A method for LEFM analysis of RPV during SBLOCA

A somewhat simplified two-dimensional linear elastic fracture mechanics (LEFM) model of the beltline of a reactor pressure vessel is presented. The fracture mechanics model used tends to be conservative in the sense that it ignores possible beneficial effects of warm prestressing and cladding.

For LEFM studies that require a large number of analyses on the same geometry but with different loads and material toughnesses, the superposition principle is an accurate and simple method to determine the stress intensity factor K₁, provided that K₁ due to a unit load (called K* in this paper), acting on an arbitrary point on the crack surface is known. The details of the superposition principle and the procedure used for determining K* have been presented.

Once these K* are determined for a specific geometry, then the determination of K₁ for the same geometry can be made accurately and in a manner that permits parametric studies involving thousands of individual analyses. It is believed that the error in the K₁ values so determined is less than 3·5%.

An example of the use of the simplified model for a parametric analysis is also presented.     

Theoretical analysis of local indentation on pressured pipes

A quasi-static analysis is presented in this paper for in-service pressurised pipelines subjected to an external impact. Based on the assumed simple rigid, perfectly plastic deformation model, a simple relationship is obtained between the external denting force F and the maximum dent depth δ₀. Results from the theoretical analysis are in reasonable agreement with results from finite element analyses. These show that the pressure p=p_in−p_out has a large influence on the pipe resistance to the indentation, where p_in and p_out are the internal and external pressure, respectively. For the same dent depth, a higher external denting force is required for pipes with higher pressure, p. The difference of the required force between a lowly pressurised pipe and a highly pressurised pipe increases with increasing denting depth.     

Transient analysis and performance prediction of a solid adsorption solar refrigerator

The transient analysis and performance prediction of a solid adsorption solar refrigerator, using activated carbon/methanol adsorbent/adsorbate pair are presented. The mathematical model is based on the thermodynamics of the adsorption process, heat transfer in the collector plate/tube arrangement, and heat and mass transfers within the adsorbent/adsorbate pair. Its numerical model developed from finite element transformation of the resulting equations computes the collector plate and tube temperatures to within 5 °C. The condensate yield and coefficient of performance, COP, were predicted to within 5% and 9%, respectively. The resulting evaporator water temperature was also predicted to within 5 °C. Thus the model is considered a useful design tool for the refrigerator to avoid costly experimentation.     

Energy decomposition analysis: IEA model versus other methods

In energy decomposition analysis, the International Energy Agency (IEA) model, which is based on the Laspeyres index method, is included in a recent international collaborative initiative on energy indicators for sustainable development for possible adoption [IAEA, 2005. Energy Indicators for Sustainable Development: Guidelines and Methodology. International Atomic Energy Agency, Vienna (www-pub.iaea.org/MTCD/publications/PDF/Pub1222_web.pdf)]. From an empirical analysis using the data of the United States, we found that the residual term given by the IEA model could be significant and that the estimates of the impacts of structure and intensity changes given by the model could be quite different from those given by other decomposition methods. The residual term tends to be large when changes in structure and/or energy intensity variables are significant. Since changes in these variables over time are generally larger in the developing countries than in the IEA countries, there is the question about whether the IEA model is an appropriate decomposition method for the developing countries.     

Thermal analysis of multibarrier interior PM synchronous Machine using lumped parameter model

This paper presents a lumped-parameter thermal model for a multi-barrier interior PM synchronous machine. The model consists of a network of 12 thermal resistances that make it possible to estimate temperatures at 9 critical points inside the machine including the stator end windings, rotor magnets, and the bearings. The details of the model are presented and two machines are analyzed, including a 6 kW 12-pole automotive starter/alternator and a 0.5 kW 4-pole electric water pump machine. The lumped-parameter model results for both machines demonstrate good agreement with results obtained using detailed thermal finite element analysis.     

An analysis of SOFC/GT CHP system based on exergetic performance criteria

In this study, we first consider developing a thermodynamic model of solid oxide fuel cell/gas turbine combined heat and power (SOFC/GT CHP) system under steady-state operation using zero-dimensional approach. Additionally, energetic performance results of the developed model are compared with the literature concerning SOFC/GT hybrid systems for its reliability. Moreover, exergy analysis is carried out based on the developed model to obtain a more efficient system by the determination of irreversibilities. For exergetic performance evaluation, exergy efficiency, exergy output and exergy loss rate of the system are considered as classical criteria. Alternatively, exergetic performance coefficient (EPC) as a new criterion is investigated with regard to main design parameters such as fuel utilization, current density, recuperator effectiveness, compressor pressure ratio and pinch point temperature, aiming at achieving higher exergy output with lower exergy loss in the system. The simulation results of the SOFC/GT CHP system investigated, working at maximum EPC conditions, show that a design based on EPC criterion has considerable advantage in terms of entropy-generation rate.     

