bluuebunny/crossref_metadata_2025 huggingface dataset:
The Perfect Storm
Authors: Nelson Gerald C.
Published: February 2010

When politicians fail to agree, very often it is the poorest who suffer most. More than 25 million additional children could go hungry through the failure of Copenhagen, says Gerald C. Nelson of the International Food Policy Research Institute. As crop yields decline, the calories available per person in sub-Saharan Africa will decline by 21%.
The effect of mechanical loads in the differentiation of precursor cells into mature cells
Authors: Shav Dalit , Einav Shmuel
Published: February 2010

Stem cell differentiation, both in vivo and in vitro, is regulated by a variety of signals. These signals can be of biochemical origin, such as those from growth factors and cytokines, or from different mechanical loads, such as fluid shear stress and matrix elasticity. The mechanisms by which the mechanical loads affect precursor cell differentiation are not entirely understood, but their role in regenerative medicine and cell therapy could be of vast importance. This paper reviews the role of mechanical loads on the differentiation of precursor cells.
Human embryonic stem cell–derived cardiomyocytes can mobilize 1,4,5‐inositol trisphosphate–operated [Ca2+]i stores
Authors: Sedan Oshra , Dolnikov Katya , Zeevi‐Levin Naama , Fleishmann Noa , Spiegel Idit , Berdichevski Sasha , Amit Michal , Itskovitz‐Eldor Joseph , Binah Ofer
Published: February 2010

Because previous findings showed that in human embryonic stem cell–derived cardiomyocytes (hESC‐CM) the machinery for Ca2+‐induced release of calcium is immature, we tested the hypothesis that hESC‐CM contain functional 1,4,5‐inositol triphosphate (IP3)–operated intracellular Ca2+ ([Ca2+]i) stores. We investigated the effects of angiotensin II (AT‐II) and endothelin 1 (ET‐1), which activate the 1,4,5‐IP3 pathway, on [Ca2+]i transients and contractions in hESC‐CM. Our major findings were that in hESC‐CM, both AT‐II (10−9–10−7 M) and ET‐1 (10−9–10−7 M) exert inotropic and lusitropic effects. The involvement of 1,4,5‐IP3‐dependent intracellular Ca2+ release in AT‐I–induced effects was supported by these findings: the effects of AT‐II were blocked by 2‐aminoethoxyphenyl borate (2‐APB, a 1,4,5‐IP3 receptor blocker) and U73122 (a phosopholipase C blocker); and hESC‐CM express AT‐II type 1 and IP3 type I and II receptors as determined by fluorescence immunostaining. In conclusion, hESC‐CM exhibit functional AT‐II and ET‐1 signaling pathways, as well as 1,4,5‐IP3–operated releasable Ca2+ stores.
Matching ATP supply and demand in mammalian heart
Authors: Yaniv Yael , Juhaszova Magdalena , Nuss H. Bradley , Wang Su , Zorov Dmitry B. , Lakatta Edward G. , Sollott Steven J.
Published: February 2010

Although the heart rapidly adapts cardiac output to match the body's circulatory demands, the regulatory mechanisms ensuring that sufficient ATP is available to perform the required cardiac work are not completely understood. Two mechanisms have been suggested to serve as key regulators: (1) ADP and Pi concentrations—ATP utilization/hydrolysis in the cytosol increases ADP and Pi fluxes to mitochondria and hence the amount of available substrates for ATP production increases; and (2) Ca2+ concentration—ATP utilization/hydrolysis is coupled to changes in free cytosolic calcium and mitochondrial calcium, the latter controlling Ca2+‐dependent activation of mitochondrial enzymes taking part in ATP production. Here we discuss the evolving perspectives of each of the putative regulatory mechanisms and the precise molecular targets (dehydrogenase enzymes, ATP synthase) based on existing experimental and theoretical evidence. The data synthesis can generate novel hypotheses and experimental designs to solve the ongoing enigma of energy supply–demand matching in the heart.
The Weitzenböck machine
Authors: Semmelmann Uwe , Weingart Gregor
Published: February 2010

Weitzenböck formulas are an important tool in relating local differential geometry to global topological properties by means of the so-called Bochner method. In this article we give a unified treatment of the construction of all possible Weitzenböck formulas for all irreducible, non-symmetric holonomy groups. We explicitly construct a basis of the space of Weitzenböck formulas. This classification allows us to find customized Weitzenböck formulas for applications such as eigenvalue estimates or Betti number estimates.
Propyretic role of the locus coeruleus nitric oxide pathway
Authors: Soriano Renato N. , Ravanelli Maria I. , Batalhao Marcelo E. , Carnio Evelin C. , Branco Luiz G. S.
Published: February 2010

