周期性环境条件下相变材料对系统热控效果的影响

运行于户外周期性环境条件下的热控系统在工业领域有重要应用价值,降低系统能耗和提高温控效果是其性能改进关键所在.为此,采用实验和仿真手段研究了热控系统围护结构中相变材料(PCM)对系统热控效果的影响.典型气象日研究结果表明,相较于聚苯乙烯,PCM在广州地区能显著降低系统能耗(75.4%)、目标表面温度波动幅度(76.1%)和轴向温差(56.9%),在南京和吐鲁番地区可分别降低目标表面温度波动幅度41.3%和30.6%,但对系统能耗和目标轴向温差无改善;典型气象年结果表明,PCM在广州地区同样表现出热控优势,但热控效果对控温设定点、PCM相变范围和环境温度波动有很强的依赖性,当所选PCM相变范围包含控温设定点且与环境温度波动范围一致时,PCM能最大限度提高热控效果.     

大功率T/R组件相变温控平板热管的散热特性实验研究

为保证大功率相控阵天线T/R组件的长时间稳定工作，提出了一种相变储能平板热管的热控设计方案，该系统中的相变材料和平板热管分别发挥储热和热扩散的作用。实验对比了铝制平板热管和铝合金板的热扩散性能，以及它们分别和相变材料结合后的热控性能。实验结果表明，铝制平板热管的传热性能优于铝合金，在40 W时其冷凝端的最大温差为3.2℃,且等效热阻可维持在0.35 K/W以下；当热源置于侧边时，相比置于中间位置时的蒸汽扩散和液体回流路径较长，平板热管的热扩散性能下降；同时，与使用铝合金作为储热容器底部基板时的局部过热现象相比，采用相变储能平板热管的热控设计，可以将热源的热量进行均匀扩散，降低热流密度，从而表现出更好的温度均匀性，再通过相变储能的方式吸收热量，可以保证天线产品持续工作90 min时的结点温度控制在70℃。对于高纵横比的槽道式平板热管，需要进一步改良槽道的毛细结构，降低蒸汽扩散和液体回流路径的差异对热扩散性能的影响。     

相变贮热材料及其在太空中的应用

相变贮热材料是绿色材料，种类达4300多种，具有清洁和节能等优点。系统地介绍了相变贮热材料分类及其特点，讨论了相变贮热材料在太阳能热动力发电、航天器仪器仪表的恒温控制、舱外航天服方面的应用。     

一种耐高温多层热防护组件结构设计与性能研究

研究了由多种功能层材料组成的热防护组件的结构设计方法与热防护性能.利用仿真计算模拟了高温热环境下由不同厚度的面板层材料与隔热层材料组成的热防护组件的热响应行为,并通过石英灯加热考核验证了优化设计的热防护组件的耐温隔热与可重复使用性能.结果表明,致密的面板层材料具有优异的耐温性能,而由气凝胶组成的隔热层材料具有极低的热导率.根据目标环境匹配设计两种功能层材料厚度,可使多层热防护组件具备经最高温度1 600℃的加热考核后,背温仅为118℃的优异耐温隔热性能.      

变轨高温发动机热辐射对空间站尾部对接机构的热影响

根据空间站尾部变轨发动机和被动式对接机构的几何特点和航天器热控理论,提出一种组合系统的热分析物理、数学模型,着重研究高温变轨发动机热辐射对邻近对接机构的热影响.计算表明,2个高温变轨发动机热辐射对空间站尾部对接机构的热影响范围大致在周向角θ=(90°±30°)～(270°±30°),材料表面的发射率εd是影响对接机构组件温度的重要因素.在整个变轨期间,对接框的周向温差和最高温度已升到90℃,温度绝对增幅高达83℃,均大大超出对接机构温度的设计值,严重威胁机构部件的运动和固定功能,空间站尾部对接机构的热控措施将必不可缺.     

