An improvement on the modelling of non-transferred plasma torches

Bianchini, Rute; Favalli, R C; Pimenta, Marcos de Mattos; Szente, R. N.

doi:10.1088/0022-3727/33/2/307

Cited by 9 publications

(9 citation statements)

References 10 publications

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“…[4][5][6][7][8][9] In the present study, the temperature and electric potential conditions are given only at the cooled surfaces of anode and cathode, represented as lines CЈDЈ, FA, in Fig. 1 without assuming the current density and temperature at the electrodes surface, represented as lines CD, FG, GB 11) and neglecting sheath boundary Vol.…”

Section: Boundary Conditionsmentioning

confidence: 99%

“…Therefore, the numerical modeling is expected to be one of the effective approach to solve this problem. [4][5][6][7] In the present study the thermofluid analysis of free burning arc and tungsten cathode life evaluation 8,9) are conducted to provide the optimum operating conditions of an arc for the high energy efficiency and for a long life of electrode. In the thermofluid analysis, the electric field is solved in the total region including an arc flow zone and both cathode and anode regions by giving heat flux condition between arc and electrodes without assuming the distributions of temperature and electric current on the electrode surfaces.…”

Section: Introductionmentioning

confidence: 99%

“…In order to derive the governing equations, the following assumptions are introduced. [4][5][6][7] (1) The argon arc is regarded as an ideal gas and a continuous fluid. It is optically thin in Local Thermodynamic Equilibrium (LTE) state.…”

Section: Introductionmentioning

confidence: 99%

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Performance Evaluation of Arc-Electrodes Systems for High Temperature Materials Processing by Computational Simulation

2003

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Thermofluid analysis of an arc flow and the evaluation of the cathode lifetime have been conducted by a computational simulation for the performance improvement of arc-electrodes systems. The effects of arc current, electrode gap, inlet gas flow rate and cathode vertex angle on the temperature and velocity fields of an arc flow are clarified by parametric computations to optimize the operating conditions and torch geometry. The temperature field by an arc flow model shows the quantitative agreement with the available experimental data in the local thermodynamic equilibrium (LTE) region. The cathode lifetime is evaluated successfully by coupling with the computated thermofluid field of an arc flow. The effects of different operating conditions on the cathode lifetime are also discussed for longer lifetime of the arc-electrodes systems.KEY WORDS: computational simulation; arc; electrode; interaction; lifetime evaluation.Under these assumptions, the governing equations for arc and electrodes regions are presented as follows: The radiation loss Ra from arc is given by the multipleterms approximation as a function of plasma temperature from the experimental data for argon.2) inside the electrode ... (5) Heat flux between arc and cathode, anode are respectively given by neglecting space charge effects 13,14) in the very thin sheath and both electrodes evaporation for simplicity 15) ........ (6) ... (7) where the emission current density j e is given by the Richardson-Dushman equationion current j i is given as follows: Boundary ConditionsIn the previous almost studies, temperature distribution on the electrode surface and the current density at the cathode spot are given in assumptions. [4][5][6][7][8][9] In the present study, the temperature and electric potential conditions are given only at the cooled surfaces of anode and cathode, represented as lines CЈDЈ, FA, in Fig. 1 without assuming the current density and temperature at the electrodes surface, represented as lines CD, FG, GB 11) and neglecting sheath boundary Vol. 43 (2003) conditions for the reduction in computation time. 15,17) Because calculated arc temperature and cathode surface temperature are relatively insensitive to those detailed properties of the sheath. Table 1 shows the discharge configuration and operating conditions referring to Gas Tungsten Arc (GTA) plasma facility. Numerical Conditions and Procedures19) A cylindrical thoriated tungsten cathode (Wϩ 2wt%Th) and a plate copper anode are investigated for lifetime evaluation in the present study. The roots of both electrodes are cooled fixedly at 300 K. The thermofluid field is solved by Semi-Implicit-Method for Pressure Linked Equation (SIMPLE) 20) method using Tri Diagonal-Matrix Algorithm (TDMA). The electromagnetic field is solved by Gauss-Seidel method. Here, the grid has 75ϫ102 meshes in the axial and radial directions, respectively. The thermodynamic and transport properties of argon 21,22) and tungsten and copper 23) are given as a function of temperature. Figure 2 shows a schematic i...