Nitric oxide has been reported to modulate fever in the brain. However, the sites where NO exerts this modulation remain somewhat unclear. Locus coeruleus (LC) neurons express not only nitric oxide synthase (NOS) but also soluble guanylyl cyclase (sGC). In the present study, we evaluated in vivo and ex vivo the putative role of the LC NO–cGMP pathway in fever. To this end, deep body temperature was measured before and after pharmacological modulations of the pathway. Moreover, nitrite/nitrate (NOx) and cGMP levels in the LC were assessed. Conscious rats were microinjected within the LC with a non‐selective NOS inhibitor (NG‐monomethyl‐l‐arginine acetate), a NO donor (NOC12), a sGC inhibitor (1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one) or a cGMP analogue (8‐bromo‐cGMP) and injected intraperitoneally with endotoxin. Inhibition of NOS or sGC before endotoxin injection significantly increased the latency to the onset of fever. During the course of fever, inhibition of NOS or sGC attenuated the febrile response, whereas microinjection of NOC12 or 8‐bromo‐cGMP increased the response. These findings indicate that the LC NO–cGMP pathway plays a propyretic role. Furthermore, we observed a significant increase in NOx and cGMP levels, indicating that the febrile response to endotoxin is accompanied by stimulation of the NO–cGMP pathway in the LC.
Thermal Characterization of Interlayer Microfluidic Cooling of Three-Dimensional Integrated Circuits With Nonuniform Heat Flux
Authors: Kim Yoon Jo , Joshi Yogendra K. , Fedorov Andrei G. , Lee Young-Joon , Lim Sung-Kyu
Published: February 2010

It is now widely recognized that the three-dimensional (3D) system integration is a key enabling technology to achieve the performance needs of future microprocessor integrated circuits (ICs). To provide modular thermal management in 3D-stacked ICs, the interlayer microfluidic cooling scheme is adopted and analyzed in this study focusing on a single cooling layer performance. The effects of cooling mode (single-phase versus phase-change) and stack/layer geometry on thermal management performance are quantitatively analyzed, and implications on the through-silicon-via scaling and electrical interconnect congestion are discussed. Also, the thermal and hydraulic performance of several two-phase refrigerants is discussed in comparison with single-phase cooling. The results show that the large internal pressure and the pumping pressure drop are significant limiting factors, along with significant mass flow rate maldistribution due to the presence of hot-spots. Nevertheless, two-phase cooling using R123 and R245ca refrigerants yields superior performance to single-phase cooling for the hot-spot fluxes approaching ∼300 W/cm2. In general, a hybrid cooling scheme with a dedicated approach to the hot-spot thermal management should greatly improve the two-phase cooling system performance and reliability by enabling a cooling-load-matched thermal design and by suppressing the mass flow rate maldistribution within the cooling layer.
Treatment of Articular Cartilage Injuries in the Knee
Authors: Wanich Tony
Published: February 2010

Articular cartilage is a unique biphasic tissue composed of chondrocytes surrounded by extracellular matrix (ECM). This thin layer of tissue covers the articular surface of diarthroidal joints and provides a durable, low friction interface which also helps to reduce the load transmitted to the underlying subchondral bone.
Characterization of a PEM Fuel Cell Stack Under Transient Conditions and Its Use in Simulating a FC Powertrain
Authors: Varde Keshav S. , Frank Deepak J.
Published: February 2010

Vehicles powered by fuel cells have received great interests in recent years because of their potential to reduce dependence on fossil fuels, reduce greenhouse gases and have some flexibility in power train configuration. Modeling of vehicle powertrains, using a combination of components and energy storage media, are widely used to predict vehicle performance under different duty cycles. A fuel cell vehicle has to meet the varying load demands for acceleration, deceleration and accessory loads. This paper deals with simulations of a fuel cell powered hybrid vehicle. The simulations were carried out using modification in the Powertrain Simulation Analysis Toolkit (PSAT) components. A small laboratory stack was used to characterize transient performance of a low temperature PEM fuel cell. The stack, with eight fuel cells, had a rating of about 1.0 kW. The transient characteristics of the PEM stack were obtained by loading and unloading the stack at different current densities, stack temperatures and reactant humidity. The information was used in the simulation to predict performance of a medium-sized crossover SUV when operated in different test cycles. Transient loads on the fuel cell produced undershoot in cell voltage when the loading exceeded 0.15 A/cm2-s. This impacts efficiency of the fuel cell. The results show that an appropriate size of fuel cell and battery combination produced best fuel economy. The optimum rating of the fuel cell varied somewhat depending on the drive cycle. The highway cycle required a larger fuel cell while a smaller fuel cell provided better fuel economy in the UDDS cycle. Incorporating transient characteristics of the fuel cell reduced fuel economy by about 3–4% over the steady state characteristics.
Using Anode-Offgas Recycling for a Propane Operated Solid Oxide Fuel Cell
Authors: Dietrich Ralph-Uwe , Lindermeir Andreas , Oelze Jana , Spitta Christian , Steffen Michael , Chen Shaofei , Schlitzberger Christian
Published: February 2010

The objective of the proposed anode-offgas recycling (AOGR) concept is to increase the overall electrical efficiency of a propane-based power system with a 300 Wel solid oxide fuel cell (SOFC) stack beyond normal system configuration with partial oxidation (POX) to syngas. Recycling the anode-offgas partially into the reformer provides steam, carbon dioxide and heat for a combined endothermic steam and dry reforming of the propane, thus replacing the POX reaction. Compared to POX mode, the AOGR concept yields considerably more fuel gas for the SOFC from the same amount of propane. The generated fuel gas is nitrogen-free, thus increasing the SOFC performance additionally. An innovative reformer/burner-reactor allows the internal usage of the anode-offgas heat without additional heat transfer units. The hot-gas injector uses the propane bottle pressure to recycle anode-offgas to the reformer. The transition from POX mode, necessary for the system startup, to the AOGR mode requires enhanced control strategies, developed with the support of dynamic simulation. Critical parameters for the system are the minimal oxygen to carbon (O/C) ratio for carbon-free reformer operation, the SOFC power output and fuel utilization, and the injector performance at a given system backpressure. The concept implementation by an interdisciplinary team of researchers resulted in evaluated process units like injector, reformer, SOFC stack, a dynamic model and controls. The experimental investigation of the whole system will follow soon.
The Safety of Hydrogen Release and Discharge From a Fuel Cell Vehicle
Authors: Kim JongSung , Lee SungHo , Hwang InChul , Lim TaeWon
Published: February 2010

