Processes and properties of electric arc stabilized by water vortex

Experimental investigation of an electric arc stabilized by a water vortex was carried out in a DC arc plasma torch for the power range 90-200 kW. Volt-ampere characteristics of the arc as well as the power balance were determined separately for the part of the arc column stabilized by water and for the remaining part between the nozzle exit and the external anode. The temperature of arc plasma close to the nozzle exit was determined by emission spectroscopy. Negatively biased electric probes in the ion collecting regime were used for determination of the plasma flow velocity. The measured temperatures up to 27000 K, and velocities up to 7 km/s are higher than the values commonly reported for plasma torches with DC arcs stabilized by a gas flow. Mass and energy balances within the arc chamber were determined from the experimental results. The radial transport of the energy by radiation was identified as a decisive process controlling the arc and plasma properties. The balance of radial energy transport was studied. The ratio of energy spent for evaporation of the water to the energy absorbed in the evaporated mass is very low in the water stabilized arc. This is the principal cause of high plasma temperatures and velocities found by the measurements     

The Rotation of Ions and Neutrals in a Cylindrical Magnetized Hollow Cathode Argon Arc

In a magnetized hollow cathode arc rotational velocities of ions and neutrals and their temperatures were measured in axial and radial dependence. In comparison with theory experimental results give a detailed analysis of radial transport phenomena.     

Spectroscopic Investigation of Plasma Composition of U-Shaped Argon Stabilized D.C. Arc

The spectroscopic analysis of emitted radiation from the U-shaped argon stabilized d.c. arc is performed when the arc was burning without and in the presence of water aerosol. The special attention is paid to the emission of molecular components. The radial distribution of rotational temperature is obtained from the OH band spectra. The arc plasma composition is also theoretically calculated supposing the state of local thermodynamic equilibrium and compared with experimental results.     

向心透平级叶轮内三维复杂流动的数值研究

对向心透平叶轮内部复杂流动在级环境下进行了全三维黏性数值模拟,结合拓扑学原理分析了设计工况和非设计工况下其内流动分离及各种涡系发展的演变过程,初步建立了向心透平叶轮内的旋涡模型,阐述了流动损失的形成机理。研究表明:向心透平叶轮内部涡系与轴流式透平存在较大差别,且流动分离及涡系主要集中在吸力面侧;设计工况下向心透平叶轮内的主要旋涡包括马蹄涡、通道涡及泄漏涡,其主要表现为通道涡与泄漏涡相互影响和掺混,是主要损失的形成原因;非设计工况下,主流在叶轮叶片前缘处发生大范围的分离及回流,造成了较大的能量损失,但二次流损失所占比例较小。     

Bestimmung von Transportfunktionen aus den Charakteristiken zylindrischer Bögen (Wasserstoff)

On a stationary and cylindersymmetrical arc produced in a cascade arc chamber measurements are performed in order to determine the transport coefficients of the H₂-plasma especially the electrical conductivityσ and the heat flux potential \(S(S = \int\limits_{T_0 }^T {\kappa dT'} \) T=temperature,κ=thermal conductivity). In a channel of 2 mm diam. and at a pressure of 1 atm. a wall-load of 19 kW/cm² and an almost complete ionization were reached. TheE-I-characteristic was measured for H₂ in a wide range of arc currents. Because of technical and physical difficulties the totalE-I-characteristic had to be composed of measurements taken from three different channel diameters and converted by scaling laws to the smallest diameter. After this reduction an effective current range from 5·10^?2 A to 150 A is covered. For the measurement of the characteristics a quasistatic method was developed which is more precise than others used before. From the measuredE-I-characteristic the radial distributions of the transport coefficients with the arc currentI as parameter were computed exactly by means of the energy balance equation using a newly developed iteration procedure. The final result is theσ(S)-function of hydrogen.     

Experimental investigation of supersonic flow over elliptic surface

The coherent structures of flow over a compression elliptic surface are experimentally investigated in a supersonic low-noise wind tunnel at Mach Number 3 using nano-tracer planar laser scattering (NPLS) and particle image velocimetry (PIV) techniques. High spacial resolution images and the average velocity profiles of both laminar inflow and turbulent inflow over the testing model were captured. From statistically significant ensembles, spatial correlation analysis of both cases is performed to quantify the mean size and orientation of large structures. The results indicate that the mean structure is elliptical in shape and structure angles in separated region of laminar inflow are slightly smaller than that of turbulent inflow. Moreover, the structure angle of both cases increases with its distance away from from the wall. POD analysis of velocity and vorticity fields is performed for both cases. The energy portion of the first mode for the velocity data is much larger than that for the vorticity field. For vorticity decompositions, the contribution from the first mode for the laminar inflow is slightly larger than that for the turbulent inflow and the cumulative contributions for laminar inflow converges slightly faster than that for turbulent inflow     

