Coaxial Dielectric Barrier Discharge Research Articles

Mathematical modeling of the electric field in the planar and coaxial dielectric barrier discharge reactor in water treatment application

PurposeTo design a pulse power water treatment system, it is necessary to design a reactor optimally. One of the most essential types of reactors used in water treatment is the dielectric barrier discharge (DBD) reactor. The purpose of this paper is to model the electric field in the two types of planar and coaxial reactors to have an accurate analytical formula for using in the optimal design according to the required electric field of the treatment.Design/methodology/approachThe method proposed in this paper focuses on the voltage of different areas in the reactor and different boundary conditions to obtain the surface charge density. In this regard, parameters of the dielectric and treated material, as well as the reactor dimension, have been affected in the equations. To confirm the analytical results, the finite element method simulation has been performed, and it shows the accuracy of this method.FindingsThe exact analytical equation of the electric field is found within the discharge zone of the planar and coaxial DBD reactors. These equations can predict the values of different parameters of the reactor required to purify the material before each design and it does not even require simulation.Originality/valueThe electric field formula presented in this paper can allow the manufacturers of pulse power water treatment systems to optimize their design easily, cost-effectively and in less time. Also, the formulas provided are completely general and remain effective for all materials.

Enhancement of Co2 Splitting in a Coaxial Dielectric Barrier Discharge by Pressure Increase, Packed Bed and Catalyst Addition

Enhancement of Co2 Splitting in a Coaxial Dielectric Barrier Discharge by Pressure Increase, Packed Bed and Catalyst Addition

In Situ Identification of NNH and N2H2 by Using Molecular-Beam Mass Spectrometry in Plasma-Assisted Catalysis for NH3 Synthesis

Ammonia synthesis at 533 K and atmospheric pressure was investigated in a coaxial dielectric barrier discharge (DBD) plasma reactor without packing and with porous γ-Al2O3, 5 wt % Ru/γ-Al2O3, or 5 ...

Effect of megapore particles packing on dielectric barrier discharge, O3 generation and benzene degradation

Recently, packed-bed discharge plasma technologies have been widely studied for treatment of volatile organic compounds (VOCs), due to the good performance in improving the degradation and mineralization of VOCs. In this paper, a coaxial cylindrical dielectric barrier discharge reactor packed with porous material of micron-sized pores was used for degradation of benzene, and the discharge characteristics and ozone generation characteristics were studied. When the discharge length was 12 cm and the filling length was 5 cm, the packed particles in the discharge area significantly increased the number of micro-discharges, and the current amplitude and density increased with the pore size of packed particles, but the discharge power and ozone concentration showed a trend of first increasing and then decreasing. The discharge power and ozone production reached the maximum when the size of pore former was 75 μm, correspondingly, the degradation efficiency of benzene was the highest.

Plasma-assisted flame stabilization by AC dielectric barrier discharge in burst mode

Compared to the continuous mode of a high-frequency alternating current (HFAC) source, the burst mode is believed to be capable of controlling flow and combustion while saving discharge energy. Thus, the effect of burst mode on plasma-assisted flame stabilization, which is driven by an HFAC source, is investigated based on a plasma manipulation diffusion flame experiment system. A specially designed injector with a coaxial dielectric barrier discharge configuration is used to generate a methane-air diffusion flame and air plasma. The influence of the actuating parameters of the burst mode on plasma flame stabilization and the discharge power consumption are studied. The results show that the plasma injector has the typical volt–ampere characteristics of dielectric barrier discharge. The discharge clearly exhibits regular unsteady operation characteristics when the source is in burst mode. Two flame stability thresholds are found with increasing discharge voltage. According to the first and second flame stability threshold values and the flame pattern, raising the control frequency and the duty cycle is favorable for flame stabilization. However, for a fixed duty cycle of 50%, because the time scale of the actuator-off duration is longer than that of combustion, when the control frequency is too low, the flame cannot be stabilized even though the applied voltage is very high. For a fixed control frequency of 100 Hz, the flame is also difficult to stabilize when the duty cycle is too small. Mainly due to the unsteady gasdynamic effects of plasma in the burst mode, this approach can achieve the same flame stabilization effect as that of the continuous mode while reducing the energy consumption. The cost-effectiveness ratios of the two optimum actuation schemes are only 6.4% and 10.1%. In addition, the burst mode is better than the continuous mode in avoiding undesirable arc discharge. To better stabilize the flame while maintaining a relatively low cost-effectiveness ratio, actuator setting schemes with high frequency and a small duty cycle should be selected.

