基于PIC-MCC实现空气介质阻挡放电过程的数值模拟

在大气压介质阻挡放电的实际应用中,空气介质阻挡放电具有极其广泛的工业化应用前景。目前,空气均匀放电的获得仍比较困难,且诊断均匀性的依据缺乏可信的依据。文章采用粒子云网格法(Particle in Cell,PIC)与蒙特卡罗碰撞（Monte Carlo Collision,MCC）方法模拟了放电过程中粒子的运动情况,研究大气压下空气介质阻挡放电的发展过程,然后讨论介质厚度、电源频率对形成均匀放电的影响,并研究这两种因素对等离子体密度的影响。模拟结果表明：介质厚度在d≥1.5 mm时可获得没有放电细丝的电流波形;电源频率高于2.5 kHz时,放电细丝是难以避免的。在能够形成均匀放电的条件下,将介质厚度适当的调整在1.5 mm附近,提高电源频率,将产生更高的等离子体密度。     

接地电极转动对电极不对称介质阻挡放电的影响

本文的目的是确定接地电极转动对介质阻挡放电的影响.采用不对称电极结构来降低外加的工作电压.实验的结果表明:接地电极静止或转动介质阻挡放电将呈现不同的放电形式和电流波形.文中对其原因进行了讨论.     

利用大气压气液介质阻挡放电等离子体对PTEF进行表面改性

本文对大气压单一空气介质阻挡放电和加去离子水的气液两相介质阻挡放电进行实验研究,对比分析了两种放电模式的开始放电和刚铺满整个电极时的稳定电压电流波形和放电照片,并用两种放电等离子体对聚四氟乙烯薄膜(PT FE)进行表面处理,对处理后薄膜表面的水接触角进行对比.结果表明,放电间隙和放电频率均相同时,大气压单一空气放电的开始放电电压峰峰值和稳定放电电压峰峰值均比气液两相放电时的高,且气液两相放电更加均匀.在相同条件下,经大气压气液两相等离子体处理后的PT FE薄膜表面水接触角比大气压单一空气等离子体处理后的低,说明大气压气液两相等离子体对PT FE薄膜的处理效果更好.     

低气压介质阻挡放电暂态过程的理论研究

介质阻挡放电是放电与淬灭的交替过程。通过电极表面电荷积累效应的一个简单模型，建立了玫组自洽方程用来描述这种介质阻挡放电的暂态过程。然后通过数值解给出了氦气放电的暂态电流曲线。此方法同样可以用于其它气体的介质阻挡放电过程。     

梳状电极结构对大气压表面放电的影响

研究了梳状电极结构对大气压表面放电的影响,发现频率固定时放电电流随着外加电压的增加而增加,而电压固定时在某个频率范围内放电电流有最大值;在相同的电压和频率下较宽的电极条宽可以产生较大的放电电流,而电极条间距对放电电流几乎没有影响;用整块金属板做接地电极相比于梳状接地电极可以产生较大的放电电流;另外,较厚的高压电极可以在介质板表面产生更明亮、厚度更大的放电等离子体.     

介质阻挡稳态丝状放电数值模拟

本文采用流体模型对纯Ne介质阻挡放电(DBD)中的丝状放电现象进行了研究.通过模拟获得了放电过程中电流、带电粒子等物理参数的时间空间分布及丝状放电的形成.结果表明,在pd值较低及方波驱动电压条件下,初始均匀的DBD中将逐渐形成多个稳定的丝状放电通道,而且所有通道的丝状放电同时进行,形成单个放电电流脉冲.同时模拟结果表明,在辉光放电范围内,升高pd值,丝状放电的数量将减少.     

