The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Lijun Wang - One of the best experts on this subject based on the ideXlab platform.
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modeling of vacuum Arc plasmas in anode spot or anode plume mode taking into account multiple ion components
Journal of Applied Physics, 2019Co-Authors: Ze Yang, Lijun Wang, Jie Deng, Shenli JiaAbstract:This work investigates the Arc behaviors with CuCr25 electrodes considering anode vapor using a magneto-hydro-dynamic model. Different kinds of components are considered including ions (Cu and Cr) with different charge numbers, electrons, and atoms (Cu and Cr). The effect of the anode sheath is also considered. The density distributions of these components are analyzed and compared with the experiments during the anode spot mode and the anode plume mode. Simulation results show that the anode vapor can enter the Arc Column forming a cool and poorly conducting region (i.e., neutral atom vapor area, NAVA) under high anode temperature. Atoms and single-charged ions mainly gather near each electrode. The highest double-charged ion density can be seen in front of the NAVA. Triple-charged ion density is negligibly low and reaches its maximum where the electron temperature is high. Cr is more likely to be ionized to a higher ionization level compared with Cu. Our results agree with experimental measurements of density distributions of different components and plasma temperature.
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study of vacuum Arc behavior under anode spot and anode plume modes
Applied Physics Letters, 2019Co-Authors: Lijun Wang, Ze Yang, Jing Jiang, Yuan Wang, Shenli JiaAbstract:Anode spot (AS) and anode plume (AP) phenomena are widely observed in vacuum Arc experiments and are related to anode melting and evaporation under strong heating from the Arc Column. Anode vapor will then strongly influence the Arc Column through ionization-recombination and energy exchange among atoms, ions, and electrons. This work investigated the characteristics of the vacuum Arc with AS or AP using the two-dimensional magnetohydro dynamic model. Formation of the AS and AP modes was studied and analyzed using numerical simulation. Friction forces between ions and atoms were also taken into account. Simulation results show that anode vapor expansion depends on the pressure balance between the anode jet and cathode plasma. Higher anode temperature produces a larger neutral atom vapor area (NAVA), which was dominated by neutral atoms. Inside the NAVA, ion and electron temperatures were low in the AS and AP mode due to ionization and energy exchange. Electric conductivity in this area was also so low that the location of the maximal current density was near the edge of the anode instead of the anode center. The asymmetric appearance of an AP was mainly caused by the asymmetric anode temperature distribution with respect to the AS center. Qualitative comparisons show that the simulation results are consistent with the experimental results.Anode spot (AS) and anode plume (AP) phenomena are widely observed in vacuum Arc experiments and are related to anode melting and evaporation under strong heating from the Arc Column. Anode vapor will then strongly influence the Arc Column through ionization-recombination and energy exchange among atoms, ions, and electrons. This work investigated the characteristics of the vacuum Arc with AS or AP using the two-dimensional magnetohydro dynamic model. Formation of the AS and AP modes was studied and analyzed using numerical simulation. Friction forces between ions and atoms were also taken into account. Simulation results show that anode vapor expansion depends on the pressure balance between the anode jet and cathode plasma. Higher anode temperature produces a larger neutral atom vapor area (NAVA), which was dominated by neutral atoms. Inside the NAVA, ion and electron temperatures were low in the AS and AP mode due to ionization and energy exchange. Electric conductivity in this area was also so low tha...
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Simulation of the Interaction between High Current Vacuum Arc and Macroparticles in Small-Size Trigatron
2018 28th International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV), 2018Co-Authors: Ze Yang, Lijun Wang, Yuan Wang, Xiao ZhangAbstract:This work investigates the interaction between high current vacuum Arc (HCVA) and the macroparticle (MP) generated from the cathode spots (CS) in the small-size vacuum trigatron. Magnetohydrodynamic (MHD) model is used to describe the Arc Column. MPs are added into MHD model, which are described by discrete phase model (DPM). The control equations of MPs include charging equation, motion equation and heat transfer equation, in which the evaporation of MPs is also considered. Based on the above model, the effects of MP diameter and Arc current on the characteristics of MPs are studied. Simulation results show that MPs leave the interelectrode gap with a deflection angle larger than the initial angle under the influence of plasma. The motion of MPs is similar to that of projectiles. MPs with smaller diameter are influenced by the Arc plasma more significantly. MPs can act as a source of the plasma, but these influences are not obvious in HCVA. What may be more harmful to the trigatron is the charging process of MPs during post-Arc process.
