Magnetic circuit modeling of the field regulated reluctancemachine. Part II: saturation modeling and results

This paper explores and offers solutions for two causes of simulation instabilities which occur when modeling machines using magnetic circuits. An algorithm for dynamic simulation of electric machines based on the magnetic circuit model (MCM) developed in part I of this paper is augmented to include the ability to model magnetic saturation without numerical oscillations. The resulting MCM algorithm is implemented in a digital computer program which is well suited for both simulation of transients in nonsinusoidally wound machines such as a field regulated reluctance machine (FRRM), and for design. The model developed is verified using a laboratory prototype FRRM, power converter, and controller. Results of computer simulations using the magnetic circuit model agree well with experimental machine data     

One-dimensional thermal model for direct methanol fuel cell stacks: Part I. Model development

A thermal energy model for the direct methanol fuel cell (DMFC) is presented, based on the differential thermal energy conservation equation. The model is used to predict the thermal behaviour of a DMFC stack comprising of many large cells in a bipolar arrangement. The model allows an assessment of the effect of operating parameters (feed and oxidant inlet temperature, flow rate and pressure, operating current density), and the system design (active area, material properties and geometry) on the temperature profile along the stack and the interactions between the various components in the cell stack. The model is designed to enable the fuel cell system designer to estimate, insulation requirements, auxiliary equipment sizing and required thermal duties and response. Furthermore, the model can be used to decide on the optimum set of operating conditions for an efficient thermal management of the whole process.     

Technical–economic analysis of wind-powered pumped hydrostorage systems. Part I: model development

In this paper the results of the application of a model for the technical and economic sizing of the various components that make up medium sized wind-powered pumped hydrostorage systems are discussed. The characteristics and unit energy cost of each technically feasible combination of components are determined by applying the model in the island of El Hierro (Canarian archipelago). This enables the selection of the most viable composition for the system from an economic point of view given certain technical restrictions. The results of the application of the model (developed in Part I) in El Hierro indicate that an annual renewable energy penetration of 68.40% can be achieved. This would mean a diesel oil saving of 7364 m³ and a decrease in CO₂ emissions of 20.91 Gg. Furthermore, the system would be economically competitive with conventional systems if fuel prices were 0.283 €/l.     

On the behaviour of hygroscopic wheels: Part I – channel modelling

In this paper a detailed mathematical formulation is developed for the numerical modelling of the behaviour of a channel of a hygroscopic compact matrix. A comparison between the detailed version and a simplified one is performed considering a two-dimensional airflow between desiccant parallel plates. The distinct heat and mass transfer phenomena are strongly coupled, and some properties of the airflow and of the desiccant medium exhibit important changes during the sorption processes. Both physical models take into account the gas side and solid side resistances to heat and mass transfer. The wall domain is treated similarly in both models, by taking into account the simultaneous heat and mass transfer together with the water adsorption/desorption process. Two phases co-exist in equilibrium inside the desiccant porous medium, the equilibrium being characterized by sorption isotherms without hysteresis. The detailed model is based on the solution of the differential equations for the conservation of mass, energy and momentum, assuming that no momentum transport exists in the porous wall domain. In the simplified model, the airflow is treated as a bulk flow, the interaction with the wall being evaluated by using appropriated convective coefficients.Both models are compared in the simulation of a parallel plate channel during an adsorption process. The results show a good agreement for channel lengths greater than 0.1 m. In part II of the paper, the simplified model is adapted to the simulation of the three-dimensional problem in the channel of a hygroscopic rotor, and it is used to perform parametric studies.     

Two-dimensional model of heat transfer in circulating fluidized beds. Part I: Model development and validation

A new model is proposed for furnace- and wall-side heat transfer in circulating fluidized beds. It assumes a wall layer of particles whose concentration varies with distance near the heat transfer surface and a thin gas gap adjacent to the wall. The model couples radiation, conduction and convection on the furnace-side to conduction and convection into the coolant on the wall-side. Keller’s method is employed to solve the set of non-linear, partial differential equations. The model gives satisfactory predictions of the suspension-to-wall heat transfer coefficient for several sets of published experimental two-dimensional data.     

