High Voltage Electrical Discharges Research Articles

Extended plasma channels created by UV laser in air and their application to control electric discharges

Results are presented from a series of experimental and theoretical studies on creating weakly ionized extended plasma channels in atmospheric air by 248-nm UV laser radiation and their application to control long high-voltage discharges. The main mechanisms of air ionization by UV laser pulses with durations from 100 fs to 25 ns and intensities in the ranges of 3×1011–1.5×1013 and 3×106–3×1011 W/cm2, respectively, which are below the threshold for optical gas breakdown, as well as the main relaxation processes in plasma with a density of 109–1017 cm−3, are considered. It is shown that plasma channels in air can be efficiently created by amplitude-modulated UV pulses consisting of a train of subpicosecond pulses producing primary photoelectrons and a long UV pulse suppressing electron attachment and sustaining the density of free electrons in plasma. Different modes of the generation and amplification of trains of subterawatt subpicosecond pulses and amplitude-modulated UV pulses with an energy of several tens of joules were implemented on the GARPUN-MTW hybrid Ti:sapphire-KrF laser facility. The filamentation of such UV laser beams during their propagation in air over distances of up to 100 m and the parameters of the corresponding plasma channels were studied experimentally and theoretically. Laser initiation of high-voltage electric discharges and control of their trajectories by means of amplitude-modulated UV pulses, as well as the spatiotemporal structure of breakdowns in air gaps with length of up to 80 cm, were studied.

Pulsed Electrical Technologies Assisted Polyphenols Extraction from Agricultural Plants and Bioresources: A Review

The application of pulsed electrical technologies such as high voltage electrical discharges (HVED) and pulsed electric fields (PEF) have been currently proposed for promoting biocompounds extraction. Even if their principles of action are different, both of these techniques have shown to be efficient for the enhancement of polyphenols extraction from different raw materials as compared to control extraction. Depending on the product, the energy consumption, the cell disruption, the polyphenols composition, the extraction and purification steps are different when applying PEF or HVED. This paper thus reviews the current status of research on the application of HVED and PEF for extraction and purification of polyphenols from plants.

Dispersion of Particles in the Emulsion by the Electric Current

AbstractPossible mechanisms of metal micropowders grinding during high-voltage electric discharge processing in hydrocarbon liquid are considered in the present paper. Conditions for melting of Fe and Ti powder particles in plasma discharge channel and in microplasma channels between particles are found out. Regularities of nanopores movement and electromagnetic particle compression are evaluated. It is shown that the current density in the discharge channel is an important parameter, allowing the assessment of the efficiency of the electrodischarge dispersion of metal particles.

Properties of UN Sintered by High Voltage Electric Discharge Consolidation

In the present work, the opportunity of the consolidation of uranium nitride tablets by high voltage electric discharge consolidation (HVEDC) is considered. It is shown that the consolidation by HVEDC allows the prevention of the expansion of uranium nitride powders and renders pellets with relative density of up to 97%. The thermal stability of the obtained samples has been investigated. The analysis of the microstructure of the processed samples indicates the retention of the initial powder structure

Treatment of azo dye (Acid Orange ii) wastewater by pulsed high-voltage hybrid gas–liquid discharge

Pulsed high-voltage electrical discharge was used in treating azo dye (Acid Orange ii, AO7) wastewater.

High Voltage Electrical Discharges, Pulsed Electric Field, and Ultrasound Assisted Extraction of Protein and Phenolic Compounds from Olive Kernel

