- Email: [email protected]
01631 Modeling NH3 and HCN emissions from biomass circulating fluidized bed gasifiers
16 Fuel science and technology (fundamental science, analysis, instrumentation) The chemistry of carbon deposition from methane as a function of methane pressure was studied at a temperature of 1100°C and surface area/volume ratios of 0.8 and 3.2 mm -1 by analysis of both gaseous and condensing, i.e. aromatic reaction products. Conversion of methane as well as the yields of the hydrocarbons formed increase with increasing pressure. The surface area/volume ratio has a significant influence on the formation of aromatic hydrocarbons showing much higher yields at the lower ratio. This result, expected from preceding studies of deposition rates, confirms that a change of this ratio leads to a change of the deposition chemistry of carbon.
combustion, but a few were for isothermal conditions and included velocity measurements. Both isothermal and combusting flows have been calculated using a commercial computational fluid dynamics (CFD) program called Star-CD. The isothermal solutions have been validated against a simpler analytical solution and against rig measurements. The solutions with combustion and radiation have been validated qualitatively against the behaviour observed during rig tests and also quantitatively against incident heat flux measurements. The basis of the CFD for both the isothermal and combusting cases is described, together with the validation that has been achieved.
04/01622 Investigation of pyrolysis of Chinese coals using thermal analysis/mass spectrometry
04/01627 Measurement and numerical simulation of soot particle size distribution functions in a laminar premixed ethylene-oxygen-argon flame
Li, X. et al. Journal of Thermal Analysis and Calorimetry, 2003, 71, (2), 601-612. TA/MS (thermal analysis coupled with mass spectrometry) was applied to the pyrolysis of different-rank coals. A total of 13 coals were investigated. The samples were chosen to represent the 13 types of Chinese coals according to the Chinese coal classification system. The experiments were carried out in an argon atmosphere with a flow rate of 150 mL rain i The samples were heated from 40 up to 1200°C with a constant heating rate of 10 K rain -1. The main evolved pyrolysis products were identified through the online-recorded mass spectra. The results showed a strong thermal and evolution behaviour dependence on the coal rank. Different aliphatic fragments and also some aromatic substances, which are of environmental concern (BTX, PAHs), were found to be released depending on the coal type.
04/01623 Latent heat storage characteristics of solid-liquid phase change heat storage microcapsule slurry by boiling heat transfer under a vacuum condition Inaba, H. et al. Nippon Reito Kucho Gakkai Ronbunshu, 2003, 20, (1), 37 47. (In Japanese) Recently, the new heat transfer medium, which fulfils both functions of heat storage and heat transportation, was developed in a heat storage field. Solid-liquid latent heat microcapsule slurry would correspond to the topical medium, so-called functionally thermal fluid. The preset study has clarified the latent heat storage characteristics of microcapsule slurry by making heat transfer enlargement with the help of slurry water pool boiling phenomenon. The paraffin wax at a melting point of 62 ° was used as a phase change material which was packed into the microcapsule. The heating surface temperature and concentration of paraffin in the microcapsule slurry was selected as experimental parameters. As a result, the dimensionless correlation equations of heat storage completion time and heat transfer were derived in terms of dimensionless parameters.
04/01624 Light emission from carbon-based materials under ITER relevant thermal shock loads Hirai, T. et al. Journal of Nuclear Materials, 2003, 321, (1), 110-114. Light emission from carbon-based materials (fine grain graphite, CFC and silicon doped CFC) was observed during ITER relevant thermal shock loads by means of in situ optical diagnostics. The light emission that corresponds to particle release clearly indicated different particle release processes in the three materials. The differences were also found in the initiation temperatures of particle release and the surface morphology of the loaded areas. These results are related to the thermal stress in bulk materials. In addition to particle release, vapour cloud formation caused by thermal shock loads were observed as CII lines and lines from the C2 Swan system. No Si lines but lines from SiC2 molecules (Merrill-Sanford bands) were observed in Si doped CFC. This indicates that atomic silicon is not released under ITER relevant thermal shock loads.
