bluuebunny/crossref_metadata_2025 huggingface dataset:
Ballistic-Diffusive Approximation for Phonon Transport Accounting for Polarization and Dispersion
Authors: Murthy J. Y. , Mathur S. R.
Published: December 2008

A ballistic-diffusive approximation to the Boltzmann transport equation is developed for describing phonon transport in semi-conductors and dielectrics. The model incorporates the effects of phonon dispersion and polarization by considering longitudinal, transverse and optical branches. Each branch is divided into frequency bands, and scattering between branches and bands is incorporated subject to conservation rules. The phonon energy in each band is divided into a boundary and a medium component, with the latter being computed using a diffusion approximation. The approximation is shown to work well by comparing its predictions to exact solutions as well thermal conductivity measurements for bulk silicon.
Apparatus for Distributed Thermal Storage
Authors: Franco Luiz Carlos D.
Published: December 2008

This work carries out a proof of concept analysis of equipment for distributed thermal storage, using ice as storage media and air flow inside plastic tubes for recovery. By making a certain number of simplifying assumptions, a model is developed and the performance curves for the apparatus calculated. Results are applied in sizing a prototype. The validity of the assumptions is discussed. In conclusion, the paper indicates that an apparatus for the intended purpose is feasible and worthy of further development.
Simulation of Vorticity-Buoyancy Interactions in Fire-Whirl-Like Phenomena
Authors: McDonough J. M. , Loh Andrew
Published: December 2008

In this study the commercial flow code STAR-CD has been used to simulate a laboratory experiment involving a so-called fire whirl. Such phenomena are typically characterized as exhibiting significantly enhanced mixing and consequently higher combustion rates due to an interaction of buoyancy and vorticity, but the details of this are only beginning to be understood. The present study focuses attention on this interaction in the absence of combustion, thus removing significant complications and allowing a clearer view of the vorticity-buoyancy interaction itself.
Domain Decomposition for 3D Boundary Elements in Non-Linear Heat Conduction
Authors: Divo Eduardo , Kassab Alain J. , Rodriguez Franklin
Published: December 2008

In this paper, we develop a domain decomposition, or the artificial sub-sectioning technique, along with a region-by-region iteration algorithm particularly tailored for parallel computation to address storage and memory issues arising from large-scale boundary element models. A coarse surface grid solution coupled with an efficient physically-based procedure provides an effective initial guess for a fine surface grid model. The process converges very efficiently offering substantial savings in memory. We discuss the implementation of the iterative domain decomposition approach for parallel computation on a modest Windows XP Pentium P4 PC-cluster running under MPI. Results from 3-D BEM heat conduction models including models of upwards of 85,000 nodes demonstrate that the BEM can practically be used to solve large-scale linear- and non-linear heat conduction problems using this algorithm.
Theoretical Phonon Thermal Conductivity of Si/Ge Superlattice Nanowires
Authors: Dames Chris , Chen Gang
Published: December 2008

The net-radiation method of radiative heat transfer has been combined with the diffuse mismatch interface condition to develop a model for the phonon thermal conductivity of superlattice nanowires. The important size effect is increased classical scattering at interfaces and side walls, which is treated as diffuse and gray (frequency independent). Coherence and quantum confinement effects are neglected, which should be appropriate for typical nanowires at room temperature. An isotropic, sine-type dispersion relation is used which is a significant improvement over the common Debye dispersion. Without any adjustable parameters, the model captures the effects of diameter, segment length, and transmissivity. A simpler picture is offered in terms of Matthiessen’s rule and effective mean free paths. The limitations of the model are also discussed. For a model Si/Ge superlattice nanowire at 300 K, the thermal conductivity is reduced below the alloy limit (7.0 W/m-K) when the diameter is less than 15 nm and/or the segment length is less than 20 nm.
Deposition of Small Particles From Turbulent Flows
Authors: Wu Z. , Young J. B.
Published: December 2008

This paper deals with particle deposition onto solid walls from turbulent flows. The aim of the study is to model particle deposition in industrial flows, such as the one in gas turbines. The numerical study has been carried out with a two fluid approach. The possible contribution to the deposition from Brownian diffusion, turbulent diffusion and shear-induced lift force are considered in the study. Three types of turbulent two-phase flows have been studied: turbulent channel flow, turbulent flow in a bent duct and turbulent flow in a turbine blade cascade. In the turbulent channel flow case, the numerical results from a two-dimensional code show good agreement with numerical and experimental results from other resources. Deposition problem in a bent duct flow is introduced to study the effect of curvature. Finally, the deposition of small particles on a cascade of turbine blades is simulated. The results show that the current two fluid models are capable of predicting particle deposition rates in complex industrial flows.
A Novel Method to Estimate Parameters of the Wall-Wetting Fuel Model in MPFI Engines for Cold Start and Warm Up Conditions
Authors: Shahbakhti M. , Ghafuri M. , Aslani A. R. , Sahraeian A. , Jazayeri S. A. , Azadi S.
Published: December 2008

