bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of Solid Oxide Fuel Cell Operation
Authors: Gemmen Randall S. , Johnson Christopher D.
Published: November 2008

The dynamics of solid oxide fuel cell operation (SOFC) have been considered previously, but mainly through the use of one-dimensional codes applied to co-flow fuel cell systems. In this paper a cross-flow geometry is considered. The details of the model are provided, and the model is compared with some initial experimental data. For parameters typical of SOFC operation, a variety of transient cases are investigated, including representative load increase and decrease and system shutdown. Of particular note are results showing cases having reverse current over significant portions of the cell, starting from the moment of load perturbation up to the point where equilibrated conditions again provide positive current. Consideration is given as to when such reverse current conditions might most significantly impact the reliability of the cell.
Design Concepts for Directed Exit Flow in Micro Fuel Cells
Authors: Shi Wei , Lee Sang-Joon
Published: November 2008

Miniature and micro fuel cells continue to advance as promising alternatives for efficient and portable electric power. This paper presents a study of experimental modifications to the exit flow configuration of microchannels used in small proton-exchange-membrane fuel cells. New concepts for exit geometry are presented, which promote effective water removal and provide reactant back-pressure in an efficient and self-contained manner. Cell assembly is designed such that reactants must necessarily flow laterally through the gas diffusion electrodes near the exit, rather than simply pass over the free backside surfaces of these electrodes. Multiple prototypes were produced using microfabrication techniques with channel sizes of 100 and 200 microns, and performance was tested using a hydrogen-air test station with programmable electronic load. One of the new concepts in particular showed a marked improvement from 28 mW/cm2 peak power density under baseline conditions to 37 mW/cm2 for the modified design under similar operating conditions. The design offers an opportunity for higher performance in miniature fuel cells with low gas consumption and no additional cost.
Marine Applications of Fuel Cell Technology
Authors: Yuan Jinliang , Sun Juncai , Sun Penting , Nakazawa Takeshi , Sunde´n Bengt
Published: November 2008

Due to potential benefits of high energy conversion efficiency and low noise/pollution, fuel cells have attracted many application areas. In general, fuel cells can be applied on-board ships as emergency power supply, electric energy generation, power output for propulsion or where appropriate, a combination of these uses. In this paper, a brief summary is presented for various fuel cells and their potential for marine applications. The characteristics and properties of fuel cells are compared with conventional energy systems, such as diesel engines and gas turbines, in terms of efficiency, power density, emissions etc. The significant barriers to implement fuel cell technology into marine applications are identified as well in this study. Fuel and the choice of suitable hydrogen supply are addressed. As a case study, a fuel cell stack applied to a ship propulsion system is discussed in details.
Analysis of the Co-Generation Potential of a 5 kW PEMFC From Experimentally Determined Performance Data
Authors: Do Val L. G. , Orlando A. F. , Siqueira C. E. R. , Oexmann J.
Published: November 2008

A 5 kW proton exchange membrane fuel cell (PEMFC) with a reformer has been installed and tested at the Pontifical Catholic University of Rio de Janeiro (PUC-Rio), Brazil, aiming the experimental determination of its performance and co-generation potential to increase the fuel chemical energy usage. The unit uses a fuel processor to convert energy from natural gas into hydrogen rich reformate. The fuel cell is totally instrumented, supplying data for calculating the overall system efficiency (total efficiency), reformer efficiency, stack efficiency, conversion efficiency (DC/AC), and co-generation potential, at previously set up output powers of 2,5 kW and 4 kW. The paper details the equations required for calculating the parameters, both theoretically, from thermodynamics and electrochemics points of view, and experimentally, from mass and energy balances, comparing the results. Steady state data were taken at 13 different days, resulting in reformer, stack, conversion and total average efficiencies, together with the calculated standard deviation. It was also found that the energy loss in the reformer and in the stack are approximately the same. The co-generation potential was estimated by calculating the heat rejected by the stack and the heat rejected in the reformer, giving a value of 67,5% and 68,9%, respectively for 2,5 kW and 4 kW. Therefore, co-generation can substantially reduce the fuel cell energy cost, and thus increasing the feasibility of its use.
Lessons Learned From Residential Experience With Proton Exchange Membrane Fuel Cell Systems for Combined Heat and Power
Authors: Boettner Daisie D. , Massie Cheryl A. , Massie Darrell D.
Published: November 2008

As part of a one-year Department of Defense demonstration project, proton exchange membrane fuel cell systems have been installed at three residences to provide electrical power and waste heat for domestic hot water and space heating. The 5 kW-capacity fuel cells operate on reformed natural gas. These systems operate at preset levels providing power to the residence and to the utility grid. During grid outages, the residential power source is disconnected from the grid and the fuel cell system operates in standby mode to provide power to critical loads in the residence. This paper describes lessons learned from installation and operation of these fuel cell systems in existing residences. Issues associated with installation of a fuel cell system for combined heat and power focus primarily on fuel cell siting, plumbing external to the fuel cell unit required to support heat recovery, and line connections between the fuel cell unit and the home interior for natural gas, water, electricity, and communications. Operational considerations of the fuel cell system are linked to heat recovery system design and conditions required for adequate flow of natural gas, air, water, and system communications. Based on actual experience with these systems in a residential setting, proper system design, component installation, and sustainment of required flows are essential for the fuel cell system to provide reliable power and waste heat.
Development of Molten Carbonater Fuel Cell at IHI
Authors: Sonoda Shogo , Tooi Masaaki , Matsuyama Toshiya , Murata Nobuhisa
Published: November 2008

