Applied Peak Voltage Research Articles

Ozone production in nanosecond pulsed dielectric barrier discharge in synthetic air: The effect of pulse width

This work investigates the effect of pulse width on the characteristics of electrical discharge, optical emission spectra and ozone production in a water electrode DBD using a modulable nanosecond pulsed power supply. Results show that the increase of pulse width tpw slightly increases the spectral intensity and the rotational temperature Trot, with a typical Trot of 299 ± 5 K at an applied peak voltage Vp of 18.6 kV and a tpw of 400 ns. The electronic excitation temperature Texc increases linearly with Vp and gradually with tpw, while the electron density ne shows a non-linear relationship with tpw. Results also show that an increase in tpw slightly increases the energy density. At low energy densities (SIE <50 J/L), increasing tpw can improve ozone generation efficiency, reaching a maximum of 99.64 ± 0.87 g/kWh at 33.60 ± 1.53 J/L at a tpw of 900 ns. This investigation provides substantial insight into the nanosecond pulsed ozone production.

Ammonia pyrolysis oxidation excited by nanosecond pulsed discharge: Global/fluid models hybrid solution

The kinetic characteristics of plasma-assisted oxidative pyrolysis of ammonia are studied by using the global/fluid models hybrid solution method. Firstly, the stable products of plasma-assisted oxidative pyrolysis of ammonia are measured. The results show that the consumption of NH3/O2 and the production of N2/H2 change linearly with the increase of voltage, which indicates the decoupling of non-equilibrium molecular excitation and oxidative pyrolysis of ammonia at low temperatures. Secondly, the detailed reaction kinetics mechanism of ammonia oxidative pyrolysis stimulated by a nanosecond pulse voltage at low pressure and room temperature is established. Based on the reaction path analysis, the simplified mechanism is obtained. The detailed and simplified mechanism simulation results are compared with experimental data to verify the accuracy of the simplified mechanism. Finally, based on the simplified mechanism, the fluid model of ammonia oxidative pyrolysis stimulated by the nanosecond pulse plasma is established to study the pre-sheath/sheath behavior and the resultant consumption and formation of key species. The results show that the generation, development, and propagation of the pre-sheath have a great influence on the formation and consumption of species. The consumption of NH3 by the cathode pre-sheath is greater than that by the anode pre-sheath, but the opposite is true for OH and O(1S). However, within the sheath, almost all reactions do not occur. Further, by changing the parameters of nanosecond pulse power supply voltage, it is found that the electron number density, electron current density, and applied peak voltages are not the direct reasons for the structural changes of the sheath and pre-sheath. Furthermore, the discharge interval has little effect on the sheath structure and gas mixture breakdown. The research results of this paper not only help to understand the kinetic promotion of non-equilibrium excitation in the process of oxidative pyrolysis but also help to explore the influence of transport and chemical reaction kinetics on the oxidative pyrolysis of ammonia.

A novel dielectric barrier discharge ozone generator with excellent microdischarge temperature behavior

In this paper, the electrical characteristics and optical emission spectroscopy of a dielectric barrier discharge ozone generator with water as the grounding electrode are investigated. The gas temperature of the microdischarge channel and at the reactor outlet have also been studied. Results show that the working plasma has a very small effect on the increase in gas temperature at the reactor outlet. At applied power frequency of 5 kHz and applied peak voltage of 7 kV, the microdischarge temperature is obtained as 310 K from N2(C3Πu → B3Πg) spectra ranging from 370-381 nm. In addition, the plasma emission spectra of gas mixtures (95 % O2 + 5 % N2) are investigated and the microdischarge temperature is determined as 309 K with applied power frequency of 5 kHz and applied peak voltage of 8 kV. It is concluded that observed microdischarge temperatures reaches the lowest values reported for filamentary air discharges, capable of promoting ozone production.

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.

CT and MRI compatibility of flexible 3D-printed materials for soft actuators and robots used in image-guided interventions.

