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03084 A numerical solution of composite heat transfer problems using meshless method
16 Fuel science and technology (fundamental science, analysis, instrumentation) The Albedo calculation model (ACM) has been developed to provide the simulation of albedos within three-dimensional urban structures. The model takes into account urban configurations and a change of solar positions, as well as the effects of multiple reflections and shading in an urban canopy. In order to perform a systematic analysis for the effect of various factors on albedo of surfaces, a large-scale numerical experiment has been conducted. The model description and experiment results of albedo characteristics are clarified in this paper. In addition, the development of two associated GUI (graphical user interface)-based applications, Albedo Calculator and Albedo Viewer is also introduced.
04/03081 A model for fission-gas-bubble behavior in amorphous uranium silicide compounds Rest, J. Journal of Nuclear Materials, 2004, 325, (2-3), 107-117. A model for the behaviour of fission gas in irradiated amorphous materials is developed. The model proposes that gas bubble nucleation occurs within shear bands initiated around free volume regions. Small gas-atom clusters that form within these regions are susceptible to dissolution by forces generated by the plastic flow of material around the cluster. The bubble coarsening process depends on the materials viscosity and on irradiation-induced re-solution. The bubble distribution eventually reaches a point where larger bubbles from the tail of the evolving lognormal size distribution begin to contact the more numerous nanometer-sized bubbles from the peak region. This condition defines the knee in the swelling curve. The fission density at which the knee occurs is a function of fission rate. Calculations for the behaviour of the knee, swelling, and the fraction of gas in bubbles in irradiated U3Si2 intermetallic compounds are compared to measured quantities.
04/03082 A modified sequential approach for solving inverse heat conduction problems Lin, S.-M. et al. International Journal of Heat and Mass Transfer, 2004, 47, (12-13), 2669-2680. A modified sequential approach is proposed to improve the performance of the sequential function specification method for inverse heat conduction problems (IHCPs). There are two essential procedures in this study: the first, derives the sequential algorithm and then performs the preliminary estimation; the second, also a key finding in this study, proposes the modified algorithm to eliminate the leading error caused by adding the use of future information in the process of preliminary estimation. One example in this study for solving the unknown source, the proposed method effectively reduces the average relative error from 17.82% to 2.65% when a 10% random measurement error is considered.
04/03083 A novel two-mode MPPT control algorithm based on comparative study of existing algorithms
spline, quartic spline, Gaussian, quadratic and hyperbolic) EFG weight functions with finite element method (FEM) for a three-dimensional composite heat transfer model problem. The validation of the EFG code has been achieved by comparing the EFG results with those obtained by FEM. The effect of scaling parameter on EFG results has also been discussed.
04•03085 A reduced order model of BWR dynamics with subcooled boiling and modal kinetics: application to out of phase oscillations Mufioz-Cobo, J. L. et al. Annals of Nuclear Energy, 2004, 31, (10), i135-1162. This study developed a reduced order model that included the subcooled boiling. New additional equations have been obtained for the following dynamics magnitudes: the effective inception length, the average void fraction in the sub-cooled boiling region, the average void fraction in the bulk boiling region, the mass fluxes at the boiling boundary and the channel exit, and so on. Each channel has three nodes, one of liquid, one with sub-cooled boiling, and one with bulk boiling. The reduced order model includes also a modal kinetics with the fundamental mode and the first sub-critical one, and two channels representing both halves of the reactor core. The model displays out of phase oscillations when enough feedback gain is provided. The feedback gain that is necessary to self sustain these oscillations is approximately one half the gain that is needed when the sub-cooled boiling node is not included.