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Simulation results of influence of constricted Arc Column on anode deformation and melting pool swirl in vacuum Arcs with AMF contacts
Physics of Plasmas, 2017Co-Authors: Lijun Wang, Xiaolong Huang, Xiao Zhang, Shenli JiaAbstract:In the process of vacuum Arc breaking, the energy injected into the anode will cause anode melting, evaporation, and deformation, resulting in the formation of the anode melting pool. The anode activities have great influence on the Arc behavior. When the Arc current is large enough, even the influence of axial magnetic field is considered, the Arc Column still is in contraction state, which means the Arc burns only on a part of the electrode. In this paper, the model of anode melting pool deformation and rotation is used, and the model includes anode melting and solidification module, magneto-hydro-dynamic module of the anode melting pool, the volume of fraction method, and the current continuity equation. In this paper, the diffuse Arc area is selected as 100%, 75%, and 50%, respectively. The anode temperature and deformation, the anode melting layer thickness, and the rotational velocity of the anode melting pool are obtained. The results show that when the current is at 17.5 kA (rms) and the diffuse a...
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Experimental Study on Deflection Behavior of Vacuum Arcs Under the Influence of External Transverse Magnetic Field
IEEE Transactions on Plasma Science, 2017Co-Authors: Shenli Jia, Jie Deng, Lijun Wang, Xiao Zhang, Zhonghao Qian, Wein Xin Shi, Zongqian ShiAbstract:In real power system, when the three-phase short-circuit fault occurs, the vacuum Arc in one phase will be influenced by the transverse magnetic field generated by neighbor phases and bus bars. This kind of effect is the main cause of the unstable Arc and deflected erosion of contact plates, which leads to the failure of vacuum circuit breakers interruption. The objective of this paper is to get more insight into the influence of external transverse magnetic field (ETMF) on vacuum Arc's behavior. The experiments were conducted in a demountable vacuum chamber with pressure about 10-4 Pa. The cup-type axial magnetic field contacts were used, whose material was pure copper and the diameter is 35 mm. The uniform ETMF in the Arc region was generated by two parallel bulk permanent magnets. The experiments were conducted under different ETMFs (0, 15, and 25 mT) and current levels (1-, 2.5-, and 4-kA rms) with different gap distances (6, 8.5, and 11 mm). The videos of Arc Column were recorded by a high-speed charge-coupled device camera. Under the action of ETMF, the vacuum Arc got deflected. Due to the retrograde motion of cathode spots and Ampere force acting on Arc Column, the deflection behaviors during three typical periods (that is, initial, peak value, and close-to-current-zero period) were different. Moreover, the deflection level of vacuum Arc at current peak value moment was greatly impacted by ETMF and gap distance. Larger the ETMF and gap distance were, higher the deflection level at current peak value moment was. The simulation results of Arc deflection based on magnetic-hydrodynamic model were in agreement with experimental results in trends.
Shenli Jia - One of the best experts on this subject based on the ideXlab platform.
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modeling of vacuum Arc plasmas in anode spot or anode plume mode taking into account multiple ion components
Journal of Applied Physics, 2019Co-Authors: Ze Yang, Lijun Wang, Jie Deng, Shenli JiaAbstract:This work investigates the Arc behaviors with CuCr25 electrodes considering anode vapor using a magneto-hydro-dynamic model. Different kinds of components are considered including ions (Cu and Cr) with different charge numbers, electrons, and atoms (Cu and Cr). The effect of the anode sheath is also considered. The density distributions of these components are analyzed and compared with the experiments during the anode spot mode and the anode plume mode. Simulation results show that the anode vapor can enter the Arc Column forming a cool and poorly conducting region (i.e., neutral atom vapor area, NAVA) under high anode temperature. Atoms and single-charged ions mainly gather near each electrode. The highest double-charged ion density can be seen in front of the NAVA. Triple-charged ion density is negligibly low and reaches its maximum where the electron temperature is high. Cr is more likely to be ionized to a higher ionization level compared with Cu. Our results agree with experimental measurements of density distributions of different components and plasma temperature.