In order to fulfill the LEV/ULEV exhaust emission standards, it is necessary to have a precise control of air fuel ratio under transient conditions especially during cold start and warm up periods. The objective in this study was to estimate parameters of a fuel delivery model and use them to provide a correct fuel injection compensation strategy. In this study, fuel transfer characteristics of intake port of a typical fuel-injected spark ignition engine have been determined for engine warm-up conditions following cold starts at temperature down to −15°C and extending to fully-warmed-up conditions, using a method based upon perturbing fuel injection rate and recording AFR (Air Fuel Ratio) response. Since there was no cold chamber available to perform tests in cold start conditions, a new method was utilized to simulate cold start conditions. This method can be used on any PFI engine with closed valve injection strategy. Following the estimation of fuel transfer model parameters, the variation of fuel film deposit factor (X), fuel film evaporation time constant (τf) and transport delay to oxygen sensor (ΔT) parameters over a range of temperatures, engine speeds and intake manifold pressures have been evaluated, providing a good insight to define transient fuel compensation requirements for cold start and warm up conditions.
Performance and Experience of the ABB TPL65VA Turbocharger With Variable Turbine Geometry on Medium-Speed Gas Engines for Generator Operation
Authors: Vlaskos Ioannis , Seiler Martin , Jacoby Pierre
Published: December 2008

This paper presents the main features of an ABB turbocharger with integrated new variable geometry for the axial flow turbine and highlights its potential for improving medium-speed gas engine performance as well as the turbocharger’s adaptability to a wide range of engine applications and operating conditions. The main findings of field tests performed on a medium-speed lean burn gas engine are reported. Calibrated engine simulation computer models based on test results from a medium-speed 4-stroke gas engine with variable turbine geometry turbochargers in generator operation are used to describe the benefits expected by introducing the variable turbine nozzle ring instead of an exhaust waste gate as a gas engine control system. Special attention is paid to the investigation of the transient engine response. A direct comparison of the waste gate and VTG-control system shows the VTG-potential for further engine optimization in terms of transient response.
Nitrogen Enriched Combustion of a Natural Gas Engine to Reduce NOx Emissions
Authors: Biruduganti Munidhar S. , Gupta Sreenath B. , McConnell Steven , Sekar Raj
Published: December 2008

Nitrogen enrichment of intake air is proposed as an alternative to Exhaust Gas Recirculation (EGR). Experimental results of nitrogen enriched combustion of a Kohler M12 engine (converted to operate with natural gas) are presented in this paper. A 70% reduction in NOx emissions was observed at full load (4 kW) and ignition timing (IT) equal to −20 ATDC with 2.1% NO2 enrichment (40 slpm). However, NOx reduction was minimal at lower loads. The effect of spark or ignition timing along with nitrogen enrichment is also reported for full load. It is recognized that advancing the ignition timing from conventional values has more advantages than retarding the same. A 68% reduction in NOx and a 0.8% drop in Fuel Conversion Efficiency (FCE) were observed at −30 ATDC ignition timing. However, the maximum ignition timing advance with stable engine operation was limited to −40 ATDC. Some of the drawbacks encountered were engine misfire at higher concentrations of nitrogen-rich air and retarded spark timing resulting in poor FCE.
A Numerical Study on the Design and Flow Patterns of Compressor Impeller in a Marine Engine Turbocharger
Authors: Kim Hong-Won , Ryu Seung-Hyup , Ghal Sang-Hak , Ha Ji-Soo
Published: December 2008

The centrifugal compressor design of the high-speed marine engine (500–900 kW) turbocharger has been done. Increased Higher compressed air and power density help improvement of the engine performance and power. The centrifugal compressor of the marine engine turbocharger is composed of impeller, 1st vaneless diffuser, vaned diffuser, 2nd vaneless diffuser and volute casing. The design process is achieved by three following stages. First, quasi-two dimensional code is used to determine the main geometry of the compressor. Second, three-dimensional compressible Navier-Stokes equation is applied to analyze the flow pattern and structures of the compressor blade loading. Here, among compressor impeller geometry, blade height variables are mainly changed. Smooth flow guidance has to precede and flow separation symptoms must not appear within compressor impeller. When the loading distribution is inadequate from blade hub to shroud, new curved profile should be designed to minimize the pressure loss. By analyzing the internal flow fields for the compressor impeller geometry variations, three dimensional impeller design profile has been confirmed. Compressed air pressure and mass flow rates from new optimized design were 2.7%, 27.3% higher than that of old one each other. Third, analyzed results are compared with experimental data for the verification of the present design method.
Friction Predictions for Piston Ring-Cylinder Liner Lubrication
Authors: Xu H. , Bryant M. D. , Matthews R. D. , Kiehne T. M. , Steenwyk B. D. , Bolander N. W. , Sadeghi F.
Published: December 2008

