bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of Methanol-Air Two-Phase Flames Using Various Turbulent Combustion Models
Authors: Wang F. , Huang Y. , Wu Y. Z.
Published: February 2010

Though fossil fuel is running out, liquid fuels nowadays still provide the most energy used by industrial furnaces, automotive and aero engines. How to predict a two-phase turbulent combustion flame is still a big problem to designers. Generally, the liquid fuel is sprayed and mixed with oxygen, and the flame characteristics depends on the fuel atomization, the fuel droplet spatial distribution, and its interaction with the turbulent oxidizer flow field: turbulent heat, mass and momentum transfer, complicated chemical kinetics, and turbulent-chemistry interaction. Turbulent combustion model is a key point for the two phase combustion simulation. For its short time consuming, Reynolds Averaged Navier Stokes (RANS) method nowadays still is the major tool for gas turbine chamber (GTC) designers, but there is not a universal method in RANS GTC spray combustion simulation at present especially for the two-phase turbulent combustion. The Eddy-Break-Up turbulent combustion model (EBU), Eddy Dissipation Concept turbulent combustion model (EDC), steady Laminar Flame-let turbulent combustion Model (LFM) and the Composition PDF transport turbulent combustion model (CPDF) are all widely used models. In this paper, these four turbulent models are used to simulate a methane-air turbulent jet flame measured by Sandia Lab first, then three methanol-air two-phase turbulent flames, in order to know the ability of these turbulent models. In the gas turbulent jet flame simulation, the result of LFM model and CPDF model are in better agreement with the experimental data than those of the EBU and the EDC models’ results. The reason is that the EBU model and EDC model are overestimated the effect of turbulent. In the three different cases of the two phase combustion simulation, CPDF is the best. The prediction ability of the other three models is different in different cases. The EDC predictions are closer to the experimental data when the air flow rate value is lower, whereas the LFM predictions are better when the air flow rate value is higher.
Simulations of Unsteady Oscillations in Turbulent Non-Premixed Swirling Flames
Authors: Dinesh Ranga , Jenkins Karl , Kirkpatrick Michael
Published: February 2010

Simulations of turbulent non-premixed swirling flames based on the Sydney swirl burner experiments under different flame characteristics are conducted using large eddy simulations (LES). The simulations attempt to capture the unsteady flame oscillations and explore the underlying instability modes responsible for a centre jet precession and the large scale recirculation zone oscillation. The selected flame series known as SMH flames have a fuel mixture of methane-hydrogen (50:50 by volume). The LES program solved the governing equations on a structured Cartesian grid using finite volume method and the subgrid turbulence and combustion models used the localized dynamic form of Smagorinsky eddy viscosity model and the steady laminar flamelet model respectively. The results show that the LES predicts two types of instability modes near fuel jet region and the bluff body stabilized recirculation zone region. The Mode I instability defined as cyclic precession of a centre jet is identified using time periodicity of the centre jet in flames SMH1 and SMH2. The Mode II instability defined as cyclic expansion and collapse of the recirculation zone is identified using time periodicity of the recirculation zone in flame SMH3. The calculated frequency spectrums found reasonably good agreement with the experimental precession frequencies. Overall, the LES yield a good qualitative and quantitative agreement with the experimental observations, although some discrepancies are apparent.
Promoting Performance Test Capabilities Using Gas Path Analysis: A Case Study
Authors: Aghaei Vahid Noei , Khaledi Hiwa , Soltani Mohsen Reza
Published: February 2010

Performance testing of gas turbine packages is becoming increasingly common to assure that the turbine output power and efficiency meet the expected values during the turbine life cycle. In the conventional Performance Test Analysis (PTA), field measurements and calculations are carried out on the basis of standard codes to find the whole engine performance parameters (i.e. power and efficiency) at test conditions and to compare them with the expected values. Recently, regarding the development of Gas Path Analysis (GPA) and diagnostic techniques to investigate the gas turbine health state, performance test capabilities can be improved by using these analyses to perform further examination on the measured test data and to determine the deviation of gas turbine component health parameters from the “new and clean” health state during the engine operation. Determining the mentioned deviations, potentials of engine improvement in the component level can be obtained and subsequently the action-oriented recommendations are reported as guidelines in the overhaul. Also in the case of performance test after the overhaul, the main result of the GPA application in PTA is the verification of the overhaul effectiveness. Using the GPA in the cases studied in this paper indicates that heath state of engine components can be investigated from the performance test data and as the main result, it is show that applying the GPA, it is possible to distinguish the effect of non-recoverable degradation and that of the poor overhaul on the engine performance and finally to assess technically the effectiveness of overhaul.
Heat Transfer and Pressure Drop Measurements in a Rib Roughened Leading Edge Cooling Channel
Authors: Domaschke Norbert , von Wolfersdorf Jens , Semmler Klaus
Published: February 2010