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study of vacuum Arc behavior under anode spot and anode plume modes
Applied Physics Letters, 2019Co-Authors: Lijun Wang, Ze Yang, Jing Jiang, Yuan Wang, Shenli JiaAbstract:Anode spot (AS) and anode plume (AP) phenomena are widely observed in vacuum Arc experiments and are related to anode melting and evaporation under strong heating from the Arc Column. Anode vapor will then strongly influence the Arc Column through ionization-recombination and energy exchange among atoms, ions, and electrons. This work investigated the characteristics of the vacuum Arc with AS or AP using the two-dimensional magnetohydro dynamic model. Formation of the AS and AP modes was studied and analyzed using numerical simulation. Friction forces between ions and atoms were also taken into account. Simulation results show that anode vapor expansion depends on the pressure balance between the anode jet and cathode plasma. Higher anode temperature produces a larger neutral atom vapor area (NAVA), which was dominated by neutral atoms. Inside the NAVA, ion and electron temperatures were low in the AS and AP mode due to ionization and energy exchange. Electric conductivity in this area was also so low that the location of the maximal current density was near the edge of the anode instead of the anode center. The asymmetric appearance of an AP was mainly caused by the asymmetric anode temperature distribution with respect to the AS center. Qualitative comparisons show that the simulation results are consistent with the experimental results.Anode spot (AS) and anode plume (AP) phenomena are widely observed in vacuum Arc experiments and are related to anode melting and evaporation under strong heating from the Arc Column. Anode vapor will then strongly influence the Arc Column through ionization-recombination and energy exchange among atoms, ions, and electrons. This work investigated the characteristics of the vacuum Arc with AS or AP using the two-dimensional magnetohydro dynamic model. Formation of the AS and AP modes was studied and analyzed using numerical simulation. Friction forces between ions and atoms were also taken into account. Simulation results show that anode vapor expansion depends on the pressure balance between the anode jet and cathode plasma. Higher anode temperature produces a larger neutral atom vapor area (NAVA), which was dominated by neutral atoms. Inside the NAVA, ion and electron temperatures were low in the AS and AP mode due to ionization and energy exchange. Electric conductivity in this area was also so low tha...
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Simulation results of influence of constricted Arc Column on anode deformation and melting pool swirl in vacuum Arcs with AMF contacts
Physics of Plasmas, 2017Co-Authors: Lijun Wang, Xiaolong Huang, Xiao Zhang, Shenli JiaAbstract:In the process of vacuum Arc breaking, the energy injected into the anode will cause anode melting, evaporation, and deformation, resulting in the formation of the anode melting pool. The anode activities have great influence on the Arc behavior. When the Arc current is large enough, even the influence of axial magnetic field is considered, the Arc Column still is in contraction state, which means the Arc burns only on a part of the electrode. In this paper, the model of anode melting pool deformation and rotation is used, and the model includes anode melting and solidification module, magneto-hydro-dynamic module of the anode melting pool, the volume of fraction method, and the current continuity equation. In this paper, the diffuse Arc area is selected as 100%, 75%, and 50%, respectively. The anode temperature and deformation, the anode melting layer thickness, and the rotational velocity of the anode melting pool are obtained. The results show that when the current is at 17.5 kA (rms) and the diffuse a...
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Experimental Study on Deflection Behavior of Vacuum Arcs Under the Influence of External Transverse Magnetic Field
IEEE Transactions on Plasma Science, 2017Co-Authors: Shenli Jia, Jie Deng, Lijun Wang, Xiao Zhang, Zhonghao Qian, Wein Xin Shi, Zongqian ShiAbstract:In real power system, when the three-phase short-circuit fault occurs, the vacuum Arc in one phase will be influenced by the transverse magnetic field generated by neighbor phases and bus bars. This kind of effect is the main cause of the unstable Arc and deflected erosion of contact plates, which leads to the failure of vacuum circuit breakers interruption. The objective of this paper is to get more insight into the influence of external transverse magnetic field (ETMF) on vacuum Arc's behavior. The experiments were conducted in a demountable vacuum chamber with pressure about 10-4 Pa. The cup-type axial magnetic field contacts were used, whose material was pure copper and the diameter is 35 mm. The uniform ETMF in the Arc region was generated by two parallel bulk permanent magnets. The experiments were conducted under different ETMFs (0, 15, and 25 mT) and current levels (1-, 2.5-, and 4-kA rms) with different gap distances (6, 8.5, and 11 mm). The videos of Arc Column were recorded by a high-speed charge-coupled device camera. Under the action of ETMF, the vacuum Arc got deflected. Due to the retrograde motion of cathode spots and Ampere force acting on Arc Column, the deflection behaviors during three typical periods (that is, initial, peak value, and close-to-current-zero period) were different. Moreover, the deflection level of vacuum Arc at current peak value moment was greatly impacted by ETMF and gap distance. Larger the ETMF and gap distance were, higher the deflection level at current peak value moment was. The simulation results of Arc deflection based on magnetic-hydrodynamic model were in agreement with experimental results in trends.