04•01625 Mathematical modelling and experimental verification of wood drying process Awadalla, H. S. F. et al. Energy Conversion and Management, 2004, 45, (2), 197 207. In this paper, the wood drying process is investigated theoretically under transient conditions. The governing equations of heat and mass transfer in wood are presented. The finite elements method is used to solve the set of governing equations by means of a simulation program. For verification of the present model, the wood model is executed within the TRNSYS program with experimental data of wood drying experiments conducted at Wood Research Institute of Munich, Germany, and with previous theoretical works. For steady state and transient conditions, the computational results show considerable agreement with previous experimental and theoretical works.
04/01626 Mathematical modelling of semi-anthracite combustion in a single burner furnace Stephenson, P. L. Fuel, 2003, 82, (15-17), 2069-2073. As part of an investigation into combustion behaviour at Aberthaw Power Station, experiments have been conducted using Innogy's 0.5 MW Combustion Test Facility (CTF) at Didcot A. Most tests involved
220
Fuel and Energy Abstracts May 2004
Zhao, B. et al. Combustion and Flame, 2003, 133, (1 2), 173-188. Spatially resolved measurement of the soot particle size distribution function (PSDF) was made in a laminar premixed ethylene-argonoxygen flame using a scanning mobility particle sizer. The emphasis of the study was to follow the evolution of the PSDF from the onset of particle inception to particle mass growth. At the onset of soot inception, the PSDF was found to follow a power-law dependence on particle diameter. The PSDF becomes bimodal at larger height above the burner surface, and remains bimodal throughout the flame. Numerical simulation using a kinetic model proposed previously and a stochastic approach to solve aerosol dynamics equations again showed a bimodal PSDF. Further analysis revealed that bimodality is intrinsic to an aerosol process involving particle-particle coagulation and particle nucleation dominated by monomer dimerization.
04•01628 Model of air gasification of a solid fuel under filtration conditions Salganskii, E. A. et al. Fizika Goreniya i Vzryva, 2003, 39, (1), 44-50. (In Russian) A double-temperature mathematical model of a steady state filtration combustion process is presented, accounting for, of course, the reactor length and dependence of the phase heat capacity at particular temperatures and compositions. The model describes the gasification of solid fuel under a filtration regime. The calculated results are given for the gasification reaction of carbon mixtures with inert components. The intervals are defined and applied to combustable components, of which the results are normalized, and the value of the inverse wave by this interval is presented.
04/01629 Model study of the thermal storage system by FEHM code Tenma, N. et al. Geothermics, 2003, 32, (4 -6), 603-607. The use of low-temperature geothermal resources is important from the viewpoint of global warming. In order to evaluate various underground projects that use low-temperature geothermal resources, the parameters of a typical underground system using the two,well model have been estimated. By changing the parameters of the system, six different heat extraction scenarios have been studied. One of these six scenarios is recommended because of its small energy loss.
04/01630 Modeling and simulation of syngas unit in large scale direct reduction plant Farhadi, F. et al. Ironmaking and Steelmaking, 2003, 30, (1), 18-24. The production of reducing gas is usually a bottleneck to capacity increase in direct reduction plants. Modelling and simulation of reducing gas production result in better design and operation of these plants. In the present work, a mathematical model is discussed that relates to a Midrex reformer, which is different from conventional steam reformers in some respects. Both process side and furnace side were included in an integrated model. Simulation results were tested against available data from an actual plant. The model predictions were reasonably accurate. The effects of three process variables, feed gas temperature, feed gas pressure and excess air, on reformer performance were investigated. Simulation results confirm that an increment in feed gas temperature is the most effective method of increasing performance.