The simulation of transients in thermal plant. Part I: Mathematical model

This paper deals with the simulation of the transient behaviour of thermal plant with control systems. It is always more difficult for a designer to predict the effects on the plant of the control processes because of the increasing complexity of plants and control systems. The easiest way to obtain information about the dynamic behaviour of a thermal plant at the design-stage involves assessing the suitability of specific computer codes. To this end, the present work demonstrates that nowadays it is possible, by using the opportunities offered by some general purpose calculation systems, to obtain such significant information. It is described how a “thermal-library” of customized blocks (one for each component of a thermal plant such as valves, boilers, and pumps) can be built and used, in an intuitive way, to study any kind of plant. As an example, the dynamic behaviour of a residential heating system will be shown in a companion paper, forming part II of the present article.     

Modeling snow melting on heated pavement surfaces. Part I: Model development

Hydronic or electric heating of pavement surfaces has been used in the prevention of ice formation and snow deposition with the aim of improving transportation safety. This paper describes a numerical model of a heated pavement and the snow melting processes occurring on its surface. A set of boundary conditions have been defined, and models of heat and mass transfer developed, that allow treatment of various surface and weather conditions associated with storm events. Given heat fluxes and weather data, this model can predict the transient surface conditions and temperatures including the extent of snow cover. Model development is described in this paper and its application to a representative snow melting system illustrated. A companion paper presents a validation exercise using data collected from a full-scale bridge snow melting system during a real storm event.     

Parameter sensitivity examination and discussion of PEM fuel cell simulation model validation: Part I. Current status of modeling research and model development

Mathematical modeling plays an important role in fuel cell design. A comprehensive review of the mathematical modeling of proton exchange membrane fuel cells is first conducted. It is found that the results computed by different models in the literature often agree well with the experimental data. This stimulates the present authors to carry out a comprehensive parameter sensitivity examination. In this first paper a three-dimensional, two-phase and non-isothermal model is developed, and numerical simulations for a basic case is performed, the results of which are regarded as the reference for further sensitivity examination. All the parameters needed for the simulation are provided in detail. In the companion paper (Part II), the results of the parameter sensitivity analyses and discussion of model validation are provided in detail.     

Novel ventilation cooling system for reducing air conditioning in buildings.: Part I: testing and theoretical modelling

A latent heat storage unit incorporating heat pipes embedded in phase change material (PCM) is developed and tested for a novel application in low energy cooling of buildings. A one-dimensional mathematical model of the heat transfer from air to PCM is presented to allow sizing of a test unit. Details of the construction and testing of one heat pipe/PCM unit in a controlled environment are described, and measurements of heat transfer rate and melting times are presented. When the difference between air and PCM temperature was 5°C, the heat transfer rate was approximately 40 W over a melt period of 19 h. The heat transfer rate could be improved, and the phase change time shortened, with an alternative design for finning of the heat pipe inside the PCM.     

Numerical analysis of the thermal behaviour of ventilated glazed facades in Mediterranean climates. Part I: development and validation of a numerical model

Ventilated glazed facades are formed by two layers of different materials, opaque or transparent, that are separated by an air channel, used to collect or evacuate the solar radiation that is absorbed by the facade. For architectonic reasons, the outer layer is usually made entirely of glass, while the indoor layer may be partially opaque. This allows direct solar gains to be reduced and increases the thermal inertia of the building. This paper is a presentation of a code for the numerical simulation of ventilated and conventional facades. It is based on time-accurate, one-dimensional discretizations for the channel and the different solid zones, and allows heat fluxes and temperature distributions in the facade to be obtained over the course of one year. The numerical code allows advanced elements to be integrated into the facade, such as phase change materials, selective surfaces and improved glasses. The code has been validated by comparing it with analytical solutions where possible, with reference situations and with experimental measurements obtained in real-site test facilities in different climatic conditions. The numerical code is a useful tool for optimising the design of facades so as to take advantage of different materials, orientations, geometries and to address different climatic conditions.     