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modeling of the anode surface deformation in high current vacuum Arcs with amf contacts
Journal of Physics D, 2016Co-Authors: Xiaolong Huang, Shenli Jia, Jie Deng, Lijun Wang, Kang Qin, Zongqian ShiAbstract:A high-current vacuum Arc subjected to an axial magnetic field is maintained in a diffuse status. With an increase in Arc current, the energy carried by the Arc Column to the anode becomes larger and finally leads to the anode temperature exceeding the melting point of the anode material. When the anode melting pool is formed, and the rotational plasma of the Arc Column delivers its momentum to the melting pool, the anode melting pool starts to rotate and also flow outwards along the radial direction, which has been photographed by some reseArchers using high-speed cameras. In this paper, the anode temperature and melting status is calculated using the melting and solidification model. The swirl flow of the anode melting pool and deformation of the anode is calculated using the magneto-hydrodynamic (MHD) model with the volume of fraction (VOF) method. All the models are transient 2D axial-rotational symmetric models. The influence of the impaction force of the Arc plasma, electromagnetic force, viscosity force, and surface tension of the liquid metal are all considered in the model. The heat flux density injected into the anode and the Arc pressure are obtained from the 3D numerical simulation of the high-current vacuum Arc using the MHD model, which gives more realistic parameters for the anode simulation. Simulation results show that the depth of the anode melting pool increases with an increase in the Arc current. Some droplets sputter out from the anode surface, which is caused by the inertial centrifugal force of the rotational melting pool and strong plasma pressure. Compared with the previous anode melting model without consideration of anode deformation, when the deformation and swirl flow of the anode melting pool are considered, the anode temperature is relatively lower, and just a little more than the melting point of Cu. This is because of liquid droplets sputtering out of the anode surface taking much of the energy away from the anode surface. The azimuthal velocity of the anode melting pool for Arc current 12.5 kA root-mean-square (rms) is larger than that for 17.5 kA (rms), which is likely to be caused by the thinner liquid layer, and also a smaller melting pool mass of 12.5 kA.
Anthony B. Murphy - One of the best experts on this subject based on the ideXlab platform.
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dominant heat transfer mechanisms in the gtaw plasma Arc Column
Plasma Chemistry and Plasma Processing, 2021Co-Authors: Alberto Velazquezsanchez, Anthony B. Murphy, Alfredo Delgadoalvarez, Patricio F Mendez, Marco A RamirezargaezAbstract:A 2D steady-state mathematical model of a GTAW electric Arc was used to analyze the relative importance of the main heat transfer mechanisms that heat or cool the plasma in the Arc Column. The analysis consisted of building a map of the dominant mechanisms for heating and cooling the Arc in each zone as well as their relative importance in terms of volumetric power. It was found that the primary inputs of energy are due to convection near the anode and Joule heating near the cathode, while the main cooling mechanisms have a complex structure that can be described in the map from cathode to anode, composed of Thomson effect, convection, radiation and conduction. A systematic analysis was conducted to evaluate the effect of the Arc current, Arc length, and plasma gas on the map of dominant mechanisms. The gases considered were Ar and He. The main effect of current is on the intensities and extent of the zones of dominance of the mechanisms. The Arc length does not significantly affect the map, and the type of gas influences most of the dominant heat transfer mechanisms. The heat transfer near the anode is governed by the momentum and thermal boundary layers due to the plasma jet, while the cathode heat transfer is dominated by the heat transfer mechanisms associated with current flow. The information provided may be used to perform simple energy balances in specific zones of the Arc to gain basic understanding of the physics in the Arc.
