A theoretical and experimental investigation of copper electrode erosion in electric arc heaters: II. The experimental determination of arc spot parameters

Abstract

Two important copper electrode parameters, namely, the volt-equivalent of the arc spot heat flux and the arc spot effective current density have been measured experimentally in magnetically driven arcs in air. The measurements were performed for currents in the range 0.025 - 1 kA, magnetic field strengths 0.133 - 0.95 T and air pressures 1 - 40 atm. The volt-equivalent of the arc spot heat flux is proposed to account for the total heat flux entering the electrode surface through the arc spot. An unsteady thermal method was applied in the measurements. To obtain the effective current density, the thermophysical experiment was combined with the application of equations of the erosion model presented in a previous companion paper. We show that the volt-equivalent of the cathode arc spot heat flux increases with increasing magnetic field. The sum of the cathode and the anode voltage drops is shown to be approximately equal to the sum of the corresponding volt-equivalents of the arc spot heat fluxes. Good agreement with the measurements of other authors is obtained. In particular, the effective arc spot current density allows one to confirm the thermophysical model for the erosion of copper electrodes indirectly.