Three-dimensional (3D) printing allows for the fabrication of medical devices with complex geometries, such as soft actuators and robots that can be used in image-guided interventions. This study investigates flexible and rigid 3D-printing materials in terms of their impact on multimodal medical imaging. The generation of artifacts in clinical computer tomography (CT) and magnetic resonance (MR) imaging was evaluated for six flexible and three rigid materials, each with a cubical and a cylindrical geometry, and for one exemplary flexible fluidic actuator. Additionally, CT Hounsfield units (HU) were quantified for various parameter sets iterating peak voltage, x-ray tube current, slice thickness, and convolution kernel. We found the image artifacts caused by the materials to be negligible in both CT and MR images. The HU values mainly depended on the elemental composition of the materials and applied peak voltage was ranging between 80 and 140kVp. Flexible, nonsilicone-based materials were ranged between 51 and 114HU. The voltage dependency was less than 29HU. Flexible, silicone-based materials were ranged between 60 and 365HU. The voltage-dependent influence was as large as 172HU. Rigid materials ranged between -69 and 132HU. The voltage-dependent influence was <33HU. All tested materials may be employed for devices placed in the field of view during CT and MR imaging as no significant artifacts were measured. Moreover, the material selection in CT could be based on the desired visibility of the material depending on the application. Given the wide availability of the tested materials, we expect our results to have a positive impact on the development of devices and robots for image-guided interventions.

Experimental investigation on the interaction of a nanopulsed plasma jet with a liquid target

Although the majority of atmospheric pressure plasma jet (APPJ) applications involve the interaction between the plasma and a surface, up to now the number of published papers focusing on this subject is limited, even though the nature of the target may strongly influence the plasma characteristics, the discharge structure, the generated reactive species, and consequently, the overall process. Under this framework, we investigated an APPJ impinging on a liquid surface and the effects of changing the stand-off distance, the applied peak voltage, and the pulse repetition frequency, looking at them as variable parameters often used to optimize plasma surface processes. Intensified charge-coupled device (iCCD) and Schlieren acquisitions suggest a key effect of gap width and peak voltage on the discharge morphology, velocity of the ionization front, and effluent fluid-dynamic behavior. The presence of a grounded liquid substrate enhances the electric field downstream of the source outlet: the smaller the gap the faster the ionization wave and the shorter the time for it to reach the surface. Consequently, a small gap favors the charging of the surface capacitance and the formation of surface ionization waves over the liquid target. Schlieren acquisitions highlight the formation of a transient turbulent structure propagating downstream of the gas flow, starting hundreds of microseconds after the initiation of the plasma discharge. The achieved results support the hypothesis that the formation of the turbulence is caused by a heating effect of the high-voltage electrode on the He gas flow. Another observed effect is the variation of the dimple caused by the He flow on the liquid surface as a consequence of the turbulence generated by the plasma discharge. The results presented here confirm how the gas dynamics and the discharge behavior are strongly affected by the presence of the liquid substrate and by its position with respect to the APPJ.

Effects of Air/H2O Discharge Plasma on Propane Combustion Enhancement Using Dielectric Barrier Discharges

Combustion provides about 80% energy for our daily life and industrial production. But thermal efficiency of traditional combustion technologies is low, which causes energy waste and serious environmental pollution. In order to improve the combustion efficiency, a combined method based on non-equilibrium plasma generated by dielectric barrier discharge and OH radicals coming from water-steam additive was proposed in this work, and plasma assisted propane combustion was examined and evaluated. The results indicated that when relative humidity (RH) was 20% and applied peak voltage was fixed at 8.75 kV, the relative intensity of OH radical and the flame temperature reached the maximum value at the flame root. At the same time, propane combustion was the most complete. In addition, we found that the erosion of the inner electrode was weakened by H2O addition, and the symmetry of discharge current was changed from symmetry to asymmetry with the increase of RH. Compared with the pure air undischarged combustion, when the relative humidity was 20% and under the discharge conditions of 8.75 kV, the lean-burn extinction limit was extended to 0.4,which is far lower than the traditional lean-burn limit (0.51).

Characteristics of a micro-gap argon barrier discharge excited by a saw-tooth voltage at atmospheric pressure

Using two water electrodes, a micro-gap dielectric barrier discharge excited by a saw-tooth voltage is investigated in atmospheric pressure argon. Through electrical and optical measurements, it is found that, at a lower driving frequency, a stepped discharge mode is obtained per half voltage cycle. Moreover, the duration and amplitude of the current plateau increase with the increase in the applied peak voltage. With the increase in the driving frequency, the stepped discharge mode transits into a pulsed one after a multi-peak mode. During this process, a diffuse discharge at a lower frequency transits into a filamentary one at a higher frequency. Temporal evolutions of the discharges are investigated axially based on fast photography. It is found that the stepped mode is in atmospheric pressure Townsend discharge (APTD) regime. However, there is a transition from APTD to atmospheric pressure glow discharge for the pulsed mode. Spectral intensity ratio of 391.4 nm to 337.1 nm is used to determine the averaged electron energy, which decreases with increasing peak voltage or driving frequency.