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Section: Boundary Conditionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Performance Evaluation of Arc-Electrodes Systems for High Temperature Materials Processing by Computational Simulation

2003

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“…Thermal plasmas can also be generated by several methods such as dc electrical discharges at current intensities higher than a few amperes and up to 10 5 A, free burning arcs [1], [2], transferred arcs [3], [4], or nontransferred plasma torches [5]- [8], [10], [11], etc.…”

Section: Introductionmentioning

confidence: 99%

Two-Dimensional and Three-Dimensional Simulation of DC Plasma Torches

Bhuyan

Goswami

2007

IEEE Trans. Plasma Sci.

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Two-dimensional modeling of non-transferred dc plasma torches have been performed using an axis symmetric geometrical configuration and boundary conditions. A control volume approach and SIMPLER algorithm is used to solve the governing equations for mass, momentum, and energy conservation coupled with the electric and magnetic fields. The results are compared with the ones obtained in 3-D simulation works of the authors. Results show substantial difference in control parameters as calculated from the two simulations, owing to local attachment of the arc over the anode surface.Index Terms-DC plasma torch, non-transferred plasma torch, thermal plasma.

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“…In order to derive the governing equations, the following assumptions are introduced here. 13) (1) The argon arc is regarded as an ideal gas and a continuous fluid. It is optically thin in Local Thermodynamic Equilibrium state.…”

Section: Introductionmentioning

confidence: 99%

Computational Simulation of Arc Melting Process with Complex Interactions

et al. 2006

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The real-time computational simulation of arc melting process with considering complex interactions and solid-liquid mushy zone in molten anode has been successfully conducted to provide the fundamental data for highly economical performance of arc melting process. The configuration of molten anode predicted by realistic numerical model shows the quantitative agreement with the experimental data. The effects of sulfur content concentration in molten metal, arc current and cathode vertex angle on the welding structure is discussed in detail. Finally, the heat exchange efficiency and molten cross-sectional area are evaluated under different arc currents and cathode vertex angles for optimum welding process with high efficiency.KEY WORDS: arc melting system; complex interactions; mushy zone; real-time computational simulation.(8) Evaporation, deformation and charge on the molten anode surfaces are neglected for simplicity. (9) Evaporation, melting and deformation on the cathode surface are neglected for simplicity. Under these assumptions, the governing equations for arc and electrodes region are presented as follows.Conservation c Ar c Ar The initial conditions of arc melting process are the steady thermofluid fields of arc without melting anode. Table 1 shows the system configuration and operating conditions. The thermofluid field is solved by SemiImplicit-Method for Pressure Linked Equation (SIMPLE) method 14) using Tri Diagonal-Matrix Algorithm (TDMA). The electromagnetic field is solved by SOR method. In this study, 90 grid points are adopted in both axial and radial directions. The thermodynamic and transport properties of argon, tungsten and stainless steel are given as a function of temperature. 10,[15][16][17][18][19][20][21] The viscosity in the solid-liquid mushy zone is as a function of liquid fraction. Numerical Conditions and Procedures 22) Numerical Results and DiscussionFigures 2(a) and 2(b) show the effect of sulfur content on the temperature fields of arc and molten pool. The steady state of molten pool is obtained approximately 20 s after arc generation. It is found that sulfur content does not affect the arc flow so much even near interface, however, the welding structure changes drastically by sulfur content. In the case of low sulfur content in SUS304 as shown in Fig. 2(a), the molten metal spreads outward. On the other hand, in the case of high sulfur content in SUS304, the molten pool penetrates downward in the core region.Figures 3(a) and 3(b) show the four kinds of driving forces which affects surface flow induced on the molten pool corresponding as shown in Figs. 2(a) and 2(b). In the case of low sulfur content in SUS304, shear force resulting from cathode jet is stronger at the inner molten region but surface tension is stronger at the outer molten region. Then, total driving force shows positive at the inner molten region but negative at the outer one, which induce the outward and inward flows correspondingly. On the other hand, in case of high sulfur content in SUS304, surface tension...

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An improvement on the modelling of non-transferred plasma torches

Cited by 9 publications

References 10 publications

Performance Evaluation of Arc-Electrodes Systems for High Temperature Materials Processing by Computational Simulation

Performance Evaluation of Arc-Electrodes Systems for High Temperature Materials Processing by Computational Simulation

Two-Dimensional and Three-Dimensional Simulation of DC Plasma Torches

Computational Simulation of Arc Melting Process with Complex Interactions

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