Analytically calculating shading in regular arrays of sun-pointing collectors

A method is presented for deriving an algorithm for analytically calculating shading of sun-pointing solar collectors by other identical collectors in the field. The method is particularly suited to regularly-spaced collectors, with convex aperture shapes. Using this method, an algorithm suitable for circular-aperture collectors is derived. The algorithm is validated against results obtained using an existing algorithm, and an example for usage of the algorithm as a tool for validating assumptions of an existing algorithm is presented.     

Eddy current and impedance evaluation using a two-dimensionalfinite element method

A finite element method is developed to evaluate cylindrical electromagnetic fields due to eddy currents inside linear conducting media. Boundary conditions are imposed in an integral form combined with Neumann conditions. The method is applied to a periodic system of slot embedded conductors in the rotor of an induction machine and is verified by comparison with an analytical method     

等温黑体空腔积分发射率的计算

黑体空腔积分发射率的计算对辐射测温黑体空腔的设计非常重要,不同计算方法之间的互相校验是保证计算准确的重要手段。提出了一种基于有限元的计算方法,计算了等温轴对称黑体空腔的积分发射率,结果与Monte Carlo法的平均相对偏差为0.000 9,表明该方法准确可靠。在此基础上,对等温非轴对称黑体空腔的积分发射率进行了计算,结果与Monte Carlo法的平均相对偏差为0.000 5,表明能够有效计算非轴对称黑体空腔积分发射率。     

Development of a 1 MJ SMES with quench enthalpy protection

As a quench protection method in an SMES, a dumping resistor method and an enthalpy method are considered. The former is a conventional method, but the latter has not been experimentally examined yet, although it has been shown to be suitable for future SMES. In addition, a new control method, QI simultaneous control, has been also developed as a practical application of the SMES. The performance or the enthalpy protection technique is verified by a helium dumping method, and the QI simultaneous control is also successfully examined using a power network simulator     

油气回收集成工艺的应用浅析

油品蒸发损耗不仅污染环境,影响人体健康,也是能源的浪费。目前,已投入使用的油气回收技术主要有吸附法、吸收法、膜分离法、冷凝法4种,而油气回收集成技术是油气回收装置的发展趋势。介绍了吸收+吸附法、吸收+膜法、冷凝+吸附法、冷凝+膜法等油气回收集成技术在国内的应用情况。吸附法在国内外应用较多,可与冷凝法或吸收法相结合,达到高回收率、低能耗和高的吸附剂使用寿命。冷凝吸附法有效解决了能耗和吸附剂寿命问题,同时提高了油气回收率,实现了冷凝吸附低能耗集成工艺的优化;可根据油气性质对冷凝终温进行优化。膜分离法具有占地少、回收效果好、安全性和稳定性较高的特点,但投资偏高,随着膜技术的进步和膜的国产化,吸收+膜法和冷凝+膜法的集成工艺将有较多的应用。油气收集系统对油气回收装置至关重要,油气收集系统必须密封性好、系统阻力小、安全性高、自动化程度高。油气回收集成技术的投资与单一技术相近,运行费用低,回收效率高,能耗小。     

A Coupled Pressure-Based Co-Located Finite-Volume Solution Method for Natural-Convection Flows

A pressure-based coupled solution method based on a finite-volume discretization is presented. The method uses a cell-centered co-located variable arrangement on a nonorthogonal two-dimensional structured grid. The coupled algebraic analogs of the mass, momentum, and energy conservation equations for incompressible flow are solved. In addition to coupling the mass and momentum equations, the energy equation is coupled to the velocities via a Newton-Raphson linearization of the energy advection terms. The momentum equations are coupled to the energy equation via an implicit temperature in the Boussinesq approximation. The convergence behavior of the new method is demonstrated on the solution of steady, laminar natural convection in an annulus for Prandtl numbers of 0.707 and 13,050 at a Rayleigh number of 1 × 10⁶. A significant reduction in the number of iterations to convergence is obtained with the new method compared to a method with only velocity-to-temperature coupling and a method with energy and momentum decoupled. An improvement to the new method was obtained by using an approach that uses a delayed time-step increase and a modified face temperature value estimation.     

