Effects Of Airflows On Dielectric Barrier Discharge At Atmospheric Pressure Air

The low temperature plasma has a great potential of application in the area of material processing because of their desirable properties of containing numbers and a variety of active species, including ions, electrons, excited atoms, molecules and free radicals. Recently, the main method of producing the uniform low temperature plasma is in the low-pressure discharges operated with the pressure order of torr, which is costly, discontinuous and inefficient in the practical industrial applications. Therefore, the generation of air discharge plasma at the atmospheric pressure is of great importance and necessity for the industrial applicaiton.Dielectric barrier discharge (DBD) could provide a simple technology to establish non-equilibrium plasma conditions in atmospheric-pressure gases. Depending on a variety of experimental conditions, the uniform glow discharge with a diffuse appearance can be realized,.with the properties of high reactive chemicals, fast processing, low temperature, low cost, and uniform distribution. But there exist some obstacles in obtaining the uniform discharge plasma in ambient air because it is difficult to control the stability of discharge in air with the pressure increasing. The microfilaments in the atmospheric air discharge will cause pitting or pinholes when they contact with the workpiece. So it is of great importance to obtain uniform and mild plasma in the atmospheric air discharge. In this work, it is found that the application of high speed air flow is helpful to enhance the stability and uniformity of atmospheric air discharge.In this paper, the discharge is driven by a sinusoidal power supply, the frequency with the range of 300 Hz-10 kHz and the maximum peak-to-peak voltage of 40 kV. The discharge is created between two circular parallel-plane electrodes (one of them being covered by an insulating layer), and a blower is used to produce the airflow. And the influence of airflow on the evolution of atmospheric air DBD is studied. Firstly, the effects of applied voltage, frequency, electrode distance but without the airflow are investigated. It is found that, with the increase of applied voltage, the discharge becomes density, and the filaments tend to become stable; when the frequency is improved, the discharge is enhanced and the positive current improves more seriously, and the micro-discharge channels become stable; As the electrode distance decreases, the breakdown voltage becomes lower, and the uniform glow discharge with a diffuse appearance is presented.Then, compared to the data above, the effect of airflow to the atmospheric air DBD is discussed. It is found that the airflow can make influence on the spatial distribution and intensity of discharge. When a fast airflow is added into the discharge gap, the discharge patterns transform from filaments to curving stripes and the curvature degree rises with the increase of the airflow speed. At the same time, the discharge intensity decreases. However, when the discharge frequency is close 500 Hz, the discharge intensity will become quite weak and never reduce with the increase of the airflow speed. To improve this result, the plasma emission spectrum is measured when the frequency is fixed at 2 kHz, 1 kHz and 500 Hz, respectively. It is also shown that the intensity of light reduces when the airflow is added into the discharge gap. The faster the airflow's speed is, the more reduction of the intensity of light is. But when the discharge frequency is close 500 Hz, the variation changes less. The measurement result here is accord with the discharge intensity observed. Furthermore, it is also found that, with a fixed flow, the curvature degree of curving stripes has no change with the variation of applied voltage, frequency and electrode distance.