found from a hydration and de-hydration cycle. Data on elastic moduli versus relative humidity showed discontinuity at the vapor and liquid water transition. We also found that creep compliance master curves can be obtained by double-shifting the compliance curves according to the time-temperature-moisture superposition principle, which significantly simplifies the modeling effort. Combining data on hygro-expansion, elastic moduli, and creep compliance data through the membrane stress model, it was found that the de-hydration process induces significant stress in the membrane. Due to fluctuations in fuel cell operating conditions, the membrane and the associated components are subject to mechanical fatigue which may mechanically degrade the membrane of PEM fuel cells and eventually lead to pinhole formation.
Hydrogen and Fuel Cell Development in China Towards 2020
Authors: Wang Hewu , Ouyang Minggao
Published: October 2008

Hydrogen is one of the perfect selections of clean end-use energy carriers due to the near zero pollution from hydrogen fuel cell. The hydrogen can be produced from all primary energy such as coal, natural gas, nuclear energy, and renewable energy (wind power, solar energy). It is a long term for the transition from the traditional fuel and power technology to hydrogen and fuel cell power technology, and some of the countries such as USA, Canada, Japan, EU (Europe Union), have made their plans or roadmaps into the hydrogen economy according to their own development and technology background. Base on the analysis of the situation of China and the reference of other country’s hydrogen development plan, the authors suggest a three-stage national hydrogen development strategy for China in this paper.
An Improved Model to Predict Flooding/Dehydration in PEM Fuel Cells
Authors: Maharudrayya S. , Jayanti S. , Deshpande A. P.
Published: October 2008

Maintaining proper water balance between the production of water due to reaction and its removal by evaporation is very important for the successful operation of a Polymer Electrolyte Membrane (PEM) fuel cell. Imbalance between the two processes can result in either flooding of the electrodes/ gas channels or the dehydration of the membrane. The water management issue is especially critical for ambient temperature operation of the fuel cell. Several experimental and theoretical studies relevant to water management have been carried out to investigate means of reducing the flooding of electrodes/channels or the dehydration of membrane. Bernardi [9] and Wang et al. [11] have developed theoretical models for the prediction of when flooding/dehydration may take place. In the present study, an improved model is developed which combines the advantages of these two models. The Bernardi [9] model is extended to include mass transfer resistances. Following Wang et al. [11], the Stefan-Maxwell description of multicomponent diffusion is replaced by Fickian diffusion. In addition, water vapour diffusion to both anode and cathode sides is included in the model. The overall model is in the form of a closed-form expression for the critical or threshold or balance current density at which the water production rate and the water vapour evacuation rate are exactly balanced. The model shows that the balance current density is a function of operating conditions, properties of electrode, flow and geometric parameters in the gas channels. It has been validated by comparing the predictions with the experimental data of Tu¨ber et al. [5] and Eckl et al. [8].
Novel AC-M-SCC Anode Materials for Solid Oxide Fuel Cells Using Methanol at Intermediate or Low Temperature
Authors: Feng Bo , Wang Cheng-Yang , Zhu Bin
Published: October 2008

In this paper, novel anode materials for solid oxide fuel cells which can directly operate liquid fuels at intermediate or low temperature were investigated. These materials were based on the activated carbons supported transition metal catalysts (AC-M) and the solid carbonate-ceria composite (SCC) materials, which were prepared via the sol-gel route. The SCCs possess both oxide-ion and proton conductivity, being used as multi-ion conductors. Activated carbons supported transition metals were used to improve the characters of anode materials and especially to enhance the anode catalyst function to liquid fuels, e.g., methanol. The internal reforming of liquid fuels was proved. There is no external reforming system needed. We used also the chemical methods to improve the commercial activated carbons. The microstructure, conductivity and electrochemical properties of anode materials were investigated as functions of the activated carbon pre-treating condition. Using these novel materials, the power intensity of 0.2 W/cm2 was achieved for fuel cells directly operating the methanol at 600 °C.
The Operating Characteristics in an Air-Breathing PEMFC
Authors: Sohn Young-Jun , Park Gu-Gon , Yim Sung-Dae , Um Sukkee , Yang Tae-Hyun , Yoon Young-Gi , Lee Won-Yong , Kim Chang-Soo
Published: October 2008

Air-breathing polymer electrolyte membrane fuel cells (PEMFC) are highly promising particularly for small-power applications up to tens watts class. A distinctive feature of the air-breathing PEMFC is its simple system configuration in which axial fans operate for dual purposes, supplying both oxidant and coolant in a single manner. In the present study, a nominal 80W air-breathing PEMFC system is developed and investigated to determine the optimal operating strategy through parametric studies (i.e., reactant humidity, and fan-blowing flow rate). The cell voltage distributions are examined as a function of time to evaluate the system performance under various operating conditions.
Stack Performance of Intermediate Temperature-Operating Solid Oxide Fuel Cells Using Stainless Steel Interconnects and Anode-Supported Single Cells
Authors: Bae Joongmyeon , Park Jae Keun , Park Jin-Woo , Lim Hee-Chun , Yoo Youngsung
Published: October 2008