Chemical bath deposition for the fabrication of antireflective coating of spherical silicon solar cells

A CdS film as an antireflective (AR) coating has been successfully deposited on spherical silicon solar cells by chemical bath deposition, which is a novel deposition method of AR coatings for spherical silicon solar cells. The CBD method is a growth method in an aqueous solution and enables film formation for electronic devices with arbitrary shapes. The solar cell performance of the cell with the CdS film showed a 16% increase in short circuit current compared to that without an ARC. The result confirms that the CBD method is useful for the ARC fabrication of spherical silicon solar cells.     

Solution of the inverse heat conduction problem described by the Poisson equation for a cooled gas-turbine blade

The presented paper describes a method of solving the inverse problems of heat conduction, consisting in solving the Poisson equation for a simply connected region instead of the Laplace equation for a multiply connected one, like a gas-turbine blade provided with cooling channels. The considered method consists in determining unknown values of the source (heat sink) power in the cooling channels for a given external heat transfer situation to achieve as close as possible an isothermal outer surface. Afterwards the temperature and heat flux distributions at the cooling channel walls are determined. Since the unknown source power is sought, the problem is an inverse one. Taking into account the sought values the method is reckoned among the class of the fictitious source methods and presents an optimization scheme. Using an exemplary gas turbine blade cooling configuration, the results of the calculation obtained with this method have been compared to the results achieved with an inverse method using the boundary element method for a multiple connected region.The results obtained with both methods within the optimization scheme approximated each other. Nevertheless, the results for the inverse method shown in the present paper gave nearly no oscillations, which is important in case of the blades with other geometric features of the cooling channels.     

插值算法在内燃机瞬时转速测量中的应用研究

提出了采样信号的插值计算公式 ;考虑到测量信号中调制现象的影响 ,提出了插值法在瞬时转速计算中的误差公式 ;并针对 6 - 135 G柴油机最高转速对两点插值和三点插值的精度进行了计算 ;最后用实测数据进行了验证。结果表明这是提高瞬时转速测量精度的一种有效方法 ,在 5 0 k Hz的低采样率下即可得到较平滑的瞬时转速波形。     

A variable material property approach for solving elastic-plastic problems

The linear elastic solution of a boundary value problem is used as a basis to generate its inelastic solution. The method considers the material parameters as field variables. Their distribution is obtained in an iterative manner using the projection method, the arc-length method, and Nueber's rule. The rate of convergence is compared. The problem of thick-walled cylinder is considered as an example. The method yields the analytical solution in the limiting case if the cylinder is made of non-hardening Tresca material and is under internal pressure. The paper also presents solutions for a Mises solid whose hardening is described by the Ramberg-Osgood formula.     

Application of residual correction method to laser heating process

In this study, the residual correction method is employed to predict the temperature distribution during laser heating process. The energy transfer induced by laser irradiation in the solid is described by Fourier’s law of conduction with an energy source modeled by Beer’s law. The approximate solution of temperature field is obtained by residual correction. Using the residual correction method, the precise average value of upper and lower approximate solutions is obtained and the error range between the analytical solution and the numerical solution can be analyzed. The results reveal that this method is an effective numerical method with satisfactory accuracy.     

多级蓄热系统性能优化研究进展

多级蓄热系统是实现能量利用的重要方式,与传统的蓄热方式相比提升了系统的整体性能,具有将不稳定的热源高效存储并利用的重要作用。本文综述了蓄热系统在材料和换热装置方面常见的优化方式,着重对于多级蓄热系统特有的优化方式,分别从层级之间的关系、材料之间的匹配以及整体?效率3个方面进行了分析和归纳,介绍了当入口流体受不稳定热源影响时系统的优化方式。     

Keller-Box shooting method and its application to nanofluid flow over convectively heated sheet with stability and convergence

Abstract

The main aim of the present contribution is to present a coupling of Keller-Box method using Jacobi and Gauss–Seidel iterative methods with shooting approach and also this method is implemented on nanofluid flow problem. Present method of Keller-Box shooting method can be considered as an explicit approach whereas the standard Keller-Box method is an implicit method. Previously constructed nanofluid flow models are extended with exothermic/endothermic chemical reactions and the flow is considered over stretching, rotating, porous disk which is convectively heated from its bottom with the hot liquid. Similarity transformations are utilized to reduce the set of nonlinear partial differential equations into nonlinear ordinary differential equations with an assumption. Presently modified Keller-Box shooting method using Jacobi and Gauss–Seidel iterative methods is applied to investigate MHD nanofluid flow problem subject to Dirichlet, Neumann, and Robin’s boundary conditions. Von Neumann stability criterion is adopted to check the stability of the present method using Gauss–Seidel iterative method. The bounds for maximum errors are found for Jacobi and Gauss–Seidel iterative methods and convergence conditions are given for the case of Gauss–Seidel iterative method. The obtained results from presently developed modified Keller-Box shooting method are in good agreement with those obtained by Matlab built in solver “bvp4c” in case of wall temperature gradient and obtained results are in good agreement with those obtained by Runge–Kutta (4, 5) shooting method in case of skin friction coefficient.     

