bluuebunny/crossref_metadata_2025 huggingface dataset:
Haemodynamics of Disturbed Flow Under Variable Shear Rate Effect
Authors: Alshorman Abdullah A.
Published: November 2008

The local blood haemodynamics at curvatures and branches of the arteries system has a crucial role in controlling the localization of blood cells (i.e., leukocytes and platelets) at these sites and at sites of inflammation or vascular injuries respectively. Commonly, the local flow has different shapes of flow separation, recirculation, and non uniform shear stress distribution. To investigate these mechanisms, simulation of cell rolling and adhesion has been performed under variable position shear rate to determine the ranges of shear rates that allow for either adhesion or rolling. The results demonstrate that the cell had the three stages of cell-surface interactions (capture, adhesive rolling and secondary adhesion) when it starts at low shear rate G = 9.06 s−1. Nevertheless, at higher shear rate (i.e., 41.12 and 85.32 s−1) the cell rolls slowly for short time before its rolling velocity gradually increases to reach a maximum value as the shear rate gets higher. On the other hand, cell adhesion is dominant within the distance between the step and the stagnation point; such that the cells in this range rolsl shortly in the direction of shear rate then adheres to the surface.
An Effective Approach for Dynamic Analysis of Rovers
Authors: Meghdari A. , Karimi R. , Pishkenari H. N. , Gaskarimahalle A. L. , Mahboobi S. H.
Published: November 2008

In this paper a novel approach to dynamic formulation of rovers has been presented. The complexity of these multi-body systems especially on rough terrain, challenged us to use the Kane’s method which has been preferred to others in these cases. As an example, symbolic equations of a six-wheeled rover, named CEDRA Rescue Robot which uses a shrimp like mechanism, have been derived and a simulation of forward and inverse dynamics has been presented. Due to the clear form of equations, each term defines a physical meaning which represents the effect of each parameter, resulting in a framework for performance comparison of rovers. Although the method has been described for a 2-D non-slipping case, it is also very useful for dimensional and dynamical optimization, high speed motion analysis, and checking various control algorithms. Furthermore, it can be extended to 3-D cases and other complicated mechanisms and rovers while conserving its inherent benefits and adding to it the easiness of handling nonholomonic constraints.
Finite Analysis of Effectiveness of Viscoelastic Damping Pockets and Sinks
Authors: Butler Nigel D. , Oyadiji S. Olutunde
Published: November 2008

This paper looks at the use of viscoelastic damping pockets and ‘damping sinks’ to suppress structural vibration. These are in the form of holes, slots and cavities filled with a viscoelastic material. The benefits of these designed-in damping treatments are highlighted and discussed. Also the vibration response of viscoelasticly-damped beams is predicted using the finite element method. A series of cantilevered beams are considered and the damping performance of several designed-in dampers are compared to traditional CLDs. It is shown that the effectiveness of the damping pockets and sinks depends on their location and size with respect to the highly stressed regions of the beams. Although there is a practical limit on the sizes of the geometrical features that can be designed-in, it is shown that if located correctly the damping pockets and sinks can be more effective at suppressing structural vibration than traditional CLD treatments.
Identification of a Simulated Continuous Structure With Discrete Non-Linear Components Using an Extended Modal Model
Authors: Platten Michael F. , Wright Jan R. , Cooper Jonathan E.
Published: November 2008

In this paper a method capable of the identification of non-linear structures with many degrees of freedom is presented. The Non-Linear Resonant Decay Method achieves this by identifying an underlying linear modal model for the system. Force appropriation is then used to apply sinusoidal bursts to the structure at high levels of force. The system responses to these bursts are used in a regression analysis in modal space to yield a limited number of additional non-linear terms. The method is applied to a simulated continuous system representing a wing/engine structure with discrete non-linear components at the engine attachment points. The resulting identified non-linear modal model is used to generate response data which are compared with responses from the original system.
Some Innovative Readily Applicable Proposals for Chemical Separation and Sequestration of CO2 Emissions From Power Plants
Authors: Fiaschi Daniele , Manfrida Giampaolo , Massini Michela , Pellegrini Giacomo
Published: November 2008

The goal of the present manuscript is the investigation of two novel systems for partial CO2 capture from the exhausts of fossil fuelled powerplants. These systems should be relatively cheap and easily applicable to existing powerplants with minor modification, in order to make them accessible by a large range of users and favour a significant diffusion of partial CO2 sequestration. Two basic processes were proposed: 1. Absorption with a liquid solution of water and NH3; 2. Absorber/desorber system with a liquid solution of water and phosphates. In the first one, the exhausts react into an absorber column with a liquid sorbent, which is a solution of water and ammonia. The process sequestrates the CO2 in carbammate and bicarbonate and the final product are salt of ammonia, i.e. ammonium carboamate (NH4HCO3) and ammonium bicarbonate (NH4NH2COO). The outgoing streams of this process are the exhaust gas with a reduced content of CO2 and a secondary product formed by salts of ammonium, which have an interesting market potential as fertilizers. The obtained CO2 reduction level was more than 40%, while the amount of secondary products is high enough to get it marketable. In the second process, the exhausts passing through an absorber column react with a liquid sorbent, which is a solution of water and sodium (or potassium) phosphate. The process sequestrates the CO2 in bicarbonate ions by means of the ions phosphate and the outlet stream is a solution of water and phosphate and carbonate ions. This stream is collected in a desorbing column, where the phosphate ions are almost completely regenerated. The CO2 reduction level is always higher than 20% and it can also reach very high values, depending on the parameters of process.
Wear of HFACVD Diamond Coated Tools in Turning of MMC
Authors: Boschetto A. , Veniali F.
Published: November 2008

