电弧等离子体一维非定常数值模拟

 通过对毛细管内等离子体工作过程的分析给出了电弧等离子体的一维非定常数学模型,以热力学参量描述了非理想条件下等离子体的状态方程和电导率计算方法。利用差分法求解该数学方程组,给出了毛细管内电弧等离子体特征参量在毛细管内沿轴向随时间的变化规律。对数值模拟结果作相应的分析,并将部分模拟结果与实验数据作了比较。     

Effect of shape factor on the electrokinetic response of slot-like capillaries

The effect of the shape factor on the electrokinetic response of pressure-driven liquid flow through slot-like capillaries is analyzed in this work. The electrokinetic response is found by first solving for the electrical potential using the Poisson–Boltzmann equation, and then using it as an input to construct an external force term in the Navier–Stokes equation. It is found that flow properties are significantly modified for small pore sizes with hydraulic radius in the range of microns and submicrons, according to the properties of the electrolyte solution. The modified flow rate in the presence of such electrokinetic effects can be less than 50% of the predictions expected with conventional flow models such as Darcy's equation. Apparent viscosities larger than expected are calculated using the reduced flow. Actual values are dependent on the capillary dimensions, pressure gradient, solid-surface conductivity, and properties of the electrolyte fluid. For a rectangular capillary cross-sectional geometry the apparent viscosity and friction coefficients values decrease with the shape factor in a nontrivial way. These results are relevant for the modelling of certain porous formations of interest to the oil industry.     

Dynamics of Interface Displacement in Capillary Flow

The dynamics of capillary flow has several practical applications in the industry and has been extensively investigated. The main focuses in these studies are the motion of the interface, especially near the three-phase contact line, and the change of contact angle during the invasion process. In this work we present several simulations results of capillary invasion in two- and three-dimensions, using the Lattice–Boltzmann model based on field mediators. We investigate the velocity field near the solid surface, the changes in the contact angle as a consequence of the flow, and the boundary conditions that can be used in the inlet and outlet of the capillary tube. In all simulations the diameter of tube is made large enough to enable the evaluation of the contact angle directly from the density field and the results of capillary rise are compared with a theoretical model based on the Bosanquet equation, which includes capillary, viscous, inertial and gravitational effects.     

Study on a New Ignition Method of the Spark Gap Based on Plasma Ejection in Air

A new ignition method of the spark gap based on plasma ejection is proposed in this paper, as the conventional trigatron spark gap performs poorly under the low working coefficient (the ratio of the charging voltage to the self‐breakdown voltage) in air. The plasma is generated by the capillary discharge, which has high pressure, high temperature and high velocity. The capillary discharge device is placed inside the low voltage electrode. As long as the triggering signal is sent to the device, a column of the plasma flow is ejected in axial direction and develops rapidly towards the high voltage electrode. Subsequently, the gap is broken down and a high resistive channel is formed, where the thermal ionization takes place and the arc across the whole gap is generated and develops into a well conductive channel. The process of the thermal ionization of the high resistive channel varies with the change of the spark gap distance. The breakdown delay and the delay jitter of the spark gap increase with the spark gap distance, as both parameters are mainly determined by the developing process of the plasma ejection. The characteristics of the plasma flow determine the possibility of the breakdown of the spark gap under the low working coefficient. The ignition method based on capillary plasma ejection has been proved by the preliminary experiments, which indicate that under the gap length of 8 cm and the working coefficient of less than 3%, the effective ignition is still achievable.     

Steady flow through a narrow capillary of an arbitrary cross-section: rigorous solution

The rigorous solution is obtained for the kinetic equation describing the steady flow of the gas in the narrow capillary of an arbitrary cross-section. The particle mass flux through the capillary cross-section is calculated. The case of the elliptic cross-section is investigated in detail as an illustrative example of the presented general solution.     

Consistent treatment of critical plasma flows in high pressuredischarge ablative capillaries

A self-consistent solution of generalized, quasi-one-dimensional nonideal fluid equations describing the steady-state critical plasma flows in high pressure capillary discharges is presented. All three equations used (continuity, momentum and energy) include (ablative effects). No limitation to the case of ideal equation of state or to the spatial uniformity of the ionization degree is imposed. A numerical algorithm enabling the determination of self-consistent boundary conditions required for the integration of the differential equations is used. Illustrative result for typical physical parameters, namely, electrical current and radius and length of the capillary, are presented for polyethylene capillaries. The effects of changes in the geometrical characteristics of the capillary as well as in the electrical and radiative characteristics of the discharge on the plasma parameters are also considered     

Simultaneous iso-electric focusing of proteins in a micro-fabricated capillary coated with hydrophobic and hydrophilic plasma polymerized films

The ability to modify and reduce the electroosmotic flow (EOF) is one of the most influential parameters which affects iso-electric focusing (IEF) of proteins. Therefore capillaries are usually coated with polymers or gels to prevent non-specific adsorption and suppress the EOF in capillary iso-electric focusing (cIEF) of proteins. In this research hexamethyldisiloxane (HMDS) and 2,3-epoxy-1-propanol (glycidol) plasma polymerized films were deposited onto both surfaces of the capillary separation channel. Cathode solution pH 3, anode solution pH 10 and a carrier ampholyte, pharmalyte provided the necessary stable pH gradient. Simultaneous IEF of proteins in capillaries coated with hydrophobic and hydrophilic plasma polymerized films occurred within minutes. The electroosmotic force of uncoated glass capillaries was suppressed by 50% after deposition of 200 nm 2,3-epoxy-1-propanol compared with a 30% reduction of EOF when the capillary was coated with 200 nm HMDS. The hydrophilic 2,3-epoxy-1-propanol plasma polymerized film was more resistant with a stronger attachment to the glass surface than previously prepared acetonitrile plasma polymerized films.     