The study was aimed at improvement of recovery of intracellular valuable compounds from olive kernels (Olea europaea). High voltage electrical discharges (HVED), pulsed electric field (PEF), and ultrasound (US) were applied as pretreatments before extraction. The influence of HVED energy input (0–109 kJ/kg), pH (2.5–12), and ethanol (0–50 %) on the efficiency of the extraction was studied. The extracts obtained immediately after pretreatments were analyzed for total phenolic compounds, antioxidant activity, proteins, and pigments. HVED treatment was demonstrated to be more effective than ultrasound and pulsed electric field in terms of energy input and effective treatment time to extract phenolic compounds and proteins. Moreover, the application of HVED increased significantly the aqueous and hydro-ethanolic extractions of total phenolic content (TPC), and proteins of the recovered extracts when energy input was augmented. pH and ethanol percentage had also a significant influence in TPC, protein, and antioxidant recovery. The interesting observation is that pH 2.5 resulted in the optimum conditions to recover TPC and antioxidant capacity. However, the higher protein content was found when pH 12 was used. Multiple response optimization showed that TPC, content of proteins, and antioxidant capacity (Trolox equivalent antioxidant capacity (TEAC) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) values) of the sample were further maximized after HVED pretreatment at energy input 66 kJ/kg at pH 2.5 followed by extraction in 49 % ethanol. TPC, content of proteins, TEAC, and DPPH values under such conditions of extraction were 626.6 mg GAE/L, 0.225 mg/mL, 9.80 mM TE, and 7.61 mM TE, respectively.

Application of pulsed electric fields and high voltage electrical discharges for oil extraction from sesame seeds

Sesame is a widely cultivated oilseed and its oil presents high nutritional quality and economic value. The objective of this work was to evaluate two different electrical technologies: pulsed electric fields (PEF) and high voltage electrical discharges (HVED), as pre-treatments to oil extraction. These treatments were performed with the objective of damaging the seed cells prior to pressing for oil expression and were compared to a control sample and to grinding. Electrical treatments were carried out with different input energies varying between 40 and 240kJ/kg. Evaluation of each treatment efficiency was performed through the analysis of the disintegration index of the seeds, oil yield, deformation curves and oil quality among others. The disintegration index increased with the energy input and it was higher for seeds treated by HVED. PEF treatment increased the oil yield by 4.9% and HVED, if accounted oil losses in water, resulted in the extraction of 22.4% more oil when samples are compared to control. The grinded sample presented higher oil yield than PEF and lower than HVED. The deformation curves were very similar for all samples, except for the grinded seed, which reached higher deformation values during pressing. Results of the HPLC analysis show that the oil lignan profile was the same for all analyzed treatments. Moreover, there were low protein and polyphenols losses during treatment and, therefore, a cake rich in these compounds is obtained as a by-product of the proposed process.

Wave mode high voltage consolidation of powder materials

The densification of electrically conductive powders by high voltage consolidation is studied. High voltage consolidation method (HVC) includes the simultaneous exposure of a powder sample to mechanical pressure (50–500MPa) and to a short (less than 300ms) high voltage (above 1kV) electric discharge with the pulse current amplitude of a few hundred kA/cm2. The densification kinetics of industrial iron powder is analyzed by ultra-rapid video-recording. The integral temperature of the sample has a maximum value at the beginning of the densification process. The compaction process lasts less than 16ms for all the values of the parameters studied. The shortness of the densification process in comparison with the cooling of the sample provides a constant temperature throughout the entire compaction process. Based on the analysis of the obtained experimental results a mathematical model of high rate wave mode compaction of a powder material under conditions of HVC is formulated. The constitutive equation of the mechanical behavior of the consolidated material accounts for the plastic flow of powder particles and for the collapse of the inter-particle pores. The numerical simulation results reveal optimal values of the dimensionless parameters controlling the HVC process.

Evaluating the potential of cell disruption technologies for green selective extraction of antioxidant compounds from Stevia rebaudiana Bertoni leaves

