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The effect of flowing air on dielectric barrier discharge excited by alternating voltage was investigated by high-speed video analysis and electrical measurements. The discharge was still in filamentary mode in flowing air, and the space-time distribution of filaments was changed by airflow. With the increase in airflow velocity, the space-time distribution of discharge filaments shown in top view images went through four phases, that is, spot-like distribution, line-like distribution, cotton-like distribution, and stripe-like distribution. Accordingly, the motion and morphology of discharge filaments shown in side view images also presented four phases: remaining still and straight between adjacent cycles, moving and bending downstream, almost remaining still and straight between adjacent cycles, and moving and bending downstream again. Different motions of filaments were considered to be the reason for the changed distribution of filaments in flowing air. In addition, the intensity of discharge in flowing air was enhanced by increasing the gas gap and discharge frequency. At high discharge current, larger airflow velocity was needed to reach phase transition. The changed distribution of micro-discharge remnants in flowing air can be responsible for the phase transition. Micro-discharge remnants redistributed during the time interval of adjacent half-cycle discharges, under the action of various forces, such as electric field force, drag force, repulsive force, electrostatic coupling force, and trap binding force. The changed position of micro-discharge remnants led to the complex motions of discharge filaments and further resulted in the changed space-time distribution of filaments. [ABSTRACT FROM AUTHOR]

An experimental study of the effects of airflow, magnetic field, and combination of airflow with magnetic field on a nanosecond pulsed dielectric barrier discharge (DBD) in atmospheric air is presented. The DBD is generated by an in-house designed DBD structure (a metal rod is inserted into the traditional parallel-plate DBD). The experimental results show that the application of airflow to the DBD can reinforce discharge and improve the discharge uniformity. When airflow increases to a certain velocity, surface discharge can transform into diffuse volume discharge. Moreover, the application of a magnetic field to DBD in static air can also enhance discharge, which is manifested as the enhancement of surface discharge. A similar but more significant effect is obtained in DBD combined airflow with magnetic field. Compared with the DBD with airflow only, the transition from surface discharge to diffuse volume discharge in DBD combined airflow with magnetic field occurs at a smaller airflow velocity. Besides, DBD combined airflow with magnetic field under different pulse repetition frequencies (PRFs) is also investigated. The results show that the minimum velocity required to generate diffuse volume discharge also shrinks with the decrease in PRF. In short, it is easier to generate diffuse volume discharge under the conditions of airflow, magnetic field, and lower PRF. The underlying physical mechanism of the above phenomena is discussed and mainly ascribed to the enhanced ionization by applying airflow, magnetic field, and lower PRF. [ABSTRACT FROM AUTHOR]

Atmospheric-pressure dielectric barrier discharge (DBD) with airflow participation has been widely used in recent years. In this experimental study, a diffuse DBD excited by repetitive nanosecond pulses is achieved in airflow. Upon the introduction of airflow to the gas gap, the discharge state transforms from a filamentary one into a diffuse one at first, followed by the generation of a thin filamentary discharge (TFD) at a high airflow rate. It is observed that the diffuse discharge (DD) and the TFD are ignited from the electrode boundary, which subsequently move toward the downstream region with a velocity below the corresponding airflow rate. Subsequent to hundreds of pulse cycles, a stationary discharge state is formed with the TFD in the upstream region and the DD in the downstream region. The length of the TFD region is associated with the airflow rate, the pulse repetition frequency (PRF), and the applied voltage. The observations presented above are ascribed to the transverse electric field at the electrode boundary and the redistribution of charges under the action of airflow. [ABSTRACT FROM AUTHOR]