超临界区水的拟临界温度的确定

以水和蒸汽性质国际协会推荐的IAPWS-IF97为基本框架，推导了临界区域内水的拟临界温度计算方程。并在此基础上得出了拟临界温度和压力的关系式，可对临界区水的拟临界温度进行快速计算。该公式可广泛应用于超临界蒸汽发生器等的设计计算。图3参3     

能源、环保与超超临界汽轮机的发展

为了节约能源、提高热效率和减少对环境的污染, 必须大力发展超超临界发电技术. 本文介绍了STC正在设计制造由“HMN” 模块组成的1000MW超超临界汽轮机, 它具有单轴、最高的进汽压力、 3-D叶片等一系列先进技术, 使机组的性能达到世界先进水平. 通过本文介绍可知, 该机型还适合作为百万千瓦超超临界的空冷、抽汽供热机组以及最高30MPa进汽压力的两排汽660MW机组, 具有广阔的市场前景.     

基于神经网络预测模型和凝结水节流的超超临界机组协调系统智能优化控制

针对某1000 MW超超临界机组,建立了具有较高精度和良好动态性能、考虑机组回热循环特性的机组负荷及主汽压力神经网络预测模型.在此基础上,提出了一种协调系统综合智能预测优化控制方法.该方法利用负荷及主汽压力预测模型在机组变负荷过程中分别对除氧器水位调门开度、汽轮机调门开度及燃料量指令进行实时优化,改善协调控制效果.借助1 000 MW超超临界机组仿真机,进行了详细的协调优化控制仿真试验.结果表明:该方法可有效提高机组动态过程负荷的响应速度和调节精度,大大减小变负荷过程中主汽压力的控制偏差,具有较好的工程实用性.     

600 MW超临界锅炉燃烧器区膜式水冷壁温度场的数值计算

基于有限元法对某电厂600 MW机组锅炉在不同超临界工况下燃烧器区膜式水冷壁的温度场进行了分析和计算.采用双线性四边形单元对水冷壁温度场进行剖分,分区段计算了向火侧的热流密度.依据水冷壁入口和出口工质的实际温度和压力,确定了管内工质温度及管内的对流换热系数,计算了超临界压力下不同工况的水冷壁温度分布,并对造成水冷壁超温的原因进行了分析.对计算结果与实测值进行了比较,误差很小.     

超(超)临界火电机组乘数型协调预测函数优化控制研究及应用

为了提高超(超)临界火电机组协调控制系统控制性能,提出了一种乘数型预测函数控制方法,设计了带扰动信号的乘数型预测函数最优控制律,并将预测函数控制系统与优化控制方法应用于超超临界机组主汽压力与过热汽温控制回路。将汽轮机调门指令和给煤量指令作为主汽压力预测系统的一种扰动信号进行控制,计算出给水优化指令,叠加前馈信号后作用于整个系统;将给水量指令作为过热汽温预测系统的一种扰动信号进行控制,计算出给煤量优化指令,叠加前馈信号后作用于整个系统。结果表明:对于三输入三输出的超临界机组来说,该方法有效地解决了系统的耦合问题,工程实践证明了其良好的应用前景。     

超超临界机组四大管道材质的选择

介绍了国产1000MW、600MW超超临界机组的参数，四大管道设计的压力、温度。 介绍了日本、欧洲一些电厂超超临界机组采用的管材。 对几种耐热钢材进行了比较，对超超临界机组四大管道选材提出了建议。对主蒸汽管道材质多采用P92，对再热汽热段管道宜采用P91，对再热汽冷段管道宜采用A672870CL32，对高压给水管道宜采用WB36。 给出了日本最新的P122和P91许用应力值，供计算壁厚参考。     

