Development of a voltage-behavior model for NiMH batteries using an impedance-based modeling concept

To handle the complexity of modern automotive power nets, simulation-based design methods are important and suitable models of all system components including the battery as a main part are therefore mandatory. However, simulation models of energy storage devices are difficult to obtain. In particular, batteries are time-variant and strongly non-linear. An impedance-based modeling approach has been applied that copes with these characteristics and offers the development and parameterization of powerful models covering a wide dynamic range. As an example, this paper outlines the development of a NiMH battery model. Besides the impedance-based part of the model, the influences of the typical hysteresis effect of NiMH batteries is described in detail and an empirical modeling approach is introduced. The presented model is already successfully used by an automotive manufacturer which reflects the applicability of the modeling approach.     

Design,experimental investigation and multi-objective optimization of a small-scale radial compressor for heat pump applications

The main driver for small scale turbomachinery in domestic heat pumps is the potential for reaching higher efficiencies than volumetric compressors currently used and the potential for making the compressor oil-free, bearing a considerable advantage in the design of advanced multi-stage heat pump cycles. An appropriate turbocompressor for driving domestic heat pumps with a high temperature lift requires the ability to operate on a wide range of pressure ratios and mass flows, confronting the designer with the necessity of a compromise between range and efficiency. The present publication shows a possible way to deal with that difficulty, by coupling an appropriate modeling tool to a multi-objective optimizer. The optimizer manages to fit the compressor design into the possible specifications field while keeping the high efficiency on a wide operational range. The 1D-tool used for the compressor stage modeling has been validated by experimentally testing an initial impeller design. The excellent experimental results, the agreement with the model and the linking of the model to a multi-objective optimizer will allow to design radial compressor stages managing to fit the wide operational range of domestic heat pumps while keeping the high efficiency level.     

Effective short-cut modelling of wind park efficiency

A short-cut model suitable for the estimation of the overall wind park efficiency was developed. Its parameters were estimated by fitting the predictions of a detailed explicit kinematic wake model for a wide range of wind velocities, number of turbines utilized, relative distances of turbines and various types of commercial wind turbines. An empirical model was used to represent the turbine power curve. The turbine grid adopted was the uniform one, where each individual machine is equally placed between its neighbours. The proposed short-cut model represented the full model in a quite satisfactory way and it was presented in a suitable formulation for dealing with wind park preliminary design problems. The effect of wind direction was also taken into consideration and was properly analysed.     

Development of a fast empirical design model for PEM stacks

A simple and fast empirical design model for a 5 kW proton exchange membrane (PEM) stack is presented in this paper. The performance analysis of the PEM stack operating on a membrane humidifying method is made through a series of experiments, including current–voltage–power characteristics, uniformity of cell unit voltages, gas pressure impact and air flux impact. Based on the above analysis, an empirical predicted model for the PEM stack has been developed by the combination of mechanistic and empirical modeling approaches to characterize and predict the voltage–current characteristics without examining in depth all physical/chemical phenomena. The good agreement between the predicted and experimental results covering a range of optimal operating conditions shows that the proposed model provides an accurate representation of the behavior for the PEM stack.     

Prediction of evaporation losses in evaporative fluid coolers

The accurate prediction of various aspects of thermal behavior of evaporative fluid coolers is very important for both design and rating calculations. Exactly predicting evaporation losses is significant since the process fluid is cooled primarily by evaporation of a portion of the recirculating water that causes the concentration of dissolved solids and other impurities to increase. An empirical relation to predict evaporation losses is developed on the basis of the rule of thumb recommended by manufacturers, which is simple and accurate with a wide range of applicability. The predicted values are in good agreement with the numerical values obtained from the calibrated model where the maximum error was found to be approximately 4% but often less than 2%.     

Optimum design of a subsonic axial-flow compressor stage

The design of an axial-flow compressor stage for subcritical Mach numbers has been formulated as a non-linear multi-objective mathematical programming problem with the objective of minimizing the aerodynamic losses and the weight of the stage, while maximizing the compressor's stall margin. Aerodynamic as well as mechanical constraints are considered in the optimization solution. The prediction model for estimating the performance characteristics, such as efficiency, weight and stall margin, of the compressor stage is presented. The present design optimization procedure can be applied to a multi-stage compressor.     

Free convective turbulent flow within the trombe wall channel

A study of free convective turbulent heat transfer between parallel plates has been made. The initial flow is assumed to remain laminar until a combination of geometry, temperature, and flow rate conditions reach a pre-defined level. At this point the model used in this study assumes transition and permits laminar flow to gradually develop into fully turbulent flow. Turbulent flow characteristics are predicted by a mixing length model which incorporates empirical parameters used in the literature. Using air as the fluid, a wide range of channel geometries, relative surface temperatures, and flow rates have been examined. Guided by the very limited available experimental data, computations were made and several correlations were developed to enable important quantities to be estimated given the channel geometry, surface temperatures, and inlet air temperature.     

