Discharge Gap Research Articles

Characterization and evaluation of cold atmospheric plasma as seedborne fungal disinfectant and promoting mediator for physico-chemical characteristics of Moringa oleifera seedlings

Non-thermal atmospheric pressure plasmas are a powerful tool to impact seed germination and microbial decontamination. Air large volume atmospheric pressure glow discharge plasma was developed and investigated to improve the biological activities of Moringa oleifera seeds. Ninty ns magnetic pulse compression high voltage system was used to generate the plasma. The plasma discharges current increases with increasing applied voltage and it decreases with increasing discharge gap. There was a steady reduction in the count of seedborne fungi on the application of air cold plasma with complete elimination of fungi at ≥ 10.94 mJ per pulse. The low doses of plasma (2.46 and 4.35 mJ) induced an increase in the seed germination, a significant increase in chlorophyll content (chl a and chl b) and antioxidant activities of the seedlings emerged from soaked or wet seeds rather than dry seeds. At lower plasma doses (2.46 and 4.35 mJ) there was a significant increase in leaf area and chlorophyll content (chl a and chl b) of the seedlings that emerged from H2O2 soaked seeds rather than that of free from H2O2. The plasma was harmful when applied at higher doses (≥ 10.94 mJ) and more harmful to the wet seeds compared to the dry ones.

Experimental study on particulate matter removal using packed-bed dielectric barrier discharge plasma reactor

In this study, a packed-bed dielectric barrier discharge (DBD) reactor was developed for particulate matter (PM) removal. The effects of operating conditions such as the packing materials, applied power, and discharging gap were systematically investigated. The results revealed that Zeolite 13X exhibited the highest PM removal efficiency based on its high electrostatic adsorption capacity. A narrow discharge gap (2.4 mm) and increased power density resulted in an enhancement of the PM removal efficiency in the system. Further, these operating conditions increased the electric field strength, which was proportional to the current density in the system. The energy yield decreased with an increase in the specific energy input into the packed-bed DBD reactor. Among the tested operating parameters, maintaining a narrow discharging gap was determined to be the most important for achieving high energy efficiency and PM removal in the system. Moreover, an air cleaning procedure was applied for the regeneration of the packing materials, resulting in a high recovery rate of over 80%.

Synergistic Effect of Co9S8 and FeS2 Inlaid on N-Doped Carbon Nanofibers toward a Bifunctional Catalyst for Zn-Air Batteries.

The development of economical and energy-efficient electrocatalysts is essential for the wide-scale application of secondary zinc-air batteries (ZABs). Herein, we prepared Co9S8 and FeS2 nanoparticles inlaid on N-doped carbon nanofibers (Co9S8-FeS2@N-CNFs), which were derived from the in situ growth of Fe-doped ZIF-67 nanosheet arrays on electrospun nanofibers and a subsequent sulfidation process. The Co9S8-FeS2@N-CNFs display excellent electrocatalytic performances for OER (Ej=10, 330 mV) and ORR (E1/2, 0.80 V) as well as a smaller charge and discharge gap (ΔE, 0.76 V) in KOH electrolyte, allowing it to be employed as an attractive air cathode bifunctional catalyst for secondary ZABs. The electrocatalytic performance of the composite materials (Co9S8-FeS2@N-CNFs) is obviously better than that of the single-component materials (FeS2@N-CNFs and Co9S8@N-CNFs). The improved catalytic performance is mainly attributed to the synergistic effect of the two transition-metal sulfides and the optimization of the structure. Furthermore, the peak power density of the assembled aqueous/solid-state ZABs based on Co9S8-FeS2@N-CNFs can reach 214 and 91 mW cm-2 with excellent stability, respectively, which outperforms the ones based on commercial precious-metal-based catalysts. We anticipate that our work will provide new inspiration for the design of MOF-derived sulfides as multifunctional catalysts.

