Thermal conductivity of hydrogen for temperatures between 78 and 310 K with pressures to 70 MPa

The paper presents new experimental measurements of the thermal conductivity of hydrogen. The ortho-para compositions covered are normal, near normal, para, and para-rich. The measurements were made with a transient hot wire apparatus. The temperatures covered the range from 78 to 310 K with pressures to 70 MPa and densities from 0 to a maximum of 40 mol · L^–1. For compositions normal and near normal, the isotherms cover the entire range of pressure, and the temperatures are 78, 100, 125, 150, 175, 200, 225, 250, 275, 294, 300, and 310K. The para measurements include eight isotherms at temperatures from 100 to 275 K with intervals of 25 K, pressures to 12 MPa, and densities from 0 to 12 mol · L^–1. Three additional isotherms at 150, 250, and 275 K cover para-rich compositions with para percentages varying from 85 to 72%. For these three isotherms the pressures reach 70 MPa and the density a maximum of 30 mol · L^–1. The data for all compositions are represented by a single thermal conductivity surface. The data are compared with the experimental measurements of others through the new correlation. The precision (2) of the hydrogen measurements is between 0.5 and 0.8% for wire temperature transients of 4 to 5 K, while the accuracy is estimated to be 1.5%.     

High-accuracy quadrature methods for solving boundary integral equations of steady-state anisotropic heat conduction problems with Dirichlet conditions

This paper presents the mechanical quadrature methods (MQMs) for solving the boundary integral equations of steady-state anisotropic heat conduction equation on the smooth domains and polygons, respectively. The costless and high-accurate Sidi–Israeli quadrature formula are applied to deal with the integrals in which the kernels have a logarithmic singularity. Especially, the Sidi transformation is used for the polygon cases in order to obtain a rapid convergence by degrading the singularity at the corners on the boundary. The convergence and stability of the MQMs solution are proved based on Anselone's collective compact theory. In addition, asymptotic error expansion of the MQMs shows that the approximation order is of O(h³), where h is the partition size of the boundary. Finally, numerical examples are tested and results verify the theoretical analysis.     

Thermophysical Analysis of Sandstone by Pulse Transient Method

Stones belong to porous materials where water in pores plays an important role during the freeze–thaw process. A thermophysical analysis based on the pulse transient method has been used to study an ageing cycle, namely the freeze–thaw cycle. Thermophysical analysis is based on measuring the thermophysical properties under specific thermodynamic conditions. The transient method determines the specific heat, thermal diffusivity, and thermal conductivity by a single measurement. A specimen of Sander sandstone was analyzed in both dry and water-saturated states. Typical anomalies of all thermophysical parameters at the freeze–thaw point as well as differences for the dry and saturated states were found. The changes of thermophysical parameters measured when using freeze–thaw cycles correspond to stone ageing. The freeze–thaw cycle can often be encountered in building physics, concrete construction, etcPaper presented at the Seventh Asian Thermophysical Properties Conference, August 23–28, 2004, Hefei and Huangshan, Anhui, P. R. China.     

A Novel Instrument for the Measurement of the Thermal Conductivity of Molten Metals. Part II: Measurements

New measurements of the thermal conductivity of molten mercury, gallium, tin, and indium are reported up to 750 K. The measurements are performed in a novel transient hot-wire instrument described elsewhere. The present experimental technique overcomes problems of convection, and it is shown that it operates in an absolute way in accord with a theoretical model. The uncertainty of the thermal conductivity results is estimated to be ± 2%, which is superior to that achieved in most earlier work. The low uncertainty of the present experimental results has allowed us to test the only significant theory for the thermal conductivity of molten metals, which relates this property to the electrical conductivity. The pattern of results among the four metals indicates that further theoretical developments would be warranted.     

特高压通道降压运行时安徽500kV西通道建设必要性分析

根据华东1000kV特高压输电通道初期降压运行的统筹安排，结合淮南煤电基地电源、平圩电厂二期及蚌埠电厂等电源的装机进度，通过对各电源接入系统方案的计算分析，最后得出结论：为保证江北地区电力送出，安徽500kV西路过江通道在“十一五”期间建成是有必要的。     

高温超导交流磁体气冷电流引线的优化设计和实验

通过研究交流超导磁体气冷电流引线两段式模型的优化设计,使得其向低温系统的漏热达到最小,并自行设计热测法实验装置进行了实验研究.结果表明在引线顶端温度为300 K、引线下端温度为77 K、引线传输电流为460 A的情况下,得到最佳引线直径为7.9 mm,与实验值8 mm符合.对交流电流引线的趋肤效应进行了分析和讨论.     

Thermophysical Properties of Porous Sandstones: Measurements and Comparative Study of Some Representative Thermal Conductivity Models

The thermal conductivity and thermal diffusivity of porous consolidated sandstones have been measured simultaneously by the transient-plane source (TPS) technique in the temperature range from 280 to 330 K at ambient pressure using air as the saturant. The porosity and density parameters are measured using standard American Society for Testing and Materials (ASTM) methods at 307 ± 1 K. Data are presented for five types of samples ranging in porosity from 8 to 17 vol. %, taken from various positions above the baseline. The thermal conductivity and constituents of the minerals vary with porosity as well as with the position of the sample from the baseline. The thermal conductivity data are discussed in the framework of simple mixing laws and empirical models. Simple correlations between the effective density and porosity, and between the effective thermal conductivity and porosity, are also established     

Optimal control of nonlinear systems: a predictive control approach

A new nonlinear predictive control law for a class of multivariable nonlinear systems is presented in this paper. It is shown that the closed-loop dynamics under this nonlinear predictive controller explicitly depend on design parameters (prediction time and control order). The main features of this result are that an explicitly analytical form of the optimal predictive controller is given, on-line optimisation is not required, stability of the closed-loop system is guaranteed, the whole design procedure is transparent to designers and the resultant controller is easy to implement. By establishing the relationship between the design parameters and time-domain transient, it is shown that the design of an optimal generalised predictive controller to achieve desired time-domain specifications for nonlinear systems can be performed by looking up tables. The design procedure is illustrated by designing an autopilot for a missile.     

电压调节和功角稳定的非线性励磁控制器

介绍使用电力系统输入－输出反馈线性化模型的非线性励磁控制器的设计，该控制器的设计与运行点无关。仿真结果表明，所研制的控制器能够跟踪参考电压且提高暂态稳定性     

配电网中性点电阻接地方式标准的研究

研究了低阻与高阻接地方式的阻值确定标准。对以电缆为主的城市电网宜采用低阻接地方式，取值标准为10～20n；而高阻接地方式仅适用于电网电容电流在10A以下，以架空线为主的电网，取值标准为。对供电可靠性要求较高的重要用户采用消弧线圈串电阻接地方式是发展的必然趋势。