彭泽县可能最大降水量估算方法及评价

以江西省彭泽县为例,选取五个雨量站的1980~2010年共31年的年最大日降水量资料,采用概率论法、当地暴雨放大法和统计估算法对可能最大降水量进行了计算。结果表明,概率论法的计算结果最大,统计估算法的计算结果最小,结合彭泽县的具体情况可知,采用当地暴雨放大法的计算结果较为合理。     

Numerical Simulation of Melting Problems Using the Lattice Boltzmann Method with the Interfacial Tracking Method

A lattice Boltzmann method with an interfacial tracking method is used to solve melting problem in an enclosure. Both conduction- and convection-controlled melting problems are solved to validate the proposed method. For the conduction-controlled melting problem, the results agreed very well with those from the analytical solution. The results for the convection-controlled melting problem also agreed with those in the literature. The proposed approach is valid for numerical simulation of the melting problem.     

Inverse determination of laser power on laser welding with a given width penetration by a modified Newton–Raphson method

In this paper, the inverse determination of the laser power in welding process with a given width penetration using the modified Newton–Raphson method (MRN) is presented. The advantage of this inverse method does not adopt the nonlinear least-squares error to formulate the inverse problem, but it is implemented a direct comparison between the known melting temperature and the computed melting temperature. The isothermal elliptic shape at the bottom surface is considered, and two “auxiliary” variables including a semi-major axis and an elliptic center are added into the formulation. Two examples are used to demonstrate the proposed method. The results shows that the proposed method is an accurate and robust method to inversely estimate the laser power for a given width penetration.     

GLOBAL CONDUCTIVITY OF REPETITIVE STRUCTURES

Abstract

A general applicable method is presented to determine conductivity properties of repetitive heterogeneous structures from the material properties of their constituents. The method is an extension of an analysis given by Rayleigh and is demonstrated to determine the global conductivity of a regularly perforated brass plate used as a flat-flame holder. The method is also applicable to other analogous transport properties in a wide variety of geometrical configurations.     

Estimation of the periodic thermal conditions on the non-Fourier fin problem

A sequential method is proposed to estimate the periodic boundary conditions on the non-Fourier fin problem. An inverse solution is deduced from a finite difference method, the concept of the future time and a modified Newton-Raphson method. Two examples are used to demonstrate the features of the proposed method. The close agreement between the exact values and the estimated results is made to confirm the validity and accuracy of the proposed method. The results show that the proposed method is an accurate and stable method to determine the periodic boundary conditions in the non-Fourier fin problems.     

小扰动理论及其在电厂热经济性分析中的应用

热力系统分析理论是热力系统性能监测和热经济性诊断的有效工具。依状态空间法将小扰动理论引入热力系统分析中,借助于矩阵性能计算模型,提出了一种新的耗差分析方法。这种方法利用汽轮机在线监测数据,其计算精度高,适于工程实际应用,对机组性能监测和运行优化有重要意义。     

NUMERICAL ANALYSIS OF NATURAL CONVECTIVE AND RADIATIVE HEAT TRANSFER IN AN ARBITRARILY SHAPED ENCLOSURE

The flow and thermal characteristics of the interactions of natural convection and radiation in an enclosure containing circular ducts are analyzed numerically. For calculation of flow fields, the SIMPLE algorithm originally developed in Cartesian coordinates is extended and modified to apply to the curvilinear coordinates system. The radiation part of the problem for an arbitrarily shaped domain is solved by using the finite volume method (FVM). Cartesian velocity components are used as the dependent variables in momentum equations, and a nonstaggered grid system is employed. The flow and thermal fields for an irregular geometry are investigated for the variation of such parameters as scattering albedo, optical thickness, and Planck number. The test problem is compared with both the exact solutions and the discrete ordinates method solution. The results show that the FVM is an effective method to predict radiative heat transfer processes in irregular geometries and that the change of optical thickness has more effect than that of scattering albedo on flow and thermal fields.