In order to enhance convective heat transfer in internal cooling channels, ribs are often used to manipulate the flow field and to benefit from their effect on thermal performance. This paper presents results from an experimental investigation into pressure loss and heat transfer in a smooth and a ribbed leading edge channel of a gas turbine blade internal cooling system. To model the cross section of a realistic leading edge cooling channel both the suction side and the leading edge of the blade profile are designed as curved walls with constant radii. The pressure side as well as the web is approximated by planar walls. For the ribbed channel, 45°-ribs related to the flow direction are placed on the pressure and the suction side with the normalized rib height e/dh = 0.10. Experiments have been carried out for the smooth and the ribbed channel. The flow rate was varied to cover a Reynolds number range from 20,000 to 50,000. The heat transfer has been determined using the transient liquid crystal method. Additional numerical simulations using the SST turbulence model were carried out to analyze the flow field in the channel. The computations were used for further interpretation of the experimental investigations, especially to determine the temperature field and velocity field and therefore the bulk temperature within the test section.
Applicability of a Flamelet and a Presumed JPDF 2-Domain-1-Step-Kinetic Turbulent Reaction Model for the Simulation of a Lifted Swirl Flame
Authors: Kern Matthias , Fokaides Paris , Habisreuther Peter , Zarzalis Nikolaos
Published: February 2010

Lifted diffusion flames are an interesting topic due to many reasons. Mainly, lifting the reaction zone provides explicit time for mixing and avoids, therefore, hot spots at near stoichiometric conditions. Hence, they promise low emissions and make them auspicious for industrial application. In comparison to lean premixed flames, which are promising in terms of emissions as well, they distinguish themselves in the nonexistence of the risk of flashback by concurrently nearly premixed flame conditions. From exploratory considerations they are an excellent case for the investigation of flame stability. However, especially this kind of flame is challenging for the reaction model due to its high turbulence and nearly premixed burning state. CFD is a powerful tool to get a clear insight in complex mechanisms, as it delivers detailed information of the flow field. Although the contribution of highly sophisticated models like LES is steadily growing in current research, fast models as RANS are most important. Solely they provide the feasibility of extensive parametric studies or the application in industrial design processes. Therefore, appropriate reaction models are needed. The applicability of two different reaction models for non-premixed flames to predict structure and stability of such flames has been investigated in this work. A stable confined diffusion flame produced by a double swirler airblast nozzle has been chosen as test case. Leaving the secondary air stream non-swirled creates a flame which stabilizes in a lifted state. The turbulent flamelet model as proposed by Peters in the early 90th basically models the impact of the turbulent strain rate on the diffusion flame. The local state of mixing is characterized by the mixture fraction, whereas the interaction of flame and turbulence is described by the mean scalar dissipation rate. The fact that the strain rate is the only non-equilibrium parameter describing the state of the reaction permits the use of detailed chemical mechanisms. The presumed jpdf model based on a 2-domain-1-step kinetic scheme has its focus on the interaction of mixing and reaction progress and uses a presumed shape for the joint probability density function. The reaction is characterized by a single variable describing the mixing state and one single additional variable, describing the state of reaction progress. In this paper assets and drawbacks of both models and their applicability to lifted flames have been discussed in detail. Furthermore, conclusions on the stability mechanism of a lifted swirl flame are taken.
The Evaluation of Coefficient of Friction for Representative and Predictive Finite Element Modelling of the Inertia Friction Welding
Authors: Mohammed M. B. , Bennett C. J. , Hyde T. H. , Williams E. J.
Published: February 2010

Inertia friction welding is the process in which stored kinetic energy in a flywheel is converted to heat by relative sliding movement between surfaces of axi-symmetric components to achieve a weld in the solid-state. The work in this paper relates to the production of dual-alloy shafts for aeroengines. Frictional characteristics determine the conditions at the weld interface and these are controlled by rotational velocity and applied axial pressure. So-called representative and predictive methods have been developed to evaluate friction conditions during the process and these are discussed in this paper. Weld data for the dissimilar weld between a high strength steel and a nickel-based super-alloy were provided by Rolls-Royce and MTU Aero Engines. The finite element software package DEFORM-2D is used to develop coupled thermo-mechanical axi-symmetric models. In previous work, methods employed to evaluate the efficiency of mechanical energy utilised during a weld, a parameter of great importance for numerical analysis, are not clear. Previous predictive approaches have employed test/weld data in one way or another to obtain the interface friction coefficient. This paper proposes a formula that incorporates the value of the mechanical energy efficiency of the welding machine into the calculation of coefficient of friction for representative modelling. It also introduces a predictive approach based on sub-layer flow theory to predict frictional behaviour during the welding process that is independent of test/weld data.
Application of RANS and FWH Modelling to the Prediction of Noise From Round Jets
Authors: Stanko T. , Ingham D. B. , Fairweather M. , Pourkashanian M.
Published: February 2010