Parametric study of coaxial dielectric barrier discharge in atmospheric pressure argon

A parametric study of the characteristics of coaxial dielectric barrier discharge sustained in atmospheric pressure argon is carried out. The numerical model is based on the drift-diffusion theory of gas discharges. The integral characteristics of the discharge, such as the root mean square of the discharge current, the period average dissipated power, and the efficiency of the power deposition, are explored in the parameter space spanned by the voltage amplitude and frequency of the applied AC field, the barrier dielectric constant, and the gas gap width.

Plasma-assisted catalysis for ammonia synthesis in a dielectric barrier discharge reactor: key surface reaction steps and potential causes of low energy yield

Ammonia synthesis experiments were carried out in a coaxial dielectric barrier discharge (DBD) reactor packed with several different supports and metal catalysts. There was a marked increase in the reaction rate, over that obtained in an empty DBD plasma reactor, upon introduction of a packed bed of γ-Al2O3, Ru/γ-Al2O3, or SiO2 particles. The difference in the reaction rates over γ-Al2O3 and Ru/γ-Al2O3 was minimal. Complementary zero-dimensional plasma kinetic model analysis was also performed using inputs from experimental data. This kinetic analysis allowed for gas phase reactions, Eley–Rideal (E–R) reactions, and direct adsorption of radical species on the γ-Al2O3 surface. On the metal surface, dissociative adsorption of N2 and H2, and Langmuir–Hinshelwood reactions were also included. This analysis revealed that, under the conditions of our experiments, ammonia synthesis proceeds principally by the formation of reactive radicals in the gas phase, which then adsorb and participate in E–R reactions on both the metal and support material surfaces. This finding illustrates a challenge for substantially increasing the energy yield for plasma-assisted ammonia synthesis in typical DBD reactors containing packed catalyst beads.

Degradation of toluene by tube-tube coaxial dielectric barrier discharge: power characteristics and power factor optimization

ABSTRACT In this paper, the power characteristics and power factor optimization were investigated in a coaxial tube–tube dielectric barrier discharge (DBD) reactor. The effects of several parameters, including discharge voltage, discharge length, discharge frequency and gas flow rate on discharge power and power factor have been evaluated. The experiment results showed that higher discharge power can be obtained by increasing the discharge voltage, discharge frequency and electrode length. But for the power factor, with the increase of discharge frequency, the power factor increased firstly and then decreased. Moreover, with the discharge length increased, the discharge frequency when the power factor reached the maximum value reduced. The response surface method (RSM) and artificial neural network (ANN) were used to optimize the power factor, and their results were relatively consistent. The result of the ANN showed that when discharge voltage was 9.58 kV, discharge frequency was 8.69 kHz, discharge length was 15.8 cm, and gas flow rate was 1.5 L/min, the power factor reached the maximum value of 0.362. The degradation experiment of toluene was carried out in the reactor and its degradation effect was analyzed. The toluene degradation rate is positively correlated with the power factor, and the discharge voltage, gas flow rate and initial concentration are also the key parameters to determine the degradation of toluene. When the discharge voltage, gas flow rate, and initial concentration are 10 kV, 70 mL/min, and 50 ppm, respectively, the power factor and toluene degradation rate reach 0.34 and 74.3%.