This paper presents two piston ring and cylinder liner lubrication models and compares the friction predictions against the experimental results from a corresponding bench test. The first model aims to solve the average Reynolds equation with corrective flow factors, which describe the influence of surface irregularities on the lubricant flow under mixed lubrication condition. The second model takes account of the lubricant film rupture and cavitation. Meanwhile, a stochastic rough contact sub-model quantifies the relation between contact pressure and mean surface separation in both cases. Numerical results on the top compression ring simulation show that both models capture hydrodynamic, mixed, and boundary lubrication regimes, which depend on the real surface topographies of the piston ring and the cylinder liner. Whenever hydrodynamic action is insufficient to maintain the equilibrium position of the ring, the restoring force will be augmented by multi-asperity contacts lubricated by a thin boundary film. Total friction will originate mainly from shearing of viscous lubricant and shearing of asperity conjunctions. The purpose of this modeling effort is to compare both lubrication models to data from an experimental test-rig. This test rig eliminates many of the factors that can make analysis of predictions for real engine operating conditions difficult.
Numerical Prediction on the Characteristics of Spray-Induced Mixing and Thermal Decomposition of Urea Solution in SCR System
Authors: Kim Joo Youn , Ryu Seung Hyup , Ha Ji Soo
Published: December 2008

The spray-induced mixing characteristics and thermal decomposition of aqueous urea solution into ammonia have been studied to design optimum sizes and geometries of the mixing chamber in SCR (Selective Catalytic Reduction) system. The cold flow tests about the urea-injection nozzle were performed to clarify the parameters of spray mixing characteristics such as mean diameter and velocity of drops and spray width determined from the interactions between incoming air and injected drops. Discrete particle model in Fluent code was adopted to simulate spray-induced mixing process and the experimental results on the spray characteristics were used as input data of numerical calculations. The simulation results on the spray-induced mixing were verified by comparing the spray width extracted from the digital images with the simulated particle tracks of injected drops. The single kinetic model was adopted to predict thermal decomposition of urea solution into ammonia and solved simultaneously along with the verified spray model. The hot air generator was designed to match the flow rate and temperature of the exhaust gas of the real engines. The measured ammonia productions in the hot air generator were compared with the numerical predictions and the comparison results showed good agreements. Finally, we concluded that the design capabilities for sizing optimum mixing chamber were established.
Laser Spark Ignition: Laser Development and Engine Testing
Authors: McMillian Michael H. , Woodruff Steven D. , Richardson Steven W. , McIntyre Dustin L.
Published: December 2008

Evermore demanding market and legislative pressures require stationary lean-burn natural gas engines to operate at higher efficiencies and reduced levels of emissions. Higher in-cylinder pressures and leaner air/fuel ratios are required in order to meet these demands. Contemporary ignition systems, more specifically spark plug performance and durability, suffer as a result of the increase in spark energy required to maintain suitable engine operation under these conditions. This paper presents a discussion of the need for an improved ignition source for advanced stationary natural gas engines and introduces laser spark ignition as a potential solution to that need. Recent laser spark ignition engine testing with natural gas fuel including NOx mapping is discussed. A prototype laser system in constructed and tested and the results are discussed and solutions provided for improving the laser system output pulse energy and pulse characteristics.
Thermal Management for 6-Cylinder HCCI Engine: Low Cost, High Efficiency, Ultra-Low NOx Power Generation
Authors: Martinez-Frias Joel , Flowers Daniel , Aceves Salvador M. , Espinos-Loza Francisco , Dibble Robert
Published: December 2008

This paper investigates a purely thermal control system for a 6-cylinder HCCI engine. Thermal energy from exhaust gas and from compression is used to condition the charge for the desired engine output. HCCI engine operation is analyzed with a detailed chemical kinetics based engine cycle simulation code. This cycle simulation code is linked to an optimizer that determines the operating conditions that result in maximum brake thermal efficiency, while meeting the restrictions of low NOx, and peak cylinder pressure. The results show the values of the operating conditions that yield optimum efficiency as a function of brake power for a constant engine speed (1800 rpm). It has been determined that a thermally controlled HCCI engine can successfully operate at high efficiency and low emissions over a wide range of conditions from idle to full load. The results show that a 42% brake thermal efficiency can be reached while the NOx emissions are kept under 2 parts per million. The analytical results shown here are expected to guide the ongoing experimental effort of converting a heavy-duty stationary engine to HCCI mode. The experimental work has the goal of meeting the very aggressive efficiency and emissions targets set by the California Energy Commission (CEC) Advanced Reciprocating Internal Combustion Engine (ARICE) Program.
Effect of Fuel Injection Pressure and Preheating on the Performance and Emissions of a Vegetable Oil Fuelled Diesel Engine
Authors: Serane Pugazhvadivu , Krishnamurthy Jeyachandran
Published: December 2008

