Microscopic Electrical Properties And Characteristics Of Excited OH Radical In Multi-needle-to-plate Corona By OES

DC corona discharge in the configuration of needle-plate electrode has been widely used in decomposing contaminants. It has advantages of low energy consumption and high removal efficiency. However, there is not enough study of its microscopic properties, such as current density, distribution of electric field, radicals, active species and etc.In this thesis, the emissions of N2 second positive band produced by multi-needle-to-plate DC corona discharge were detected using OES. The spectral intensity ISPB at different point was calculated by detecting the intensity ISPB in different area of the ionization region, and the distribution of ISPB was drawn accurately. The microscopic electrical properties of the ionization region were analyzed according to the trend line of the distribution of ISPB. The electric field and the current density were analyzed theoretically according to Possion equation. Thus, the relationships between microscopic and macroscopic electrical properties were analyzed. Then, the emissions of excited OH radicals were detected in multi-needle-to-plate negative corona discharge and streamer discharge. The effects of relative humidity and electrical properties in the negative corona discharge (including U, I, P and d) on excited OH radicals were investigated experimentally, and some important rules of the characteristics of OH radicals were obtained. The distribution of excited OH radicals in streamer discharge was drawn accurately according to the detected data, and the distribution characteristics of excited OH radicals were summarized.The main conclusions are as follows:The intensity of N2 second positive band firstly increases and then reduces in the ionization region. The distribution of ISPB in the middle and outer layers of the ionization region is corresponding to the density of energetic electrons, and the ISPB reduces from the middle layer to the outer layer. The distribution of ISPB in negative glow discharge is similar to that in positive glow discharge; According to Poisson equation, the expressions of the electric field intensity and the current density were deduced respectively. In the ionization region, the electric field intensity firstly increases and then reduces with the increase of r. The position of the maximum value of ISPB is consistent with that of the maximum electric field intensity obtained from theoretical analysis. The current density reduces along the needle axis, and it is linearly proportional toISPB in the middle and outer layers of the ionization region. The mobility of charged particles in the outer layers of ionization region plays a certain role in discharge current formation. The current is irrelevant to r in the migration area.With the increases of the applied voltage U and the discharge current I, the number of excited OH radical increases in negative glow discharge. The number of excited OH radical per unit power reduces with the discharge power increase. In the ionization region, the density of excited OH radical firstly increases and then reduces along the needle axis. With the space between electrodes increase, the density of excited OH radical reduces; In streamer discharge, the emission spectrum of excited OH radical can be detected almost in whole discharge gap. The shape of the region around the needlepoint looks like a bullet, and the density of excited OH radical reduces with the r increase. The distribution of OH radical farther away from the needlepoint firstly increases and then reduces along the radius direction; Both in positive and negative corona discharges, the number of excited OH radical firstly increases and then reduces with the relative humidity increase. In practical application, the better RH ranges for positive and negative corona discharges are 40-60% and 40-55% respectively.