Revealing the active sites of the structured Ni-based catalysts for one-step CO2/CH4 conversion into oxygenates by plasma-catalysis

The direct conversion of CO2/CH4 into liquid chemicals is an attractive way for using carbon resources, but it is still unclear which types of catalysts are suitable for plasma-involved catalysis. Herein, a serious of nickel foam (NF) supported Ni-based catalysts derived from Layered double hydroxides (LDH) were newly designed by a green hydrothermal strategy. The crystal structures, morphologies, and the redox behaviors of these catalysts (NiAl-LDH/NF, NiO/NF, Ni/NF and NiGa/NF) were systemically characterized. Plasma-enabled direct conversion of CO2/CH4 was performed in a co-axial dielectric barrier discharge reactor using a nanosecond repetitive-pulse power, and the results showed that the selectivities of the liquid oxygenates were strongly depended on their microstructures, surface compositions (valence states) and reducibilities. The zero-valent Ni/NF and NiGa/NF showed high total liquid selectivity (> 30 %) and dominant CH3COOH (> 15 %), while the Ni2+ in NiO/NF gave the comparable activities for CH3OH (8.9 %) and CH3COOH (9.6 %). Unexpectedly, NiAl-LDH/NF exhibited the highest CH3OH selectivity (12.3 %) and negligible carbon deposition. According to systemic characterizations, an “−OH reservoir” mechanism was proposed that numerous −OH groups over the ultrathin nanosheets (∼60 nm) of NiAl-LDH may react with the interfacial CHx* radicals and, on the other hand, possess inferior electron affinity for electronegative C atom, thus endowing NiAl-LDH the prominent CH3OH selectivity and high resistance to carbon deposition.

A surface dielectric barrier discharge non-thermal plasma to induce cell death in colorectal cancer cells

A novel coaxial surface dielectric barrier discharge (SDBD) non-thermal atmospheric pressure plasma device, driven by a 35.7-kHz DC pulse and adjustable by a pulse-width modulation, was developed in this study and preliminarily tested for its killing effects of a cancer cell type. This study was divided into three phases, namely, air phase, liquid phase, and cell phase. First, the electrical characteristics and emissions were examined. Two-beam UV-LED absorption spectroscopy was also newly developed to measure the absolute hydroxyl radical (OH⋅) density in the filamentary discharge. Then, the effects of energy doses and treatment durations on three types of liquids and on the colorectal adenocarcinoma cell, SW620, were examined. From Lissajous figures (Q–V plot), the developed SDBD possesses the maximum power density and energy dose of 0.33 ± 0.05 W/cm2 and 19.5 ± 3.00 J/cm2, respectively, when the voltage was set at 3.44 kV and the power at 115 mW. From two-beam UV-LED absorption spectroscopy results, the OH⋅ density increased by 0.32, 0.58, and 0.86 × 1019 m−3, with operational powers of 29, 58, and 115 mW, respectively, within 1-min treatment. In liquid phases, the plasma device can increase the concentrations of H2O2 and NO2− in a time-dependent manner. Finally, cell-phase studies, including the examination of the cell morphology, cell viability, and gene expression of the SW620 cell, show that the device can time-dependently induce the mortality of the SW620 cell, relevant to the up-regulation of the Bax/Bcl-2 expression ratio. Taken together, this novel SDBD plasma device shows potential as another alternative for cancer treatment, although further modification is required.

Ozone Production in Cylindrical Co-axial Double Dielectric Barrier Discharge Ozone Generator

