轿车车室内温度场和速度场的数值模拟北大核心

数值模拟了汽车车室内的温度场和速度场,忽略太阳辐射,采用RNG模型,近壁面用壁面函数法进行处理,分析了不同的送风速度,送风温度,出口压力对汽车室内温度场和速度场分布的影响,对车室内的温度场和速度场的均匀性做出评价并对其优化。结果表明在车室后排空间添加一个送风口,可以有效地改善车室内温度场和速度场分布的均匀性,温度场均匀性提高了36.5%,速度场均匀性提高了45.2%。     

轿车车室内温度场和速度场的数值模拟

数值模拟了汽车车室内的温度场和速度场,忽略太阳辐射,采用RNG模型,近壁面用壁面函数法进行处理,分析了不同的送风速度,送风温度,出口压力对汽车室内温度场和速度场分布的影响,对车室内的温度场和速度场的均匀性做出评价并对其优化。结果表明在车室后排空间添加一个送风口,可以有效地改善车室内温度场和速度场分布的均匀性,温度场均匀性提高了36.5%,速度场均匀性提高了45.2%。     

结构内部非均匀温度场的重建方法研究

结构内部温度的测量与控制在国防军事、机械制造、材料加工、火灾防治和医疗卫生等领域都具有十分重要的作用。本文建立了超声波法测量结构内部非均匀温度场的理论模型,发展了预测结构内部温度场的解析方法和反演方法,系统分析了采样点数、测量误差、模型边界等对重建方法精度的影响。研究表明,该方法能够准确地预测结构内部非均匀温度场分布状态,并具有非常好的抗噪性,对高温物体的温度测量具有更佳的预测精度。     

均匀和非均匀温度场条件下的长周期光纤光栅透射谱的研究

从理论上推导了长周期光纤光栅在均匀温度场和非均匀温度场中透射谱的特性,并实验验证长周期光纤光栅在均匀温度场中和非均匀温度场的光谱特性。实验证明,随温度升高,光纤光栅谐振波中心向长波方向漂移,反之亦然,且漂移量与温度的变化量呈线性关系。在非均匀温度场中,当长周期光纤光栅的光栅两端温度差改变时,谐振波的3dB展宽呈线性递增趋势。     

定向红外光空间分布误差对冷冻靶温度场的影响分析

在惯性约束核聚变中,决定点火成功与否的关键因素在于靶丸内燃料冰层的均匀性,而影响靶丸内燃料冰层均匀性的主要因素为靶丸温度场均匀性.为了提升靶丸温度场均匀性,采用定向红外辅助均化装置实现对靶丸表面温度场的局部调控.在定向红外装置的运行过程中,红外光空间分布误差会影响到靶丸温度场的调控效果.建立了定向红外光线追踪与温度场计算耦合的数值模型,并与实验进行对照分析,确定了数值模型良好的计算精度.采用三维的冷冻靶物理模型,研究了不同形式的定向红外光空间分布误差对靶丸温度场的影响规律.结果表明:光轴偏心对靶丸温度场均匀性的影响最为剧烈,光带间距变化的影响次之,光带宽度的变化对靶丸温度场均匀性的影响最小.在实验中应当尽可能避免南北两侧光带光轴的偏心,从而保证靶丸表面温度均匀性,进而可以保证靶丸内燃料冰层的均匀性.     

急冻间内流场对冻品温度均匀性的影响

针对急冻间内冻品摆放方式对内部流场和温度场的影响,采用CFD模拟与实验相结合的方法,在空载工况下将数值模拟结果与实验测量的速度分布数据进行对比,验证标准k-ε模型的合理性。采用标准k-ε模型,通过数值计算获得不同货架位置、冻品层间距离对冻结均匀性的影响。研究结果表明,货架距离过大或过小都将导致温度不均匀性较高,最优货架距离为100 mm,达到完全冷冻需要6.9 h。优化冻品层间距离后达到完全冷冻需要6.8 h,比优化前减少了6.8%。     

