超超临界1000MW机组运行方式分析

汽轮机长期低负荷运行,在变负荷运行时可采用定压和滑压两种运行方式,介绍了这两种运行方式的特点,分析比较了它们对热经济性的影响。通过热经济性数学模型的计算,以热耗率作为汽轮机定压和滑压运行热经济性比较指标,指出了某超超临界机组低负荷时的经济运行方式。     

额定功率下抽汽压损对机组热经济性的影响

基于热力系统矩阵热平衡方程,建立了机组在额定功率运行时抽汽压损变化对其热经济性影响的数学模型.数学模型与热耗变换系数有关,在该模型中考虑了辅助汽水系统的影响,并对热力系统中加热器的不同型式和连接方式进行了讨论.运用该模型计算了某600 MW机组在额定功率下,各级抽汽压损增大5%时对机组热经济性的影响,其结果与热平衡法计算的结果一致.通过数值拟合,给出了该机组抽汽压损变化对热经济性影响的特性曲线,它表明抽汽压损越大,机组的热经济性越低.     

中间再热式汽轮机理想循环热效率定义方法的改进

针对常规的汽轮机理想循环热效率受到汽轮机本体相对内效率的影响而不能准确反映汽轮机回热系统运行热经济性的问题,对汽轮机理想循环热效率定义方法进行了改进,并对改进后的汽轮机理想循环热效率进行了分析。指出改进后的汽轮机理想循环热效率不仅能准确反映汽轮机回热系统运行经济性的变化,而且不受汽轮机本体相对内效率的影响,从而更适合于对汽轮机的热经济性进行诊断。     

基于BP网络的汽轮机运行特性方程

对现有的汽轮机运行特性方程的建立方法进行了分析,指出其各自存在的问题,然后采用人工神经网络中相对成熟的BP网络建立了汽轮机特性的数学模型,并与常规的线性和非线性模型进行了比较。结果表明,采用BP网络能更准确地反映汽轮机的运行特性,为评价汽轮机运行性能及热经济性诊断奠定了理论基础。     

单元机组运行经济性在线数学模型研究

在电厂实时信息系统的基础上,开发了实用的单元机组运行经济性在数学模型。该模型不仅可以对单元机组的主要经济指标进行在线监测,还可以对机组运行经济性进行诊断分析,并且已经在电厂应用,效果良好。     

主蒸汽压力变化对机组煤耗率的影响分析

主蒸汽压力是机组实际运行中必须密切监视和调节的主要参数之一,在机组实际运行中会不可避免的偏离设计值,从而影响机组的发电标准煤耗率,影响机组的热经济性和安全性.在火电厂热经济性统一物理模型和数学模型的基础上,根据多元扰动下的热力系统能效分析模型得到主汽压变化对煤耗率影响的计算模型,并以某电厂660 MW机组为例进行验证,并计算了此机组不同工况下主汽压变化对机组煤耗的影响,并绘制成图,对其规律进行了分析.此计算模型得到的计算结果误差较小,足以满足工程实际的需要.     

参数和系统对汽轮发电机组运行经济性的影响

从汽轮发电机组实际运行角度，分析了运行中参数和系统与设计值的偏差对机组热经济性的影响，并计算了这类偏差对目前国内３００ＭＷ发电机组热经济性的影响。     

加热器端差对机组热经济性影响的定量分析方法

建立了定流量下加热器端差对机组热经济性影响的数学模型。该模型针对加热器的不同类型进行了讨论,应用时不再需要单独计算端差变化对锅炉吸热量的影响,并全面考虑了热力系统的结构特点及辅助汽水系统,从整体上定量分析加热器端差对机组热经济性的影响,为火电机组节能降耗以及热力系统定量分析提供了理论依据。对某600MW机组进行了算例分析,表明端差越大,机组的热经济性越低;端差越小,机组的热经济性越高。     

母管制汽轮发电机组的热耗数学模型

对母管制火电厂汽轮发电机组,提出了一种在线监测热经济指标的数学模型。通过实际应用证实,该模型所需测点少、投资省、适应性较强、运行可靠,能满足机组热经济性指标在线监测分析的需要。     