04•01631 Modeling NHa and HCN emissions from biomass circulating fluidized bed gasifiers Liu, H. and Gibbs, M. Fuel, 2003, 82, (13), 1591-1604. A circulating fiuidized bed biomass gasification model is developed in the present study, The model consists of sub-models for devolatilization, tar cracking and a chemical reaction network of main gasification reactions and nitrogen chemistry. A total of 40 global chemical reactions are included in the model, of which 28 reactions belong to fuel-nitrogen reaction network. Individual reaction rates are selected from the literature, wherever possible, based on studies of woody biomass fuels. Volatile nitrogen is assumed to consist of NH3, HCN and N2 with the distribution between three species as input parameters to the model. Modelling of the hydrodynamics of the riser is simplified by using solids concentration profile along the riser as an input to the
16 Fuel science and technology (fundamental science, analysis, instrumentation) model. Both gaseous phase and solids phase are assumed to be in plug flow. Modelling results are compared with the experimental results published in the literature. Predicted effects of bed temperature, equivalence ratio and fuel moisture content on main gaseous composition, tar and NH3 emissions generally agree with the literature data. A sensitivity analysis of some reaction rates included in the model on NH3 emissions has also been carried out. It has been revealed that the catalytic activity of bed materials towards the oxidation of NH3 has the greatest influence on the predicted NH2 emissions. In addition, the predicted NH3 emissions are also affected by the catalytic activity of bed materials towards the decomposition of NH2 and the homogenous reaction rates of NH3 decomposition and the reduction of NO by NH3 in the presence of oxygen.
04/01632 Modeling strategy of the source and sink terms in the two-group interfacial area transport equation Ishii, M. et al. Annals' of Nuclear Energy, 2003, 30, (13), 1309-1331. This paper presents the general strategy for modelling the source and sink terms in the two-group interracial area transport equation. The two-group transport equation is applicable in bubbly, cap bubbly, slug, and churn-turbulent flow regimes to predict the change of the interfacial area concentration. This dynamic approach has an advantage of flow regime-independence over the conventional empirical correlation approach for the interracial area concentration in the applications with the two-fluid model. In the two-group interracial area transport equation, bubbles are categorized into two groups: spherical/ distorted bubbles as Group 1 and cap/slug/churn-turbulent bubbles as Group 2. Thus, two sets of equations are used to describe the generation and destruction rates of bubble number density, void fraction, and interracial area concentration for the two groups of bubbles due to bubble expansion and compression, coalescence and disintegration, and phase change. Based upon a detailed literature review of the research on the bubble interactions, five major bubble interaction mechanisms are identified for the gas-liquid two-phase flow of interest. A systematic integral approach, in which the significant variations of bubble volume and shape are accounted for, is suggested for the modelling of two-group bubble interactions. To obtain analytical forms for the various bubble interactions, a simplification is made for the bubble number density distribution function.
04/01633 Modeling the effects of operating conditions on fuel and environmental costs for a 310 MW boiler firing fuel oil Kouprianov, V. I. and Kaewboonsong, W. Energy Conversion and Management, 2004, 45, (1), 1-14. A computational model for analysis and minimizing the fuel and environmental costs was applied to a 310 MW fuel oil fired boiler. The effects of the main operating variables (load and excess air ratio) on these costs were studied in this work. The emission rates of the gaseous pollutants (NOx, SO3, SO2 and CO) were estimated with the use of emission models considering the boiler furnace as a control volume. The predicted emissions for NOx, SO3 and CO were compared with the values obtained in experimental tests on this boiler operated at different loads and various excess air ratios. The major (i.e. fuel, CO3 and SO3) cost items are weakly dependent on the excess air ratio and mainly affected by the boiler load. Meanwhile, the effects of the excess air ratio, as well as boiler load, on the minor costs (associated with NOx, SO3 and CO emissions) are found to be noticeable. Optimum and 'compromise' excess air ratios were quantified for the boiler loads in the range of 80-100%. Switching the boiler to firing the fuel at the 'compromise' excess air ratio leads to a reduction in the total (fuel and environmental) costs for this boiler.
04/01634 Modeling the optical absorption within conjugated polymer/fullerene-based bulk-heterojunction organic solar cells Hoppe, H. et al. Solar Energy Materials and Solar Cells, 2003, 80, (1), 105-113. This paper reports results on the modelling of the optical properties of the bulk-heterojunction 'plastic solar ceils', consisting of a solid-state blend of the conjugated polymer poly-[2-(37-dimethyloctyloxy)-5methyloxy]-para-phenylene-vinylene and the fullerene C60 derivative 1-(3-methoxycarbonyl) propyl-l-phenyl [66]C61. Upon illuminating these cells with the standard AM 1.5 solar spectrum, the short circuit current can be determined for any given internal quantum efficiency as a function of the active layer thickness. In addition, the depth profiles of photo-induced charge generation rates are calculated. Based on the agreement of this modelling with experimentally determined efficiencies of these solar cells, an internal quantum efficiency of about 80% has been estimated.