Development of a molten carbonate fuel cell (MCFC) has entered the next stage of evolving into commercialization. IHI has been taking part in the Phase III MCFC Development Program in Japan started in 2000. This program has the following development plans. (1) 300 kW class pressurized MCFC power generation system combined with micro Gas turbine. (2) High-pressurized operation technologies and modularization technologies of MCFC which become indispensable to realization of medium- to large-scale MCFC - Gas turbine combined power generation system. At the first step of MCFC commercialization, these systems will be introduced into several hundreds kW cogeneration and several MW distributed power resources. In the future, MCFC will be introduced as substitution of the thermal power plants.
A Comparison Between Life Cycle Assessment of an MCFC System, An LFG-MCFC System, and Traditional Energy Conversion Systems
Authors: Desideri U. , Lunghi P. , Zepparelli F.
Published: November 2008

The present work aims at evaluating the environmental impact caused by fuel cell systems in the production of electric energy. The very low pollutant emission levels in fuel cells makes them an attractive alternative in ultra clean energy conversion systems. Actually, to truly understand the environmental impact related to fuel cells, it is necessary to study their “cradle-to-grave” life, from the construction phase, during the conversion of primary fuel into hydrogen, to its disposal. The tool used in this analysis is the Life Cycle Assessment approach; in particular the environmental impact of a fuel cell system has been simulated through the software SimaPro 5.0. Thanks to this approach, once the critical process regarding the production of energy by fuel cell system, (i.e. the production of hydrogen by natural gas steam reforming), has been determined, an analysis of the use of landfill gas as a renewable source to produce hydrogen was done. Finally, the production of electric energy by fuel cell systems was compared to that by some conventional energy conversion systems. A second comparison was done between the Molten Carbonate Fuel Cell (MCFC) fuelled by landfill gas and natural gas.
A Theoretical Study of the Carbon/Carbonate/Hydroxide (Electro-) Chemical System in a Direct Carbon Fuel Cell
Authors: Hemmes Kas , Cassir Michel
Published: November 2008

Both the hydroxide and the carbonate melt are proposed and tested by researchers trying to develop a DCFC (Direct Carbon Fuel Cell). It is well known that the hydroxide melt is not stable due to the carbon dioxide formed in the fuel cell reaction. The hydroxide ion OH− reacts with CO2 to form carbonate ions and water. From this reaction it is clear that in either approach the melt is a mixture of carbonate and hydroxide depending on the partial pressures of water and CO2 above the melt. Therefore a good insight in the equilibria present in the melts is essential for understanding and optimizing the DCFC. Following the method introduced by Smith and Missen a complete and independent set of equilibria describing the chemical equilibrium in the melt can be obtained using linear algebra6. Using the modification proposed by Coleman and White also electrochemical equilibria are included7. This will be done for the cathode as well as the anode environment of a DCFC.
Advanced Ceramic Fuel Cell R&D
Authors: Zhu Bin
Published: November 2008

Since many years in Swedish national research project and Swedish-Chinese research framework we have carried out advanced ceramic fuel cell research and development, targeting for intermediate and low temperature ceramic or solid oxide fuel cells (ILTCFCs or ILTSOFCs, 300–700°C) based on ceramic-based composite materials. The ceramic composite material developments in Sweden have been experienced from the oxyacid-salts oxide proton-based conductors, non-oxide containment salts, the ceria-based composite electrolytes and nano-composites. Among them the ceria-based composites showed excellent ionic conductivity of 0.01 to 1 Scm−1 and ILTCFCs using these composites as electrolytes have achieved high performances of 200 to 1000 mWcm−2 at temperatures between 400 and 700°C. The excellent ion conduction was resulted from hybrid proton and oxygen ion conduction. The hybrid ion conduction and dual electrode reactions and processes create a new fuel cell system. Advanced ceramic fuel cell aims at developing a new generation to realize the challenges for fuel cell commercialization. This paper reviews our more than 14 years R&D on the field with emphasis on the recent progresses and achievements.
Development of Solid Oxide Fuel Cells and the Component Materials
Authors: Eguchi Koichi , Kikuchi Ryuji
Published: November 2008