04/03086 An experimental study of enhanced heat transfer in rectangular PCM thermal storage Stritih, U. International Journal of Heat and Mass Transfer, 2004, 47, (12-13), 2841-2847. The heat-transfer characteristics of a latent-heat storage unit with a finned surface have been experimentally studied in terms of the solidification and melting processes by comparing them with those of a heat-storage unit with a plain surface. Paraffin with a melting point of 30°C was used in the investigations because it is appropriate for thermal storage applications in buildings. Time-based variations of the temperature distributions and heat flux are explained from the results of observations of the melting and the solidification layers. The dimensionless Nusselt number was calculated as a function of the Rayleigh number for natural convection in the paraffin for both the melting and the solidification processes. The effectiveness of the fins was calculated from the quotient of the heat flux with fins and the heat flux without fins.
04•03087 An exploration of alternative approaches to the representation of uncertainty in model predictions
Yu, G. J. et al. Solar Energy, 2004, 76, (4), 455-463. In this paper, the effectiveness of these three different control algorithms is thoroughly investigated via simulation and a proposed efficiency evaluation method of experimentation. Both the steady-state and transient characteristics of each control algorithms along with its measured efficiency are analysed. Finally, a novel two-mode maximum power point tracking (MPPT) control algorithm combining the modified constant voltage control and IncCond method is proposed to improve the efficiency of the 3 kW PV power generation system at different insolation conditions. Finally, a novel two-mode MPPT control algorithm combining the modified constant voltage control and IncCond method is proposed to improve the efficiency of the 3 kW PV power generation system at different insolation conditions. Experimental results show that the proposed two-mode MPPT control provides excellent performance at less than 30% insolation intensity, covering the whole insolation area without additional hardware circuitry.
Helton, J. C. et al. Reliability Engineering & System Safety, 2004, 85, (1-3), 39-71. Several simple test problems are used to explore the following approaches to the representation of the uncertainty in model predictions that derives from uncertainty in model inputs: probability theory, evidence theory, possibility theory, and interval analysis. Each of the test problems has rather diffuse characterizations of the uncertainty in model inputs obtained from one or more equally credible sources. These given uncertainty characterizations are translated into the mathematical structure associated with each of the indicated approaches to the representation of uncertainty and then propagated through the model with Monte Carlo techniques to obtain the corresponding representation of the uncertainty in one or more model predictions. The different approaches to the representation of uncertainty can lead to very different appearing representations of the uncertainty in model predictions even though the starting information is exactly the same for each approach. To avoid misunderstandings and, potentially, bad decisions, these representations must be interpreted in the context of the theory/procedure from which they derive.
04•03084 A numerical solution of composite heat transfer problems using meshless method
04/03088 Analysis of air return alternatives for CRS-type open volumetric receiver
Singh, I. V. International Journal of Heat and Mass Transfer, 2004, 47, (10-11), 2123-2138. This paper deals with the three-dimensional numerical solution of composite heat transfer problems using meshless element free Galerkin method (EFG). The EFG method utilizes moving least square (MLS) approximants to approximate the unknown function of temperature T(x) with Th(x). These MLS approximants are constructed by using a weight function, a basis function and a set of non-constants coefficients. Variational method is utilized for the discretization of the governing equations. The essential boundary conditions are enforced using Lagrange multiplier technique. The MATLAB codes have been developed to obtain the numerical solution. The EFG results are obtained for a model problem using different weight functions. Three new weight functions namely exponential, rational and cosine have been proposed. A comparison is made among the results obtained using proposed (exponential, rational and cosine) and existing (R&R, cubic
Marcos, M. J. et al. Energy, 2004, 29, (5-6), 677-686. Even though air-cooled receivers provide substantial benefits, such as low inertia and quick sun-following dispatchability, and the volumetric effect leads to designs with aperture areas similar to those used in molten salt or water/steam receivers, some concern persists regarding absorber durability, reduction of radiation losses and improvement of the air return ratio (ARR). The paper focuses On this last issue, since the A R R is a source of significant receiver losses in current designs. Today's sealed-up receivers claim values between 45 and 70% for ARR, which means, in terms of energy loss, between 5 and 15%. As a consequence of A R R and the radiation loss stemming from high working temperatures, open volumetric receivers efficiencies below 75% are reported at temperatures usable by the power block. Those values may be acceptable for a first demonstration plant, but are categorically not competitive for commercial schemes in which receiver efficiency should approach 90%. This paper discusses the impact of