04/01635 Optimization of a hydrocarbon fuel ignition model for two single component surrogates of diesel fuel Hamosfakidis, V. and Reitz, R. D. Combustion and Flame, 2003, 132, (3), 433-450.
The auto-ignition predictions of the Shell hydrocarbon fuel ignition model have been improved for initial conditions similar to those in diesel engine environments. A series of modifications were made to the model, including a more accurate calculation of the heat release of the fuel, a new mass balance for the products of the termination reactions, and the enthalpies of the Shell model species, R*, B and Q were revised. In addition the 26 kinetic parameters of the revised model were determined using a genetic algorithm optimization methodology guided by auto-ignition results obtained from a detailed chemical kinetic mechanism. The optimization was performed for a broad range of conditions that is representative of the operating conditions in diesel engines at the start-of-injection (SOI). This range includes: equivalence ratios from 0.5-4.0, initial pressures from 40-120 bar, initial temperatures from 650 K to 1175 K and E G R percentages from 0-75%. The model constants were optimized for two single component hydrocarbons species, n-heptane and tetradecane, that are representative of diesel fuel. Finally, the model was implemented into the KIVA3V CFD code and a series of engine simulations was performed in order to assess its agreement with experimental data for engine applications. The results were found to be promising in both cases of short and long ignition delays.
04/01636 Parametric study of a corrosion model applied to lead-bismuth flow systems Zhang, J. and Li, N. Journal of Nuclear Materials, 2003, 321, (2-3), 184-191. The corrosion of steels exposed to flowing liquid metals is influenced by local and axial conditions of the flow systems. Despite of this, most existing corrosion models only consider the mean values based on local conditions. The present study refines a model for flowing liquid metal under non-isothermal conditions. The model is based on solving the mass transport equation in the boundary layer. Two kinds of flows are investigated: through an open pipe system and through a closed loop system. The model is applied to a lead-bismuth eutectic (LBE) test loop. A parametric study illustrates the effects of the axial temperature profile on corrosion. The study provides important insight to the design, operation and testing of such loop systems.
04•01637
Power system instability and chaos
Yu, Y. et al. Electric Power Systems Research, 2003, 65, (3), 187-195. In this paper routes to chaotic oscillation in power systems and relationships between chaos and various power system instability modes are deeply studied. Firstly, using a three-bus simple system, three routes may cause power systems to chaos are illustrated and discussed. They are route of cascading period doubling bifurcation (PDB), route of torus bifurcation (TB) and route of directly initiated by a large disturbance of energy. The route of cascading PDB is a typical route to chaos, where PDB is caused by a real Floquet multiplier (FM) moving counter to the real axis and going out of the unit circle from point ( - 1 , 0) in the complex plane. TB is caused by a couple of conjugate FMs going out of the unit circle with a nonzero imaginary part in the complex plane. Chaos caused by TB has some interesting features, such as self-organizing phenomenon, coexistence of divergent and chaotic subspaces, etc. The last route, which is directly initiated by a large disturbance of energy, is reported and studied for the first time so far as we know. Secondly, relationships between chaos and various instability modes are discussed. Also using a simple system, the study illustrates the scenes that chaos leads power system to voltage collapse, angle divergence, or voltage collapse with angle divergence simultaneously when the stability conditions of the chaotic oscillation are broken. It tells us that chaos is very likely to be an intergrade existing in the transient stage after a large disturbance. In order to prevent the appearance of instability incidents effectively, it is necessary to keep up on the study of chaotic phenomena in power systems. All these studies are helpful to deeply understand the mechanism of various instability modes and to find effective antichaos strategies.
04/01638 Power system reliability evaluation using learning vector quantization and Monte Carlo simulation Luo, X. et al. Electric Power Systems Research, 2003, 66, (2), 163-169. Artificial neural networks (ANN) based on the learning vector quantization (LVQ) algorithm have received considerable attention as pattern classifiers. This paper proposes a new method for power system reliability evaluation combining Monte Carlo simulation and LVQ which greatly reduces the computing burden of the loss of load probability calculation compared to Monte Carlo simulation only. A case study of the IEEE RTS system is presented demonstrating the efficiency of this approach.
