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Currently, China is using the SF6/N2 gas mixture to gradually replace SF6 in GIS and other equipment. However, gas-insulated equipment will inevitably have local overheating faults. The SF6/N2 gas mixture will decompose to some extent at high temperatures. Impurities such as moisture in the equipment can affect this decomposition process. At present, there are fewer studies on the moisture content of the superheated decomposition of the SF6/N2 gas mixture. Therefore, this paper carries out the SF6/N2 mixed gas superheat decomposition experiment on the constructed superheat decomposition simulation experiment platform. By changing the content of trace water, the influence of trace water on the decomposition of the SF6/N2 mixed gas insulation medium with superheat failure was initially investigated. It is found that trace H2O will promote the generation of SF6 characteristic decomposition products, especially for the generation of SO2F2. The generation of SO2 in the product is the largest, and its generation process needs the full participation of H2O. In addition, the addition of trace water will also improve the yield of nitrogen-containing products NO and NO2, and under the experimental conditions of this paper, by adding the microwater, the yield reaches 100–300 µl/l. The reaction mechanism of H2O decomposition and combining with N atoms to generate NO and NO2 at high temperatures was analyzed in this paper. The thermodynamic properties of the main reaction paths and the equilibrium constants were calculated based on the density functional theory, which provided theoretical references for the further study of the mechanism of SF6/N2 superheated decomposition. [ABSTRACT FROM AUTHOR]

In this paper, the effects of transition metal atom Pt doping on the structural parameters and electronic properties of the two-dimensional material Ti3C2Tx MXene (T = OH, O or F) as well as the adsorption interaction between the doped material and SF6 are investigated based on density functional theory calculations. To investigate the SF6 adsorption mechanism, the adsorption structure, adsorption energy, charge transfer, and density of states of Pt atom-doped Ti3C2Tx after the adsorption of SF6 molecules were analyzed. The results showed that the electronic properties and chemical activity of the doped Ti3C2Tx changed significantly compared to those before doping. In addition, Pt-doped Ti3C2(OH)2 has good adsorption ability on SF6 molecules, and its adsorption type is chemisorption; in the relevant sites, SF6 undergoes chemical bond breaking, and the doping of Pt improves the catalytic effect of Ti3C2(OH)2. The adsorption capacity of Pt-doped Ti3C2O2 and Ti3C2F2 for SF6 molecules is much weaker than that of Pt-doped Ti3C2(OH)2, physical adsorption occurred, and there was almost no degradation of SF6; the doping of Pt did not improve the catalytic effect of Ti3C2O2 and Ti3C2F2. [ABSTRACT FROM AUTHOR]

C5F10O has been widely studied as a promising environmentally friendly substitute to SF6 in power equipment. Up to now, the environmentally friendly gas insulated equipment developed still uses the same sealing materials as SF6 gas insulation equipment. However, whether these sealing materials are chronically compatible with C5F10O has always been a fundamental problem that perplexes the industry and academia. In this study, a thermally accelerated aging experiment on four rubber materials contacted with C5F10O/N2 was carried out. During the experiment, aged rubbers were analyzed using scanning electron microscopy and x-ray photoelectron spectroscopy to obtain the surface morphology characteristic and element composition. The gas samples were collected periodically and detected through gas chromatography mass spectrometry. Meanwhile, the degradation of the rubbers' mechanical property is tested to figure out their long-term compatibility with C5F10O/N2 mixtures. Surface analysis of the rubber samples showed that after thermal accelerated aging, F in the form of C–F bonding and metal fluorides were detected on the surface of the ethylene propylene diene monomer (EPDM), nitrile butadiene rubber (NBR), chloroprene rubber (CR), and methyl vinyl silicone rubber (VMQ), which did not exist in origin samples. The main gaseous decomposition products of C5F10O include CO, CO2, C3F6, and C3F7H, and the concentration when coexisting with rubber is significantly higher than that in the control group. The compression performance of aged rubbers all reduced, and the compression performance of EPDM and NBR is better than that of CR and VMQ. The experimental results proved the incompatibility between C5F10O and these four rubbers, while EPDM and NBR showed less deterioration in compression properties and could be more suitable for the C5F10O power equipment. [ABSTRACT FROM AUTHOR]

In contrast to van der Waals (vdW) forces, Coulombic dipolar forces may play a significant role in the coagulation of nanoparticles (NPs) but has received little or no attention. In this work, the effect of dipole-dipole interaction on the enhancement of the coagulation of two spherically shaped charge-neutral TiO2 NPs, in the free molecular regime, is studied using classical molecular dynamics (MD) simulation. The enhancement factor is evaluated by determining the critical capture radius of two approaching NPs for different cases of initial dipole direction with respect to path (parallel/perpendicular) and orientation with respect to each other (co-orientated/counterorientated). As particle diameter decreases, the enhancement of coagulation is augmented as the ratio of dipole-dipole force to vdW force becomes larger. For 2-nm TiO2 NPs at 273 K, the MD simulation predicts an average enhancement factor of about 8.59, which is much greater than the value of 3.78 when only the vdW force is considered. Nevertheless, as temperature increases, the enhancement factor due to dipole-dipole interaction drops quickly because the time-averaged dipole moment becomes small due to increased thermal fluctuations (in both magnitude and direction) of the instantaneous dipole moment. [ABSTRACT FROM AUTHOR]

The flow structure and velocity fluctuation generated downstream from coaxial geometry dielectric-barrier-discharges are investigated at atmospheric pressure. The discharges are characterized using in-situ electrical measurements and optical diagnostics. Both streamers and glow-like discharges are detected in each alternating-current cycle. The flow structure is temporally and spatially resolved using tracer particles, and vortices are visualized in planar velocity distribution patterns. The flow upstream of the discharge is laminar; however, we discover that the spectrum of downstream fluctuation velocity exhibits a nearly Kolmogorov −5/3 slope, which is a typical feature for high Reynolds number turbulent flows. Based on the electron density measured through a line-ratio method, the dimensionless electrical body force derived from the Navier-Stokes equation is estimated to illustrate the generation of Reynolds stress. It is found that although less than 0.1% of the discharge power is converted into the fluctuation kinetic energy, the electrical body force rather than Joule heating plays a dominant role in flow fluctuation. [ABSTRACT FROM AUTHOR]