A new turbulence model for porous media flows. Part I: Constitutive equations and model closure

A new model for turbulent flows in porous media is developed. The spatial- and time fluctuations in this new model are tied together and treated as a single quantity. This novel treatment of the fluctuations leads to a natural construction of the k and ε type equations for rigid and isotropic porous media in which all the kinetic energy filtered in the averaging process is modeled. The same terms as those found in the corresponding equations for clear flow, plus additional terms resulting from the interaction between solid walls in the porous media and the fluid characterize the model. These extra terms arise in a boundary integral form, facilitating their modeling. The model is closed by assuming the eddy viscosity approximation to be valid, and using simple models to represent the interaction between the walls in the porous media and the fluid.     

Experimental and theoretical performance of a demonstration solar chimney model—Part I: mathematical model development

The solar chimney is a natural draft device which uses solar radiation to provide upward momentum to the in-flowing air, thereby converting the thermal energy into kinetic energy. A study was undertaken to evaluate the performance characteristics of solar chimneys both theoretically and experimentally. In this paper, a mathematical model which was developed to study the effect of various parameters on the air temperature, air velocity, and power output of the solar chimney, is presented. Tests were conducted on a demonstration model which was designed and built for that purpose. The mathematical model presented here, was verified against experimental test results and the overall results were encouraging. © 1998 John Wiley & Sons, Ltd.     

The distributed-energy chain model for rapid coal devolatilization kinetics. Part I: Formulation

The distributed-energy chain model (DISCHAIN) interprets coal devolatilization in terms of independent influences from chemical reaction rates and from macromolecular configuration. Coal is represented by three components: (1) aromatic units that are attached pairwise by (2) labile bridges to form nominally infinite linear chains, with (3) peripheral groups branching from the aromatic units. These components are the building blocks for unreacted coal, free monomers (mobile aromatic units), gas, tar, and char. Four chemical reactions represent bridge dissociation, peripheral group elimination, and tar and char formation. Analytic probability expressions and competitive reactions describe the conversion of bound aromatic units into free monomers, and enter into the formation of all products except gas. There are no hypothetical ultimate yields.The model is introduced in two parts. Here in Part I, the coal model, chemical reactions, and chain statistics are derived and formulated into rate equations. Mechanisms leading to major products are identified, including a novel mechanism for yield enhancement by faster heating. Whenever bridge dissociation and char formation occur concurrently, as for slow heating, the subsequent generation of monomers is inhibited. Aromatic units are thereby excluded from the competition between tar and char formation. Conversely, bridge dissociation and char formation occur consecutively for rapid heating, and a greater proportion of the original bound aromatic units become monomers and, ultimately, tar.     

A Computational Model for Two—stage 4K—Pulse Tube Cooler：part I.Theoretical Model and Numerical Method

IntroduedonThe need for ctyogenic coOling of magnehcresonance imaging (MRI), superconduchng quantUminterfernce devices (SQUIDs) and the associatedsuperconduchng devices has brought about a strOngdemand for high reliability and efficiency in coolers.SWg and GM coolers, which are very compact andreliable machines and have already commercial products,are widely used for such aPplications in the last decades.However, they have a tnoving pistOn at the cold end,which caused evidenily mechotal …     

Transient modeling of an air-cooled chiller with economized compressor. Part I: Model development and validation

Air-cooled chillers are widely used and the control design is important for the chiller performance and reliability under the varying operating conditions. A mathematical model is developed for a chiller with an economized screw compressor and to assist the controller design. The model covers both the economized mode and non-economized mode. The two modes can be automatically switched depending on the operating conditions. Comparisons made between simulations and experiments indicate that the model can reasonably simulate the transients of the chiller. Based on the validated model, a follow-up paper will describe its application to the controller design.     

