共查询到20条相似文献,搜索用时 140 毫秒
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HFC-32饱和气导热系数的实验研究 总被引:5,自引:0,他引:5
1研究背景自《蒙特利尔议定书》签定后,特别是1992年11月哥本哈根会议以来,HCFCS的替代日程已经确定。目前以含有HFC-32的混合物替代HCFC-22的呼声很高,而且国外正开始着手应用。有关HFC-32的饱和气的导热系数现在还没有见文献报导。在本文中,作者自行开发设计了一套双热线法测量导热系数的实验装置,并对HFC-32的饱和气的导热系数进行了测量,经分析测量结果是令人满意的。2实验装置及实验原理热线法是测量导热系数的瞬态方法之一,其基本原理是Carslaw提出的半径趋于零的无限长线热源在无限大介质中的导热方程的解山文献… 相似文献
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四丁基溴化铵(TBAB)水合物浆体在常压下的相变温度介于0-12℃之间,作为蓄冷材料使用时由于相变过程的存在使得其蓄冷能力较高,而且在管道中具有良好的流动特性,因而是一种理想的蓄冷和冷量输送材料。对比分析了传统导热系数计算公式和基于一维非稳态导热模型导出的导热系数计算公式的区别。利用热线装置分别测量了TBAB溶液和水合物浆体的导热系数。实验得出5-30 wt%TBAB溶液的导热系数在0.4-0.6 W.m-1.K-1之间,并随浓度的增加而减小;10-40vol%的水合物浆体的导热系数在0.5-0.6 W.m-1.K-1之间,并随体积分数的增加而增大;相同体积浓度时A型水合物浆体的导热系数大于B型水合物浆体的导热系数。 相似文献
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三氟碘甲烷的新气相状态方程和输运物性 总被引:2,自引:0,他引:2
提出了三氟碘甲烷(CF3I)的新蒸气压方程和新状态方程;给出了CF3I的偏心因子、正常沸点等物性参数,并与文献值进行了比较.使用毛细管粘度计测量了CF3I的253~338K的饱和液粘度,采用以钽丝为热线的双线瞬态热线法测量了CF3I的气相导热系数,并分别给出了关联式. 相似文献
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《Journal of Electrostatics》2007,65(8):535-541
This work is in the research field of partial discharges to electrical insulating materials. A theoretical model is proposed that simulates the partial discharge's development within a metal (solid insulating material) metal structure. A nonlinear, time-dependent resistance using a new formula simulates the activity of partial discharges in dielectrics and the suggested equivalent circuit is analysed. Comparison of the experimental results and the outcome of the model demonstrates satisfactory consistency. Slight deviations consist of a minor phase shift between the computed and measured waveforms, as well as small oscillations of the waveform measured in the vicinity of the potential steps. These deviations are attributed to a very small parasitic inductance, which is always present in the measuring circuit. 相似文献
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Zoltán ádám Tamus 《Journal of Electrostatics》2009,67(2-3):154-157
The possible use of insulating materials is basically determined by their electrical properties (i.e. resistivity, dielectric strength) in many new technologies in several branches of the industry. The application of these materials is strongly determined by the physical and chemical properties resulting from the material structure. During lifetime many chemical processes start up in the material (e.g. decreasing of the content of the additives, breaking of polymeric chains) and the molecular structure of material is altered. The changes are reflected in the physical properties and it can dramatically decrease the applicability of the insulating materials. According to the complexity of the materials and the complexity of the stresses the changing of material properties can only be precisely investigated by complex diagnostic measurements.The use of complex investigation (parallel electrical, chemical, mechanical examinations) of insulating materials is introduced in the paper. Based upon the complex insulation diagnostics and the resulted database of different insulating materials to be applied in industrial electrostatics the possible use of complex non-destructive insulation diagnostics is drawn for practical purposes. 相似文献
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Thermodepolarizing current spectra for components of mica-based insulating composites are presented. The variation of the thermograms with experimental conditions is revealed. The data reported are the initial results of elaborate measurements in this area and can be used in devising new insulating materials and new methods for the quality control of insulators. 相似文献
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A technique developed for calculating the discontinuity flaw of an adhesive contact and the adhesion energy for two bodies makes it possible to take into account these effects in designing a multilayer cermet wall (insulating barrier) of the liquid-metal blanket in a fusion-type reactor. The technique is based on a model of a linearly elastic medium, in which strains are proportional to external forces, and on the assumption that any body in equilibrium possesses minimum internal potential energy. Expressions are derived for calculating the area of an adhesive contact between two bodies and their adhesion energy. Calculation data illustrate the dependence of these two parameters on the values of the Young modulus and Poisson’s ratio for various pairs of materials, including the most suitable materials for insulating barriers of liquid-metal blankets. 相似文献
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In this work, the insulating layer with a weakly conductive layer on its surface is charged with a needle electrode. The quantities that are measured and calculated are the transients of charging current and transferred charge. In addition, we calculate charge distribution in the weakly conductive layer at various moments of time, and potential kinetics. By comparing the calculation results with measurement data, it is possible to determine sheet resistance of the investigated weakly conductive layer. This sheet resistance can be also determined experimentally: during charging of the weakly conductive layer (deposited onto the insulating layer), the charging current and the deposited charge increase with decreasing sheet resistance of the weakly conductive material, hence its sheet resistance can be related to the measured charging current or to the deposited charge. The proposed method can be applied for measuring sheet resistances from 10+8 Ω/sq to 10+12 Ω/sq, and those measurements can be done in a second. It is also possible to use the contact-free method proposed in this work to measure various properties of the medium related to the material sheet resistance, e. g. relative air humidity, illumination, sample thickness, intensity of ionizing radiation, etc. This method is also suitable for measuring sheet resistance of island-type (discontinuous) layers, which is difficult to measure using usual methods. Results of this work make it possible to determine potential of a two-layer system consisting of a charged low-conductance layer and an insulator, as well as the radius of an electrographically developed area, which is important, for example, when the image is created using a needle electrode. 相似文献
