Sheath and arc-column voltages in high-pressure arc discharges

Abstract

Electrical characteristics of a 1 cm-long free-burning atmospheric-pressure argon arc are calculated by means of a model taking into account the existence of a near-cathode space-charge sheath and the discrepancy between the electron and heavy-particle temperatures in the arc column. The computed arc voltage exhibits a variation with the arc current I similar to the one revealed by the experiment and exceeds experimental values by no more than approximately 2 V in the current range 20-175 A. The sheath contributes about two-thirds or more of the arc voltage. The LTE model predicts a different variation of the arc voltage with I and underestimates the experimental values appreciably for low currents but by no more than approximately 2 V for I 120 A. However, the latter can hardly be considered as a proof of unimportance of the space-charge sheath at high currents: the LTE model overestimates both the resistance of the bulk of the arc column and the resistance of the part of the column that is adjacent to the cathode, and this overestimation to a certain extent compensates for the neglect of the voltage drop in the sheath. Furthermore, if the latter resistance were evaluated in the framework of the LTE model in an accurate way, then the overestimation would be still much stronger and the obtained voltage would significantly exceed those observed in the experiment.

Cathode fall voltage of TIG arcs from a non-equilibrium arc model

“…This fact can be considered in a proper way replacing the LTE arc model by a two-temperature plasma model. This option has been applied recently to the description of a TIG arc including the cathode fall and the tungsten cathode temperature [10]. The results are in a good agreement with the measurements.…”

“…A more detailed validation of the model results for the arc properties with spectroscopic measurements was the subject of a recent work [10].…”

“…Such a model has been developed recently for a simplified TIG process (tungsten thermionic cathode and cooled copper plate as anode) and validated by spectroscopic measurements [11]. The model has been also applied to the configuration of the TIG arc in [10], and the results in particular for the voltage drops have been compared for varying currents [12]. A general agreement of the results has been found, but the non-equilibrium model provides an even more precise estimation of the measured voltages.…”

A Perspective on Arc Welding Research: The Importance of the Arc, Unresolved Questions and Future Directions

“…In the first approach, LTE is generally assumed, while in the second, a two-temperature treatment is necessary, since the sheath is a critical component of the model, being responsible for transport of power to both the electrode and the arc column. Two main two-temperature models have been developed; in that of Baeva et al [37], deviations from ionization equilibrium (i.e., from local chemical equilibrium) are also taken into account in both the sheath and arc column, while in that of Benilov et al [38], deviations from ionization equilibrium are only considered in the sheath. The two-temperature models were compared recently [36], and shown to give similar results in the arc column.…”

Joule heat generation in thermionic cathodes of high-pressure arc discharges

“…In recent years, different variants of this model have been used also for high currents typical of arc welding. [10][11][12][13] In this work, the model of nonlinear surface heating is written with account of Joule heating, similarly to Refs. 2 and 3.…”