HFACVD (Hot Filament Assisted Chemical Vapour Deposition) is a typical technology which permits the coating of soft materials with hard or super hard layers which lead to ultra wear resistant tools. Typical tools obtained with this technology are based on a diamond layer. Unfortunately, these tools are not suitable for machining of ferrous alloys due to chemical issues, yet their use is very promising in the machining of composites based on aluminium matrix and reinforced with alumina or silicon carbide. In this paper HFACVD diamond coated, WC and PCD tools are used in turning of Al2O3/Al composites until they are completely worn out. The results show that the diamond tools can be competitive with both the WC and PCD ones in the industrial applications.
Relevant Geometric Features in the Percussion Laser Microdrilling of Different Alloys
Authors: Bassani Paola , Capello Edoardo , Gallus Enrico , Gariboldi Elisabetta , Longoni Luca , Previtali Barbara
Published: November 2008

In the recent decade the laser drilling process has continually attracted new interests and has found increasing applications in the industry. Nowadays the most common industrial laser sources for laser drilling are the solid state ones with pulse length of the order of milliseconds, even if nanosecond and femtosecond pulse sources can also be found in industrial applications. The latter, short and ultrashort laser sources, are very promising since they are expected to generate the hole directly by vaporisation, leaving the hole surfaces free of molten and resolified layer, as well as very low amount of spatter. This paper reports an experimental study on microhole laser machining and on influence of some process parameters on the hole shape. The laser source used in the study was a pulsed, diode pumped, Q-switched Nd:YAG laser. The materials investigated were four different alloys (AISI 304 stainless steel, cp titanium, CuZn35 brass and IN718 alloy), provided as 0.5 mm thick commercial sheets. Since an experimental approach has been here preferred, the performed experimental plan has been designed by the analysis of variance technique. The influence of material type, as well as laser process parameters, like pulse frequency and pulse energy, have been investigated. Relevant geometrical features, like top and bottom hole diameter, taper angle, top and bottom aspect ratio, have been measured and analysed. Moreover, the geometric features of the top spatter as well as the metallurgical characteristics of heat affected zone has been investigated. The results have shown that pulse energy strongly affects both geometric and metallurgical hole features. On the other hand, pulse frequency does not seem to influence the hole shape in all material. The presence of spatter and metallographic analysis confirmed the production of molten layers in all material mainly around the hole entrance.
Investigation of Critical Stresses of a Single Lap-Jointed Cantilevered Beam
Authors: He Xiaocong , Oyadiji S. Olutunde
Published: November 2008

The stress distribution along the whole single lap-jointed cantilevered beam has been investigated using the 3-D linear elastic finite element method. Specifically, finite element solutions of the stress distributions in the bonded section have been obtained for four typical characteristics of adhesives. The FE analyses results indicated that there are stress gaps existing at the lower interface and the upper interface for the stress components S11, S22, S12 and S13: the bigger the shore hardness of the adhesive, the smaller the stress gaps. The FE analyses results also indicated that the stress field in the whole single lap-jointed cantilevered beam is dominated by the normal stresses components S11, S33 and the shear stress component S13. The stress component S11 is the biggest component in the order of magnitude but S33 is potentially the most dengerous component because it is associated with the peel stress which is the enemy of bonded joints. The numerical results show that the stress ratios are different for different stress components as well as different adhesives. However the stress ratios of the two ends of the bonded section are nearly same.
Thermal Modeling of a PEM Fuel Cell
Authors: Fagley John , Gu Wenbin , Whitehead Lee
Published: November 2008