Generation of High-Density Pulsed Gas–Liquid Discharge Plasma Using Floating Electrode Configuration at Atmospheric Pressure

In this paper, a high-density gas–liquid discharge plasma is obtained combined with nanosecond pulse voltage and a floating electrode. The discharge images, the waveforms of pulse voltage and discharge current, and the optical emission spectra are recorded. Gas temperature and electron density are calculated by the optical emission spectra of N2 (C3Πu → B3Πg) and the Stark broadening of Hα, respectively. The emission intensities of N2 (C3Πu → B3Πg), N2+ (B2Σ → X2Π), OH (A2Σ → X2Π), O (3p5P → 3s5S0), He (3d3D → 3p3P20), gas temperature, and electron density are acquired by optical emission spectra to discuss plasma characteristics varying with spatial distribution, discharge gap, and gas flow rate. The spatial distributions of discharge characteristics, including gas temperature, electron density, and emission intensities of N2 (C3Πu → B3Πg), N2+ (B2Σ → X2Π), OH (A2Σ → X2Π), O (3p5P → 3s5S0), and He (3d3D → 3p3P20), are presented. It is found that a high-density discharge plasma with the electron density of 2.2 × 1015 cm−3 and low gas temperature close to room temperature is generated. While setting the discharge gap distance at 10 mm, the discharge area over liquid surface has the largest diameter of 20 mm; under the same conditions, electron density is in the order of 1015 cm−3, and gas temperature is approximately 330 K. In addition, the discharge plasma characteristics are not kept consistent in the axial direction, in which the emission intensities of N2+ (B2Σ → X2Π), N2 (C3Πu → B3Πg), OH (A2Σ → X2Π), and gas temperature increased near the liquid surface. As the discharge gap is enlarged, the gas temperature increases, whereas the electron density remains almost constant. Moreover, as the gas flow rate was turned up, the electron density increased and the gas temperature was kept constant at 320 K.

Numerical study of various scenarios for the formation of atmospheric pressure DC discharge characteristics in argon: from glow to arc discharge

In this work, on the basis of a unified model from the point of view of describing the gas discharge gap and electrodes for 2D geometry, numerical calculations were carried out to study various modes of direct current discharges in argon at atmospheric pressure. The influence of the cooling conditions of the electrodes on the current–voltage characteristic of the discharge is shown: the transition from normal glow to arc discharge with the formation of an abnormal glow mode and without it. It is shown that, depending on the cooling conditions of the electrodes, two forms of arc discharge can be obtained: with a diffuse or contracted current spot. In the low-current mode, current and voltage oscillations were obtained during the transition from the Townsend to the normal glow discharge.

Current pulses and their influences on ozone production in oxygen-fed dielectric barrier discharge

The aim of this study is to investigate the current pulses and their effects on ozone generation during the process of ozone production in oxygen-fed dielectric barrier discharge. The experimental results show that there are large numbers of current pulses in the positive half-period of the current waveform but no obvious in the negative half-period. Moreover, the number of the current pulses in an AC cycle increases roughly linearly from 200 to 882 when applied voltage increases from 5 kV to 9 kV at 5 kHz. The number of these current pulses is almost independent of frequency. And these substantial current pulses occurring can be attributed to strong partial discharges generated in discharge gap may mainly resulting from the rough dielectric surface. Besides, these current pulses play an important role in the discharge characteristics and they are not in favor of ozone generation. The discharge power within current pulses is 1.47–1.76 times higher than the discharge power without current pulses and the ozone yield within current pulses is much lower than the ozone yield without current pulses. The decrease of ozone yield within current pulses is slightly more remarkable than the one without current pulses, because the discharge power within current pulses enhances more quickly.

Fabrication and characteristics of electret using fine silica powder and its application of ultrasonic sensor

Electrets were prepared by spin-coating the dispersion of fine silica powders, and their charge retention characteristics were investigated. Finer silica aggregates were formed on the PTFE surface layer by spin-coating the dispersed solution of fine silica powder than those formed by spray-coating colloidal silica. Electrets using fine silica powder also showed better charge retention characteristics than those using colloidal silica. Such an improvement in the charge retention might be due to the suppression of discharge in the excessive gap caused by coarse silica aggregates. Then, ECSs were fabricated using the prepared electrets, and their transmitting and receiving characteristics of airborne ultrasound were also investigated. The peak sensitivity of the ECS using a spin coating of fine powdered silica dispersion was slightly improved from those using spray coating of colloidal silica. On the other hand, the peak frequency and frequency band were greatly improved using spin coating of fine powdered silica dispersion. Therefore, ECS using fine silica powder is expected to be applied as a broadband airborne ultrasonic sensor.