超（超）临界锅炉用新材料的特性及其焊接

电力是我国国民经济发展的基础产业之一。从目前国内外火力发电技术水平来看，提高火力发电厂效率的主要途径是提高工作介质（蒸汽）的参数，即提高蒸汽温度和压力。发展超临界（SC）和超超临界（USC）火电机组，提高蒸汽参数对提高火力发电厂效率的作用是十分明显的。随着蒸汽温度和压力的提高．电厂锅炉的效率在大幅度提高，供电煤耗大幅度下降，提高蒸汽参数遇到的主要技术难题是金属材料耐高温、耐高压及其性能的问题。我国自本世纪初以来引进超（超）临界锅炉，到目前包括在建的机组在内已经达到100多台．新材料在超（超）临界锅炉上应用在提高机组参数的同时，也对电站工作者熟悉这些材料的性能提出了新的要求。     

基于BEST系统超超临界1000 MW二次再热蒸汽机组的参数选取

为研究抽汽背压式汽轮机(BEST)系统超超临界1 000 MW二次再热蒸汽机组参数的选取,基于某电厂二期2×1 000 MW超超临界机组扩建项目,建立1 000 MW超超临界高效二次再热蒸汽机组的设计计算,使用EBSILON软件建立完整的热力系统模型,得出主蒸汽温度、再热蒸汽温度、主蒸汽压力、再热蒸汽压力和锅炉效率等参数对BEST系统的影响规律。研究结果表明：对于12级回热的BEST系统来说提高主蒸汽的温度比提高主蒸汽的压力更能提高系统的发电热效率;BEST系统最佳工况点的再热蒸汽压力是15.028 MPa/4.079 MPa;锅炉效率变化范围在85%～95%时,随着锅炉效率变化1%,系统发电热效率随之变化0.51%。     

某型1000MW超超临界机组低压模块结构分析研究

介绍了某型1 000MW超超临界机组经常发生汽轮机低压部分动静碰磨,引发机组振动,排汽导流环连接螺栓断裂等问题.通过试验并结合有限元计算对事故原因进行分析,找出问题的根源,提出对该型机组低压缸结构的改进方案.     

660MW超超临界锅炉再热抽汽安全性分析

某电厂660 MW超超临界锅炉为单炉膛П型布置,尾部烟气挡板调节再热汽温。机组运行后拟抽取再热蒸汽满足外部供热。锅炉受热面布置按照不抽汽设计,假如抽汽运行,随着再热流量降低,再热器受热面冷却能力不足易超温影响机组安全运行。通过对660MW额定工况、75%负荷和50%负荷工况下不同抽汽量的计算对比,分析了机组负荷和抽汽量变化关系、比较了再热器受热面最高管壁温度和管子材料许用温度,对不同工况下锅炉的最大可能抽汽量进行预估。通过计算对比结果表明对机组再热系统的抽汽改造方案选择具有一定指导意义。     

Numerical Investigation of Jet Impingement Cooling of a Flat Plate with Carbon Dioxide at Supercritical Pressures

Confined round jet impingement cooling of a flat plate at constant heat flux with carbon dioxide at supercritical pressures was investigated numerically. The pressure ranged from 7.8 to 10.0 MPa, which is greater than the critical pressure of carbon dioxide, 7.38 MPa. The inlet temperature varied from 270 to 320 K and the heat flux ranged from 0.6 to 1.6 MW/m². The shear-stress transport turbulence model was used and the numerical model was validated by comparison with experimental results for jet impingement heating with hot water at supercritical pressures. Radial conduction in the jet impingement plate was also considered. The sharp variations of the thermal-physical properties of the fluid near the pseudocritical point significantly influence heat transfer on the target wall. For a given heat flux, the high specific heat near the wall for the proper inlet temperature and pressure maximizes the average heat transfer coefficient. For a given inlet temperature, the heat transfer coefficient remains almost unchanged with increasing surface heat flux at first and then decreases rapidly as the heat flux becomes higher due to the combined effects of the thinner high specific heat layer and the smaller thermal conductivity at higher temperature.     