This paper focuses on the CFD modelling of the aerodynamic noise generated by a hot non-reacting turbulent jet. A commercial CFD code is used to model the aerodynamic flow as well as in providing noise calculations. The main advantage of using CFD is the relatively low cost of the computational prediction in comparison with alternative experimental investigations. In addition, the CFD simulations provide detailed information on the aerodynamic sources of noise at every point in a flow, something that is difficult to achieve experimentally. The accuracy of the noise predictions is highly dependent on the means used to simulate the turbulent flow field, as well as the acoustic model applied. In this paper different approaches to predicting both the turbulent flow and acoustic noise are studied. For the jet investigated, the accuracy of various modelling approach is assessed against available data, with particular attention placed on the use of RANS simulations for the flow field prediction coupled to the Ffowcs Williams-Hawkings acoustic model. The aim of this paper is to demonstrate the level of flow field and acoustic modelling required to provide accurate predictions of noise emissions from jets with a view to their ultimate application as an aeroacoustic tool that can be used in identifying components or surfaces that generate significant amounts of noise, thereby providing opportunities for early design changes to aircraft and gas turbine components.
A Dynamic Convergence Control Algorithm for the Solution of Two-Dimensional Streamline Curvature Methods
Authors: Pachidis Vassilios , Templalexis Ioannis , Pilidis Pericles
Published: February 2010

Frequently, the analysis of complex phenomena falls beyond the range of applicability of the numerical methods available in the public domain, and demands the design of dedicated algorithms that will approximate, to a specified precision, the mathematical solution of specific problems. These algorithms can be developed from scratch or through the amalgamation of existing techniques. In any case, they need to execute efficiently and robustly. The accurate solution of the full Radial Equilibrium Equation (REE) in Streamline Curvature (SLC) through-flow analyses presents such a case. This manuscript discusses the development, validation and application of an ‘intelligent’ Dynamic Convergence Control (DCC) algorithm for the fast, accurate and robust numerical solution of the non-linear equations of motion for two-dimensional flow fields. The algorithm was developed to eliminate the large user intervention, usually required by standard numerical methods. Although this hybrid DCC algorithm was specifically developed around a conventional Newton-Raphson scheme, to address the computational challenges presented by SLC-type of analyses, it can also be used in many other applications. The DCC algorithm was integrated into a compressor SLC software and was tested rigorously, particularly at compressor operating regimes traditionally exhibiting convergence difficulties (i.e. far off-design conditions). Typical error histories and comparisons of simulated results against experimental are presented in this manuscript for a particular case-study. For all case-studies examined, it was found that the algorithm could successfully ‘guide’ the solution down to the specified error tolerance, at the expense of a slightly slower iteration process (compared to a conventional Newton-Raphson scheme).
Principles of Thermodynamic Preliminary Design of Civil Turbofan Engines
Authors: Kyritsis Vasileios E. , Pilidis Pericles
Published: February 2010

The design process of a civil turbofan engine is a continuous iteration among a variety of disciplines. From the performance point of view, its main target is the accomplishment of a specified thermodynamic cycle, which is optimised in terms of block fuel for a specified airframe and typical mission, while meeting a variety of multidisciplinary restrictions. Engine performance and component areas are engaged in an interactive collaboration. Performance provides component designers with precious information regarding component operating points and boundary conditions at critical flight conditions and power levels. In the opposite direction, component design is revised to provide performance with the most up-to-date overall component behaviour. Such an iterative process is initiated based on fundamental assumptions regarding the engine architecture, the available proven technology and the customer demands. Scope of the current work is to investigate the effect of engine architecture, component related restrictions and aircraft requirements on engine performance during the preliminary design phase. Given the multi-disciplinary nature of engine design, the conflicting interaction of various design parameters is discussed considering aerodynamic, mechanical and lifing issues. The parameters selected to form the mathematical problem all reflect a level of compromise among the various disciplines. The study aims at justifying the result of an optimal solution, which satisfies the requirements and restrictions set.
Application of Conjugate Heat Transfer for Cooling Optimization of a Turbine Airfoil
Authors: Nowak Grzegorz , Wro´blewski Włodzimierz
Published: February 2010

