Air Dielectric Barrier Discharge Research Articles

The efficacy of non-equilibrium dielectric barrier discharge in air on the elimination of phytopathogenic fungi from wooden surface

Despite the use of modern transport and storage techniques, post-harvest losses of fruit and vegetables due to diseases are a major global problem. Therefore, it is necessary to stop or prevent the development of infectious diseases at all stages of plant production. In response to this problem, we proposed an atmospheric plasma with a dielectric barrier discharge (DBD) in air as a biocidal technique for the eradication of phytopathogens: Fusarium oxysporum, Alternaria alternata, and Botrytis cinerea. The reactor used in our experiments generates UV photons, electrons, ions and reactive oxygen/nitrogen species, which are highly effective as biocidal agents. The effectiveness of eliminating these fungi using DBD plasma was initially studied on artificially inoculated wooden discs and it was shown that plasma treatment for 3 min (27 ± 13) s, 5 min (32 ± 7) s, and 9 min (53 ± 30) s resulted in the destruction of 90% of F. oxysporum, A. alternata, and B. cinerea, respectively. Extending the treatment time to 20 min was sufficient to cause a lethal effect on fungi naturally contaminating the surfaces of wooden storage boxes. Plasma treatment induced damage to the cell envelope and stimulated the formation of intracellular ROS, leading to leakage of cytoplasmic contents and ultimately cell death. It was confirmed that multiple exposures of these microorganisms to plasma did not induce fungal resistance to this disinfection method.

Dynamics of NO, N2O, and ONOOH in atmospheric-pressure air dielectric barrier discharge: decoupling energy density and gas temperature effects varying with discharge voltage

The dose regulation of reactive nitrogen species is crucial for biomedical applications. In this study, we develop a global chemical kinetics model comprising 92 species and 1018 reactions to investigate the regulatory dynamics of three types of reactive nitrogen species, i.e. NO, N2O, and ONOOH, which vary with the discharge voltage in an air coaxial dielectric barrier discharge. Based on the experimental results, the model can describe the density variations of NO, N2O, and ONOOH. The simulation results indicate that the O, NO3− , NO2− , and O3 are essential intermediate species related to NO generation; N, NO2, O-, N2*, and O(1D) are essential intermediate species related to N2O generation; and O2− , NO, NO2, OH, O4− , and O3 are essential intermediate species related to ONOOH generation. The individual and comprehensive effects of the energy density and gas temperature on the densities of NO, N2O, and ONOOH and the corresponding intermediate species are quantified under increasing discharge voltages. The simulation results indicate that the energy density is the primary factor affecting the number density of NO, N2O, and ONOOH, whereas the gas temperature exerts a completely different effect on these three species. These insights are valuable for plasma applications in biomedicine, where the selective and controlled production of reactive nitrogen species is key for achieving the desired plasma performance.

Microdischarge dynamics of volume DBD under the natural convection airflow

The dielectric barrier discharge (DBD) at ambient air conditions exhibits discrete structure and contains thin microdischarge plasma filaments. Understanding the formation, self-interaction, and dynamics of such filaments is crucial towards the generation of uniform diffuse-like DBD in air, and also for the study of the memory effects and self-organized complex patterns. In this paper, the impact of natural convective flow, driven by the temperature gradient between self-heated discharge cell electrodes and ambient air, on the collective dynamics of microdischarges was studied in parallel-plate volume dielectric barrier discharge for the different geometrical arrangements. The horizontal arrangement corresponds to the parallel direction of discharge propagation and convective flow, while in the vertical arrangement buoyancy flow transverse to the discharge propagation column. For the horizontal arrangement, the randomly directed motion of microdischarges was observed. While at the vertical arrangement of the discharge cell, the buoyancy flow initiates the directed motion of the microdischarges following the gas flow. The continuous self-heating of the barrier electrodes during the DBD operation leads to a larger thermal gradient and increasing in the microdischarge channels. The larger thermal gradient results in a more pronounced directed motion of microdischarges with a higher velocity. The velocity of convective flow in the discharge gap was estimated by the simulation and compared with the mean velocity of MD channels obtained by the particle image velocimetry method.