The safety of hydrogen release and discharge from a fuel cell vehicle was evaluated using CFD (Computational Fluid Dynamics) tests in various situations. First, the validity of the locations of the hydrogen sensors installed in Hyundai fuel cell vehicle and the workshop were tested. In addition, the discharge tests of the fuel cell vehicle based on SAE J2578 were conducted in non-ventilated, ventilated and outdoor modes. Through these tests, it was verified that the hydrogen sensor locations are suitable for the detection of hydrogen leakage and SAE J2578 regulation is satisfied in the fuel cell vehicle.
Water Transport in the MEA of a PEM Fuel Cell
Authors: Liu JuanFang , Oshima Nobuyuki , Kurihara Eru , Saha LitanKumar
Published: February 2010

In the paper, a one-dimensional model of water transport across the entire cell is presented for the proton exchange membrane fuel cell. In the model, the catalyst layer is treated as a separate computing domain, not an interface between the gas diffusion layer and membrane. Meanwhile, in the membrane mechanisms of back diffusion and electro-osmotic drag are considered, while pure diffusion process is taken into account for the gas-phase flow in the cell. In the catalyst layer, except for Knudsen diffusion, water vapor in the pore is coupled with liquid water in the ionomor phase by the isotherm sorption and in equilibrium with each other. The results indicate both the operating pressure and mean current density are the important factors to affect the water transport process in the cell. Moreover, it is found that the liquid water diffusivity dependent on water content in the ionomer phase would lead to the water content distribution at the different degree nonuniformity. Additionally, the thinner membranes result in the higher and more uniform distribution of water content in the membrane phase. Furthermore, the concentration-gradient driven water flux based on Henry’law is exposed on the anode surface of the membrane as the boundary condition, which is more appropriate to present the reality of water content in the ionomer phase. The numerical results imply that it is very necessary to investigate the interaction among different components of a cell, so as to predict correctly the coupled transport phenomena occurred in the entire fuel cell.
An Easy-to-Approach Mathematical Model and Optimization of Planar Type Proton-Conductive SOFC
Authors: Li P.-W , Sahrawat S. , Sepulveda J. L. , Loutfy R. O. , Chang S.
Published: February 2010

A mathematical model for proton-conductive solid oxide fuel cell (H-SOFC) is presented in this work. The analysis and optimization of fuel cell components is to help the design and fabrication of H-SOFCs which are experimentally studied by the current authors. The mathematical model considers mass transfer and concentration polarization using an average mass transfer model analogous to the convective heat transfer in a duct flow and across a wall. The average concentrations of species at interfaces of electrodes/electrolyte at any operating current densities are calculated, and therefore the species concentrations are included in the calculation for activation polarizations. The ohmic loss is considered through analysis of a circuit simulating the electron and proton conduction. Empirical coefficients for the exchange current density in activation polarization analysis were determined and validated by referring to experimental results from multiple publications. Parametric analysis has also been done to show how the performance of H-SOFC is dependent on properties of fuel cell components.
Performance Metrics for Solid Oxide Fuel Cell Cross-Section Design
Authors: Nelson George J. , Haynes Comas , Wepfer William
Published: February 2010

Analytical models have been developed to describe the partial pressure distributions of reactants within solid oxide fuel cell (SOFC) electrodes and introduce the concept of a reactant depletion current density. These existing analytical expressions for two-dimensional reactant partial pressure distributions and the reactant depletion current density are presented in non-dimensional form. Performance metrics for SOFC electrodes are developed including a correction factor that can be applied to button-cell predictions of pressure distribution and two forms of dimensionless reactant depletion current density. Performance predictions based on these metrics are compared to numerical predictions of partial pressure and depletion current density based on a finite element solution of the dusty-gas model (DGM) within SOFC electrodes. It is shown that the pressure correction factor developed provides a reasonable prediction of interconnect geometry effects. Thus, it is presented as a modeling tool that can be applied to translate component level fidelity to cell and stack level models. The depletion current density metrics developed are used to present basic design maps for SOFC unit cell cross-sections. These dimensionless forms of the depletion current density quantify the influence of sheet resistance effects on reactant depletion and can predict the deviation from the limiting current behavior predicted using a button-cell model.
Effects of Ceria Addition on Ni/YSZ Anodes for SOFC’s Operating With Syngas and n-Butane
Authors: Patel Siddharth , Jawlik Paul F. , Jackson Gregory S.
Published: February 2010