This paper discusses the problem of airfoil cooling system optimization connected with Conjugate Heat Transfer (CHT) analysis for reliable thermal field prediction within a cooled component. Since the full CHT solution, which involves the main flow, blade material and the coolant flow domains is computationally expensive from the point of view of optimization process, it was decided to reduce the problem by fixing the boundary conditions at the blade surface and solving the task for the interior only (both solid material and coolant). Such assumption, on one hand, makes the problem computationally feasible, and on the other, provides more reliable thermal field prediction than it used to be with the empirical relationships. The analysis involves the optimization of location and size of internal cooling passages within an airfoil. Initially, cooling is provided with circular passages and heat is transported by convection. The task is approached in 3D configuration. Each passage is fed with cooling air of constant parameters at the inlet. In the present study the airfoil profile is taken as aerodynamically optimal. The optimization is done with an evolutionary algorithm within a 30 dimensional design space, composed of space coordinates and radii of cooling channels. The search is realized with a weighted single objective function, which consisted of three objectives formulated on the basis of the airfoil’s thermal field and coolant mass flow.
System Dynamics of a Hardware in the Loop Simulation of a Hybrid Power Plant
Authors: Kroll Florian , Sandor Ivo , Staudacher Stephan
Published: February 2010

The system dynamics of a planned system test facility for the hardware in the loop simulation of a hybrid power plant featuring a Turbec T100 and dummy hardware for the SOFC have been investigated. The model of the micro gas turbine including effects like moment of inertia, heat soakage and volume packing has been calibrated against measured cycle data with good accuracy. Special attention has been dedicated to the dynamics of the actuators. Hence their steady state and transient performance has been identified experimentally. In accordance to published data of SOFC the SOFC dummy hardware is designed to be a first order time delay element (PT1). Important aspects of the control strategy as a major part of the operational concept are described. The results show that the chosen control strategy is suitable to control the system test facility within the set boundary conditions with the dynamics of the actuators being a limiting factor.
New Steel Alloys for the Design of Heat Recovery Steam Generator Components of Combined Cycle Gas Plants
Authors: Pinto Fernandes Jorge , Dias Lopes Eduardo Manuel , Maneta Vicente
Published: February 2010

Demand of Power is growing everyday, mainly due to emerging economies in CRIB countries (China, Russia, India and Brazil). During the last fifty years steam pressure and temperature in power plants have been continuously raised to improve thermal efficiency. Recent efforts to improve efficiency leads to the development of a new generation of Heat Recovery Steam Generator (HRSG) where the Benson Once-Through Technology is applied to improve thermal efficiency. The main purpose of this paper is to analyse the mechanical behaviour of a High Pressure Superheater Manifold by applying Finite Element Modelling (FEM) and a Finite Element Analysis with the objective to analyse stress propagation leading to the study of damage mechanism e.g. Uniaxial Fatigue, Uniaxial Creep for life prediction. The objective of this paper is also to analyse the mechanical properties of the new high temperature resistant materials in the market such as 2Cr Bainitic steels (T/P23, T/P24) and also the 9–12Cr Martensitic steels (T/P91, T/P92, E911 and P/T122). For this study the design rules for construction of power boilers to define the geometry of the HPSH Manifold were applied.
Performance Simulation and Economic Evaluation of Tri-Generation Plant, Based on a Single Shaft Gas Turbine
Authors: Polyzakis A. L. , Malkogianni A. K. , Stamatis A. , Papadopoulos D.
Published: February 2010

This paper provides an intergraded realistic tool, which simulates the future operation (technical and economic) of a tri-generation plant, capable of helping the potential investor decide if it is profitable to proceed with the investment. The paper is based on an overall technical-economic analysis of the tri-generation system, including the following steps: Firstly, the data research concerning the energy demands of an actual case. The second part deals with the prime mover (namely the GT) modelling and simulation, including the Design Point (DP) and Off-Design (OD) performance analysis of the GT. The third part includes the simulation of the absorption cooling system alone and/or in co-operation with the prime mover. Finally, an evaluation methodology of tri-generation plants is introduced taking into account both technical facts and realistic economic data helping the potential users to decide whether it is profitable to use such technology or not. The economic scene will include the basic economic facts such as initial cost, handling and operational cost (fuel prices, maintenance etc), using methodology based on NPV. The results are valuated using suitable sensitivity analysis. The results of the analysis generally shown, that the tri-generation plant is more profitable than the conventional way of energy production.
Aerodynamic Design and Numerical Investigation on Overall Performance of a Micro Radial Turbine With Millimeter-Scale
Authors: Fu Lei , Shi Yan , Deng Qinghua , Feng Zhenping
Published: February 2010