We are continuing a national project to develop 1 kW-class SOFC system for Residential Power Generation (RPG) application supported by Korean Government. For intermediate temperature operation, we chose anode-supported, planar type SOFC design to have advantages for commercialization of SOFCs considering mass production and using cost-effective interconnects such as ferritic stainless steels. Anode-supported single cells with thin electrolyte layer of YSZ or ScSZ, respectively, were fabricated and their small stacks were built and evaluated. The size of anode-supported single cells finally sintered was about 10 × 10 cm2, and the thickness of electrolyte and the cathode layer was about 20μm and 30μm, respectively. The I-V and AC impedance characteristics of these single cells and small stacks were evaluated at intermediate temperature (650 ∼ 800°C) by using hydrogen gas as a fuel. We have already carried out long-term performance test for YSZ thin electrolyte single cell for above 33,000 h (3.8 years) at 750°C, applying 0.76 V with power density of 200 mW/cm2. Using these YSZ thin electrolyte 10 × 10 cm2 cells and Inconel interconnect plates coated by silver paste, the 15-cell and 60-cell short stack were prepared. The initial stack voltage at 150 mW/cm2 was 12.5 V in hydrogen as fuel of 120 sccm/cell at 750°C and decreased to about 10.9 V at 500 h operation time. It was then stabilized until 4,000 h with a degradation rate of 10 mV/(1000h, 1 cell). AC impedance of this small stack and microstructure of cell components were analyzed during and after the operation. Furthermore ScSZ thin electrolyte 10 × 10 cm2 cells and ferritic stainless steel interconnects were built into a 5-cell stack and the small stack was operated at 650°C for cost-effective planar SOFC RPG system. I-V and AC impedance characteristics of the small stack were evaluated at 650°C by using hydrogen gas or methane gas as fuel.
Internal Reforming SOFC System for Flexible Coproduction of Hydrogen and Power
Authors: Hemmes Kas , Patil Anish , Woudstra Nico
Published: October 2008

In the framework of the project Greening of Gas, in which the feasibility of mixing hydrogen into the natural gas network in the NL is studied, we are exploring alternative hydrogen production methods. Fuel cells are usually only seen as devices that convert hydrogen into power and heat. It is less well known that these electrochemical energy converters can produce hydrogen, or form an essential component in systems for co-production of hydrogen and power. Co-production of hydrogen and power from NG in an Internal reforming fuel cell (IR FC) is worked out by flow sheet calculations on an Internal reforming Solid Oxide fuel cell (IR-SOFC) system. It is shown that the system can operate in a wide range of fuel utilization values at least from 60% representing highest hydrogen production mode to 95% corresponding to ‘normal’ fuel cell operation mode. For the atmospheric pressure system studied here hydrogen and CO content increase up to 22.6 and 13.5 % respectively at a fuel utilization of 60%. Total system efficiency (power + H2/CO) is increasing significantly at lower fuel utilization and can reach 94 %. Our study confirms that the calculations of Vollmar et al1) on an IR-SOFC stack also hold for a complete FC system. Notably that paradoxically a system with the same fuel cell stack when switched to hydrogen production mode can yield more power in addition to the H2 and CO produced. This is because the hydrogen production mode allows for operation at high current and power densities. The same system can double its power output (e.g. from 1.26 MW to 2.5 MW) while simultaneously increasing the H2 /CO output to 3.1MW). Economics of these systems is greatly improved. These systems can also be considered for hydrogen production for the purpose of mixing it with natural gas in the natural gas grid in order to reduce CO2 emissions at the end users, because of the ability to adopt the system rapidly to fluctuations in natural gas/hydrogen demand.
Computation of Dehydration Effects of the Membrane in a PEM Fuel Cell
Authors: Shan Yuyao , Choe Song-Yul
Published: October 2008

The water management is one of crucial issues to secure a safe and reliable operation of a fuel cell system. Particularly, water flooding blocks influx of reactants in the porous materials or a lack of water in membrane may lead to decrease proton conductivity. Computational methodologies using 3D CFD are employed to conduct analyses. However, the exponentially increasing computational time and the complexity of the validation process necessary for the models are impeding further dynamic study. On the other hand, most of the current models used for the analysis are based on the empirical polarization curve, which does not include the phenomena of water dehydration. We developed a dynamic quasi-1D model for a membrane layer appropriate for an analysis of the dehydration, which considers two aspects: (1) water removed by the outlet gases at the two electrodes; (2) water transported by diffusion and electro-osmotic forces in the membrane. Simulations have been conducted to analyze the effects of load currents and anode/cathode inlet pressure as well as flow rates on the dynamic variation of water content in the membrane and derive impacts on the behavior of the whole PEM fuel cell system.
Direct Oxidation of Waste Vegetable Oil in Solid Oxide Fuel Cells
Authors: Zhou Z. F. , Kumar R. , Thakur S. T. , Rudnick L. R. , Schobert H. , Lvov S. N.
Published: October 2008