抽汽压损影响火电机组热经济性的计算分析

抽汽压损是一种不明显的热力损失,对热经济性的影响与其大小、抽汽压力、热力系统的结构等因素有关。应用等效焓降方法和热力系统状态方程,经过严格的数学推导,构建了抽汽压损对热经济性影响的数学模型,该模型具有通用性强、适于程序化的特点。以600MW机组为例进行了算例分析,方便快捷地计算出各级抽汽压损对机组热经济性的影响,并分析其影响规律。     

A critical review of mathematical models used to determine the density of hydrogen trapping sites in steels and alloys

Different mathematical models based on electrochemical permeation tests have been proposed to determine the density of hydrogen trapping sites (N_T) in metals. However, recent mathematical models that have been used to determine N_T contain mathematical errors or have been based on the work of researchers whose works contain no mention of equations or mathematical terms related to hydrogen trapping, which calls into doubt the validity of the models' applicability. In this work, based on permeation test results for X65 steel, we show that the use of incorrect mathematical models leads to values of N_T that differ by four orders of magnitude.     

Predictive models for PEM-electrolyzer performance using adaptive neuro-fuzzy inference systems

Predictive models were built using neural network based Adaptive Neuro-Fuzzy Inference Systems for hydrogen flow rate, electrolyzer system-efficiency and stack-efficiency respectively. A comprehensive experimental database forms the foundation for the predictive models. It is argued that, due to the high costs associated with the hydrogen measuring equipment; these reliable predictive models can be implemented as virtual sensors. These models can also be used on-line for monitoring and safety of hydrogen equipment. The quantitative accuracy of the predictive models is appraised using statistical techniques. These mathematical models are found to be reliable predictive tools with an excellent accuracy of ±3% compared with experimental values. The predictive nature of these models did not show any significant bias to either over prediction or under prediction. These predictive models, built on a sound mathematical and quantitative basis, can be seen as a step towards establishing hydrogen performance prediction models as generic virtual sensors for wider safety and monitoring applications.     

On the application of standard isotherms to hydrogen adsorption in microporous materials

A mathematical framework for simulating equilibrium hydrogen adsorption isotherms in porous materials and estimating the values of key parameters associated with the adsorption process is developed. Explicit expressions for the excess, adsorbed, compressed and absolute masses, for any model isotherm, are derived. The modelling framework is used in combination with five standard equilibrium isotherm models to simulateexperimental data for Prussian blue analogues, nitropussides and metal-organic frameworks via nonlinear regression. The surface areas, the affinity and heterogeneity factors, and the pressure-dependent adsorption volumes are calculatedand compared to values available in the literature and the sensitivity of the results to the number of data points is quantified. The consistency of the results using different isotherm models is evaluated.     

Mathematical modelling of the thin layer solar drying of banana, mango and cassava

The main objectives of this paper are firstly to investigate the behaviour of the thin layer drying of plantain banana, mango and cassava experimentally in a direct solar dryer and secondly to perform mathematical modelling by using thin layer drying models encountered in literature. The variation of the moisture content of the products studied and principal drying parameters are analysed. Seven statistical models, which are empirical or semi-empirical, are tested to validate the experimental data. A non-linear regression analysis using a statistical computer program is used to evaluate the constants of the models. The Henderson and Pabis drying model is found to be the most suitable for describing the solar drying curves of plantain banana, mango and cassava. The drying data of these products have been analysed to obtain the values of the effective diffusivity during the falling drying rate phase.     

发动机冷却系统陈述式动态模型

鉴于发动机冷却系统传统过程式模型在模块化、重用性、参数化等方面的不足,在详细分析发动机冷却系统部件数学模型的基础上,采用面向对象的陈述式建模方式在多领域仿真平台MWorks上建立了易于管理、修改、重用和扩充的发动机冷却系统陈述式动态模型库,模型库各重要部件均采用动态表征。为更精确地计算散热器动态性能,提出了二维离散方法构建散热器模型。通过试验数据验证了散热器模型,散热器出口冷却液温度和空气温度的稳态仿真值与试验值误差分别为4.20%和4.75%。通过调用模型库中的部件模型构建了结构典型的发动机冷却系统,并对仿真结果进行了理论对比分析。     

