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1.
在研究层流扩散火焰时,很多人都忽略了轴向扩散作用。而一般的层流扩散火焰应该具有轴向扩散现象,尤其是在研究短火焰时更不应该加以忽略。本文在扩散的意义上既考虑了一般的径向扩散,又考虑了轴向扩散,推广了文献[1]的理论。此外还计算了几个例子,初步作了一些分析,说明忽略轴向扩散时所造成的误差。 相似文献
2.
湍流扩散多相流在许多工程和环境科学实际应用中十分常见.流体相中的湍流和扩散相的随机本质使得湍流扩散多相流中遇到的问题远比单一流体中遇到的湍流现象复杂得多.首先评述了湍流扩散多相流研究中实验技术和数值计算方面的现状、各自的优点与局限性,以及该领域研究中未来面临的挑战.主要关注湍流扩散多相流研究中以下3方面重点内容:颗粒、液滴和气泡的选择性聚积;湍流对流体相和扩散相耦合作用的影响以及颗粒物和气泡的存在对流体相中湍流的调节机制. 相似文献
3.
本文利用适当的标度变换将欧氏空间中的经典扩散方程抗议为分形点阵上的标准扩散方程,并应用该标准扩散方程证明了分形布朗粒子的运动服从反常扩散,同时还讨论了一般分形扩散方程及其渐进解。 相似文献
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大气边界层内羽流扩散研究 总被引:5,自引:0,他引:5
主要研究了高架点源的污染,即``羽流扩散'. 由于大气边界层内的湍流运动,引
起污染物扩散的主要因素是湍流扩散,
研究湍流扩散有两种基本方法:统计理论和梯度理论. 采用拉格朗日粒子扩散模型
(Lagrangian particle dispersion model,
LPDM)来评价羽流扩散的平均浓度,分别计算了表征扩散程度的3个参数:沿烟轴方向的
着地浓度、水平方向的羽流扩散宽度和垂直方向的羽流扩散宽度. 从计算结果和风洞实验的
数据对比来看,用该模式可以较好地模拟大气边界层内复杂气候条件下的羽流扩散. 相似文献
7.
本文通过合理地引入反常扩散系数,以均匀的,各向同性的分形介质中的反常扩散方程为基础,推导出了存在等待时间幂律分布的d≥2和d〈2两种情况下渗流网络上的一般反常扩散方程。 相似文献
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在工程技术问题中,譬如冲压发动机燃烧室内燃料逆气流方向喷射发展的下游流动以及为了防热目的采用所谓气膜冷却等实际问题中,往往遇到湍流射流在等速流动中的热量扩散与质量扩散过程。本文建议采用扩散系数随流动发展距离与流动速度的乘积而变的关系来求解两个简单问题:1.无限平面平行射流的扩散;2.距射流出口相当远处的扩散。 相似文献
10.
钎焊过程中在焊锡接点中形成的金属间化合物(IMC)对焊锡接点可靠性具有重要影响。在原子扩散效应下,回流焊和等温时效过程中IMC层的生长会在其内部产生应力,其微结构也发生变化,致使IMC层和整个焊点的力学性能下降。本文基于扩散反应机制,研究了由于原子扩散产生的IMC层的扩散应力。首先建立了焊锡接点IMC层生长早期微结构特征的2界面(Cu/Cu6Sn5/Solder)分析模型,然后运用Laplace变换法求解扩散方程得到了Cu原子在IMC层中的浓度分布;采用把原子扩散作用转换为体应变方法,计算了IMC层在形成和生长过程中应力的解析解。结果表明:IMC层中的扩散应力为压应力,最大值位于Cu/IMC界面处,大小与扩散原子浓度密切相关;随着时效时间的增加,扩散应力增大,但最终趋于稳定并沿IMC厚度方向线性变化。 相似文献
11.
In the present paper, based on the conservation law of mass and momentum for ion and electron, the distribution of velocity,
density of ions and electrons along radial direction are solved numerically. Furthermore, the comparison between MHD properties
of ambipolar and quasi-ambipolar diffusion is made. The numerical calculation is carried out for argon plasma. The results
show that the ion density, ratio of ion and electron velocity at the cathode sheath boundary surface increase with the intensity
of magnetic induction, meanwhile, the distance between sheaths decreases as well as the radial velocity of ion and electron
at the anode sheath boundary. The ion density varies in accord with experiment qualitatively[1]. All parameters mentioned above are not sensitive to magnetic field in ambipolar diffusion. 相似文献
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Nonlinear Dynamics - The generation of ion-acoustic solitary waves is investigated in a nonuniform multicomponent collisional plasma sheath containing cold ions and Boltzmann electrons to probe the... 相似文献
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V. K. Kalashnikov Yu. V. Sanochkin 《Journal of Applied Mechanics and Technical Physics》1976,17(2):150-155
The structure of the anode sheath and the characteristics of the closed Hall current discharge occurring in plasma accelerators are investigated in the diffusion approximation. The analysis takes account of weak processes (variation of ionization frequency with electron energy, electron energy losses, presence of a detachment region at the anode). The distributions along the sheath of potential, particle densities, currents, and other parameters are obtained. The effect on the characteristics of the discharge of varying the magnetic field and the input of working substance is considered. Weak processes are shown to have a significant effect on the structure of the sheath.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 9–16, March–April, 1976. 相似文献
14.