04•01639 Quantitative determination of modal content and morphological properties of coal sulphides by digital image analysis as a tool to check their flotation behaviour Coz, E. et al. Fuel, 2003, 82, (15-17), 1921-1929.
Fuel and Energy Abstracts
May 2004
221
combustion, but a few were for isothermal conditions and included velocity measurements. Both isothermal and combusting flows have been calculated using a commercial computational fluid dynamics (CFD) program called Star-CD. The isothermal solutions have been validated against a simpler analytical solution and against rig measurements. The solutions with combustion and radiation have been validated qualitatively against the behaviour observed during rig tests and also quantitatively against incident heat flux measurements. The basis of the CFD for both the isothermal and combusting cases is described, together with the validation that has been achieved.
04/01622 Investigation of pyrolysis of Chinese coals using thermal analysis/mass spectrometry
04/01627 Measurement and numerical simulation of soot particle size distribution functions in a laminar premixed ethylene-oxygen-argon flame
Li, X. et al. Journal of Thermal Analysis and Calorimetry, 2003, 71, (2), 601-612. TA/MS (thermal analysis coupled with mass spectrometry) was applied to the pyrolysis of different-rank coals. A total of 13 coals were investigated. The samples were chosen to represent the 13 types of Chinese coals according to the Chinese coal classification system. The experiments were carried out in an argon atmosphere with a flow rate of 150 mL rain i The samples were heated from 40 up to 1200°C with a constant heating rate of 10 K rain -1. The main evolved pyrolysis products were identified through the online-recorded mass spectra. The results showed a strong thermal and evolution behaviour dependence on the coal rank. Different aliphatic fragments and also some aromatic substances, which are of environmental concern (BTX, PAHs), were found to be released depending on the coal type.
04/01623 Latent heat storage characteristics of solid-liquid phase change heat storage microcapsule slurry by boiling heat transfer under a vacuum condition Inaba, H. et al. Nippon Reito Kucho Gakkai Ronbunshu, 2003, 20, (1), 37 47. (In Japanese) Recently, the new heat transfer medium, which fulfils both functions of heat storage and heat transportation, was developed in a heat storage field. Solid-liquid latent heat microcapsule slurry would correspond to the topical medium, so-called functionally thermal fluid. The preset study has clarified the latent heat storage characteristics of microcapsule slurry by making heat transfer enlargement with the help of slurry water pool boiling phenomenon. The paraffin wax at a melting point of 62 ° was used as a phase change material which was packed into the microcapsule. The heating surface temperature and concentration of paraffin in the microcapsule slurry was selected as experimental parameters. As a result, the dimensionless correlation equations of heat storage completion time and heat transfer were derived in terms of dimensionless parameters.
04/01624 Light emission from carbon-based materials under ITER relevant thermal shock loads Hirai, T. et al. Journal of Nuclear Materials, 2003, 321, (1), 110-114. Light emission from carbon-based materials (fine grain graphite, CFC and silicon doped CFC) was observed during ITER relevant thermal shock loads by means of in situ optical diagnostics. The light emission that corresponds to particle release clearly indicated different particle release processes in the three materials. The differences were also found in the initiation temperatures of particle release and the surface morphology of the loaded areas. These results are related to the thermal stress in bulk materials. In addition to particle release, vapour cloud formation caused by thermal shock loads were observed as CII lines and lines from the C2 Swan system. No Si lines but lines from SiC2 molecules (Merrill-Sanford bands) were observed in Si doped CFC. This indicates that atomic silicon is not released under ITER relevant thermal shock loads.
04•01625 Mathematical modelling and experimental verification of wood drying process Awadalla, H. S. F. et al. Energy Conversion and Management, 2004, 45, (2), 197 207. In this paper, the wood drying process is investigated theoretically under transient conditions. The governing equations of heat and mass transfer in wood are presented. The finite elements method is used to solve the set of governing equations by means of a simulation program. For verification of the present model, the wood model is executed within the TRNSYS program with experimental data of wood drying experiments conducted at Wood Research Institute of Munich, Germany, and with previous theoretical works. For steady state and transient conditions, the computational results show considerable agreement with previous experimental and theoretical works.