In addition to the high conversion efficiency, the solid oxide fuel cell (SOFC) is quite attractive from the viewpoint of fuel flexibility, especially the possibility of internal reforming of methane and other hydrocarbons for power generation. The systems with several kW to tens kW-class modules have been successfully operated and tested in Japan. The SOFC systems with internal steam reforming reaction over a Ni-YSZ anode or pressurized condition have been tested as a suitable operation mode. Methane internal reforming proceeded without deterioration with time, whereas the power generation with ethane and ethylene suffered from carbon deposition even at high steam-to-carbon ratio. Carbon deposition region and equilibrium partial pressure of oxygen in the C-H-O diagram were estimated from the thermodynamic data. Reduced temperature SOFC operation is another approach, especially for small scale applications, in which scandia-stabilized zirconia, lanthanum gallate, or rare earth-doped ceria were employed as candidate for the electrolyte.
PEM Fuel Cell Stack Development: Grafoil Bipolar Materials — A Feasibility Study
Authors: Rajalakshmi N. , Vijay V. , Pandian S. , Dhathathreyan K. S.
Published: November 2008

In the production of Proton Exchange Membrane Fuel Cell (PEMFC) stacks with multiple cell units, graphite has been widely used as a bipolar material. Graphite has excellent electrical conductivity, high electrochemical stability, and good machining characteristics, enabling fine and complex fuel/oxidant flow fields to be used. In spite of the above advantages, search for alternate materials is counting owing mainly to the present requirement of reduced cell volume and weight per power yield (kW) in many applications. Cost reduction for this component and volume production are other driving forces for the continuous thrust in this subject. Flexible (exfoliated) graphite is an alternate material that could meet many of the above requirements. We have made use of flexible graphite to fabricate a PEM fuel cell stack. The flow fields were introduced by stamping. An optimization study has been carried out for the width and depth of the flow field designs in terms of applied pressure to accommodate the resilience of the flexible graphite sheet. The performance of the 500 watts stack fabricated using this material compares well with that fabricated using the conventional graphite plates. However there are some technical issues still to be sorted out which will be discussed.
Modeling the System and Component Performance Interactions of a SOFC Based APU for Changes in Application Load: Transient Response and Control Strategy
Authors: Rancruel D. F. , von Spakovsky M. R.
Published: November 2008

Solid-Oxide-Fuel-Cell (SOFC) stacks respond in seconds to changes in load while the balance of plant subsystem (BOPS) responds in times several orders of magnitude higher. This dichotomy diminishes the reliability and performance of SOFC electrodes with changes in load. In the same manner current and voltage ripples which result from particular power electronic subsystem (PES) topologies and operation produce a negative effect on the SOFC stack subsystem (SS) performance. The difference in transient response among the sub-systems must be approached in a way which makes operation of the entire system not only feasible but ensures that efficiency and power density, fuel utilization, fuel conversion, and system response are optimal at all load conditions. Thus, a need exists for the development of transient component- and system-level models of SOFC based auxiliary power units (APUs), i.e. coupled BOPS, SS, and PES, and the development of methodologies for optimizing subsystem responses and for investigating system-interaction issues. In fact the transient process occurring in a SOFC based APU should be systematically treated during the entire creative process of synthesis, design, and operational control, leading in its most general sense to a dynamic optimization problem. This entails finding an optimal system/component synthesis/design, taking into account on- and off-design operation, which in turn entails finding an optimal control strategy and control profile for each sub-system/component and control variable. Such an optimization minimizes an appropriate objective function while satisfying all system constraints. A preliminary set of chemical, thermal, electrochemical, electrical, and mechanical models based on first principles and validated with experimental data have been developed and implemented using a number of different platforms. These models have been integrated in order to be able to perform component, subsystem, and system analyses as well as develop optimal syntheses/designs and control strategies for transportation and stationary SOFC based APUs. Some pertinent results of these efforts are presented here.
Saccharide Fuel Cell (SFC)
Authors: Schechner Pinchas , Mor Lea , Kimchie Shlomo , Tarabeah Hussein , Dosoretz Carlos , Hemmes Kas
Published: November 2008

A study on the possibility to use saccharides as fuels in a Fuel Cell is presented. The study deals with the abundance of saccharides and ways to extract them from solid organic urban, forest and agricultural wastes, and from food industry effluents. The use of saccharides as fuel is treated from the thermodynamic point of view and compared with other common fuels currently used in fuel cells. Other properties of saccharides, relevant to their use as fuels, such as: safety, transportability, storage, inflammability, poisonous character and volatility, are also considered. The different possible catalytic electrodes needed to create a Saccharide Fuel Cell are discussed. Three options are considered: Microbiological, Enzymatic and Inorganic. None of the available catalytic electrodes has satisfactory performance. We conclude that since sacharides are human friendly, abundant, have high-energy content and are relatively easy to extract, efforts should be given to develop a Saccharide Fuel Cell. These fuel cells have the potential to become the basis of a decentralized power economy and open economical ways to deal with the environmental problems caused by organic wastes. The concept exposed in this paper will be tested in a Pilot-Demonstration Project, planned in the Agan Beit Natufa (ABN) region in Israel. We estimate a production of about 11 GWh/year from this project.
A Novel Approach to Designing Highly Efficient and Commercially Viable Biofuel Cells
Authors: Akers Nick L. , Minteer Shelley D.
Published: November 2008