434
Fuel and Energy Abstracts
November 2004
04/03081 A model for fission-gas-bubble behavior in amorphous uranium silicide compounds Rest, J. Journal of Nuclear Materials, 2004, 325, (2-3), 107-117. A model for the behaviour of fission gas in irradiated amorphous materials is developed. The model proposes that gas bubble nucleation occurs within shear bands initiated around free volume regions. Small gas-atom clusters that form within these regions are susceptible to dissolution by forces generated by the plastic flow of material around the cluster. The bubble coarsening process depends on the materials viscosity and on irradiation-induced re-solution. The bubble distribution eventually reaches a point where larger bubbles from the tail of the evolving lognormal size distribution begin to contact the more numerous nanometer-sized bubbles from the peak region. This condition defines the knee in the swelling curve. The fission density at which the knee occurs is a function of fission rate. Calculations for the behaviour of the knee, swelling, and the fraction of gas in bubbles in irradiated U3Si2 intermetallic compounds are compared to measured quantities.
04/03082 A modified sequential approach for solving inverse heat conduction problems Lin, S.-M. et al. International Journal of Heat and Mass Transfer, 2004, 47, (12-13), 2669-2680. A modified sequential approach is proposed to improve the performance of the sequential function specification method for inverse heat conduction problems (IHCPs). There are two essential procedures in this study: the first, derives the sequential algorithm and then performs the preliminary estimation; the second, also a key finding in this study, proposes the modified algorithm to eliminate the leading error caused by adding the use of future information in the process of preliminary estimation. One example in this study for solving the unknown source, the proposed method effectively reduces the average relative error from 17.82% to 2.65% when a 10% random measurement error is considered.
04/03083 A novel two-mode MPPT control algorithm based on comparative study of existing algorithms
spline, quartic spline, Gaussian, quadratic and hyperbolic) EFG weight functions with finite element method (FEM) for a three-dimensional composite heat transfer model problem. The validation of the EFG code has been achieved by comparing the EFG results with those obtained by FEM. The effect of scaling parameter on EFG results has also been discussed.
04•03085 A reduced order model of BWR dynamics with subcooled boiling and modal kinetics: application to out of phase oscillations Mufioz-Cobo, J. L. et al. Annals of Nuclear Energy, 2004, 31, (10), i135-1162. This study developed a reduced order model that included the subcooled boiling. New additional equations have been obtained for the following dynamics magnitudes: the effective inception length, the average void fraction in the sub-cooled boiling region, the average void fraction in the bulk boiling region, the mass fluxes at the boiling boundary and the channel exit, and so on. Each channel has three nodes, one of liquid, one with sub-cooled boiling, and one with bulk boiling. The reduced order model includes also a modal kinetics with the fundamental mode and the first sub-critical one, and two channels representing both halves of the reactor core. The model displays out of phase oscillations when enough feedback gain is provided. The feedback gain that is necessary to self sustain these oscillations is approximately one half the gain that is needed when the sub-cooled boiling node is not included.
04/03086 An experimental study of enhanced heat transfer in rectangular PCM thermal storage Stritih, U. International Journal of Heat and Mass Transfer, 2004, 47, (12-13), 2841-2847. The heat-transfer characteristics of a latent-heat storage unit with a finned surface have been experimentally studied in terms of the solidification and melting processes by comparing them with those of a heat-storage unit with a plain surface. Paraffin with a melting point of 30°C was used in the investigations because it is appropriate for thermal storage applications in buildings. Time-based variations of the temperature distributions and heat flux are explained from the results of observations of the melting and the solidification layers. The dimensionless Nusselt number was calculated as a function of the Rayleigh number for natural convection in the paraffin for both the melting and the solidification processes. The effectiveness of the fins was calculated from the quotient of the heat flux with fins and the heat flux without fins.
