bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of the Flow Field of a Swirl Stabilised Premixed Burner in an Annular and a Single Burner Combustion Chamber
Authors: Fanaca D. , Alemela P. R. , Hirsch C. , Sattelmayer T. , Schuermans B.
Published: February 2010

An experimental investigation of the flow field of a 12 burner annular combustor and a single burner combustor with the same burner was performed. It has revealed the aerodynamic effect which causes the discrepancies in the flame transfer function behavior measured at the same operating conditions in the single and the annular combustion chambers. The results have shown significant differences in the flow field. In particular it is seen that for the investigated system in the annular combustor a free swirling jet flow forms while in the single burner configuration a swirling wall jet flow regime exists. In this paper we discuss the physical mechanism and show how to generalize an earlier finding which identified a critical confinement value for a given swirler. We propose a new correlation for co-swirling burners which explains the changes found for the investigated system. It compares also well with experimental data from other burner geometries. The correlation should allow to design single burner tests as to match the annular combustor flow regime.
Numerical Investigation of Char Reactivity in Oxy-Coal Combustion in Carbon Capture and Sequestration Technologies
Authors: Gharebaghi M. , Goh B. , Jones J. M. , Ma L. , Pourkashanian M. , Williams A.
Published: February 2010

Oxy-coal combustion with CO2 capture from flue gas is an emerging technology that can be adapted to both new and existing coal-fired power stations leading to substantial reduction in carbon emission from the power generation industry. However, switching to oxy-coal brings a number of uncertainties to the combustion process and there is a significant knowledge gap in this new technology. Computational Fluid Dynamic (CFD) studies can be used as one of the tool to identify the extent of the modifications required due to changes in the process. One of the possible challenges is related to the the changes in char combustion and char reactivity which may have an impact on unburned carbon in the furnace. In this study, two approaches have been undertaken to investigate the impact of oxy-coal combustion on char reactivity: simple equilibrium calculations and numerical 3-D simulations. As the focus of this study, the influence of CO2-O2 combustion environment on char reactivity and particularly carbon in ash has been investigated. It has been found that the effect of C-CO2 and C-H2O reactions on overall char reactivity cannot be disregarded. In addition, in this study, it is suggested that using the Langmuir-Hinshelwood mechanism can provide a more accurate prediction for the effect of gasification reactions on unburnt carbon and char reactivity. The accuracy of the CFD modeling has been investigated using experimental data from a one MWth combustion test facility. In order to improve the validity of the CFD code for design purposes, further modeling improvements for accurate predictions are addressed.
Performance Evaluation of the IPRP Technology When Fueled With Biomass Residuals and Waste Feedstocks
Authors: Fantozzi Francesco , D’Alessandro Bruno , Bartocci Pietro , Desideri Umberto , Bidini Gianni
Published: February 2010

The Integrated Pyrolysis Regenerated Plant (IPRP) concept is based on a rotary kiln pyrolyzer that converts biomass or wastes (B&W) in a rich gas used to fuel a gas turbine (GT); the combustion of pyrolysis by-products (char or tar), is used to provide heat to the pyrolyzer together with the GT exhaust gases. The IPRP concept was modelled through an homemade software, that utilizes thermodynamic relations, energy balances and data available in the Literature for BW pyrolysis products. The analysis was carried out investigating the influence on the plant performances of main thermodynamic parameters like the Turbine Inlet Temperature (TIT), the Regeneration Ratio (RR) and the manometric compression ratio (β) of the gas turbine; when data on the pyrolysis process where available for different pyrolysis temperature, also the different pyrolysis temperature (TP) was considered. Finally, data obtained from the analysis where collected for the typical parameters of different GT sizes, namely the manometric compression ratio and the turbine inlet temperature. For the other parameters, where considered the ones that give the highest efficiencies. The paper shows the IPRP efficiency, when fuelled with different biomass or wastes materials and for different GT (plant) size.
Advanced Exhaust Performance Modelling of Mixed Turbofan Engines: Less is More
Authors: Wachter J. , Ko¨pf F.
Published: February 2010

Forced mixing devices are commonly used to augment exhaust performance for turbofan engines with low and intermediate bypass ratios as emerging effects like noise and fuel burn reduction associated with the mixing of core and bypass gas streams outbalance the detrimental impacts like additional drag and weight for this engine size. However, the highly three-dimensional flow characteristics cause major challenges for a proper accounting in a simplified one-dimensional thermodynamic performance model of the mixer and nozzle component, which impact the overall engine cycle significantly. It is especially crucial for the determination of fan working lines as well as the generated gross thrust to feed the model with accurate input values. The present paper introduces the usage of stringent flow separated exhaust system models and its impact on rig-test execution and engine analysis. Benefits concerning off-design modeling as well as challenges arising with the outlined methodology are discussed in detail. Furthermore its capability as analysis pretest model is demonstrated by means of sea level testing of a midsized turbofan engine.
Fuel Vapor Concentration Measurements by Laser Induced Fluorescence and Infra-Red Extinction: An Investigation on a Monodisperse Droplet Stream
Authors: Wagner Bernhard , Frackowiak Bruno , Gajan Pierre , Strzelecki Alain
Published: February 2010