04/01626 Mathematical modelling of semi-anthracite combustion in a single burner furnace Stephenson, P. L. Fuel, 2003, 82, (15-17), 2069-2073. As part of an investigation into combustion behaviour at Aberthaw Power Station, experiments have been conducted using Innogy's 0.5 MW Combustion Test Facility (CTF) at Didcot A. Most tests involved
220
Fuel and Energy Abstracts May 2004
Zhao, B. et al. Combustion and Flame, 2003, 133, (1 2), 173-188. Spatially resolved measurement of the soot particle size distribution function (PSDF) was made in a laminar premixed ethylene-argonoxygen flame using a scanning mobility particle sizer. The emphasis of the study was to follow the evolution of the PSDF from the onset of particle inception to particle mass growth. At the onset of soot inception, the PSDF was found to follow a power-law dependence on particle diameter. The PSDF becomes bimodal at larger height above the burner surface, and remains bimodal throughout the flame. Numerical simulation using a kinetic model proposed previously and a stochastic approach to solve aerosol dynamics equations again showed a bimodal PSDF. Further analysis revealed that bimodality is intrinsic to an aerosol process involving particle-particle coagulation and particle nucleation dominated by monomer dimerization.
04•01628 Model of air gasification of a solid fuel under filtration conditions Salganskii, E. A. et al. Fizika Goreniya i Vzryva, 2003, 39, (1), 44-50. (In Russian) A double-temperature mathematical model of a steady state filtration combustion process is presented, accounting for, of course, the reactor length and dependence of the phase heat capacity at particular temperatures and compositions. The model describes the gasification of solid fuel under a filtration regime. The calculated results are given for the gasification reaction of carbon mixtures with inert components. The intervals are defined and applied to combustable components, of which the results are normalized, and the value of the inverse wave by this interval is presented.
04/01629 Model study of the thermal storage system by FEHM code Tenma, N. et al. Geothermics, 2003, 32, (4 -6), 603-607. The use of low-temperature geothermal resources is important from the viewpoint of global warming. In order to evaluate various underground projects that use low-temperature geothermal resources, the parameters of a typical underground system using the two,well model have been estimated. By changing the parameters of the system, six different heat extraction scenarios have been studied. One of these six scenarios is recommended because of its small energy loss.
04/01630 Modeling and simulation of syngas unit in large scale direct reduction plant Farhadi, F. et al. Ironmaking and Steelmaking, 2003, 30, (1), 18-24. The production of reducing gas is usually a bottleneck to capacity increase in direct reduction plants. Modelling and simulation of reducing gas production result in better design and operation of these plants. In the present work, a mathematical model is discussed that relates to a Midrex reformer, which is different from conventional steam reformers in some respects. Both process side and furnace side were included in an integrated model. Simulation results were tested against available data from an actual plant. The model predictions were reasonably accurate. The effects of three process variables, feed gas temperature, feed gas pressure and excess air, on reformer performance were investigated. Simulation results confirm that an increment in feed gas temperature is the most effective method of increasing performance.
04•01631 Modeling NHa and HCN emissions from biomass circulating fluidized bed gasifiers Liu, H. and Gibbs, M. Fuel, 2003, 82, (13), 1591-1604. A circulating fiuidized bed biomass gasification model is developed in the present study, The model consists of sub-models for devolatilization, tar cracking and a chemical reaction network of main gasification reactions and nitrogen chemistry. A total of 40 global chemical reactions are included in the model, of which 28 reactions belong to fuel-nitrogen reaction network. Individual reaction rates are selected from the literature, wherever possible, based on studies of woody biomass fuels. Volatile nitrogen is assumed to consist of NH3, HCN and N2 with the distribution between three species as input parameters to the model. Modelling of the hydrodynamics of the riser is simplified by using solids concentration profile along the riser as an input to the
16 Fuel science and technology (fundamental science, analysis, instrumentation) model. Both gaseous phase and solids phase are assumed to be in plug flow. Modelling results are compared with the experimental results published in the literature. Predicted effects of bed temperature, equivalence ratio and fuel moisture content on main gaseous composition, tar and NH3 emissions generally agree with the literature data. A sensitivity analysis of some reaction rates included in the model on NH3 emissions has also been carried out. It has been revealed that the catalytic activity of bed materials towards the oxidation of NH3 has the greatest influence on the predicted NH2 emissions. In addition, the predicted NH3 emissions are also affected by the catalytic activity of bed materials towards the decomposition of NH2 and the homogenous reaction rates of NH3 decomposition and the reduction of NO by NH3 in the presence of oxygen.