大气压氦气射频介质阻挡辉光放电的均匀性研究

为了研究大气压射频介质阻挡辉光放电的时空特性,采用一个表面覆盖有石英介质的铜电极和一个自制水电极的放电系统,在氦气中获得了大面积和较大电极间距下的辉光放电。对ICCD高速相机拍摄的径向放电图像和轴向放电图像分析揭示了射频介质阻挡辉光放电不仅具有较好的径向均匀性,而且具有很好的轴向均匀性,并不存在沿径向的发展。这是不同于中频介质阻挡辉光放电的一个显著特征。此外,注意到射频介质阻挡辉光放电在径向和轴向上的发展均与射频周期有很强的关联性。分析认为这是由于空间电荷在射频介质阻挡辉光放电的形成和发展中发挥主导作用。因此,可以认为射频介质阻挡辉光放电所具备非常好的径向和轴向均匀性,与中频介质阻挡辉光放电相比,可能会更有利于工业生产中进行均匀薄膜沉积和对薄膜表面改性处理等。     

人体可接触的悬浮电极介质阻挡放电研究

针对低温等离子体处理人体皮肤和组织等生物医学应用中开发人体可接触低温等离子体源的需求,本文设计了一种灵活的悬浮电极结构的介质阻挡放电低温等离子体发生装置,来在空气中产生人体可接触的低温等离子体。通过合理的选择绝缘外套来实现手持灵活移动电极,通过合理选择阻挡介质来限制放电电流,实现人体安全接触。本文通过电气和光学特性诊断研究了所设计装置的放电特性,在进行人体接触试验基础上,建立了装置的等效电路模型,来对人体接触的安全性进行论证。结果表明,所设计的电极结构灵活安全,人体可以安全接触,当外加电压在低于5 kV且气隙间距为0.5 mm时,消耗的放电功率小于0.5W,传输电荷小于50nC,放电电流幅值小于10 mA。等效电路模型分析结果表明,当外加电压4 kV至6 kV,且气隙间距小于1 mm时,流过人体的工作电流不超过3.82 mA。     

H2对彩色AC-PDP中Ne-Xe混合气体放电性能的影响

使用AC—PDP宏放电单元测试了AC—PDP放电单元加入少量H2对Ne-Xe混合气体放电性能的影响。结果表明，Ne-Xe混合气体中加入少量H2时会显著改变AC—PDP的着火电压、维持电压和放电电流等放电性能参数。当输入电压频率一定时，着火电压和最小维持电压都会随着H2含量的变化而变化，并且着火电压和最小维持电压在某-H2含量下存在最小值；当心含量一定时，着火电压和最小维持电压随着输入电压频率的增大而增大；在Ne-Xe混合气体中加入H2后，起始放电电流会随着心含量的增加而增大。但是，当H2含量一定时，起始放电电流会随着输入电压频率的增加而增加，并在某一特定频率下达到最大值；当输入电压频率继续增加达到某一更高的值时，加入H2的Ne-Xe混合气体的起始放电电流反而会降低至未加入H2时相同。     

多孔阳极氧化铝介质对大气压介质阻挡放电等离子体的影响北大核心CSCD

为了提高大气压下介质阻挡放电的稳定性,采用阳极氧化方式在铝板表面制备一层多孔阳极氧化铝(Porous anodic alumina,PAA)。运用扫描电子显微镜、划痕仪、金相显微镜和台阶仪测试了阳极氧化铝的表面形貌、厚度等特性。比较分析了石英、陶瓷和PAA为介质的大气压下介质阻挡放电的放电过程图片和放电波形。实验表明:应用阳极氧化法制备的多孔阳极氧化铝具有规则的纳米级多孔结构,膜基结合力好;应用多孔阳极氧化铝作为介质的介质阻挡放电更稳定,放电中产生的更密的微放电有助于降低放电击穿电压和提高放电稳定性;更厚的多孔阳极氧化铝膜为介质的大气压介质阻挡放电具有更好的放电稳定性。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

水三相点复现的不确定度评定

水三相点是开尔文热力学温度的唯一基准点，也是ITS-90国际温标重要的定义固定点。因此，水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来，中国计量科学研究院研制出一系列高质量的水三相点容器，加强了水三相点的研究，为不确定度的分析提供了更为可靠的实验依据。同时，不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此，根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明，其扩展不确定度为0．16mK(k=2．69，P=0．99)。