Effect of current connection to the anode nozzle on plasma torchefficiency

Experiments have been performed to demonstrate the influence of the location of the electric power connection to the anode nozzle on the efficiency of DC plasma torches. The DC plasma torch used in these experiments offers the flexibility to work with different anode geometries and the possibility of connecting the electrical power to the anode at two different locations. For each set of experiments, the controllable parameters such as total gas flow rate, gas composition, and electric current were kept constant, changing only the location of the electrical connection to the anode nozzle. The efficiency of the torch, derived from a conventional energy balance, shows a significant change as the location of the electrical connection to the anode nozzle is changed. The measured mean voltage as well as the amplitude of the voltage fluctuations were also affected by the location of the electrical connection to the anode nozzle. An explanation for the arc behavior is given, based on an analysis of the forces acting on the anode arc column and their influeuce on the variation of the arc column length. Experimental data are in good agreement with analytical predictions     

Numerical model of the anode region of high-current electric arcs

A two-dimensional, two-temperature axisymmetric numerical model has been formulated for the flow-affected region and the boundary layer in front of high-intensity electric arc anodes. The plasma flow is laminar, steady, incompressible, and the plasma composition is found from the diffusion equation because chemical nonequilibrium is expected. Computational results are obtained for an atmospheric pressure argon arc considering two different situations: a free-burning electric arc and an arc with a constrictor tube. The solutions indicate two different anode attachments modes-a constricted and a diffuse attachment. It is found that under the conditions considered in the calculations, the gradient-induced current densities become significant at distances in the order of 1 mm from the anode surface. The thermal anode boundary layer is compressed with increasing current. The thickness of the thermal boundary layer for the constricted mode is approximately three times smaller than for the diffuse mode. A reversal of the electric field strength occurs over the entire thickness of the boundary layer in all calculated cases. A satisfactory agreement is reached between the calculated heat flux values and experimental results obtained for a 200-A free-burning electric arc     

Numerical simulation of anode heat transfer of nitrogen arc utilizing two-temperature chemical non-equilibrium model

A detailed understanding of anode heat transfer is important for the optimization of arc processing technology. In this paper, a two-temperature chemical non-equilibrium model considering the collisionless space charge sheath is developed to investigate the anode heat transfer of nitrogen free-burning arc. The temperature, total heat flux and different heat flux components are analyzed in detail under different arc currents and anode materials. It is found that the arc current can affect the parameter distributions of anode region by changing plasma characteristics in arc column. As the arc current increases from 100 A to 200 A, the total anode heat flux increases, however, the maximum electron condensation heat flux decreases due to the arc expansion. The anode materials have a significant effect on the temperature and heat flux distributions in the anode region. The total heat flux on thoriated tungsten anode is lower than that on copper anode, while the maximum temperature is higher. The power transferred to thoriated tungsten anode, ranked in descending order, is heat flux from heavy-species, electron condensation heat, heat flux from electrons and ion recombination heat. However, the electron condensation heat makes the largest contribution for power transferred to copper anode.     

Numerical and experimental investigation of burner device for anode gas reburning

A complex numerical and experimental investigation of burner devices for a reburning of the anode gas of aluminum production was carried out. The chosen mathematical model of the processes of aerodynamics, heat exchange, and gas burning was identified and adapted on the basis of data of real-scale measurements. Basing on computational experiments the optimization of the design of elements of the system for anode gas detoxication and transport was carried out. A new system was proposed and tested for reburning the anode gases of electrolysis production, which consists of an improved burner device and a dust-sedimenting chamber with a possibility of regulating the amount of gas suction.     

Numerical simulation of ion beam generated in diode with anode plasma column

Ion beam generation in a high current diode with anode plasma slab has been studied. Ions are extracted from the anode plasma by a strong electric field of deep potential well (virtual cathode), arising after the propagation of relativistic electrons through the anode plasma slab. The movement of this potential well with the front part of the ion beam leads to a collective ion acceleration up to 10 MeV energy range.The authors wish to thank Dr. K. Jungwirth and Dr. J. Ullschmied for their interest and support and many helpful discussions.     

Experimental investigation of the anode region of a free-burning atmospheric-pressure inert-gas arc. II. Intermediate current regime—multiple anode constriction

This paper reports the experimental investigation of multiple anode constriction in atmospheric-pressure arcs in argon and xenon. The investigations were carried out in a free-burning arc with water-cooled electrodes. Results are presented from spectroscopic measurements of the electron temperature and density in the arc column and near the anode in various regimes of burning. Analysis of the experimental data leads to the conclusion that the constriction occurs because of the development of an overheating instability near the anode due to the disruption of the balance between Joule heating of the plasma and its cooling via the emission of radiation. Zh. Tekh. Fiz. 67, 41–45 (January 1997)     

Numerical analysis of chemical reaction processes in different anode attachments of a high-intensity argon arc

The attachment mode of arc on anode is closely related to the non-equilibrium chemical kinetics process of the anode region of arc. In this paper, the detailed chemical reaction mechanisms in the flow-affected region for both diffuse and constricted argon arc attachments are investigated by means of one-dimensional discharge coupled with a single-fluid, two-temperature model. The collisional-radiative model is used to examine the chemical reaction processes occurring in the anode region, including the arc centreline and fringe region. The numerical results are validated by comparison with available experimental data. The obtained radial distributions of electron temperature, electron density, excited states densities, ionization, and recombination processes reveal that different mechanisms dominate the diffuse and constricted arc-anode attachments.     