Development of a neural network based saturation model forsynchronous generator analysis

This paper presents a new approach to model synchronous generator saturation based on a feedforward artificial neural network (ANN) model. The machine loading conditions, excitation levels and rotor positions are all included in the modeling process. The nonlinear saturation characteristics of a three-phase salient-pole synchronous machine rated at 5 kVA and 240 V is studied using the ANN model. An appropriate selection of input/output pattern for the ANN model training based on an error back-propagation scheme is developed using the on-line small-disturbance responses and the well-known maximum-likelihood estimation algorithm. The developed ANN model is implemented in the generator dynamic transient stability study requiring only small computational alteration in saturation model representation     

An electromagnetic and thermal analysis of a cold crucible melting

To investigate the performance of a cold crucible employed for the melting of corium, which is a mixture of UO₂ and ZrO₂, a computational analysis of the coupled electro-magnetic field, heat transfer, and fluid flow is carried out. Governing differential equations, basic numerical methods, computational model, and the results of the simulation of cold crucible melting are discussed. By comparing the analysis results with the experimental data, it is shown that the proposed computational model reasonably predicts the fundamental characteristics of a cold crucible melting.     

A three-dimensional thermal-fluid analysis of flat heat pipes

A detailed, three-dimensional model has been developed to analyze the thermal hydrodynamic behaviors of flat heat pipes without empirical correlations. The model accounts for the heat conduction in the wall, fluid flow in the vapor chambers and porous wicks, and the coupled heat and mass transfer at the liquid/vapor interface. The flat pipes with and without vertical wick columns in the vapor channel are intensively investigated in the model. Parametric effects, including evaporative heat input and size on the thermal and hydrodynamic behavior in the heat pipes, are investigated. The results show that, the vertical wick columns in the vapor core can improve the thermal and hydrodynamic performance of the heat pipes, including thermal resistance, capillary limit, wall temperature, pressure drop, and fluid velocities due to the enhancement of the fluid/heat mechanism form the bottom condenser to the top evaporator. The results predict that higher evaporative heat input improves the thermal and hydrodynamic performance of the heat pipe, and shortening the size of heat pipe degrades the thermal performance of the heat pipe.     

Experimental and numerical analysis of natural ventilation with combined light/vent pipes

Both experimental and numerical procedures were developed for studying natural ventilation in combined light/vent pipes. An experimental tracer gas technique was used to measure ventilation rates in a test cell. Two different pipe terminals were simultaneously used, dividing the cell in two identical volumes, in order to allow a direct comparison of their performance. A 3D numerical model was developed using ansys5.5/flotran. Experimental and numerical results are shown and compared. It is concluded that pipe terminals significantly enhance ventilation, that one type of terminal has a better performance and that the numerical model underestimates measured flows.     

Performance analysis of solar ethanol distillation

Continuous solar ethanol distillation systems having flat-plate and evacuated heat pipe solar collectors are constructed to study their performances and economic viability. The mathematical model of each main component is carried out and the system simulation is developed. The simulated outputs express a reasonable agreement with the experimental results within 14% accuracy. From the simulation, start up with 10% alcohol concentration, the production cost of 80% alcohol concentration from the distillation system of which the yield at 12,500 l/year is evaluated. With the economic analysis, the results show that the use of solar distillation systems appear to be economical compared to the conventional distillation system using fuel oil as heat source. The minimum production cost of the system is 0.39 US$/l.     

