The Effect of Corona Current on the Cooling of a Hot Wire

This article describes an experimental study of the cooling of a hot wire in air, when the air is disturbed by a corona discharge to the wire. With a copper wire, No. 30 B. & S. gauge, in still air, no effect was found with corona current less than 3 microamperes per cm of wire; but beginning with about that value, the cooling power of the wire increases, at first rapidly, and then more slowly, possibly passing through a poorly defined maximum. A corona current as great as 12 microamperes per cm is sufficient to give nearly the maximum effect. With small currents of air past the wire, a gradual increase of corona current, starting with zero, often shows first a heating effect, followed by a cooling effect. The slow currents of air seem to be appreciably retarded by the cross-flow of the ions carrying the corona current. The number of ions required for appreciable cooling is estimated to be considerably less than one ion per million molecules of the gas.