An Investigation on Heat Transfer to Supercritical Water in Inclined Upward Smooth Tubes

Within the range of pressures from 23 to 30 MPa, mass velocities from 600 to 1200 kg/(m²s), and heat fluxes from 200 to 600 kW/m², experiments have been performed for an investigation on heat transfer to supercritical water in inclined upward smooth tubes with an inner diameter of 26 mm and an inclined angle of 20° from the horizon. The results indicated that heat transfer characteristics of supercritical water are not uniform along the circumference of the inclined tube. An increase in the mass velocity of the working fluid can decrease and even eliminate the non-uniformity. Properties of supercritical fluid acutely vary with the temperature near the pseudocritical point. While the ratio of the mass velocity to the heat flux exceeded 2.16 kg/(kWs), heat transfer enhancement occurred near the pseudocritical point; conversely, heat transfer deterioration occurred while the ratio of the mass velocity to the heat flux was lower than 2.16 kg/(kWs). As the pressure increased far from the critical pressure, the amount of deterioration decreased. Correlations of heat transfer coefficients of the forced-convection heat transfer on the top and bottom of the tube have been provided, and can be used to predict heat transfer coefficient of spirally water wall in supercritical boilers.     

Transient convective heat transfer to water near the critical region in a vertical tube

Numerical analysis has been carried out to investigate transient forced convective heat transfer to water near the critical region in developing flow through a vertical tube. With large variations of thermophysical properties such as density, specific heat, viscosity, and thermal conductivity near the thermodynamic critical point, heat transfer in the tube is strongly coupled with fluid flow. Buoyancy force parameter has also large variation with fluid temperature and pressure in the tube. Time dependent characteristics of fluid velocity, temperature, and heat transfer coefficient with water properties are presented and analyzed. Transient Nusselt and Stanton number distributions along the tube are also compared for various pressures in the tube. Because of heat transfer from the wall transition behavior from liquid-like phase to gas-like phase of heat transfer coefficient occurs when the fluid passes through pseudocritical temperature region in the tube. Turbulent viscosity ratio also has steep variation near the pseudocritical temperature close to the wall.     

Forced convective heat transfer to supercritical water flowing in tubes

Experimental investigations were made of heat transfer to supercritical water flowing in a horizontal tube and vertical tubes. A comprehensive set of data was obtained for pressures from 226 to 294 bar, bulk temperatures from 230 to 540°C, heat fluxes from 116 to 930 kW/m² and mass velocities from 310 to 1830 kg/m²s. Because the physical properties of supercritical fluids change rapidly with temperature in the pseudocritical region, the heat transfer coefficients show unusual behavior depending upon the heat flux. At low or modetate heat fluxes relatively to the flow rate, a satisfactory correlation was obtained, which predicts reasonably well the enhanced heat transfer coefficients near the pseudocritical point. The several characteristics of the deterioration in heat transfer which occurs at high heat fluxes were clarified, and the limit heat flux for the occurrence of the deterioration was determined in connection with the flow rate.     

Effect of heat extraction optimization with supercritical carbon dioxide on transcritical power cycle

An experimental and thermodynamic analysis was conducted to explore the match in operating conditions for the heat extraction of supercritical CO₂ and the CO₂ transcritical organic Rankine cycle (CTORC). The results revealed that in the optimal conditions of the experiment, the difference between the pseudocritical temperature and the inlet temperature ( ΔT _{pc − in} ) was <10 K and T _b/T _pc (ratio of the bulk temperature to the pseudocritical temperature) was ≤1 (ideal scenario: T _b/T _pc = 1). Furthermore, the heat transfer and fluid flow of CO₂ as well as the CTORC system performance at the optimal T _b/T _pc could be simultaneously improved with respect to those at ΔT _{pc − in} < 10 K. The peak values of system efficiency for the inlet temperature of the expander of 100°C and 150°C were 5.1% at 12.5 MPa and 8.0% at 17 MPa, with the corresponding T _b/T _pc being 1.24 (T _pc of 55.9°C) and 1.45 (T _pc of 70°C), respectively. Consequently, to simultaneously improve the heat transfer, fluid flow and system efficiency, T _pc of the supercritical CO₂ in the CTORC should be sufficiently high to approach half the inlet temperature of the expander for obtaining an optimal T _b/T _pc at a low condensing temperature.     