In the present investigation, waste frying oil, a non-edible vegetable oil is used as a diesel fuel substitute. Performance and emission tests were carried out in a naturally aspirated, single cylinder, direct injection diesel engine with and without preheating the waste frying oil and with fuel injection pressures of 190 bar, 210 bar, 230 bar and 250 bar. Performance parameters such as brake specific energy consumption and brake thermal efficiency and emission parameters such as NOx and smoke density were evaluated at various operating conditions. Increasing the injection pressure with and without preheating the fuel is found to improve the performance and reduce smoke emissions. At these conditions, the NOx concentration is seen to increase, however it is lower than pure diesel operation.
A Three-Dimensional Model for Piston Ring-Pack Dynamics and Blow-By Gas Flow
Authors: Liu Liang , Tian Tian
Published: December 2008

A three-dimensional (3D) model for piston ring-pack dynamics and blow-by gas flow was developed to enable more in-depth analyses of the ring-pack performance. This model predicts the 3D dynamic behavior of compression rings and twin-land oil control ring due to the ring’s non-axisymmetric properties, bore distortion and piston secondary motion. Finite element beam theory is used for ring structure calculation. Gas flows along the axial and circumferential directions of the power cylinder system are resolved simultaneously with the ring dynamics. The model was applied to a heavy-duty diesel engine. Particular emphasis was placed on the dynamics of keystone type of top ring, and the stability of the second ring with a twist chamfer and twin-land oil control ring under the influence of piston secondary motion. The variations of the gas pressure and ring dynamic behavior along the circumference are discussed.
Vehicle Thermal Management: A Model-Based Approach
Authors: Cipollone Roberto , Villante Carlo
Published: December 2008

Cooling system design has a crucial role in defining engine performance, operational limits and thermal comfort. Many further improvements with respect to the actual situation can be obtained through a more accurate control of an-board thermal needs. To this new interest the definition of new technical specifications must follow. The technical literature, however, seems not fully satisfying this need, not focusing on the influence of these technical specifications on system design, reliability and costs. In this paper the authors present a contribution in this direction, showing the capabilities of an active intelligent management of the engine cooling system. This can be obtained through different control strategies, strongly diversified for their cost-performance ratio. The potentiality of a model-based controller has been also investigated and compared with the correspondent closed-loop controller.
Multi-Stage Collector Design and Applications
Authors: Krigmont Henry V.
Published: December 2008

The Multi Stage Collector (MSC™) concept for ultra-fine particulate control not only retains the best advantages of current state-of-the-art technology but also makes significant improvements. The new MSC™ design provides a synergistic combination of both single- and two-stage electrostatic precipitation while incorporating an additional collector-stage by filtering the gas exiting the collector through a barrier collector-zone. This arrangement ensures that essentially all dust would be detained in this final stage. The MSC™ contains multiple narrow and wide zones formed by a plurality of parallel corrugated plates. Enclosed in the narrow zones are discharge electrodes. These electrodes provide a non-uniform electric field leading to corona discharge. The corona discharge causes particulate matter in the gas flow to become charged. Wide regions contain barrier filters thus creating the two-stage precipitator with relatively uniform electric field. In these regions, particles are collected on both plates and on the porous barrier elements, which also act as the final filtering stage. Results of the applications analyses and future development work are discussed. The gas flow analyses with an aid of the CFD model are presented below.
Coal Fired MHD Technology: A Prospective Power Generation Method
Authors: Kulkarni Manohar , Gong Xiangyang
Published: December 2008

By passing the combustion gases through magnetic field, magneto generator converts heat directly to electric power without moving parts. The inherent characteristic of high efficiency and low emission makes Coal fired MHD power generation technology attractive to be a potential alternative power generation method in the future. This paper presents the working principle of MHD generator and describes the coal fired MHD power plant systems and the key components in these systems. It also reviews the batch research of Department of Energy on coal fired MHD electric power generation—Proof of Concept Program from 1987 to 1993 and states some challenges remained on its way to commercial use.
Statistical Process Control for Power Plants
Authors: Flesch Philip J.
Published: December 2008