Mathematical modeling of fuel cells can take place at many different levels of detail, from simplified spreadsheet representations to detailed CFD (computational fluid dynamics) models. All of these levels are utilized within General Motors Corporation Fuel Cell Activities. This paper describes the development and application of a model used for analysis of the thermal aspects of a PEM fuel cell. The model domain is a single cell in a fuel cell stack, which is broken into between ten and two hundred control volumes. Each control volume includes eleven lumps; one each for anode, cathode and coolant streams, three for diffusion media/membrane electrode assembly (DM/MEA), four for the cathode portion of the bipolar plate, and four for the anode portion of the bipolar plate. The resulting simulation has the following features; (1) Unlike most CFD representations which typically contain hundreds of thousands or even millions of elements, the model described here does not solve the equations of motion to determine velocity profiles in the anode, cathode or coolant channels. Rather, the flow rates in the anode and cathode flow fields are specified by the user. Typically, uniform flow profiles are assumed, although maldistributed flows may be specified as well. (2) By using between ten and two hundred control volumes, the model can represent the spatial variations of RH (relative humidity) and temperature, (3) The relatively low computational overhead of the modeling approach described here (as compared to a more detailed CFD approach) facilitates dynamic simulation of the cell, i.e. transient thermal response of the system can be simulated, (4) Heat effects simulated include heat released by electrochemical reaction, convection from the fluid streams to the solid lumps (DM/MEA, cathode and anode plates), and conduction in the bipolar plates. This paper also describes some of the ways the model has been used to analyze thermal aspects of fuel cell operations; (1) Sensitivity of the temperature difference between the DM/MEA and coolant plate thermal conductivity and contact resistance, and (2) Impact of coolant flow field (cross-flow and co-flow) on cathode RH. Other potential applications of this type of model are also outlined, including modeling of the cell during transient operation, and start-up.
Combining CFD and Stress Models for PEM Cells: Initial Development
Authors: Martinez-Baca Carlos , Travis Rowland
Published: November 2008

The aim of this work is to determine the relationship between the operational characteristics of a Polymer Electrolyte Membrane (PEM) fuel cell, and the relevant materials issues and in particular mechanical stresses that develop. A three dimensional, non-isothernal, single phase model of a single channel PEM fuel cell is developed to investigate the impact of temperature variation on the Membrane Electrode Assembly (MEA). The model accounts for heat transfer in solids as well as in the multi-component mixture of gases, convection and diffusion of different species in the porous electrodes and the channels, electrochemical reactions and transport of water and ions through the PEM. This model has been numerically implemented in a commercial Computational Fluid Dynamic (CFD), finite volume based code. Temperature contours derived from the model were then exported to a commercial Finite Element (FE) code to analyse the relevant mechanical issues of the PEM and in particular thermomechanical stresses that develop. Initial results verify that, even considering the polymer electrolyte membrane in isolation with mechanically free boundary conditions, there is a significant temperature difference leading to tensile stresses of up to 2.1 MPa within the membrane.
Performance Characterization of Solid-Oxide Electrolysis Cells for Hydrogen Production
Authors: O’Brien J. E. , Stoots C. M. , Herring J. S. , Lessing P. A.
Published: November 2008

An experimental study has been completed to assess the hydrogen-production performance of single solid-oxide electrolysis cells operating over a temperature range of 800 to 900°C. The experiments were performed over a range of steam inlet partial pressures (2.3 – 12.2 kPa), carrier gas flow rates (50–200 sccm), and current densities (−0.75 to 0.25 A/cm2) using single electrolyte-supported button cells of scandia-stabilized zirconia. 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. Values of area-specific resistance and hydrogen production rate are presented as a function of current density. Cell performance is shown to be continuous from the fuel-cell mode to the electrolysis mode of operation. The effects of steam starvation and thermal cycling on cell performance parameters are discussed. Laboratory capabilities are currently being expanded to allow for testing and characterization of multiple-cell electrolysis stacks. Some fundamental differences between the fuel-cell and electrolysis modes of operation have been summarized.
Mathematical Modeling of an Internal-Reforming, Carbonate Fuel Cell Stack
Authors: Ma Zhiwen , Blanchet Scott , Venkataraman Ramki , Iaccarino Gianluca , Moin Parviz
Published: November 2008

The objective of this work is the development of a practical computational model of a carbonate fuel cell stack. Previously published carbonate fuel cell models have focused more on the fundamental mechanisms of fuel cell operation than on evaluation of practical fuel cell product designs. Efficient development of a fuel cell product requires a predictive tool that couples all the important mechanisms with the capability to evaluate the performance of many design iterations quickly. The important mechanisms typically include three dimensional fluid flow, heat and mass transfer, gas-phase and surface chemistry, electrochemistry and structural mechanics. For large-scale fuel cell with applications in the power generation industry, thermal management is of significant interest for stack performance, reliability and life. Minimizing peak cell temperatures improves cell life and minimizing stack temperature gradients reduces stack thermal stress and improves cell performance. In this paper, the fuel cell model is presented along with experimental data validating its accuracy and predictive capabilities. The tool has proven to be a valuable asset for design evaluation and optimization of fuel cell stack designs at FuelCell Energy.
Energy Recovery From Wastewater Treatment Biogas: Integration of an Anaerobic Digester With a High Temperature Fuel Cell
Authors: Lunghi Piero , Bove Roberto , Cerluini Emiliano , Moreno Angelo
Published: November 2008

Wastewater treatment facilities operating with anaerobic digesters produce a methane-rich gas as by-product of the process. In most cases, this gas is released into the atmosphere, thus increasing the greenhouse effect, due to the presence of methane. At the same time, the methane content makes the biogas an interesting source of energy. An efficient energy recovery presents the dual benefits of reducing greenhouse gas emissions and of producing a usable form of energy (typically electric current or heat), using a renewable source of energy, thus diminishing fossil fuel consumption. Due to the high operating temperature, Molten Carbonate Fuel Cells (MCFCs) and Solid Oxide Fuel Cells (SOFCs) present the advantage of being able to operate with a wide variety of fuels, of achieving high energy efficiency and of releasing near-zero emissions. In the present study, the possibility of integrating an anaerobic digester with a high temperature fuel cell is presented. The result of the study illustrates the options, opportunities and the relative benefits and disadvantages related to this energy recovery option.
Dynamic Modeling and Simulation of a Hybrid Fuel Cell/Gas Turbine Power Plant for Control System Development
Authors: Ghezel-Ayagh Hossein , Lukas Michael D. , Junker S. Tobias
Published: November 2008