The vapor mole fraction field around a stream of monodisperse acetone droplets is investigated by Planar Laser Induced Fluorescence (PLIF) and Infra-Red Extinction (IRE). The PLIF works develop an interface positioning method based on the Lorenz-Mie Theory and on geometrical optics, which can be applied to the images despite the blooming effect caused by the liquid phase. Quantitative results obtained at two different injection temperatures concur with the numerical predictions. IRE results — taken at a high repetition rate on the same configuration — are presented. The dynamical behavior, possibilities and constraints of the employed techniques are discussed and an outlook to following investigations is given. This paper presents some PLIF and IRE basics, a description of the test rigs, the post processing of the obtained data and a comparison of the results to a simplified numerical calculation. Finally a discussion of the results and suggestions for improvements are proposed.
Multiple Faults Detection of Gas Turbine by MLP Neural Network
Authors: Matuck Gustavo R. , Barbosa Joa˜o Roberto , Bringhenti Cleverson , Lima Isaias
Published: February 2010

This paper describes a procedure to measure the performance of detection and isolation of multiple faults in gas turbines using artificial neural network and optimization techniques. It is on a particular form of artificial neural networks, the traditional multi-layer perceptron (MLP). Error back-propagation and different activation functions are used. The main goal is to recognize single, double and triple faults in a turboshaft engine, whose performance data were output from a gas turbine simulator program, tuned to represent the engine running at an existing power station. MLP network is a nonlinear interpolation function usually made of input layer, hidden-layer and output-layer, with different neuronal units, but in this work, only one hidden-layer was used. Weights were altered by error back-propagation from the initial values established from a seed fixed between 0 and 1. The activation function in the MLP algorithm is the sigmoid function. The best moment to stop the training process and avoid the over fitting problem was chosen by cross-validation. Optimization of convergence error was achieved using the momentum criteria and reducing the oscillation problem in all nets trained. Several configurations of the neural network have been compared and evaluated, using several noise graduations incorporated to the data, aiming at finding the network most suitable to detect and isolate multiple faults in gas turbines. Based on the results obtained it is inferred that the procedure reported herein may be applied to actual systems in order to assist in maintenance programs, at least.
Numerical Simulation of Non-Reacting and Reacting Flows in a 5MW Commercial Gas Turbine Combustor
Authors: Jeong Daero , Huh Kang Y.
Published: February 2010

This study is concerned with numerical simulation of a simple swirl flame and a 5MW commercial gas turbine combustor both operating on methane/air. Validation is performed for turbulent flow and combustion models against some measurement data (http://public.ca.sandia.gov/TNF/swirlflames.html). Evaluation is performed for the standard k-e and the realizable k-e models in the nonreacting swirl flow and the EBU (eddy breakup) and the PPDF (presumed probability density function) models in the reacting flow of the 5 MW commercial combustor. Independent simulations are carried out for the main and pilot nozzles to avoid flashback and to provide realistic inflow boundary conditions for the combustor. Important geometrical details such as air swirlers, vane passages and liner holes are taken into account. Different turbulence models result in similar flow patterns with varying sizes of the recirculation pockets in the central region and at the outside corner. The EBU and the PPDF models show similar downstream distributions of mean flow and temperature, while the EBU shows a lifted flame with a stronger effect of swirl due to limited increase of axial momentum by volume expansion near the nozzle.
Application of Existing Turbomachinery for Zero Emissions Oxy-Fuel Power Systems
Authors: Anderson Roger , Viteri Fermin , Hollis Rebecca , Hebbar Mohan , Downs James , Davies Daniel , Harris Mark
Published: February 2010

Future fossil-fuel-based power generation systems must include decarbonizing technologies to capture and store (CCS) carbon dioxide (CO2). Oxy-fuel (O-F) combustion-based power systems are uniquely capable of capturing almost all CO2. In the O-F power plant cycle, fuel and nearly pure oxygen, delivered from an air separation unit (ASU), are burned to form a working fluid composed primarily of steam and CO2. Clean Energy Systems (CES), Siemens Energy, Inc. and Florida Turbine Technologies, Inc. (FIT) are jointly developing turbomachinery systems driven by O-F working fluids and have adopted a stepped development approach to advance the technology toward product realization through an initial proof-of-concept phase and subsequent development of 1st and 2nd generation power plant systems. Specific goals and objectives target incremental advancements of power plant efficiency and output while reducing capital costs and cost of electricity. In the initial proof-of-concept phase, bench-level research was performed on a primary combustion system. A 20MWth development gas generator was used to explore operability and performance limits while operating on a variety of fuels over a wide range of conditions. Further, the working fluid produced by this combustor was used to drive an existing turbine/generator set at CES’ Kimberlina prototype power plant located near Bakersfield, California. This paper summarizes the recent follow-on work to develop and demonstrate 1st and 2nd generation O-F power plant systems. Successful completion of the proof-of-concept phase led to the development of the 1st generation power plant system. Specific equipment required for this operation included a larger 170MWth combustor, which was constructed to produce additional power in this phase. An existing General Electric GE-J79 turbine was modified to extract power from this unit. All equipment required for this system has been assembled at CES’ Kimberlina power plant. In addition, a reheat combustion system is being developed to enhance the 1st generation power plant cycle. In a logical next step, a larger power output, increased-efficiency 2nd generation power plant system was defined. For this application, the Siemens SGT-900 gas turbine was selected as the basis for the Intermediate Pressure Turbine. Conceptual design studies were performed to identify the modifications needed in order to adapt the hardware to accept O-F drive gases. Specific challenges related to the mechanical design configuration, and thermal/structural behaviors of the system are delineated. Testing is being performed to characterize the behavior of materials when exposed to the steam/CO2 working fluid environment. Necessary development of long-lead items required for this system is also described.
Film Cooling Study of Novel Orthogonal Entrance and Shaped Exit Holes
Authors: Abraham Santosh , Navin Alexander Ritchie , Ekkad Srinath V.
Published: February 2010