超临界锅炉前屏过热器传热特性分析

过热器超温爆管是造成火电机组非计划停机的重要原因之一。通过对600MW超临界机组的前屏过热器进行分析，计算25MPa、22MPa、19MPa的壁温、吸热量以及传热系数，优化过热器管的设计与选材。计算结果表明，对于以带基本负荷为设计原则的锅炉，长期在低负荷下运行，发生过热器超温爆管的可能性会增大。     

Effect of cooling surface temperature difference on the performance of high-temperature PEMFCs

Internal temperature distribution of the high-temperature proton exchange membrane fuel cell (HT-PEMFC) is affected by the cooling temperature, heat generation and reactant gas flow. Reasonable temperature control is helpful to improve the fuel cell performance and durability. In this work, a three-dimensional model that couples the reactant flows, species transport, heat transfer, charge transfer, and electrochemical reaction, was developed to simulate the HT-PEMFC operation. A solid mechanics model was established to analyze the stress distribution of the fuel cell. The polarization curves, distributions of temperature, membrane proton conductivity, current density and stress are investigated for different cooling surface temperature. Furthermore, the effect of assembly temperature on the stress of phosphoric acid-doped polybenzimidazole (PBI) membrane is discussed. Results reveals that the peak power density and uniformity of current density decrease with the increase of cooling surface temperature difference. The peak power density decreases by 9.14% when the temperature difference increases from 0 K to 40 K. The cooling surface temperature difference of less than 10 K and the voltage range in 0.5–0.7 V can achieve better current density uniformity and smaller current density change rate. In addition, the membrane in fuel cell has the highest stress, and increasing the assembly temperature is helpful to reduce the membrane stress. When the assembly temperature increases from 293.15 K to 343.15 K, the max and min compressive stresses in membrane in-plane decrease from 39.436 MPa to 31.416 MPa–24.934 MPa and 17.369 MPa at the temperature difference of 30 K, which decreases by 36.77% and 44.7%, respectively.     

Convective heat transfer to water near the critical region in a horizontal square duct

Numerical analysis has been carried out to investigate forced convective heat transfer to water near the critical region in a horizontal square duct. Near the critical point convective heat transfer in the duct is strongly coupled with large variation of thermophysical properties such as density and specific heat. Buoyancy force parameter has also severe variation with fluid temperature and pressure in the duct. There is flow acceleration along the horizontal duct resulted from fluid density decrease due to the heat transfer from the wall. Local heat transfer coefficient has large variation along the inner surface of the duct section and it depends on pressure. Nusselt number on the center of the bottom surface also has a peak where bulk fluid temperature is higher than the pseudocritical temperature and the peak decreases with the increase of pressure. Flow characteristics of velocity, temperature, and local heat transfer coefficient with water properties are presented and analyzed. Nusselt number distributions are also compared with other correlations for various pressures in the duct.     

Numerical study of convective heat transfer to supercritical water in rectangular ducts

Numerical investigation has been performed to analyze forced convective heat transfer to supercritical water in horizontal rectangular ducts. Convective heat transfer near the critical region in the rectangular ducts is strongly influenced by large variations of thermodynamic and transport properties of supercritical fluid with gravity force, especially close to pseudocritical temperature. Fluid flow and heat transfer characteristics such as velocity, temperature, and local heat transfer coefficient with water properties distribution in the ducts are presented. Flow accelerates along the horizontal ducts because of decreased water density from heat transfer at the duct walls. Center of large flow recirculation in the duct section locates near the middle of vertical surface and additional secondary recirculation in clockwise direction appears with the increase of duct height. Local wall temperature severely varies along the inner surface of the duct section and its variation depends on aspect ratio of the duct. The heat transfer coefficient distributions along the ducts for various aspect ratios are compared with the proximity effect to the critical pressure.