Experimental investigation of the shape of a heavy-current air discharge without blowing

The results of investigating experimentally the shape of an are discharge burning between two electrodes in air at atmospheric pressure in the absence of blowing when the currents are less than 100 A are reported. In certain experiments the distance between the electrodes was varied in order to solve special problems. The effect of the electrode material on the shape of the discharge is investigated. It is found that the electrode material does not have a qualitative effect on the shape of the discharge but can lead to a significant variation in the parameter distribution over the discharge gap. The study is a continuation of the research described in [1].     

Experimental Investigation of the Interaction between an Electric Arc and a Gas Flow

The results of investigating the shape of an electric arc carrying an electric current of less than 100 A and exposed to an air, nitrogen, or argon stream at a stream velocity of from zero to 20 m/s, when the interelectrode gap is less than 20 mm, are reported. The shape of the arc is qualitatively investigated as a function of the gas type, blowing velocity, and interelectrode gap. It is shown that an arc burning in a channel with insulated walls is much more stable under these conditions than an arc with the same parameters burning in free space.     

Corona discharge in a moving gas

Some aspects of the theory of corona discharges in a moving medium are considered. Two situations are analyzed: a corona discharge at a negative electrode under the condition that in the region of electrogasdynamic flow exterior and interior regions of the discharge can be distinguished, the motion of the gas being taken into account only in the exterior region, and corona discharge at a negative electrode under the condition that the effects of the motion of the gas are important in both the exterior and the interior regions of the discharge. For the first situation, a mathmatical generalization is proposed of the traditional model of the interior region, and dimensional and similarity methods are used to obtain functional relationships for the current—voltage characteristics of the discharge in the moving medium. The second situation is investigated for the example of a corona discharge between cylindrical electrodes through which gas is blown or sucked. In this case, the solution to the problem is found without dividing the flow region into exterior and interior regions of the discharge, a system of kinetic equations describing the flow in the complete interelectrode gap being used.     

Experimental investigation of the distribution of the charged particle concentration in the interelectrode gap of a freely burning atmospheric arc

The results of an investigation of the distribution of the charged particle concentration in the interelectrode gap of an arc burning freely in an air atmosphere for currents I = 50–100 A by means of a moving dual electric probe are presented. The methods used enable the probe voltage-current characteristic to be measured in times ～ 100 µs. This makes it possible to estimate the distribution of the charged particle concentration in the interelectrode gap during a single experiment. The charged particle distributions obtained are compared with the distribution of the various glow-level zones [1, 2]. On the basis of this comparison it is shown that the characteristic transverse dimension of the zone in which the current flows in the arc far away from the electrodes is of the order of a centimeter.     

Theoretical investigation of a low-pressure arc discharge in a cylindrical diode

Using systematic numerical calculations of an arc discharge in a coaxial interelectrode gap, the potential drops and the electron density and temperature are obtained as a function of the current density, the plasma pressure, the azimuthal magnetic field, and the interelectrode distance. General conclusions are drawn from the relations obtained.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 170–174, November–December, 1971.     

Modeling of the transient processes in the channels of an EHD pump

The nonstationary process of development of weakly conducting electrohydrodynamic flow in the channel of an EHD pump with plane permeable electrodes, between which a potential difference is created from an external source, is considered in the hydraulic approximation within the framework of the model proposed in [1, 2]. It is shown that the efficiency of the EHD device can be improved if in the fluid the spatial process of ion formation is retarded, while the recombination process is intense. The effect of the flow velocity on the formation of a space charge region in the interelectrode gap is investigated. On a certain range of the problem parameters the flow induced in the channel substantially modifies the space charge distribution as a result of the blowoff of narrow diffusion electrode ion layers. This creates a nonmonotonic dependence of the fluid velocity on the applied potential difference.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.3, pp. 30–41, May–June, 1994.     

基于材料相变的声子晶体带隙可调结构设计与性能分析

提出一种基于材料相变的穿孔型带隙可调声子晶体结构.其结构形式为含缝隙的形状记忆合金和环氧树脂的组合体,通过温度变化诱发相变引起的形状记忆合金材料性质的变化,实现声子晶体的带隙变化;通过合理布置缝隙与形状记忆合金相变材料的位置,实现声子晶体带隙性质的可调设计.基于有限元方法,建立了可调声子晶体的分析模型,分析了形状记忆合...     

Use of shutdown of the capacitive storage in implementing electrical action on metallic shaped-charge jets

Tto improve the efficiency of electrical action on metallic shaped-charge jets, it is proposed to use shutdown of the capacitive storage at the time when the voltage on it during passage of an alternating discharge becomes zero. It has been shown that using this expedient eliminates recharging of the capacitive storage and provides better matching between the current pulse and the time of motion of various parts of the shaped-charge jet through the electrode gap. Studies have been conducted using a computational procedure in which the development of magnetohydrodynamic instability of the jet and the dispersion of its material are considered possible physical mechanisms reducing the penetration capability of shaped-charge jets under the action of high current pulses.     