Film cooling effectiveness depends on several geometrical parameters like location on the airfoil, exit shape, orientation and arrangement of the holes. The focus of this investigation is to propose and explore a new film cooling hole geometry. The adiabatic film cooling effectiveness is determined experimentally, downstream of the exit of the film cooling holes on a flat plate using a steady state IR thermography technique. Coolant holes that are perpendicular to the direction of flow detach from the surface and enhance the heat transfer coefficient on the turbine blade without providing any coolant coverage, while angled holes along the mainstream direction result in superior film cooling effectiveness and lower heat transfer to the surface. The objective of this study is to examine the external cooling effects using coolant holes that are a combination of both angled shaped holes as well as perpendicular holes. The inlet of the coolant hole is kept perpendicular to the direction of flow to enhance the internal side heat transfer coefficient and the exit of the coolant hole is expanded and angled along the mainstream flow to prevent the coolant jet from lifting off from the blade external surface. A total of six different cases with variations in exit shape geometry are investigated at different blowing ratios (BR varying from 0.5 to 2.0). Results suggest that the film cooling effectiveness values obtained from these geometries are comparable with those of conventional angled holes. With the added advantage of enhanced heat transfer coefficient on the coolant channel internal side, as proven earlier by Byerley [3], overall superior cooling is accomplished. Furthermore this shaped hole can be made using the same technology being presently used in the industry.
Development of a New-Style Micro Diffuser
Authors: Chen Jie , Huang Guoping , Zhu Liangcong , Zhang Qiang
Published: February 2010

The vaned diffuser is advantageous in turbo-machinery which needs smaller size, so the vaned diffuser is widely used in the micro/small turbine engine. But the separation and strong mixing are often existent in the flow filed of such diffuser, and the viscous force, precision loss and frictional losses go up as size goes down, so the performance of micro diffuser is decreased. To improve the performance of diffuser in micro turbine engine, a new-style micro diffuser is presented in this investigation, which is composed of full blades and splitters. It is regarded as a series of ducts in design, and the effect of cross-section area distribution along the flow path on the new-style diffuser performance is studied. It not only can improve the performances, but also be easy to manufacture for micro turbine engines. The new-style micro diffuser was applied to replace the traditional vaned diffuser in an 11cm-diameter prototype engine, and the improvement of performance is verified by CFD and experiment. The advanced performance of the optimal micro diffuser (Cp above 0.65, σ above 0.9), is obtained with same external size.
Windage Power Loss in Gas Foil Bearings and the Rotor-Stator Clearance of High Speed Generators Operating in High Pressure Environments
Authors: Bruckner Robert J.
Published: February 2010

Closed Brayton Cycle (CBC) and Closed Supercritical Cycle (CSC) engines are prime candidates to convert heat from a reactor into electric power for robotic space exploration and habitation. These engine concepts incorporate a permanent magnet starter / generator mounted on the engine shaft along with the requisite turbomachinery. Successful completion of the long duration missions currently anticipated for these engines will require designs that adequately address all losses within the machine. The preliminary thermal management concept for these engine types is to use the cycle working fluid to provide the required cooling. In addition to providing cooling, the working fluid will also serve as the bearing lubricant. Additional requirements due to the unique application of these microturbines are zero contamination of the working fluid and entirely maintenance-free operation for many years. Losses in the gas foil bearings and within the rotor-stator gap of the generator become increasingly important as both rotational speed and mean operating pressure are increased. This paper presents the results of an experimental study, which obtained direct torque measurements on gas foil bearings and generator rotor-stator gaps. Test conditions for these measurements included rotational speeds up to 42000 revolutions per minute, pressures up to 45 atmospheres, and test gases of Nitrogen, Helium, and Carbon Dioxide. These conditions provided a maximum test Taylor number of nearly one million. The results show an exponential rise in power loss as mean operating density is increased for both the gas foil bearing and generator windage. These typical “secondary” losses can become larger than the total system output power if conventional design paradigms are followed. A non-dimensional analysis is presented to extend the experimental results into the CSC range for the generator windage.
Modeling of Turbulent Combustion Process and Lean Blowout of Diffusion and Premixed Flames Using a Combined Approach
Authors: Kutsenko Yu. G. , Inozemtsev A. A. , Gomzikov L. Y.
Published: February 2010