Process modeling for control of a batch heat treatment furnace with low NOx radiant tube burner

In this first part of a two part problem, a process model for control of a batch type heat treatment furnace with low NO_x radiant tube burner has been developed. The model considers coupling between the different components and the wide variation in time scales of the processes involved. The heat transport between the gas stream and the radiant tube is modeled by a conjugate convection–radiation mode using an empirical correlation for the convection and an optically thin radiation model. The combustion is considered in a highly pre-heated and diluted mode with single step modeling of the chemical kinetics. The heat transfer between the radiant tube and the load is considered to be only through radiation. The model is used in the companion paper to generate optimal operating conditions for the desired performance and emission characteristics.     

An improved thermal lattice Boltzmann model for rarefied gas flows in wide range of Knudsen number

In order to covering a wide range of the flow regimes, a new relaxation time formulation for the lattice Boltzmann method, LBM, by considering the rarefaction effect on the viscosity and thermal conductivity has been presented. To validate the presented model, fully developed pressure driven flow and developing thermal flow in micro/nano channel have been modeled. The results show that in spite of the standard LBM, the velocity and temperature distributions, the volumetric flow rate and the local Nusselt number obtained from this modified thermal LBM, agree well with the other numerical and empirical results in a wide range of Knudsen numbers.     

An analytical solution for the stationary behaviour of binary mixtures and pure fluids in a horizontal annular cavity

This study aims at analysing the characteristics of the two-dimensional flow established by binary mixtures and pure fluids in a horizontal annular cavity isothermally heated inside and cooled outside. Some complications arise considering binary mixtures, as a consequence of thermogravitational diffusion due to the coupling of convection with thermodiffusion.An analytical model has been defined assuming a two-dimensional laminar flow of a visco-elastic fluid, under validity of Boussinesq’s assumption and negligible viscous dissipation. For the case of binary mixtures, the buoyancy determined by concentration variations has been ignored, so that momentum equation is independent on concentration and is only coupled with the energy balance equation.The analytical model has been validated, for both cases of binary mixtures and pure fluids, through comparison with numerical results in a wide range of the non-dimensional parameters that govern the problem. In particular, the effect of the geometry and of the boundary conditions on the separation of the mixture compounds due to thermogravitational diffusion has been exploited.     

Performance and optimum design analysis of an absorber plate fin using recto-trapezoidal profile

This paper establishes a new profile, viz. recto-trapezoidal (RT) of an absorber plate fin on the basis of ease of fabrication as well as augmentation of heat transfer rate per unit fin volume. An analytical model has been developed for evaluating the thermal performance and optimum dimensions of an absorber plate fin using this typical profile. The present study is equally suitable for an absorber plate fin having a rectangular, trapezoidal or triangular profile also with consideration of their respective geometrical parameters. The optimization of the RT profile has been cast in a generalized form either by maximizing heat transfer rate for a given fin volume or by minimizing fin volume for a given heat transfer duty. From the optimum design analysis, significant results have been noticed when an additional constraint is imposed with the fin volume. Under this design condition, it may also be highlighted that for an optimal circumstance, the heat transfer rate through a RT profile absorber plate fin is greater than a trapezoidal or triangular profile for the same fin volume. However, this observation may be restricted to the limited values of fin volume only. The optimum design analysis for the RT profiled absorber plate fin has also been studied under the different design constants. Finally, for the variation of all the design variables, optimum design curves have been generated for a wide range of thermo-geometric parameters.     

Optimal integration strategies for a syngas fuelled SOFC and gas turbine hybrid

This article aims to develop a thermodynamic modelling and optimization framework for a thorough understanding of the optimal integration of fuel cell, gas turbine and other components in an ambient pressure SOFC-GT hybrid power plant. This method is based on the coupling of a syngas-fed SOFC model and an associated irreversible GT model, with an optimization algorithm developed using MATLAB to efficiently explore the range of possible operating conditions. Energy and entropy balance analysis has been carried out for the entire system to observe the irreversibility distribution within the plant and the contribution of different components. Based on the methodology developed, a comprehensive parametric analysis has been performed to explore the optimum system behavior, and predict the sensitivity of system performance to the variations in major design and operating parameters. The current density, operating temperature, fuel utilization and temperature gradient of the fuel cell, as well as the isentropic efficiencies and temperature ratio of the gas turbine cycle, together with three parameters related to the heat transfer between subsystems are all set to be controllable variables. Other factors affecting the hybrid efficiency have been further simulated and analysed. The model developed is able to predict the performance characteristics of a wide range of hybrid systems potentially sizing from 2000 to 2500 W m⁻² with efficiencies varying between 50% and 60%. The analysis enables us to identify the system design tradeoffs, and therefore to determine better integration strategies for advanced SOFC-GT systems.     

