Increase Of Discharge Power Research Articles

Oxidation of lean methane by dielectric barrier discharge plasma and Mn–Ce catalyst

The synergistic dielectric barrier discharge plasma and Mn-Ce catalysts are employed to facilitate the low temperature and highly efficient oxidation of lean methane. The effect of the catalyst alone, plasma alone, and their synergistic effect on CH4 conversion are experimentally analyzed. It shows that the CH4 conversion rate under plasma catalysis is more than three times that of catalyst alone and plasma alone, with a maximum of 66.7% at 375 °C and 21 W, revealing a significant synergistic effect of plasma catalysis. The influence of Mn/Ce mass ratios (11Mn/Ce and 45Mn/Ce) and operational conditions (CH4/O2 molar ratio, preheating temperature, and discharge power) on CH4 conversion by plasma catalysis are also investigated. The CH4 conversion rate increases with the decrease of the CH4/O2 molar ratio and the increase in preheating temperature and discharge power. Meanwhile, the Mn/Ce mass ratio affects the CH4 oxidation and the synergistic effect of plasma catalysis. The oxidation activity of the 11Mn/Ce catalyst is mostly affected by the power at the preheating temperature below 325 °C. However, the 45Mn/Ce catalyst is affected by both preheating temperature and power. In addition, as the discharge power increases, the CH4 conversion rate exhibits a linear increase for 11Mn/Ce but exponential for 45Mn/Ce.

Toluene degradation in air/H2O DBD plasma: A reaction mechanism investigation based on detailed kinetic modeling and emission spectrum analysis

Non-thermal plasma (NTP) is emerging as an attractive method for decomposing volatile organic compounds (VOCs). In this paper, to study toluene degradation mechanism in air/H2O dielectric barrier discharge (DBD) plasma, optical emission spectrometry (OES) was employed to in-situ monitor active species in plasma, with the permanent degradation products being detected by on-line mass spectrometry under various operations. A detailed kinetic model of NTP with incorporation of non-constant electron filed and thermal effects has also been established. A toluene degradation efficiency > 82% could be achieved at P = 115 W, Cin, toluene = 1000 ppm. The relative spectrum intensity of excited OH, O, H and N2 (A3Σ+u) increased with increase of discharge power and was decreased at higher gas flowrates. Toluene degradation was mainly induced by oxidation of OH and O at afterglow stage, while part of toluene was decomposed by attack of electrons and reactive particles N2 (A3Σ+u) in discharge stage. A toluene degradation pathway has been proposed as: toluene→benzyl→benzaldehyde→benzene→phenoxy→cyclopentadiene→polycarbenes/alkynol→CO2/H2O. Benzoquinone, benzaldehyde, cyclopentadiene and cyclopentadienyl are supposed to be important intermediates for the ring-opening of toluene. Clarification of toluene degradation behaviors at discharge and afterglowing stage could provide new insights for plasma-catalytic process in future.

Plasma-catalytic steam reforming of benzene as a tar model compound over Ni-HAP and Ni-γAl2O3 catalysts: Insights into the importance of steam and catalyst support

Non-thermal plasma (NTP) coupled Ni-based catalysts are a promising method for tar steam reforming to syngas. In this work, Ni-based catalysts supported on hydroxyapatite (Ni-HAP) and γAl2O3 (Ni-γAl2O3) coupled with a coaxial dielectric barrier discharge (DBD) plasma were used to degrade biomass tar, and benzene was selected as a typical unbranched benzene ring structured tar model compound. In the NTP alone system, an increase in discharge power leads to benzene deep cracking to carbon deposition. In the NTP-catalytic system, the reaction temperature is a critical factor for catalysis, and the catalyst leads to a significant increase in benzene conversion and total gas yield, prompting the conversion of more cracking intermediates to gaseous products. Steam in the system has both positive and negative effects: a certain amount of steam can increase the amount of H· and ·OH, promoting benzene decomposition and carbon deposit elimination; excessive steam will compete for energetic electrons or oxidize the active metal in the catalyst, inhibiting benzene conversion. The Ni3-HAP catalyst exhibits the maximum benzene conversion (92.13 %) and energy efficiency (8.49 g/kWh), thanks to the formed Ni2+[I] and Ni2+[II] in the lattice due to the flexible ion exchange properties of the HAP support. The main reason for the catalyst activity degradation is carbon deposition rather than catalyst sintering. A good match among tar conversion rate, degree of decomposition, steam content and steam decomposition rate is critical for efficient and stable operation of the NTP-catalytic system.