An increased interest has been shown by both food technologists and food industry regarding Stevia rebaudiana Bertoni leaves (Stevia) for their high content of bioactive components (phenolic compounds, vitamin C, carotenoids). The aim of this work was to study the effect of emerging technologies such as high voltage electrical discharges (HVED) and pulsed electric fields (PEF) and ultrasounds (US) on the intensification of the extraction of valuable compounds from Stevia leaves. The proposed processes combined pretreatment (HVED, PEF and US) and extraction of intracellular compounds using water as solvent at ambient temperature. The energy inputs of the treatments varied from 24 to 141kJ/kg and the results were compared to control diffusion experiments. Chlorophyll a, and b, total carotenoid, total phenolic compounds and antioxidant capacity (DPPH) were determined. A significant increase in soluble matter and antioxidant compounds was found after HVED, PEF and US-assisted extraction as compared to control samples. Results showed that HVED, PEF and US treatments improved both kinetics and extraction yield of soluble matter. These results show the ability of HVED to be used as a potential technology to enhance protein recovery using water and avoiding the use of other solvents and grinding. Chlorophyll content was significantly higher (3-fold increase) after HVED assisted extraction at 141kJ/kg in comparison to control sample (0.352 and 0.355mg/L for chlorophyll a and b, respectively). The same energy input for HVED permitted attain highest extraction diffusivities of total soluble matter (D=3.06×10−09m2/s), followed by total phenolic compounds (D=2.60×10−10m2/s) and then proteins (D=6.00×10−11m2/s).

New Approaches for the Use of Non-conventional Cell Disruption Technologies to Extract Potential Food Additives and Nutraceuticals from Microalgae

In recent decades, microalgae species have focused the attention of several research groups and food industry as they are a great source of nutritionally valuable compounds. The use of environmentally friendly technologies has led to researchers and food industry to develop new alternative processes that can extract nutritionally valuable compounds from different sources, including microalgae. This note describes the potential use of some non-conventional methods including sub- and supercritical fluid extraction, pulsed electric fields, high-voltage electric discharges, high-pressure homogenization, ultrasound- and microwave-assisted extraction, which involve cell disruption to recover nutritionally valuable compounds from microalgae and can help to comply with criteria of green chemistry concepts and sustainability.

Impact of pulsed electric fields and high voltage electrical discharges on extraction of high-added value compounds from papaya peels

Extraction of the nutritionally valuable and antioxidant compounds from papaya peels using conventional aqueous extraction (E) (at 20°C, 50°C, and 60°C) and extraction assisted by pulsed electric field (PEF) or by high voltage electrical discharges (HVED) was studied. Increase of extraction temperature or extraction in basic media (pH=11) not always resulted in an increase of the yields or TEAC values. E.g., the concentration of proteins and TEAC values at pH=7 and pH=11 were noticeably smaller at 60°C as compared to those measured at 50°C. HVED-assisted technique showed a higher extraction efficiency of high-added value compounds compared to PEF-assisted extraction. E.g., the concentrations of proteins obtained for the HVED- or PEF-assisted extractions were 60mg/L and 20mg/L, respectively (pH=7 at 20°C and time of extraction of≈3/4h). The better efficiency of HVED-assisted extraction can reflect turbulation of suspension and fragmentation of pills provoked by electrical discharges. However, electrical discharges may produce chemical products of electrolysis and free reactive radicals, which can reduce the nutritional quality of high-added value compounds. Application of the two-stage method (PEF+supplementary aqueous extraction at 50°C) allowed a significant enhancement of the yields and antioxidant capacities of the extracted components from papaya peels even at neutral pH.

Ignition and flameholding in a supersonic combustor by an electrical discharge combined with a fuel injector

The paper presents the results of an experimental study of supersonic combustor operation enhanced by an electrical discharge. A novel scheme of plasma assisted ignition and flameholding is demonstrated, which combines a wall fuel injector and a high-voltage electric discharge into a single module. The experimental combustor with the cross section of 72mm (width)×60mm (height) and length of 600mm operates at a Mach number of M=2, initial stagnation temperature of airflow of T0=290–300K, and stagnation pressure of P0=1.3–2.0Bar. The combustor is equipped with four plasma ignition modules, flush-mounted side-by-side on the plane wall of the combustion chamber. The combustion tests were performed using ethylene injection with a total mass flow rate of GC2H4<10g/s and discharge power in the range of Wpl=3–24kW. The scope of the experiments includes characterization of the discharge interacting with the main flow and fuel injection jet, parametric study of ignition and flame front dynamics, and comparison of the present scheme to previously tested configuration. The present approach demonstrates a significant advantage in terms of flameholding limits. An operation mode with strong combustion oscillations was observed at high fuel injection flow rates. Methods of flame front stabilization based on plasma application are discussed. The technique studied in the present work has significant potential for high-speed combustion applications, including cold start/restart of scramjet engines and support of transition regime in dual-mode and off-design operation.

