Calculation of Laminar Flows of Plasma in the Channel of a Plasmatron with the Self-Adjusting Length of the Electric Arc

A simplified method is suggested for the calculation of the parameters of laminar flows of plasma in the channel of a plasmatron. A new analytical solution of the Elenbaas–Heller equation is derived, which generalizes the channel model of electric arc to the case when the volume radiation makes a significant contribution to the electric arc energy balance. Numerical calculations are performed in order to determine the electric field intensity, the longitudinal pressure gradient, and the heat transfer to the electric arc channel wall depending on the working parameters of the plasmatron in a laminar flow of gas in a stabilized section. In determining the arc length, it is assumed that the electric arc is shifted downstream of the flow and, at the same time, performs random walks over the channel cross section. The walks occur under the effect of vortexes whose characteristic size is of the order of the arc diameter.     

Calculation of the Dynamics of Ignition of an Air-Hydrogen Mixture by Nonequilibrium Discharge in a High-Velocity Flow

The paper deals with the problem of initiation of ignition of an air-hydrogen mixture by means of a nonequilibrium electric discharge under conditions of high-velocity flow. A model is constructed of calculation of the parameters of electric discharge in a chemically reacting gas in view of the heating and motion of gas in a channel of uniform cross section. It is demonstrated that a minor energy contribution may be accompanied by a strong reduction of the time of ignition induction, which cannot be attained in the case of thermal heating of gas corresponding to this energy contribution.     

Spectral measurements of the gas and electron temperatures in the flame of a single-phase ac plasma generator

High-power electric-arc ac plasma generators find extensive application which is primarily associated with the problem of processing of organic waste and production of synthesis gas. The structure of a high-power single-chamber multiphase ac plasma generator with rail-type electrodes includes an injector of primary charge carriers which is a single-phase high-voltage plasma generator with a power of 10 kW or lower. This latter plasma generator may be further employed for solving other problems. Results are given of spectroscopic measurements of gas temperature fields at the nozzle exit section of a high-voltage plasma generator with rod electrodes located in a cylindrical channel. The pattern of variation of the temperature fields as a function of working gas flow rate is investigated.     

Numerical Analysis of the Characteristics of an Arc in Laminar and Turbulent Gas Flows

The equations of magnetic gas dynamics are used to calculate the characteristics of an electric arc in a plasmotron channel versus the gas flow rate. The results obtained with the aid of the laminar and the two-parameter k– model of turbulence with allowance for deviations from equilibrium in the plasma and for the swirling of the gas are compared with experimental data. The stability of a laminar flow to the effect of weak hydrodynamic perturbations is investigated.     

Analysis of a Swirling Flow of Gas in the Diaphragmed Channel of a Plasma Generator

A two-temperature magnetogasdynamic model of plasma is used to calculate a swirling flow of gas (argon) in the diaphragmed channel of a plasma generator and the heating of this flow and to investigate the dependence of the flow on the strength of the current, geometry of the channel, and the flow rate and swirling moment of gas. The effect of the velocity field of swirling flow on the disequilibrium of plasma and on the arc characteristics in varying-area channels is treated. The calculation results are in qualitative agreement with the experimental data.     

The Shunting of Current and the Resultant Variation of Voltage in Channels of Plasmatrons with Self-Adjusting Length of Electric Arc

The characteristics of pulsation processes in dc plasmatrons with the cathode located in the channel center and the anode in the form of a cylindrical or a conical channel wall are investigated in plasmas of argon and nitrogen at atmospheric pressure. The fast Fourier transform of signals and their subsequent computer processing are used to obtain the dependences of the frequency of fluctuations of the arcing voltage on the working parameters of the plasmatron, namely, the electric arc current, the flow rate of plasma-forming gas, and the channel diameter. For plasmatrons with the self-adjusting length of the electric arc, analysis is performed of the mechanism of reclosing of the anode region of the arc, i.e., of the electric arc shunting associated with the stretching of the current filament by a flow of gas and with the electrodynamic interaction of different filament regions. A formula is derived which defines the dependence of the characteristic frequency of fluctuations of the arcing voltage on the external parameters of the problem, namely, the arc current, the flow rate of the working gas, and the characteristic channel diameter. It is demonstrated that the pattern of the dependence of the frequency of voltage fluctuations on the gas flow rate may vary with the values of the parameter of magnetohydrodynamic interaction. The formula generalizes the experimental results of numerous researchers obtained in a wide range of variation of the external parameters.     