Statistical Process Control (SPC) is successfully used by manufacturing and service organizations to control processes. The advent of SPC has created significant improvements in manufacturing, and SPC is a key element in six sigma quality programs. The application of SPC allows trained professionals to analyze any process to better understand and control that process. SPC has been in steady use for decades, and numerous books have been written on its application. “SPC is a decision-making tool, and change is the foundation of SPC. When a process changes (goes beyond established limits), SPC helps the quality specialist identify the change and decide if the change is good or bad.” 1. “If the change is bad, the reason for the change is identified and every attempt is made to eliminate the occurrence of the cause of the change.” 2. “If the change is good, the reason for the change is identified and every attempt is made to make the occurrence of the cause of the change common practice.” [Statistical Quality Control, Seventh Edition] SPC may be applied to component and system monitoring at power plants. Equipment reliability, preventive maintenance effectiveness and plant aging have become more important to the owners and operators of power plants. These issues directly affect the plant’s capacity factor and operating costs. SPC provides feedback on measured process parameters, and power plants measure process parameters. SPC can be used to identify early indication of changes in these parameters. This allows plant personnel to identify performance changes that may be indicative of failing equipment reliability. Since it is a fairly simple tool, SPC is easily available to any power plant operator. Data can be loaded into Excel templates, and the appropriate graphs can be easily generated. Since many personnel are familiar with Excel, the application of SPC can be relatively easy initiate. Other statistical analysis programs are available (ex: EPRI MSET) for process parameter review. However, the other tools are not as simple as SPC. Examples will be provided that demonstrate how SPC can be applied to measured power plant parameters. These examples will also demonstrate how the results of SPC can be used to identify potential equipment reliability issues or to control parameters within narrow bands. Finally, the examples will demonstrate how SPC is superior to run graphs (i.e. a parameter graphed over time — over a “run”) as an analysis tool.
Optimization of Steam Turbine Extraction Pressures
Authors: Egelioglu Fuat , Aybar Hikmet S.
Published: December 2008

A power plant has to be simulated to perform parametric study, to make optimization, to set operation characteristics, etc. There are many methodologies for modeling and simulation of power plants. In this study, a very simple yet detailed power plant simulation has been developed by Vis-Sim that is visual block oriented visualization package. An iterative method (or algorithm) has been developed to obtain the optimum extraction pressures. As an application of the simulator and optimization algorithm, a 60-MWe oil-fired power plant, which is a local power plant, has been simulated. The results of the simulator are in good agreement with the actual plant data without optimization, and the optimized extraction pressures for this power plant have been obtained.
Steam-Injected GT Cycles Offer More Power in a Hot Season
Authors: Hanawa Kirk
Published: December 2008

It is said that gas turbine generating plants on simple cycle reduce the power output by 3% in variation with 1% increase of ambient temperature change. When maintaining maximum cycle temperature, i.e., turbine inlet temperature (T4), the reduction of temperature ratio cannot be avoided by increasing minimum cycle temperature, i.e., ambient temperature (T2). Accordingly, the useful power output must be reduced and the thermal energy would be emitted into the atmosphere. The widely used combined cycle plant is an idea to recover the not-used thermal energy into the power, and it is still losing power by 2% in variation with 1% of the ambient temperature. In order to recover effectively such waste thermal energy into the power output, many ideas are adopted to mainly aim the thermal efficiency exceeding 60%, like “Steam-Cooled Combined Cycle”, “Kalina Cycle” etc. It was confirmed that the water/steam-injected WI/GAS3D GT version of modified LM6000 could produce 106 MW with 56% thermal efficiency at ISO conditions *6, and it is demonstrated, this time, that the power curve of the plant in variation with ambient temperature is very flat, comparing with those of conventional GT plants. It might be recommended to establish advantageous cycle plants using the more advanced gas turbines derived from like GE90, PW4000, and Trent800, in order to get exceeding 60% thermal efficiency in hot climate conditions, and it would be expected that such technology application might contribute to execute the worldwide COP3 agreement by saving the fossil fuel usage, resulting in minimal CO2 emissions.
Optimization of a MCFC/Turbine Hybrid System for Cogeneration
Authors: Karvountzi Georgia C. , Price Clifford M. , Duby Paul F.
Published: December 2008

High temperature fuel cells can be integrated in a hybrid cycle with a gas turbine and achieve lower heating value (LHV) efficiencies of about 70%. A hybrid cycle designed for cogeneration applications could lead to even higher LHV efficiencies such as 78% to 80% without post combustion and 85%–90% with post combustion. The purpose of the present paper is to optimize the integration of a high temperature fuel cell in a cogeneration cycle. We used Gatecycle™ heat balance software by GE Enter Software, LLC, to design a 20–80 MW high efficiency cogeneration plant. Since Gatecycle™ does not have an icon for the fuel cell, we calculated the heat balance for the fuel cell stack in Microsoft® Excel and we imported the results into Gatecycle™. We considered a 8.5 MW, a 17 MW and a 34 MW fuel cell by scaling up of the commercially available 3MW molten carbonate fuel cell (MCFC). Our goal was to evaluate the optimum ratio between the fuel cell size and gas turbine size using a family of curves we developed showing LHV “electric” efficiency versus power for different ratios of “fuel cell–to–gas turbines size”. Similar curves showing LHV “cogeneration” efficiency are also presented. In addition configurations with a back pressure steam turbine and with a condensing steam turbine are evaluated. The influence of steam generation pressure in the overall system efficiency is discussed, as well as the performance of the hybrid system for different temperatures (0°F–80°F) and elevations (0 ft–3000 ft). Our conclusion is that high temperature fuel cells in a hybrid configuration with gas turbines could be successfully integrated into a cogeneration plant to achieve very high efficiencies.
A Pragmatic Approach to Evaluation of Inlet Fogging System Effectiveness
Authors: Willems Daniel E. , Ritland Paul D.
Published: December 2008