涡流管冷却的旋转晶体窗口有限元分析

采用有限元分析方法,考虑到输出窗口在空间上的分布不均匀性,对白宝石、石英晶体窗口在光强分布均匀/不均匀、有/无冷却、是否旋转等各种情况下的温度场进行了分析和讨论.结果表明当光强分布不均匀时,采用旋转方法能有效地减小温度场的不均匀性;当对输出窗口进行强迫冷却时,输出窗口温度场不均匀性明显减小.因此采用涡流管冷却的旋转晶体窗口能有效改善输出窗口的输出特性.     

冷藏集装箱内部温度场的理论与实验研究

冷藏集装箱内部的温度分布是冷藏集装箱设计中关注的要点,因此文中通过建立冷藏集装箱物理模型和数学模型对其温度场进行了数值模拟和实验研究。利用稳态不可压缩N-S时均方程及k-ε模型进行模拟分析,结果表明:冷藏集装箱内部温度场存在明显的不均匀性,箱体前部与后部的温度存在明显的差异,不利于货物的储存。实验实测温度与模拟温度的偏差低于16.4%,说明所建立的模型适用于冷藏集装箱内部温度场的模拟。研究结论对进一步开展冷藏集装箱货物配载以及结构设计研究具有一定的指导与借鉴意义。     

三维复杂温度场高精度声学测量方法

声学温度场检测技术通过多路径声波传播时间数据,反演被测区域的温度分布。提供了一种高精度的三维复杂温度场的声学测量方法。首先从射线声学角度给出了三维非均匀温度场中声波传播路径的数学模型。在此基础上,将三维温度场的重建问题转化为声波传播路径的求解和温度场的反演问题,建立了基于多项式修正径向基函数(RBF-PR)和改进的Tikhonov正则化三维温度场重建算法。采用两种典型的炉膛三维温度场模型,在信噪比SNR=35 dB下进行了数值模拟,分析了声波传播路径在非均匀温度场中的弯曲特性、算法的重建质量和抗噪性,同时进行了实际炉膛内二维温度场的重建。结果表明了提出的考虑声线弯曲的温度场重建算法具有精度高,抗噪性强、适用性好的特点,为实现高精度的复杂温度场的声学测量提供了有效方法。      

蓄热换热与有害气体分解的实验研究

采用蜂窝陶瓷蓄热换热器实现高温烟气与空气的高效换热,实验研究了蓄放热时间对高温温度场均匀性的影响, 探讨了蓄热周期对烟气和空气进出口温度特性的影响,利用燃烧产物实现了四氟化炭高温分解。     

Complex diagnostics of insulating materials in industrial electrostatics

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.     

Trap-assisted tunnelling current in MIM structures

A new model is presented of current transport in Metal Insulator Metal (MIM) structures by quantum mechanical tunnelling. In addition to direct tunnelling through an insulating layer, tunnelling via defects present in the insulating layer plays an important role. Examples of the influence of the material and thickness of the insulating layer, energy distribution of traps, and metal work functions are also provided.     

用1064nm激光脉冲触发半绝缘GaAs光电导开关的研究

报道了用1064nm激光脉冲触发电极间隙为8mm的半绝缘GaAs光电导开关的实验结果.在触发光能为1.9mJ,偏置电压分别为3kV和5kV条件下,光电导开关分别工作于线性和非线性模式,结果表明半绝缘GaAs光电导开关可以吸收1064nm波长的激光脉冲.讨论了半绝缘GaAs材料对1064nm激光脉冲的非本征吸收机制,指出GaAs材料禁带内的EL2深能级和双光子吸收对半绝缘GaAs吸收1064nm光脉冲起主导作用.     