轮背空腔-密封气对CAES向心涡轮变工况流动损失的影响

本文以国内首套MW级压缩空气储能(CAES)系统末级向心涡轮为研究对象,通过数值模拟分析了变工况条件下轮背空腔-密封气对等熵效率和流场结构的影响.结果表明:在求解中考虑轮背空腔-密封气结构能够使等熵效率数值解的偏差减小0.7%;随涡轮进口压力增加,轮背空腔泄漏流由叶片吸力面中部叶高区域逐渐向轮毂转移,流动损失先增加后减小;合理降低轮背空腔泄漏气体的轴向速度,能够减弱轮背空腔-密封气结构对等熵效率的负面影响,使向心涡轮在较宽的变工况范围内都保持高效运行.     

Time constants for nonstationary arcs

The time constants associated with the initial deviations of an arc column from a static state have been studied analytically. The basic approach is to use a Taylor series expansion in powers of time of the energy balance equation. It is assumed that the arc gas is optically thin and is in local thermal equilibrium. Initially the effects of radial gas flow (which must exist for dynamic arcs) are neglected, but this simplification is later relaxed. The initial conditions are given by the properties of a cylindrically symmetric, wall-stabilized DC positive column. The interrupted (freely decaying) and the step-modulated arcs are considered, and initial time constants for conductance, electric field, and heat flux potential are computed. For numerical results the best available values of thermodynamic and transport properties have been used.     

Transportfunktionen von Stickstoff bis 26000 °K

TheE(I)-characteristic and a large number ofT(r, I)-distributions measured in a 5 mm ØN ₂ cascade arc at normal pressure are used to evaluate the transport properties of nitrogen up to 26,000 °K. The electrical conductivityσ(T) and from this the cross-section for atom-electron collision and the Coulomb-cross-section are determined directly from theE(I)- and severalT(r, I)-curves. For the evaluation of the thermal conductivityκ(T) three temperature regions are discerned: Up to about 10,000 °Kκ(T) is derived directly from the energy equation since here the energy transport by radiation does not play an important role. Between 10,000 and 15,000 °K the radiative energy flux for different arc currents, the thermal conductivity and from this the charge exchange cross-section are determined in a good approximation utilizing the large number of measured temperature distributions. Above 15,000 °K the already evaluated collision cross-sections are used to computeκ(T). Withκ(T) known the radial distribution of the balance between emission and absorption of radiative power per unit volume is evaluated for different arc currents. It turns out, that at the highest measured arc current, i.e. 570 A, in the axial region of the arc about 95% of the supplied energy is carried off by radiation.     

Nonlinear vortex dynamics in open nonequilibrium systems with bulk mass loss and a generation mechanism for tornadoes and typhoons

Based on a general model of nonlinear vortex dynamics in open thermodynamically nonequilibrium systems with bulk or surface mass losses, an analysis is presented of the mechanism of generation of violent atmospheric vortices (tornadoes, typhoons, cyclones) associated with the formation of deep cloud systems by intense condensation of water vapor from moist air cooled below the dew point. Simple particular solutions to the Navier-Stokes equations are found that describe both axisymmetric and nonaxisymmetric incompressible vortex motions involving radial and vertical flows with viscous dissipation vanishing identically everywhere except for a thin shear layer at the boundary of the condensation region. It is shown that the nonlinear convective and local Coriolis forces generated by radial inflow in the presence of a background vorticity due to a global Coriolis force (the Earth’s rotation) accelerate the solid-body rotation in the vortex core either exponentially or in a nonlinear regime of finite-time blow-up. Due to updrafts, such a vortex is characterized by a strong helicity. This mechanism explains a number of observed properties and characteristics of the structure and evolution of tornadoes and typhoons. Upper estimates are found for the kinetic energies of violent atmospheric vortices. It is shown that increase in rotational kinetic energy of atmospheric vortices with constant vortex-core radii is consistent with energy and momentum conservation, because radial inflow continually supplies the required amount of rotational kinetic energy drawn from the ambient atmosphere to an open system.     

