Measurement of atmospheric pressure plasma properties as functions of voltages and gas flow rates by non-invasive diagnostic methods

• Main Authors: Yu-Chun Lin, 林育鈞
• Other Authors: Meng-Jiy Wang
• Format: Others
• Language: en_US
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/zh3bns

博士 === 國立臺灣科技大學 === 化學工程系 === 107 === Plasma diagnostics played important roles in providing the flux of reactive species, the composition of plasmas, and the status of plasma processes. In this regard, the analytical methods were widely utilized to investigate the effects of operational parameters of the properties of atmospheric pressure plasma (APP) including temperature, density, discharge, and flow behaviors. In this thesis, the non-invasive diagnostic techniques including power waveform measurement, Schlieren analysis, optical emission spectroscopy (OES), laser scattering, and laser-induced fluorescence (LIF) were used to determine the type of discharges, flow behavior, rotational temperature (Tr), electron density (ne), electron temperature (Te), and the generation of hydroxyl radical (OH), respectively, as the functions of gas flow rates and applied voltages. For the first plasma system, the 120 Hz AC atmospheric pressure plasma (120-Hz-AC-APP) was used to demonstrate the effects of gas flow rates and applied voltages on the discharge properties. The results indicated that the increase of gas flow rate caused the formation of spark discharge, due to the 3 spikes of high voltage response that were obtained when flow rate increased from 2 slm to 5 slm. This may be due to the increase of gas flow rates that resulted in the increase of the resistance between two electrodes and further perturbed the discharge. Additionally, the increase of gas flow rates and applied voltages resulted in the shortening of the laminar flow region, due to the turbulence behavior that took place by the Rayleigh-Taylor instability and Kelvin-Helmholtz instability. On the other hand, Tr increased from 1400 K to 1550 K by increasing the applied voltage from 5 kV to 12 kV at 2 slm discharge. Moreover, Tr increased from 950 K to 1180 K by increasing gas flow rate to 8 slm. Interestingly, the maximum concentration of OH was obtained at the position where the laminar flow turned into turbulence, due to the air species started to be dissociated by plasma and resulted in the recombination of reactive species. In the second part of the thesis, the microwave APP jet (MWAPPJ) were employed to determine the influences of gas flow rates on the physical properties by Thomson scattering techniques. The variations of the physical properties were investigated by performing the Schlieren analyses. The results demonstrated that the increase of gas flow rate from 2 to 6 slm led the increase of Te from 1.28 ± 0.41 to 2.33 ± 0. 72 eV and the decrease of ne from 4.09 ± 2.01 × 1015 cm-3 to 2.13 ± 0.41 × 1015 cm-3. Furthermore, by increasing the gas flow rate to 8 slm, it was found that Te decreased to 1.99 ± 0.56 eV and the ne increased to 3.09 ± 2.27 × 1015 cm-3. The reason may be owing to the acquisition position is closed to the end of the plasma jet, in which the electrons avalanched to maintain the discharge and thus resulted in the high electron field and momentum.