Solid oxide fuel cells with ceria, ceria-Cu, and ceria-Rh anode were demonstrated to generate stable electric power with waste vegetable oil through direct oxidation of the fuel. The only pre-treatment to the fuel was a filtration to remove particulates. The performance of the fuel cell was stable over 100 hours for the waste vegetable oil without dilution. The generated power was up to 0.25 W/cm2 for ceria-Rh fuel cell. This compares favorably with previously studied hydrocarbon fuels including jet fuels and Pennsylvania crude oil.
Hydrogen Production Performance of a 10-Cell Planar Solid-Oxide Electrolysis Stack
Authors: O’Brien J. E. , Stoots C. M. , Herring J. S. , Hartvigsen J.
Published: October 2008

An experimental study is under way to assess the performance of solid-oxide cells operating in the steam electrolysis mode for hydrogen production over a temperature range of 800 to 900°C. Results presented in this paper were obtained from a ten-cell planar electrolysis stack, with an active area of 64 cm2 per cell. The electrolysis cells are electrolyte-supported, with scandia-stabilized zirconia electrolytes (∼140 μm thick), nickel-cermet steam/hydrogen electrodes, and manganite air-side electrodes. The metallic interconnect plates are fabricated from ferritic stainless steel. The experiments were performed over a range of steam inlet mole fractions (0.1–0.6), gas flow rates (1000–4000 sccm), and current densities (0 to 0.38 A/cm2). Steam consumption rates associated with electrolysis were measured directly using inlet and outlet dewpoint instrumentation. Cell operating potentials and cell current were varied using a programmable power supply. Hydrogen production rates up to 100 Normal liters per hour were demonstrated. Values of area-specific resistance and stack internal temperatures are presented as a function of current density. Stack performance is shown to be dependent on inlet steam flow rate.
Heat Exchangers for Fuel Cell and Hybrid System Applications
Authors: Magistri L. , Traverso A. , Massardo A. F. , Shah R. K.
Published: October 2008

The fuel cell system and fuel cell gas turbine hybrid system represent an emerging technology for power generation because of its higher energy conversion efficiency, extremely low environmental pollution and potential use of some renewable energy sources as fuels. Depending upon the type and size of applications, from domestic heating to industrial cogeneration, there are different types of fuel cell technologies to be employed. The fuel cells considered in this paper are the proton exchange membrane (PEMFC), the molten carbonate (MCFC) and the solid oxide (SOFC) fuel cells. In all these systems, heat exchangers play an important and critical role in the thermal management of the fuel cell itself and the boundary components, such as the fuel reformer (when methane or natural gas is used), the air preheating and the fuel cell cooling. In this paper, the impact of heat exchangers on the performance of PEMFC systems and SOFC-MCFC gas turbine hybrid systems is investigated. Several options in terms of cycle layout and heat exchanger technology are discussed from the on-design, off-design and control perspectives. A general overview of the main issues related to heat exchangers performance, cost and durability is presented and the most promising configurations identified.
High Power Density Solid Oxide Fuel Cells for Auxiliary Power Unit Applications
Authors: Draper Robert , DiGiuseppe Gianfranco
Published: October 2008

High Power Density (HPD) Solid Oxide Fuel Cells (SOFC) possess the attributes of reduced ohmic polarization, and greater active area per unit volume, relative to current state-of-the-art circular cylindrical SOFCs’. Several variations of the basic “flattened cylinder” HPD geometry are being analyzed and tested. For example, the HPD10 cell enjoys a 58% gain in power density over current practice. In this variation ten air channels are separated by nine ribs that connect the flat faces of the cell. Other cell geometries and advanced cell materials are under consideration and have the potential for further improvement in power density. This makes the application of HPD SOFCs’ to compact Auxiliary Power Units (APU) attractive. This paper reviews geometric and performance characteristics for HPD cells and presents a conceptual design for an APU of 5 kW net output.
Fuel Cell Power Conditioner for Stationary Power System: Towards Optimal Design From Reliability, Efficiency, and Cost Standpoint
Authors: Mazumder Sudip K. , Burra Rajni K.
Published: October 2008

We describe an energy-efficient, fuel cell (FC) powerconditioning system (PCS) for stationary application, which draws practically zero switching-ripple current from the FC and can potentially meet the $40/kW cost target. The PCS consists of a zero-ripple boost converter (ZRBC) followed by a soft-switched and multi-level high-frequency (HF) inverter and a single-phase cycloconverter. The zero-ripple input inductor significantly reduces the input current ripple which may be necessary to enhance the long-term durability of the fuel cell. A new phase-shifted sine-wave modulation of the multi-level high frequency inverter is proposed which results in the zero voltage turn-on (ZVS) of all four switches (without the use of any auxiliary circuit components). For such a sine-wave modulation technique a > 90 % ZVS range is obtained from 25% of the full load to full load. Further, the line-frequency switching of the cycloconverter (at close to unity power factor) results in extremely low switching losses. The intermediate high voltage DC (HVDC) bus facilitates the inclusion of power systems based on other forms of alternative-energy techniques. A cost effective 1 kW prototype of the proposed PCS is built, which achieved a high overall efficiency. We present a detailed description of the operation of the PCS along with its key features and advantages. Finally, experimental results showing the performance and operation of the PCS are demonstrated.