Growth of buckytubes on the anode at are discharge

It is shown that for an arc discharge between carbon electrodes in an inert gas atmosphere the temperatures at the electrode surfaces play a key role in determining the structure and the electrode on which a deposit can grow. The heat balance equations determine that the anode temperature is higher due to the energy carried by the electrons. This leads to anode sublimation and deposition on the cathode. It is shown that by cathode heating, by anode cooling or by a combination of these, a deposit may be obtained on the anode due to cathode erosion. The deposit grown by the “inverse” method is compared with a deposit obtained on the cathode under the same conditions but at reverse supply voltage polarity. The material from both deposits, studied by TEM, shows that there are graphite crystals within the anode deposit, and that the carbon forms within have a relatively small number of structural defects while the buckytubes are greater in length than those within the cathode deposit. The reasons for these differences are discussed. In the “inverse” method, the constant decrease in cooling of the anode surface leads to an equalization of the anode and cathode temperatures. This creates conditions that favor buckytube growth.     

Experimental investigation of the anode region of a free-burning atmospheric-pressure inert-gas arc I. General characteristics of the discharge. Low-current regime

This paper reports the experimental investigation of the anode region of a free-burning inert-gas arc at atmospheric pressure in the current range from a few amperes to hundreds of amperes. The tungsten thermionic-emission cathode and the large-diameter water-cooled copper anode that were used permitted the anode arc root to assume its natural form. The general characteristics of the discharge are given and results are presented from investigations of the anode region at low currents, where the anode arc root is single and constricted, but erosion-free. Measurements of the plasma parameters as well as the current density in the arc root are reported, and a comparison is made between the values obtained and those characteristic of the region of the cathode arc root. Zh. Tekh. Fiz. 67, 35–40 (January 1997)     

Influence of the anode material on an argon arc

The interaction between the arc and the anode was experimentally studied by means of a transferred arc burning in argon with copper, iron, or steel anodes. Depending on the rate of anode cooling, a stable plasma was obtained just above the anode, established either in pure argon (strong cooling) or in a mixture of argon with metal vapor. Temperature and metal concentration fields were deduced from spectroscopic measurements. Two important results were reached: the arc radius near the anode depends on the nature of the electrode, even without anode erosion; and the presence of metal vapor leads to a cooling of the plasma. The same arc configurations were theoretically simulated by a two-dimensional model. The comparison between experimental and numerical results allows a large proportion of the observed phenomena to be interpreted, in spite of partial discrepancies between predicted and measured values. The dimension of the arc root at the anode depends on the thermal conductivity of the solid metal, whereas the cooling effect due to metal vapor in the plasma is explained by the increases of electrical conductivity and of radiative losses in the presence of the vapor     

Growth of buckytubes on the anode at are discharge

It is shown that for an arc discharge between carbon electrodes in an inert gas atmosphere the temperatures at the electrode surfaces play a key role in determining the structure and the electrode on which a deposit can grow. The heat balance equations determine that the anode temperature is higher due to the energy carried by the electrons. This leads to anode sublimation and deposition on the cathode. It is shown that by cathode heating, by anode cooling or by a combination of these, a deposit may be obtained on the anode due to cathode erosion. The deposit grown by the “inverse” method is compared with a deposit obtained on the cathode under the same conditions but at reverse supply voltage polarity. The material from both deposits, studied by TEM, shows that there are graphite crystals within the anode deposit, and that the carbon forms within have a relatively small number of structural defects while the buckytubes are greater in length than those within the cathode deposit. The reasons for these differences are discussed. In the “inverse” method, the constant decrease in cooling of the anode surface leads to an equalization of the anode and cathode temperatures. This creates conditions that favor buckytube growth.     

Time-spatial structure of an electric arc anode region

This paper studies the anode region of an eroding anode with a nonstationary arc-root attachment. High-current free-burning short as well as long arcs at atmospheric pressure are investigated. A technique to study the anode region of the arc is suggested. An anode moving perpendicular to the arc axis was used for estimating parameters of the anode jets at a given moment of their development. The mechanism of current transfer in the anode region is considered on the basis of electrophysical and optical-spectroscopic investigations of the arc attachment traces and plasma parameters both of the anode jet and arc column. The anode jet was found to be of importance in the stationary arc operation. The near-anode plasma parameters depend on the effect of the cathode jet. In short arcs (L_a~2 mm), the plasma temperature at the anode exceeds 20000 K, while in long arcs (L_a >50 mm), it falls below 7000 K. At plasma temperature T_a >11000 K, the total arc current in the anode region is transferred through the arc plasma, while at lower temperatures, both the arc column and the anode jet take part in the current transfer     

