Search

Silicone rubber is widely used in power system insulation for its hydrophobicity and hydrophobicity transfer to prevent pollution flashover. The influence of low molecular weight (LMW) siloxanes on hydrophobicity of contaminated silicone rubber after plasma jet treatment was investigated in this study. Experimental results show that plasma jet treatment for several seconds can significantly improve the hydrophobicity of contaminated silicone rubber. LMW siloxanes play an important role in the quick recovery of hydrophobicity induced by plasma jet treatment. Extraction of the LWM siloxanes from the silicone rubber decreases the contact angle after plasma treatment. Fourier transform infrared (FTIR) spectroscopy shows that hydrophobic groups appear on the surface of the contamination layer. The hydrophobicity improvement of contaminated silicone rubber results from LMW siloxanes transferred to the contamination layer during plasma treatment and the LMW siloxanes are mostly original uncrosslinked siloxanes in the silicone rubber. The molar mass distributions of the LMW siloxanes in hydrophobic contamination of treated specimens were similar with naturally transferred ones. X-ray photoelectron spectroscopy shows that an inorganic layer appears after plasma aging, which obscures the transfer of LMW siloxanes and reduce the hydrophobicity during plasma treatment. [ABSTRACT FROM AUTHOR]

Pulsed electric fields (PEFs) are employed in a newly developed food sterilization technology via repetitive electric pulses. The evolution of bubbles and the consequent electrical breakdown of the liquid treatment chamber are the main technical hurdles for industrial applications of this technology. The evolution pattern of the bubbles and the effect of pulse parameters on the bubbles under repetitive pulses are studied. Repetitive bipolar rectangular pulses (6–10 kV, 20–80 μs in duration, with a 50–200 Hz repetition rate) are applied to a gap (1 cm) containing sodium chloride solution (with a conductivity of 30 μS/cm). A high-precision bubble monitoring system is developed to recognize and count microbubbles with diameters greater than 50 μm. The pattern of the bubble evolution can be divided into 4 stages: the initial stage, developing stage, converging stage and discharging stage. The saturated time, number, area and average diameter of the bubbles are introduced as feature parameters to better characterize the bubble evolution, and the relevant time-varying curves for different pulse parameters are obtained based on experimental images. The experimental results show that a stronger electric field, a longer pulse duration and a higher repetition rate speed up the evolution of the bubbles. The growth of the bubbles depends more on the effect of continuous long pulses, and the electric field might be a deciding factor concerning the initiation of microbubbles, while the increase in bubble volume is mainly a result of the thermal effect of current. [ABSTRACT FROM AUTHOR]

Hydrophobicity improvement of contaminated high temperature vulcanization (HTV) silicone rubber is of great significance to avoid risk of pollution flashover during wetting events. In the present investigation, low-temperature plasma jet produced by dielectric barrier discharge (DBD) under atmospheric pressure was used to quickly increase the hydrophobicity of contaminated HTV surface. Effects of the processing time, non-soluble deposit density (NSDD) and transfer time on the hydrophobicity improvement were studied and the long term stability of hydrophobicity was investigated. Experimental results proved that: hydrophobicity of contaminated HTV silicone rubber was significantly improved after a quick exposure to low-temperature plasma jet; and with the increase of exposure time, hydrophobicity transfer increased and a larger contact angle was obtained for the same transfer time. For the low discharge power plasma treatment, NSDD had a negative effect on hydrophobicity improvement and with the increase of the NSDD, increment of the contact angle decreased. In addition, hydrophobicity improvement had long term stability. Control experiment proved that interaction of plasma jet with silicone rubber played an important role in accelerating the transfer of low molecular weight (LMW) silane chains from the silicone rubber to the pollution layer, which finally resulted in the hydrophobicity improvement. [ABSTRACT FROM PUBLISHER]

Electrical breakdown of the treatment chambers under repetitive high-intensity pulses impedes the industrial application of pulsed electric field (PEF) technology. In this paper, phenomenon and laws of electric discharges in the PEF treatment chambers were studied. The experimental results indicate that temperature increase and formation of gas bubbles under high electric field strength reduces insulation of water solution. Air dissolved in the samples is only a small part of the bubble and hardly affects the size of bubble formed. The majority part of the gas in the bubble comes from the vaporization of liquid. Fluctuations in the temperature curve may be a direct indication of the beginning of bubble formation. Partial electrical discharges occur inside the gas bubble and are the precursor of dielectric breakdown of PEF treatment chambers. Solution temperature and conductivity have significant effect on electrical discharges. Electric field strength needed for the electrical discharge decreases as the initial temperature increases. As the solution conductivity increases, the lowest electric field strength required for electrical discharge occurrence decreases. Findings in the present investigation reveal that measures that help to reduce the bubble formation are helpful to safe operation of the PEF system. [ABSTRACT FROM PUBLISHER]

In the process of water treatment by bipolar pulsed discharge plasma, there are not only the chemical effects such as the active species formed in the plasma channel, but also the physical effects like the ultraviolet radiation. Power energy consumed in form of optical radiation can be used by photocatalyst to improve the energy efficiency of the discharge system. Therefore, the effects of the photocatalyst on the formation of active species and degradation of the organic pollutant in the packed bed plasma reactor were studied in this paper. The nanoparticle TiO2 photocatalyst was obtained using the sol-gel method, structure and characteristics of TiO2 films were investigated via X-ray diffraction and scanning electron microscope. Formation of H2O2 and O3 under different conditions (applied voltage, air flow rate, diameter of solid packing, etc.) in the plasma and hybrid plasma–catalysis system was investigated. The experimental results proved that the combination of the pulsed discharge plasma process with TiO2 catalysis enhanced concentration of active species generated, and improved water treatment efficiency. In addition, the synergistic effect on H2O2 and O3 concentration increased with the increase of applied voltage, the gas flow rate and the amount of TiO2 photocatalyst. A small part of the TiO2 film fell off rough surface of the glass beads even after 5-h electric discharge treatment, and then remained almost constant. No obvious differences were found in the removal rate of indigo carmine after the catalyst loss. [ABSTRACT FROM PUBLISHER]

Bipolar pulsed discharges were investigated in columns containing glass spheres and water, and with air bubbling through, using a coaxial electrode configuration. The effect of sphere size on the discharge characteristics was studied, and results showed that the diameter of the glass spheres had a significant effect on the electrical discharges in the three-phase mixture. As the sphere size increased from 2 to 12 mm, no significant changes occurred in the peak voltage and rise time of the load voltage, but a clear maximum in the tail voltage, and a minimum in the injected power per pulse, occurred in the sphere diameter range from 5 to 8 mm. The greatest electric field in the interstices between the spheres, and the rate at which a dye could be removed from the water, both exhibited a maximum in the sphere diameter range from 5 to 8 mm. [ABSTRACT FROM AUTHOR]

In this paper, the method of reducing the rise time of high-voltage pulse transformer output rectangular pulses using a magnetic compression switch has been studied. An equivalent circuit consisting of pulse transformer and magnetic switch was used to describe the behavior of a transformer operating with magnetic switch. Meanwhile, four simplified equivalent sub-circuits and corresponding differential calculation models were used to analysis the influence of the magnetic switch module on the waveform characteristics of load resistance. The simulation and experiment results showed that the rise time of rectangular pulses could be reduced from more than 1 ?s to less than 150 ns while keeping pulse duration constant which was considered as the principle of rectangular pulse sharpening. Moreover, the pulse waveform performance on load resistance was determined by the pulse transformer, magnetic switch module and their coupling effects. [ABSTRACT FROM AUTHOR]