Discharge Characteristics and Hydrogen Peroxide Generation of Multi-Needles Plate Discharge Under Pulsed Power

In this article, discharge characteristics and hydrogen peroxide (H2O2) generation of multi-needles plate discharge under pulsed power are investigated. By changing the voltage peak value, the pulse repetition frequency, voltage rising edge time, and the number of needles, the change laws of discharge characteristics, molecular emission spectrum, and H2O2 concentration are studied. The results show that as the number of needles increases, the discharge power increases. Through the emission spectra showed, the emission spectrum intensity of OH ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{A}^{2}\sum + \to \,\,\text{X}^{2}\prod $ </tex-math></inline-formula> , 0–0, 309 nm) and N2 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{C}^{3}\prod \text{u}~\to ~\text{B}^{3}\prod \text{g}$ </tex-math></inline-formula> , 0–0, 337 nm) also increases with the number of needles. The changes in the vibrational temperature and rotational temperature of N2 molecules show a steady process. As the number of needles increases, the vibrational temperature is 2835–3100 K and the rotational temperature is 342–410 K. They all belong to the low-temperature plasma range. As the number of needles increased, the concentration of H2O2 in the solution also increased. The concentration of H2O2 in the solution corresponds to the emission spectrum intensities of OH ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{A}^{2}\sum + \to \,\,\text{X}^{2}\prod$ </tex-math></inline-formula> ). When the peak value is 14 kV, the pulse frequency is 1 kHz. The maximum concentration of H2O2 reached 15.277 mg/L with 14 needles.

Electrical and optical characterization of multi-hollow surface dielectric barrier discharge in configuration with the air-exposed electrode

In this paper, multi-hollow surface dielectric barrier discharge generated by a perforated ceramic substrate in a configuration with the air-exposed electrode was investigated. The electrical characteristics (discharge power, peak, and average amplitude of current pulses) and optical characteristics (emission intensity) of the discharge were evaluated under various conditions of applied voltage (peak voltage 3–6 kV, frequency 200–2000 Hz), air flow rate (0.5–2.4 L/min), and air relative humidity (0%–80%). Temperature of ceramic substrate was also monitored. Statistical analysis of current pulses was also performed, and histograms of amplitudes of current pulses were calculated. The results showed that discharge characteristics strictly depend on given working conditions. The analysis of current pulses showed opposite trends in average overall number of positive and negative pulses with an increase of discharge power: number of positive current pulses gradually increased, while number of negative current pulses slightly decreased. The highest peak currents were found at 4 kV (1.8 W). With further increase of peak voltage, peak current decreased and beginning of detection of current pulses upon a rising (declining) slope of applied voltage was slightly shifted toward earlier times. At the highest applied peak voltage, pulses appeared even before polarity of applied voltage reversed. Therefore, we suppose that a residual charge accumulated on dielectric surface plays a crucial role in characteristics of the current pulses. Significant influence on current pulses and discharge emission intensity was also found with a change of air relative humidity, while the effect of air flow rate was found weaker.