Most of the modern combustor’s designs use staged concepts for reducing thermal NO emissions. Usually, a combustion process takes place inside the main zone, which uses very lean premixed fuel/air mixtures. A diffusion pilot zone supports combustion process inside a lean main zone. Thermal NO formation process takes place predominantly inside hot diffusion flame. So, operation modes of pilot and main zones must be arranged to provide low NO emissions of pilot zone and maintain flame stability inside the main zone simultaneously. In this paper, a new turbulent combustion model is presented. This model allows to model diffusion and premixed flames and takes into account various physical processes, which lead to flame destabilization. The model uses an equation for reaction progress variable. Within the considered approach this equation has two source terms. These terms are responsible for different conditions of combustion process: diffusion flames and premixed flames, and distributed reacting zones. This paper studies the problem, concerning modeling of lean blowout process of diffusion flame front. To test the proposed combustion model we have simulated lean blowout process inside combustion zone of a gas turbine combustor. Good predictions of lean blowout limits were obtained.
Experimental Testing Techniques for Kevlar® Fiber Brush Seals
Authors: Ruggiero Eric J. , Allen Jason , Lusted Mark
Published: February 2010

Non-metallic brush seals, and more specifically, Kevlar® (aramid) fiber brush seals, are an emerging sealing technology in low-pressure, low temperature applications. Compared to metallic brush seals, aramid fibers are an order of magnitude smaller in diameter and consequently offer much tighter sealing capability. Further, their compliant nature requires minimal pressure drops across the seal to encourage blow-down of the bristle pack onto the rotor during operation. Similarly, their compliant nature also enables the bristle pack to correct for alignment issues and to recover from radial growth transients of the rotor. Proper design of the bristle pack stiffness is critical to the successful operation of the seal. If the seal is designed to be too soft, frictional forces prohibit the recovery of the bristle pack if pressed away from the rotor. Conversely, if designed too stiffly, then the heat generation at the sliding interface of the seal accelerates the degradation of the seal. The goal of the present paper is to present the experimental techniques developed to guide the design of aramid fiber brush seals. Two experimental test methodologies will be presented: a direct stiffness measurement and a heat generation measurement. Both testing procedures have been used to successfully design seals for various GE turbomachinery products.
Development of Alumina-Forming Austenitic Alloys for Advanced Recuperators
Authors: Pint Bruce A. , Brady Michael P. , Yamamoto Yukinori , Santella Michael L. , Howe Jane Y. , Trejo Rosa , Maziasz Philip J.
Published: February 2010

A new class of corrosion- and creep-resistant austenitic stainless steels has been developed for advanced recuperator applications. The Al and Cr contents have been optimized to maintain a fully austenitic composition for creep strength while allowing the formation of a highly-protective external alumina scale at temperatures up to 900°C in the presence of water vapor. Strengthening was achieved via the formation of stable nano-scale MC type carbides and creep properties were comparable to commercially available advanced austenitic stainless steel alloys. These properties are particularly well-suited for thin-walled recuperators for both small and large gas turbines and fuel cells. By forming an alumina scale, long-term problems with Cr evaporation in the presence of water vapor in the exhaust gas are eliminated. Laboratory data are presented from humid air and microturbine exhaust gas to illustrate the oxidation resistance of this class of alloys at 650°–900°C and compared to results for some current commercial alloys. Alloy development is continuing in order to determine the effect of composition on performance over this temperature range.
Computational Design of a Louver Particle Separator for Gas Turbine Engines
Authors: Musgrove Grant O. , Barringer Michael D. , Thole Karen A. , Grover Eric , Barker Joseph
Published: February 2010

The extreme temperatures in a jet engine require the use of thermal barrier coatings and internal cooling channels to keep the components in the turbine section below their melting temperature. The presence of solid particles in the engine’s gas path can erode thermal coatings and clog cooling channels, thereby reducing part life and engine performance. This study uses computational fluid dynamics to design the geometry of a static, inertial particle separator to remove small particles, such as sand, from the engine flow. The concept for the inertial separator includes the usage of a multiple louver array followed by a particle collector. The results of the study show a louver design can separate particles while not incurring large pressure loss.
Thermoeconomic Evaluation of CO2 Compression Strategies for Post-Combustion CO2 Capture Applications
Authors: Botero Cristina , Finkenrath Matthias , Belloni Clarissa , Bertolo Simone , D’Ercole Michele , Gori Enrico , Tacconelli Remo
Published: February 2010