A model for the development of a power production system in Greece,Part I: Where RES do not meet EU targets

This paper studies the electricity production system of the Greek Interconnected Electric Production System using a model created with the software package WASP-IV. The period of study is from 2009 to 2030. It consists of three scenarios using three different criteria: energy, environmental and economic. The three scenarios are the business as usual, the lignite and the natural gas. Subsequently, a sensitivity analysis is carried out for the annual growth rate of electricity consumption and load demand. The paper examines how the three criteria change, when there are no other energy sources beyond those already in use (lignite, oil, natural gas, biomass, solar, wind and hydropower) with no CO₂ capture policies and with the electricity production from Renewable Energy Sources not to reach the targets of the European Union for 2020. In a second paper, three other scenarios examine production with the Renewable Energy Sources to reach the targets of the European Union for 2020.     

Extended combustion model for single boron particles - Part I: Theory

Ramjet engines have significant advantages when compared to conventional rocket motors concerning specific impulse, manoeuvrability, and range. Boron particle addition to the propellant of ducted rockets further increases this potential due to a very high heating value. However, the combustion of boron particles is a very complex process because of an inhibiting oxide layer covering the particles. This layer has to be removed before vigorous combustion can start. The boron particle combustion process runs in two distinct stages. In the literature review presented in this article two combustion models for single boron particles are outstanding. A very detailed model by the Princeton/Aerodyne group features hundreds of elementary reactions and considers all physical processes in the particle environment. It is very elaborate and, thus, not suitable for incorporation into three-dimensional CFD-calculations at present. The second model developed at Penn State University takes on a global approach with only a few reactions which makes it promising for CFD applications. A careful analysis of this model revealed some inconsistencies, errors and drawbacks which gave rise to the new model presented in this paper. The new model comprises a consistent formulation of the heat and mass transfer processes in the particle environment based on a quasi-steady approach, accounts for boron evaporation which is a relevant process despite the high boiling point of boron, and it considers the influence of forced convection on the particle conversion. The chemical reaction rates adopted from the original model were revised and are slightly changed, the differential equations to be solved are corrected and an iterative solution algorithm is introduced. A careful validation of the model is presented in Part II of this paper showing that the new model is suitable for boron particle sizes relevant for ramjet combustion chambers.     

Isothermal composite adsorbent. Part I: Thermal characterisation

Adsorption and desorption are respectively exo and endothermic phenomena leading to significant temperature changes in adsorption columns. Enhanced efficiency of a sorption process could be obtained under isothermal conditions, either for gas storage, purification or separation applications. The heat transfer within the adsorbent beds can be managed in situ, using thermal energy storage material: a phase change materials (PCM) for example. The thermal behaviour of a mixture of activated carbon and PCM during CO₂ adsorption has been studied. The thermal characteristics of the involved materials have been determined and experiments carried out to highlight the positive effect of the PCM to reduce the CO₂ adsorption heat effects on an activated carbon bed. Calorimetry was the technique used for all the thermal characterisations. It appears that the heat effects induced by CO₂ adsorption are reduced by the presence of the PCM together with the adsorbent. The endothermic effect of fusion balances the heat effect of adsorption and significantly reduces the temperature changes.     

Computations of film boiling. Part I: numerical method

A numerical method for direct simulations of boiling flows is presented. The method is similar to the front tracking/finite difference technique of Juric and Tryggvason [Int. J. Multiphase Flow 24 (1998) 387], where one set of conservation equations is used to represent the mass transfer, heat transfer, and fluid flow in the liquid and the vapor, but improves on their numerical technique by elimination of their iterative algorithm. The justification of the mathematical formulation is presented and the numerical method and the code is validated by comparison of the results with the exact solutions of a few analytical problems. A grid refinement test for film boiling on a horizontal surface shows the convergence of results.     

飞轮用永磁悬浮轴承的磁路设计及磁力解析模型

飞轮储能以其突出优势广泛应用于电网调频领域,为进一步提升飞轮储能技术的能量密度和功率密度,飞轮储能转子趋向于重型化、高速化,其通常采用磁悬浮轴承进行轴向卸载,而大承载力、高安全性、低损耗能的永磁轴承设计是关键技术.目前研究的双环、多环和Halbach阵列的永磁轴承卸载结构,在长期高速旋转下存在着与转子固联的动磁环材料会...