The effect of a diaphragm on the vortex thermoinsulation of arc in a plasmatron channel

The pattern of gas (argon) flow and heating in a diaphragmed plasmatron channel is calculated within the framework of an equilibrium magnetogasdynamic model, depending on the diaphragm position and hole size and on the gas flow rate and twist momentum. Special features of the arc characteristics in a channel of variable cross section are established for streams with and without twist.     

Study of a low temperature plasma generator with a divergent output electrode channel

Results of experimental studies of a plasma generator with a divergent output electrode channel are presented, and a comparative analysis is performed of operation of this plasma generator and plasma generator with cylindrical channel of constant cross section. Studies of sectioned output electrodes are performed along with plasma generators with solid electrodes. The influence of sectioning on the parameters of electric discharge is studied. It is shown that the optimal degree of divergence of the output electrode channel is a complex function of different parameters.     

Influence of inlet conditions on vortex characteristics

Vortex chambers are normally used for arc stabilization in linear plasma torches. In the present work, the effect of uniformity of the gas inlet channel distribution on the stabilizing characteristics of a swirled flow is studied numerically. The formation of a complex flow pattern with a toroidal recirculating flow area inside the vortex chamber is observed. For some regimes, two local maxima of the tangential velocity are observed in the middle section of the chamber. It is shown that an increment of the number of gas inlet channels leads to a more uniform gas input with disappearance of the second maximum, which increases the velocity amplification coefficient and, correspondingly, results in a better stabilizing effect. The obtained profiles of the radial distribution of the tangential velocity are compared with the results of Oseen’s equation for an unconfined vortex.     

Calculation of the parameters of a two-phase mixture flow in a channel of variable cross section

The case of steady-state one-dimensional flow in a channel of variable cross section is examined for a two-phase gas-solids mixture. Equations relating the parameters of a gas-dust mixture and the dimensionless gas velocity are derived on the assumption that the velocities and temperatures of the two phases are equal. A formula is obtained for the coefficient of polytropy with allowance for flow friction against the channel walls.     

A criterion of similarity and transition to turbulence for electric arc flows

A method is suggested for determining the similarity criterion and the criterion of transition of an electric arc flow in a plasmatron channel from a laminar regime to a turbulent one (equivalent Reynolds number) that does not require using any reference temperature. Application of this method to the available experimental data on the transition to turbulence demonstrates its correctness and efficiency. The critical value of the proposed similarity criterion corresponding to the boundary of the transition from a laminar regime to a turbulent one has been revealed. A marginal curve separating the regions of the laminar and turbulent regimes of the plasma flow has been plotted in the space of the operating plasmatron parameters. A phenomenon of a double change of the electric arc flow regime with electric current rise upon constant plasma-forming gas flow rate has been discovered.     

Relaxation of the shock-wave configuration in a diffuser after termination of the action of magnetic and electric fields

The pulsed interaction of an ionized gas flow in a full-internal-compression diffuser with magnetic and electric fields has been experimentally studied. The interaction is determined by the shape of the electric current pulse between electrodes situated in the initial part of a hypersonic diffuser. It is established that, after termination of the current pulse, some characteristics of the shock wave front configuration in the gas flow exhibit relaxation with a significant delay to the unperturbed values.     

An Investigation of Spatial Distribution of Characteristics of a Plasma Stream Formed by a Hall Discharge in a Channel with Metal Walls

The effect of the system of delivery of the working medium on the characteristics of a plasma stream in a Hall accelerator with closed azimuthal current is experimentally investigated. The gas delivery system utilizes a porous diaphragm from a carbon–carbon composite material whose pore size is comparable with the Debye radius of the electrons of plasma formed in a discharge channel. The calorimetric method is used to determine the degree of azimuthal and radial nonuniformity of distribution of the energy of plasma stream developed by the accelerator, namely, the distribution of temperature of a titanium target mounted perpendicularly to the incident stream is taken with the aid of an infrared imager. The probe method is used to measure the spatial distribution of temperature and the concentration of charge-exchange plasma at the accelerator channel exit. It is shown that the ratio of the kinetic energy of the flow of heavy particles to the expended electric energy (energy efficiency) exceeds 0.5.     

The condition of steady-state flow in a channel of variable cross section in the presence of heat supply and kinetic energy dissipation

An expression for maximum permissible entropy gain is obtained and the condition of passage via the velocity of sound is found for the steady-state flow of an ideal gas in a channel of variable cross section in the presence of heat supply and kinetic energy dissipation. Particular flow examples are considered.     