Conditions near the electrode in a plasma with an alkali admixture

An analysis is made of the effects of certain processes in the interior of the gas and at the electrode surface on the potential drop near the electrode in a discharge in a dense, slightly ionized gas. Thermionic emission from the electrode, the Schottky effect, diffusion, and volume and surface ionization and recombination are taken into account. The analysis is carried out for a simple discharge-gap geometry: two infinite, plane-parallel electrodes. Relations are found for the potential drop near the electrode in a two-temperature plasma as a function of the discharge parameters and emission characteristics of the material. The calculated results are compared with experiment.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 4, pp. 3–12, July–August, 1971.The authors thank G. A. Lyubimov for interest in the study and for discussion of the results, and B. V. Parfenov for graciously furnishing the necessary experimental data from [13].     

Balancing particle properties for practical lithium-ion batteries

As a state-of-the-art secondary battery, lithium-ion batteries (LIBs) have dominated the consumer electronics market since Sony unveiled the commercial secondary battery with LiCoO₂ as the negative electrode material in the early 1990s. The key to the efficient operation of LIBs lies in the effective contact between the Li-ion-rich electrolyte and the active material particles in the electrode. The particle properties of the electrode materials affect the lithium ion diffusion path, diffusion resistance, contact area with the active material, the electrochemical performance and the energy density of batteries. To achieve satisfied comprehensive performance and of LIBs, it is not only necessary to focus on the modification of materials, but also to balance the properties of electrode material particles. Therefore, in this review, we analyze the influence of particle properties on the battery performance from three perspectives: particle size, particle size distribution, and particle shape. A deep understanding of the effect and mechanism of particles on electrodes and batteries will help develop and manufacture practical LIBs.     

Thermodynamic coupling between gradient elasticity and a Cahn–Hilliard type of diffusion: size-dependent spinodal gaps

In the electrode materials of lithium ion batteries, the large variations of Li concentration during the charge and discharge processes are often accompanied by phase separations to lithium-rich and lithium-poor states. In particular, when the composition of the material moves into the spinodal region (linearly unstable uniform compositions) or into the miscibility gap (metastable uniform compositions), it tends to decompose spontaneously under composition fluctuations. If the lattice mismatch of the two phases is not negligible, coherency strains arise affecting the decomposition process. Furthermore, when the dimensions of a specimen or a grain reduce down to the nanometer level, the phase transition mechanisms are also substantially influenced by the domain size. This size effect is interpreted in the present article by developing a thermodynamically consistent model of gradient elastodiffusion. The proposed formulation is based on the coupling of the standard Cahn–Hilliard type of diffusion and a simple gradient elasticity model that includes the gradient of volumetric strain in the expression of the Helmholtz free energy density. An initial boundary value problem is derived in terms of concentration and displacement fields, and linear stability analysis is employed to determine the contribution of concentration and strain gradient terms on the instability leading to spinodal decomposition. It is shown that the theoretical predictions are in accordance with the experimental trends, i.e., the spinodal concentration range shrinks (i.e., the tendency for phase separation is reduced) as the crystal size decreases. Moreover, depending on the interplay between the strain and the concentration gradient coefficients, the spinodal region can be completely suppressed below a critical crystal size. Spinodal characteristic length and time are also evaluated by considering the dominant instability mode during the primary stages of the decomposition process, and it is found that they are increasing functions of the strain gradient coefficient.     

Quantification of the effect of surface heating on shock wave modification by a plasma actuator in a low-density supersonic flow over a flat plate

This paper describes experimental and numerical investigations focused on the shock wave modification induced by a dc glow discharge. The model is a flat plate in a Mach 2 air flow, equipped with a plasma actuator composed of two electrodes. A weakly ionized plasma was created above the plate by generating a glow discharge with a negative dc potential applied to the upstream electrode. The natural flow exhibited a shock wave with a hyperbolic shape. Pitot measurements and ICCD images of the modified flow revealed that when the discharge was ignited, the shock wave angle increased with the discharge current. The spatial distribution of the surface temperature was measured with an IR camera. The surface temperature increased with the current and decreased along the model. The temperature distribution was reproduced experimentally by placing a heating element instead of the active electrode, and numerically by modifying the boundary condition at the model surface. For the same surface temperature, experimental investigations showed that the shock wave angle was lower with the heating element than for the case with the discharge switched on. The results show that surface heating is responsible for roughly 50 % of the shock wave angle increase, meaning that purely plasma effects must also be considered to fully explain the flow modifications observed.     

Modified boundary layer analysis of an electrode in an electrostrictive material

A thin electrode embedded in an electrostrictive material under electric loading is investigated. In order to obtain an asymptotic form of electric fields and elastic fields near the electrode edge, we consider a modified boundary layer problem of an electrode in an electrostrictive material under the small scale saturation condition. The exact electric solution for the electrode is obtained by using the complex function theory. It is found that the shape of the electric displacement saturation zone is sensitive to the transverse electric displacement. A perturbation solution of stress fields induced by incompatible electrostrictive strains for the small value of the transverse electric displacement is obtained. The influence of transverse electric displacement on a microcrack initiation from the electrode edge is also discussed.     