The inlet fogging of gas turbine engines has been extensively applied over the past several years. Fogging systems have been predicted to increase gas turbine power output by 10 to 15% based on theoretical and laboratory test results. This paper describes methodology to validate the evaporative cooling effect and quantify performance of inlet fogging systems. A quantitative analysis of inlet fogging systems is provided based on gas turbines operating in different environmental conditions. The tests were conducted on SWPC W501FD Frame gas turbines nominally rated at 185 MW. The data presented herein considers the actual combustion turbine operating conditions, psychrometric considerations and field measurements. This paper also considers the application of specialized temperature measurement equipment suitable for accurate drybulb temperature detection in an environment that may contain free water in the airstream. Theoretical and actual application results are presented to validate the instrument accuracy.
Study of Mixing Enhancement From a 12-Lobe Convoluted Mixer
Authors: Yimer Ibrahim , Jiang Leiyong , Campbell Ian , Manipurath Shaji
Published: December 2008

Lobed mixers have been used in a variety of engineering applications, such as jet noise reduction, infrared suppression and improvement of propulsive efficiency for turbine engines. More recently, they have emerged as an attractive method to enhance mixing between fuel and air in advanced low-emission gas turbine combustors. The objectives of the present work were to assess the effectiveness of these devices for use inside the combustor and provide experimental data to validate CFD predictions. The mixing enhancements due to streamwise vortices generated from a 12-lobe convoluted mixer were characterized using Planar Laser Induced Fluorescence (PLIF) measurements, while 2-D PIV measurements established the underlying velocity field. The geometrical set-up of the mixing system is pertinent to many combustion systems using advanced lean premixed concepts with gaseous fuels. In addition to the benchmark case with no mixer, two different lobe geometries were considered, a semi-circle (or round) lobe and a square lobe. In this paper the experimental results are presented and discussed. Numerical predictions were performed for the semi-circle lobe geometry using a Reynolds-averaged Navier-Stokes (RANS) code and the results are compared with experimental measurements.
Optimization Concerns for Combined Cycle Power Plants: II — Optimum Fuel Gas Heating
Authors: Serbetci Walter I.
Published: December 2008

As the second study in a sequence of studies conducted on the optimization of combined cycle plants [Ref. 1], this paper presents the effects of fuel gas heating on plant performance and plant economics for various 1×1×1 configurations. First, the theoretical background is presented to explain the effects of fuel gas heating on combustion turbine efficiency and on the overall efficiency of the combined cycle plant. Then, *CycleDeck-Performance Estimator™ and *GateCycle™ computer codes were used to investigate the impact of fuel gas heating on various 1×1×1 configurations. The configurations studied here are: 1) GE CC107FA with three pressure/reheat HRSG and General Electric PG7241(FA) gas turbine (Fig. 1), 2) GE CC106FA with three pressure/reheat HRSG and General Electric PG6101(FA) gas turbine and, 3) GE CC 107EA with three pressure/non-reheat HRSG with General Electric PG7121(EA) gas turbine. In all calculations, natural gas with high methane percentage is used as a typical fuel gas. Hot water from the outlet of IP economizer is used to heat the fuel gas from its supply temperature of 80 °F (27 °C). Heating the fuel gas to target temperatures of 150 °F, 200 °F, 250° F, 300 °F, 350 °F, 375 °F, 400 °F and 425 °F ( 66, 93, 121, 149, 177, 191, 204 and 218 °C), the combustion turbine power output, the combustion turbine heat rate and the plant power output and the corresponding heat rate are determined for each target fuel temperature. For each configuration, the heat transfer surface required to heat the fuel gas to the given target temperatures are also determined and budgetary price quotes are obtained for the fuel gas heaters. As expected, as the fuel temperature is increased, the overall efficiency (therefore the heat rate) improved, however at the expense of some small power output loss. Factoring in the fuel cost savings, the opportunity cost of the power lost, the cost of the various size performance heaters and the incremental auxiliary power consumption (if any), a cost-benefit analysis is carried out and the economically optimum fuel temperature and the corresponding performance heater size are determined for each 1×1×1 configuration.
An Experimental Study of Labyrinth Seal Flow
Authors: Michaud Mike , Vakili Ahmad , Meganathan Abraham , Zielke Robert , Shuster Lewis , Terrell James
Published: December 2008

