Investigation On The Uniformity Of Dielectric Barrier Discharge(DBD) With Rotating Electrode And Its Application

Low-temperature plasma has a broad application prospects in the field of ozone generation, surface treatment of materials, fluid control, sterilization, et.al. The dielectric barrier discharge is an effective means to produce a large volume of low-temperature plasma under atmospheric conditions. However, it is apt to form filamentary discharge, and the spatial distribution of discharge is uneven, which limits its industrial applications. Over the past decade, the atmospheric pressure homogeneous dielectric barrier discharge research focus mainly on the glow and Townsend discharge which is charateristiced as the absent of micro-discharge. While it requires harsh conditions and is not conducive to industrial applications. From the perspective of industrial applications, even in the presence of micro-discharge, if the microdischarges are evenly distributed on a material surface within a certain time, it is possible to achieve a good treatment effect. Hence improving the spatioal distribution of microdischarges to obtain a long time scale uniform discharge is also an important issue to be examined.Based on our previous researches, it is demonstrated that the standard deviation of gray levels could quantitatively reflect the discharge uniformity by a microdischarge superposition model. The smaller the standard deviation, the more uniform the discharge. This is a theoretical foundation for the quantitative evluation of the long time scale discharge.We observed a long time-scale DBD transient process, that is, the standard deviation of gray levels gradually reduces with an increase of the discharge time, and finally keeps stable. From the discharge gray curves of different times, it is apt to form relatively strong discharge filaments at the initial state of the transient process, when the discharge reach a steady state, the discharge filaments strength gradually weakened and fusion and some ’clustered’ discharges form. The microdischarge interaction caused by the dispersion of the discharge remnant may be the reason for the transient process. With an increase of discharge time, a temperature rise will accelerate the air convection and thus the expansion and interaction of the discharge remnant, which results the seed electron distribution more uniform.In this paper, a DBD with rotating electrode is developed to achieve a long time scale uniform discharge. Experimental results show that the transient process of the rotating electrode ends faster than that of the stationary electrode, and the grayscale standard deviation is smaller. The standard deviation of gray levels decreases with the speed increase. When the the electrode speed is over3000rpm, the standard deviation of gray levels keeps about4, which is comparable with that of the discharge at atmospheric pressure helium2. When the rotating rate is4000rpm, the effect of voltage, frequency, and gap distance on the discharge uniformity is small. This suggests that a long time scale uniform discharge can be achieved when the speed exceeds3000rpm.When the electrode is rotating, at the initial state of the transient process, the discharge forms lighting bands distribution; at the stable state of the transient process, the discharge becomes diffuse and changes little with the electrode rotation. The discharge image and gas flow simulation results show that the discharge remnant has a dominant effect on the discharge distribution at the initial state. The ICCD images show that the intensity difference of the discharge filaments is obvious, which has an important effect on the discharge uniformity. At the steady state of the discharge, the discharge intensity is relatively weak, which could prevent the burning down of the material surface.Mesh and barrier coated electrode are used to investigated the effects of the spatiotemporal periodic boundary on the discharge uniformity. The results show that the same uniform discharge could be obtained at a smaller rotating rate. When the speed is1000rpm, the uniformity of discharge changes little with the variation of the voltage, frequency, and gap. Moreover, the mesh electrode can be obtained in a relatively low voltage, the stronger intensity discharge.Rotary electrode is used for the ozone preparation. It is found that voltage and frequency have a significant effect on the ozone concentration, but if the voltage and frequency is too large, the the yield of ozone will reduce. Flow rate has a significant effect on the yield, while the flow rate through the assembly will reduce the ozone concentration. Between the voltage, frequency and flow rate has a best fit. In the case of a higher voltage, regardless of the electrodes is rotated or not, the final ozone will reach a higher concentration; rotation ozone concentration and the yield can be improved when the voltage is low. The electrode rotation will change the air flow field and increase the contact time between the air and the discharge, which could improve the discharge uniformity and the ozone yield.