Electrostatic ignition hazards due to pneumatic transport of flammable powders through insulating or dissipative tubes and hoses – New experiments and calculations

During transportation of powder through pipes or hoses made from insulating materials, electrostatic discharges can occur. To define the resistivity limit of the insulating material for the avoidance of propagating brush discharges, the charging current due to the powder transfer was determined experimentally using different types of hoses and bulk material. The subsequent modeling shows that propagating brush discharges will not occur if such hoses are constructed from dissipative materials or when the resistance measured from the inner surface to the conductive structure of the hose multiplied with the contact area of the electrode is below 4 MΩ m².     

Electrostatic behaviour of wood and laminate floor coverings and current situation in standardisation

The tendency for laminate floor coverings to electrically charge can have consequences for the user. A charge can build when an insulating material, such as insulating flooring, comes into contact to another material, such as footwear. For human beings the threshold of sensation is roughly 2 kV of body voltage when touching grounded objects. As a consequence, manufacturers of laminate floor coverings strive to find technical solutions for antistatic laminate floor coverings to be able to declare products as “antistatic”, defined in EN 14041. This standard is based on measurements of a bodies’ voltage, according to the new EN 1815.     

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介绍了EAST快速控制线圈的设计参数、电磁水冷分析和安装过程。引线部分受到巨大的垂直于自身方向的震荡力,常规的有机绝缘材料不能满足要求。线圈的绝缘材料采用MgO粉末,并在引线两端增加支撑固定。水冷计算表明,铜导体和水的稳定温度与点到进水口的距离成线性关系;当线圈通电电流为20kA时,为了保证出水口的水温不被加热至100℃,水的最小流速与运行效率的关系为v≈6K。     

Fabrication and characterization of epoxy/silica functionally graded composite material

Increased use of composites in aerospace and defense application induces the search for heat resistant material. In present study silica reinforced epoxy functionally graded material using quartz fabric is prepared with different thickness. The gradation in silica : epoxy matrix is maintained with one side pure epoxy to opposite side pure silica. Thermal and mechanical behaviour of the composites were studied. It was found that the temperature gradient of 350°C to 950°C could be maintained for 2 to 5 min if the thickness of insulating silica layer is increased from 0.5 mm to 16 mm. Mechanical properties such as flexural modulus and strength of FGM composites were also evaluated. Strength and modulus decreased with increase of insulating layer.     

Prebreakdown State and Its Diagnostics in Multilayer 0.55Pb–Mg1/3Nb2/3O3–0.45PbSc1/2Nb1/2O3 Compounds

Physics of the Solid State - The determination of the breakdown voltage and the diagnostics of the prebreakdown state of a material is a topical problem of studying characteristics of insulating...     

Polaron defects in a charge density wave: a model for lightly doped BaBiO3

A model for BaBiO₃ was introduced by Rice and Sneddon, which treats this material as a simple three-dimensional version of a Peierls insulator, where the insulating gap is a consequence of the ordered distortion of the oxygen atoms. Charge accumulates on half the atoms and depletes from the other half. Experimentally, when holes are added to BaBiO₃ by doping, it remains insulating until a very large hole concentration is reached, at which point it becomes superconducting. In the Rice-Sneddon model, at large enough electron-phonon coupling, a mechanism for insulating behavior of doped samples is formation of small polarons or bipolarons which trap carriers in bound states in the Peierls gap. A variational calculation of the polaron binding in this model is given, and compared with “exact” numerical results on large clusters with periodic boundary conditions.     

Sound insulating characteristics of porous ceramic Al2O3-SiO2

In a previous paper,¹ the sound absorbing capacity of porous ceramic materials was found to increase with increasing flow resistance up to a certain value of such resistance, and then to decrease. When the sound absorbing capacity decreases with an increase in flow resistance, it may be estimated that the sound insulating capacity will increase. In the present investigation, the sound insulating characteristic in porous ceramic Al₂O₃-SiO₂ has been treated on the basis of Beranek's theoretical treatment of an acoustical material. The theoretical and experimental results show that the sound insulating capacity, usually called the transmission loss, increases with increasing flow resistance.