Mutual relationship of adsorption processes on the surface of a cathode and the processes taking place in the parts of a heavy-current plasma discharge close to the electrodes

The effect of alkali metal vapor on the work function of the cathode material in various MHD installations has as yet been little studied [1]. Nor has the mutual influence of adsorption processes on the cathode surface and processes taking place in the parts of a plasma discharge close to the electrodes, although this information is extremely vital in order to make a correct determination of the emission characteristics of cathodes in plasma. The manner in which the electrode becomes coated with the plasma material determines the work function of the electrode and thus the discharge current density and cathode potential drop _s. On the other hand, the degree of coverage of the cathode with the adsorbed particles depends substantially on the value of _s. In this paper we shall propose a method of calculating the emission characteristics of cathodes during a heavy-current plasma discharge allowing for the mutual influence of the processes in question. The problem is solved in a one-dimensional setting for an automatic thermionic-emission discharge (discharge of the spotless type).Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 5, pp. 29–32, September–October, 1972.     

Stability of a high-frequency glow discharge in the normal combustion regime

A high frequency glow discharge in its high current form differs from a dc discharge in that there is a significant decrease in the role of the pre-anode region in plasma generation [1], thus leading to greater stability [2]. In a dc discharge the pre-anode current-voltage characteristic (CVC) is falling [3], which causes electrodynamic instability of the plasma column and leads to its contraction over times much shorter than the thermal times [4]. It is characteristic that conductivity in the volume of a dc discharge at moderate pressures is caused by drift of ions from the pre-anode region. In an hf discharge the plasma distribution is symmetric about the midpoint of the interelectrode gap and the space charge zones near the electrodes are separated from the volume by narrow zones with high conductivity. Under such conditions, together with volume ionization processes a noticeable contribution to maintenance of conductivity can be produced by ambipolar diffusion and plasma drift due to disruption of quasineutrality [5, 6]. In order to study the stability of an hf discharge plasma column it is of interest to find the current-voltage characteristic of this part of the discharge under conditions of high longitudinal inhomogeneity and low values of E/p. In connection with the experimentally observed weak current form of the discharge [1, 2], which is characterized by a unique value of the normal current density and lacks a proper theoretical explanation, there has been increased interest in the properties of the hf discharge which are produced by phenomena in the pre-electrode regions. In particular, it is necessary to theoretically confirm the similar properties of the dc discharge and the hf discharge in the normal current density regime. The present study will present results of a numerical calculation of an hf discharge in nitrogen with consideration of space charge effects within the framework of a two-dimensional model and calculated the CVC of a plasma column with the diffusion-drift mechanism for maintenance of conductivity.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 16–26, November–December, 1986.The authors express their gratitude to N. A. Yatsenko for information provided during the course of the study, and to L. G. Gryukanov for performing the numerical calculations and assistance in formulating the results.     

Calculation of the thermally nonequilibrium near-electrode region in an alkali-metal-seeded plasma

Distribution of parameters in the region of disturbance of a plasma near the surface of an electrode is considered based on diffusion equations. Thermoelectronic and thermionic emission from the electrode surface, the Schottky effect, and volume ionization and recombination are borne in mind. Two regions are assumed in the solution, namely, the region of ambipolar diffusion and the region of the space charge. A comparatively simple geometry for the discharge gap, given in the form of two infinite plane-parallel electrodes, is considered. A comparison is carried out with calculations for a thermally balanced region of a plasma disturbance.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 13–17, January–February, 1976.     

Influence of magnetic reynolds number on the current distribution in a magnetohydrodynamic channel with allowance for the Hall effect

Stationary plane flow of a conducting gas across a magnetic field in a magnetohydrodynamic channel of constant cross section made up of electrodes of finite length and insulators is considered in the linear approximation. It is assumed that the electromagnetic forces are small. It is shown that the current density increases near the exit from the interelectrode gap with increasing magnetic Reynolds number. The mutual influence of the Hall parameter and of the magnetic Reynolds number on the distribution of the currents in the channel is investigated.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 148–152, May–June, 1971.     

Control of separated flows with the ionic wind generated by a DC corona discharge

This paper describes the investigation of a DC surface corona discharge established on a rounded edge of a dielectric material. The ionic wind induced by the discharge was measured with the Particle Image Velocimetry system. A physical induced flow model is proposed to interpret the shape of the velocity field. Experiments on a flat plate and a NACA 0015 were performed in a subsonic wind tunnel. They showed that the flow induced by this discharge acted close to the wall and modified the fully detached flow on the airfoil up to Re = 267,000 and 17.5° by a combined effect of the discharge and a Reynolds effect.     

On analysis of physical processes on the electrode surface in a rail launcher

This paper analyzes some physical effects that occur on the electrode surface in plasmaarmature rail launchers when the linear current density is higher than critical value. It is shown that under typical experimental conditions, Rayleigh–Taylor and Kelvin–Helmholtz instabilities and magnetohydrodynamic instabilities, which arise from the interaction of the current with the selfmagnetic field, can develop over times much smaller than the launcher operation time and can be responsible for the entry of the electrode material into the discharge. Flash radiography of the electrode surface confirmed the presence of inhomogeneities and ejection of the material from the surface. Under certain conditions, the emergence of conducting metal jets from the electrode surface was detected.