Numerical analysis of an air condenser working with the refrigerant fluid R407C

As CFC (clorofluorocarbon) and HCFC (hydrochlorofluorocarbon) refrigerants which have been used as refrigerants in a vapour compression refrigeration system were know to provide a principal cause to ozone depletion and global warming, production and use of these refrigerants have been restricted. Therefore, new alternative refrigerants should be searched for, which fit to the requirements in an air conditioner or a heat pump, and refrigerant mixtures which are composed of HFC (hydrofluorocarbon) refrigerants having zero ODP (ozone depletion potential) are now being suggested as drop-in or mid-term replacement. However also these refrigerants, as the CFC and HCFC refrigerants, present a greenhouse effect.The zeotropic mixture designated as R407C (R32/R125/R134a 23/25/52% in mass) represents a substitute of the HCFC22 for high evaporation temperature applications as the air-conditioning.Aim of the paper is a numerical–experimental analysis for an air condenser working with the non azeotropic mixture R407C in steady-state conditions. A homogeneous model for the condensing refrigerant is considered to forecast the performances of the condenser; this model is capable of predicting the distributions of the refrigerant temperature, the velocity, the void fraction, the tube wall temperature and the air temperature along the test condenser. Obviously in the refrigerant de-superheating phase the numerical analysis becomes very simple. A comparison with the measurements on an air condenser mounted in an air channel linked to a vapour compression plant is discussed. The results show that the simplified model provides a reasonable estimation of the steady-state response and that this model is useful to design purposes.     

Experimental and numerical analysis of a methane thermal decomposition reactor

An indirectly heated tubular reactor is fabricated and used to study methane thermal decomposition conversion and determine kinetic parameters. A combined perfectly mixed reactor with bypass (CPMR) is proposed as an alternative to the traditional perfectly mixed and plug flow reactors. The CPMR model is used in order to account for buoyancy flow in the reactor. Results comparing the numerical predictions from all three models to experimental data show that buoyancy effects are significant in the reactor under study and also in most reactors in the literature. Including this effect might significantly improve the accuracy of the model predictions. The CPMR reactor model with a reaction rate constant of 5.43 × 10¹⁵ 1/s and an activation energy of 420.7 kJ/mol is capable of reproducing the obtained experimental data in this study and in the literature.     

An experimental analysis of a thermodynamic model of a vapour compression refrigeration plant on varying the compressor speed

The principal aim of this paper is the study of a thermodynamic model that simulates the working of a vapour compression refrigeration plant. The model allows the evaluation of plant performances when the compressor capacity is regulated varying its velocity by means of an inverter inserted into the compressor electric motor feeder. This type of control allows to match continuously the compressor refrigeration capacity to the load, determining an energy saving in comparison with the classical thermostatic control. In particular, in this paper the outputs of the model are compared with the experimental results. The vapour compression experimental refrigeration plant, whose evaporator is located in a commercially available cold store, presents a semi‐hermetic reciprocating compressor able to work with the R22 and some its substitutes, and designed for a revolution speed corresponding to a 50 Hz frequency of a compressor electric motor supply current. The comparison of model and experimental results is realized by varying the supply current frequency of the compressor in the range 30–50 Hz using the R407C (R32/R125/R134a 23/25/52% in mass) that represents the most suitable working fluid for the R22 substitution. The model‐experimental comparison results reported in terms of condensation temperature, compression ratio, condensation power and Coefficient Of Performance are completely acceptable. Moreover, an exergetic analysis is realized to explain the performances of the plant components when the compressor speed is varied. Copyright © 2004 John Wiley & Sons, Ltd.     

Thermochemical analysis of ACFB-based gas and power cogeneration

A first- and second-law analysis is presented for a process developed for simultaneous generation of a fuel gas and electric power (gas and power cogeneration) based on atmospheric circulating-fluidized-bed (ACFB) combustion of coal. The mathematical model has a zone structure, multi-species equilibrium calculations for applicable zone conditions at high temperatures (50 gas-phase and seven solid-phase chemical species) and the concept of freezing of the gas composition at low temperatures. Our analysis shows that the process utilizes coal in a simple, effective and environmentally clean manner. The first- and second-law efficiencies of the process are, respectively, 35.0 and 27.6% for gas generation, 15.4 and 14.6% for power generation, 50.4 and 42.2% overall. The heating value of the gas is 11 MJ/Nm³ (medium). Desulphurization is achieved by using CaS-based sulphur capture during limestone addition to the gasifier bed. Results are compared with data from a 150 kg of coal/h experimental plant.     

Thermodynamic analysis of steam gasification of municipal solid waste

The main objective of this work is to understand steam gasification performance of municipal solid wastes (MSWs). The thermodynamic analysis was carried out by using seven different kinds of MSWs as the feedstock with the temperature ranging from 773 to 1773 K and steam to MSW ratio ranging from 0.5 to 1.5. It is summarized that temperature and the effective mole ratio of H/C (R_H/C) are two key factors, and lower temperature and/or larger R_H/C result in a larger mole ratio of H₂/CO. The model predictions agree very well with the referenced experimental results, which can predict steam gasification performance of MSWs.     