CO2 compression significantly contributes to the overall efficiency penalty and capital cost increase resulting from CO2 capture. Performance improvement measures for this process step hence have the potential of considerably improving the overall economic picture for CO2-lean power generation from fossil fuels. The present paper gives an insight into the thermodynamics of CO2 compression in a natural gas combined cycle power plant with post-combustion CO2 capture. The work aims at gaining a better understanding of the boundary conditions, thermodynamic limitations, and performance entitlement governing the CO2 compression process. With the help of process simulation, different technically feasible strategies for compressing CO2 are evaluated, quantified, and compared against their thermodynamic entitlement; the compression power reduction and the maximum cost allowable for the performance improvement measures suggested are estimated.
Identifying Inefficiencies in Unsteady Pin Fin Heat Transfer
Authors: Schwa¨nen Markus , Duggleby Andrew
Published: February 2010

Internal cooling of the trailing edge region in a gas turbine blade is typically achieved with an array of pin fins. In order to better understand the effectiveness of this configuration for heat transfer, an unsteady Reynolds-averaged Navier Stokes computation is performed on a single row of cylindrical pin fins with a spanwise distance to fin diameter ratio of 2 and height over fin diameter ratio of one. With a locally adapted mesh, the boundary layer is resolved throughout the domain. For validation purposes, the flow Reynolds number based on hydraulic channel diameter ReDH = 12,800 was set to match experiments available in the open literature. The resulting time-dependent flow field was analyzed using a variation of Proper Orthogonal Decomposition (POD), where the correlation matrices were built using the internal energy in addition to the three velocity components. This enables a flow decomposition with respect to the flow structure’s influence on surface heat transfer. The second and third most energetic modes showed a zero temperature eigenfunction, which means that a considerable amount of energy is contained in flow structures that don’t contribute to increasing endwall heat transfer. It was also found that the vortex shedding frequency changes over time and both lift coefficient and Strouhal number increase compared to experimental values for a single cylinder.
An Experimental and Computational Study of a Swirl-Stabilized Premixed Flame
Authors: De Ashoke , Zhu Shengrong , Acharya Sumanta
Published: February 2010

An unconfined strongly swirled flow is investigated for different Reynolds numbers using particle image velocimetry (PIV) and Large Eddy Simulation (LES) with a Thickened Flame (TF) model. Both reacting and non-reacting flow results are presented. In the LES-TF approach, the flame front is resolved on the computational grid through artificial thickening and the individual species transport equations are directly solved with the reaction rates specified using Arrhenius chemistry. Good agreement is found when comparing predictions with the experimental data for the non-reacting cases studied. For the reacting flows, the mean axial velocity profiles are in good agreement with measurements at lower Re; at high Re, the computations show a more compact and attached flame whereas experimental observations show a slightly lifted flame. Tangential velocity predictions consistently show the peak at the flame front location while measurements show greater radial spreading of the tangential momentum. The predicted RMS fluctuations exhibit a double-peak profile with one peak in the burnt and the other in the unburnt region. The measured and predicted heat release distributions are in qualitative agreement with each other and exhibit the highest values along the inner edge of the shear layer. The precessing vortex core (PVC) is clearly observed in both the non-reacting and reacting cases. However, it appears more axially-elongated for the reacting cases.
Distributed Micro Fuel Injection for Improved Premixing: Lean Blowout, Emissions, and Dynamics
Authors: Giglio Anthony L. , Acharya Sumanta , Kelly Kevin
Published: February 2010

Reduction in NOx are generally obtained by lowering the flame temperature and locally improving the homogeneity of the reacting mixture. In this study, a novel premixer, the Micro Fuel Injection Swirler (MFIS) has been developed and manufactured to provide efficient and rapid mixing through distributed fuel injection, grid generated turbulence and countercurrent shear flow. The MFIS uses a circular array of porous swirl-panels that are hollow for micro scale distributed fuel injection. The fuel is introduced at multiple locations perpendicular to the plane of each swirl vane and countercurrent to the oncoming stream of air. The opposed injection enhances mixing, the porous-swirler grid introduces small-scale turbulence that further promotes mixing, and the swirl-panels provide the needed swirl for flame stability. Combustion tests were run in a cylindrical combustion chamber with inlet conditions at standard temperature (300K) and pressure (1 atm), and at firing rates of 10–58 kW. Measured parameters included lean blowout limits, flame temperature, NOx emissions, heat release rate (represented by CH light emission), and the pressure fluctuations upstream and downstream of the dump plane. The MFIS was located just upstream of the dump plane. In addition, a standard 8 vane, 45 degree solid swirler (SS) with fuel injection considerably upstream, was tested to provide a benchmark comparison. Combustion results indicated that the MFIS was capable of achieving lower equivalence ratios at lean blowout compared to the solid swirler cases tested. At a set thermal load, the MFIS produced higher flame temperatures, higher heat release rates near the dump plane, and comparable NOx emissions to the solid swirler cases. At equivalent operating temperatures, the MFIS produced nearly equal NOx emissions compared to the perfectly premixed solid swirler case in which fuel was injected far upstream of the dump plane. In summary, the MFIS was capable of providing efficient air/fuel mixing over a short premixing distance, affirming its effectiveness in lean premixed combustion systems.
Characterization of a Multi-Swirler Fuel Injector Using Simultaneous Laser Based Planar Measurements of Reaction Zone, Flow Field, and Fuel Distribution
Authors: Iudiciani P. , Hosseini S. M. , Zoltan-Szasz R. , Duwig C. , Fuchs L. , Collin R. , Lantz A. , Alde´n M. , Gutmark E. J.
Published: February 2010

