Encapsulation of PV modules using ethylene vinyl acetate copolymer as a pottant: A critical review

The primary purpose of this work is to review the literature about what is and is not known about using ethylene vinyl acetate (EVA0 copolymer as the encapsulant (or pottant) material in photovoltaic (PV) modules. Secondary purposes include elucidating the complexity of the encapsulation problem, providing an overview about encapsulation of PV cells and modules, providing a historical overview of the relevant research and development on EVA, summarizing performance losses reported for PV systems deployed since ca. 1981, and summarizing the general problems of polymer stability in a solar environment. We also provide a critical review of aspects of reported work for cases that we believe are important.Failure modes resolved in the early work to establish reliability of deployed modules and the purposes and properties of pottants, are summarized. Typical performance losses in large field-deployed, large-scale systems ranging from 1% to 10% per year are given quantitatively, and qualitative reports of EVA discoloration are summarized with respect to ultraviolet (UV), world-wide location and site dependence.The general stability of polymers and their desirable bulk properties for solar utilization are given. The stabilization formulation for EVA, its effectiveness, and changes in it during degradation are discussed. The degradation mechanisms for the base resin, e.g., unstabilized Elvax 150^TM, and stabilized EVA are indicated for literature dating to the early 1950s, and the role played by unsaturated chromophores is indicated. The limited number of studies relating discoloration and PV cell efficiency are summarized.Observed degradation of EVA or the unstabilized base resin in the laboratory and examples used to measure the degradation are summarized in sections entitled: (1) thermally-induced degradation; (2) photodegradation and photothermal degradation of EVA in different temperature regimes; (3) photobleaching and photodegradation of the UV absorber and cross-linking agent; (4) acetic acid and metal and metal-oxide catalyzed oxidative degradation; and (5) discolaration and PV cell efficiency losses.Processing effects/influences on EVA stability are discussed in sections entitled: (1) EVA raw materials and extruded, uncured films; (2) thermal encapsulation processes; (3) effects of lamination, curing, and curing peroxide on gel content and chromophores formed; and (4) incomplete shielding of curing-generated chromophores. A summary is given for the limited number of accelerated lifetime testing efforts and examples of erroneous service lifetime predictions for EVA are discussed. The known factors that effect the discoloration rate of several EVA formulations are discussed in which the reduction in rate by using UV-absorbing superstrates is a prime example. A summary is given of what is and is not known about EVA degradation mechanisms, degradation from exposures in field-deployed modeules and/or laboratory testing, and factors that contribute to EVA stability or degradation. Finally, conclusions about using Elvax 150 in EVA formulations are summarized, and future prospects for developing the next-generation pottant for encapsulating PV modules are discussed.     

Geometric features of the flame propagation process for an SI engine having dual‐ignition system

Flame front surface area and enflamed volume (the volume enclosed with flame front) is theoretically analysed for a spark‐ignition engine, having cylindrical disc‐shaped combustion chamber with two spark plugs located axisymmetrically on cylinder head, between cylinder axis and cylinder wall. Spherical flame front assumption is used. A computer code is developed based on purely geometric consideration of the flame development process in combustion chamber, and is used to investigate the effects of variations of spark plugs' locations on geometric features of the flame front. A comparison has also been made with a spark‐ignition engine having one spark plug at the same location. Copyright © 2002 John Wiley & Sons, Ltd.     

代数曲面的几何连续过渡及其应用

本文对代数曲面的几何连续拼接作了研究，给出了多个代数曲面的几何连续过渡方法，同时给出了一种基于分片的曲面过渡方法。     

矢量图的参数化重建系统——VACAD

本文重点探讨了如何将矢量图形进行参数化重建，即从只具备纯几何信息的矢量图中抽取元素间的拓扑信息，从而保证尺寸变动时保持拓扑关系不变，并能对多视图进行同步处理。这一方法的最大优点是用户作图时不受约束，因为系统只处理最终图形。另外，该思想并不局限于Ａｕｔｏ ＣＡＤ环境上，可方便地推广到其它二维绘图系统中。     

超声波处理石油污水的实验研究

考察了在不同空化状态下超声波对石油污水化学耗氧量(COD)的降低作用。探讨了时间、功率、pH值及温度对石油污水化学耗氧量降低作用的影响。结果表明，石油污水化学耗氧量的降低率随着时间增大而增大，随着温度、pH值的增加而减小，随着功率的增加，先增加，然后再减小。     

TiO_2纤维的制备、表征及其光催化活性

采用常压乙二醇法制备出在可见光下具有较高催化活性的TiO2纤维。扫描电子显微镜表征结果表明,TiO2纤维直径为0.8～2.0μm、长度为5～25μm;BET比表面积和X射线衍射表征结果表明,随焙烧温度的升高,比表面积减小,TiO2纤维晶型逐渐由锐钛矿型向金红石型转变;紫外-可见漫反射光谱分析结果表明,TiO2纤维在可见光区有明显的吸收。在可见光下对甲基橙和苯酚的降解实验表明,焙烧温度为400℃时TiO2纤维的催化活性最好,对甲基橙和苯酚的降解率分别达到90.3%和84.0%;所制备的TiO2纤维比溶胶-凝胶法制备的锐钛矿型TiO2在可见光下具有更好的催化活性,原因是其能带间隙减小和吸收波长扩展到可见光区所致。     

应用线性相关分析方法探讨国土卫片几何畸变纠正的精度

我国卫星影像具有空间分辫率高，比例尺适中的特点。由于国土片是全.景成像比例尺变化大，用它来编绘专业地图，给精度衡蚤带来很大困难，需要对国土片进行几何校正。本文试图用线性相关分析方法，分析经过AR月尧卜n图像处理系统刘正的国土片几何精度。以便为分析专题图精度提供依据，同时也为分析遥感影像几何精度介绍一种方法。     

Urban growth and environmental degradation: The case of Cairo, Egypt

The immense growth of cities, especially in developing countries, is resulting in the urbanization of both poverty and environmental degradation to a greater degree than ever before. This paper examines the processes of growth and degradation in the Greater Cairo Metropolitan Region (GCMR), currently the world’s tenth largest mega-city. It reviews the region’s growth and selected environmental issues as well as impacts of current efforts on managing the region. The assertion of this paper is that current management policies and bodies lack a comprehensive view of urban governance for the region, which does not bode well for the future environmental and economic sustainability of the region.     

Investigations of surface characterization of silicone rubber due to tracking phenomena under a.c. and d.c. voltages

In the present work, tracking phenomena has been studied with silicone rubber material under the a.c. and d.c. voltages following IEC-587 standards. The surface condition of the tracked zone was analysed using wide angle X-ray diffraction (WAXD) and thermogravimetric differential thermal analysis (TG-DTA) studies. The tracking time was different for a.c. and d.c. voltages.     

Thermal degradation of cinnamoylated poly(vinyl alcohol)

Thermogravimetry and pyrolysis in combination with gas chromatography and infrared spectroscopy were the experimental techniques applied to the thermal degradation of cinnamoylated poly(vinyl alcohol) samples, constituted from vinyl alcohol-vinyl cinnamate photocrosslinkable copolymers. The thermal decomposition products include gases, liquids and solids. The gases are formed from saturated and unsaturated volatile hydrocarbons C₁? C₄, carbon monoxide and carbon dioxide. The liquid fraction includes aromatic hydrocarbons and some oxygenated organic compounds. The solid product identified in the greatest amount was cinnamic acid. The content in the thermal decomposition products varies considerably both with copolymer composition and temperature.