This study developed an ozone generator of a double co-axial cylindrical dielectric barrier discharge system with air, argon, and oxygen as the working gases. The discharge was produced by using a high voltage power supply of 0 - 18 kV and a line frequency of 50 Hz. The flow rate of air, argon, and oxygen was varied from 1 to 6 L/min. A comparison of O3 generation in air, argon, and oxygen using brass as a central electrode was conducted and it was found that O3 concentration was higher in the case of oxygen than in the air and in argon gases environment for given fixed discharge time, applied voltage, and diameter of the brass electrode. This study revealed that the concentration of ozone increased along with the increase in the applied voltage for constant discharge time and gas flow rate. The O3 concentration also increased with the increase in the discharge time at fixed applied voltage and gas flow rate; however, the concentration decreased with the increase in the gas flow rate at fixed discharge time, applied voltage, and diameter of the electrode. A small reactor with a large inner electrode generated a high concentration of O3. Yet, a reactor with a small diameter, there seemed to have an optimum inner electrode diameter. The glass tube reactor of the internal diameter of 18 mm and the brass electrode of diameter 8 mm were utilized in this study. The ozone concentration was higher for oxygen as feed gas than both in the air and in argon and the O3 concentration was also higher in the air than in argon at fixed discharge time, applied voltage, and diameter of ozone generator. HIGHLIGHTS Ozone concentration increases with increasing applied voltage and discharge time but concentration decreases with increasing gas flow rates Low cost ozone can be produced in DBD reactor at atmospheric pressure Oxygen can be used as feed gas to generate high concentration of ozone than other gases inside DBD generator Optimization of central electrode diameter and gap space inside DBD reactor can help to increase ozone concentration, yield, and efficiency Proper choice of central high voltage electrode also can play the important role for the generation of ozone in DBD chamber GRAPHICAL ABSTRACT

The role of O3 on the selective formation of nitrate and nitrite in plasma-treated water

This study is to investigate the role of O3 on NO and NO2 oxidations to selective formations of NO2 − and NO3 − in plasma-treated water. Two plasma reactors, a surface dielectric-barrier discharge (DBD) and a coaxial DBD jet, are employed to water treatment with a working gas primarily consisting of N2 and O2. Results of surface DBD show that O3 first is increased with plasma treatment time, reaching a maximum, and then decreased. NO takes time to grow and the grow of NO is accompanied by O3 decrease. Formations of NO2 − and NO3 − are associated with gas-phase nitrogen oxides while the presence of O3 has a critical influence on a selective formation of NO2 − and NO3 −. The strong oxidation of O3 favors the formation of NO3 − while inhibits NO2 − formation. O3 serving as an inhibitor of NO2 − is confirmed with the DBD jet experiment where O3 is admixed in the downstream of the post discharge. O3 enhancement on NO3 − formation is demonstrated by exposing water to a synthetic NO gas with and without O3. In addition to O3, the presence of water vapor in the working gas, presumably facilitating formation of HNO2 and HNO3, greatly promotes NO2 − and NO3 − concentrations in solution. This is thought to be due to the stronger dissolution susceptibility and the relatively larger rate constant of HNO2 and HNO3 than those of N2O3 and N2O5. Finally, based on observations obtained here, a schematic roadmap of selective NO2 − and NO3 − formations is presented.

A non-equal gap distance dielectric barrier discharge: between a wedge-shaped and a plane-shaped electrode

For all volume dielectric barrier discharges (DBDs) reported, including both planar configuration volume DBDs and cylindrical or coaxial volume DBDs, the gap distance between the two electrodes is always a constant. In this paper, a non-equal gap distance DBD between a wedge electrode and a plane-shaped electrode is reported. It is found that the plasma can self-organize into a striped shape, which makes it possible to achieve a homogeneous plasma treatment effect by scanning the plasma over the surface. The high-speed photographs show that the discharge first occurs at the center of the wedge-shaped electrode where the gap distance is smallest, and it jumps to the next position with a relatively larger gap distance after a certain delay time. This is because of the build up of the reverse voltage due to the deposit of charges at the locations where discharge is ignited. Detailed analysis shows that the width of the equivalent charge deposit region is larger than that of the bright plasma stripe. According to the intensity ratio of N2 + (391.4 nm) and N2 (394.3 nm), the reduced electric field strength is evaluated to be in the range of 250–370 Td. It decreases with the increase in the gap distance. In addition, plasma of another type of non-equal gap distance DBD with a conical shape and a plane-shaped electrode is explored, and it is found that the plasma can also self-organize into concentric rings.