航天器热控系统的可靠性设计与分析

针对国内外航天器热控制、热管理技术的发展现状,在详细调研各种航天器热控系统组成原理与功能实现方式的基础上,从可靠性的角度出发,归纳、总结了航天器热控系统中串联、并联、表决、储备四种常见的可靠性设计模式及其相应的可靠性分析计算模型,介绍了其在空间站、月球探测系统、火星探测系统等典型航天器上的应用范例,为进一步的航天器热控系统可靠性设计方法与理论分析奠定了基础。     

相变微胶囊半径及含量对织物热湿性能影响数值研究

为了指导织物内相变材料的设计,基于织物热湿耦合模型,发展了一个考虑附加相变微胶囊影响的织物内热湿传递模型．采用控制体积法和有限差分法对模型方程进行了求解．预测结果和实验数据吻合良好．基于所建模型,研究了相变微胶囊半径及含量对织物热湿性能影响．数值结果表明,在当织物温度达到相变材料（PCM）的相变温度区间时,相变材料具有延迟织物内温度变化作用．PCM半径越小延迟温度变化幅度越大,但延迟时间短．PCM含量越多延迟织物温度变化的效果越好．     

激光载荷相变材料热控装置力学性能及升温特性研究

针对登月航天器激光载荷热控要求设计了一种采用十八烷作为相变材料的热控装置,使用ANSYS有限元分析软件对该装置的壳体进行了耐压强度分析,并搭建了实验装置,对该热控装置在振动条件以及真空热条件下的力学特性进行了实验研究.结果表明,在实验范围内,相变材料热控装置的壳体不会发生塑性形变和泄露.同时对其升温特性进行了实验研究,分别探讨了不同加热功率以及重力对相变材料升温特性的影响,实验结果表明,相变材料固液共存阶段比单相阶段的升温速率慢、历时长且吸收的热量多,同时,相变材料在发生相变时引起的自然对流对换热的整体效果影响可以忽略.     

相变蓄能砌体外墙中间歇通风的热过程分析

基于焓法模型,利用Fluent软件模拟分析南京地区民用建筑南外墙在夏季典型气候与太阳辐射共同作用下,绝热材料发泡聚苯乙烯(EPS)与相变材料(PCM)在三排孔砌块中不同组合时,间歇通风风速变化对室内的热影响.结果表明:相变墙外孔中为保温材料、内孔中为相变材料(构造B)在流速为2 m/s时效果最佳,在此流速下稳定后的一个周期内,室内温度波动值与热流密度相对于无机械通风分别降低了67.5％和74.04％,且温度波动平均值等于相变温度31.1℃,这样能充分发挥相变材料的作用.     

基于相变材料的锂离子电池热管理

相变材料被动式冷却利用相变材料相变时温度基本保持不变吸收或放出热量的特性,对电池组进行热管理。该冷却方式具有寄生功耗低、温度均匀性好、吸收或释放热量多等特点。但由于相变材料导热系数普遍较低,难以满足电动汽车在高电流密度工况下的电池热管理要求,从而限制了相变材料在电池热管理中的进一步应用。如何有效地提高相变材料的导热系数,同时保证其储热能力和化学稳定性,成为了研究相变材料电池热管理系统的关键问题。通过强化传热措施包括添加导热颗粒、金属翅片、泡沫金属和膨胀石墨可提高相变材料的导热系数。总结了四种强化相变材料传热的措施的研究进展,并概述了其传热措施的影响因素和强化传热效果。     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