Studies and Research on Obtaining Multifunctional Thin Films by Magnetron-Assisted PVD Process

The paper aims to obtain thin films of nickel and zinc through the magnetron-assisted spraying process and their characterization from a structural point of view, of electrical, optical properties and corrosion resistance. It was found that as the intensity and discharge power increase, changes occur in the structure and properties of the deposited films.&#x0D;

Plasma-enhanced Si-SiC low-temperature bonding based on graphene composite slurry interlayer

Recently, silicon carbide (SiC) has replaced silicon (Si) as a potential material for next-generation power devices. In this study, a Si-SiC low-temperature bonding method based on graphene composite slurry as an interlayer was developed. Ar plasma was used to treat the surfaces of Si and SiC to improve surface hydrophilicity for higher strength bonding. With the increase of discharge power, the root-mean -square (RMS) surface roughness of Si and SiC has obviously increased and the bonding quality was also greatly improved. For 70 W discharge power, the RMS surface roughness values of Si and SiC were 3.22 nm and 1.67 nm respectively, and the bonding strength reached approximately 10 MPa. Through SEM interface analysis, it can be found that a seamless bonding interface was obtained using this bonding process.

Decomposition of xylene in strong ionization non-thermal plasma at atmospheric pressure

A large amount of volatile organic compounds (VOCs) produced by industry have caused serious environmental pollution. In this paper, the removal effect of simulated xylene by strong ionization dielectric barrier discharge (DBD) plasma at atmospheric pressure and its degradation mechanism and pathway were studied. The effect of gas residence time, and initial xylene concentration was studied. The results showed that higher voltage caused an increase in discharge power, and with the increase of voltage, the concentration of ozone and nitrogen oxide in the reactor increased. The degradation efficiency decreased from 98.1% to 80.2% when xylene concentration increased from 50 ppm to 550 ppm at 4kV. And with the increase of residence time from 0.301s to 1s, the degradation efficiency increased from 78.5% to 98.6%. According to GC-MS analysis, the degradation products were ethyl acetate and n-hexylmethylamine at 4kv. And the main intermediates are 2,4-2-tert-butylphenol, 2-aminopentane, 2-methyl-5 - (2-aminopropyl) - phenol and propionamide at 1.5kV.

Effective generation of atmospheric pressure plasma in a sandwich-type honeycomb monolith reactor by humidity control

Large-volume atmospheric-pressure plasma based on corona discharge was successfully generated in a sandwich-type plasma reactor by controlling the humidity of the feed gas. The reactor comprised a 5-cm-high and 9-cm-wide commercial honeycomb monolith and two perforated stainless-steel disk electrodes with 3-mm holes, which covered up both sides of the monolith. The high-voltage applied disk electrode was placed 2 ~ 6 mm away from the monolith, whereas the counter ground electrode typically touched it. The characteristics of air plasma such as power delivery, breakdown voltage, current, and impedance were found to strongly depend on the water vapor content in the feed gas as well as in the monolith, exhibiting an exponential increase of discharge power with increasing the humidity. The discharge characteristics also depended on the gas flow rate and the electrode-monolith distance. Better discharge performance was observed as the electrode was closer to the monolith, and as the air flow rate was higher. Discharge power above 30 W was achieved under the condition of gas flow rate 75 L/min, applied voltage 25 kV, and humidity 2.1%(v/v) when the high-voltage electrode was 2 mm away from the monolith, and the ground electrode kept up against it. The air plasma produced reactive species, being demonstrated by the formation of ozone at several tens of ppm, depending on specific energy input. The plasma source has potential applications in the abatements of odor, organic compounds, and NOx with high throughputs.

Discharge characterization of a multi-anode electrode geometry for vacuum arc thruster

Vacuum arc thrusters (VATs) have the potential to be used in nanosatellites and a multi-anode electrode geometry (MAEG) suitable for VATs is proposed in this paper. A unique electric field distribution is formed in the MAEG because of its anode configuration, which is different from conventional electrode geometry (CEG). There exists a region where the electric field vector has opposite directions in the electrode geometry. This region affects the directional drift of electrons in the initial stage of the discharge, thereby changing the process of vacuum breakdown. The variation of the discharge process affects the generation and propagation mechanism of the plasma, forming a plasma plume in favor of the propulsion performance of thrusters. The photographs of the plasma plume are captured and the electron density distributions are measured, which prove the pinch effect on the plasma plume of the MAEG. The propulsion performance of MAEG VATs is found to be superior to CEG VATs with the same discharge condition and increases radically with the increase of discharge power. The impulse bit and thrust-to-power ratio of MAEG VATs have been found to increase by a factor of 26 and 4.5 at most compared with the CEG VAT. It is found that MAEG VATs have a potential application advantage in the field of nanosatellite propulsion.