A biofuel cell is an electrochemical device in which the energy stored in a fuel, such as ethanol, is converted to electrical energy by the means of the catalytic activity of enzymes. Biofuel cells have traditionally suffered from low power densities and short lifetimes due to the fragility of the enzyme catalyst. Utilizing a novel quaternary ammonium salt treated Nafion membrane for enzyme immobilization in a biofuel cell results in increases in power densities and enzyme lifetimes to commercially viable levels. Additionally, this method provides sufficient protection to develop a membrane electrode assembly style (MEA) biofuel cell, an important step for commercialization. Previously, it has not been possible to create a MEA-style biofuel cell due to the denaturing of the enzyme that would occur at the high temperatures experienced during the heat pressing step of fabrication. Quaternary ammonium salt treated Nafion membranes provide sufficient protection for the enzyme to retain activity after exposure to temperatures of 140°C. Thus, a MEA-style biofuel cell can be created. Preliminary results yield biofuel cell MEAs with power densities ranging from 0.15 to 1.49 mW/cm2 and open circuit potentials of 0.360 to 0.599 V.
Polymeric Electrode for Sodium Borohydride Fuel Cell
Authors: Deshmukh K. , Santhanam K. S. V.
Published: November 2008

Reported here is the first example of sodium borohydride fuel cell constructed with electro-active conducting Polycarbazole (Pcz) and oxygen cathode. A Pcz electrode is made by depositing a thin film of the polymer on Stainless Steel (SS) substrate. The multistage oxidation process of borohydride is expected to involve 8e− with borate as the end product. The oxidative process at the Pcz electrode has been examined by Cyclic Voltametry (CV). The direct oxidation of borohydride on SS was not observed in CV; however it is distinctly visible at the Pcz electrode. The borohydride oxidation at the Pcz electrode occurs at Ep = −0.29 V vs. saturated calomel electrode (SCE). The process was studied using scan rates of 10 mV/s to 100 mV/s. The anodic peak current increases linearly with the sweep rate and also with concentration of borohydride, suggesting that the oxidative process is diffusion controlled. The mechanism of borohydride oxidation has been investigated and compared with the oxidation on platinum or gold electrode. The results suggest that the borohydride fuel cell as operating efficiently with the Pcz anode or cathode. Preliminary results will be reported.
A Compact Membrane Reactor for Producing Pure Hydrogen From Anhydrous Ammonia
Authors: Vencill Thomas R. , Chellappa Amand S. , Powell Mike R.
Published: November 2008

A significant barrier to the use of fuel cells for portable and small stationary applications is the lack of a supply of pure hydrogen with high specific energy. Anhydrous ammonia is an attractive fuel because it has very high intrinsic specific energy, requires no water for decomposition, and has established distribution channels throughout the world. A compact membrane reactor hydrogen generation system using anhydrous ammonia as a fuel has been developed which produces greater than 99.95% purity hydrogen at a rate sufficient to power a 100 We PEM fuel cell. Ammonia concentrations in the resultant hydrogen product are non-detectable. Hydrogen recovery through the membrane is as high as 80% and the membrane reactor thermal efficiency (LHV) is 70%. The primary features of this system are a catalytic reactor, a hydrogen separation membrane integrated into the reaction chamber, and a catalytic combustion module to provide heat for the ammonia decomposition reaction and subsequent conversion of trace ammonia reject. The membrane reactor is planar in configuration and allows for a simple, single unit design to provide pure hydrogen for fuel cell applications. The total system can provide specific energies of greater than 500 Wh/kg for a 72 hour run making it an attractive solution of portable and long unattended run time applications.
Development of Methanol Reformer for the Portable PEFC Power System by ITRI
Authors: Lee C. H. , Huang C. H. , Lin C. T. , Liu Y. C. , Chu Hsin-Sen
Published: November 2008

In order to apply the PEFC power generation system in near future, ITRI is cooperating with Taiwanese local electrical company to develop a compact methanol reformer. This methanol reformer can simultaneously catalyze autothermal and steam reforming reactions, depending on the application. Except the catalyst for methanol steam reforming and low temperature water gas shift reactions, ITRI has developed several catalysts for autothermal reforming, high temperature water-gas shift, and CO preferential oxidation reactions. We have integrated these catalysts to assemble a methanol reformer prototype. The characteristics of this methanol reformer operated at steady state are the maximum flow rate of hydrogen being 39 L/min (corresponding to 2.4 kWe), H2 concentration being 45∼65%, CO concentration less than 50 ppm, and the cold startup time less than 35 minutes. In addition, we have been developing a catalyst for methanation reaction. We hope to shorten the start-up time to less than 20 minutes and the volume of the reformer being reduced in half by integrating a good methanation catalyst into my next generation methanol reformer.
Development of a Flexible Pilot High Temperature MEA Manufacturing Line
Authors: Puffer Raymond H. , Hoppes Glen H.
Published: November 2008

