A Numerical Investigation on the Effects of Water Vapor on Electron Energy and OH Production in Atmospheric-Pressure He/H2O and Ar/H2O Plasma Jets

In this paper, a comparative investigation has been performed on the effects of water vapor on electron energy in He/H
₂
O and Ar/H
₂
O plasma jets at atmospheric pressure. The investigation is based on a needle-plane discharge system and the numerical simulation with the use of a 2-D fluid model. The OH production and its correlation with electron energy in the two gases have also been calculated. This paper gives the following significant results. The averaged electron energy in He/H
₂
O keeps basically a constant at water vapor concentrations below about 0.1%, and then it evidently decreases. However, the averaged electron energy in Ar/H
₂
O is hardly changed with the increase in the water vapor concentration. This difference from that in He/H
₂
O is mainly due to different energy thresholds for the electron collision reactions related to helium and argon. The averaged OH densities in He/H
₂
O and Ar/H
₂
O increase with increasing the water vapor concentration, but that for He/H
₂
O is evidently large at water vapor concentrations below about 0.5%, compared to Ar/H
₂
O. The reason for this can be attributed to more electrons participating in the excitation reaction related to H
₂
O and large reaction rate of OH production in He/H
₂
O. Finally, this paper suggests that a proper high water vapor concentration in He/H
₂
O plasma jets may allow an expected electron energy and also generates abundant OH radicals.