Surface Dielectric Barrier Discharge

This project is concerned with surface dielectric barrier discharge (DBD), which involve designing the configuration of discharge and experiment, collecting and analysis data from experiment and simulation. Therefore, this report includes the objective of the project and general information of background. It also briefly introduces the history and theory of dielectric barrier discharge. For the experiment how to design the discharge implement and why. Then it will show the experiment in different configurations, and the analysis data collected in experiment also explain the data for finding out the properties of surface dielectric barrier discharge and what the difference between surface discharge and vertical discharge are. High frequency power supplied will be used for viewing the phenomenon of discharge. Compare the spectrums of discharge on dielectric and air discharge. Finally, it is the main conclusions and introduction of the difference of surface dielectric barrier discharge and vertical discharge. There are some conclusions. Discharge voltage increase linearly with applied voltage. Discharge power increase non-linearly with the discharge voltage. The gap of high voltage electrodes will not affect discharge voltage and discharge power. Discharge power increases with the frequency of power supply. Discharge area will expand when the applied voltage increases.

Experimental Study on LED Heat Dissipation Based on Enhanced Corona Wind by Graphene Decoration

To enhance the heat dissipation of high-power light-emitting diodes (LEDs), corona wind based on corona discharge was promoted. In this paper, we aimed at reinforcing the intensity of corona wind by modifying the needle electrode with graphene solution. To explore the differences in the graphene-coated electrode and the original bare electrode on the electrical characteristics, the intensity of corona wind, and LED heat dissipation, a corona wind cooling system and a thermal test system were built for the experimental study. The results showed that the graphene-coated electrode system could produce corona wind at a lower voltage. In addition, the discharge current of the graphene-coated electrode system is higher than that of the bare electrode system under the same discharge voltage. The graphene-coated electrode system can induce a faster corona wind and the highest speed is about 3.4 m/s, showing that it is more efficient than the bare electrode system in corona wind production. Moreover, the temperature drop of LEDs for the graphene-coated system is greater, which means that the corona wind cooling system can reduce the junction temperature of the LED chips effectively. Ultimately, as the discharge power increases, the average convective heat transfer coefficient increases. Indeed, the result of this paper can be used for the wide variety of the graphene-coated corona wind generator application as a promising technology for the LED heat management.

Decomposition of formaldehyde in strong ionization non-thermal plasma at atmospheric pressure

Atmospheric emissions of volatile organic compounds possess a major threat to the environment, and controlling them is a key task for air pollution prevention and control. This paper presents a comprehensive discussion on the degradation mechanism and pathways for the efficient removal of formaldehyde (HCHO) in a synthetic polluted air stream by strong ionization dielectric barrier discharge (DBD) plasma at atmospheric pressure. The effect of specific input energy, oxygen concentration, relative humidity (RH), gas residence time, and initial HCHO concentration was studied. Findings reveal that higher voltage caused an increase in discharge power, while the current density dropped from 180.53 to 55.10 mA and 71.06 to 51.99 mA when oxygen concentration and RH increased from 2.4 to 20.6% and 18.9 to 84.1%, respectively. The key degradation active species were ·O and ·OH generated from the electrical breakdown of oxygen molecules and water vapour. Also, the removal efficiency reached 95.12% for the lowest initial concentration of 100 ppm at ambient temperature. Destruction of HCHO molecules can be achieved via direct electron attack or indirect gas-phase radical reaction. The strong ionization DBD is a promising technology to remove low concentration formaldehyde from polluted air streams.

