Investigation Methods for Thermal Shock Crack Problems of Functionally Graded Materials–Part II: Combined Analytical-Numerical Method

Fractures phenomena can be often found in functionally graded materials (FGMs) subjected to thermal shock loadings. This paper aims to develop a set of analytical-numerical methods for analyzing the mixed-mode thermal shock crack problems of a functionally graded plate (FGP). First, a domain-independent interaction energy integral method is developed for obtaining the mixed-mode transient thermal stress intensity factors (TSIFs). A perturbation method is adopted to obtain the transient temperature field. Then an analytical-numerical method combining the interaction energy integral method, a perturbation method, and the finite element method is developed to solve the present crack problem. Particularly, the influences of the materials parameters, crack length, and crack angle on the TSIFs and the crack growth angle are investigated. The results show that the present analytical-numerical method can be used to solve the thermal shock crack problem with high efficiency. The present work will be significant for the fracture mechanics analysis and design of FGM structures.     

基于改进拉格朗日算法的风光互补系统优化设计研究

从风光互补系统的经济性出发研究了风光互补系统的优化设计问题。以年度平均电量成本最小化作为目标,将太阳能光伏板面积、风电机组额定功率和蓄电池最大储能容量作为决策变量,构建了风光互补系统优化设计模型,并通过引入互补约束条件,将分段函数转化为连续函数,利用改进的拉格朗日分解法,由上而下分阶段求解模型。实例应用结果表明,利用优化模型计算所得结果在经济性和运算效率上有明显提高,验证了模型的可行性和算法的有效性。     

Numerical simulation of the He II/He I phase transition in superconducting magnets

In this paper we simulate a special type of Stefan problem in large-scale superconducting magnet systems in which superfluid helium (He II) is used as the coolant for the system. Liquid helium in a narrow channel called a “cable-in-conduit” conductor (CICC) is used to remove the heat load from the conductors. Liquid helium exhibits a phase change transition to normal helium (He I) when its temperature rises above the lambda point (2.716 K under saturated vapor pressure). A simple one-dimensional model is described to analyze this special He II/He I Stefan problem. A moving mesh technique is used to solve this model to improve the numerical efficiency compared with front-tracking methods. The results illustrate the simplicity and efficiency of this model.     

二次响应面法在材料分区结构中的可靠度精度研究

通过一个复杂材料分区工程实例讨论了有交叉项和无交叉项二次响应面的计算精度和效率,并分别用二次响应面法和蒙特卡罗数值模拟法计算了可靠度指标,借助于F检验还可大大简化该模型.结果表明,基于正交试验抽样的无交叉项二次响应面耗时较少,适于大型复杂结构的可靠度计算;与传统响应面方法相比,这种二次响应面在构建响应面和可靠度计算时完全解耦.     

水管冷却混凝土温度场的精确计算与应用

简要介绍了基于水管与混凝土之间热量交换的能量守恒原理、水管冷却混凝土温度场的精确算法及有限元数值计算方法。算例和试验验证，该迭代方法具有很高的计算效率和精度。应用该精确算法为几个大坝仿真分析，均取得了很好的效果，证明该算法具有良好的工程应用前景。     

二维燃烧系统气体发热量的确定

开发了一种求解二维燃烧系统气体发热量和气体温度分布的辐射热负荷反问题的新方法－蒙特卡罗法、共轭梯度法和最小二乘法相结合的方法。讨论了气体吸收系数、固体表面发射率和对流传热系数对反问题计算结果的影响。结果表明，即使测量误差存在，辐射热负荷反问题也能得到较准确的结果。     

压缩式热泵系统火用效率定义方法初探

对压缩式热泵系统(火用)效率的定义式进行了分析,指出了该定义式在实际应用过程中存在的一些不足.即当低温热源为环境时,此定义式合理,否则即使热泵系统内部可逆,系统火用效率仍不为1,文中对产生这一问题的原因进行了分析.以热泵系统的火用平衡方程为依据,参照火用效率定义方法及火用效率的基本特征,对压缩式热泵的系统(火用)效率进行了重新定义.通过对两个不违背火用效率定义特征的表达式的对比分析,确定了热泵系统合理的(火用)效率表达式.最后说明,在压缩式制冷系统中当高温热源不为环境时,(火用)效率定义也存在同样缺陷,改进方法与本文类似.     

