| Characterized by sharp rising edge, short pulse duration time, and effectively preventing glow to arc transition, high voltage nanosecond pulse can be utilized to drive dielectric barrier discharge in air, nitrogen and gas mixtures, for its unique advantages in achieving homogenous and cold plasma source, i.e. high energy efficiency, concentrations of active particles, and maintaining the gas at room temperature, which has great application prospects and research values in the field of biomedicine, aviation, material, energy, and chemical industry, etc. This article reports the spectral characteristics, active particles diagnosis, and crucial parameters investigation including rotational, vibrational and electron excitation temperatures of nanosecond pulsed air diffuse/uniform discharge plasma in different electrode structures, i.e. multiwires-plate, plate-plate and wire-cylinder. And as a typical application, bipolar nanosecond pulsed, unipolar nanosecond pulsed and sinusoidal alternating current wire-cylinder dielectric barrier discharge plasma in air for removal of gaseous formaldehyde have been compared. Main results for this study are as follows1. A diffuse dielectric barrier discharge plasma generated by nanosecond pulse power had been achieved using a multiwires-plate electrode configuration in atmospheric air. The discharge image and optical emission spectra, as well as rotational, vibrational and electron excitation temperatures are investigated and compared with those of discharges in nitrogen. The experiment results show that under both air and nitrogen environment, the discharge is diffuse and the optical emission spectra are dominated by N2 (C3??B3?g). However, the emission spectra intensity of N2 (C3?u?B3?g) in air is 1/5 of that in nitrogen, and the spectra of NO (A2??X2?) or OH (A2??X2?) are very weak. The rotational, vibrational and electron excitation temperatures are 320±5 K,2175±50K and 2145±50K in air discharge while 400 ±5K,1860±50 K,1690±50K in nitrogen discharge. With the rise of pulse peak voltage and the decrease of discharge gap distance, the intensities of NO (A2??X2?), OH (A2??X2?, 0-0), N2 (C3?u?B3?g) and N2+(B2?u+?X2?g+,0-0,391.4 nm) and rotational temperatures raise markedly, while vibrational temperatures and electron excitation temperatures decrease slightly. Nevertheless, pulse repetition rate has little effects on the intensity of emission spectra and temperatues. Moreover, the effects of oxygen and argon on emission spectra intensities of NO (A2??X2?), OH (A2??X2?,0-0), N2 (C3?B?3?g) and N2+(B2?u+?X2?g+,0-0, 391.4 nm) and plasma temperatures in nitrogen discharges are also obtained. The emission spectra intensities decreased sharply in range of 0%-5% concentration of oxygen, and then much slowly when the concentration of oxygen is over 5%. Meanwhile, rotational temperature increases and vibrational and electron excitation temperatures decreased. While with the increase of argon, the spectra intensities and rotational temperature rise and vibrational and electron excitation temperatures almost keep invariant.2. The effect of dielectric barrier material (ceramic, quartz, epoxy and PTFE) and thickness on the uniformity of nanosecond pulse dielectric barrier discharge plasma under plate-plate electrode structure in atmospheric air have been investigated. Also, the uniformity and breakdown mode of discharge have been examined by utilizing the discharge image, typical waveforms of pulse voltage and current, and emission spectrum of N2+(B2?u+?X2?g+,0-0, 391.4 nm).The discharge plasma is in uniform mode, the emission spectrum of N2+(B2?u+? X2?g+,0-0,391.4 nm) are very weak,and the rotational and vibrational temperatures(Trot and Tvib) are 350 ± 5 K and 3045 K, when using 1 mm ceramic dielectric plates under the condition of the pulse peak voltage of 30 kV, the pulse repetition rate of 150 Hz, and the gas discharge gap of 3 mm, which indicates that the discharge plasma is in high non-equilibrium degree and uniform mode. In the selected four kinds of dielectirc materials, with the increase of the permittivity of dielectric barrier, the initial discharge voltage decreases and the discharge termination gap distance augments. With the increase of the thickness of ceramic plates, the spectrum intensities decreases, the initial discharge voltage increases and the uniformity of discharge turns poor. The ratio of N2+/N2 is utilized to estimate reduced field strength E/N and the relationship of discharge uniformly and N2+/N2 ratio is discussed. The results show that with the decrease of discharge gap distance and dielectric thickness and the increase of pulse peak voltage, the ratio of N2+/N2 decreases and reduced field strength E/N reduces, leading to the improving of discharge uniformly of nanosecond pulse dielectric barrier discharge plasma.3. Atmospheric pressure air discharge plasma under wire-cylinder electrode structure in quartz tube is excited by high-voltage nanosecond pulse power and sinusoidal alternating current power, respectively. And a comparison study of these two kinds of discharges is made through visual image, electrical characterization, optical detection of active species, and plasma gas temperature. The results declare that discharge plasma generated by sinusoidal alternating current power presents filamentary mode, while that of nanosecond pulse power presents a better uniformity. In the same discharge cycles, the intensities of N2 (C3?u?B3?g) and N2 (B3?g?A3?u+) of nanosecond pulsed dielectric barrier discharge are 6?10 times higher than those of sinusoidal alternating current dielectric barrier discharge and OH (A2??X2?,0-0), N2+(B2?u+?X2?g+,0-0,391.4 nm) and O (3p?3s) are about 2.5 times, while the average energy consumption of nanosecond pulsed dielectric barrier discharge was about 1/13 of that of the sinusoidal alternating current dielectric barrier discharge.Meanwhile, the gas temperature of nanosecond pulsed discharge plasma is about 305 ± 5K, which is close to room temperature, and stayed nearly constant with the increase of duration time. By contrast, gas temperature of discharge plasma excited by sinusoidal alternating current power is about 200 K higher and continually increases as discharge duration time goes on. As an important application of nanosecond pulsed discharge, a contrastive analysis of the effects of bipolar nanosecond pulsed, unipolar nanosecond pulsed, and sinusoidal alternating current dielectric barrier discharges on removal of low concentration gaseous formaldehyde (154 ppm) have been investigated. The results demonstrate that the removal efficiencies of gaseous formaldehyde by bipolar nanosecond pulsed, unipolar nanosecond pulsed, and sinusoidal alternating current dielectric barrier discharges are 67%,63.8% and 73.8%, respectively, and typical power consumptions are calculated to be 0.325 W,0.3 W, and 8.9 W. When the packed-bed Al2O3 pellets exist, the removal efficiencies of formaldehyde increase approximately 10?20% in all the three types of plasma sources. Analysis suggests that it increaseses the discharge current, enhances the discharge intensity, and increases the active particles, in spite of reducing the residence time. Removal efficiencies can reach up to almost 95% when TiO2 or CeO2 nanoparticles are used. |
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