氦−氩混合保护气体角接头旋转激光+电弧复合焊电弧特性数值分析

目的 研究激光+电弧复合焊中氦−氩混合保护气体成分对电弧等离子体物理特性的影响,从而改善焊接性能。方法 综合考虑角接头几何特性和氦−氩混合保护气体的物理特性,建立氦−氩混合保护气体角接头旋转激光+电弧复合焊电弧行为的数值分析模型。使用FLUENT软件对不同体积比氦−氩保护气体下电弧等离子体的温度场、流场、压力场和电势场进行模拟计算,对比分析保护气体成分改变对电弧等离子体的影响规律,考虑其对焊接性能的影响,并将计算结果与高速摄影试验进行对比,验证数值分析模型的准确性与合理性。结果 保护气体分别为纯Ar、95%Ar+5%He、90%Ar+10%He时,电弧向激光侧偏移收缩,电弧整体形貌被压缩,位置A纵截面处电弧等离子体的峰值温度分别为25 603、25 080、23 904 K,最大流速分别为336.34、334.34、317.58 m/s,压力最大值分别为899.08、943.40、957.67 Pa,电势梯度分别为11.56、12.17、13.18 V。结论 在氦−氩混合保护气体激光+电弧复合焊中,当保护气体中氦气体积分数增加到5%和10%时,随着氦气所占比例的增大,电弧处于动态变化过程,电弧被压缩,等离子体的峰值温度逐渐降低,最大流速下降,电弧压力和电势梯度增大,有利于焊缝熔深的增大。     

Laminar heat transfer over the initial section of a rectangular channel

The author describes a study, based on the linearized energy equation, of heat transfer over the initial section of a rectangular channel with a laminar incompressible flow and both uniform and nonuniform temperature fields at the inlet. Temperature and Nusselt number distributions over the channel perimeter are given.     

Motion of a viscous fluid in the initial section of a flat channel

The laminar flow of a viscous incompressible fluid in the initial section of a flat channel is investigated on the basis of the linearized boundary layer equations. Formulas are obtained for the longitudinal velocity component and the friction at the wall. The approximate and exact solutions are compared, and the agreement is shown to be satisfactory.     

Effect of distributed injection of atomic gas on the electric and thermal characteristics of the positive column of a low-pressure discharge

The positive column of a low-pressure electric discharge in the flow of atomic gas in a flat channel with additional injection through the side walls is studied. Expressions for its basic characteristics are derived and analyzed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 51, No. 3, pp. 487–492, September, 1986.     

Investigation of low-temperature plasma generator with divergent channel of the output electrode and some applications of this generator

A review is made of experimental and theoretical investigations of processes occurring in low-temperature plasma generators (LTPG) with divergent channel of the output electrode, and the possibilities of utilizing these generators in new plasma technologies are analyzed. Comparison is made of the characteristics of discharge (including the current-voltage characteristic) in a divergent channel and in a cylindrical channel of uniform cross section. The effect of divergent channel of the output electrode and of its expansion ratio on the pattern of physical processes in LTPGs of different designs is studied. Investigations are performed of the distribution of electric current and heat flux density along a channel with a segmented output electrode. The voltaic equivalents of heat fluxes to cathode and anode are determined. The process of “shunting” of discharge is investigated, which causes fluctuations of electric arc-burning voltage. The investigations involving an LTPG with divergent channel reveal that the voltage amplitude in the case of shunting decreases with increasing current strength and, at high currents of argon arc, does not exceed 1–2 V. Results are given of spectral and visual investigations of LTPG. It is demonstrated that, in an LTPG with divergent channel, the plasma temperature in the region of energy input at currents of 300 A and higher exceeds 30 000 K. The significant part is found which is played by vacuum ultraviolet radiation in the process of closing the arc to anode. The mechanisms of erosion of the tungsten cathode tip are investigated, which play an important part in increasing the cathode service life by way of recirculation of tungsten atoms because of their ionization in the discharge gap. Results are given of using an LTPG with divergent channel of the output electrode in plasma technologies of surface hardening, cutting, and hard-facing of metals. The technology of plasma hardening of wheel pairs, adopted by the RZhD (Russian Railroads) Joint-Stock Company, provides for increasing the service life of railroad wheels by a factor of 1.5–2.