Despite the fact that the invention of the fuel cell is more than 160 years old, the fuel cell industry today is still in its infancy. While there are many large companies active in the industry, it is, for the most part, dominated by many small and startup companies focused on the design and development of fuel cell systems. Relatively little attention has been given to the cost effective high-volume (i.e., automated) manufacture of the resulting systems and components. If the wide spread commercial use of fuel cells is to become a reality, and we are to realize the potential benefits to our environment and mankind it is essential that we also put the appropriate level of attention on the enabling manufacturing technologies. Celanese Ventures GmbH is a “new venture” arm of Celanese AG, located in Frankfurt, Germany. They are focused on developing the market for their high temperature polybenzimidazole (PBI®)-based membrane material for use in Proton Exchange Membrane (PEM) fuel cells. Several years ago Celanese realized that the best way to ensure the market for their membrane material is to develop the capability to produce complete membrane electrode assemblies (MEAs) that can be incorporated into fuel cell systems being developed by other companies. Furthermore, such value-added processing can be economically advantageous. This paper will describe the multi-phased collaboration between Celanese, the Flexible Manufacturing Center (FMC) located at Rensselaer Polytechnic Institute (RPI), and Progressive Machine and Design (PMD) to develop a fully automated high temperature MEA pilot manufacturing line that began operation in September, 2002. The FMC has and continues to serve in a unique role for a university research center. The FMC has been involved in the concept development, laboratory proof of principle, acquisition management, technical representation during the design, build and implementation phases, and the ongoing optimization of and improvements to the operational pilot line. We will describe the unique properties of the high temperature PBI® membrane and the benefits of this form of membrane in PEM fuel cell operations. The specific role of the FMC during each phase of the project will be highlighted, and a description of the resulting pilot line will be provided. Finally, we will discuss the important role that effective technology transfer plays in a project with the magnitude and complexity described herein.
The Effects of Porosity Distribution Variation in GDL on PEM Fuel Cell Performance
Authors: Roshandel R. , Farhanieh B. , Saievar-Iranizad E.
Published: November 2008

Gas diffusion layers are one of the important parts of the PEM fuel cell as they serve to transport to transport the reactant gases to the catalyst layer. Porosity of this layer has a large effect on the PEM fuel cell performance. The spatial variation in porosity arises due to two effects: 1. Compression of the electrode on the solid landing areas and 2. Water produced at the cathode side of gas diffusion layers. Both of these factors change the porosity of gas diffusion layers affects fuel cell performance. To implement this performance analysis, a mathematical model which considers oxygen and hydrogen mass fraction in gas diffusion layer and the electrical current density in the catalyst layer, and the fuel cell potentials is investigated. The porosity variation in the GDL is calculated by considering the applied pressure and the amount of the water generated in the cell. The validity of the model is assessed by comparing the computed results with experimental data. The obtained results show that the decrease in the average porosity causes the reduction in oxygen consumption, so that a lower electrical current density is generated. It is also shown that when the electrical current density is low, the porosity variation in gas diffusion layer has no significant influence on the level of polarization whereas at higher current density the influence is very significant. The porosity variation causes non-uniformity in the mass transport which in turn reduces the current density and a lower fuel cell performance is obtained.
Effect of Fuel Cell Operation Pressure on the Optimization of a Hybrid System SOFC/Turbine for Cogeneration
Authors: Karvountzi Georgia C. , Price Clifford M. , Duby Paul F.
Published: November 2008

A solid oxide fuel cell (SOFC) integrated in a hybrid system with a gas turbine can achieve lower heating value (LHV) power of efficiencies of about 70%. Given the high operating temperature of the SOFC, it produces high grade heat, and a hybrid system designed for cogeneration may achieve total LHV efficiencies of 78% of 80% without post combustion and 85%–88% with post combustion. The present paper illustrates the optimum integration of a tubular solid oxide fuel cell in a cogeneration cycle with a multiple pressure heat recovery steam generator (HRSG) and a back pressure steam turbine. We considered fuel cells of 7.5 MW, 9 MW, 15 MW, 15 MW, 18 MW, 22.5 MW and 27 MW by scaling up published data for a 1.2 MW tubular solid oxide fuel cell. The operating pressures were 3 and 9atm. We used GateCycle™ heat balance software by GE Enter Software, LLC, to design a 20–40 MW high efficiency cogeneration plant. We performed a calculation of the heat balance of the fuel cell stack in Microsoft® Excel and then we imported the results into GateCycle™. We developed curves showing LHV “electric” efficiency versus power for different ratios of “fuel cell-to-gas turbine size”. Pressurization has a positive impact on the fuel cell polarization curve leading to higher power output. The gain in electric power, however, is offset by the additional power requirement of the compressor at higher pressures. Our analysis shows that an optimum pressure of about 9 atmospheres results in an overall hybrid system power efficiency of about 70% and a LHV “cogeneration” efficiency of about 80%. In conclusion, high efficiencies are obtained by optimization of a hybrid system consisting of pressurized high temperature fuel cells with gas turbines and a steam turbine.
Evaluation of an Alkaline Fuel Cell for Multi-Fuel System
Authors: Verma A. , Jha A. K. , Basu S.
Published: November 2008