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numerical analysis of non equilibrium plasma property in anode boundary layer of argon gas tungsten Arc
Surface & Coatings Technology, 2010Co-Authors: Shinichi Tashiro, Manabu Tanaka, Anthony B. MurphyAbstract:Although the LTE assumption is effective to evaluate high temperature region in the Arc Column in Gas Tungsten Arc (GTA) which is a kind of a transfer-type plasma torch, it is difficult to apply it to low temperature region such as the fringe of the Arc Column or an electrical sheath due to decrease of collision frequency. Especially, in order to consider the effect of chemical reaction between the Arc plasma and the surface of the anode material, non-equilibrium property of the Arc plasma should be considered without the LTE assumption, since it is required to understand precise property of the Arc plasma close to the anode surface. Therefore, we have developed non-equilibrium simulation model of GTA. In this paper, the reliability of the model was confirmed for comparing the simulation result with the experimental result. Furthermore, it was found that the thickness of non-equilibrium region in case of 150 A is approximately 0.3 mm near the anode surface and that in case of 50 A exceeds 1 mm.
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the influence of electrode erosion on the air Arc in a low voltage circuit breaker
Journal of Applied Physics, 2009Co-Authors: Mingzhe Rong, Anthony B. MurphyAbstract:This paper focuses on the numerical reseArch of the influence of electrode erosion on the Arc behavior during opening process of low-voltage circuit breakers. The mathematical model of three-dimensional air Arc plasma considering electrode erosion is built based on magnetic hydrodynamics. The mass fraction equation of copper vapor is introduced to the model on the basis of traditional mass, momentum, and energy balance equations. The influence of copper vapor on the thermodynamic and transport properties of the gas mixture is considered in this paper. The distributions of temperature field, gas flow field, and mass fraction of copper vapor in the Arc chamber are simulated. The Arc root displacements and Arc voltage, which takes account of the influence of electrode erosion, are calculated. The simulation results indicate that the immobility time of both moving contact and stationary contact is much longer considering electrodes erosion. The calculated voltage of the Arc Column during Arc motion considerin...
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Simulation study of the influence of wall ablation on Arc behavior in a low-voltage circuit breaker
IEEE Transactions on Plasma Science, 2009Co-Authors: Qiang Ma, Mingzhe Rong, Anthony B. Murphy, Yi Wu, Tie Jun XuAbstract:This paper focuses on the numerical reseArch of the influence of polymer (polyoxymethylene) on the Arc behavior during Arc-motion process. The mathematical model of 3-D air-Arc plasma considering the ablation of sidewalls is built based on magnetic hydrodynamics. The mass-fraction equation is introduced to the model on the basis of traditional mass, momentum, and energy-balance equations. The influence of wall ablation on the thermodynamic and transport properties of air-polymer mixtures is considered in this paper. The distributions of temperature field, pressure field, and mass fraction in the Arc chamber are calculated. The simulation results indicate that the vapor concentration behind the Arc Column is higher than that in front of the Arc Column because of the existence of ldquovortexrdquo in the Arc chamber. The use of polymers could accelerate Arc movement and reduce the probability of occurrence of back-striking. Using polymers can also increase Arc voltage, which can be explained by the change of electrical conductivity for air-polymer vapor mixtures.
Vincent Rat - One of the best experts on this subject based on the ideXlab platform.
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Electric Arc in a plasma spray torch under modulated current
Journal of Physics D: Applied Physics, 2018Co-Authors: F. Mavier, Fadi Zoubian, Vincent RatAbstract:Plasma spraying of liquid feedstock is a relevant process for the deposition of finely structured ceramic coatings. The control of Arc instabilities makes obtaining the desired material properties challenging; hence efforts are devoted to developing segmented direct current torches that intend to fix the length of the Arc. An alternative method involves promoting the Arc oscillations and associating a pulsed liquid injection with the torch. This paper presents a study of the influence of the amplitude modulation of a direct current on the Arc dynamics confined in a plasma spray torch. The dependence of the electrical features of the torch on the current amplitude modulation is presented. Plasma speed and temperature are also measured. Time-resolved imaging of the Arc attachment permits us to correlate its motion, particularly the Arc reattachment on the anode surface, with Arc current and voltage. Measurements are compared with a simplified model providing the time-dependence of the plasma properties. It is shown that the current modulation favors the Arc restrike by modulating the Arc radius, but also that the electric field strength of the Arc Column should be modified during current variations.