For millimeter-scale microturbines, the principal challenge is to achieve a design scheme to meet the aerothermodynamics, geometry restriction, structural strength and component functionality requirements while in consideration of the applicable materials, realizable manufacturing and installation technology. This paper mainly presents numerical investigations on the aerothermodynamic design, geometrical design and overall performance prediction of a millimeter-scale radial turbine with rotor diameter of 10mm. Four kinds of turbine rotor profiles were designed, and they were compared with one another in order to select the suitable profile for the micro radial turbine. The leaving velocity loss in micro gas turbines was found to be a large source of inefficiency. The approach of refining the geometric structure of rotor blades and the profile of diffuser were adopted to reduce the exit Mach number thus improving the total-static efficiency. Different from general gas turbines, micro gas turbines are operated in low Reynolds numbers, 104∼105, which has significant effect on flow separation, heat transfer and laminar to turbulent flow transition. Based on the selected rotor profile, several micro gas turbine configurations with different tip clearances of 0.1mm, 0.2mm and 0.3mm, respectively; two different isothermal wall conditions; and two laminar-turbulent transition models were investigated to understand the particular influence of low Reynolds number. These influences on the overall performance of the micro gas turbine were analyzed in details. The results indicate that these configurations should be included and emphasized during the design process of the millimeter-scale micro radial turbines.
Experimental Validation of Linear Stability Analysis in a Premixed Combustor by Actively Tuning Its Acoustic Boundary Conditions
Authors: Bothien Mirko R. , Moeck Jonas P. , Paschereit Christian Oliver
Published: February 2010

Linear stability analysis by means of low-order network models is widely spread in industry and academia to predict the thermoacoustic characteristics of combustion systems. Even though a vast amount of publications on this topic exists, much less is reported on the predictive capabilities of such stability analyses with respect to real system behaviour. In this sense, little effort has been made on investigating if predicted critical parameter values, for which the combustion system switches from stability to instability, agree with experimental observations. Here, this lack of a comprehensive experimental validation is addressed by using a model-based control scheme. This scheme is able to actively manipulate the acoustic field of a combustion test rig by imposing quasi arbitrary reflection coefficients. It is employed to continuously vary the downstream reflection coefficient of an atmospheric swirl-stabilized combustion test rig from fully reflecting to anechoic. By doing so, the transient behaviour of the system can be studied. In addition to that, an extension of the common procedure, where the stability of an operating point is classified solely based on the presence of high amplitude pressure pulsations and their frequency, is given. Generally, the predicted growth rates are only compared to measurements with respect to their sign, which obviously lacks a quantitative component. In contrast to that, in this paper, validation of linear stability analysis is conducted by comparing calculated and experimentally determined linear growth rates of unstable modes. Besides this, experimental results and model predictions are also compared in terms of frequency of the least stable mode. Excellent agreement between computations from the model and experiments is found. The concept is also used for active control of combustion instabilities. By tuning the downstream reflectivity of the combustion test rig, thermoacoustic instabilities can be suppressed. the underlying mechanism is an increase of the acoustic energy losses across the system boundary.
Integrating HRSG Technical Dimensioning in Overall CCPP Cycle Optimization of Performance and Cost
Authors: Pedretti Camille , Kjellberg Tobias , Nugroho Tjiptady
Published: February 2010

This article presents an initial design methodology of the water/steam cycle of combined-cycle power plants. From prescribed boundary conditions such as the GT type or ambient conditions, the water/steam cycle process model performs a computation and initial design of all key components, leading to cycle performance and cost. Particular focus is given here to the Heat Recovery Steam Generator (HRSG), a key component for heat integration having a large impact on both plant cost and performance. With the assistance of an optimization toolbox, optimal designs are found with respect to cost and performance. The process model allows a number of water/steam cycle configurations. Features include the number of pressure levels, the choice of single or double reheat, options for supplementary firing in the HRSG, heat integration with GT coolers, fuel gas preheating and steam extraction from the steam turbine. From prescribed thermodynamic inputs, the model computes and/or selects key components and systems from the Original Equipment Manufacturer (OEM) portfolio: HRSG, piping, steam turbine, condenser and generator. For each key component and system, the performance and cost are derived. The initial design of the HRSG fully integrates all interfaces and is supported by a sub-optimization step, which provides proper surfacing and sequencing of heat exchanger components with the target of minimizing cost. To achieve the required accuracy, the HRSG is first designed technically in detail, namely dimensioning and material selection of finned tubes, structural steel, casing and insulation. The resulting partial bill of quantities is then converted into cost, applying appropriate material rates. This approach guarantees full sensitivity of the model to mass flow, pressure or temperature changes at any location in the HRSG. Coupled to this process model, the multi-objective optimization toolbox allows identifying the pareto front for plant net performance and plant cost, clearly two conflicting objectives. In the example application of a KA26–1 combined-cycle power plant, steps are identified on the pareto front, which can be associated with the number of HRSG modules. For selected project economic conditions and plant operation profile, the pareto front can be post-processed to identify the design with minimum COE or maximum project NPV. Simultaneous optimization of the complete cycle ensures the best possible integration of all key components. Flexibility, speed and effectiveness of the methodology allow exploring many cycle variants, maximizing the chances of finding the global plant optimum in less time. Having been thoroughly validated, the initial design methodology is applicable for development of standard plants as well as integration of specific customer requirements.
Robustness Assessment of a Prediffuser, Strut, and Frame
Authors: Garrison Loren , Walter Sarah
Published: February 2010