Characteristics of high-repetition-rate bipolar pulse DBD under various electrical conditions in atmospheric-pressure air

Numerous studies have been conducted on pulse dielectric barrier discharge (DBD) because it can produce powerful discharges uniformly at atmospheric pressure with a fast rise time. Although much research has been conducted on pulse DBD below 10 kHz, relatively little has been conducted on pulse DBD at high pulse repetition rates (PRRs). Therefore, in this study, the ozone generation and discharge characteristics of bipolar pulse DBD in atmospheric-pressure air at a high PRR of 10 kHz or above were investigated. According to the results of this study, with the exception of electron temperature, most discharge characteristics need for practical applications—like transfer charge, electron density, and discharge uniformity—improved as the voltage and duty ratio increased at high PRR. On the contrary, increasing the PRR exhibited trade-off features like low electron temperature, low discharge uniformity, and a high number of discharges per unit time. Ozone generation demonstrated good results at high voltage, appropriate PRR, and low duty ratio, but applying suitable electrical conditions is crucial considering ozone generation speed and power consumption. The findings of this study will be very beneficial for high-PRR pulse DBD applications that require quick and effective processing. Additionally, they will be useful for researching the characteristics of pulse DBD at high PRR.

Synergistic degradation levofloxacin through dielectric barrier discharge and sodium persulfate

The release of antibiotics that are difficult to degrade by themselves into the environment have received increasing attention because they have posed great threat to natural ecosystem and human health. Sodium persulfate (PS) is used to treat organic wastewater because of its strong oxidation, but it needs to be activated. Dielectric barrier discharge (DBD) can product stable gas discharge plasma that is suitable for activating PS. The synergistic degradation process of levofloxacin (LFX) by air DBD plasma with PS were investigated. The effects on the degradation ratio and energy efficiency of LFX were studied, including input power, air flow rate, original concentration, discharge spacing, and PS dosage. The degradation kinetics and synergistic factors were calculated under different PS additions. After plasma alone treatment 45 min, the maximum degradation ratio of LFX was 58.74 % and 88.63 % via plasma alone and plasma synergistic with PS under 15 W input power and 50 mg·L−1 LFX original concentration. The energy efficiency, the first-order reaction rate constant and the synergistic factor SI was 0.1532 g·(kW·h)−1, 4.116 × 10−2 min−1 and 1.64, respectively. The change of ozone concentration in the reaction system after adding PS was measured. The effects on the synergistic degradation of LFX of two radical scavengers, methanol (MeOH), and tert-butanol (TBA), were investigated. After calculation, the contribution ratios of ·OH and SO4-· were 48.08 % and 26.97 %, respectively. The intermediate products were analyzed by LC-MS in the decomposition process of LFX, and the probable decomposition pathway of LFX was presented.

Surface modification of aramid fiber by cascade process with atmospheric plasma and TDI grafting

Aramid fiber (AF)/epoxy composites are often used as mechanical and insulating materials for ultra-high voltage gas-insulated switchgear (GIS) insulation pull rods. However, the product performance is believed to be restricted by the poor adhesion between AF and the resin matrix, affecting the operation reliability of GIS. In this work, a cascade process was applied to modify the AF surface to improve interfacial behavior. The AF was first treated with air dielectric barrier discharge at atmospheric pressure to obtain a rough surface and then reacted with toluene-2,4-diisocyanate (TDI) to introduce polar functional groups onto the surface. The plasma discharge power and treatment time were investigated as major parameters, and the aging effect was studied. The modified AF was characterized by scanning electron microscope, Fourier transform infrared spectrometer, x-ray photoelectron spectroscopy, atomic force microscope, and filament yarn tensile test. The interfacial behavior of the AF/epoxy composite was analyzed by interfacial shear strength (IFSS) test of micro-bond specimen and interlaminar shear strength (ILSS) test of Naval Ordnance Laboratory rings. Experimental results showed that polar functional groups were introduced onto the AF surface. The IFSS and ILSS of AF/epoxy composite were increased by 32.8% and 20.2% at most, respectively, and the tensile strength of the AF was mostly preserved. Moreover, with the increase in plasma discharge power, the interfacial strength of the modified AF/epoxy interface increased firstly and then decreased. The AF modified by TDI retained a relatively good modification effect after aging for some time. This study presents a cascade process for the AF surface modification with simplicity, effectiveness, and resource-saving, which is suitable for industrial applications.