04/01632 Modeling strategy of the source and sink terms in the two-group interfacial area transport equation Ishii, M. et al. Annals' of Nuclear Energy, 2003, 30, (13), 1309-1331. This paper presents the general strategy for modelling the source and sink terms in the two-group interracial area transport equation. The two-group transport equation is applicable in bubbly, cap bubbly, slug, and churn-turbulent flow regimes to predict the change of the interfacial area concentration. This dynamic approach has an advantage of flow regime-independence over the conventional empirical correlation approach for the interracial area concentration in the applications with the two-fluid model. In the two-group interracial area transport equation, bubbles are categorized into two groups: spherical/ distorted bubbles as Group 1 and cap/slug/churn-turbulent bubbles as Group 2. Thus, two sets of equations are used to describe the generation and destruction rates of bubble number density, void fraction, and interracial area concentration for the two groups of bubbles due to bubble expansion and compression, coalescence and disintegration, and phase change. Based upon a detailed literature review of the research on the bubble interactions, five major bubble interaction mechanisms are identified for the gas-liquid two-phase flow of interest. A systematic integral approach, in which the significant variations of bubble volume and shape are accounted for, is suggested for the modelling of two-group bubble interactions. To obtain analytical forms for the various bubble interactions, a simplification is made for the bubble number density distribution function.
04/01633 Modeling the effects of operating conditions on fuel and environmental costs for a 310 MW boiler firing fuel oil Kouprianov, V. I. and Kaewboonsong, W. Energy Conversion and Management, 2004, 45, (1), 1-14. A computational model for analysis and minimizing the fuel and environmental costs was applied to a 310 MW fuel oil fired boiler. The effects of the main operating variables (load and excess air ratio) on these costs were studied in this work. The emission rates of the gaseous pollutants (NOx, SO3, SO2 and CO) were estimated with the use of emission models considering the boiler furnace as a control volume. The predicted emissions for NOx, SO3 and CO were compared with the values obtained in experimental tests on this boiler operated at different loads and various excess air ratios. The major (i.e. fuel, CO3 and SO3) cost items are weakly dependent on the excess air ratio and mainly affected by the boiler load. Meanwhile, the effects of the excess air ratio, as well as boiler load, on the minor costs (associated with NOx, SO3 and CO emissions) are found to be noticeable. Optimum and 'compromise' excess air ratios were quantified for the boiler loads in the range of 80-100%. Switching the boiler to firing the fuel at the 'compromise' excess air ratio leads to a reduction in the total (fuel and environmental) costs for this boiler.
04/01634 Modeling the optical absorption within conjugated polymer/fullerene-based bulk-heterojunction organic solar cells Hoppe, H. et al. Solar Energy Materials and Solar Cells, 2003, 80, (1), 105-113. This paper reports results on the modelling of the optical properties of the bulk-heterojunction 'plastic solar ceils', consisting of a solid-state blend of the conjugated polymer poly-[2-(37-dimethyloctyloxy)-5methyloxy]-para-phenylene-vinylene and the fullerene C60 derivative 1-(3-methoxycarbonyl) propyl-l-phenyl [66]C61. Upon illuminating these cells with the standard AM 1.5 solar spectrum, the short circuit current can be determined for any given internal quantum efficiency as a function of the active layer thickness. In addition, the depth profiles of photo-induced charge generation rates are calculated. Based on the agreement of this modelling with experimentally determined efficiencies of these solar cells, an internal quantum efficiency of about 80% has been estimated.
04/01635 Optimization of a hydrocarbon fuel ignition model for two single component surrogates of diesel fuel Hamosfakidis, V. and Reitz, R. D. Combustion and Flame, 2003, 132, (3), 433-450.