Strategies of Power Measurement and Energy Coupling Enhancement in Nanosecond Pulsed Coaxial Dielectric Barrier Discharges

Dielectric barrier discharges (DBDs) driven by nanosecond high-voltage pulses can be quite different from those driven by alternating current (ac) sources, on both electrical characteristics and plasma microparameters. In this article, the power measurement strategy in nanosecond pulsed coaxial DBDs is optimized. The effect of different experimental parameters on energy deposition and reduced electric field in plasma is investigated. First, the results measured using the instantaneous power (from the production of voltage and current) method and that using the v- q trace (Lissajous curve) method are compared and the source of divergence is analyzed. By comparing monitor capacitors with different materials and capacitances, it is demonstrated that the high-frequency response of the monitor capacitor is essential and the capacitance value can be adjusted according to the applied voltage, taking both the dynamic range of oscilloscope and the signal-to-noise ratio into consideration. Second, the influence of morphology of ground electrode, voltage rising time, and pulse width on energy deposition per-pulse and reduced electric field, obtained from the nitrogen spectral line-ratio, is studied. It is found that the copper foil promotes the discharge energy coupling per-pulse compared with the copper grid, while the reduced electric field obtained from the nitrogen line-ratio with the copper foil is weaker. A shorter rising time will also enhance the energy coupling per-pulse, as well as the reduced electric field.

"Insert-and-Go" Activated Carbon Electrode Tip for Heavy Metal Capture and In Situ Analysis by Microplasma Optical Emission Spectrometry.

The miniaturized optical emission spectrometry (OES) devices based on various microplasma excitation sources provide reliable tools for on-site analysis of heavy metal pollution, while the development of convenient and efficient sample introduction approaches is essential to improve their performances for field analysis. Herein, a small activated carbon electrode tip is employed as solid support to preconcentrate heavy metals in water and subsequently served as an inner electrode of the coaxial dielectric barrier discharge (DBD) to generate microplasma. In this case, heavy metal analytes in water are first adsorbed on the surface of the activated carbon electrode tip via a simple liquid-solid phase transformation during the sample loading process, and then, fast released to produce OES during the DBD microplasma excitation process. The corresponding OES signals are synchronously recorded by a charge-coupled device (CCD) spectrometer for quantitative analysis. This activated carbon electrode tip provides a new tool for sample introduction into the DBD microplasma and facilitates "insert-and-go" in subsequent DBD-OES analysis. With a multiplexed activated carbon electrode tip array, a batch of water samples (50 mL) can be loaded in parallel within 5 min. After drying the activated carbon electrode tips for 5 min, the DBD-OES analysis is maintained at a rate of 6 s per sample. Under the optimized conditions, the detection limits of 0.03 and 0.6 μg L-1 are obtained for Cd and Pb, respectively. The accuracy and practicability of the present DBD-OES system have been verified by measuring several certified reference materials and real water samples. This analytical strategy not only simplifies the sample pretreatment steps but also significantly improves the sensitivity of the DBD-OES system for heavy metal detection. By virtue of the advantages of high sensitivity, fast analysis speed, simple operation, low cost, and favorable portability, the upgraded DBD-OES system provides a more powerful tool for on-site analysis of heavy metal pollution.

CO2 conversion promoted by potassium intercalated g-C3N4 catalyst in DBD plasma system

The direct conversion of CO2 to CO and O2 has attracted extensive attention as CO is a key C1 feedstock for chemical synthesis. The CO2 conversion promoted by γ-Al2O3 supported potassium intercalated g-C3N4 (KuCN/AO) catalyst in a packed-bed dielectric barrier discharge (DBD) plasma system was investigated. A coaxial cylinder DBD plasma reactor was used with Cu powder as the high voltage electrode. Reactor temperature showed converse effect on CO2 conversion. As the reactor temperature decreased from 120 ℃ to 50 ℃, CO2 conversion rate and energy efficiency both increased by ca. 50%. After the catalyst was filled into the discharge area, the discharge mode changed from filamentary discharge to the combination of filamentary-surface discharge. The morphology and structure of KuCN was characterized by SEM, XRD, FTIR and XPS. KuCN kept a porous structure and K element distributed uniformly between CN interlayer spacing. In KuCN/AO assisted DBD plasma system, the highest CO2 conversion rate, CO yield and energy efficiency were increased from 11.1%, 10.0% and 9.41% to 19.3%, 18.1% and 20.6% compared with pure DBD/γ-Al2O3 system, respectively. The main mechanism of KuCN assisted enhancing CO2 conversion in packed-bed DBD reactor was analyzed. The larger specific surface area, layers bridging and charge redistribution enabled KuCN/AO to obtain good plasma-catalytic CO2 conversion performance.

