M. Z. Rong

Aqueous reactive species induced by a surface air discharge: Heterogeneous mass transfer and liquid chemistry pathways.

Plasma-liquid interaction is a critical area of plasma science and a knowledge bottleneck for many promising applications. In this paper, the interaction between a surface air discharge and its downstream sample of deionized water is studied with a system-level computational model, which has previously reached good agreement with experimental results. Our computational results reveal that the plasma-induced aqueous species are mainly H+, nitrate, nitrite, H2O2 and O3. In addition, various short-lived aqueous species are also induced, regardless whether they are generated in the gas phase first. The production/loss pathways for aqueous species are quantified for an air gap width ranging from 0.1 to 2 cm, of which heterogeneous mass transfer and liquid chemistry are found to play a dominant role. The short-lived reactive oxygen species (ROS) and reactive nitrogen species (RNS) are strongly coupled in liquid-phase reactions: NO3 is an important precursor for short-lived ROS, and in turn OH, O2− and HO2 play a crucial role for the production of short-lived RNS. Also, heterogeneous mass transfer depends strongly on the air gap width, resulting in two distinct scenarios separated by a critical air gap of 0.5 cm. The liquid chemistry is significantly different in these two scenarios.

He+O2+H2O plasmas as a source of reactive oxygen species

The effect of water in the chemistry of atmospheric-pressure He+O2 plasmas is studied by means of a comprehensive global model. Water enables the generation of reactive oxygen species (ROS) cocktails that are rich not only in O, O2∗, and O3 but also in OH and H2O2. Due to its polar nature, water also leads to cluster formation, possibly affecting the plasma dynamics. Since the lifetime of many of the ROS is short, the plasma chemistry plays two roles: (i) direct interaction with superficial cells and (ii) triggering of a secondary chemistry that propagates the plasma treatment to regions away from the plasma-surface interface.

Prediction of critical dielectric strength of hot CF 4 gas in the temperature range of 300-3500 K

Sulfur hexafluoride (SF6) gas has a quite high global warming potential and hence it is required that applying any substitute for SF6 gas. Much interest in fluorine-containing compounds appears due to their widespread use as gaseous candidate of SF6 in fault current interruption process considering its relatively high performance of dielectric insulation and arc quenching. The critical reduced electric field strengths of hot CF4 gas corresponding to the dielectric recovery phase of a high voltage circuit breaker are calculated in the temperature range from 300 to 3500 K. The equilibrium compositions of hot CF4 gas at various pressures were determined based on Gibbs free energy minimization. Additionally, adopting full sets of improved cross sections, the critical reduced electric field strength of this derived composition was obtained by a balancing electron generation and loss modeled by the interactions between electrons and the dissociated species of hot gas evaluated by the electron energy distribution function (EEDF) derived from the Boltzmann transport equation. In order to confirm the validity of the present calculation, the predicted result for hot CF4 gas was compared with experimental results and previous calculations and there exists a generally good agreement. We have presented that the dielectric strength of hot CF4 gas experiences a fast reduction as the continuous dissociation occurs with increasing temperature. Comparison with dielectric properties of hot SF6, regardless of reduced dielectric properties in the low temperature range, replacing SF6 with CF4 brings an increase of the critical reduced electric field strength for temperatures above 2200 K, indicating possible theoretical verification of the practical applications that CF4 is an admixture to SF6 gas as the arc extinguishing and insulation medium in high voltage circuit breakers.

Influence of ablated PTFE vapor entrainment on critical dielectric strength of hot SF 6 gas

The influence of PTFE vapor injected into the SF6 on dielectric strength of hot gas mixture which corresponds to the dielectric recovery phase of a high voltage circuit breaker are investigated in the temperature range from 300K to 3500K. The equilibrium compositions of hot SF6/PTFE vapor mixture were determined based on Gibbs free energy minimization. Additionally, adopting full sets of improved cross sections, the critical reduced electric field strength of this derived composition was obtained by a balancing electron generation and loss modeled by the interactions between electrons and the dissociated species of hot gas evaluated by the electron energy distribution function (EEDF) derived from the Boltzmann transport equation. Results indicates that above the temperature of 2500K, the addition of PTFE vapor leads to a higher critical breakdown field which is an important result for practical applications.

A pilot study on the vacuum degree online detection of vacuum interrupter using laser-induced breakdown spectroscopy

Vacuum degree online detection of vacuum interrupter has been a great challenge for decades. In this letter, a novel approach based on laser induced breakdown spectroscopy (LIBS) was proposed to solve this tough problem, which is suitable for non-intrusive, electro-magnetic interference free and remote detection. The spectral lines of Cu, H, N and O elements from the interrupter shield were detected for a large gas pressure range from p = 1 × 10−3 Pa to 1 × 105 Pa. It was found that the spectral intensities of O and H increase monotonically with gas pressure, in contrast the spectral intensity of Cu first decreases slightly and then increases. Their intensity ratios, especially for that of Cu to O, change dramatically and monotonically with the gas pressure when p ≤ 0.1 Pa, indicating that they can be used for determining the vacuum degree values. Spectral ratio method fundamentally reduces the influences of the possible variation in measuring distance and the laser power fluctuation, making LIBS a promising method for vacuum degree online detection of vacuum interrupters.