A comparative study of physical pretreatments for the extraction of polyphenols and proteins from vine shoots

This work examined the potential of valorization of vine shoots through their polyphenol and protein contents. However the choice of the experimental conditions targeted polyphenol extraction at the expense of proteins for further simplification of the purification process. The intensification of polyphenol and protein extraction by physical treatments (pulsed electric fields (PEF), high-voltage electrical discharges (HVED) and ultrasound (US)) was studied. A significant enhancement of polyphenol extraction was noticed with HVED, PEF and US. However, and for each treatment, the improvement of the extraction process started beyond a specific energetic threshold (HVED (10kJ/kg), PEF (50kJ/kg) and US (1010kJ/kg)). HVED had the highest polyphenol and protein extraction yields with the lowest energetic prerequisite. Extracts of high polyphenol yield (34.5mg of gallic acid equivalent (GAE) per g of dry matter (DM)) and high purity (89%) were obtained with HVED. Polyphenol and protein diffusion coefficients (m2/s) demonstrated HVED to better enhance the extraction process of those biomolecules. Similarly, the calculation of the electrical conductivity disintegration index, Z, showed the highest tissue damage for HVED and a rising cellular damage with the increased energetic requirement of each treatment.

Structure of Zirconium Alloy Powder Coatings Processed by High Voltage Electric Discharge Consolidation

Zirconium alloy powders (Zr + 1% Nb) of spherical and flake forms have been consolidated by high voltage electric discharge processing. The consolidation enabled the fabrication of coatings on ceramic and metallic substrates as well as of freestanding powder components. The experimental dependence of the electric conductivity of the powders of spherical shape and flake shape on the applied pressure has been investigated. The influence of the current pulse amplitude on the final density of the consolidated zirconium powder alloy coatings on ceramic and metallic substrates and of the produced free‐standing powder samples has been analyzed for different applied pressures. The maximum amplitude of the electric current density above, which the consolidation process is unstable and has a nature of blowout has been determined. The conducted metallographic analysis showed the preservation of the microstructure of initial powder particles after the process of high voltage electric discharge consolidation.

Gasdynamic instabilities during decay of the submicrosecond spark discharge channel

This work is devoted to studying the dynamics of breakdowns of submicrosecond high-voltage electric discharge and discharge-accompanying hydrodynamic phenomena and to analyzing the possibility of its application for acceleration of the component mixing in solving high-speed combustion problem. This work presents the results of experimental and numerical studies of the development of gasdynamic disturbances during the afterspark channel decay. The main parameters of the discharge are as follows: the typical length is 50–60 mm, the breakdown voltage is up to 120 kV, the duration time is 80–100 ns, the energy is up to 2 J, and the order of magnitude of the instantaneous power is 100 MW. For the first time, jet-type instabilities have been studied in detail and described. It is shown that the development of large-scale instabilities is tightly related to the discharge channel geometry. The mechanism of the breakdown development and the related possibility of controlling the discharge channel shape are discussed.

Conducting Miller-Urey Experiments

In 1953, Stanley Miller reported the production of biomolecules from simple gaseous starting materials, using an apparatus constructed to simulate the primordial Earth's atmosphere-ocean system. Miller introduced 200 ml of water, 100 mmHg of H2, 200 mmHg of CH4, and 200 mmHg of NH3 into the apparatus, then subjected this mixture, under reflux, to an electric discharge for a week, while the water was simultaneously heated. The purpose of this manuscript is to provide the reader with a general experimental protocol that can be used to conduct a Miller-Urey type spark discharge experiment, using a simplified 3 L reaction flask. Since the experiment involves exposing inflammable gases to a high voltage electric discharge, it is worth highlighting important steps that reduce the risk of explosion. The general procedures described in this work can be extrapolated to design and conduct a wide variety of electric discharge experiments simulating primitive planetary environments.