Theoretical analysis of the dynamic interactions of vapor compression heat pumps

A detailed mathematical model of vapor compression heat pumps is described. Model derivations of the various heat pump components are given. The component models include the condenser, evaporator, accumulator, expansion device, and compressor. Details of the modeling techniques are presented, as is the solution methodology. Preliminary simulation results are also illustrated. The model developed predicts the spatial values of temperature and enthalpy as functions of time for the two heat exchangers. The temperatures and enthalpies in the accumulator, compressor and expansion device are modeled in lumped-parameter fashion. Pressure responses are determined by using continuity satisfying models for both the condenser and evaporator. The discussion of the solution methodology describes the combined implicit/explicit integration formulation that is used to solve the governing equations. The summary provides a list of future work anticipated in the area of dynamic heat pump modeling.     

Thermal analysis of lithium-ion batteries

A detailed three-dimensional thermal model has been developed to examine the thermal behaviour of a lithium-ion battery. This model precisely considers the layered-structure of the cell stacks, the case of a battery pack, and the gap between both elements to achieve a comprehensive analysis. Both location-dependent convection and radiation are adopted at boundaries to reflect different heat dissipation performances on all surfaces. Furthermore, a simplified thermal model is proposed according to the examination of various simplification strategies and validation from the detailed thermal model. Based on the examination, the calculation speed of the simplified model is comparable with that of a one-dimensional model with a maximum error less than 0.54 K. These models successfully describe asymmetric temperature distribution inside a battery, and they predict an anomaly of temperature distribution on the surface if a metal case is used. Based on the simulation results from the detailed thermal model, radiation could contribute 43–63% at most to the overall heat dissipation under natural convection. Forced convection is effective in depressing the maximum temperature, and the temperature uniformity does not necessarily decrease infinitely when the extent of forced convection is enhanced. The metal battery case serves as a heat spreader, and the contact layer provides extra thermal resistance and heat capacity for the system. These factors are important and should be considered seriously in the design of battery systems.     

Modeling and simulation of a grid-connected PV generation system for electromagnetic transient analysis

This paper addresses modeling and simulation of a grid-connected photovoltaic system (GCPS) to analyze its grid interface behavior and control performance in the system design. A simple circuit model of the solar array is used to easily simulate its inherent characteristics with the basic specification data. Detailed power and protection control of the GCPS as well as its electrical circuits have been represented by user-defined and built-in components to take into account transients in normal and fault conditions, which are dominated by its power electronic controller. The model has been described with the reference to and implemented in PSCAD/EMTDC, a power system transient software package. Extensive simulation results are presented and analyzed to validate that the proposed simulation model is effective for control and protection performance evaluation of the GCPS in terms of electromagnetic transient analysis.     

Elastic-plastic FE calculations for a fracture mechanics analysis of a weld in the ligament of a CT specimen

Results of elastic-plastic FE calculations on four plane strain models of a CT-100 specimen, (a) with a weld in the ligament, (b) of base material only, (c) of welding simulated material only and (d) of weld material only, are compared and discussed in the light of fracture mechanics aspects. Regarding the cleavage fracture regime, considerably higher crack opening stresses are obtained in the welded specimen than in the base material specimen, as soon as small-scale yielding occurs. Conservative evaluation of the crack opening stresses of the welded joint can be achieved by using the welding simulated material properties. The J-integrals determined by the energy release rate using the method of virtual crack extension are equal for the four material models up to about 200 N mm⁻¹. Above this level, the behaviour of the welded specimen and that of the base material model are still similar, while a higher force is necessary for the welding simulated material model and the weld material model to reach the same J-value as for the two others. The crack opening profile of the welded specimen is asymmetric to the fusion line which lies in the ligament. The half profile of the heat-affected zone side is comparable to that of the welding simulated material model and the half profile of the weld material side to that of the base material model. A higher maximum of the equivalent strain on the heat-affected zone side than on the weld material side may explain why cracks tend to run into the base material region of the weld under conditions of stable crack growth. General yield of the welded specimen occurs on the base material side, whereas on the weld material side only a small plastic zone is visible, comparable to that in welding simulated material at the same load.