Electromechanical actuators based on poly(vinylidene fluoride) with [N1 1 1 2(OH)][NTf2] and [C2mim] [C2SO4

Actuators based on electroactive polymers are increasingly used in applications including microelectronic devices and artificial muscles, demanding low voltage operation and controllable switching response. This work reports on the preparation of electroactive actuators based on poly(vinylidene fluoride) (PVDF) composites with 10, 25, and 40 wt% N,N,N-trimethyl-N-(2-hydroxyethyl)ammonium bis(trifluoromethylsulfonyl)imide ([N1 1 1 2(OH)][NTf2]) and 1-Ethyl-3-methylimidazolium Ethylsulfate ([C2mim][C2SO4]) ionic liquids (ILs) prepared by solvent casting. Independent of the IL type, its presence leads to the crystallization of PVDF in the piezoelectric β-phase. The degree of crystallinity and electrical conductivity of the samples strongly depends on ILs type and content. The highest electrical conductivity was found for PVDF/IL composites with 40 wt% of [N1 1 1 2(OH)][NTf2]. The strain displacement and bending of the PVDF/IL composites were evaluated as a function of IL type and content under applied peak voltages of 2.0, 5.0, and 10.0 V at a frequency of 10 mHz. Strain displacement of the actuators depends more on IL content than on IL type, and the best strain bending response was found for the PVDF/IL composite with 25 wt% of [N1 1 1 2(OH)][NTf2] at 5.0 V. Further, it is shown that [C2mim] [C2SO4]/PVDF composites do not show cytotoxic behavior, being suitable for biomedical applications.

Analysis on CO2 reforming of CH4 by corona discharge process for various process variables

The CO2 reforming of CH4 to syngas by corona discharge at atmospheric pressure has been investigated for various process variables. The experiments were operated systematically in wide regions of process variables such as CO2/CH4 ratio, total flow rate, pulse frequency and applied peak voltage. The conversions of methane and carbon dioxide increase with increasing the applied peak voltage or pulse frequency and decrease with increasing the total flow rate. Selectivities of H2 and CO increase with the increase of applied peak voltage, while increasing total flow rate and pulsed frequency does not affect H2 and CO selectivities significantly.

Low-temperature plasma nitrocarburizing of the AISI 420 martensitic stainless steel: Microstructure and process kinetics

Low-temperature plasma nitrocarburizing was performed in order to study the effect of treatment temperature and time on the microstructure, mechanical properties and growth kinetics of the AISI420 martensitic stainless steel treated layers. Plasma nitrocarburizing was carried out using DC-pulsed power supply in a 71%N2+18%H2+10%Ar+1%CH4 gas mixture, at temperatures of 300, 350, 400 and 450°C, and times of 2, 4, 6 and 12h. The applied peak voltage, gas flow rate and pressure were kept constant at 600V, 3.32×10−6Nm3s−1 and 400Pa, respectively. The treated samples were characterized by optical microscopy, X-ray diffractometry and microhardness measurements. A maximum surface hardness of 1280±16HV0.3 was obtained for samples treated for 4h at 400°C. Grain boundary chromium carbide/nitride precipitation has started for treatments of 4h at 400°C, which can be avoided by using lower nitrocarburizing temperature or time. It was verified that nitride/carbide precipitation tends to occur at lower temperatures and times when compared with the low-temperature nitriding and carburizing treatments. Finally, the nitrocarburized layer growth is proportional to the square root of treatment time and follows an Arrhenius law for the treatment temperature, with an activation energy of 76kJ mol−1.

Decomposition of Pharmaceuticals by Pulsed Corona Discharges in Water Depending on Streamer Length

Pulsed corona discharges generated in water provide a possibility for the abatement of even stable organic compounds. Decomposition efficacy correlates with the length of streamers, which in turn depends on water conductivity and applied voltage. We investigated the relation between conductivities from 25 to 500 μS/cm, pulse duration, and visible streamer length for applied peak voltages of 70 and 82 kV. Streamer development for an initially applied peak voltage of 70 kV was related to the decomposition rates of the pharmaceutical carbamazepine that was dissolved in solutions with conductivities in the same range.