The auto-ignition predictions of the Shell hydrocarbon fuel ignition model have been improved for initial conditions similar to those in diesel engine environments. A series of modifications were made to the model, including a more accurate calculation of the heat release of the fuel, a new mass balance for the products of the termination reactions, and the enthalpies of the Shell model species, R*, B and Q were revised. In addition the 26 kinetic parameters of the revised model were determined using a genetic algorithm optimization methodology guided by auto-ignition results obtained from a detailed chemical kinetic mechanism. The optimization was performed for a broad range of conditions that is representative of the operating conditions in diesel engines at the start-of-injection (SOI). This range includes: equivalence ratios from 0.5-4.0, initial pressures from 40-120 bar, initial temperatures from 650 K to 1175 K and E G R percentages from 0-75%. The model constants were optimized for two single component hydrocarbons species, n-heptane and tetradecane, that are representative of diesel fuel. Finally, the model was implemented into the KIVA3V CFD code and a series of engine simulations was performed in order to assess its agreement with experimental data for engine applications. The results were found to be promising in both cases of short and long ignition delays.
04/01636 Parametric study of a corrosion model applied to lead-bismuth flow systems Zhang, J. and Li, N. Journal of Nuclear Materials, 2003, 321, (2-3), 184-191. The corrosion of steels exposed to flowing liquid metals is influenced by local and axial conditions of the flow systems. Despite of this, most existing corrosion models only consider the mean values based on local conditions. The present study refines a model for flowing liquid metal under non-isothermal conditions. The model is based on solving the mass transport equation in the boundary layer. Two kinds of flows are investigated: through an open pipe system and through a closed loop system. The model is applied to a lead-bismuth eutectic (LBE) test loop. A parametric study illustrates the effects of the axial temperature profile on corrosion. The study provides important insight to the design, operation and testing of such loop systems.
04•01637
Power system instability and chaos
Yu, Y. et al. Electric Power Systems Research, 2003, 65, (3), 187-195. In this paper routes to chaotic oscillation in power systems and relationships between chaos and various power system instability modes are deeply studied. Firstly, using a three-bus simple system, three routes may cause power systems to chaos are illustrated and discussed. They are route of cascading period doubling bifurcation (PDB), route of torus bifurcation (TB) and route of directly initiated by a large disturbance of energy. The route of cascading PDB is a typical route to chaos, where PDB is caused by a real Floquet multiplier (FM) moving counter to the real axis and going out of the unit circle from point ( - 1 , 0) in the complex plane. TB is caused by a couple of conjugate FMs going out of the unit circle with a nonzero imaginary part in the complex plane. Chaos caused by TB has some interesting features, such as self-organizing phenomenon, coexistence of divergent and chaotic subspaces, etc. The last route, which is directly initiated by a large disturbance of energy, is reported and studied for the first time so far as we know. Secondly, relationships between chaos and various instability modes are discussed. Also using a simple system, the study illustrates the scenes that chaos leads power system to voltage collapse, angle divergence, or voltage collapse with angle divergence simultaneously when the stability conditions of the chaotic oscillation are broken. It tells us that chaos is very likely to be an intergrade existing in the transient stage after a large disturbance. In order to prevent the appearance of instability incidents effectively, it is necessary to keep up on the study of chaotic phenomena in power systems. All these studies are helpful to deeply understand the mechanism of various instability modes and to find effective antichaos strategies.
04/01638 Power system reliability evaluation using learning vector quantization and Monte Carlo simulation Luo, X. et al. Electric Power Systems Research, 2003, 66, (2), 163-169. Artificial neural networks (ANN) based on the learning vector quantization (LVQ) algorithm have received considerable attention as pattern classifiers. This paper proposes a new method for power system reliability evaluation combining Monte Carlo simulation and LVQ which greatly reduces the computing burden of the loss of load probability calculation compared to Monte Carlo simulation only. A case study of the IEEE RTS system is presented demonstrating the efficiency of this approach.
04•01639 Quantitative determination of modal content and morphological properties of coal sulphides by digital image analysis as a tool to check their flotation behaviour Coz, E. et al. Fuel, 2003, 82, (15-17), 1921-1929.
Fuel and Energy Abstracts
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