Effect of rotating a dielectric barrier on discharge energy and uniformity in an atmospheric pressure air DBD

The application performance of the dielectric barrier discharge (DBD) depends on plasma characteristics, especially discharge energy and uniformity. In this study, the plasma characteristics are investigated in a DBD device with a rotating dielectric barrier. The statistical results indicate that rotating a dielectric barrier can effectively improve discharge power and the number of current pulses. Compared to a stationary DBD, the grayscale standard deviation of the discharge images can be significantly reduced, and the microdischarges present a rather diffuse distribution in the rotational DBD. This rotation also leads to an increase in the number of microdischarges and their movement in the direction of rotation. Additionally, a computational fluid dynamics numerical simulation together with the solution of the diffusion and recombination equations for space charges is implemented to study the diffusion, recombination, and transfer with airflow of space residual charges. The results reveal that the space charges move farther than their diffusion limit in most regions when the rotating speed reaches 30 rps (revolution per second). The mechanism of enhancing the discharge energy and uniformity by rotating a dielectric barrier is analyzed based on the local electric field enhancement induced by surface charges and electron detachment from space negative charges.

Fast degradation of carbamazepine in water by electric discharge plasma

The proliferation of pharmaceuticals in the aqueous environment has adversely impact on human health and ecosystem balance. Pharmaceutical contaminations are difficult to remove effectively by conventional treatment technologies. In order to degrade carbamazepine (CBZ) efficiently, a common antiepileptic drug, three plasma discharge modes were studied, including liquid-phase discharge, air gas-liquid jet and dielectric barrier discharge. It is noteworthy that the degradation efficiency and energy yield reached to highest levels (0.11 g/kWh) when operating at 225 W input power under liquid phase discharge, compared with the other discharge modes. The parameters of concentration, electrode distance, volume, input power and frequency of the discharge were also evaluated and optimized. Plasma emission spectroscopy revealed the degradation process is mainly attributed to reactive oxygen species (ROS), while the role of reactive nitrogen species was not significant. The contributions of diverse ROS were assessed by radical quenching experiments, including p-benzoquinone, p-phthalic acid and tert-butanol. The possible degradation intermediates and pathways of CBZ were tested and analyzed by liquid chromatography-mass spectrometry (LC-MS). Comprehensively consideration of cleanliness, degradation efficiency and application difficulty, liquid-phase discharge treatment is a promising technology for water treatment.

Non-thermal plasma actuator mechanism in interaction with fluid flow structure for aeronautical flow control

Plasma actuators generated by surface dielectric barrier discharge are developed for controlling flow in aeronautics applications. This research studies the simulation of cold plasma discharge at atmospheric pressure coupled with compressible fluid dynamics using COMSOL Multiphysics 5.4. Modeling of dielectric barrier discharge in air at high voltages is carried out in two dimensions. The development of electric field and space charge density are discussed in several cases to determine the discharge regime. Non-thermal plasma generates tangential ionic winds at the surface during corona discharge. The results are validated by the experimental results of the literature. The maximum electric wind velocity above the actuator grows linearly with the applied voltage, and simultaneously, the horizontal extension of the discharge grows with the applied voltage. The induced electrohydrodynamic force augments with the applied voltage amplitude, reaching saturation at higher voltages. Moreover, as the voltage rises, the discharge becomes filamentary, inducing a higher number of streamer pulses. Hence, the power consumption discharge increases abruptly as the voltage rises. In addition, the efficiency increases at higher voltage amplitudes and with the dielectric thickness. Our findings give a clear description of physical atmospheric plasma parameters in the surface discharge mechanism and the efficiency of the actuator plasma.

Anticancer effects of DBD plasma-activated saline within different discharge modes

