Caractérisation d'une décharge à barrière diélectrique à pression atmosphérique et son afterglow
Other titre : Characterization of an atmospheric pressure dielectric barrier discharge torch and its afterglow
Ionascut Nedelcescu, Anca Marina
This study presents a detailed optical characterization of a throughflow Atmospheric Pressure Dielectric Barrier Discharge and its afterglow, using emission spectroscopy. The electrical properties such as the power fed into discharge, the energy consumption during one cycle, the dielectric and total capacitance are determined using Lissajous figures. The values of the determined capacities and those theoretically calculated are in agreement. The afterglow length and the effect of the air entrainment at different operating conditions are studied using photographic technique. The non-equilibrium feature of the plasma in the discharge gap and in the afterglow is studied by the analysis of the rotational, vibrational and electronic excitation temperature, using Boltzmann plots. In helium flow, under the same operating conditions, the values determined are: T[indice inférieur r] = 533 « 15 K, T[indice inférieur v] = 2500 « 500 K, T[indice inférieur e] = 2800 « 570 K - in the gap-space, and T[indice inférieur r] = 466 « 10K, T[indice inférieur v] = 2100 « 430K, T[indice inférieur e] = 2600 « 530 K - in the afterglow. In helium flow, spectral line-shape analysis of the He (587.5 nm) and H[bêta] transitions is used to determine the contributions of the Doppler, Stark and Van der Waals effects. An innovative approach to determine the gas temperature T[indice inférieur g], defined as the mean kinetic energy of the gas particles, is given by establishing two parametric equations, one for each transition. These are applied to study the Tîndice inférieur g] variation with the applied voltage, and to determine the accuracy of the use of rotational temperatures as an approximation for T[indice inférieur g]. A linear increase of the gas temperature from 310 K to 460 K with the increase of the applied voltage from 5.8 kV to 10.8 kV is found for both studied lines. The slope of the rotational temperature variation with the applied voltage shows a 35% overestimation of the gas temperature as compared to that obtained from the line shape analysis. On the other hand, no significant variation of the gas temperature with the flow rate could be detected. The upper limit for the electron density at the highest voltage applied is established to be 4 x 10[indice supérieur 12] cm[indice supérieur -3], from the Stark broadening of H[bêta]. Finally, a detailed identification of the active species and their excitation mechanisms, in He and its gas mixtures such as: He-Ar, He-N[indice inférieur 2], He-H[indice inférieur 2]O, He-CH[indice inférieur 4], and He-O[indice inférieur 2], is presented by analyzing the emission spectra in the wavelength interval 300 nm to 900 nm.
- Génie – Thèses