Degradation and mineralization of ciprofloxacin by gas–liquid discharge non-thermal plasma

A typical quinolones antibiotic ciprofloxacin (CIP) in aqueous solution was degraded by a gas–liquid discharge non-thermal plasma system. The discharge plasma power and the emission intensity of the excited reactive species (RS) generated in the gas phase were detected by the oscilloscope and the optical emission spectroscopy. The effects of various parameters on CIP degradation, i.e. input powers, initial concentrations addition of radical scavengers and pH values were investigated. With the increase of discharge power, the degradation efficiency increased but the energy efficiency significantly reduced. The degradation efficiency also reduced under high concentration of initial CIP conditions due to the competitive reactions between the plasma-induced RS with the degradation intermediates of CIP. Different radical scavengers (isopropanol and CCl4) on ·OH and H· were added into the reaction system and the oxidation effects of ·OH radicals have been proved with high degradation capacity on CIP. Moreover, the long-term degradation effect on CIP in the plasma-treated aqueous solution proved that the long-lived RS (H2O2 and O3, etc) might play key roles on the stay effect through multiple aqueous reactions leading to production of ·OH. The degradation intermediates were determined by the method of electrospray ionization (+)-mass spectroscopy, and the possible degradation mechanism were presented.

CO2 conversion in non-thermal plasma and plasma/g-C3N4 catalyst hybrid processes

Carbon dioxide conversion at atmosphere pressure and low temperature has been studied in a cylindrical dielectric barrier discharge (DBD) reactor. Pure CO2 feed flows to the discharge zone and typical filamentary discharges were obtained in each half-cycle of the applied voltage. The gas temperature increased with discharge time and discharge power, which was found to affect the CO2 decomposition deeply. As the DBD reactor was cooled to ambient temperature, both the conversion of CO2 and the CO yield were enhanced. Especially the energy efficiencies changed slightly with the increase of discharge power and were much higher in cooling condition comparing to those without cooling. At a discharge power of 40 W, the energy efficiency under cooling condition was approximately six times more than that without cooling. Gas flow rate was observed to affect CO2 conversion and 0.1 L min−1 was obtained as optimum gas flow rate under cooling condition. In addition, the CO2 conversion rate in plasma/g-C3N4 catalyst hybrid system was twice times as that in plasma-alone system. In case of cooling, the existence of g-C3N4 catalyst contributed to a 47% increase of CO2 conversion compared to the sole plasma process. The maximum energy-efficiency with g-C3N4 was 0.26 mmol kJ−1 at 20 W, which increased by 157% compared to that without g-C3N4. The synergistic effect of DBD plasma with g-C3N4 on pure CO2 conversion was verified.

Carbon nanoparticles production by pulsed discharge in liquid alcohols

Carbon nanoparticles produced from alcohols by pulsed spark discharge in liquid (PSDL) was investigated in this work. The spherical carbon particles with about 10 nm diameter can be produced by PSDL, which were similar to the commercial carbon particles. With the increase of discharge power, the mean diameter of carbon particles was decreased and the size distribution was more uniform. Meanwhile, the yield of carbon produced from ethanol was more than from methanol that may be attributed to the more carbon atoms in ethanol compared with the same volume of methanol. In addition, the mechanism of carbon produced from alcohols by PSDL was also analyzed. The possible reactions were given according to the production analysis. This work presents a new method for carbon nanoparticles production and the results can play a guidance role in producing nanometer materials by plasma reforming.