With a change in ambient temperature and discharge power, air discharge plasma can switch between two typical modes, namely the ozone mode and the NO x mode. Here, we analyze the physicochemical properties and anticancer effects of air dielectric barrier discharge (DBD) plasma-activated saline (PAS) treated by ozone-riched gas produced in an ozone discharge mode, NO x -riched gas produced in a NO x discharge mode, and a mixture of both produced in the combined two modes simultaneously. The results show that gaseous and aqueous reactive oxygen species (ROS) and reactive nitrogen species (RNS) generated by plasma vary in different discharge modes, correlating to the amount of high-valance nitroxides. In the ozone mode, ozone and minor N2O5 are generated in the gaseous phase and are transformed to aqueous ROS and RNS. In the NO x mode, low-valance RNS are generated in the gaseous phase but are transformed into less aqueous RNS. For the PAS produced by the mixed gases, not only the highest concentrated ROS are generated, but also the most abundant gaseous high-valence RNS are produced and transformed to aqueous RNS in the saline. In vitro experiments reveal that, although A375 cells incubated with these three PASs (30%) could all inhibit their viability by enhancing intracellular oxidative stress and inducing cell apoptosis, the PAS produced by the mixed gases has the strongest anticancer effects. Further studies suggest that high-valence RNS play a key role in PAS-induced anticancer effects.

Surface electric charge decay behavior of Polypropylene (PP) films treated by atmospheric air dielectric barrier discharge

Atmospheric air dielectric barrier discharge (DBD) is one of the most effective physical techniques for the cold plasma source. It is a promising technique used to modify the surface properties of polymers. This modification leads to improving wetting and adhesion properties, a change in surface roughness and other significant technological features. In recent studies, researchers have showed that DBD plasma exposure can modify the electric properties of insulating materials. In this study, we focused our attention on the influence of DBD plasma treatment on the surface electric charge behavior in polypropylene (PP) thin films. The effect of DBD plasma has been studied as a function of treatment time for two values of applied discharge voltages; 7 and 12 kV. After being exposed to DBD plasma, the samples were charged for 5 seconds in ambient air using a negative triode corona electrode system. The influence of DBD plasma treatment on the surface electric charge behaviour in PP thin films was investigated. The surface characterization of the untreated and treated PP films is performed using surface electric charge decay measurements, for identical charging conditions.

Analysis of ozone generation in a planar atmospheric pressure air dielectric barrier discharge reactor

This work investigates O3 production in a planar atmospheric pressure air dielectric barrier discharge reactor numerically and experimentally. The surface temperature of the reactor is measured by an infrared (IR) thermal imager, and the O3 densities of cases in the reactive zone are measured by ultraviolet absorption spectroscopy. The 1.5D plasma fluid model (PFM) with transverse convection is employed to capture the average properties of a single microdischarge (MD) generated in the reactor. The concept of equivalent reaction is proposed to calculate spatial-cyclic average species sources obtained by the 1.5D PFM and provided to the chemical model of a 3D gas flow model (GFM) for obtaining density distributions of reactive species generated by MDs in the reactive zone. The simulated temperature distribution of the reactor surface is validated by that measured with the IR thermal imager since the gas temperature was reported as a critical discharge parameter for O3 generation. The simulated O3 densities show the same trend as the flow rate changes, which demonstrates the proposed model captures the average discharge dynamics in different operating conditions. In the 1.5D PFM, the simulated results show that the O3 molecules produced in the case of 4 SLM are much more than those produced in the case of 1 SLM though the O atoms produced in the case of 1 SLM are around 20% more than those produced in the case of 4 SLM. In the case of 1 SLM, more than 48% of O3 molecular generated are destructed, while only around 14% of O3 molecules are destructed in the case of 4 SLM. The analysis shows that around 73% of O atoms generated in the 1.5D PFM are consumed in the formation of O3 molecules in the case of 4 SLM, while only 18% of O atoms generated in the case of 1 SLM are consumed in the formation of O3 molecules. In the 3D GFM, the O3 destructed is around 24% of that destructed in the 1.5D PFM in the case of 4 SLM due to the oxidation reaction of NO, while only 11% of O3 molecules destructed as that destructed in the 1.5D PFM in the case of 1 SLM. The amounts of O3 molecules generated in the 3D GFM are minor if they are compared with those generated in the 1.5D PFM in all cases. The overall O3 yield efficiency reaches 97 g kWh−1 with the O3 concentration increasing up to 2700 ppm in the case of 4 SLM, while the O3 yield efficiency decreases to 10 g kWh−1 and O3 concentration drops to 1400 ppm in the case of 1 SLM.