一种新型大气压毛细管介质阻挡放电冷等离子体射流技术

介绍一种结构设计简单、操作运行方便的新型毫米量级大气压冷等离子体射流发生技术.这种射流可以在大气压条件下，利用多种工作气体(如Ar,He,N₂)，通过毛细管介质阻挡放电(DBD)的方式实现.使用频率为33kHz，峰值电压为1—12kV的双向脉冲电源，利用Ar,He,N₂等工作气体，在毛细管内形成了稳定的冷等离子体射流.放电区域的光辐射空间分布利用商用CCD摄像机记录，从中研究放电形态和空间分布，观察到了在DBD区域的流动气体放电和在毛细管出口处形成的等离子体射流 关键词： 冷等离子体射流 毛细管介质阻挡放电 射流射程 射流激发温度     

Low-frequency potential structures in a nonuniform dusty magnetoplasma

The linear and nonlinear properties of a modified convective cell (MCC) in a nonuniform dusty magnetoplasma with a perpendicular plasma flow are investigated. It is shown that the free energy of the equilibrium plasma flow can drive the MCC at nonthermal levels. By choosing some specific profiles for the sheared plasma flow and the dust number density, we analyze the eigenvalue equation for deducing the growth rate and the threshold of a convective mode instability which arises due to its interaction with the shear plasma flows. Our analytical results show that a Rayleigh-type instability sets in provided that the characteristic width of the flow does not exceed a certain value. On the other hand, the nonlinear equation, which governs the dynamics of the nonlinearly interacting convective modes, admits stationary solutions in the form of a vortex chain associated with zonal flows, as well as tripolar and global vortices. The relevance of our investigation to a laboratory experiment is discussed.     

Transient electro-osmotic flow of generalized Maxwell fluids in a straight pipe of circular cross section

The transient electro-osmotic flow of a generalized Maxwell fluid with fractional derivative in a narrow capillary tube is examined. With the help of an integral transform method, analytical expressions are derived for the electric potential and transient velocity profile by solving the linearized Poisson-Boltzmann equation and the Navier-Stokes equation. It was shown that the distribution and establishment of the velocity consists of two parts, the steady part and the unsteady one. The effects of relaxation time, fractional derivative parameter, and the Debye-Hückel parameter on the generation of flow are shown graphically and analyzed numerically. The velocity overshoot and oscillation are observed and discussed.     

激光驱动的毛细管等离子体尾波特性

基于激光等离子体尾波解析模型,分析了毛细管中激光与等离子体相互作用,数值计算了尾波中基本物理量。计算结果表明:毛细管等离子体尾波幅度与毛细管半径有关,在较小的毛细管中尾波幅度更大。在相同的激光与等离子体参数情况下,与无界等离子体尾波相比较,毛细管等离子体尾波中电子空泡纵向尺度、电场强度峰值、角向自生磁场强度峰值提高了60%,这些特征都表明毛细管等离子体尾波更有利于电子加速。     

毛细管电泳和电感耦合等离子体质谱接口技术进展

毛细管电泳与电感耦合等离子体质谱联用 (CE ICP MS)具有分离效率高、灵敏度高、分辨率高、样品用量少和检测限低等优点。已广泛应用于环境、生物等样品的元素形态分析。毛细管电泳与ICP MS雾化器之间的接口是CE ICP MS联用技术的关键。本文综述了影响接口性能的重要因素 ,包括毛细管出口端的电流导通、雾化器的设计和流速匹配等 ;讨论了保证毛细管内电流导通并稳定四种方法 :同心包层液导电、不锈钢组件导电、银箔导电及铂丝导电等 ;综述并比较了同心气动雾化器、微同心雾化器、高效雾化器、新接口技术、超声雾化器、直接注射雾化器六种类型的雾化器的结构和性能。引用文献 35篇。     

常气压辉光放电等离子体对边界层流动的影响

基于Shyy提出的常气压下均匀辉光放电等离子体与空气干扰的物理模型,通过求解电位势方程得到电场分布及作用于流体上的电场力.以NACA0015翼型低速绕流为对象,通过数值求解考虑等离子体作用的流体运动控制方程,研究等离子体位置和个数控制对翼型绕流分离的影响.位于分离点上游的等离子体能够有效地抑制流动分离,而在分离区的等离子体对流动影响很弱,这一结论同实验观察一致,并给出等离子体对翼型壁面压力和气动力影响的规律.     