This study explores the incorporation of ceria (CeO2) into Ni/YSZ cermet anodes for solid oxide fuel cell performance with both syngas and n-butane/steam feeds to suppress carbon deposits and expand operability of Ni-based anodes with carbonaceous fuel feeds. CeO2 was co-fired with Ni/YSZ cermets to form a porous anode support layer (1 mm thick), which was tested in SOFC button cells with dense YSZ electrolytes (10–20 μm thick) and porous LSM/YSZ cathodes (∼50 μm thick). The co-fired Ni/CeO2/YSZ anode-supported cells were tested from 700 to 800 °C on various fuels including syngas and n-butane with H2O added at a 1.5-to-1 and a 1-to-1 steam-to-carbon (S/C) ratio. Electrochemical characterization revealed that CeO2 addition provided stable performance with high power densities at 800 °C — up to 0.6 W/cm2 on syngas and 0.35 W/cm2 on direct butane feeds — without significant carbon deposition as observed for Ni/YSZ anodes without CeO2. Testing with syngas at different H2 and CO partial pressures indicated that high power densities can be maintained along an anode channel for up to 50% fuel conversion. The results indicate that CeO2 addition to Ni/YSZ may provide a viable means for stable SOFC operation on either pre-reformed or direct light-hydrocarbon fuel feeds.
Accelerating Production Readiness Using Lean Product Development
Authors: Parsons Michael J. , Josefik Nicholas M.
Published: February 2010

Lean manufacturing and accelerated product development, two forces when combined into lean product development, can accelerate time-to-market and manufacturing scale-up, achieving production readiness in the shortest possible time. This paper presents what is possible when the two underlying themes of lean manufacturing and new product development unite with the orchestrated chaos of a high performing team. A benchmark value stream has been documented along with product development cycle time examples ranging from 4 to 16 months for concept-to-production readiness.
Dynamic Analysis and Control of a Planar IT-SOFC System
Authors: Salogni A. , Iora P. , Campanari S.
Published: February 2010

This paper analyzes the dynamic behaviour of a 5 kW fuel cell system based on planar co-flow Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFC) stack, with internal reforming. The system is composed by the SOFC stack, a combustor of the cell exhausts, two heat exchangers for fuel and air preheating and the related control valves, where the air temperature at the stack exit and the fuel utilization is controlled by means of a PI (proportional integral) device. The model of the stack is based on a lumped parameters dynamic model of a single cell, which is composed of the fuel and air channels, the electrochemically active three layer region representative of the anode, the cathode and the electrolyte. The stack model is first used here for a qualitative steady-state validation, reproducing the cell characteristic curve. Then it is presented the dynamic model of the system, which has been implemented using an a-causal software based on the open-source Modelica modelling language, which allows for future integration in complex power-plant configurations. After a description of the plant layout and of the dynamic model, we present and discuss the results obtained by applying the PI controls to different load changes and with different tuning of the controller parameters, evidencing the amplitudes of load changes, the extent of the transient phase to the new steady-state conditions, the internal cell temperature distribution and the thermal gradients along the PEN structure, giving the possibilities to adapt the control system to the requirements of specific SOFC technologies.
Experimental Evaluation of CO Poisoning of a 5-Cell Stack High Temperature PEM Fuel Cell Prototype
Authors: Das Susanta K. , Reis Antonio , Berry K. Joel
Published: February 2010

In this study, we experimentally studied our newly designed and built 5-cell stack high temperature PEM fuel cell prototype at different operating conditions to investigate the effects of CO poisoning on the cell performance. The effects of temperature variations with different amount of CO poisoning on the current-voltage characteristics of the fuel cell stack are investigated. Experimental data of this type would be very useful to develop design parameters for fuel reformer. The high CO tolerance of high temperature PEM fuel cell stack makes it possible to feed the reformate gas directly from the reformer without further CO removal. Thus, upon considering the fact that a steam reformer is a consumer of heat and water, and the fuel cell stacks are a producer of heat and water, the integration of the fuel cell stack and the reformer is expected to improve the entire system performance. The results obtained from our 5-cell stack test showed variations in current-voltage characteristics at different temperatures with different CO poisoning rates. The results are promising to understand the overall system performance development strategy of high temperature PEM fuel cell in terms of current-voltage characteristics while fed with on-site reformate hydrogen gas with different CO concentrations in the anode feed stream.
The Effects of Oxygen Vacancy Concentration on the Mechanical Properties of Zirconia and Ceria-Based Electrolytes for SOFCs
Authors: Hashida Toshiyuki , Takeyama Yohei , Sato Kazuhisa
Published: February 2010

In this paper, we discuss the effects of different oxygen partial pressures on the deformation property and fracture characteristics of representative constituent materials for solid oxide fuel cells (SOFCs). The elastic modulus and fracture strength of 8 mol% yittria stabilized zirconia (8YSZ) and 10 mol% gadolinia doped ceria (10GDC) treated under different oxygen partial pressures were evaluated using the small-punch testing method in this study. The specimens of 8YSZ and 10GDC prepared by a sintering process were treated at 800 °C under an oxygen partial pressure in the range of 0.21 to 10−22 atm for 1 hour. The treated specimens were then fast cooled down to a room temperature, and their mechanical properties were measured under an atmospheric pressure condition by using the small-punch testing method. The experimental results revealed that both the elastic modulus and fracture strength of the 10GDC decreased drastically when the oxygen partial pressure of the treatment was less than 10−15 atm, whereas no significant variation in both the mechanical properties was observed for the 8YSZ. The elastic modulus and fracture strength of 10GDC for the treatment under 10−22 atm was reduced down to 10–20% of those treated under the atmospheric pressure. SEM observations revealed that the fracture surface of the 10GDC specimens was changed from transgranular mode to intergranular mode when the oxygen partial pressure was reduced, whereas the fracture surface of the 8YSZ specimens was transgranular regardless of the different oxygen partial pressures.
Effect of Co-Doping on Microstructure, Thermal and Mechanical Properties of Ternary Zirconia-Based Thermal Barrier Coating Materials
Authors: Huang Xiao
Published: February 2010