The performance of an alkaline fuel cell is investigated using three different fuels, e g., methanol, ethanol and sodium borohydride. Pt/C/Ni was used as anode whereas Mn/C/Ni was used as standard (Electro-Chem-Technic, UK) cathode for all the fuels. Thus, the alkaline fuel cell is used for multi-fuel system. Fresh mixture of electrolyte, potassium hydroxide (5M), and fuel (2M) was fed to and withdrawn from the AFC at a rate of 1 ml/min. The anode was prepared by dispersing platinum and activated carbon in Nafion® (DuPont USA) dispersion and placing it onto a carbon paper (Lydall, USA). Finally prepared anode sheet was pressed onto Ni mesh and sintered to produce the required anode. The maximum power density of 16.5 mW/cm2 is obtained at 28 mA/cm2 of current density for sodium borohydride at 25 °C. Whereas, methanol produces 31.5 mW/cm2 of maximum power density at 44 mA/cm2 of current density at 60 °C.
Performance of a Novel Combined Cooling and Power Gas Turbine With Water Harvesting
Authors: Khan J. R. , Lear W. E. , Sherif S. A.
Published: November 2008

A thermodynamic performance analysis is performed on a novel cooling and power cycle that combines a semi-closed cycle gas turbine called the High Pressure Regenerative Turbine Engine (HPRTE) with an absorption refrigeration unit. Waste heat from the recirculated combustion gas of the HPRTE is used to power the absorption refrigeration unit, which cools the high-pressure compressor inlet of the HPRTE to below ambient conditions and also produces excess refrigeration, in an amount which depends on ambient conditions. The cycle is modeled using traditional one-dimensional steady-state thermodynamics, with state-of-the-art polytropic efficiencies and pressure drops for the turbo-machinery and heat exchangers, and accurate y correlations for the properties of the LiBr-water mixture and the combustion products. Water produced as a product of combustion is intentionally condensed in the evaporator of the vapor absorption refrigeration system. The mixture properties of air account for the water removal rate. The vapor absorption refrigeration unit is designed to provide sufficient cooling for water extraction. The cycle is shown to operate with a thermal efficiency approaching 58% for a turbine inlet temperature of 1400 °C in addition to producing about 0.45 liters of water per liter of fuel consumed. Also at the above operating condition the ratio of the refrigeration effect to the net work output from the system is equal to 0.8. The ratio of mass of water extracted to the mass of fresh air inlet into the combined cycle is obtained for different values of cycle parameters, namely turbine inlet temperature, recuperator inlet temperature and the low pressure compressor ratio. The maximum value of this ratio is found to be around 0.11. It is found that it is a strong function of the recirculation ratio and it decreased by 22% as the recirculation ratio is decreased by 70%. The thermodynamic impacts of water extraction on the system performance are also discussed. Based on these results, and prior results, which showed that the HPRTE is very compact, it appears that this cycle would be ideally suited for distributed power and vehicle applications, especially ones with associated air conditioning loads.
A Performance Diagnosis of the 1939 Heinkel He S3B Turbojet
Authors: Rodgers C.
Published: November 2008

The historical development of the world’s first pure jet propelled aircraft, the Heinkel He 178, and its turbojet the He S3B has been extensively documented, however only limited descriptions of the engine and component aero-thermo-dynamic performances have, as yet, been published in open English literature. The basic He S3B engine flowpath configuration of a radial compressor mounted back-to-back with a radial inflow turbine, intrigued the author as one excellent example of the pre WW11 radial turbomachinery ingenuity and expertise, to the extent that it prompted this diagnosis. Recognizing that some of the historically quoted HeS3B performance data may be dubious, attempts have been made to coalesce data from multiple sources into a more consistent account by conducting a detailed engine performance analysis. HeS3B engine performance characteristics are recreated based upon predicted meanline component maps derived from engine drawings and supporting data recently published by AIAA in his biography “Dr Hans von Ohain — Excellence in Flight”. Predicted engine performance parameters at both a five minute and maximum continuous rating are itemized, together with thrust/rpm/temperature variations at part speed conditions.
A Novel Cooling Method for Turbine Rotor-Stator Rim Cavities Affected by Mainstream Ingress
Authors: Okita Y. , Nishiura M. , Yamawaki S. , Hironaka Y.
Published: November 2008

