Atmospheric Pressure Gas-Liquid Discharge Plasma And Its Optical Emission Spectrum Diagnosis

Gas-liquid discharge plasma technology uses high-energy electrons generated by discharge,abundant active species and a variety of physicochemical effects to convert N₂ in large quantities in the air into nitrogen oxides that can be used to achieve nitrogen fixation.Atmospheric pressure gas-liquid discharge plasma is different from general non-thermodynamically balanced plasma in that the nitrogen oxides produced by the plasma can be directly stored in liquid for crop irrigation or hydroponics.In this thesis,the nitrogen fixation effect of gas-liquid discharge plasma is studied preliminarily.The results show that the gas-liquid discharge plasma can convert N₂ from air to nitrate in liquid phase.Based on the experimental results,further improve the discharge structure,use of the area of the discharge plasma emission spectrometry detection N₂（C³Π_u→B³Π_g）,N₂⁺（B²Σ→X²Π）.Due to the generation mechanism of plasma emission spectrum,the basic parameters of plasma,including gas temperature and electron density,are further calculated by using emission light spectrum.Specific research contents are as follows:（1）A kind of gas-liquid discharge plasma was generated by the linear tube discharge structure.The area of interaction between the plasma and the liquid was mainly under the liquid level.NO₃^-was detected in the plasma activated water treated by the plasma.Based on its nitrogen-fixing characteristics,the spectral diagnosis of discharge plasma was carried out,and the optimal discharge conditions were explored by adjusting the applied voltage amplitude and discharge time.Studies show that discharge process of active species mainly for N₂（C³Π_u→B³Π_g）,N₂⁺（B²Σ→X²Π）and O（3p⁵P→3s⁵S₂^o）.The amplitude and discharge time of AC voltage applied by the line-tube gas-liquid discharge plasma were adjusted.Considering the discharge stability and the balance relationship between efficiency and concentration in the process of producing NO₃^-,the optimal discharge parameter was 5 min discharge at 55 kV AC voltage amplitude.（2）On the basis of the original,another gas-liquid discharge plasma device is proposed.The square region of the interaction between plasma and liquid is mainly the horizontal plane.The device adopts stainless steel material as suspension electrode at the gas outlet.The discharge plasma was analyzed by taking discharge photos.It can be seen from the discharge image that the main discharge area in the center has stronger visible light,and there is an obvious weak discharge area in the periphery,which runs through the suspended electrode and liquid level,showing the characteristics of large volume stability.At the same time,the diameter of the plasma region and the surface interaction region is 20 mm.（3）The basic principle of diagnosing discharge plasma by emission spectroscopy is introduced,including electron density and plasma gas temperature.On this basis,the consideration of the above theoretical analysis in the experimental analysis is expounded.Taking the discharge plasma on the liquid surface as an example,the full spectrum of its emission spectrum is given.By analyzing its spectral lines and bands,the plasma electron density and plasma mass particle temperature are obtained.The plasma gas temperature is obtained by fitting N₂（C³Π_u→B³Π_g,Δν=-2）rotation band with less interference and relatively complete band.The simulation results show that the plasma gas temperature of discharge plasma on the liquid surface studied in this thesis is about 320 K.The electron density of plasma is calculated according to the mathematical relationship between Stark broadening and electron density by simulating the emission spectra of hydrogen atoms in plasma.In the specific calculation of electron density,the open atmosphere environment of the reaction device in this study was taken into account,and the temperature of its gas was 320 K,which was not enough to boil the liquid,and there was little water vapor in the plasma region,so the self-absorption effect of H atom was not taken into account.In addition,the magnitude of natural broadening is estimated,and the weight of natural broadening in the calculation of electron density on the Balmer family line is further shown.Based on the above considerations,the electron density of the plasma is calculated to be 2.2×10¹⁵cm^-3.