Direct Observation of Discharge Phenomena in Vibration-Assisted Micro EDM of Array Structures.

The batch mode electrical discharge machining (EDM) method has been developed to improve the throughput and accuracy in fabricating array structures, but the process suffers from insufficient debris removal caused by the complex electrode geometry. Tool vibration has been used to improve flushing conditions, but to date the underlying mechanism of the tool vibration on the micro EDM of array structures remains unclear. This study aimed to investigate the effect of tool vibration on the machining process by direct observation of the discharge phenomena in the discharge gap by using a high-speed camera. Micro EDM experiments using 9 and 25 array electrodes were performed, and the effect of tool vibration on the discharge uniformity and tool wear was evaluated. It was found that tool vibration improved the uniformity of the discharge distribution, increased the machining efficiency, and suppressed the tool wear. The discharges occurred in periodic intervals, and the intensity increased with the amplitude of tool vibration. The results of this study indicate that the vibration parameters determine the discharge period duration and intensity to achieve optimum stability and efficiency of the machining process.

Gas-Discharge Point Source of UV Radiation Based on a Gas-Vapor Mixture of Argon and Copper

The characteristics of a pulse periodic source of a long-range UV radiation with overvoltage pumping by a bipolar discharge of nanosecond duration between copper electrodes in argon at atmospheric pressure are investigated. Copper vapors were introduced into the discharge due to the ectonic mechanism, in which a sufficient amount of the electrode material vapors is introduced into the discharge gap due to microexplosions of inhomogeneities of the surface of metal electrodes in a strong electric field of an overvoltage high-current nanosecond discharge. The characteristics of an overvoltage nanosecond discharge at a distance between the electrodes of 2 mm are studied. The emission spectra of the discharge were analysed, and the intensity of the UV radiation of a point emitter was optimized depending on the supply voltage of the high-voltage modulator and the repeti-tion rate of discharge pulses. The identification of the emission spectra of plasma made it possible to establish the main excited plasma products that form the spectrum of the UV radiation of the plas-ma. The study of the spectral characteristics of plasma based on gas-vapor mixtures "copper – ar-gon" showed that the most intense were the spectral resonance spectral lines of the copper atom and ion. It was found that a space-uniform overvoltage nanosecond discharge was ignited between copper electrodes at an inter-electrode distance of 2 mm. It was found that the maximum value of the average UV power at p(Ar) = 101 kPa was observed for the UV-A range.

Experimental investigations on optimizing manufacturing parameters for electrospark deposition diamond wire saw

The third generation of superhard semiconductor materials, represented by single-crystal SiC, is used widely in microelectronics due to their excellent physical and mechanical properties. However, their high hardness and brittleness have become bottlenecks in their development. A diamond wire saw (DWS) has become the mainstream tool for sawing hard and brittle crystal materials. However, the diamond abrasive is consolidated on the core wire through resin or electroplated nickel, and the holding strength is not high. When sawing superhard crystal materials, the efficiency is low. To improve the sawing efficiency of superhard crystal materials, it is of great significance to improve the wear resistance of the wire saw and the holding strength of abrasive particles. Electrospark deposition (ESD) can deposit electrode materials on the substrate with low heat input to achieve metallurgical bonding between metal materials. It can effectively improve the gripping strength of the abrasive grains. The sawing ability of the wire saw to make the consolidated DWS by the ESD process. In this paper, ESD equipment was designed according to the characteristics of the ESDDWS process. The discharge gap size and electrode consumption are monitored in real time by a single-chip microcomputer (SCM). Orthogonal experiments were carried out for the two motion modes. The effects of process parameters, such as (A) grain size, (B) abrasive content, (C) pulse duration time, (D) compacting pressure, (E) current, (F) electrode diameter, (G) pulse interval time, (H) reciprocating times, and (I) wire feed speed, on the quality of ESDDWS were analyzed. Through extreme difference analysis (EDA), the optimal parameter combinations of ESDDWS were obtained. In motion mode 1, a combination of grain size W10, abrasive content 1 wt%, pulse duration time 20 μs, compacting pressure 400 MPa, current 19 A, electrode diameter 3 mm, and pulse interval time 2 ms can obtain the optimal value of the number of deposition points and protrusion abrasive particles at the same time. The sequence of manufacturing parameters affecting the two indicators is F > A > G > E > B > D > C. In motion mode 2, the combination of grain size W40, abrasive content 4 wt%, pulse duration time 20 μs, compacting pressure 300 MPa, current 23 A, electrode diameter 3 mm, reciprocating times 1, and wire feed speed 2 mm/step can obtain the optimal value of the number of deposition points and protrusion abrasive particles at the same time. The sequence of manufacturing parameters affecting the two indicators is C > I > F > E > B > H > D > A.