For most industrial applications, design and analysis is typically performed using only a nominal geometry at nominal operating conditions due to limitations in the design process, analysis capability, and computational resources. In the present study, full lifecycle management and assessment during the early stages of design was conducted through the completion of a robustness assessment, in addition to performance analysis, of a prediffuser flow path, strut, and frame in order to identify significant factors influencing performance and cost. Application of Quality Function Deployment (QFD) was utilized to capture the critical-to-quality customer requirements in relation to the functional requirements of the component. Key sources of variation influencing the component were then identified and prioritized based on legacy component service and design experience using robust design (also know as design for process excellence, or design for six sigma) tools. Results from the application of the robust design tools indicate that manufacturing and usage variations are likely to have a larger impact on the aerodynamic performance than structural performance. Aerodynamic analysis of the prediffuser and strut was performed to quantify the sensitivity of the aerodynamic performance to manufacturing and usage variations. Full three-dimensional computational fluid dynamics (CFD) analysis was performed using a series of latin hypercube design of experiments to statistically quantify the variation in the aerodynamic performance metrics of the prediffuser with a strut. It was determined that manufacturing and/or usage variations had a significant impact on the variation in aerodynamic performance. In addition, for some cases the variation in aerodynamic performance resulting from variations in noise factors was greater than those resulting from changes in the strut design parameters.
Repowering of a Gas Turbine Based CHP in a Pulp and Paper Industry
Authors: Desideri Umberto , Garroni Emanuele , Proietti Stefania
Published: February 2010

Paper mills are industries that require large amounts of electricity and heat. Most paper mills produce the energy required by the process using cogeneration plants based on steam or gas turbines. In the present case study the original power plant was a 2 MWe gas turbine with a heat recovery steam generator (HRSG) equipped with 6 MWt afterburners and a steam turbine. With the increase of paper production, the electric power produced by the power plant was not enough for the factory and the steam produced by the gas turbine was not enough for the paper drying process. After the analysis of the plant, a different solution for its repowering was proposed. The guidelines, for the considered project, are the total electrical autonomy of the factory, the continuity of production in case of failure of a gas turbine or a steam generator and the possibility of enabling the increase of the paper production with additional steam. All the proposed solutions will be analyzed in terms of technical feasibility and operating costs.
Modeling of Radiative Heat Transfer in 2D Complex Furnace of Biomass Pyrolysis Fumes: A Study of Shadow Effect
Authors: Abbassi Mohamed Ammar , Guedri Kamel , Borjini Mohamed Naceur , Halouani Kamel , Zeghmati Belkacem
Published: February 2010

The radiative heat transfer problem is investigated numerically for 2D complex pilot plant of biomass pyrolysis composed by two pyrolysis chambers and a heat recuperator. In order to increase gases residence time and heat transfer, the heat recuperator is provided with many inclined, vertical, horizontal, diffuse and gray baffles of finite thickness and has a complex geometry. The Finite Volume Method (FVM) is applied to study radiative heat transfer. The blocked-off region procedure is used to treat the geometrical irregularities. Seven cases are considered in order to demonstrate the effect of adding baffles on the walls of the heat recuperator and on the walls of the pyrolysis rooms then choose the best case giving the maximum heat flux transferred to the biomass in the pyrolysis chambers. Shadow effect caused by the presence of the baffles is also studied.
Temperature Dependence of Hot Carrier Relaxation in a PBSE Quantum Dot: An Ab Initio Study
Authors: Bao Hua , Ruan Xiulin , Habenicht Bradley F. , Prezhdo Oleg V.
Published: February 2010

Temperature dependent dynamics of phonon-assisted relaxation of hot carriers, both electrons and holes, is studied in a PbSe quantum dot using ab initio time-domain density functional theory. The electronic structure is first calculated, showing that the hole states are denser than the electron states. Fourier transforms of the time resolved energy levels show that the hot carriers couple to both acoustic and optical phonons. At higher temperature, more phonon modes in the high frequency range participate in the relaxation process due to their increased occupation number. The phonon-assisted hot carrier decay dynamics is predicted using non-adiabatic molecular dynamics, and the calculated relaxation rates clearly show a temperature-activation behavior. The complex temperature dependence is attributed to the combined effects of the phonon occupation number and thermal expansion. Comparing the simulation results with experiments, we suggest that the multiphonon relaxation channel is efficient at high temperature, while the Auger-like process may dominate the relaxation at low temperature. This combined mechanism can explain the weak temperature dependence at low temperature and stronger temperature dependence at higher temperature.
Employing Exergy-Optimized Pin Fins in the Design of an Absorber in a Solar Air Heater
Authors: Nwosu Nwachukwu P.
Published: February 2010