04•03087 An exploration of alternative approaches to the representation of uncertainty in model predictions
Yu, G. J. et al. Solar Energy, 2004, 76, (4), 455-463. In this paper, the effectiveness of these three different control algorithms is thoroughly investigated via simulation and a proposed efficiency evaluation method of experimentation. Both the steady-state and transient characteristics of each control algorithms along with its measured efficiency are analysed. Finally, a novel two-mode maximum power point tracking (MPPT) control algorithm combining the modified constant voltage control and IncCond method is proposed to improve the efficiency of the 3 kW PV power generation system at different insolation conditions. Finally, a novel two-mode MPPT control algorithm combining the modified constant voltage control and IncCond method is proposed to improve the efficiency of the 3 kW PV power generation system at different insolation conditions. Experimental results show that the proposed two-mode MPPT control provides excellent performance at less than 30% insolation intensity, covering the whole insolation area without additional hardware circuitry.
Helton, J. C. et al. Reliability Engineering & System Safety, 2004, 85, (1-3), 39-71. Several simple test problems are used to explore the following approaches to the representation of the uncertainty in model predictions that derives from uncertainty in model inputs: probability theory, evidence theory, possibility theory, and interval analysis. Each of the test problems has rather diffuse characterizations of the uncertainty in model inputs obtained from one or more equally credible sources. These given uncertainty characterizations are translated into the mathematical structure associated with each of the indicated approaches to the representation of uncertainty and then propagated through the model with Monte Carlo techniques to obtain the corresponding representation of the uncertainty in one or more model predictions. The different approaches to the representation of uncertainty can lead to very different appearing representations of the uncertainty in model predictions even though the starting information is exactly the same for each approach. To avoid misunderstandings and, potentially, bad decisions, these representations must be interpreted in the context of the theory/procedure from which they derive.
04•03084 A numerical solution of composite heat transfer problems using meshless method
04/03088 Analysis of air return alternatives for CRS-type open volumetric receiver
Singh, I. V. International Journal of Heat and Mass Transfer, 2004, 47, (10-11), 2123-2138. This paper deals with the three-dimensional numerical solution of composite heat transfer problems using meshless element free Galerkin method (EFG). The EFG method utilizes moving least square (MLS) approximants to approximate the unknown function of temperature T(x) with Th(x). These MLS approximants are constructed by using a weight function, a basis function and a set of non-constants coefficients. Variational method is utilized for the discretization of the governing equations. The essential boundary conditions are enforced using Lagrange multiplier technique. The MATLAB codes have been developed to obtain the numerical solution. The EFG results are obtained for a model problem using different weight functions. Three new weight functions namely exponential, rational and cosine have been proposed. A comparison is made among the results obtained using proposed (exponential, rational and cosine) and existing (R&R, cubic
Marcos, M. J. et al. Energy, 2004, 29, (5-6), 677-686. Even though air-cooled receivers provide substantial benefits, such as low inertia and quick sun-following dispatchability, and the volumetric effect leads to designs with aperture areas similar to those used in molten salt or water/steam receivers, some concern persists regarding absorber durability, reduction of radiation losses and improvement of the air return ratio (ARR). The paper focuses On this last issue, since the A R R is a source of significant receiver losses in current designs. Today's sealed-up receivers claim values between 45 and 70% for ARR, which means, in terms of energy loss, between 5 and 15%. As a consequence of A R R and the radiation loss stemming from high working temperatures, open volumetric receivers efficiencies below 75% are reported at temperatures usable by the power block. Those values may be acceptable for a first demonstration plant, but are categorically not competitive for commercial schemes in which receiver efficiency should approach 90%. This paper discusses the impact of
434
Fuel and Energy Abstracts
November 2004