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William M. Yen 《Physics of the Solid State》1999,41(5):693-696
In this paper we shall review techniques for the growth of single crystal, mostly of insulating material, which are shaped
during the growth process. In particular, we shall focus on the growth of single-crystal fibers of optically activated materials;
the emphasis will be placed on the so-called Laser Heated Pedestal Growth (LHPG) method of pulling crystalline fibers. LHPG
offers a number of logistical advantages which can be exploited as a tool for materials research. Progress in the synthesis
of materials using LHPG is described, as are spectroscopic techniques which are employed in characterizing the optical and
physical properties of the crystal fibers obtained by this method.
Fiz. Tverd. Tela (St. Petersburg) 41, 770–773 (May 1999)
Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor. 相似文献
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This work is mainly based on the paper “R. Rinkunas, S. Kuskevicius, A contactless method of resistance measurement, Tech. Phys., 59 (2009) 133–137”. This paper contains a proposed contact less method for measuring resistivity of various materials, as well as various ambient parameters related to resistivity, e.g., humidity, intensity of illumination, sample thickness, etc. The mentioned paper describes experimental applications of the proposed method for measuring resistances in the range from 107 Ω to 1013 Ω.In this work, a model of the method proposed previously is presented. On the basis of that model, it has been determined that during charging of an insulating layer of a material (on whose surface the deposited ions are immobile), the charge flux becomes wider as it approaches the surface of the insulator. For example, the diameter of the charge flow region may increase from 0.2 mm (near the needle tip) up to 2 cm near the surface of the insulator. [Those numbers correspond to the distance h = 1 mm between the needle and the substrate, insulating layer thickness 40 μm and needle–substrate voltage of 4000 V. A change of those parameters would cause a change of the size of the spot on the layer surface].It has been determined experimentally that resistance of the air gap between the needle and the substrate is linearly dependent only on h, whereas the electromotive force, which is responsible for the electric current from the needle to the substrate, also depends only on h.The radial coordinate of the points where the gradient of the electric charge density is largest is equal to h/2 (a zero radial coordinate corresponds to the point that is directly below the needle).During transfer of charge carriers from the needle onto the surface of the insulating layer, the largest potential is obtained at the point corresponding to radial coordinate r = 0, but this potential is still smaller than the electromotive force that causes electric current in the circuit (i.e., the difference between the power supply voltage and the voltage on the capacitor formed by the needle and the substrate, when no charge has been deposited yet).The time dependence of charging current and of the potential difference between the needle and the substrate is not monotonic: at first the current increases, then it begins to decrease, and the potential difference at first decreases, then it begins to increase. The initial parts of those dependences can be explained by the “breakdown” of the capacitor formed by the needle and the substrate, and the subsequent time dependence is determined by the increase of the insulating layer potential due to accumulation of charge on it. 相似文献
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Feng Chen 《固体与材料科学评论》2008,33(3-4):165-182
Ion beam implantation has been used not only to modify some properties of the bulk materials but also to construct waveguide structures in many optical substrates by accurate control the refractive index in selected regions. This paper reviews the recent development of ion beam implantations on fabrication of two-dimensional (2D) optical waveguides, i.e., in cases of channel or ridge configurations, in diverse insulating optical materials by giving detailed fabrication methods and research progress obtained to date. Future prospects of practical applications in photonics are also discussed briefly. Another aim of this work is to show the challenging task of this field, that is, to create practical 2D waveguide devices applicable in any existing insulating optical materials. 相似文献
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《Journal of Electrostatics》2014,72(1):59-64
A new experimental procedure is proposed which uses the Scanning Electron Microscope Mirror Effect (SEMME) for the dynamic investigation of charge trapping in insulating materials. This experimental procedure allows to the mirror method which is usually described as static to be considered as dynamic. The dynamic trapping properties of the polymethyl-methacrylate (PMMA) polymer material are investigated and the time constants of charge processes are evaluated for various accelerating voltages. The experimental results reveal that the values of trapped charge at steady state obtained by the proposed procedure are in good agreement with these obtained using the electrostatic influence method (EIM) under the identical experimental conditions of electron irradiation. 相似文献