Conducting Miller-Urey Experiments

In 1953, Stanley Miller reported the production of biomolecules from simple gaseous starting materials, using an apparatus constructed to simulate the primordial Earth's atmosphere-ocean system. Miller introduced 200 ml of water, 100 mmHg of H2, 200 mmHg of CH4, and 200 mmHg of NH3 into the apparatus, then subjected this mixture, under reflux, to an electric discharge for a week, while the water was simultaneously heated. The purpose of this manuscript is to provide the reader with a general experimental protocol that can be used to conduct a Miller-Urey type spark discharge experiment, using a simplified 3 L reaction flask. Since the experiment involves exposing inflammable gases to a high voltage electric discharge, it is worth highlighting important steps that reduce the risk of explosion. The general procedures described in this work can be extrapolated to design and conduct a wide variety of electric discharge experiments simulating primitive planetary environments.

Extraction of valuable biocompounds assisted by high voltage electrical discharges: A review

Abstract The application of strong electric fields in gases, water and organic liquids has been studied for several years, because of its importance in electrical transmission processes and its practical applications in biology, chemistry, and electrochemistry. More recently, electrical discharges have been investigated and are being developed in water for enhancing the extraction of biocompounds from different raw materials. This paper reviews the current status of research on the application of high voltage electrical discharges for promoting cell disruption in aqueous suspension of biological materials, with particular emphasis on application to biocompounds extraction.

Selective extraction from microalgae Nannochloropsis sp. using different methods of cell disruption

This work studies the extraction of intracellular components from microalgae Nannochloropsis sp. with application of different cell disruption techniques, including pulsed electric field (PEF) (20kV/cm, 1-4ms, 13.3-53.1kJ/kg), high voltage electrical discharge (HVED) (40kV/cm, 1-4ms, 13.3-53.1kJ/kg), ultrasonication (USN) (200W, 1-8min, 12-96kJ/kg), and high pressure homogenization (HPH) (150MPa, 1-10 passes, 150-1500kJ/kg). The data evidence that electrically based disruption techniques (PEF and HVED) allowed selective extraction of water soluble ionic components and microelements, small molecular weight organic compounds and water soluble proteins. Microscopic and sedimentation stability analyses have shown that microalgae cells in HVED-treated suspension were noticeably agglomerated and could be easily settled in centrifuge. The electrically based disruption techniques were ineffective for delivery of pigments (e.g., chlorophylls or carotenoids) and their extraction required subsequent application of more potent disruption techniques. The obtained data have shown that HPH disruption technique was the most effective; however, this mode required the highest power consumption.

Oxidation of S(IV) in Seawater by Pulsed High Voltage Discharge Plasma with TiO2/Ti Electrode as Catalyst

Oxidation of S(IV) to S(VI) in the effluent of a flue gas desulfurization(FGD) system is very critical for industrial applications of seawater FGD. This paper reports a pulsed corona discharge oxidation process combined with a TiO2 photocatalyst to convert S(IV) to S(VI) in artificial seawater. Experimental results show that the oxidation of S(IV) in artificial seawater is enhanced in the pulsed discharge plasma process through the application of TiO2 coating electrodes. The oxidation rate of S(IV) using Ti metal as a ground electrode is about 2.0×10−4 mol · L−1 · min−1, the oxidation rate using TiO2/Ti electrode prepared by annealing at 500°C in air is 4.5×10−4 mol · L−1 · min−1, an increase with a factor 2.25. The annealing temperature for preparing TiO2/Ti electrode has a strong effect on the oxidation of S(IV) in artificial seawater. The results of in-situ emission spectroscopic analysis show that chemically active species (i.e. hydroxyl radicals and oxygen radicals) are produced in the pulsed discharge plasma process. Compared with the traditional air oxidation process and the sole plasma-induced oxidation process, the combined application of TiO2 photocatalysts and a pulsed high-voltage electrical discharge process is useful in enhancing the energy and conversion efficiency of S(IV) for the seawater FGD system.