气流对氮气介质阻挡放电气体温度及放电模式的影响

Influences of gas flow on gas temperature and discharge mode in dielectric barrier discharge of nitrogen at atmospheric pressure

利用光谱测量和高速照相的方法,对大气压氮气介质阻挡放电进行了研究.在气流的帮助下,2mm气隙中的均匀放电可以长时间得以维持.根据放电电流波形和1μs曝光时间的放电图像,这种均匀放电被判定为汤森放电.用氦氖激光器对实验中所用的光谱仪带来的谱线轮廓展宽进行了标定,并将得到的仪器展宽数据输入Specair软件,计算了不同气体温度下氮分子二正系0—2谱带的谱线轮廓.通过用计算谱线轮廓去拟合实验谱线轮廓,确定了氮分子的转动温度并将其近似为气体温度.结果表明:大气压氮气介质阻挡汤森放电并不能使气体温度大幅上升(ΔTg≤50K),气体温度的小幅上升不会引起热不稳定性而导致放电发展成为细丝放电.气流确实可以降低放电气体温度,但这不是使汤森放电得以维持的原因.通过比较加入气流前后的放电光谱可知,气流降低了气隙中杂质氧的含量,使得更多的氮分子亚稳态N2(A3Σu+)的寿命延长到下一次放电的起始时刻,为汤森放电提供了必需的大量种子电子.

Dielectric barrier discharge in nitrogen at atmospheric pressure is studied with the spectroscopy and the fast photography of the discharge.By the introduction of a nitrogen flow into the discharge gap,the homogeneous discharge in a 2 mm gap can be maintained.Based on the waveform of the discharge current characterized by a current pulse per half cycle of the applied voltage and the 1 μs exposure discharge photograph showing a luminous layer covering the entire surface of the anode,the homogeneous discharge is identified with a Townsend discharge.The instrumental broadening of the spectrometer used in the experiment is calibrated with a helium-neon laser.The data relevant to the instrumental broadening are input into a code called Specair for calculating the spectrum profiles of 0—2 band in the second positive system of nitrogen molecules at different gas temperatures.By fitting the calculated spectrum profiles to the experimental one,the rotational temperature of the nitrogen molecules is determined.The results show that the dielectric barrier Townsend discharge in nitrogen at atmospheric pressure cannot heat the nitrogen to a high temperature（ΔTg≤50 K） and the small rising in temperature does not induce the thermal instability that leads to the transition of the Townsend discharge to a filamentary discharge.By the addition of a gas flow into the discharge gap,the nitrogen is indeed cooled down to a lower temperature.However,it is not the reason for the Townsend discharge to be maintained.By comparing the discharge spectra with and without the gas flow,it could be concluded that the gas flow much reduces the density of the impurity oxygen desorbed from the dielectric by the discharge and makes it possible for more nitrogen metastables to survive to the beginning time of the next discharge and to provide sufficient seed electrons which are necessary for Townsend discharge.