Strahlungsenergietransport mit Absorption in zylindrischen Bögen

For temperatures above 12,000 °K the contribution of non-transparent radiation becomes very important for the energy transport in argon and nitrogen arc plasmas. Formulas for the radiation flux and the difference between emission and absorption of radiation per unit volume and time are given generally and furthermore for arcs of cylindrical symmetry. For argon arcs at normal pressure with axial temperatures between 10,000 and 16,000 °K the radiative behaviour is investigated and the share of transparent and non-transparent radiation on the total energy flux is computed. The influence of different assumptions made on the amount of emission and absorption on theE(I)-characteristic and the radial temperature distributions is shown.     

Behavior of a High Current Vacuum Arc between Hollow Cylindrical Electrodes in a Radial Magnetic Field

Experimental observations were conducted on the behavior of a high current vacuum arc on cylindrical electrodes in a radial magnetic field. The arc was sustained between the ends of two cylindrical Cu electrodes, 54-mm diam and 1.5-mm wall thickness separated by 5 mm. Arc current pulses with peak values in the range 4-15 kA with a half amplitude full width (HAFW) duration of 8 ms were investigated with radial magnetic fields proportional to the instantaneous current with proportionality constants of 4.0 and 6.5 × 10-6 T/A. The arcs were photographed simultaneously with a streak camera and by a high speed framing camera and the arc voltage was recorded on a digitizing transient recorder. The results indicated that the arc in this geometry, both with and without an imposed radial magnetic field, can be characterized by three development stages: a) arc formation, b) diffuse arc along the electrode perimeter, and c) simultaneous existence of several concentrated arc columns. When a radial magnetic field was imposed two changes were noted: 1) the arc appeared somewhat more distributed in that a greater number of constricted columns were observed, and they were distributed more evenly; and 2) the constricted columns moved in the J? × B? direction with velocities in the range 5-35 m/s.     

活性剂等离子弧焊焊接电弧的光谱与热分析

针对活性剂等离子弧焊焊接过程,利用光谱分析方法对活性剂等离子弧焊焊接电弧进行光谱分析,采用红外热像伪着色法测定活性剂等离子弧焊焊接电弧温度场,并建立活性剂等离子弧焊焊接电弧热流密度径向分布模型,对焊接电弧的成分及焊接电弧温度场进行了研究。研究结果表明,常规等离子焊焊接电弧以氩原子和氩一次电离离子的谱线为主,金属蒸气谱线不突出,焊接电弧以气体粒子为主,属于气体电弧;活性剂等离子弧焊焊接电弧的光谱中氩原子及氩一次离子谱线的辐射强度增强,Ti,Cr,Fe金属谱线大量涌现;活性剂等离子弧焊焊接电弧的温度分布比较紧凑,温度场外形窄,温度分布范围较集中,电弧径向温度梯度较大;电弧径向温度分布呈现正态Gauss分布模式。     

Analytical Models of Free-Burning Electric Arcs

Two-dimensional electric arc model based on the solution of the energy equation by means of variables separation method in curve-line orthogonal coordinates, associated with electrical arc characteristics, is suggested. Quite accurate solution of MGD-equations complete system for the arc with radial current spreading out of the top nozzle of the conic electrode is produced. Influence of electrode geometry on arc column characteristics in some particular cases has been analysed.     

极性对自保护药芯焊丝电弧焊光谱特征的影响

由于自保护药芯焊丝具有抗风性以及优异的焊缝性能,已广泛应用于野外管道焊接以及大型机械的修复过程。电极极性是影响焊接过程的重要工艺参数。为了研究电极极性对电弧等离子体的影响机理,设计电弧等离子体空域中各点逐步扫描的同步采集系统,通过光谱特征谱线的分析,采用Stark谱线轮廓法计算电子密度,并且基于Boltzmann作图法计算电弧等离子体的温度,同时针对Al和Mg活性元素的分布特征进行分析。结果表明,靠近电极处,沿y轴负方向,直流正接时（焊丝接电源负极性）,弧柱中心区电弧电子密度、电弧温度和活性元素呈现“水滴状”分布。而直流反接时（焊丝接电源正极性）,弧柱中心区电弧电子密度、电弧温度和活性元素的分布特征表现为“手指状”分布。根据“自磁收缩”的原理,直流正接条件下,活性元素在径向方向受到的电磁力较小,整体分布呈现发散状。直流反接条件下,活性元素在径向方向受到的电磁力较大,收缩较为严重,整体表现为收缩状态。采用相同的电参数时,直流反接条件下弧柱中心区的电弧电子密度、电弧温度均大于直流正接条件下得到的电子密度和电弧温度,其中电子密度分布特征和带电粒子的电离程度是影响电弧温度的主要因素。在相同的电极极性下,随着电流、电压的增大,电弧等离子体的温度和电子密度都在显著增大。     

