Thermal boundary-layer effects on Langmuir probe measurements in flowing gases

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Abstract
The flow of a weakly ionized gas past a planar probe is considered. In order to assess the errors incurred using the standard uniform-electron-temperature models, calculations are made of the electron temperature in the boundary layer under conditions of subsonic low-temperature plasma flow typical of flames. It is found that for the usual experimental case of small currents the electrotemperature is only uniform if the parameter α/aless, similar02, and is equal to the wall temperature if α/agreater, similar10. The parameter α2 is equal to the ratio of the gas flow time past the probe to the characteristic electron cooling time, and a is the reduced gas temperature gradient at the wall.