Kinetic analysis of rare gas metastable production and optically pumped Xe lasers

Optically pumped all-rare-gas lasers use metastable rare gas atoms as the lasing species in mixtures with He or Ar buffer gas. The metastables are generated in a glow discharge, and we report model calculations for the optimal production of Ne*, Ar*, Kr* and Xe*. Discharge efficiency was estimated by solving the Boltzmann equation.Laser efficiency, gain and output power of the CW optically pumped Xe laser were assessed as functions of heavier rare gas content, pressure, optical pump intensity and the optical path length. It was found that, for efficient operation the heavier rare gas content has to be of the order of one percent or less, and the total pressure—in the range 0.3–1.5 atm. Output power and specific discharge power increase approximately linearly with pump intensity over the output range from 300–500 W cm−2. Ternary mixtures Xe:Ar:He were found to be the most promising. Total laser efficiency was found to be nearly the same for pumping the 2p8 or 2p9 state, reaching 61%–70% for a pump intensity of ~720 W cm−2 when the Xe fraction was in the range 0.001 ÷ 0.01 and Ar fraction—0.1 ÷ 0.5. However, when the 2p8 state was pumped, the maximum total efficiency occurred at larger pressures than for pumping of the 2p9 state. The discharge power density required to sustain a sufficient Xe* number density was in the range of tens of watts per cubic centimeter for 50% Ar in the mixture.

The influence of oxygen ratio on the plasma parameters of argon RF inductively coupled discharge

In this paper, the RF-coupled plasma characteristics of argon and oxygen mixed gases were analyzed by emission spectra and Langmuir single probes. The experimental pressure was kept at 0.63 Pa, and the electron temperature and electron density were measured by Boltzmann curve method and Langmuir single probe respectively under different oxygen ratio. The results demonstrate that increasing the oxygen content reduces the plasma electron density, and the plasma will change from E mode to H mode when the discharge power increase from 350 W to 400 W if the discharge gas is pure argon or oxygen ratio is low, but the plasma is in a single E-mode at relatively high oxygen ratios. When the power reaches 450 W, the plasma becomes unstable and the state of plasma will change no matter what mode it is (H mode or E mode). In addition, as the oxygen ratio increases, there is a good agreement between the plasma electron density and the argon 738.74 nm line intensity. However, the electron temperature will decrease in H mode.

Influence of secondary electron yield of material on two-sided multipactor discharge in cavity

The influences of secondary electron yield (SEY) of material on the transient and saturation characteristics of two-sided multipactor discharge in cavity are numerically investigated by using particle-in-cell and Monte-Carlo methods. The numerical results indicate that as the SEY increases, the rate of electron number increases and the average value and magnitude of steady electron number also increase. The oscillation start-time of discharge current is shortened, and the steady value of discharge current increases and tends to be saturated. Both the average value and magnitude of steady discharge power increase and tend to be saturated. Both the time-delay and pulse width of deposited power waveform increase and also tend to be saturated. Under the circumstances of higher and lower value of SEY, the physical images of electron phase space, charge density, average impact energy, average SEY, electron number and discharge current are in detail shown in particle-in-cell simulation. The results can be concluded as follows. Under the circumstances of lower value of SEY, the saturation characteristics is determined by both debunching and reverse field of space charge effects. But under the circumstances of higher value of SEY, the multipactor mechanism tends to be one-sided mode in the steady stage which can be obviously determined by reverse-field of space charge effect.

Dissociation of CO2 by thermal plasma with contracting nozzle quenching

CO2 decomposition is carried out by a binode thermal plasma reactor with a contracting nozzle quenching. The effects of CO2/Ar and CO2/N2 mixture, CO2 feed rate, and plasma discharge power on CO2 conversion and energy efficiency are investigated. The experimental results have turned out the CO2 conversion increased with the decrease of CO2 feed rate and increase of discharge power, but energy efficiency shows an opposite tendency. The excellent results of CO2 conversion 45–48%, energy efficiency 18–19% were achieved by the experimental conditions of N2/CO2=1, CO2 flow rate 25L/min, discharge power 12–15kW. The results, better than what ever reported, may be contributed to the application of contracting nozzle in combination with a proper cooling tube, which bring about a quick quenching at cooling rate of 107K/s. Moreover, the discharge power, feed flow rate, and the configuration of contracting nozzle must be matched.