Dynamic development model for long gap discharge streamer-leader system based on fractal theory

Establishing a long air gap discharge model considering the streamer-leader transition and randomness of the discharge path is of great significance to improve the accuracy of discharge characteristic prediction and optimize external insulation design. Based on fractal theory and thermal ionization theory of streamer-leader transition, this work establishes a dynamic development model for the long air gap discharge streamer-leader system, which includes streamer inception, streamer development, leader inception, development of streamer-leader system and final jump. The positive discharge process of a 3 m rod plate is simulated to obtain the fractal distribution of the discharge path and the law of leader development for comparison with the discharge test results. The results show that the simulation model is similar to test results in the development characteristics of leader path distribution, each stage time and leader velocity. Finally, a simulation calculation of a 50% breakdown voltage of the rod-plate gap and ball-plate gap is carried out, with results fairly consistent with test data, proving the effectiveness and practicality of the model.

Initial transient stage of pin-to-pin nanosecond repetitively pulsed discharges in air

In this work, evolution of parameters of nanosecond repetitively pulsed (NRP) discharges in pin-to-pin configuration in air was studied during the transient stage of initial 20 discharge pulses. Gas and plasma parameters in the discharge gap were measured using coherent microwave scattering, optical emission spectroscopy, and laser Rayleigh scattering for NRP discharges at repetition frequencies of 1, 10, and 100 kHz. Memory effects (when perturbations induced by the previous discharge pulse would not decay fully until the subsequent pulse) were detected for the repetition frequencies of 10 and 100 kHz. For 10 kHz NRP discharge, the discharge parameters experienced significant change after the first pulse and continued to substantially fluctuate between subsequent pulses due to rapid evolution of gas density and temperature during the 100 μs inter-pulse time caused by intense redistribution of the flow field in the gap on that time scale. For 100 kHz NRP discharge, the discharge pulse parameters reached a new steady-state at about five pulses after initiation. This new steady-state was associated with well-reproducible parameters between the discharge pulses and substantial reduction in breakdown voltage, discharge pulse energy, and electron number density in comparison to the first discharge pulse. For repetition frequencies 1–100 kHz considered in this work, the memory effects can be likely attributed to the reduction in gas number density and increase in the gas temperature that cannot fully recover to ambient conditions before subsequent discharge pulses.

Electrohydrodynamic and heat transfer characteristics of a planar ionic wind generator with flat electrodes

• Two corona discharges with different polarities are produced simultaneously. • The minimum discharge gap to maintain a stable corona discharge is determined. • The intensity and direction of the generated ionic wind is revealed. • The relationship between the heat transfer enhancement ratio and power consumption is established. In this study, a planar ionic wind generator with two flat electrodes was investigated numerically and experimentally to reveal its electrohydrodynamic and heat transfer characteristics. The multi-physical characteristics, including the discharge process, movement of electrons, positive ions, and negative ions, as well as the formation of ionic wind and its flow characteristics were simulated numerically. It was found that two corona discharges with different polarities were produced simultaneously when a high voltage was applied between the emitting and the ground electrodes. The intensity and direction of ionic wind produced by planar ionic wind generator was revealed. The effects of discharge gap, flat electrode thickness, and discharge polarity on the heat transfer characteristics and power consumption of the planar ionic wind generator were also investigated experimentally. The minimum discharge gap to maintain a stable corona discharge is determined. A better heat dissipation capacity of the planar ionic wind generator can be obtained with a larger electrode gap, and the optimized ionic wind generator can reduce the surface temperature of a 2.05 W powered heat source by more than 46 °C compared with natural cooling. The maximum heat transfer coefficient is 35 W∙m −2 ∙K −1 . This study can provide a theoretical guidance for the application of planar ionic wind generators to highly compact electronic devices.