Catalytic and time stability effects of photocatalysts on ozone production of a surface dielectric barrier discharge in air

We investigated the effect of various photocatalysts - titanium, zinc, barium, and tungsten oxides on ozone generation of the surface dielectric barrier discharge in air. The layers of these catalysts were deposited on the side of the glass plate opposite the active electrode so that the emission from the discharge irradiated them. We found that TiO2, ZnO, and BaTiO3 catalysts increase the concentration of ozone generated by the discharge. On the other hand, the presence of WO3 in the discharge does not affect the ozone concentration. All these catalysts show no substantial effect on the electrical parameters of the discharge.

Uniform-saturation modification for hydrophilicity improvement of large-scale PET by plasma-electrified treatment

Low surface energy and poor hydrophilicity of the polymer film reduces its working stability and service life in various application fields, but the industrial surface modification for the large-scale film requires the dynamic and efficient processing techniques with the uniform treatment effects. In this study, an efficient air dielectric barrier discharge (DBD) tube electrode array for large-scale polyethylene glycol terephthalate (PET) film treatment was established, and its discharge characteristics and treatment effects were further investigated by experiment and simulation at a microscopic scale. It shows that the increase in the number of electrodes and the applied voltage leads to diffuse and uniform discharge with strong luminous intensity, where the emission spectra is dominated by the second positive band of nitrogen molecules. Moreover, the increase in applied voltage and the decrease in treatment speed both enhance the surface hydrophilicity and the modification uniformity, which is caused by the rough surface and the introduction of oxygen-containing groups by the air DBD treatment. Combined with quantum chemistry calculations, it is speculated that the further modification reaches saturation with particles (COOH group) that causes hydrophilicity. It reveals that the introduction of OH groups on PET surface accounts for the increase in the molecular dipole moment and hydrophilicity; by contrast, the COOH group issued from the further oxidation of OH group decreases the molecular polarity, thereby causing the saturation of particles which causes the hydrophilicity by the air DBD treatment.

Simulation on oily contamination removal by ozone using molecular dynamics

Ozone (O3) is characteristic of high oxidative activity. It displays a high potential value in sterilization and decontamination. Although O3 has been widely investigated for its efficiency and environmentally friendly effectiveness, the fundamental issue regarding the complicated microscopic interaction mechanism between O3 and contaminant molecules remains largely unaddressed. We addressed this knowledge gap through molecular dynamics (MD) simulation at the molecular scale. Results indicated that five representative hydrocarbon molecules (n-hexadecane, phytane, terpane, naphthalin and acenaphthylene) on a rough silica (SiO2) surface were almost removed after about 300 ps simulation. And the aromatic molecules were easier to be removed than aliphatic ones. The hydroxyl oxidation reaction was demonstrated as a predominant mechanism. As the large dose of O3 was supplied by atmospheric air dielectric barrier discharge (DBD) plasma, this work provided an important theoretical reference for better using plasma technology for oily contaminant removal.

Numerical simulation of air DBD under standard atmospheric pressure

In order to study the mechanism of dielectric barrier discharge (DBD) producing non-equilibrium plasma, the DBD equipment was simplified into a one-dimensional model. The AC power supply voltage was set as 18 kV, the frequency was set as 10 kHz, and the discharge medium was N2 and O2 with a mass fraction of 4:1 to simulate the air. The impact cross-section, electron mobility and initial electron temperature of the discharge reaction were determined by BOLSIG+. The electric potential field diagram, voltage current relation diagram, electron density diagram, temperature distribution diagram and electron energy distribution function EEDF diagram are obtained. The results show that the electric field reaches the maximum near the gap sheath. Due to the generation of an additional electric field, the current density reaches the maximum at the rising edge of the air gap voltage. The continuous ionization of air particles in the discharge process leads to the accumulation of electrons and the formation of electron collapse, which leads to the increase in electron density and the decrease in electron temperature. As the reduced electric field E/N increases, the proportion of high-energy electrons in the total electron number increases. At this time, the reaction of non-equilibrium plasma intensifies, and more active substances can be produced.