The Energy Transport, Including Emission and Absorption, in N2-Arcs of Different Radii

Steady, motionless cascaded N2-arcs with tube diameters of 2, 3, and 5 mm are investigated at atmospheric pressure to gain insight into the radiative energy transport for temperatures up to 27,000 K. From the electrical characteristics, the total emitted radiation, and the temperature distributions, the electrical conductivity and the transparent emission are evaluated. It is shown that transparent emission can be neglected in the energy transport of nitrogen. The thermal conductivity and the radiative balance as the difference between total emission and absorption per unit volume are determined by introducing the concept of a zero radius arc. Extrapolation to the zero radius arc also permits the determination of the total emission alone. The emission and reabsorption of radiation plays a decisive role in the energy transport for temperatures above 13,000 K.     

Investigations of the Arc Burning in the Water Vapour Atmosphere

The functions of thermal conductivity α(T) and electrical conductivity σ(T) for water vapour, within the temperature intervals 7700–8000 K and 2000–3500 K, were calculated. These calculations were performed by using the UHLENBUSCH'S method and the empirical one. Calculations were based on experimentally determined electric field strength as a function of the arc current and radial temperature distribution in the central zone and in the surrounding of the arc burning in water vapour atmosphere.     

Measurements of Stark broadening of He(II) 4686Å

Side-on observations were performed on a Stark-broadened He(II) 4686Å line emitted from a pulsed, high-current arc plasma preionized by CW microwave radiation at atmospheric pressure. A two-dimensional, multichannel detection method was used to obtain the radial distribution of the line profile in a single test. The line was emitted from the central hot core of the plasma, which had a homogeneous radial electron-density distribution. Comparisons with theoretical predictions show that the inclusion of ion-dynamic effects leads to better agreement between experiment and theory.     

Numerical description of axisymmetric blue whirls over liquid-fuel pools

This numerical investigation is focused on determining the structures of blue whirls, recently found to occur in laboratory investigations of fire whirls when the circulation becomes sufficiently large to produce a vortex breakdown that drastically shortens the fire whirl and correspondingly reduces residence times, so that the yellow flames turn blue. The computations address axisymmetric configurations for round pools of liquid fuels flush with and at the center of a larger solid horizontal disc, at the outer edge of which vanes of adjustable angles cause the entrained air to enter with a controllable azimuthal component of velocity. The nondimensionlized conservation equations employed include realistic Lewis numbers with temperature-dependent transport coefficients and a one-step chemical-kinetic approximation that correctly reproduces laminar burning velocities. Buoyancy and radiant energy transport from the flames to the liquid surface are both taken into account, the latter being found to be essential for the blue whirl. Along with the vaporization-equilibrium and energy-conservation boundary conditions at the fuel surface, inflow boundary conditions are provided by a recently developed solution for the boundary-layer flow over the solid disc, while zero-gradient outflow conditions are applied above the whirl. Controlling nondimensional parameters, besides Reynolds, Damköhler, and Froude numbers, are a ratio of radiant to convective energy flux and a ratio of azimuthal to inward radial flow velocity in the boundary layer at the edge of the disc. The computed conditions for the onset of the blue whirl, as well as the computed structure of the whirl itself, bear close resemblance to what was found experimentally.     

Magnetic resonance imaging of molecular transport in living morning glory stems

MRI was applied to investigate the transport pathways in Morning Glory plant stems. The study was carried out on living plants without affecting their integrity. The architecture of a dicotyledonous plant was deeply characterized: the root system structure and the vascular bundle location were identified, the presence of central voids caused by cell maturation and loss were observed in the stem. Molecular transport components were recognized, by observing the concentration profile of a tracer, which changed with time after its absorption by the plant roots. MRI analysis revealed the presence of an axial transport as the progress of the tracer front through the vascular bundles and a radial molecular transport from the vascular bundles toward the surface of the stem. As a result, the tracer molecular transport formed the parabolic tracer front (PTF). A model was built up through the analysis of the PTF that consisted of an axial front at the peak position and a radial front at the width of the parabolic tail. PTF analysis revealed differences between the tracer transport velocities in the axial and the radial directions in the plant stem. The model revealed that the width of the parabolic tail reflected the magnitudes of diffusion and permeation of the tracer in the plant stem.