Effects of TiO2 coating on zeolite particles for NO and SO2 removal by dielectric barrier discharge process

The dielectric barrier discharge-catalyst (DBD-C) hybrid process and the dielectric barrier discharge-catalyst-photocatalyst (DBD-C-P) hybrid process were analyzed for NO and SO2 removal. In the DBD-C hybrid process, zeolite particles were used as dielectric materials and catalysts for dielectric barrier discharge; in the DBD-C-P hybrid process, zeolite particles were coated with TiO2 photocatalyst to investigate the combined effects of plasma-catalyst-photocatalyst on NO and SO2 removal. Zeolite particles were coated with TiO2 photocatalyst by means of a rotating cylindrical PCVD reactor. TiO2 photocatalyst was coated partially on the zeolite surface while preserving the porous structure of zeolite. NO and SO2 removal was studied for various process variables such as applied peak voltage, initial NO and SO2 concentrations, pulse frequency, and residence time. The effects of TiO2 photocatalyst coating on NO and SO2 removal efficiencies by the DBD-C-P hybrid process are significant for low and medium applied voltage (<14kV). The NO and SO2 removal efficiencies in the DBD-C-P hybrid process are 1.02–3.4 times and 1.03–4 times higher, respectively, than those in the DBD-C hybrid process for the process variables used in this study. We found that the zeolite particles coated with TiO2 photocatalyst by means of a rotating cylindrical PCVD reactor could be effectively used to remove NO and SO2 in the DBD-C-P hybrid process.

Effect of TiO2 Thin Film Thickness on NO and SO2 Removals by Dielectric Barrier Discharge-Photocatalyst Hybrid Process

We coated the glass beads with TiO2 thin films by a rotating cylindrical plasma chemical vapor deposition (PCVD) reactor and applied the TiO2–coated glass beads to remove NO and SO2 in a dielectric barrier discharge-photocatalyst hybrid (DBD-PH) process. The thickness of TiO2 thin films on glass beads was controlled precisely by changing the deposition time. The UV light generated from the plasma discharge in DBD-PH process activates the TiO2 photocatalyst on glass beads and the NO and SO2 removal efficiency are removed more easily by the reactive radicals generated from plasma reactions and TiO2 photocatalyst. We found the optimum thickness of TiO2 thin film on glass beads was about 600 nm to remove NO and SO2 by the DBD-PH process. The NO and SO2 removal efficiencies increase as applied peak voltage, residence time or pulsed frequency increases or as initial NO and SO2 concentration decreases.

Inactivation of Escherichia coli phage by pulsed electric field treatment and analysis of inactivation mechanism

Inactivation of bacteriophage by pulsed electric field (PEF) treatment, one of the effective procedures for bacteria nonthermal inactivation, was studied. Model phage particles Escherichia coli bacteriophages M13mp18 and λ phage, were successfully inactivated by PEF treatment. The survival ratios of both bacteriophages decreased depending on the PEF treatment time when applied peak voltage was 5 or 7 kV, and the survival ratios after 12 min PEF treatment were 10−4 – 10−5. Electrophoresis analyses of biological molecules of inactivated λ phage detected no degradation of total protein and genomic DNA. These results suggested that the factor of phage inactivation by PEF treatment was not based on the degradation of protein or DNA, but on the destruction of phage particle structure. Sensitivity of E. coli phage to PEF treatment was compared with that of E. coli cell. Phage and MV1184 cell were treated with same condition PEF at 5 kV, respectively. After 12 min treatment, the survival ration of λ phage and MV1184 were 4.0 × 10−5 and 1.7 × 10−3, respectively. The survival ratio of phage was lower than that of MV1184. E. coli cell is more tolerant to inactivation with PEF treatment than coli phage.

Fluid Modeling of a Nitrogen Atmospheric-Pressure Planar Dielectric Barrier Discharge Driven by a Realistic Distorted Sinusoidal Alternating Current Power Source

One-dimensional self-consistent simulations of a parallel-plate atmospheric-pressure nitrogen dielectric barrier discharge (DBD) are presented. The DBD was driven by a realistic distorted-sinusoidal voltage power source with a frequency of 60 kHz. The simulated discharge currents are in quantitative agreement with experimental measurements. N4+ ions gain more of the input electric power than electrons, which is unlike most glow discharges. The densities of all charged and neutral species increase exponentially with increasing applied peak voltage in the range of 6.2–8.6 kV. The higher the permittivity of the dielectric material, the larger the discharge current and the longer the period of gas breakdown. In addition, the quantity of accumulated charges at each electrode increases with increasing permittivity of the dielectric material. Finally, the increase in dielectric thickness from 1.0 to 2.0 mm greatly reduces the densities of all species and also the plasma absorbed by the power.