Investigation on multi-objective performance optimization algorithm application of fan based on response surface method and entropy method

A multi-objective performance optimization method is proposed,and the problem that single structural parameters of small fan balance the optimization between the static characteristics and the aerodynamic noise is solved.In this method,three structural parameters are selected as the optimization variables.Besides,the static pressure efficiency and the aerodynamic noise of the fan are regarded as the multi-objective performance.Furthermore,the response surface method and the entropy method are used to establish the optimization function between the optimization variables and the multi-objective performances.Finally,the optimized model is found when the optimization function reaches its maximum value.Experimental data shows that the optimized model not only enhances the static characteristics of the fan but also obviously reduces the noise.The results of the study will provide some reference for the optimization of multi-objective performance of other types of rotating machinery.     

29MW链条热水锅炉改造及运行调试

对１４ＭＷ以上链条锅炉运行中的效率低问题，进行诊断调查而做出的改造措施。     

基于双光程法液体分频PV/T系统分频液性能分析

液体分频型PV/T系统总效率包含分频液集热效率和光伏电池发电效率。分频光谱对于光伏电池响应波段的匹配程度和分频液在不同波段的透过率是关键影响因素,直接导致分频液的集热效果、电池板温度及到达电池板的光谱发生改变,从而影响系统性能。然而当前关于分频液分频性能研究测试结果的数据差异较大,大部分文献没有解决比色皿等容器的误差问题。为提高液体分频型PV/T系统性能,利用分光光度计测量多种液体不同样本厚度的透过率,采用双光程测量方法去除比色皿误差,以获取分频液较精准的透过率,同时考察分频液对镓铟磷电池的响应。研究结果表明：200~1 020 nm,水与丙三醇的平均光谱透过率最大,但分频性能不佳;丙三醇作为分频液时镓铟磷电池平均光电转换率最高;硫酸铜溶液的分频性能较好,且与镓铟磷电池的匹配度最好。研究结果可为液体分频型PV/T系统分频液的选取提供可靠理论依据。     

燃烧室内三维温度场的辐射反问题

本文提出了一种在介质辐射特性已知的条件下,由壁面入射辐射热流的测量值反演燃烧室内三维温度场的方法。该方法是在辐射传递方程离散坐标近似的基础上,用求目标函数极小值的共轭梯度法进行反演计算。通过对吸收系数、散射不对称因子、反照率、壁面黑度和燃烧室大小尺寸等参数对反演精度影响的分析,结果表明,即使存在随机测量误差,这些参数对温度场反演精度的影响也不大,本文所提出的方法可较精确地反演燃烧室内三维温度场。     

Effects of particle fouling and magnetic field on porous fin for improved cooling of consumer electronics

The combined effect of particulate fouling and magnetic field on the efficiency of a convective–radiative porous fin heatsink with temperature‐dependent thermal conductivity is presented. The developed thermal models are solved using differential transformation method. The effects of thermal conductivity, porosity, convection, radiation parameter, and thermal fouling number on the fin thermal efficiency are investigated. The presence of thermal fouling on the surface of the fin is shown to increase the temperature distribution. The presence of particle deposition on the fin surface significantly decreases the rate of heat transfer as additional thermal resistance of the fouling layer decreases the thermal performance of porous fin heatsink. Moreover, the fin efficiency decreases as the value of fouled Biot, Darcy, radiation number, and thermogeometric parameter increases. It is established that M_f < M_c, which indicates that the efficiency of the fouled fin is greater than the efficiency of the clean fin. Furthermore, the result of the present study is validated with the established results of Chebyshev spectral collocation method and fourth‐order Runge–Kutta with shooting method and an error margin of 0.000000023 is established.     

矩阵方程在加热器变工况分析中的应用

基于有效热降理论的热力系统热经济性计算通用矩阵方程,能有效克服热经济性矩阵分析方法需要联立其它方程才能求解热力系统最终热经济性指标的缺陷,并将其应用到回热系统中。得出在机组负荷偏离额定负荷运行时,系统效率的变化情况。研究和分析加热器的经济性指标与运行工况的关系,更好地掌握加热器系统特征和提高系统的运行水平,是提高机组的经济性和安全性的关键。     

水热法制备TiO2纳米晶胶体及其在DSSC电池中的应用

采用钛酸异丙酯作前驱体，利用水热法制备了TiO2纳米溶胶溶液。以此制备了染料敏化太阳能电池的光阳极并组装电池。对产物采用激光粒度仪（HPPS）、X射线衍射（XRD）、扫描电镜（SEM）等进行表征。XRD显示了TiO2纳米颗粒为纯锐钛矿结构，SEM观察薄膜电极呈多孔结构。表征电池的光电化学性能，所制备的TiO2纳米晶薄膜的光电转换效率达到3．03％。     