Modern gas turbine spray combustors feature multiple swirlers with distributed fuel injection system for rapid fuel/air mixing and flame stabilization ensuring low NOx operations. In the present paper, we investigate the effects of different swirler designs on flame characteristics, stabilization, and behavior at lean blow out using a Triple Annular Research Swirler (TARS) burner. Simultaneous planar measurements using laser diagnostics, namely, Planar Laser Induced Fluorescence (LIF) of OH radicals indicating the reacting zone, LIF Acetone indicating unburnt fuel distribution and Particle Image Velocimetry (PIV) for flow field mapping, were applied to study the flow dynamics, fuel distribution and flame dynamics for different swirler geometries, air flow rates, and equivalence ratios. Both axial and nearly perpendicular to axis cross-sectional planes were investigated. The three swirler configurations allowed getting stable and repeatable flames over a wide range of different flow and fuel equivalence ratio conditions, confirming the good flexibility and operability of the TARS burner. Averaged fields are presented to compare the effect of different flow conditions using the same swirler configuration, and the effect of different swirler configurations at the same flow conditions. LIF and PIV instantaneous samples are also shown, both in axial and cross sectional planes, with structures captured in detail. Perfect matching is found between unburnt and burnt field, as well as agreement between axial and cross-sectional measurements. Particular attention has been placed on unstable flames and a highly unsteady flame near the lean blow out (LBO) is shown. Local extinctions are occasionally seen on instantaneous snapshots. Unsteadiness of such flame is suitable to exemplify the use of Proper Orthogonal Decomposition (POD) analysis that identifies the most “energetic” large scale structures or modes of the flame. In particular, rotational and helical modes are observed which can contribute to the swirling flame instability. The results show the effect of the strength and rotation direction of the swirlers can lead to strong flame stratification or to a more homogenous flames. Analysis of the flame dynamics, indicates that the flame can be stabilized dynamically without the presence of a Central Recirculation Zone (CRZ) through flame quenching and flame propagation.
Adjoint Equations and Error Measure in Radiative Heat Transfer With Diffuse Reflection
Authors: Vueghs Pierre E. , Rochus Pierre
Published: February 2010

In this paper, we develop an application of the importance equation (which is an adjoint equation of the radiosity equation) in the case of isothermal, diffuse surfaces. We recall the formulation of the radiosity equation, in function of the nature of the boundary condition (either known temperature or fixed radiative heat flux). We define the importance as the quantity dual to radiosity. We explain how these equations can be used after the resolution of a radiative heat transfer situation, as a post processing step, to establish the accuracy of each individual radiative link between the active faces of a tri-dimensional surface geometrical model.
Low-Profile Chipset Microprocessor Heatsink Optimization for Server Form Factor
Authors: Merrikh Ali Akbar , Sundaram Sridhar , Walshak David , Yang Yizhang , Dolbear Tom
Published: February 2010

We present a methodology for optimizing footprint, metal mass and thermal performance of an aluminum extruded heatsink for cooling chipset microprocessors in server form-factor. The analysis is based on predefined volume flow rate of air at a constant temperature assumed to be available upstream of the package. The front-to-back cooling assumption covers the worst case ambient conditions, typical of chipset boundary condition in servers. We present studies covering a range of heatsink footprints in order to compare and minimize the heatsink footprint, at the same time satisfying thermal specification of the chipset microprocessor. The study also focuses on the system-level assessment of the optimum 60×40 mm2 footprint and corner cases by studying the effect of motherboard thermal conductivity as well as blockages on the heatsink case-to-ambient thermal resistance.
Heat Transfer Analysis of a Novel Pressurized Air Receiver for Concentrated Solar Power Via Combined Cycles
Authors: Hischier Illias , Hess Daniel , Lipin´ski Wojciech , Modest Michael , Steinfeld Aldo
Published: February 2010

A novel design of a high-temperature pressurized solar air receiver for power generation via combined Brayton-Rankine cycles is proposed. It consists of an annular reticulate porous ceramic (RPC) bounded by two concentric cylinders. The inner cylinder, which serves as the solar absorber, has a cavity-type configuration and a small aperture for the access of concentrated solar radiation. Absorbed heat is transferred by conduction, radiation, and convection to the pressurized air flowing across the RPC. A 2D steady-state energy conservation equation coupling the three modes of heat transfer is formulated and solved by the finite volume technique and by applying the Rosseland diffusion, P1, and Monte Carlo radiation methods. Key results include the temperature distribution and the thermal efficiency as a function of the geometrical and operational parameters. For a solar concentration ratio of 3000 suns, the outlet air temperature reaches 1000°C at 10 bars, yielding a thermal efficiency of 78%.
Air-Side Heat Transfer Enhancement by a Novel Winglet-Type Vortex Generator Array in a Round-Tube Plain-Fin Heat Exchanger
Authors: He Jing , Liu Liping , Jacobi Anthony M.
Published: February 2010