The leakage flow in a 2-D stationary stepped labyrinth seal is investigated by means of flow visualization, pressure field measurements, and Particle Image Velocimetry. The basis of investigation is a generic stepped labyrinth seal currently used by the industry in steam turbine generators. Geometric and flow parameters were varied in order to examine their influence on leakage through seals. Flow visualization results revealed inter-related mechanisms of energy loss in labyrinth seals to include turbulence induced viscous losses, chamber vortex generation, flow stagnation, and increased flow streamline curvature. A five times scale model was constructed and tested over a range of seal pressure ratios from 1:1 to 10:1. Model configurations included a baseline and six variants of the basic design that were conceptually devised to be superior and by varying step height and knife angle. Detail pressure and velocity measurements were carried out. Results show that with relatively minor changes in geometry, determined based on our understanding of the physics of the flow, leakage reductions of up to 17% were accomplished.
Development of Brush Seal Technology for Steam Turbine Retrofit Applications
Authors: Stephen Don , Hogg Simon I.
Published: December 2008

Increased cylinder efficiency is one of the main drivers in the steam turbine retrofit market, particularly for HP and IP modules. To-date most retrofit turbine suppliers have concentrated their efforts on improving the aerodynamic efficiency of blades and other steampath components, optimizing stage numbers and reducing leakage losses. Developments in all of these areas rely heavily on improved design and analysis tools to refine existing designs and evaluate new concepts. The opportunity exists to further reduce leakage losses by replacing conventional labyrinth seal designs by more advanced turbomachinery sealing technology. Brush seals, which have now been used successfully in some gas turbine (mainly aero-engines) applications for several years, are a natural candidate for steam turbine retrofits. Careful thought is needed when applying brush seals as the mechanical integrity of the cylinder needs to be maintained at all times. Attempts to increase performance should never be at the expense of availability and reliability. This paper describes the development work undertaken by the authors’ company and covers research in the areas of brush seal design, performance improvement, operational issues, and life assessment.
A New Flywheel Energy Storage System for Distributed Generation
Authors: Tang Shuangqing , Zuo Weiwei , Liao Daoxun
Published: December 2008

It is necessary to install flywheel energy storage (FES) system in distributed generation, which can improve the quality and the reliability of electric power. The proposed system is composed of four parts: flywheel, magnetic bearing, motor/generator, and power converter. A permanent magnet motor-generator is incorporated in a composite flywheel, running at high speed in a vacuum containment to minimize air friction losses. The flywheel is to be suspended on magnet bearings. A 3-phase, switch mode bridge inverter, driven by a pulse width modulation board, achieves the variable speed control for the motor/generator and the control for the DC bus voltage. The presentation will explain the schematics of the flywheel battery, control diagram, power electronics and motor/generator. The overall operation will be described.
Combustion Improvement System in Boilers and Incinerators
Authors: Blasiak Wlodzimierz , Yang Weihong
Published: December 2008

This work presents the main features, advantages and evaluation of applications of the novel “Ecotube” combustion improvement and emission reduction system by Ecomb AB of Sweden and Synterprise, LLC of Chattanooga, Tennessee. In the Ecotube system, the nozzles used for mixing are put on the suitable position inside the combustion chamber to control uniformity of temperature, mixing and reactants distribution in boilers and incinerators since the formation and reduction of pollutants (NO, CO and VOC) and in-furnace reduction processes (Air/Fuel staging, SNCR, flue gas recirculation and SOx reduction by dry sorbent injection) are related directly to mixing in a combustion chamber. The novel Ecotube combustion improvement system allows better control of mixing of the gases for example from a primary combustion zone with secondary combustion air or a recirculated flue gas. By means of the novel system it is possible to better control the residence time and to some degree gas phase temperature distribution as well as the heat release distribution in the furnace of the waste incinerators or boilers. This new combustion improvement system can be applied to supply different gas or liquid media — for example air, fuel, urea or even solid powder. Using the system a more efficient and environmentally clean combustion or incineration process can be performed. The Ecotube System may be used to meet increasingly stringent environmental emissions regulations, such as NOx SIP Call, while it delivers added benefits of reduced and stabilized CO and reduced fly ash and improved boiler efficiency. The study tool used in this work to present influence of the Ecotube system design on temperature as well as uniformity of reactants and flow field is numerical modeling. Using this tool, the influence of the position of the Ecotube system and the injection angle of the nozzles are studied. The studied boilers included the biomass waste incinerator, municipal solid waste incinerator and coal fired boiler. The concept of the Heat Release Distribution Ratio is proposed to classify the heat release inside the upper furnace of the boilers or incinerators. The results show that Ecotube spreads reaction zone over a larger furnace volume. The furnace flame occupation coefficient can be as high as 45% with the Ecotube system and it is around 40% higher comparing with the conventional multinozzle mixing system. Ecotube system allows keeping far more uniform heat release distribution, more uniform temperature distribution, and thus longer life of the heat transfer surfaces inside the furnace. Position of the Ecotube system and the injection angle of the nozzles are of primary importance and can be used as a technical parameter to control the boiler operation at different loads and varying operating conditions.
A New Combined Power and Cooling Cycle for Low Temperature Heat Sources
Authors: Goswami D. Y. , Tamm Gunnar , Vijayaraghavan Sanjay
Published: December 2008