A combined experimental and numerical study of interaction between cooling flow and mainstream gas flow in a turbine rotor-stator rim cavity is reported. Particular emphasis is put on the flow phenomena in a rim cavity downstream of rotor blades. The experiments are conducted on a rig simulating a engine HP-turbine in which cooling effectiveness distributions as well as velocities, turbulence quantities, pressure and temperature profiles are measured. Numerical calculation, especially at a full 3D, unsteady solution level, can lead to satisfactory predictions in fluid and mass transfer inside the cavity. Both experimental and numerical results indicate that large turbulence stresses near the rotor disk intensify turbulent diffusion across the cavity and consequently axial distribution of the cooling effectiveness inside the cavity becomes uniform. In order to obtain an adequate distribution of cooling effectiveness across the rim cavity and to suppress the turbulence level near the rotor surface for more efficient cooling, a novel cooling method is developed using numerical simulation. The disk-front and -rear cavities are then redesigned according to the new cooling strategy and integrated in the test rig. Experimental results verify a significant advance in cooling performance with the new method.
Experimental and Numerical Investigation Into the Unsteady Interaction of Labyrinth Seal Leakage Flow and Main Flow in a 1.5-Stage Axial Turbine
Authors: Giboni A. , Wolter K. , Menter J. R. , Pfost H.
Published: November 2008

This paper presents the results of experimental and numerical investigations into the flow in a 1.5-stage low-speed axial turbine with a straight labyrinth seal on the rotor shroud. The paper focuses on the time dependent interaction between the leakage flow and the main flow. The experimental program consists of time accurate measurements of the three-dimensional properties of the main flow. The region of the entering leakage flow downstream of the rotor trailing edge was of special interest. The measurements were carried out using pneumatic five-hole probes and three dimensional hot-wire probes at the design operating point of the turbine. The measurement planes behind the three blade rows extend over one pitch from the shroud to the casing. The complex three-dimensional flow field is mapped in great detail by 1,008 points per measurement plane. The time-accurate experimental data of the three measurement planes was compared with the results of unsteady, numerical simulations of the turbine flow. The 3D-Navier-Stokes Solver CFX-TASCflow was used. The experimental and numerical results correspond well and allow detailed analysis of the mixing process. As demonstrated in this paper, the leakage flow causes strong fluctuations of the secondary flow behind the rotor and the second stator. Above all, the high number of numerical grid points reveals both the secondary flow phenomena and the vortex structures of the mixing zone. The time-dependence of both position and intensity of the vortices is shown. The development of the important leakage vortex is illustrated and explained. The paper shows that even at realistic clearance heights the leakage flow gives rise to negative incidence of considerable parts of the downstream stator which causes the flow to separate. Thus, labyrinth seal leakage flow should be taken properly into account in the design or optimization process of turbomachinery.
Application of GPA to Combined Cycle Gas Turbine Plants
Authors: Zwebek A. I. , Pilidis P.
Published: November 2008

This paper investigates the possibility of applying a new technique called Gas/Steam Path Analysis (GSPA), that is based on the principles of Gas Path Analysis (GPA), to gas as well as steam turbine plants (as one unit) that are main parts of a combined cycle power plant by way of simulation. In order to facilitate this investigation two pieces of software were developed at Cranfield University. With this technique, it was possible to monitor the major components of the combined cycle, and hence predict the faults that may occur within the cycle beforehand. Faults looked at were, fouling and erosion of gas and steam turbine units, heat recovery steam generator degradation (scaling and/or ashe deposition), and condenser degradation. The obtained results from GSPA calculations of the cases investigated showed that “GSPA” technique can be equally applied to either gas turbine cycle, steam turbine cycle, or to the combination of the two in a form of combined cycle. The procedure, assumptions made, and the results obtained are presented and discussed herein.
Development of Higher Temperature Abradable Seals for Gas Turbine Applications
Authors: Chupp Raymond E. , Lau Yuk-Chiu , Ghasripoor Farshad , Baldwin Donald J. , Ng Chek , McGovern Tara , Berkeley Dalero
Published: November 2008

Improving sealing between rotating and stationary parts in industrial turbines can significantly increase unit performance. Abradable seals are being developed to reduce blade-tip clearances where an abradable material is placed on the stationary shroud or casing opposite the rotating blade tips to reduce clearances with minimum risk to the turbine components during rubs. A newly developed metallic abradable material is a thermally sprayed coating on the first stage of gas turbine shrouds to reduce tip clearances; thereby, improving turbine power and efficiency by about 1/2 percent. This material is an improvement over currently available metallic abradables increasing the maximum operating temperature from 750°C to about 950°C with no special treatments required on the rotating blade tips. Initial engine field tests have shown the new material to be abradable and on target to meet life requirements.
Surge Cycle of Turbochargers: Simulation and Comparison to Experiments
Authors: Schmitz M. B. , Fitzky G.
Published: November 2008