7YSZ (yttria stabilized zirconia) was co-doped with metal oxides of different valence, ionic radius and mass in order to investigate microstructural and property changes as a result of co-doping. Mechanical alloying process was used to produce the powder blends which were subsequently sintered at 1500°C for 120 hours. The results from SEM, XRD and DSC showed that the microstructures of the co-doped ternary oxides were affected by the amount of oxygen vacancies in the system, the co-dopant cation radius and mass. Increasing the number of oxygen vacancies by the addition of trivalent co-dopant (Yb2O3 and Sc2O3) as well as the use of larger cations promoted the stabilization of cubic phase. The tetravalent co-dopant (CeO2), on the other hand, had the effect of stabilizing tetragonal phase which may transform into monoclinic phase during cooling, depending on the concentration of tetravalent co-dopant and the mass. Smaller cation mass had the effect of reducing the transformation temperature from tetragonal to monoclinic phase. Pentavalent co-dopants (Nb2O5 and Ta2O5) were found to stabilize the tetragonal phase at high temperature; however, the stability of the tetragonal phase upon cooling was determined by the mass and ionic radius of the co-dopants. Cation clustering was observed during cooling in trivalent oxide co-doped 7YSZ while clustering of trivalent and pentavalent cations in pentavalent co-doped 7YSZ was not detected. Additionally, from the thermal conductivity measurement results, it was found that trivalent oxides exhibited the most significant effect on reducing the thermal conductivity of ternary oxides; this trend was followed by pentavalent co-doping oxides whereas the tetravalent CeO2 co-doped 7YSZ showed marginal effect. A semi-empirical thermal conductivity model was established based on defect cluster model and the predicted room temperature thermal conductivity values were found to be consistent with that measured experimentally. Furthermore, the incorporation of co-dopant oxide in 7YSZ was observed to substantially modify the elastic modulus of the ternary oxides. More specifically, the addition of co-dopant with larger cation radius was found to reduce the elastic modulus of 7YSZ due to the increase in lattice parameter(s).
Study of the Flow in Centrifugal Compressor
Authors: Xu C. , Amano R. S.
Published: February 2010

An unshrouded centrifugal compressor would give up clearance very large in relation to the span of the blades, because centrifugal compressors produce a sufficiently large pressure rise in fewer stages. This problem is more acute for a low flow high-pressure ratio impeller. The large tip clearance would cause flow separations, and as a result it would drop both the efficiency and surge margin. Thus a design of a high efficiency and wide operation range for a centrifugal compressor is a great challenge. This paper describes a new development of high efficiency and a large surge margin flow coefficient of 0.145 centrifugal compressor. A viscous turbomachinery optimal design method developed by the authors for axial flow machine was further extended and used in this centrifugal compressor design. The new compressor has three main parts: impeller, a low solidity diffuser and volute. The tip clearance is under a special consideration in this design to allow impeller insensitiveness to the clearance. A three-dimensional low solidity diffuser design method is proposed and applied to this design. This design demonstrated to be successful to extend the low solidarity diffusers to high-pressure ratio compressor. The design performance range showed the total to static efficiency of the compressor being about 85% and stability range over 35%. The experimental results showed that the test results are in good agreement with the design.
Biodiesel as an Alternative Fuel in Siemens DLE Combustors: Atmospheric and High Pressure Rig Testing
Authors: Liu Kexin , Wood John P. , Buchanan Eoghan R. , Martin Pete , Sanderson Victoria E.
Published: February 2010

Atmospheric and high pressure rig tests were conducted to investigate the feasibility of using biodiesel as an alternative fuel to power industrial gas turbines in one of the world’s leading Dry Low Emissions (DLE) combustion systems, the SGT-100. At the same conditions, tests were also carried out for mineral diesel to provide reference information to evaluate biodiesel as an alternative fuel. In the atmospheric pressure rig tests, the likelihood of the machine lighting was identified based on the measured probability of the ignition of a single combustor. Lean ignition and extinction limits at various air temperatures were also investigated with different air assist pressures. The ignition test results reveal that reliable ignition can be achieved with biodiesel across a range of air mass flow rates and air fuel ratios. In the high pressure rig tests, emissions and combustion dynamics were measured for various combustor air inlet pressures, temperatures, combustor wall pressure drops and flame temperatures. These high pressure rig results show that biodiesel produced less NOx than mineral diesel. The test results indicate that the Siemens DLE combustion system can be adapted to use biodiesel as an alternative fuel without major modification.
Effect of Tungsten Addition on the Nucleation of Borides in Wide Gap Brazed Joint
Authors: McGuire Daniel , Huang Xiao , Nagy Doug , Chen Weijie
Published: February 2010