Detection of NO3− introduced in plasma-irradiated dry lettuce seeds using liquid chromatography-electrospray ionization quantum mass spectrometry (LC-ESI QMS)

Discharge plasma irradiates seeds with reactive oxygen and nitrogen species (RONS). However, RONS introduced in seeds by plasma irradiation have not been successfully detected thus far. This study provides experimental evidence that nitrate ion NO3− is introduced in lettuce seeds as RONS upon irradiation with atmospheric-pressure air dielectric barrier discharge plasma. Plasma irradiation for 5 min promotes seed germination. The components of the plasma-irradiated seeds were examined using electrospray ionization quantum mass spectrometry (ESI QMS), which revealed that the plasma irradiation introduced an ion with a mass of 62 m/z in detectable amounts. This ion was identified as NO3− by liquid chromatography (LC), multiple wavelength detector (MWD), and LC-ESI QMS. A one-dimensional simulation at electron temperature Te = 1 eV, electron density Ne = 1013/m3, and gas temperature Tg = 300 K indicated the introduction of NO3−, involving nitric oxide NO. NO3− is one of the most important ions that trigger signal transduction for germination when introduced in seeds. The scanning electron microscopy (SEM) images revealed that there was no change on the surface of the seeds after plasma irradiation. Plasma irradiation is an effective method of introducing NO3− in seeds in a dry process without causing damage.

Cockcroft–Walton Generator: An Effective Voltage Multiplier for Power Supplies of Square Pulses Driving DBD Plasmas

This report gives prominence to the importance of the traditional Cockcroft–Walton voltage multiplier to the design of pulsed power supplies for dielectric barrier discharge (DBD) applications. Following an inventive concept, a simple Cockcroft–Walton generator is combined with a MOSFET-based switch (in either “push” or “pull” mode). Thus, the to-be-chopped stabilized dc high voltage is produced by a compact, transformer-less, modular unit, having high flexibility in terms of engineering. This approach leads to well-defined, square, high-voltage pulses of variable amplitude, frequency, and duty cycle. Design, implementation, and proof test of such a prototype are here demonstrated. The prototype yields square pulses as high as 10 kV (plateau value), as narrow as 350 ns (variable pulsewidth up to millisecond, depending on the frequency), rising or falling time close to 20 ns, pulse repetition rates up to 4 kHz, and output mean power up to 150 W. The functionality of the system is demonstrated by driving coaxial, ambient air DBDs of variable lengths, while principal electrical and optical parameters are recorded. Peak power values higher than 70 kW are measured on the DBD side, while the voltage multiplier power efficiency factor remains close to 95%.

Inactivation of E. coli, S. aureus, and Bacteriophages in Biofilms by Humidified Air Plasma.

In this study, humidified air dielectric barrier discharge (DBD) plasma was used to inactivate Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and bacteriophages in biofilms containing DNA, NaCl, carbohydrates, and proteins. The humidified DBD plasma was very effective in the inactivation of microbes in the (≤1.0 μm) biofilms. The number of surviving E. coli, S. aureus, and bacteriophages in the biofilms was strongly dependent on the constituent and thickness of the biofilms and was greatly reduced when the plasma treatment time increased from 5 s to 150 s. Our analysis shows that the UV irradiation was not responsible for the inactivation of microbes in biofilms. The short-lived RONS generated in the humidified air DBD plasma were not directly involved in the inactivation process; however, they recombined or reacted with other species to generate the long-lived RONS. Long-lived RONS diffused into the biofilms to generate very active species, such as ONOOH and OH. This study indicates that the geminated NO2 and OH pair formed due to the homolysis of ONOOH can cause the synergistic oxidation of various organic molecules in the aqueous solution. Proteins in the biofilm were highly resistant to the inactivation of microbes in biofilms, which is presumably due to the existence of the unstable functional groups in the proteins. The unsaturated fatty acids, cysteine-rich proteins, and sulfur–methyl thioether groups in the proteins were easily oxidized by the geminated NO2 and OH pair.

Ozone production in a dielectric barrier discharge in air- and oxygen–methane mixtures. Experiment and modeling

The effect of methane on ozone production in a dielectric barrier discharge (DBD) was studied in mixtures of CH4 with synthesized air and oxygen. It was found that addition of CH4 significantly reduced the number density of ozone other conditions being equal. A DBD model was developed that takes into account the spatial structure of microdischarges and the fact that near the electrodes their filaments transform into surface discharges, where most of ozone is produced. In addition, in air and air–CH4 mixtures the successive microdischarges were considered to occur not randomly in space, but at the same positions on the electrodes or moving with the flow occurring in the same volumes. The measured values of ozone number density downstream of the DBD were compared with simulation results, obtained with this novel DBD model. A good agreement between experiment and calculations was observed.