This paper presents dynamic modeling and simulation results for a Fuel Cell/Turbine Hybrid Power System and describes the overall use of modeling/simulation as a tool in the design of advanced controllers for Fuel Cell/Turbine systems. The simulation includes representation of the fuel cell stack integrated with balance-of-plant, including microturbine generator and heat recovery. A conventional control system based on PID controllers is also represented. Motivation for this work is to help sustain and enhance commercial viability of hybrid systems by operating them at maximum possible reliability, efficiency, and load range.
Multi-Scale Analysis of Transport Phenomenon Inside the SOFC Using MD and CFD Techniques
Authors: Cheng C. H. , Chang Y. W. , Hong C. W.
Published: November 2008

This paper analyzes the transport phenomenon of a solid oxide fuel cell (SOFC) from micro and macro aspects. The micro-scale model focuses on the ion hopping transportation inside the solid electrolyte and the macro-scale model aims at the flow phenomenon and thermal management inside the diffusion layers and the flow channel. In SOFCs, oxygen ions are conducted through the ceramic membrane of Yttria-Stablized Ziconia (YSZ), which is composed of ZrO2 and Y2O3. This paper uses molecular dynamics (MD) method to evaluate the ion conductivity of the solid electrolyte. Doping with different percentage of Y2O3, the ion hopping simulation shows that about 8 mole % gives the optimal performance. Also the higher the operation temperature, the better the ion conduction. Temperature field management is also a critical issue in the SOFC design. A set of three-dimensional computational fluid dynamics (CFD) model (including mass, momentum, energy and concentration equations) inside the porous diffusion layers and the flow channel of the SOFC were employed to estimate the cooling effect under different pattern of flow channel designs. All simulation results were validated with experiments reported from other literatures. The integration of the micro and macro-scale analyses proves to be versatile in the SOFC prototype design.
Direct Conversion of Coal and Coal-Derived Carbon in Fuel Cells
Authors: Cooper John F.
Published: November 2008

A direct carbon fuel cell (DCFC) using a carbon-rich derivative of coal would maximize the conversion efficiency of this vast energy resource by avoiding the efficiency limitations of heat engines. A total conversion efficiency of 80% (based on heat of combustion of carbon) has been achieved at 30–120 mA/cm2 using carbon materials extracted from coal and other fossil resources. High experimental efficiency is grounded in two favorable aspects of the reaction thermodynamics. The net fuel cell reaction (C + O2 = CO2) has a nearly zero entropy change and therefore a theoretical efficiency of 100%. The fixed chemical potentials of carbon reactant and CO2 product make possible the full utilization of fuel in a single pass through the cell. The pure CO2 product can be used directly in enhanced oil and gas recovery, or sequestered. Historically, the development of carbon fuel cells have been limited by low anode rates, accumulation of impurities in the electrolyte, logistics of refueling, and lack of suitable cathodes. These problems are being addressed by recent developments of highly reactive carbon materials, low-cost techniques for separation of coal from ash, the possibility of pneumatic distribution of solid particulate fuel to the cells, and availability of cathodes from the molten carbonate fuel cell technology. Rate depends on atomic scale disorder and accessibility of reactive sites, but not on purity. Sources of suitable anode fuel include thermally decomposed products of (1) mechanical and chemical coal/ash separation or (2) solvent extraction. With current understanding of the cell basics, the next steps are demonstration of an engineering scale fuel cell stack (∼1 kW), supported by development of coal-to-carbon processes and techniques of electrolyte management. Successful development of a direct conversion fuel cell for coal (or coal-derived carbon) has extraordinary implications in extending the energy reserves of coal-producing nations, easing the control of regulated emissions at the plant, and expanding the use the earth’s greatest fossil resource while decreasing emissions of greenhouse gas.
Effects of Conductive Vinyl Ester Sealant in Bonding Separator Plate Composites
Authors: Clulow John G.
Published: November 2008

In order to pack the largest number of PEM cells into the smallest space for transportation applications, bipolar plate assemblies must be thin. The brittleness of thermoset composites relative to metal poses a practical limit with respect to handling, assembly, and physical strength in the stack environment. A conductive thermoset vinyl ester adhesive-sealant was developed using resin technology from BMC’s 940 bipolar plate composites. Strength and conductivity effects were evaluated along with percent property retention following 2500 hour, 85°C immersion in water and water-glycol solutions. Analysis of variance was employed to assess statistical significance and estimate relative effect size. It was found that flexural strength of bonded specimens exceeded that of solid specimens of equivalent thickness. Its use reduced voltage drop by up to 50% compared with un-bonded specimens. Bonded specimens also showed significant improvement versus solid specimens in retention of properties following immersion. Bonded bipolar assemblies with flow channels showed little change in voltage drop over 2000 hours immersion in water and water-glycol solution at 85°C. These observations suggest the potential to utilize the adhesive to achieve thinner assembly designs with enhanced performance characteristics.
Direct Alcohol Fuel Cell for Automotive Applications and Vehicle Modeling
Authors: Branda˜o M. O. , Almeida S. C. A.
Published: November 2008