Wide gap brazing (WGB) is a cost effective and reliable means to repair gas turbine hot section components with defect sizes exceeding 0.3 mm. However, it has been shown that WGB joints of nickel-based superalloys suffer from reduced ductility and thermal fatigue life due to the presence of brittle intermetallics and porosities in the brazed joint. In order to disperse the brittle intermetallic compounds, potentially increase the ductility of the repaired region, and reduce the risk of the thermo-mechanical fatigue failure, elemental tungsten (W) was added to the braze additive filler alloy IN738 by mechanical alloying. The alloyed IN738 was then brazed with the addition of 30, 50 and 80 wt% of braze alloy (BNi-9). After brazing at 1200°C for 20 minutes, microstructural analysis of WGB joints showed a decreasing trend of discrete boride size and the amount of eutectic and script-shaped borides with the increases of W. The increase in the braze alloy to additive filler alloy ratio diminished the effect of W addition due the dissolution of W particulates.
Feasibility Study of a Conventional Turbofan With a Constant Volume Combustor
Authors: Colmenares Quintero Fernando , Coutinho Aristo , Ogaji Stephen , Singh Riti , Pincay Gordillo Nestor A. , Herna´ndez Pin˜a Juan Carlos
Published: February 2010

The conventional Brayton CPC (constant pressure combustion) cycle engines have almost reached maturity in terms of thermal efficiency and SFC (specific fuel consumption). With environmental norms taking the front seat in civilian applications, the goal is to think of innovative concepts that are faster, cheaper, cleaner and quieter. Among many proposed concepts, the patented wave rotor – PDE (pulse detonation engine) combined combustor has generated much interest of producing a workable Humphrey CVC (constant volume combustion) cycle engine, with the potential to replace the conventional CP combustor with its inherently higher thermal efficiency, which translates to lower SFC, fuel burn and thus lower CO2 emissions. However, with the higher flame temperatures and pressure gain (i.e.: pressure rise minus pressure losses) in the combustor, the NOx emissions are expected to increase, but at the same time limited by the lower residence times on account of detonative combustion. This study seeks to investigate if the NOx will indeed rise even with shorter residence times. ACARE (Advisory Council for Aeronautics Research in Europe) has set ambitious goals to reduce the LTO (landing and take-off) NOx by 80% by 2020. This study mainly considers the overall NOx emissions besides the LTO NOx, which is not currently regulated, but steps are being taken towards covering this in future revisions of the regulations. The approach used is to develop a performance-based emissions model that could be used for the CVC engine, and also for the conventional CPC baseline engine, in order to compare both using a multidisciplinary design tool (PMDF) for a medium-haul flight of 2500 nm. PMDF is coupled to an optimiser in order to assess and optimise the CVC for best fuel burn and NOx emissions without compromising on thrust. The results of this preliminary study does indeed show an increase in NOx emissions index, but interestingly, it also shows that the overall emissions are reduced when comparing the two engines at bypass ratios higher than 7. Moreover, there are strategies to reduce NOx formation in parallel to techniques used today.
Evaluation of Alternate High Temperature Coatings to Improve Hot Corrosion Resistance in a Shipboard Environment
Authors: Shifler David A. , Russom Dennis M. , Rodman Bruce E.
Published: February 2010

501-K34 marine gas turbine engines serve as auxiliary power sources for the U.S. Navy’s DDG-51 Class. It is desired that 501-K34 marine gas turbine engines have a mean time between removal of 20K hours. While some engines have approached this goal, others have fallen significantly short. A primary reason for this shortfall is hot corrosion (Type I and Type II) damage in the turbine area (more specifically the first row turbine hardware) due to both intrusion of salts from the marine air and from sulfur in the gas turbine combustion fuel. The Navy’s technical community recognizes that engine corrosion problems are complex in nature and are often tied to the design of the overall system. For this reason, two working groups were formed. One group focuses on the overall ship system design and operation, including the inlet and fuel systems. The second, the corrosion issues working group, will review the design and performance of the turbine itself and develop sound, practical, economical, and executable changes to engine design that will make it more robust and durable in the shipboard operating environment. Metallographic examination of unfailed blades removed from a marine gas turbine engine with 18000 operating hours showed that the coating thickness under the platform and in the curved area of transition between the platform to the blade stem was either very thin, or in a few cases, non-existent on each unfailed blade. Type II hot corrosion was evident at these locations under the platform. It was also observed that this corrosion under the platform led to corrosion fatigue cracking of first stage turbine blades due to poor coating quality (high porosity and variable thickness). Corrosion fatigue cracks initiated at several hot corrosion sites and had advanced through the stems to varying degrees. Cracking in a few blades had advanced to the point that would have led to premature blade failure. Low velocity, atmospheric-pressure burner-rig (LVBR) tests were conducted for 1000 hours to evaluate several alternative high-temperature coatings in both Type I and Type II hot corrosion environments. The objectives of this paper are to: (1) report the results of the hot corrosion performance of alternative high temperature coating systems for under the platform of the 1st stage blade of 501-K34 gas turbine engine, (2) compare the performance of these alternative coating systems to the current baseline 1st stage blade coating, and (3) down select the best performing coating systems (in terms of their LVBR hot corrosion and thermal cycling resistance) to implement on future 501-K34 first stage blades for the Fleet.
Cracking Behaviour of an Air-Plasma-Sprayed Thermal Barrier Coating
Authors: Chen W. R. , Wu X. , Marple B. R. , Huang X. , Patnaik P. C.
Published: February 2010

