Heat deposition in the thermal field of a micro-glow discharge: effect of humidity

Abstract

The humidity effect on the thermal field of an atmospheric pressure DC micro-glow discharge generated in an Ar laminar flow with water vapor is investigated. Two diagnostic methods of calibrated schlieren (CS) photography and space-resolved optical emission spectroscopy (SR-OES) were applied to determine the gas temperature (Tg) distributions in the micro-discharge. It shows that a narrow but hot zone representing the discharge core is characterized by the plasma-induced emissions. On the other hand, a much broader full thermal field was visualized through schlieren imaging. The central luminous region covers only about one-third of the full Tg map. From schlieren photography, we observed that with a rise of mixed water vapor, the discharge thermal pattern expanded, achieving higher temperature levels, indicating that more electrical energy was deposited in the form of heat. Further analysis demonstrates, however, that only an ignorable part of heat was stored by water molecules. It shows that the water molecules act as an important intermediate role of energy transfer in-between hot electrons and the cool gas bulk through fast vibration-translation collision processes of H2O−H2O and H2O-Ar, enhancing the whole thermal field of the gaseous discharge.