This paper describes the study made by COPPE/UFRJ which goal is the development of fuel cells systems for automotive applications. The study is divided in two parts. The first is the development of a PEM direct fuel cell. In addition a method for experimentally determine the possibility of using a fuel in a fuel cell is developed. The components of catalysts are also tested such as Tin and Ruthenium in a Platinum coated electrode. The second part is the control system for a fuel cell powered vehicle. The vehicle power is modeled from its actions and losses. A power of 80kW seems to be a great choice if made of 50kW from the fuel cell system and 30kW from an accumulator such as a pack of batteries or a super capacitor.
Stack Compression of PEM Fuel Cells
Authors: Lai Yeh-Hung , Miller Daniel P. , Ji Chunxin , Trabold Thomas A.
Published: November 2008

The effect of dimensional changes of fuel cell components from temperature and hydration cycles on the stack compression is investigated in this paper. Using a simple spring model including the membrane electrode assembly (MEA), gas diffusion layers (GDL), bipolar plates, seal gaskets, current collectors, insulation plates, end plates, and side plates, we find significant compression changes from 30% over-compression to 23% compression loss from both temperature and humidity changes. The wide range of variation in stack compression is attributed to the swelling behavior of polymer electrolyte membranes, the compression behavior of gas diffusion layers, and the design of stack assembly. This paper also reports the use of finite element method to investigate the compression of MEA and GDL over the channel area where MEA buckling from membrane swelling can result in separation of MEA and GDL. It is suggested that the compression over channels can be improved with higher transverse shear modulus in the GDL in addition to the use of narrower channels. In this paper, we will also discuss the challenges facing the fuel cell manufacturers and component suppliers on the needs for new materials with improved mechanical properties and better testing/modeling techniques to help achieving stable compression and better fuel cell stack designs.
New Developments in Atomic Hydrogen Permeation Measurements Using a Bimetallic Sensor
Authors: Maul Alexandre M. , Correa Luiz A. , Ponte Haroldo A.
Published: November 2008

Hydrogen is becoming an important issue due to its characteristics and future applications as it opens access to a broad range of primary energy sources, including fossil fuels, nuclear energy and increasingly renewable energy sources (e.g. wind, solar and biomass) as they become more widely available. Hydrogen in fuel cells can be generated from hydrocarbons, usually alcohols, naphtas or natural gas. In this condition, hydrogen is the desired product. Unfortunately, systems dealing with hydrogen and some hydrocarbons often suffer from hydrogen damage. These damages include: hydrogen induced cracking (HIC), blistering, sulfur stress cracking (SSC) or stress oriented hydrogen induced cracking (SOHIC). These damages are also easily found in corrosive processes at equipments and pipes used in petroleum refining processes and petrochemical plants. The hydrogen, at these processes, is produced by acid media (H+) or chemical processes leading to protons formation (corrosion). The main problem is how to detect, in a safe, fast and economically feasible way, the formation of hydrogen — in this case, an undesirable product. For this work, it was built a cell for hydrogen permeation to study and evaluate a new sensor for atomic hydrogen permeating through a metallic wall. This new sensor is composed of two parts, each one build with a couple of dissimilar materials, being one a sensor couple, for hydrogen flux measurements, and a reference couple, for compensation of temperature variations. The results obtained showed good agreement between the Devanathan-Stachurski Cell (DSC) and the Bimetallic Sensor (BS) (Correˆa, 1999). Both sensors had a sharp increase in current or potential, for DSC and BS, respectively, when the charging side of the permeation cell was polarized. Both sides in the permeation cell were filled with 0.1 M NaOH (continuous N2 bubbling) and the generation side polarized cathodicaly at 3 mA/cm2. The peak potential for the BS was about 30 μV, obtained 12 to 15 h after the polarization.
Quantitative Imaging of Flow Structures in a U-Shaped Fuel Cell Flow Channel
Authors: Martin J. , Oshkai P. , Djilali N.
Published: November 2008

Flow through an experimental model of a U-shaped fuel cell channel is used to investigate the hydrodynamic phenomena that occur within serpentine reactant transport channels of fuel cells. Achieving effective mixing within these channels can significantly improve the performance of the fuel cell and proper understanding and characterization of the underlying fluid dynamics is required. Classes of vortex formation within a U-shaped channels of square cross-section are characterized using high-image-density particle imaging velocimetry (PIV). A range of Reynolds numbers, 109≤Re≤872, corresponding to flow rates encountered in a fuel cell operating at low to medium current densities is investigated. The flow fields are characterized in terms of the instantaneous and time-averaged representations of the velocity, streamline topology, and vorticity contours. The critical Reynolds number necessary for the onset of the instability is determined. Generally speaking, the flow undergoes a transition to a different regime when two recirculation zones, which originally develop in the U-bend region, merge into one separation region.
The Influence of Air-Bleeding on Co-Poisoning of PEM Fuel Cell
Authors: Sung L. Y. , Yan Y. Y. , Chu H. S. , Shyu R. J. , Chen F.
Published: November 2008