The impact of vortex generator (VG) arrays for air-side heat transfer enhancement is experimentally investigated by full-scale wind-tunnel testing of a plain-fin-and-tube heat exchanger. The VG array is deployed in a “V” to try to create a constructive interference between vortices. Each array is composed of two delta-winglet pairs (four VGs), and placed at an attack angle of 10° or 30°. The frontal air velocity considered is between 2.3–5.4 m/s, corresponding to a Reynolds number range based on the hydraulic diameter of 1500–3400. The thermal-hydraulic performance of the heat exchanger with and without VG enhancement is provided under dry-surface conditions. The experimental results indicate little impact at a relatively small attack angle of 10°. While for the 30° array, a 25–55% augmentation in air-side heat transfer coefficient is measured, but with a pressure drop penalty of 100%. Nevertheless, performance evaluation using the area goodness factor and the volume goodness factor both indicate the superiority of the enhanced heat exchanger by the 30° array over the entire Reynolds number range. The proposed array is found more effective at comparatively low Reynolds numbers, representative of many HVAC&R applications and compact heat exchanger designs.
Experimental and Numerical Studies of Shell-and-Tube Heat Exchangers With Helical Baffles
Authors: Chen Guidong , Wang Qiuwang
Published: February 2010

In the present paper, flow and heat transfer characteristics of shell-and-tube heat exchanger with continuous helical baffles (CH-STHX) is experimentally studied. Correlations for heat transfer and pressure drop, which are estimated by Nusselt number and friction factor, are fitted by experiment data for thermal design. Computational Fluid Dynamic (CFD) method is also used to compare the heat transfer and flow performance of STHX with continuous helical baffles (CH-STHX), STHX with combined helical baffles (CMH-STHX) and STHX with discontinuous helical baffles (DCH-STHX). The numerical results show that, for the same Reynolds number, the Nusselt numbers Nuo of the CMH-STHX and CH-STHX is about 37.6%, 78.2% higher than that of the DCH-STHX; the friction factor fo of the CH-STHX is about 14.8% and 150.2% higher than that of CMH-STHX and DCH-STHX. If the velocity ratios RCMH, CH and RDCH, CH are bigger than 1.55 and 4.0 in the Nusselt number range from 40 to 70, the CMH-STHX and the DCH-STHX may have higher Nusselt numbers than the CH-STHX for the same mass flow rate in the shell side.
A Numerical Study on the Slab Heating Characteristics in a Reheating Furnace With the Formation and Growth of Scale on the Slab Surface
Authors: Lee Dong Eun , Jang Jung Hyun , Kim Man Young
Published: February 2010

In this work, the development of a mathematical heat transfer model for a walking-beam type reheating furnace is described and preliminary model predictions are presented. The model can predict the heat flux distribution within the furnace and the temperature distribution in the slab throughout the reheating furnace process by considering the heat exchange between the slab and its surroundings, including the radiant heat transfer among the slabs, the skids, the hot combustion gases and the furnace wall as well as the gas convection heat transfer in the furnace. In addition, present model is designed to be able to predict the formation and growth of the scale layer on the slab in order to investigate its effect on the slab heating. A comparison is made between the predictions of the present model and the data from an in situ measurement in the furnace, and a reasonable agreement is found. The results of the present simulation show that the effect of the scale layer on the slab heating is considerable.
An Experimental and Theoretical Study of Finned and Finless Heat Sinks for Low Profile Applications
Authors: Stafford Jason , Walsh Ed , Egan Vanessa , Walsh Pat , Muzychka Yuri S.
Published: February 2010

This paper discusses the importance of developing cooling solutions for low profile devices. This is addressed with an experimental and theoretical study on forced convection cooling solution designs that could be implemented into such devices. Conventional finned and corresponding finless designs of equal exterior dimensions are considered for three different heat sink profiles ranging from 1mm to 4mm profile in combination with a commercially available radial blower. The results show that forced convection heat transfer rates can be enhanced by up to 55% using finless designs at low profiles with relatively small footprint areas. The advantages of both finned and finless geometries are presented along with the limitations of the customary finned heat sink design at low profile scales. The results also show large increases in heat transfer rates over that predicted which can be attained at the low profile scale based on geometry selection. Dimensionless comparisons are made between experimental results and combined hydrodynamic and thermally developing duct flow theory which is representative of the flow regime within both the finned and finless geometries. Overall, this paper provides optimization and geometry selection criteria which are relevant to designers of low profile cooling solutions.
Single Microjet Heat Transfer
Authors: Michna Gregory J. , Browne Eric A. , Peles Yoav , Jensen Michael K.
Published: February 2010

