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

Abstract

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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Magnetohydrodynamic Simulation of DC Arc Plasma under AC Magnetic Field

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