The PEM fuel cell has broad applications such as stationary power generation, transportation power sources and portable power generators. From commercial considerations, most anodes of PEM fuel cells use reformate gas as their fuels. However, reformate gas will have small content of carbon monoxide (CO) which will seriously poison platinum (Pt) catalyst electrode, and result in cell performance degradation significantly. The anode air-bleeding method is a preferable way to solve this CO-poisoning problem due to its simplicity, low cost and effectiveness. In this study, a test PEM fuel cell (single cell, active area 5cm × 5 cm) is assembled, its anode fuel uses hydrogen with 52.7ppm CO. Air-bleeding method then is applied to investigate and analyze the influence of CO poisoning on the performance of this PEM fuel cell.
Preliminary Aeronautical Design Considerations of “High NOS” SOFC/GT Hybrids
Authors: Haynes Comas
Published: November 2008

Aerovehicular application of solid oxide fuel cell/gas turbine (SOFC/GT) auxiliary power units (APUs) is a promising concept that may significantly aid the advent of next-generation, environmentally benign aircrafts. The hybrid concept may not only be a novelty, but a necessity, for viably realizing the benefits of fuel cells on-board. A generic design concept is proposed wherein the strategic integration of the cell stack with a bottoming turbine for APU duty, along with regenerative fuel recirculation, could be used to foster larger reactant “numbers-of-stoichs” (NOS) levels within the stack. This may engender larger gravimetric power densities, capacitance for load following and thermal reliability. Fuel utilization/NOS may then be a significant design degree-of-freedom to include within the design process.
Study of a Hybrid Solid Oxide Fuel Cell: Energetic Analysis and Sankey Diagram
Authors: Luz-Silveira Jose´ , Caetano de Souza Antonio Carlos , Gallo Giulliano Batelochi
Published: November 2008

In this paper a hybrid solid oxide fuel cell (SOFC) system is analyzed. This system applies a combined cycle utilizing gas turbine associated to a SOFC for rational decentralized energy production. Initially the relative concepts about the fuel cell are presented, followed by some chemical and technical informations such as the change of Gibbs free energy in isothermal fuel oxidation (or combustion) directly into electricity. This represents a very high fraction of the lower heating value (LHV) of a hydrocarbon fuel. In the next step a methodology for the study of SOFC associated with a gas turbine system is developed, considering the electricity and steam production for a hospital, as regard to the Brazilian conditions. This methodology is applied to energetic analysis. Natural gas is considered as a fuel. In conclusion, it is shown by a Sankey Diagram that the hybrid SOFC system may be an excellent opportunity to strengthen the decentralized energy production in Brazil. It is necessary to consider that the cogeneration in this version also is a sensible alternative from the technical point of view, demanding special methods of design, equipment selection and mainly of the contractual deals associated to electricity and fuel supply.
Constraint on Aeroengine Design by Loss of Grounding in Vibration Physics
Authors: Klompas Nicholas
Published: November 2008

The need for a broad, design-oriented view of engine dynamics is illustrated by four incidents where “today’s science” missed mechanisms critical in the high-bypass turbofan. In missing the significance of Rankine’s 1869 observation of the destabilizing/stabilizing mechanism in line shafts, experts for over 88 years have discounted the action of drive torque on turbomachine whirl. As a consequence, a vital lesson in the Lockheed Electra crashes of 1959–1960 was missed. The suspected Electra propeller-nacelle whirl is examined to create a simple & realistic analytical model showing how coupling between forward and backward whirl in the whole power plant, including associated propeller flexing, poses potential whirl amplification/modulation by torque loading. The model illustrates mechanisms essential to the cited new, physics-based, design analysis of vibrations in a whole engine via distinct waves. The prevailing presumption that an interlocked shroud inevitably produces friction damping is contradicted by a 1989 airline crash investigation.
Prediction of Turbofan Vibrations via Distinct Waves
Authors: Klompas Nicholas
Published: November 2008

Excitation frequency approaching a “split peak” causes only one blade in a shroudless fan — the “rogue blade” — to respond in the full resonant condition, as revealed through extension of previously published inter-transformable coordinate systems, which enable formulation of elliptical whirl in a whole engine as distinct waves to encompass nonuniform blade flexing. A plan for step-by-step, physics-based computations to predict critical vibratory stresses in the “rogue blade”, disk and fan shaft due to inlet flow distortion and/or engine whirl, given a specific distribution of blades with individually predetermined response as applicable in the step and as varying with axial slope and displacement at the root, is advanced. The analysis correlates with Campbell’s 1924 experimental results. The mechanism through which nonuniformity actually reduces potential nonsynchronous vibratory stresses in a fan with an interlocked part-span shroud is examined through experimental evidence secured during investigation of a 1989 airline crash.
Alloy Selection for Honeycomb Gas Path Seal Systems
Authors: Sporer Dieter R. , Shiembob Lawrence T.
Published: November 2008

