| Dielectric barrier discharge(DBD)is one of the most simple and effective methods to generate non-equilibrium plasma at atmospheric pressure.Due to its advantages of simple operation and low production cost,DBD has a wide application aspect in many fields,such as material modification,bio-medicine,energy environment,and aerospace.But atmospheric pressure DBD is usually presented as a filamentary discharge mode,but the uniform discharge has a higher guiding value in the practical application.Therefore,how to improve the uniformity of discharge is one of the key issues that researchers pay attention to.Relevant studies have shown that the airflow and magnetic field can not only improve the uniformity of discharge,but also affect the discharge characteristics,which requires further understanding about the influence mechanisms.In this paper,the nanosecond pulse power supply is used to excite the DBD to generate plasma under the conditions of airflow and magnetic field.The discharge is combined with the electrical and optical measurement methods.The following researches are carried out:1.An asymmetric plate-plate electrode structure is adopted to generate the transverse component of electric field parallel to the electrode plane.The effects of the transverse electric field on discharge are studied in the range of airflow velocity of 0-40 m/s.It is found that the misaligned region of electrodes is characterized by diffuse discharge,and the micro-discharge channels in the aligned region moves directionally,which indicates that the generation of diffuse discharge is related to the movement of the micro-discharge channel.The moving velocity of the micro-discharge channel calculated by taking the discharge temporal evolution images increases with the decrease of the discharge gap and pulse repetition frequency(PRF),which is consistent with the variation of the diffuse discharge area in the misaligned region.It is further verified that the movement of the micro-discharge channel is the key to the generation of diffuse discharge.After introducing airflow,dense filamentary discharge begins to appear in the airflow inlet,which gradually expands to the downstream with the increase of airflow velocity.When airflow is introduced into the discharge space in the same direction as the transverse electric field,the dense filamentary discharge area of asymmetric electrode geometry is larger than that of symmetric electrode geometry.However,when the direction of the airflow is opposite to that of the transverse electric field,the dense filamentary discharge area of asymmetric electrode geometry is reduced.2.The effects of airflow and magnetic field on pin-plate DBD are studied by measuring the electrical and optical characteristics.The results show that the state of micro-discharge channel undergoes a transition from upright to curving to upright with the increase of the airflow velocity,and the discharge is weakened by introducing airflow,which is reflected in the decrease of the current and photo-current intensity.On the one hand,airflow blows part of the heat,charged particles and metastable particles out of the discharge space.On the other hand,the path growth of micro-discharge channel leads to the increase of the resistive component of the gas gap and breakdown voltage.Moreover,the current and photo-current waveforms indicate that the magnetic field can enhance the discharge with or without airflow,but the weaken effect of airflow on discharge is more obvious when magnetic field is applied.Under the conditions of higher applied voltage and PRF,the current and photo-current intensity is higher.At this time,the weaken effect of airflow on discharge is more obvious,while airflow has little effect on discharge when the applied voltage and PRF are low.With the increase of the applied voltage and PRF,the maximum airflow velocity corresponding to the curving state of micro-discharge channel is increased. |
PDF Full Text Request