Modelling of a heavy-current intensively blasted electric arc at atmospheric pressure

Abstract

The paper deals with intensively blasted electric arc burning in argon in a cylindrical channel of a designed experimental arc heater. The measured values of the arc current, the total voltage between a tungsten cathode and a grounded copper anode, the argon flow rate, and the water flow rates and temperature increments in individual parts of the arc heater characterize the operational conditions, but the parameters of the arc inside remain hidden. The simplified mathematical model has been designed to reveal the arc behavior in the arc heater channel, namely the arc radius and arc temperature development. The model is based on the energy and mass conservation laws and Ohm’s law and utilizes theoretically calculated transport and thermodynamic properties of argon altogether with the measured results as input data. Some simplifying assumptions are applied. A two-zone arrangement with a hot arc zone in the middle and a cold zone near the channel wall is supposed. The arc radius development along the arc heater’s channel is described by Schlichting’s formula for a free beam. Such combinations of three characteristic values of exponent n r, current density j 0 at the cathode tip, and arc temperature T A(s) at the end of the near-cathode layer are sought to enable as close as possible accordance between the computed and experimental data. Thereafter, a slight tuning of these parameters is needed to avoid extreme values of electric field intensity and temperature oscillations near the cathode while not to substantially worsen the reached agreement of measured and computed values. The functionality of the model is demonstrated using four typical sets of experimental data.