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为了提高等离子体废物处理效率,根据磁流体动力学理论,利用计算流体力学软件FLUENT,采用磁矢量势的方法对直流双阳极非转移型电弧等离子体炬进行了二维轴对称数值模拟。计算中采用了SIMPLE算法。数值模拟得到了等离子体的温度、速度等分布。结果表明,等离子体的温度随着轴向距离的增加而减小,随弧电流增加而增加;其速度随着轴向距离的增加而先增大后减小,随弧电流增加而增加;等离子体炬出口处的温度和速度随着径向距离的增加而减小。这些结果与实验结果基本相符。     

Snapback-free shorted anode LIGBT with controlled anode barrier and resistance

A novel shorted anode lateral-insulated gate bipolar transistor(SA LIGBT)with snapback-free characteristic is proposed and investigated.The device features a controlled barrier V_barrierand resistance R_SAin anode,named CBR LIGBT.The electron barrier is formed by the P-float/N-buffer junction,while the anode resistance includes the polysilicon layer and N-float.At forward conduction stage,the V_barrierand R_SAcan be increased by adjusting the doping of the P-float and polysilicon layer,respectively,which can suppress the unipolar mode to eliminate the snapback.At turn-off stage,the low-resistance extraction path(N-buffer/P-float/polysilicon layer/N-float)can quickly extract the electrons in the N-drift,which can effectively accelerate the turn-off speed of the device.The simulation results show that at the same V_on of 1.3 V,the E_offof the CBR LIGBT is reduced by 85%,73%,and 59.6%compared with the SSA LIGBT,conventional LIGBT,and TSA LIGBT,respectively.Additionally,at the same Eoffof 1.5 m J/cm²,the CBR LIGBT achieves the lowest V_on of 1.1 V compared with the other LIGBTs.     

Ultraviolet imaging of the anode attachment in transferred-arcplasma cutting

The anode phenomena occurring at the location of current transfer from the plasma jet to the plate affects cut quality in plasma cutting of mild steel plate. To understand these phenomena, an ultraviolet imaging technique was used to visualize the anode attachment spot under various cutting conditions. This technique has provided a unique view and fostered a better understanding of the plasma-arc cutting process     

Mechanisms of anode power deposition in a low pressure free burningarc

Anode power deposition is a dominant power loss mechanism for arcjets and magnetoplasmadynamic (MPD) thrusters. In this study, a free burning arc experiment was operated at pressures and current densities similar to those in arcjets and MPD thrusters in an attempt to identify the physics controlling this loss mechanism. Use of a free burning arc allowed for the isolation of independent variables controlling anode power deposition and provided a convenient and flexible way to cover a broad range of currents, anode surface pressures, and applied magnetic field strengths and orientations using an argon gas. Test results showed that anode power deposition decreased with increasing anode surface pressure up to 6.7 Pa and then became insensitive to pressure. Anode power increased with increasing arc current, while the electron number density near the anode surface increased linearly. Anode power also increased with increasing applied magnetic field strength due to an increasing anode fall voltage. Applied magnetic field orientation had an effect only at high currents and low anode surface pressures, where anode power decreased when applied-field lines intercepted the anode surface. The results demonstrated that anode power deposition was dominated by the kinetic energy of the current-carrying electrons acquired over the anode fall region. Furthermore, the results showed that anode power deposition can be reduced by operating at increased anode pressures, reduced arc currents, anode current densities, and applied magnetic field strengths, and with magnetic field lines intercepting the anode     

Effect of anode microstructure on the performance of micro tubular SOFCs

Here we report the effect of anode microstructure on the SOFC performance using two types of micro tubular SOFCs, 0.8 and 1.6mm in diameter with different anode microstructure (Cells A and B). The cells consisted of NiO-Gd doped ceria (GDC) as an anode (support tube), GDC as an electrolyte and (La, Sr)(Fe, Co)O₃ (LSCF)-GDC as a cathode. The anode tube for Cell A was prepared using NiO (d_g~ 5µm) and GDC (d_g~ 0.2µm) powders without using a pore former, while the anode tube for Cell B was prepared using NiO (d_g~ 0.5µm)and GDC(d_g~ 0.2µm) powders using a pore former. The peak power density of these cells were shown to be 203, 400 and 857mW cm^{? 2} for Cell A and 273, 628 and 1017mW cm^{? 2} for Cell B, respectively at 450, 500, and 550°C operating temperature. Both cells showed outstanding performance, and furthermore the anode microstructure of Cell B was shown to be more optimized for better cell performance.     

Numerical modelling of unsteady heating and melting of the anode by electric arc. Part 1. Mathematical model and computed characteristics of the arc column

The two-dimensional mathematical model in the approximation of a partial local thermodynamic equilibrium of plasma and the technique for numerical computation of the unsteady electric arc characteristics, including the conjugate heat exchange of the electric-arc plasma flow with the treated product (anode) are considered. The results of overall testing of the numerical algorithm point to the correctness of the model and computational technique. The results of the computation of the arc characteristics from the conventional ignition moment until the passage to stationary regime are presented. It is found that a single thermal torus, which scatters fairly quickly in the ambient medium, forms around the arc column.