The performance of a solar air heater is primarily based on the design of the absorber plate and a substantial fraction of the cost of the heater is covered by the cost of the absorber plate. Heat transfer augmentation features for the improvement of heat transfer from the plate to the working fluid are mostly fins however these features also increase pressure drop in the flow channel. The exergy optimization philosophy is adopted in the fin sizing for this air heating application; this optimization philosophy ensures that the maximum quantity of heat is transferred by the fins while generating the least entropy in the system thus conserving exergy. Some important observations relevant in design are made.
Thermal Performance of Two and Three Dimensional Radial Flow Heat Sinks
Authors: Grimes Ronan , Hanly Kieran , Walsh Edmond
Published: February 2010

Space and power constraints in many contemporary electronic systems place a greater importance than ever on efficient thermal management solutions. This paper investigates the performance and optimisation of air cooled heat sinks suitable for deployment in compact electronic devices. The heat sinks examined have circular footprint, with air flowing from the centre, radially outwards through radially aligned channels. Heat sink height is examined through experiments which were performed on heat sinks with high and low fins, with two and three dimensional flow and heat transfer phenomena respectively. In both cases the effect of angular fin spacing is investigated to determine optimum fin spacing for a range of heat sink pressure drops. Heat transfer correlations from literature which were originally developed for parallel finned heat sinks are compared with the experimental data. The main findings of the paper are that the performance of the high profile two dimensional heat sink is more sensitive to fin angular displacement than low profile three dimensional heat sinks. The parallel fin correlations from literature were found to predict the performance of the three dimensional heat sinks more accurately than the two dimensional heat sinks.
Optimal Shape Design for Radiative Enclosures Using NURBS
Authors: Fakhrabadi Farbod , Kowsary Farshad
Published: February 2010

This article presents an optimal shape design methodology for diffuse-walled radiant enclosures. In this study, the shape of the enclosure is parameterized by means of non-uniform rational B-spline (NURBS) surfaces, and their control points represent the design variables. The enclosure geometry is discretized by choosing the parameters of NURBS surfaces as generalized curvilinear coordinates, and the radiosity equation is solved using the infinitesimal-area analysis technique developed by Daun and Hollands [1]. The simplified conjugate-gradient method (SCGM) is used as the optimization method to obtain the optimal shape and adjust the design variables intelligently. The methodology is demonstrated by optimizing the shape profile of a cavity with the objective of enhancing the apparent emittance.
The Enhancement Ratio of Corresponding Convection Heat Transfer Coefficient Using Electrospray Evaporative Cooling System
Authors: Wang H. C. , Hsu C. P. , Mamishev A. V.
Published: February 2010

The thermal management of microelectronics demands high heat flux removal solutions due to a rapid increase in component and heat flux densities generated from the integrated circuits (ICs) per unit area. Electrospray evaporative cooling (ESEC), which combines two-phase cooling and an electrospray technique, is presented to be the thermal management solution for next generation microelectronics in order to overcome the heat transfer cooling limits for traditional cooling technologies. In this paper, the enhancement ratio of the corresponding convection heat transfer coefficients and heat removal ability of the ESEC system are investigated in terms of the number of spraying nozzles, total volume flow rates of ethanol alcohol, DC potentials, and gaps between the spraying nozzle and a thermal exchange surface. As the results show, thermal images have indicated the cooling ability of the ESEC system. Additionally, the electrospray modes induced by the distribution of electrostatic fields have a great impact on the heat transfer performance of the ESEC system. The maximum enhancement ratio, 1.61, and heat removal ratio, 61%, has been achieved by the 4-nozzle array. The corresponding calculated heat flux difference and convection heat transfer coefficient were approximately 123.19 W/cm2 and 3.99 W/cm2K, respectively. Furthermore, the results also indicate that increase the number of the spraying nozzle and decrease the flow rate per nozzle is regarded as the effective way of improving the heat transfer performance of ESEC devices. A simple regression curve for the relationship between the heat removal ratio and enhancement ratio was also addressed.
Development of a SH Wave Single Unit Electromagnetic Acoustic Transducer (EMAT) for MONJU Reactor Vessel In-Service Inspection
Authors: Xu Yang , Tagawa Akihiro , Fujiki Kazunari , Ueda Masashi , Yamashita Takuya
Published: February 2010

In-service inspection (ISI) is carried out to confirm the integrity of the main components of a Fast Breeder Reactor (FBR) “MONJU”. The ambient temperature during the inspection is 200 degree C and the irradiation field is about 10 Gy/hr. A Periodic Permanent Magnet (PPM) structure has been used for electromagnetic acoustic transducer (EMAT). The PPM structure is the structure of putting in order alternately the S pole and N pole laterally magnetized magnets. A Halbach magnet structure is the structure which sandwiched the longitudinally magnetized magnets between each magnet of PPM structure. Thereby, magnetic flux density is improved to 1.4 times. Moreover, it is also shown that the detection sensitivity increased to 4 times by using a new signal processing method. The magnetic flux density of a SH wave EMAT with a Halbach magnet structure is calculated from room temperature up to 240 degree C. The characteristics and durability at elevated temperature for Halbach type EMAT in 200 hours under the 200 degree C are reported. Twenty to thirty percents of sensitivity reduction can be observed but this is enough for MONJU ISI.
Implementing Improvements to Nuclear Asset Management
Authors: Granger Jessica , Hess Stephen M. , Mengers Charles A.
Published: February 2010