Thermal noise influences fluid flow in thin films during spinodal dewetting

Experiments on dewetting thin polymer films confirm the theoretical prediction that thermal noise can strongly influence characteristic time scales of fluid flow and cause coarsening of typical length scales. Comparing the experiments with deterministic simulations, we show that the Navier-Stokes equation has to be extended by a conserved bulk noise term to accomplish the observed spectrum of capillary waves. Because of thermal fluctuations the spectrum changes from an exponential to a power law decay for large wave vectors. Also the time evolution of the typical wave vector of unstable perturbations exhibits noise-induced coarsening that is absent in deterministic hydrodynamic flow.     

Double layers in an inhomogeneous magnetized bi‐ion plasma

A simpler analytical approach is employed to obtain energy integral equation for a pseudo‐particle in a pseudo‐potential, which admits double layer (DL) solutions for the non‐linear low‐frequency electrostatic perturbations in non‐uniform plasma consisting of electrons and two kinds of ions. One of the ion species has field‐aligned shear flow and electrons are superthermal kappa distributed. This theoretical model is applied to the upper ionospheric oxygen‐dominated plasma that has small concentration of protons along with upward flow of oxygen ions. Under suitable boundary conditions, both rarefactive (density dip) and compressive (density hump) DLs are obtained solving energy integral equation using the plasma parameters of ionosphere around altitude of 800 km. The amplitude and width of the DLs depend upon the scale lengths of density and temperature gradients as well as on the ratio of equilibrium densities of oxygen and hydrogen.     

两间隙毛细管等离子体射流发生器主放电数值模拟

 消融放电毛细管等离子体发生器产生的等离子体射流具有密度高和温度相对低的特性,在许多领域都具有潜在的应用前景。利用1维流体模型对两间隙毛细管等离子体射流发生器的主放电特性进行了模拟计算分析。模型考虑了焦耳热效应和管壁烧蚀对放电特性的影响。在管壁消融这种反馈稳定机制作用下,毛细管放电处于准稳态,其产生的等离子体温度在放电期间保持恒定。在放电能量为1 kJ的条件下,聚乙烯毛细管等离子体温度可达3 eV,电子密度可达1025 m-3量级,射流速度接近10 km/s。改变放电输入的焦耳热功率密度,等离子体温度和速度变化较小,但气压、质量密度以及等离子体电子密度等特性参数均可以获得较大幅度的改变。     

Instabilities of uniform filtration flows with phase transition

New mechanisms of instability are described for vertical flows with phase transition through horizontally extended two-dimensional regions of a porous medium. A plane surface of phase transition becomes unstable at an infinitely large wavenumber and at zero wavenumber. In the latter case, the unstable flow undergoes reversible subcritical bifurcations leading to the development of secondary flows (which may not be horizontally uniform). The evolution of subcritical modes near the instability threshold is governed by the Kolmogorov-Petrovskii-Piskunov equation. Two examples of flow through a porous medium are considered. One is the unstable flow across a water-bearing layer above a layer that carries a vapor-air mixture under isothermal conditions in the presence of capillary forces at the phase transition interface. The other is the vertical flow with phase transition in a high-temperature geothermal reservoir consisting of two high-permeability regions separated by a low-permeability stratum.     

微通道内红细胞流动与变形的可视化研究

微循环条件下,红细胞的尺寸与血管相近,血液不能视为均质流体,其流动表现出较强的颗粒性,红细胞流变特性对血液流动有较大影响。本文使用高倍显微镜对微流控芯片矩形截面微通道内红细胞的流动和变形特性进行可视化观察研究,并使用高速CCD相机拍摄和捕捉了红细胞在微通道内的流动和变形过程。通过观察不同浓度、粘度和速度下红细胞的聚集性、变形性以及常见的运动形态,发现红细胞在低粘度、低速流动条件下表现为两面凹圆盘形,沿流动方向运动过程总是伴随着翻转与旋转;在高粘度、高速运动条件下,红细胞表现为扁平椭圆形、呈坦克履带式(TTM)前进。     

On the rate of descent of powder in a vibrating tube

The flow rate of powder in an open vertical capillary subject to transverse acoustic vibration is predicted using an explicit equation by considering the intermittent arrest and stasis of particles subject to acceleration in a field. The analysis rests solely on physical quantities that are easily measured by experiment. The calculation is supported by measured flow rate and by direct observation using high speed photography. Increasing the horizontal component of acceleration of a particle should not influence rate of descent but the overall time of flight is increased both by re-initiation of descent after collision at the wall and by fixed stationary periods on each cycle. Since flow stops when acoustic vibration stops, the vibrating tube is a valve that provides computer-controlled powder flow metering, mixing and dispensing. The valve is capable of adjusting the flow rate with a ratio of minimum to maximum flow rate of 0.1. It is being used to make three-dimensional functional gradients by solid freeforming operations, notably selective laser sintering.     

一个推广的回旋动力方程

本文导出了一个新的回旋动力方程。该方程能够描述沿磁力线有宏观速度的环形等离子体的低频不稳定性,也适用于有外加极向电场的环形等离子体。