Formation of Hydroxyl Radicals and Hydrogen Peroxide by a Novel Nanosecond Pulsed Plasma Power in Water

The initiation reaction rate constants for the formation of ·OH and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> were produced in water by a novel nanosecond pulsed plasma power, which was developed for wastewater treatment based on the theory of magnetic pulse compression and SOS effect. The output voltage was observed where the peak voltage, rise time, and pulsewidth were 51 kV, 60 ns, and 120 ns, respectively. The results show that the concentrations of ·OH and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> both increased with increasing the peak voltage; the initial rates of ·OH are 4.1, 5.7, and 7.7 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-10</sup> mol·s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at 30, 35, and 40 kV, respectively, and the initial rates of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> are 1.2, 1.9, and 2.6 × 10 9 mol·s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at 30, 35, and 40 kV, respectively. The energy efficiency of the production of ·OH was found to be independent of the applied peak voltage, but the energy efficiency of the production of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> increased with increasing the discharge peak voltage.

Improvement of Polytetrafluoroethylene Surface Energy by Repetitive Pulse Non-Thermal Plasma Treatment in Atmospheric Air

Improvement of polytetrafluoroethylene surface energy by non-thermal plasma treatment is presented, using a nanosecond-positive-edge repetitive pulsed dielectric barrier discharge generator in atmospheric air. The electrical parameters including discharging power, peak and density of micro-discharge current were calculated, and the electron energy was estimated. Surface treatment experiments of polytetrafluoroethylene films were conducted for both different applied voltages and different treating durations. Results show that the surface energy of polytetrafluoroethylene film could be improved to 40 mJ/m2 or more by plasma treatment. Surface roughness measurement and surface X-ray photoelectron spectroscopy analysis indicate that there are chemical etching and implantation of polar oxygen groups in the sample surface treating process, resulting in the improvement of the sample surface energy. Compared with an AC source of 50 Hz, the dielectric barrier discharges generated by a repetitive pulsed source could provide higher peak power, lower mean power, larger micro-discharge current density and higher electron energy. Therefore, with the same applied peak voltage and treating duration, the improvement of polytetrafluoroethylene surface energy using repetitive pulsed plasma is more effective, and the plasma treatment process based on repetitive pulsed dielectric barrier discharges in air is thus feasible and applicable.

Cold deposition of large-area amorphous hydrogenated silicon films by dielectric barrier discharge chemical vapor deposition

Amorphous hydrogenated silicon films were deposited on glass substrates at room temperature. This cold deposition process was operated in a dielectric barrier discharge CVD reactor with a fixed strip-shaped plasma matched with a moving substrate holder. The maximum film area was 300 × 600 mm 2. The film deposition rate as a function of applied peak voltage of DBD power was investigated under different hydrogen-diluted silane concentrations, and the film surface smoothness, continuity, and film/glass adherence were also studied. The maximum deposition rate was 12.2 Å/s, which was performed under the applied peak voltage of 16 kV and a hydrogen-diluted silane concentration of 50%. IR measurements reveal that the silane concentration plays a key role in determining the hydrogen-silicon bonding configurations. With increasing hydrogen-diluted silane concentration, the H–Si bonding configurations shift gradually from Si–H 3 to Si–H. The variation of photo/dark conductivity ratio and optical bandgap versus hydrogen-diluted silane concentration were investigated. The use of DBD-CVD for deposition of a-Si:H films offers certain advantages, such as colder substrate, faster film growth rate, and larger deposition area. However, the consumption of silane for the DBD-PECVD procedure is much greater than for the RF-PECVD process.

Negative impulse flashover along cylindrical insulating surfaces bridging a short rod-plane gap under variable humidity

Negative impulse flashover along insulating surfaces bridging a short rod-plane gap is investigated under variable humidity. The specimens, cylindrical in shape and with a smooth surface, were made of PTFE, silicone-rubber, nylon and glazed porcelain and were bridging the gap, which was stressed by standard lightning and switching impulse voltages. Breakdown probability distributions were obtained and the breakdown voltage and time to breakdown were measured. The gap was overstressed by applying voltages higher than that causing 100% breakdown so as to study the effects of the applied peak voltage on breakdown characteristics. When breakdown occurs over an insulating surface the breakdown voltage is significantly lower compared to that obtained for air alone, especially at lower breakdown probabilities and under switching impulse voltages. It is also lower for lightning than switching impulse voltages, this being less marked with increasing material permittivity. Breakdown is closely related to negative corona growth. The effect of absolute humidity on breakdown voltage is minimal. The IEC atmospheric conditions correction procedure yields satisfactory results when breakdown occurs both in air alone and along an insulating surface.