In this paper, we describe the development of a generic process model to support improvements in Nuclear Asset Management (NAM) and present some key results and insights obtained from it. We also provide details associated with one portion of the model as an illustration of it and describe its application. Finally, we discuss how the model could be used to improve the effectiveness and integration of a plant’s asset management program.
Development of Ex-Vessel Debris Agglomeration Mode Map for a LWR Severe Accident Conditions
Authors: Kudinov P. , Davydov M.
Published: February 2010

Ex-vessel debris bed coolability is cornerstone for severe core melt accident mitigation scheme adopted in Swedish type BWRs. Debris agglomeration can significantly affect coolability of the debris bed. The paper discusses an approach for conservative-mechanistic assessment of the debris agglomeration. In order to tackle with considerable aleatory and epistemic uncertainties which present in accident scenario and in the debris agglomeration phenomena we apply mechanistic simulation tool VAPEX code and conservative assumptions about agglomeration related phenomena and accident scenario. Results of systematic analysis are presented in a form of agglomeration mode map. The map shows conditions for transition between different modes of debris agglomeration. Assessments of the influence of epistemic uncertainties and of numerical discretization errors on simulation result are provided. Safety implication aspects of the proposed agglomeration mode map are discussed in the present paper.
Adaptation of FEMAXI-6 Code for Fuel Rods of RBMK-1500 and Employment of Uncertainty and Sensitivity Analysis
Authors: Kaliatka Tadas , Jusevicˇiu¯te˙ Ausˇra , Usˇpuras Eugenijus
Published: February 2010

This paper provides information about possibility to apply FEMAXI-6 code for RBMK-1500. According to RBMK-1500 specification new thermal properties and models responsible for thermal analysis (thermal conductivity and heat capacity) were included in FEMAXI-6 code. Using adapted FEMAXI-6 code model of RBMK-1500 fuel rod was developed and tested by employing uncertainty and sensitivity analysis. The processes of fuel rods during normal plant operation were modelled. The received results were compared with calculations performed by specialists from Kurchatov Institute (designers of RBMK). The reasonable agreement of both calculation results shows that adapted FEMAXI-6 code and developed model are suitable for future analysis of processes in fuel rods of RBMK-1500.
Comparison of Thermal Hydraulic Simulations of Beyond Design Basis Events Using the MAAP4 and CENTS Computer Codes
Authors: LaBarge N. Reed , Baron Barbara R. , Schneider Raymond E. , Jacob Mathew C.
Published: February 2010

The MAAP4 computer code (Reference 1) is often used to perform thermal hydraulic simulations of severe accident sequences for nuclear power plant Probabilistic Risk Assessments (PRAs). MAAP4 can be used to simulate accidents for both Boiling Water Reactors (BWRs) as well as Pressurized Water Reactors (PWRs). This assessment employs MAAP 4.0.6a for PWRs (References 1 and 5), which incorporates explicit thermal hydraulic modeling of the Reactor Coolant System (RCS) and Steam Generators (SGs), along with a nodalized integrated containment model. In the PRA environment, MAAP4 has been used for applications such as the development of PRA Level 1 and Level 2 success criteria and human action timings. The CENTS computer code (Reference 2) is a simulation tool that is typically used to analyze non-Loss of Coolant Accident (non-LOCA) events postulated to occur in nuclear power plants incorporating Combustion Engineering (CE) and Westinghouse Nuclear Steam Supply System (NSSS) designs. It is licensed by the NRC perform design basis non-LOCA safety analyses. It is a best estimate code which uses detailed thermal hydraulic modeling of the RCS and SGs; however, it does not model the containment performance. It is used to perform a wide spectrum of licensing and best estimate non-LOCA event analysis and has the capability to simulate operator actions. The CENTS models are the basis for several full scope simulators in the industry. The purpose of the analyses described in this paper is to compare MAAP4 and CENTS predictions for the Station Blackout (SBO) and Total Loss of Feedwater (TLOFW) scenarios for a representative PWR in the Westinghouse fleet that employs a CE NSSS design. The results of this comparison are used to highlight postulated MAAP4 user challenges and assist in developing guidance on selecting MAAP4 parameters for use in these scenarios. The results of the analyses presented in this paper indicate several useful insights. Overall, this paper shows that when care is taken to normalize the MAAP4 and CENTS primary side natural circulation flowrate and SG modeling, the trends of the MAAP4 and CENTS predictions of core uncovery agree reasonably well.