Probe Measurements on High Pressure Arcs

Abstract

The introduction of a probe in a carbon arc in air at atmospheric pressure has been found to increase the arc voltage by several volts, the increase being almost independent of the velocity with which the probe is moved, but being a function of probe perimeter. Observation showed that the probe was surrounded by a dark space, with a fairly definite boundary several times the diameter of the probe, which was uninfluenced by the potential applied to the probe. The gas temperature fell from several thousand degrees at the outer boundary of the dark space to a few hundred degrees at the probe surface. The rate of flow of energy to the probe was measured to be about 50 watts per cm length of probe, for a 0.03 cm diameter probe at the center of a 6-amp. arc; calculations show about half the energy was carried by thermal conduction across the dark space, and about half came from recombination of dissociated molecules upon the probe surface.