Metallic honeycombs are widely used in gas turbine engines as inner and outer abradable gas path seals. The ever increasing gas temperatures encountered in the high and low pressure turbine modules of modern engine designs challenge the durability of the thin foil metals used to fabricate seal type honeycomb. In this paper the performance of a number of alloys in turbine seal applications is reviewed. Emphasis is placed on resistance to hot gas corrosion attack and microstructural integrity after exposure to elevated temperatures. The abradability of fabricated seal structures under two distinctly different rub test conditions is reviewed. Among the alloys considered, the Fe-Cr-Al-Y alloy MI 2100 offers a potentially superior combination of oxidation resistance, abradability, fabricability and material cost for seal honeycomb applications.
Design and Evaluation of the AIMS Combustor
Authors: Colibaba-Evulet Andrei , Bowman Michael J. , Brand Anthony R.
Published: November 2008

This paper describes a reduced NOx and CO, partially premixed flame combustor that has been developed for the 175 kW Advanced Integrated Microturbine System (AIMS) recuperated cycle gas micro-turbine. The AIMS turbine is equipped with a recuperated silo combustor. The new, reduced emissions combustor retains key features of the conventional Dry Low NOx (DLN) combustors; the differences are the arrangement of the premixers, the novel head-end assembly design, and the liner cooling and dilution features. The combustion system was designed and tested at the GE Global Research facilities in Niskayuna, NY and leverages technology developed by GE Power Systems (GEPS) and GE Aircraft Engines (GEAE). Laboratory tests show that when firing with natural gas, without water or steam injection, NOx and CO emissions from the new combustor are in single digits at full-speed, full-load conditions. CO emissions show a strong pressure effect, increasing at base load (when compared to similar conditions in commercial combustors running at higher pressures). The standard combustor on the AIMS gas turbine is a reversed flow cylindrical can. An array of 4 fuel nozzles is located at the head end of the can and produces a swirl stabilized premixed flame. The liner contains an array of cooling and dilution holes that provide the air needed to dilute the burned gas to the desired turbine inlet temperature.
Ultra-Compact Combustors for Advanced Gas Turbine Engines
Authors: Zelina J. , Shouse D. T. , Hancock R. D.
Published: November 2008

Current gas turbine design practice for military and commercial aircraft is becoming marginal to meet the increasingly severe, yet conflicting requirements for reduced fuel burn, engine weight, and exhaust emissions, while achieving enhanced parts durability. The engine combustion system can be a key enabler in achieving future design goals. In both conventional single-stage and staged combustors, attention is focused on incremental fluid dynamic changes to enhance fuel-air mixing. In addition, dramatic materials development appears necessary to permit the increased operating temperatures that will ensue from advanced Brayton cycles. This paper describes a revolutionary combustion system that is far from incremental, but appears to offer the potential for continuing advances in engine performance. A gas turbine engine has been proposed that uses a near-constant-temperature (NCT) cycle and an Inter-Turbine Burner (ITB) to provide large amounts of power extraction from the low-pressure turbine. This level of energy is achieved with a modest temperature rise across the ITB. The additional energy can be used to power a large fan for an ultra-high bypass ratio transport aircraft, or to drive an alternator for large amounts of electrical power extraction. Conventional gas turbine engines cannot drive ultra-large diameter fans without the use of excessive turbine temperatures, or a substantial number of turbine stages. In addition, these conventional systems cannot meet high power extraction demands without a loss of engine thrust. The objective is to demonstrate an Ultra-Compact Combustor (UCC) that can be used as a main burner or an ITB that does not impact engine thrust-to-weight, pollutant emissions, or overall system performance. Concepts for an Ultra-Compact Combustor (UCC) are being explored experimentally. This system uses high swirl in a circumferential cavity to enhance reaction rates via high cavity g-loading on the order of 3000 g’s. Increase in reaction rates translates to a reduced combustor volume. The UCC design integrates compressor and turbine features which will enable a shorter and potentially less complex gas turbine engine. This paper will describe different variations of the UCC design where both the fuel injection method, turbine vane design, and the fuel injection angles are varied in the UCC. Experimental results from the UCC at atmospheric pressure indicate that the combustion system operates at 95–99% combustion efficiency over a wide range of operating conditions burning JP-8 +100 fuels. Axial flame lengths were extremely short, at about 50% those of conventional systems.
Optimization of the Rib Structure Inside a 2D Cooling Channel
Authors: Haasenritter Andrea , Weigand Bernhard
Published: November 2008