An interval fixed-mix stochastic programming method for greenhouse gas mitigation in energy systems under uncertainty

In this study, an interval fixed-mix stochastic programming (IFSP) model is developed for greenhouse gas (GHG) emissions reduction management under uncertainties. In the IFSP model, methods of interval-parameter programming (IPP) and fixed-mix stochastic programming (FSP) are introduced into an integer programming framework, such that the developed model can tackle uncertainties described in terms of interval values and probability distributions over a multi-stage context. Moreover, it can reflect dynamic decisions for facility-capacity expansion during the planning horizon. The developed model is applied to a case of planning GHG-emission mitigation, demonstrating that IFSP is applicable to reflecting complexities of multi-uncertainty, dynamic and interactive energy management systems, and capable of addressing the problem of GHG-emission reduction. A number of scenarios corresponding to different GHG-emission mitigation levels are examined; the results suggest that reasonable solutions have been generated. They can be used for generating plans for energy resource/electricity allocation and capacity expansion and help decision makers identify desired GHG mitigation policies under various economic costs and environmental requirements.     

An analysis on the prediction of temperature distribution in an annular radiative recuperator

Axial temperature distribution for the combustion gas, air and walls of an annular radiation recuperator have been predicted with the use of the model, which A. Schack has developed. The model is based on a kind of the zone method to treat radiation exchange between the combustion gas and its boundaries, which can be used for a wide range of design and operating conditions. Parametric calculations have been done to determine the effects of these on recuperator design. Copyright © 1999 John Wiley & Sons, Ltd.     

Thermal and technical analyses of solar chimneys

An analysis for the solar chimneys has been developed, aimed particularly at a comprehensive analytical and numerical model, which describes the performance of solar chimneys. This model was developed to estimate power output of solar chimneys as well as to examine the effect of various ambient conditions and structural dimensions on the power output. Results from the mathematical model were compared with experimental results and the model was further used to predict the performance characteristics of large-scale commercial solar chimneys. The results show that the height of chimney, the factor of pressure drop at the turbine, the diameter and the optical properties of the collector are important parameters for the design of solar chimneys.     

A prototype design model for deep low-enthalpy hydrothermal systems

This paper introduces a prototype design model for deep low-enthalpy hydrothermal systems. The model predicts, empirically, the lifetime of a hydrothermal system as a function of reservoir porosity, discharge rate, well spacing, average initial temperature of the reservoir, and injection temperature. The finite element method is utilized for this purpose. An extensive parametric analysis on a wide range of physical parameters and operational scenarios, for a typical geometry, has been conducted to derive the model. The proposed model can provide geothermal engineers and decision makers with a preliminary conjecture about the lifetime of a deep low-enthalpy hydrothermal system. The proposed modelling technique can be utilized as a base to derive elaborate models that include more parameters and operational scenarios.     

Rural energy consumption patterns with multiple objectives

The problem of designing a rural energy centre and thus obtain the emerging energy consumption patterns with multiple objectives, can be viewed as matching the various energy sources to cater fully to the energy needs of a wide variety of tasks such as cooking, lighting, ploughing, pumping water for irrigation, rural transport, etc. This, in fact, should satisfy several economic, technical as well as social objectives or goals. In order to arrive at a satisfactory solution, this has to be viewed as a multi-objective optimization problem. This communication develops a mathematical model for optimum energy planning in a rural environment. Goal programming approach is used in evolving a satisfactory solution to the above problem. The model developed is applied in the case of a typical South Indian village situated in a semi-arid region especially with respect to the major domestic energy needs of cooking and lighting. Results from the computer-simulated model are given.     

Modelling,simulation and control of a fuel cell-powered laptop computer voltage regulator module

An air-breathing fuel cell was investigated as an alternate power source for a laptop computer application. An empirical model was developed to include the phenomena of activation and ohmic polarisation as well as mass transport effects in order to simulate the behaviour of an air-breathing fuel cell. The model was used as the input source for a quadratic buck converter, which is used to power the central processing unit (CPU) core at 1 V. To achieve tight voltage regulation and good dynamic performance, the quadratic buck converter was implemented with average current mode control. The quadratic buck converter hardware setup has been developed with a fabricated fuel cell module in order to validate the model of the air-breathing fuel cell as well as the voltage regulator module.     

等效二次规划算法在电力系统经济调度中的应用

本文采用了等效二次规划算法处理电力系统经济调度问题。本文基于以全网发电成本为目标函数,以发电机有功出力限制和支路有功限值为约束的电力系统经济调度数学模型,提出了利用二次规划的凸性条件,将具有函数约束的电力系统经济调度二次规划模型转化为只有变量约束的等效二次规划模型。用本文算法对IEEE系统和三个实际系统进行了数值试验。实验结果使得全网发电成本减少和约束条件满足。等效二次规划模型对电力系统经济调度问题具有收敛性好、快及较高精度,具有在线应用能力和能作为调度培训系统仿真软件的潜力。