Influence of Water Cooling for Outer Electrode on the Discharge Characteristics of an Atmospheric Coaxial DBD Reactor

Dielectric barrier discharge (DBD) has attracted increasing attention for the applications in the gas phase plasma chemical reactions. The utilization of electrode cooling has been proved to enhance the performance of plasma chemical reactions in the coaxial DBD reactor. However, the universal understanding on how the electrode cooling improves the plasma reaction is very limited. Here, we investigated the discharge characteristics in the N2 DBD with and without water cooling for outer electrode. The influence of water cooling on the discharge characteristics of the N2 DBD was examined by the diagnostics of electrical, optical, and temperature characters. The results showed that at the same initial applied voltage, the N2 DBD with water cooling exhibited a more stable discharge with higher intensity in comparison with that without water cooling, which was reflected by the smaller decrease and higher level in applied voltage, number of current pulses, transferred charge, relative intensity of the main reactive species, and energy efficiency as a function of discharge time. From the temperature measurement, the temperature of the DBD reactor was maintained in the lower and more stable level in the presence of water cooling, indicating that more energy was injected into the plasma reactions rather than wasted as heat dissipation to the environment, which led to the higher energy efficiency in the N2 DBD with water cooling. Overall, this work provides essential references for the development and optimization of the DBD reactors in practical applications (e.g., chemical synthesis using plasma processes).

Dry Reforming of Methane over Ni/γ‐MgO Catalysts in a Coaxial Dielectric Barrier Discharge Reactor

AbstractDry reforming of methane (DRM) over Ni/γ‐MgO catalysts in a coaxial dielectric barrier discharge (DBD) reactor was investigated and compared with DRM without catalysts. Firstly, the catalysts Ni/MgO, Ni/5%CeO2/MgO, and Ni/7%CeO2/MgO were prepared, their characteristics were specified by X‐ray diffraction, and then, they were partially packed into the DBD reactor. Various parameters such as the discharge power, flow rate, and CH4/CO2 molar ratio were explored. The presence of catalysts in the plasma reactor increased the yield and selectivity of H2 and CO. Furthermore, the effect of a reduced catalyst (Ni/7%CeO2/MgO reduced in argon‐hydrogen plasma) was evaluated, showing that CH4 can be converted with activated catalyst without extra power. Activated Ni/7%CeO2/MgO alone was able to convert CH4 to over 99 % for 30 min after reduction.

Numerical analysis of plasma formation process in a coaxial dielectric barrier discharge

Numerical analysis of plasma formation process in a coaxial dielectric barrier discharge

Ni and Cu oxide supported γ-Al2O3 packed DBD plasma reactor for CO2 activation

The direct activation of undiluted CO2 is carried out in a co-axial dielectric barrier discharge (DBD) reactor. The variation of the electrical discharge parameters and their influence on CO2 decomposition is investigated with the integration of 15 % MO/γ-Al2O3 (M = Ni, Cu) catalyst in the discharge zone. The electrical discharge is found to shift from the filamentary to a combination of surface and micro filamentary discharge on catalyst integration to NTP and also leads to the higher conversion of CO2 than DBD alone. The highest conversion of CO2 (15.7 %) with the energy efficiency of 1.597 mmol/kJ is achieved under CuO/γ-Al2O3 integrated NTP system, whereas the maximum of carbon balance (94.4 %) reaches with 4% CeO2 addition to CuO/Al2O3 catalyst. The oxygen vacancy of the catalyst plays a vital role in improving the performance, especially, the oxygen buffer property of CeO2 facilitates the recombination reaction and contributes to obtaining the highest carbon balance.