Modelling of scattering and absorption coefficients for a polydispersion

An adequate treatment of the thermal radiation heat transfer mechanism is essential to a mathematical model of the combustion process or to design a combustion device. Predictive tools using flux models, such as the discrete transfer method, the discrete ordinates method and the spherical harmonics method, that solve the radiative heat transfer equation, require as input the values of the absorption and scattering coefficients of the participating media. Such coefficients must be evaluated in an expedite fashion since computational fluid dynamics and radiative flux models are extremely time demanding by themselves. In this work, a curve fitting approach to the Mie theory is used to evaluate the above-mentioned coefficients for intermediate and large particles, ensuring a compromise between accuracy and computational economy. The same coefficients for small particles are calculated using power series to represent the Mie coefficients accurately and economically. Predictions with the present models were performed for soot, carbon particles and fly ash and are presented herein. The results have proved that the models proposed in this work are computationally much faster than the prohibitive Mie theory calculations: reductions in computing times as high as three-hundred fold. Additionally, the referred models allow for the achievement of very accurate results: a relative error between approximated values and the corresponding Mie exact solution almost always below 5%.     

Novel method for setting up the relay protection of power systems containing renewable energy sources and hydrogen energy storage systems

Integration of renewable energy sources (RES) together with energy storage systems (ESS) changes processes in electric power systems (EPS) significantly. Specifically, rate of change and the lowest values of operating conditions during the emergencies are got influenced. Such changes can cause incorrect actions of relay protection (RP) as it was designed and adjusted with no regard for influence of RES and ESS. Detailed research on processes during the different normal and abnormal modes in both EPS and primary transducers and also in RP devices should be done to take preventive actions. To do this research mathematical modeling based on detailed and authentic models of all elements including RP should be used. HRTSim (which was developed by authors) software for simulating EPS provides the opportunity to create such models of EPS of any size without simplifications and limits. Using of this instrument together with detailed mathematical models of RP which were developed before provided the opportunity to investigate them rigorously in RES-integrated EPS. Settings providing adequate action of RP in certain conditions were performed as a result of this investigation. Fragments of these investigations are performed in this paper. Results of these investigations would be useful for designing new methods and tools of RP adjustment.     

Computing diffuse fraction of global horizontal solar radiation: A model comparison

For simulation-based prediction of buildings’ energy use or expected gains from building-integrated solar energy systems, information on both direct and diffuse component of solar radiation is necessary. Available measured data are, however, typically restricted to global horizontal irradiance. There have been thus many efforts in the past to develop algorithms for the derivation of the diffuse fraction of solar irradiance. In this context, the present paper compares eight models for estimating diffuse fraction of irradiance based on a database of measured irradiance from Vienna, Austria. These models generally involve mathematical formulations with multiple coefficients whose values are typically valid for a specific location. Subsequent to a first comparison of these eight models, three better performing models were selected for a more detailed analysis. Thereby, the coefficients of the models were modified to account for Vienna data. The results suggest that some models can provide relatively reliable estimations of the diffuse fractions of the global irradiance. The calibration procedure could only slightly improve the models’ performance.     

Analysis of self-dual excited synchronous machine. I. Developmentof the general mathematical model and steady-state performanceexperimental verification

The use of the dual excitation system for improving the overall performance of a self-excited synchronous machines is considered, along with the replacement of the compound transformer and rectifier bridge by a potential transformer and thyristor bridge for the self-excitation system. The output DC voltage of the bridge is controlled over a wide range by an automatic feedback control circuit to vary the firing angle of the thyristors in such a way that the terminal voltage is sustained at a constant value. The mathematical models for two distinctive alternatives of the excitation system are derived. The mathematical model thus derived is suitable for transient, dynamic as well as steady-state analysis. However it should be modified to investigate the steady-state and dynamic performance. Exact steady-state operating points are achieved by solving the steady-state equations obtained from the general model. Charts describing the performance of the self-dual excited synchronous machine under steady-state operation for the two alternatives of the excitation system have been calculated at different values of the power factor, i.e., the turns ratio of the transformer and the ratio of field currents. The experimental results obtained on a 7.6 kVA induction machine converted to a d-q synchronous machine confirm the validity and accuracy of the analysis and mathematical models developed     

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.