Study On The Uniformity And Mode Transition Of Dielectric Barrier Discharge

Dielectric barrier discharge (DBD) can produce low temperature and non-thermal plasma at atmospheric pressure. However, DBD usually shows the mode of the micro streamer discharge with many bright filaments between electrodes. The non-uniformity of the spatial properties of micro streamer discharge limits the further application of DBD. Therefore, it is of great significance to study how to improve the DBD discharge efficiency and spatial uniformity. In order to further investigate the method and mechanism for developing homogeneous DBD. In this paper, based on atmospheric pressure coaxial electrode configuration DBD reactor, the influences of the driving frequency and airflow rate on the optical and electronic properties of discharge reactor have been investigated by using the plasma optical emission spectra (OES), Q-V Lissajous figures and the DBD equivalent electrical circuit model. Finally, the mechanism for the discharge mode transition is studied in detail.The influences of airflow rate on the spectral properties and the mechanism for the discharge mode transition were comparatively studied between nitrogen and air by using the plasma optical emission spectra. The results showed that:1) With increasing of the flow rate, the vibrational temperature of nitrogen increases at first and then decreases, the vibrational temperature of air increases at first and then tends to be stable, all of the rotational temperature decreases at first and then tends to be stable; 2) The intensity of the plasma optical emission spectra in air is less than in nitrogen under the same condition. The intensity of the typical band series of the second positive band system and the first negative band system of the nitrogen molecule exhibit similar evolution with increasing the flow rate to those of the vibrational and rotational temperature respectively; 3) The mechanism for the discharge mode transition influenced by airflow rate has experienced three development stages. At the first stage, the filamentary discharge mode is maintained by enlarging the streamer head which can increase the electron energy and ionization rate. At the second stage, the transitional diffusion mode is maintained by enlarging the streamer head and electronic collision avalanche ionization (a ionization). At the third stage, the glow-like discharge mode is mainly maintained by a ionization.The influences of the driving frequency and airflow rate on the electronic properties and the mechanism for the discharge mode transition of discharge reactor have been studied by using Q-V Lissajous figures and the DBD equivalent electrical circuit model. The results showed that:1) With increasing of the flow rate, the energy DBD reactor consumes in one period and power factor gradually tend to reduce, the load voltage almost keeps a constant, the amplitude of current pulse decreases at first and then shows an approximately constant with the lapse of time and the homogeneous discharge is appeared at the same time. With increasing of the flow rate, the average current, electrical power consumption and the branch conductance of DBD reactor gradually decrease and then tend to be stable, the gap capacitance increases gradually, the branch impedance of DBD reactor increases at first and then tends to be stable; 2) When the gas flow rate is less than the threshold value, the filamentary discharge is more obvious. On the contrary, the glow-like discharge with high efficiency is shown; 3) The main factor for the discharge mode transition of discharge reactor is the proportion of the space charge and the charges on barrier surface; 4) With increasing of the driving frequency, the load voltage, discharge current, average current, electrical power consumption, power factor, dielectric capacitance and the branch conductance of DBD reactor are increase at first and then decrease, the gap capacitance decreases at first and then tends to be stable, the branch impedance of DBD reactor decreases at first and then increases, all of them extreme values are reached respectively at resonance point; 5)The resonance frequency of the reactor increases at first with the rise of airflow rate and then tends to be stable. The change of dielectric capacitance influenced by airflow rate is the underlying reason for this phenomenon.