An investigation of the stagnation point heat transfer coefficient of such a single-phase, microscale impinging jet is discussed. Standard MEMS processes were used to fabricate a heat transfer measurement device. In this device, a water jet issued from a 67-μm orifice and impinged on an 80-μm square heated normal surface 200 μm from the orifice. Heat transfer coefficients up to 80,000 W/m2-K were measured. This heat transfer coefficient results in a heat flux greater than 400 W/cm2 given a 50°C temperature difference. However, this heat transfer coefficient is an order-of-magnitude less than that predicted by correlations developed from larger jets. In addition, the heat transfer coefficients were relatively insensitive to Reynolds number. Further investigation of microjet heat transfer is needed to explain this deviation from expected behavior. The pressure drop across the jet orifice was measured, and the calculated pressure loss coefficients agree well with available correlations. Curve fits for the Nusselt number and pressure loss coefficient are given.
Heat and Mass Transport in Metal Hydride Based Hydrogen Storage Systems
Authors: Dedrick Daniel E. , Kanouff Michael P. , Larson Richard S. , Johnson Terry A. , Jorgensen Scott W.
Published: February 2010

Hydrogen storage technologies based on solid-phase materials involve highly coupled transport processes including heat transfer, mass transfer, and chemical kinetics. A full understanding of these processes and their relative impact on system performance is required to enable the design and optimization of efficient systems. This paper examines the coupled transport processes of titanium doped sodium alanates (NaAlH4, Na3AlH6) enhanced with excess aluminum and expanded natural graphite. Through validated modeling and simulation, we have illuminated transport bottlenecks that arise due to mass transfer limitations in scaled-up systems. Individual heat transport, mass transport, and chemical kinetic processes were isolated and experimentally characterized to generate a robust set of model parameters for all relevant operational states. The individual transport models were then coupled to simulate absorption processes associated with rapid refueling of scaled-up systems. Using experimental data for the absorption performance of a 1.6 kg sodium alanate system, comparisons were made to computed results to identify dominant transport mechanisms. The results indicated that channeling around the compacted porous solid can contribute significantly to the overall transport of hydrogen into and out of the system. The application of these transport models is generally applicable to a variety of condensed-phase hydrogen sorption materials and facilitates the design of optimally performing systems.
Symbiotic Cultures for Increasing the Solar Energy Conversion Efficiency of Outdoor Photobioreactors
Authors: Berberog˘lu Halil , Pilon Laurent
Published: February 2010

A numerical study is presented aiming to maximize the solar to hydrogen energy conversion efficiency of a symbiotic culture containing microorganisms with different absorption characteristics. The green algae Chlamydomonas reinhardtii CC125 and the purple non-sulfur bacteria Rhodobacter sphearoides ATCC 49419 are chosen for illustration purposes. The previously measured radiation characteristics of each microorganism are used as input parameters in the radiative transport equation for calculating the local spectral incident radiation within a flat panel photobioreactor. The specific hydrogen production rate for each microorganism as a function of the available incident radiation is recovered from data reported in the literature. The overall solar to hydrogen energy conversion efficiency of symbiotic cultures of varying microorganism concentrations have been computed for photobioreactor thicknesses from 1 to 10 cm. The results show that for a given photobioreactor thickness a saturation microorganism concentration exists above which the solar energy conversion efficiency does not increase. The maximum solar energy conversion efficiencies of solo cultures of C. reinhardtii and R. spaheroides at their respective saturation concentrations are 0.06 and 0.055%, respectively. Using symbiotic cultures, a total conversion efficiency of about 0.075% is achieved within the parameter range explored. It has been shown that the choice of microorganism concentrations for maximum solar energy conversion efficiency is non-trivial and requires careful radiation transfer analysis coupled with H2 production kinetics taking into account the photobioreactor thickness. The presented numerical tool can be used for simulating any photobiological or photochemical process involving more than one species with different radiation characteristics provided the closure laws for the reaction kinetics are known as a function of spectral incident radiation. Examples include (i) the symbiotic cultivation of more than one microorganism for biomass or lipid production in a photobioreactor and (ii) a photochemical reactor containing a number of absorbing and scattering photocatalysts with different band gaps.
Study of PCM-Based Pin-Fin Heat Sinks
Authors: Dubovsky V. , Barzilay G. , Granot G. , Ziskind G. , Letan R.
Published: February 2010

This study deals with heat transfer from pin-fin aluminum heat sinks to a phase-change material (PCM) which fills the inter-fin space. The sinks have a horizontal base and accordingly their fins are vertical. The sink base dimensions are 100 mm by 100 mm, with fin height of 10 mm, 20 mm or 30 mm, and cross section of 4 mm×4 mm. The number of fins varies, e.g. 49, 64, 81, etc. The applied power is between 50 W to 250 W, corresponding to the heat fluxes of 5–25 kW/m2. The present paper reports mostly numerical results, but the numerical model is validated using the findings from an ongoing experimental investigation, in which a commercially available paraffin wax RT-35 is used as the PCM, with the melting temperature of about 35 °C. The simulations reflect the material properties, geometry, and other features of the experimental set-up, including heating with an electrical foil heater. Accordingly, the base temperature serves as the dependent parameter. Numerical simulations, performed using the Fluent 6.2 software, serve to obtain detailed melting patterns and explain the effect of fin size and number on sink performance.