The degradation of a thermal barrier coating (TBC) system is dominated by the formation and growth of a thermally grown oxide (TGO) layer between the ceramic topcoat and metallic bond coat, leading to a separation near the ceramic/bond coat interface during service. Crack propagation in a thermally sprayed TBC normally proceeds via the opening and growth of pre-existing discontinuities in the ceramic layer near the ceramic/bond coat interface region assisted by cracking associated with the evolution of the TGO. The combined effect of these degradation processes results in premature TBC failure. In the present study, TGO growth and cracking behaviours were investigated under cyclic oxidation conditions with different cycle frequencies. The results showed a likely relationship between the maximum crack length and TGO thickness, suggesting that the establishment of an empirical formula may be possible to serve as the basis for a TBC life prediction model.
CFD Predictions of Cascade Pressure Losses Due to Compressor Fouling
Authors: Fouflias Dimitrios , Gannan Aiad , Ramsden Kenneth , Pilidis Pericles , Lambart Paul
Published: February 2010

The performance of the compressor component of an industrial gas turbine can suffer seriously from fouling due to the ingestion of particulate matter like sand and dust. In particular, in very hostile environments when mixed with oil vapour, the outcome is a substantial loss in power and efficiency due to compressor fouling. To recover this performance loss and subject to manufacturer’s firing temperature limitations, the engine fuel flow could be increased. This in turn would reduce the creep life of the turbine blades and result in large increases in engine operating costs. These effects can be reduced markedly by keeping the compressor as clean as possible through a combination of intake filtration and compressor washing. Against this background, the ongoing research involves the design and commissioning of a 2-D cascade tunnel to facilitate estimation of pressure losses and associated compressor inefficiencies as a function of degree of fouling (surface roughness). This paper presents preliminary CFD predictions for smooth clean cascade blades and for fouled blades applying on them different levels of fouling. For all these cases, velocity distributions and exit flow angles one chord downstream of the blades towards the cascade flow stramtube at a midspan height have been investigated. Also the pressure losses associated are presented. All these CFD results will be used to complement the future experimental measurements not yet obtained, which will be undertaken at different fouling level and blade washing scheme as well.
Characteristics of an Underexpanded Jet and Its Surface Impingement for Combustion Burnthrough
Authors: Hussain Zahid M. , Coney Michael H. , Moss J. Barrie , Ireland Peter T. , Jagger Stuart
Published: February 2010

The flow from an underexpanded free jet and a jet impinging on a perpendicular planar surface has been characterised for a pressure ratio (N) of 40 with a nozzle to plate spacing (L/D) of 3 nozzle diameters. Surface heatflux (Q), temperature (T), pressure (P) and flow visualisation techniques have been used extensively to examine the flow within the jet and on the plate surface. From these it is shown that the flow is non-axisymmetric in nature. The experimental programme has been conducted across several facilities within the UK which has allowed the influence of Reynolds number to be determined. The results of this work show marked similarities in flow characteristics irrespective of Reynolds number variation. Heat transfer on the impingement plate is largely determined by Taylor-Go¨rtler vortex flow and total temperature separation resulting from shearing flows. Evidence for Taylor-Go¨rtler vortex flow within the jet has been reinforced by comparison of the free jet element of this work with other research. Infra-Red camera measurements have confirmed the presence of strong total temperature separation on the impingement surface with local surface temperature step variation of greater than 200K (360°F) in the presence of a high temperature jet running at approximately 1900K (2960°F). This feature is dictated by this N and L/D and is shown to occur over a wide range of jet total temperature.
An Investigation of Turbine Wheelspace Cooling Flow Interactions With a Transonic Hot Gas Path—Part 2: CFD Simulations
Authors: Laskowski G. M. , Bunker R. S. , Bailey J. C. , Ledezma G. , Kapetanovic S. , Itzel G. M. , Sullivan M. A. , Farrell T. R.
Published: February 2010

A computational model has been developed to study the mechanisms responsible for hot gas ingestion into the wheel-space cavity of a stationary HPT cascade rig. Simulations were undertaken for the stationary rig described by Bunker et al. (2009) in a companion paper. The rig consists of 5 vanes, a wheel-space cavity and 5 cylinders that represent the blockage due to the leading edge of the rotor airfoils. The experimental program investigated two cylinder diameters and three clocking positions for a nominal coolant flow rate. Comparisons are made between the computed and measured flow-field for the smaller of the two cylinders. It is demonstrated that the circumferential variation of pressure established by the vane wake and leading edge bow wave results in an unstable shear layer over the rim seal axial gap (trench) that causes hot gases to ingest for a nominal coolant flow. Steady state CFD simulations did not capture this effect and it was determined that a unsteady analysis was required in order to match the experimental data. Favorable agreement is noted between the time-averaged computed and measured pressure distributions in the circumferential direction both upstream and downstream of the trench, as well as within the trench itself. Furthermore, it is noted that time-averaged buffer cavity effectiveness agrees to within 5% of the experimental data for the cases studied. The validated CFD model is then used to simulate the effect of rotation by rotating the cylinders and disk at rotational rate that scales with a typical engine. A sliding mesh interface is utilized to communicate data between the stator and rotor domains. The stationary cases tend to ingest past the first angel wing for a nominal coolant flow condition the effect of rotation helps pressurize the cavity and is responsible for preventing hot gas from entering the buffer cavity.
Turbine Blade Tip Cooling Modeling and Optimization
Authors: Vogel Gregory , Agrawal Anmol , Nannapaneni Praneetha
Published: February 2010