J. A. Kok 《Applied Scientific Research》1956,5(1):445-453
Summary In this paper experiments are described showing the different types of electrical discharges in a gas-filled triode. The determining parameters are the following: the cathode emission, the spacing of cathode, grid and anode, the diameter of the meshes of the grid, the potentials of the grid and the anode, the gas pressure and the differential ionization function of the gas. The anode voltage may be concentrated in a space charge sheath. If this space charge sheath is located at the grid, the anode current may be modulated with moderate grid potentials. If not, much larger voltages are required for modulation. 相似文献
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R. Sh. Ismalov 《Fluid Dynamics》1994,29(2):291-298
The structure of the glow-discharge anode sheath is investigated analytically in the one-dimensional formulation within the
framework of a diffusion-drift approximation. Charged particle recombination reduces significantly the anode potential drop
and the width of the anode zone. Given fairly heavy current, which is typical of anode spots, the contribution of the diffusion
processes becomes significant because of the reduced width of the anode sheath. Analytical estimates of the anode potential
drop and the width of the anode sheath which satisfactorily describe the results of numerical calculations are obtained.
Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.2, pp. 172–180, March–April, 1994. 相似文献
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V. Zh. Madirbaev A. E. Zarvin V. V. Kalyada N. G. Korobeishchikov 《Journal of Applied Mechanics and Technical Physics》2000,41(2):220-224
The excitation of light emission of the 0-0 band of the first negative system of the nitrogen ion by activation of nitrogen
molecules using short pulses of fast electrons was studied. The intensity and width of the light response were measured as
functions of the duration and amplitude of the exciting current pulse and of the density of nitrogen molecules. The contribution
of slow secondary electrons to the excitation of the ions increases with increase in both the gas density and the duration
of the current pulse. Since the processes of excitation of ions by fast primary and slow secondary electrons are separated
in time, when measuring the light-signal intensity, it is possible to determine the contribution of secondary electrons to
the excitation.
Novosibirsk State University, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 41,
No. 2, pp. 20–24, March–April, 2000. 相似文献
17.
The electric characteristics of a sphere located in a flow of viscous, electrically quasi-neutral weakly-ionized gas containing electrons and monovalent ions are investigated theoretically and numerically. As in the majority of applications, the electrogasdynamic (EGD) interaction parameter is assumed to be small. This makes it possible to solve the gasdynamic and electric equations successively. The spherical surface is assumed to be conducting and heat-insulated. At low free-stream Mach numbers the gas temperature is almost constant in the region of flow past the sphere. This makes it possible to use the model of a viscous incompressible medium. The flow past a sphere is analyzed for gasdynamic Reynolds numbers varying over the interval 0 ≤ Re ≤ 1000. The electrodynamic equations in which the convection and diffusion of the electrons and ions and their electrical drift are taken into account are reduced to three elliptic equations for the electron and ion concentrations and the electric potential. A constant potential is assigned on the boundary of the computation region simulating infinity. The entire problem is simulated numerically using specially constructed grids. The charged-component, potential, and electric current fields are determined and the volt-ampere characteristics of the sphere are constructed for various gas velocities. The results obtained generalize the available data on the voltampere characteristics of a sphere (probe) in a weakly-ionized medium at rest. 相似文献
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本文围绕新型对称双阴极固体氧化物燃料电池电堆单元在不同集流位置下热应力分布情况和优化集流方式,建立了一个基于电-化-热-力多场耦合理论的三维SOFC 电堆单元数值模型.引入固体力学热-力学理论,结合Weibull 失效概率分析方法,讨论了不同集流方式对SOFC 内部应力分布及失效的影响.研究结果表明,双侧阴极同时开展电子集流方式下的电解质平均电流密度比单侧单一集流方式下高,改变阳极集流位置会改变电极高温区的分布;SOFC 电堆单元上电极结构处的最大主应力明显大于其他组件上的最大主应力;阳极集流位置设置在阳极气体入口处时电极结构上的最大主应力和失效概率大于集流位置设置在阳极气体出口处的最大主应力和失效概率. 相似文献
19.
Max Hoyaux 《Applied Scientific Research》1956,5(1):253-258
Summary A new theory of the mercury arc has been developed which allows the calculation of some parameters of an industrial rectifier. It takes into account the following phenomena: gas ionization by electrons, electron extraction at the cathode spot by ionic bombardment, magnetic autostriction and the scattering of electrons by the Coulomb field of positive ions. Agreement with experiment is very good.The latter part of this work has been sponsored by the European Office of A.R.D.C., U.S.A.F. 相似文献
20.
The effective collision frequency of electrons and ions which leads to temperature equalization in a plasma in a constant magnetic field and a weak high-frequency electric field when the gyroscopic radius of the electrons is less than the Debye screening radius is determined. The corresponding values of the relaxation time are determined over a wide range of values of the ratio between the electron and ion temperatures, over a wide range of values of the magnetic and electric fields, and also as a function of the frequency of the external electric field.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 41–48, November–December, 1970. 相似文献