Experimental Analysis of Cold Plasma With Glow Discharge Mechanism Under a Variety of Input Parameters

Cold plasma with a glow discharge mechanism is a homogeneous and effective mechanism of nonthermal plasma for industrial applications due to the continuous and stable discharge process compared with the filamentary discharge. The discharge mechanism is essentially dependent upon the input parameters of the plasma system, such as the voltage supply, excitation frequency, and the flow rate of the background gas. This article discusses the effects of input parameters on plasma discharge characteristics produced from the plasma jet reactor. The voltage and supply frequency are tuned to match the discharge gap and background gas flow rate in producing the homogeneous glow plasma discharge. The characteristics of the glow plasma discharge produced were analyzed based on the characteristics of the time–domain discharge current and charge-voltage Lissajous figure techniques. Results show that the most efficient and uniform plasma was disclosed by the configuration of input parameters such as 0.5 kV of the applied voltage, 20 kHz of operating frequency, and 0.8 L/min of purified helium gas flow rate. The single pulse of discharge current and parallelogram-like Lissajous figure obtained indicating the homogeneous plasma discharge with a constant value of discharge capacitance.

Schlieren techniques for observations of long positive sparks: Review and application

Understanding the mechanism of positive leader discharge is important in lightning protection engineering and the external insulation design in high voltage power transmission systems. During the propagation of a positive leader, some processes without light-emitting, for example, the insulation recovery process after the breakdown, cannot be observed by optical photography techniques. With the combination of the digital high-speed imaging system, the conventional Schlieren techniques offer new vistas in the long air gap discharge observation. The important features of high spatial resolution, high sensitivity, and easy arrangement make Schlieren techniques powerful and effective tools for characterising the discharge processes without light-emitting. This work presents a brief review of current Schlieren techniques and discusses the design of the Schlieren optics system for long spark observations. Several interesting phenomena discovered at different phases of long sparks with high-speed Schlieren techniques are also presented.

Electrophysical Characteristics of Gas-Discharge Synthesis of Thin Films On The Basis Of a Superion Conductor (Ag2s) In Air

The electrophysical characteristics of an overvoltage nanosecond discharge in air at atmospheric pressure between electrodes made of a superionic conductor, Ag2S, are presented. In the process of microexplosions of inhomogeneities on the working surfaces of electrodes in a strong electric field, vapors of the Ag2S compound and its dissociation products in plasma are introduced into the interelectrode space. This creates the prerequisites for the synthesis of thin structured films that have the properties of superionic conductors and can be deposited on a dielectric substrate placed near the discharge gap. The spatial and electrical characteristics of an overvoltage nanosecond discharge, the Raman scattering spectra of the synthesized films and their surfaces are studied.

Distribution characteristics for initial time delay of streamer of shielding spheres under operating impulse voltage at high altitudes

With continuous promotion of construction of ultra high voltage DC projects in high-altitude areas, it is of important theoretical and practical engineering significance to study long gap discharge characteristics at high altitudes. As the initial and key stage for development of long air gap discharge, the initial stage of streamer reflects the randomness of long gap discharge to a certain extent, and time delay characteristics are important indicators to reflect the randomness. In this paper, we build a photoelectric detection system based on the photomultiplier tube and photoelectric integrated sensor, carry out an operating impulse discharge test of long gap of the shielding sphere-plate with different diameters at altitudes of 50 m and 2200 m respectively, obtain the space field strength, optical power, discharge current and voltage of the whole process of discharge development, and analyze the characteristics of boost time delay and statistical time delay of streamer based on the photoionization model and Weibull Distribution model. According to study results, the average value and dispersibility of initial time delay of streamer increase with the increase of altitude and electrode diameter; the boost time delay t 0 of streamer decreases with increase of altitude and increases with increase of electrode size; the statistical time delay t s of streamer can properly comply with Weibull distribution, and its characteristic parameter has a clear physical meaning. The dispersibility of statistical time delay will increase with altitude and electrode size, and compared with electrode size, altitude has a greater impact on the dispersibility of statistical time delay. The study results of this paper have important guiding value for selection and optimization on clear distance of the valve hall of a converter station in high altitude areas.