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Electric Arc Fluctuations in DC Plasma Spray Torch
Plasma Chemistry and Plasma Processing, 2017Co-Authors: Vincent Rat, F. Mavier, Jean François CoudertAbstract:Direct current plasma torches for plasma spraying applications generate electric Arc instabilities. The resulting fluctuations of input electrical power hamper a proper control of heat and momentum transfers to materials for coating deposition. This paper gives an overview of major issues about Arc instabilities in conventional DC plasma torches. Evidences of Arc fluctuations and their consequences on plasma properties and on material treatments are illustrated. Driving forces applied to the Arc creating its motion are described and emphasis is put on the restrike mode that depends on the Arc reattachment and the boundary layer properties around the Arc Column. Besides the Arc root shown as a key region of instability, the Helmholtz oscillation is also described and accounts for the whole plasma torch domain that can generate pressure fluctuations coupled with voltage ones.
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A simplified analytical model for dc plasma spray torch : influence of gas properties and experimental conditions
Journal of Physics D: Applied Physics, 2006Co-Authors: Vincent Rat, Jean François CoudertAbstract:A simplified analytical model is proposed to evaluate some characteristics of the Arc jet generated with a dc plasma torch, in the restricted area of atmospheric plasma spraying conditions. The plasma inside the anode nozzle is considered as stationary and is divided into the Arc Column and a surrounding cold layer which electrically insulates the plasma from the nozzle wall. Radiation and processes related to the Arc attachment at the electrodes are not explicitly taken into account. Heat conduction is evaluated by using Kirchoff's potential, which is described, as it is done also for the electrical conductivity, as a function of the gas specific enthalpy instead of temperature. The model is used to calculate the specific enthalpy radial distribution. From that, and by introducing a mean isentropic coefficient, it is possible to calculate the axial velocity of the plasma jet at the nozzle exit and to evaluate the different pressure contributions. The comparison between predicted and previously measured plasma jet velocities shows good agreement for various experimental conditions.
Jean François Coudert - One of the best experts on this subject based on the ideXlab platform.
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Electric Arc Fluctuations in DC Plasma Spray Torch
Plasma Chemistry and Plasma Processing, 2017Co-Authors: Vincent Rat, F. Mavier, Jean François CoudertAbstract:Direct current plasma torches for plasma spraying applications generate electric Arc instabilities. The resulting fluctuations of input electrical power hamper a proper control of heat and momentum transfers to materials for coating deposition. This paper gives an overview of major issues about Arc instabilities in conventional DC plasma torches. Evidences of Arc fluctuations and their consequences on plasma properties and on material treatments are illustrated. Driving forces applied to the Arc creating its motion are described and emphasis is put on the restrike mode that depends on the Arc reattachment and the boundary layer properties around the Arc Column. Besides the Arc root shown as a key region of instability, the Helmholtz oscillation is also described and accounts for the whole plasma torch domain that can generate pressure fluctuations coupled with voltage ones.
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A simplified analytical model for dc plasma spray torch : influence of gas properties and experimental conditions
Journal of Physics D: Applied Physics, 2006Co-Authors: Vincent Rat, Jean François CoudertAbstract:A simplified analytical model is proposed to evaluate some characteristics of the Arc jet generated with a dc plasma torch, in the restricted area of atmospheric plasma spraying conditions. The plasma inside the anode nozzle is considered as stationary and is divided into the Arc Column and a surrounding cold layer which electrically insulates the plasma from the nozzle wall. Radiation and processes related to the Arc attachment at the electrodes are not explicitly taken into account. Heat conduction is evaluated by using Kirchoff's potential, which is described, as it is done also for the electrical conductivity, as a function of the gas specific enthalpy instead of temperature. The model is used to calculate the specific enthalpy radial distribution. From that, and by introducing a mean isentropic coefficient, it is possible to calculate the axial velocity of the plasma jet at the nozzle exit and to evaluate the different pressure contributions. The comparison between predicted and previously measured plasma jet velocities shows good agreement for various experimental conditions.
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Transient Phenomena in Plasma Torches and in Plasma Sprayed Coating Generation
Journal De Physique Iv, 1997Co-Authors: Pierre Fauchais, Jean François Coudert, Michel VardelleAbstract:D.C. plasma torches are more and more widely used for different applications among which cutting, welding and spraying are probably the most developed. For a long period it is mainly their static characteristics which have been considered and their applications were studied on a macroscopic scale. However many transient phenomena occur, the systematic study of which has started only a few years ago. To limit the discussion we present only the case of plasma spraying with: . the transient phenomena, at the anode, and their evolution with the torch working parameters and the electrodes erosion, . the consequences of these fluctuations on plasma jet temperature and velocity fields as well as mean electric field in the Arc Column, . the characterization of the molten particles flattening and resulting splat cooling and consequences on coating properties.