The turbine blade tip is considered as one of the most critical areas of gas turbine engines. The tip region often lacks durability and is challenging to cool. To achieve successful blade tip cooling designs, ALSTOM engineers are performing state of the art aero thermal analyses of blade tip cooling configurations. This paper describes the approach used for this analysis and draws conclusion for blade tip cooling optimization. Numerical simulations of flow and heat transfer are presented for a modern industrial gas turbine blade with a film cooled tip. The blade tip metal temperature distribution is analyzed for three different blade tip clearances with a detailed CFD analysis around the blade tip performed. The CFD analysis provides flow streamlines through the blade tip as well as a total blade tip leakage flow. Rough streamlines estimates are then used to define a set of control volumes for which dedicated cooling flow mixing is considered. The total mass flowing through all volumes corresponds to the CFD blade tip leakage. For each control volume corresponds a specific Reynolds number that is used to define a corresponding heat transfer coefficient. The latter is obtained from experimental Nusselt number correlations for the different regions of a blade squealer tip (crown, fillet and cavity). Application of the obtained heat transfer coefficient and mixing temperature boundary conditions on a 3D blade tip finite element model, together with an internal cooling flow network associated to the 3D model allows calculating the blade tip metal temperature. Results for two different tip clearances relative to nominal blade tip gap are presented and discussed. Comparison with experimental data such as thermal paint test and metallurgical data are given, showing good agreement with the blade tip cooling modeling introduced in this paper. Cooling performance of the blade tip is discussed based on the modeling approach proposed in this paper. The latter allows drawing conclusions for blade tip cooling optimization.
Effect of Blowing Ratio on Syngas Flyash Particle Deposition on a Three-Row Leading Edge Film Cooling Geometry Using Large Eddy Simulations
Authors: Sreedharan Sai Shrinivas , Tafti Danesh K.
Published: February 2010

A numerical study is performed to investigate deposition and erosion of Syngas ash in the leading edge region of a turbine vane. The leading edge of the vane is modeled as a symmetric semi-cylinder with a flat after body. Three rows of coolant holes located at stagnation and at ±21.3° from stagnation are simulated at blowing ratios of 0.5, 1.0, 1.5 and 2.0. Large Eddy Simulation (LES) is used to model the flow field of the coolant jet-mainstream interaction and syngas ash particles are modeled using a Lagrangian framework. Ash particle sizes of 5 and 7 micron are considered. Under the conditions of the current simulations, both ash particles have Stokes numbers less than unity of O(1) and hence are strongly affected by the flow and thermal field generated by the coolant interaction with the mainstream. Because of this, the stagnation coolant jets are quite successful in pushing the particles away from the surface and minimizing deposition and erosion in the stagnation region. Overall, about 10% of the 5 μm particles versus 20% of the 7 μm particles are deposited on the surface at B.R. = 0.5. An increase to B.R. = 2, increases deposition of the 5 micron particles to 14% while decreasing deposition of the 7 micron particles to 15%. Erosive ash particles of 5 μm size increase from 5% of the total to 10% as the blowing ratio increases from 0.5 to 2.0, whereas 7 μm erosive particles remain nearly constant at 15%. Overall, for particles of size 5 μm, there is a combined increase in deposition and erosive particles from 16% to 24% as the blowing ratio increases from 0.5 to 2.0. The 7 μm particles, on the other hand decrease from 35% to about 30% as the blowing ratio increases from 0.5 to 2.
Influence of Coolant Density on Turbine Blade Platform Film-Cooling
Authors: Narzary Diganta P. , Liu Kuo-Chun , Han Je-Chin
Published: February 2010

Detailed parametric study of film-cooling effectiveness was carried out on a turbine blade platform of a five-blade linear cascade. The parameters chosen were — freestream turbulence intensity, upstream stator-rotor purge flow rate, discrete-hole film-cooling blowing ratio, and coolant-to-mainstream density ratio. The measurement technique adopted was temperature sensitive paint (TSP) technique. Two turbulence intensities of 4.2% and 10.5%; three purge flows between the range of 0.25% and 0.75% of mainstream flow rate; three blowing ratios between 1.0 and 2.0; and three density ratios between 1.1 and 2.1 were investigated. Purge flow was supplied via a typical double-toothed stator-rotor seal, whereas the discrete-hole film cooling was accomplished via two rows of cylindrical holes arranged along the length of the platform. The inlet and the exit Mach numbers were 0.27 and 0.44, respectively. Reynolds number of the mainstream flow was 7.5*105 based on the exit velocity and chord length of the blade. Results indicated that platform film-cooling effectiveness decreased with turbulence intensity, increased with purge flow rate and density ratio, and possessed an optimum blowing ratio value. The improved effectiveness with density ratio was further validated by the pressure sensitive paint (PSP) technique.