考虑间歇性电源的微电网经济调度模型与算法

微网系统的有功调度是具有重大经济效益的复杂问题,关键问题是要正确处理好微网有功调度过程中的不确定性因素。基于微网经济调度模型,采用场景法描述间歇性电源的出力,并简化了调度模型,采用原对偶内点算法对模型进行求解。实例应用结果表明,当风电波动较大时,传统调度方式下微网系统在某些时段可能出现功率缺额,鲁棒调度方式则能通过调整可控机组的出力使微网系统保持功率平衡;传统调度方式更具有经济性,鲁棒调度方式则是以损失经济性为代价换取微网系统对风电不确定性的适应能力。     

Performance optimization in switched reluctance motor drives with online commutation angle control

The problem of performance optimization in current controlled switched reluctance motor (SRM) drives is investigated. Two controllers are proposed that determine the optimal turn-on and turn-off angles, respectively, for improving motor efficiency and torque ripple. The suggested controllers are simple, do not affect the complexity of the drive, and are easily implemented since the knowledge of torque-angle-current characteristics or magnetization curves is not required. The proposed control scheme is demonstrated on a prototype experimental system.     

Inverse analysis for estimating the unsteady inlet temperature distribution for two-phase laminar flow in a channel

An inverse thermal problem was considered for two-phase laminar flow in a parallel plate duct. The inlet temperature, which varies temporally as well as spatially, was estimated when measured temperatures were available at downstream of the duct. In the present study, the problem is solved through a minimization of an objective function by using two regularization methods, i.e., the iterative conjugate gradient method (CGM) and the Tikhonov regularization method (TRM). The effects of the functional form of inlet temperature profile, the number of the measurement points and the measurement errors are investigated and discussed. The computational accuracy and efficiency of these two regularization method are compared and discussed.     

大型燃煤机组SCR脱硝催化剂失活研究

催化剂是燃煤电厂选择性催化还原(SCR)烟气脱硝技术的核心,催化剂的活性和寿命决定了脱硝效率和脱硝成本.针对目前国内燃煤机组脱硝催化剂易失活、更换频率高等问题,通过查阅相关文献对催化剂磨蚀、堵塞、烧结、中毒等四种主要失活现象进行了研究.从四种主要失活现象的微观机理入手进行分析,并结合实际运行经验,总结了不同失活现象产生的原因,提出了在燃煤电厂实际运行中可有效抑制催化剂失活的方法.研究对提高脱硝效率、降低脱硝成本具有一定的指导意义.     

Performance investigation of a two-stage sorption hydrogen compressor

Metal hydrides (MH) are widely investigated for several thermodynamic applications; sorption hydrogen compressor (SHC) is one among them. In this study, the thermodynamic performance and heat – mass transfer behaviour of a two-stage sorption hydrogen compressor (TSSHC) are investigated with the employment of La_0·9Ce_0·1Ni₅ and MmNi_4.8Al_0.2 alloys in series. The hydrogen supply and the discharge temperatures are chosen as 20 °C and 80 °C, respectively. The thermodynamic performance data, i.e. compressor work and efficiency, are evaluated using the experimentally measured pressure-concentration-isotherm (PCI) and thermodynamic properties. In contrast, the heat and mass transfer behaviour is predicted by solving governing equations through the finite volume method (FVM). The numerical model is validated with experimental PCIs, and the results are in close agreement. The predicted cycle time is 75 min, comprising hydrogen supply, sensible heating and cooling, and hydrogen delivery. The TSSHC possessed a compression ratio of 9.5 and a cycle efficiency of 11.4% in which the hydrogen supply pressure is 9 bar using 0.5 kg of each alloy. Later, the influence of mass transfer on overall compressor work, heat input and efficiency is also presented.     

Investigation of heat transfer in a geometry with variable cross section

In this paper, the thermal conductivity that plays an important role in heat transfer efficiency is investigated. He's homotopy perturbation method (HPM) and Adomian decomposition method (ADM) are applied to the nonlinear heat transfer equations and the comparison between results is illustrated within several plots. Here, thermal conductivity has been considered as a function of temperature. Also the variable heat generation has been taken into account. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20266 Copyright © 2009 Wiley Periodicals, Inc.