A New Wire Electrode for Improving the Machining Characteristics of High-Volume Fraction SiCp/Al Composite in WEDM.

In wire electrical discharge machining, due to the random distribution of the insulating SiC particles, frequent wire rupture, low machining efficiency and surface quality when the common brass wire electrode (BWE) is used to process high-volume content SiCp/Al composite often appears. To address this issue, this paper proposes a new preparation method of zinc coating and surface microstructure on wire electrodes (ZCSMWE). The preparation process of ZCSMWE includes casting, coating, annealing and plastic processing. The experimental results show that, compared with BWE, ZCSMWE can increase material removal rate (MRR) by 16.67%, reduce surface roughness (Ra) by 21.18% and reduce wire rupture under the same discharge parameters. The analysis of workpiece surface topography shows that ZCSMWE can significantly decrease the recast layer and microcrack on the machined surface. The improvement mechanism of ZCSMWE main includes: The low work function zinc can promote the forming of the discharge channel. The vaporization of low boiling temperature zinc can reduce the temperature of the discharge gap and promote the ejecting of workpiece material. In addition, the surface microstructure on ZCSMWE can make the discharge spark more uniformly distributed and increase the proportion of the effective discharge, which contributes to making the discharge crater on the workpiece and wire electrode shallower and more uniform. The surface microstructure on ZCSMWE can also effectively improve the dielectric circulation, which can promote discharge debris to be expelled out and reduce the temperature in the discharge gap. Then, the wire rupture and microcracks on the workpiece surface can be reduced.

Hospital Discharge Summaries Are Insufficient Following ICU Stays: A Qualitative Study.

Semistructured interviews with PCPs conducted between September 2020 and April 2021. Academic health system with central quaternary-care hospital and associated Veterans Affairs medical center. Fourteen attending internal medicine or family medicine physicians working in seven clinics across Southeast Michigan (median, 10.5 yr in practice). We analyzed using a modified Rigorous and Accelerated Data Reduction (RADaR) technique to identify gaps in current discharge summaries for patients with ICU stays, impacts of these gaps, and desired ICU-specific information. We employed RADaR to efficiently consolidate data in Excel Microsoft (Redmond, WA) tables across multiple formats (lists, themes, etc.). PCPs reported receiving limited ICU-specific information in hospital discharge summaries. PCPs often spent significant time reading inpatient records for additional information. Information desired included life-support interventions provided and duration (mechanical ventilation, dialysis, etc.), reasons for treatment decisions (code status changes, medication changes, etc.), and potential complications (delirium, dysphagia, postintensive care syndrome, etc.). Pervasive discharge gaps (ongoing needs, incidental findings, etc.) were described as worse among patients with ICU stays due to more complex illness and required interventions. Insufficient information was felt to lead to incomplete follow-up on critical issues, PCP frustration, and patient harm. PCPs stated that the COVID-19 pandemic exacerbated gaps due to decreased staffing, limited visitation policies, and reliance on telehealth follow-up visits. Our results identified key data elements sought by PCPs about patients' ICU stays and suggest opportunities to improve care through developing tools/templates to provide PCPs with ICU-specific information for outpatient follow-up.

Emission of anomalously hard x-ray radiation by a target upon exposition with an electron beam, ejected by a low-energy vacuum discharge with laser ignition

The characteristics of x-ray radiation of a target that is bombarded by a beam of accelerated electrons ejected by a low-power vacuum discharge with laser ignition are studied. It is shown that the maximum radiation energy exceeds the applied potential difference across the discharge gap by almost an order of magnitude and is inversely proportional to the mass of the cathode material ablated by laser radiation. The energy spectrum of x-ray radiation reconstructed from the radiation attenuation curve by filters-absorbers of various thicknesses showed that in the maximum acceleration mode the average energy of the main part of the spectrum is more than four times higher than the voltage across the discharge gap at the moment of beam emission. Possible mechanisms providing anomalous acceleration of electrons in the discharge are considered.