The turbocharger test facility can be operated in two different modes. In the first mode, the turbocharger turbine is driven by an external blower and a combustor. The compressor blows off through the chimney. In the second mode the turbocharger is operated similar to a gas turbine: the turbine drives the turbocharger compressor which pressurizes the combustion chamber. This study is focused on the surge cycle of the turbocharger for both operation modes of the test facility. The turbocharger has to withstand surge for all pressure ratios it is designed for without damaging the test rig. Especially for small compressors large plenum volumes can cause such damages. The dynamical model of the system is developed based on the work done by Greitzer [5], [6] and has been extended to the special requirements of the turbocharger test rig. For the components of the turbocharger a quasi-steady behavior with respect to the time scales of the surge cycle is assumed. Consequently, the experimentally obtained steady state characteristics for both compressor and turbine are applied to the model. In order to describe the compressor behavior for backflow conditions, the compressor map is extended for negative mass flow. The theoretical model is calibrated on experimental data. Thereafter the model is used to predict the surge cycle for different operation conditions. For the two operation modes, the blow-off and the recirculation operation, the time resolved values of static pressure and speed oscillation were recorded and compared to the theoretical predictions.
Finite Element Model Updating in the Vibration of Bladed Disk: Shaft Assemblies
Authors: Irwanto B. , Schmidt Rolf , Pawandenat D. , Hardtke H.-J.
Published: November 2008

This work provides a preliminary study of finite element model updating in bladed disk-shaft assemblies. The use of finite element method has been widely found and accepted in engineering analysis. However, the limitations of numerical modeling, in this case finite element model, cannot be avoided. The approach of numerical modeling is limited by the assumptions made in the development such as insufficient information on material, geometry etc. Hence, model updating is required to improve the modeling results. Since model updating involves experimental results, the measurement limitations also affect the accuracy of updated model. In this paper, a model updating technique is applied to study mistuned bladed disks. Important parameters for model updating are discussed and the updating process is carried out on an industrial radial blisk. By using the model updating technique, the model of mistuned bladed disk can be enhanced.
A Parametric Study of Interstage Injection on GE Frame 7EA Gas Turbine
Authors: Bagnoli M. , Bianchi M. , Melino F. , Peretto A. , Spina P. R. , Bhargava R. , Ingistov S.
Published: November 2008

In recent years, among various available inlet air cooling techniques for gas turbine power enhancement, high pressure fogging has seen an increasing attention mainly because of its comparatively low initial investment cost and less downtime for its installation. The various fogging strategies such as inlet evaporative, overspray (or wet compression) and interstage injection have been implemented in simple and combined cycle applications. Unlike wet compression, air at the compressor inlet is not fully saturated with the interstage injection. However, both wet compression and interstage injection involve multi-phase flow and water evaporation during the compression process. The phenomenon of two phase flow compression in axial compressor is not yet fully understood. This paper investigates effects of interstage injection on the performance of a GE Frame 7EA gas turbine using aero-thermodynamic modeling. In addition to estimating the overall gas turbine performance changes achievable with the interstage injection approach, the study presented here discusses impact of interstage injection on the stage-by-stage compressor performance characteristics of the selected gas turbine. The plausible reasons for the observed performance changes are discussed.
A Novel Approach to Mechanism Reduction Optimisation for Aviation Fuel/Air Reaction Mechanism Using a Genetic Algorithm
Authors: Elliott L. , Ingham D. B. , Kyne A. G. , Mera N. S. , Pourkashanian M. , Wilson C. W.
Published: November 2008

This study presents the use of a genetic algorithm to produce a new reduced chemical kinetic reaction mechanism to simulate aviation fuel combustion under various operating conditions. The mechanism is used to predict the flame structure of a aviation fuel/O2/N2 flame in both spatially homogeneous and one-dimensional premixed combustion. Complex hydrocarbon fuels, such as aviation fuel, involve large numbers of reaction steps with many species. As all the reaction rate data is not well known, there is a high degree of uncertainty in the results obtained using these large detailed reaction mechanisms. In this study a genetic algorithm approach is employed for determining new reaction rate parameters for a reduced reaction mechanism for the combustion of aviation fuel/air mixtures. The genetic algorithm employed incorporates both perfectly stirred reactor and laminar premixed flame data in the inversion process, thus producing an efficient reaction mechanism. This study provides an optimised reduced aviation fuel/air reaction scheme whose performance in predicting experimental major species profiles and ignition delay times is not only an improvement on the starting reduced mechanism but also on the full mechanism.
Measurement of Air Film Damping Effectiveness
Authors: Mathison R. M. , Dunn M. G. , Weaver M. M. , Dushko A.
Published: November 2008

Air film damping systems have attracted considerable interest within the gas turbine industry because of their effectiveness at controlling modes of vibration without environmental limitations. Though still in the early stages of development, air film dampers have promise for improving the high cycle fatigue characteristics of solid gas turbine airfoils. This study used experimental methods to compare the vibrational response of a solid flat plate with the response of an identically sized plate that incorporated an air film damper. It also investigated the influence of elevated pressures on air film damping effectiveness, the impact of the damper on the various vibration modes, and the relative strain levels of the air film cover plate to the solid backing. The results show that the air film damper is very effective in controlling the Two-Stripe Mode for which it was designed. Increasing the surrounding air pressure makes the damper more effective and shifts the ressonant frequencies lower.