To increase the thermal efficiency of industrial gas turbines, the performance of the internal cooling channels is of main importance. These cooling channels are often equipped with ribs on the top and bottom walls to increase the turbulence and the mixing of the flow. Depending on the position of the cooling channel in the turbine blade and the external heat load, the ribs have to be designed differently. Up to now the decision of the optimal design parameters was mainly based on the knowledge of the engineer. The present work investigates genetic algorithms as optimization methods to find an optimal design for the rib configuration in a 2d internal cooling channel. The main optimization targets are the reduction of the friction factor and the enhancement of the heat transfer. The paper shows that the basic approach seems to be successful and that an extension of the work to 3d real geometries is promising.
Low Noise FEGV Designed by Numerical Method Based on CFD
Authors: Tsuchiya Naoki , Nakamura Yoshiya , Goto Shinya , Kodama Hidekazu , Nozaki Osamu , Nishizawa Toshio , Yamamoto Kazuomi
Published: November 2008

This paper describes a low noise FEGV (Fan Exit Guide Vane), which is designed by a fan noise prediction method based on CFD. Fan noise is predicted by a hybrid scheme, which is the combination of three-dimensional CFD and three-dimensional linear theory. Characteristics of noise sources are investigated in some kinds of FEGV shapes. High amplitude areas spread not only along the leading edge but also in the span-wise positions along the mid-chord. It is found that high amplitude areas around the mid-chord make an important role in noise generation, and appropriate aft-ward swept angle and span-wise distribution of leaned angle could reduce the amplitude of the noise sources keeping aerodynamic performance. A fan noise test for fan scale models has been conducted at an anechoic test facility in IHI Mizuho to demonstrate noise reduction and performance of low noise FEGV. Noise reduction can be achieved keeping aerodynamic performance compared to conventional straight FEGV.
Turbulent Flow and Heat Transfer in Stationary and Rotating Cooling Passages With Inclined Ribs on Opposite Walls
Authors: Iacovides Hector , Raisee Mehrdad
Published: November 2008

This paper discusses the results of a numerical study of water flow through a straight, orthogonally rotating duct, with ribs along the leading and trailing walls, in a staggered arrangement and at an angle of 45° to the main flow direction. The rib spacing to duct height ratio (P/H) is 1, the rib height to duct height ratio (h/H) is 0.1 and the ribs are of square cross-section (h/w = 1). The two ribbed walls are heated, while the two smooth walls are thermally insulated. Flow computations have been produced using a three-dimensional, non-orthogonal flow solver, with two 2-layer models of turbulence (an effective-viscosity model and a second-moment closure), in which across the near-wall regions the dissipation rate of turbulence is obtained from the wall distance. The numerical predictions are first validated through comparisons with available flow and thermal measurements for stationary and rotating passages and are then used to explain how the inclined ribs and the orthogonal rotation influence the flow and thermal development. Flow comparisons have been carried out for a Reynolds number of 100,000 and for rotation numbers of 0 (stationary) and 0.1. Temperature comparisons have been obtained for a Reynolds number of 36,000, a Prandl number of 5.9 (water) and rotation numbers of 0 and 0.2. For the stationary case additional computations using air as the working fluid (Pr = 0.7), help to assess the effect of the molecular Prandtl number on the thermal characteristics. As we have also found in a recent study of flow through a stationary passage with inclined ribs, both 2-layer models returned similar flow and thermal predictions. The former are in close agreement with available LDA data and the latter are also consistent with available liquid crystal measurements. The flow and thermal developments are found to be dominated by the rib-induced secondary motion, which leads to strong spanwise variations in the mean flow and the local Nusselt number and to a uniform distribution of turbulence intensities across the duct. A reduction in the value of the Prandtl number, to that of air, leads to less rapid changes in the local Nusselt number, but does not change the overall thermal characteristics. Rotation causes the development of stronger secondary motion along the pressure side of the duct and also the transfer of the faster fluid to this side. As a result, along the pressure side the Nusselt number after each rib remains high across the ribbed side, while along suction side, the Nusselt number exhibits stronger reduction in the lateral direction. The flow predictions of both models are in close agreement with the rotating flow measurements. The thermal predictions, especially those of the second-moment closure, reproduce the levels and most of the local features of the measured Nusselt number, but over the second half of the rib interval over-predict the local Nusselt number.
Effectiveness of Normal and Angled Slot Cooling
Authors: Smith A. C. , Hatchett J. H. , Nix A. C. , Ng W. F. , Thole K. A. , Cunha Frank J.
Published: November 2008

An experimental and numerical investigation was conducted to determine the film cooling effectiveness of a normal slot and angled slot under realistic engine Mach number conditions. Freestream Mach numbers of 0.65 and 1.3 were tested. For the normal slot, hot gas ingestion into the slot was observed at low blowing ratios (M < 0.25). At high blowing ratios (M > 0.6) the cooling film was observed to “lift off” from the surface. For the 30° angled slot, the data was found to collapse using the blowing ratio as a scaling parameter. Results from the current experiment were compared with the subsonic data previously published. For the angle slot, at supersonic freestream Mach number, the current experiment shows that at the same x/Ms, the film-cooling effectiveness increases by as much as 25% as compared to the subsonic case. The results of the experiment also show that at the same x/Ms, the film cooling effectiveness of the angle slot is considerably higher than the normal slot, at both subsonic and supersonic Mach numbers. The flow physics for the slot tests considered here are also described with computational fluid dynamic (CFD) simulations in the subsonic and supersonic regimes.