Wuhan University Journal of Natural Sciences TOTAL CONTENTS

<正>~~     

Advances in broadband wireless communications under high-mobility scenarios

Future mobile communication systems aim at providing very high data transmission rates, even in high-mobility scenarios such as high-speed wheel-track trains, maglev trains, highway vehicles, airplanes, guided missiles or spacecraft. A particularly important commercial application is the strong and increasing worldwide demand for high- speed broadband wireless communications （up to 574.8 km/ h test speeds or 380 km/h commercial speeds） in railways, providing data, voice and video services for applications such as onboard entertainment services to passengers, train control, train dispatch, train sensor status handling and sur- veillance. In such high-mobility scenarios, there are a number of communication challenges, including fast hand- over, location updating, high-speed channel modeling, estimation and equalization, anti-Doppler spreading tech- niques, fast power control, and dedicated network architec- ture. Because signal transmission in very high-speed scenarios will inevitably experience serious deterioration, it is imperative to develop key broadband mobile communi- cation techniques for such high-speed vehicles.     

Perspherical Approaches for Electrons in Atoms and Charged Excitons in Quantum Wells

Instead of following Fock’s expansion,we solve the Schrodinger equation for some quantum mechanical manybody systems such as electrons in atoms and charged excitons in quantum wells in a similar way in hyperspherical coordinates by expanding the wave functions into orthonormal complete basis sets of the hyperspherical hannonics(HHs)of hyperangles and generalized Laguerre polynomials(GLPs)of the hyperradius.This leads the equation to     

Scale-based spatial data model for GIS

Being the primary media of geographical information and the elementary objects manipulated, almost all of maps adopt the layer-based model to represent geographic information in the existent GIS. However, it is difficult to extend the map represented in layer-based model. Furthermore, in Web-Based GIS, It is slow to transmit the spatial data for map viewing. In this paper, for solving the questions above, we have proposed a new method for representing the spatial data. That is scale-based model. In this model we represent maps in three levels: scale-view, block, and spatial object, and organize the maps in a set of map layers, named Scale-View, which associates some given scales.Lastly, a prototype Web-Based GIS using the proposed spatial data representation is described briefly.     

英文诗歌中的喻类修辞

为了有助于提高英文爱好者的个人情操、文化素养和学习兴趣,以及专业人员对英语学习和研究进行多途径的探索,本文通过一些精选诗歌的引证和分析,着重论述了喻类修辞法在英文诗歌中的运用其及效果。     

Man Is Unable to Change the Miserable Life——Analysis of the Arrangement of Four Characters in The Glass Menagerie

Tennessee Williams is considered as one of the most important American playwrights since World War II.The Glass Menagerie is his first successful drama,which describes a tragic situation of family and means to say that Man is unable to change the miserable life,no matter whatever means he try,This essay focuses on the analysis of the arrangement of the four main characters:Laura.Amanda,Jim and Tom to reveal the theme.Laura is fragile.Amanda is brave.Jim is vital.Tom is sensible.And all of them develop and try the different means to struggle against life,but fail tragically.With the evidence,the paper comes to conclusion naturally that Man is unable to change the miserable life,and he dooms to fail.     

Characterization of root-nodulating bacteria on Retama raetam in arid Tunisian soils

The aim of this study is to investigate the diversity of Retama raetam root-nodule bacteria isolated from arid regions of Tunisia. Twelve isolates, chosen as representative for different 16S rRNA gene patterns, were characterized by 16S rRNA gene sequencing and phenotypic analysis. Isolates were assigned to Sinorhizobium, Rhizobium and Agrobacterium. Symbiotic properties of Sinorhizobium and Rhizobium isolates showed a large diversity in their capacity to infect their host plant and fix atmospheric nitrogen. Strain RK 22 identified as Rhizobium was the most effective isolate.     

Features of Women''s language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

An Affordable Accurate Evaluation of the Binding Conformations Predicted by Molecular Docking Studies in Bio-System

正Recently,docking has been widely used to predict the binding-modes of protein-inhibitors,when the crystal complexes structure was absent.Most docking algorithms are able to generate a large number of probable conformations,it,however,is difficult to effectively evaluate these docking poses and identify the most reasonable bindingmode.In the present study,on the basis of the crystallographic data of human 3-hydroxy-3-methylglutaryl coenzyme