A new thermodynamic cycle has been developed for the simultaneous production of power and cooling from low temperature heat sources. The proposed cycle combines the Rankine and absorption refrigeration cycles, providing power and cooling in desired ratios to best suit the application. A binary mixture of ammonia and water is used as the working fluid, providing a good thermal match with the sensible heat source over a range of boiling temperatures. Due to its low boiling point, the ammonia-rich vapor expands to refrigeration temperatures while work is extracted through the turbine. Absorption condensation of the vapor back into the bulk solution occurs near ambient temperatures. The proposed cycle is suitable as a bottoming cycle using waste heat from conventional power generation systems, or can utilize low temperature solar or geothermal renewable resources. The cycle can be scaled to residential, commercial or industrial uses, providing power as the primary goal while satisfying some of the cooling requirements of the application. The cycle is under both theoretical and experimental investigations. Initial parametric studies of how the cycle performs at various operating conditions showed the potential for the cycle to be optimized. Optimization studies performed over a range of heat source and heat sink temperatures showed that the cycle could be optimized for maximum work or cooling output, or for first or second law efficiencies. Depending on the heat source temperatures, as much as half of the output may be obtained as refrigeration under optimized conditions, with refrigeration temperatures as low as 205 K being achievable. Maximum second law efficiencies over 60% have been found with the heat source between 350 and 450 K. An experimental system was constructed to verify the theoretical results and to demonstrate the feasibility of the cycle. The investigation focused on the vapor generation and absorption processes, setting up for the power and refrigeration studies to come later. The turbine was simulated with an equivalent expansion process in this initial phase of testing. Results showed that the vapor generation and absorption processes work experimentally, over a range of operating conditions and in simulating the sources and sinks of interest. The potential for combined work and cooling output was evidenced in operating the system. Comparison to ideally simulated results verified that there are thermal and flow losses present, which were assessed to make both improvements in the experimental system and modifications in the simulations to include realistic losses.
Replacing a Fixed Tubesheet Feedwater Heater Design Installed in a Condenser Neck With a U-Tube Design
Authors: Yokell Stanley , Hughes Danny
Published: December 2008

In 1969 Arkansas Nuclear One Unit 1 (ANO 1), which Entergy Operations Inc. operates in Russellville, Arkansas, installed SWECO-built LP Feedwater Heaters E-5A and E-5B in the condenser neck. The heaters are 1205.4 × 13970 mm (51-inch. ID × 45 ft 10-inch) straight length, fixed-tubesheet design. When the condition of the heaters required replacement, on advice of their Engineering Consultant, ANO 1 decided to replace the fixed tubesheet heater bundle sections with U-tube bundles. The replacements were required to meet upgraded performance requirements and to fit into the existing heater shells with limited changes to length. This paper describes the problems that were encountered and their solutions used to prepare the purchase specification for the replacement bundles and the modifications to the existing heater shells.
Advanced Gas Turbine Monitoring and Diagnostic Technology for Modern Power Plants
Authors: Andersen Helmer , Chen Pen-Chung , Hartmann Theo
Published: December 2008

Alstom has developed a monitoring and optimization system to offer the power plant an integrated maintenance and diagnosis system. This system is capable of monitoring all Alstom machines and processes in a combined cycle power plant: the gas turbine, steam turbine, generator, HRSG, and cooling system. All data archived in a central database server. Any personal computer networked with the server can display the process data and calculated results. To limit the scope of current paper, only the gas turbine monitoring and diagnostic module is presented. The system concept, configuration, and the environment of gas turbine module as well as capability will be discussed in this paper. The Gas Turbine Module (GTM) provides continuous monitoring of the GT process and continuous displaying of certain calculated results. The GTM provides a tool aimed to help the operator to make decisions, which affect efficiency, reliability and damage control. The monitoring areas include combustion stability (pulsation analysis), exhaust temperature distribution, compressor fouling and surge margin, and thermal performance. Furthermore, the GTM can provide the thermodynamic variables at the gas turbine exhaust for other applications in the combined cycle calculation. The implementation of this module is based on the users’ requirements to optimize the operation, to increase plant reliability and availability, and to optimize equipment performance. The GTM is a PC-based monitoring and diagnostic system. A guiding principal is that the retrofit of the GTM should have minimal impact on the gas turbine control system. This is the reason the system is PC based. A remote connection can be made via network. Users can access and see all real time and historical data by means of a networked computer. The real key success of the GTM is to be able to detect an early component failure and abnormalities during normal plant operation. Therefore, this information can be used for plant management, production forecast, equipment maintenance, and part replacement decision strategy.