High Voltage Electrical Discharges Research Articles

Effect of High-Voltage Electrical Discharge Treatment of Diamond Powders on Their Mechanical Characteristics

The effect of pulsed high-voltage electrical discharge (HVED) treatment on the morphometrical, structural adsorption, and mechanical properties of diamond micropowders and abrasive powders is examined. These properties largely determine the performance and wear resistance of abrasive tools for machining process. It is shown that pulsed HVED treatment is efficient in the production of diamond micropowders and abrasive powders with low impurity content and high abrasive ability.

Dispersion and Carburization of Titanium Powders by Electric Discharge

The effect of high-voltage electrical discharge in a titanium powder suspension in a hydrocarbon liquid on the dispersion and formation of titanium carbide is studied. The dependence of the resulting fine titanium carbide on the current density in the discharge channel is experimentally determined. The average diameter of powder particles after treatment with specific energy W sp = 1.3 MJ/dm3 at various current densities in the discharge channel reduces from a starting size of ~1000 to <1 μm. The increase of current density in the channel from 0.08 to 0.56 kA/mm2 (at specific energy W sp = 1.3 MJ/dm3) leads to an increase in the yield of titanium carbide from 32 up to 57 %.

Effect of high voltage electrical discharges, heating and ethanol concentration on the extraction of total polyphenols and lignans from flaxseed cake

The aim of this work was to study the effects of high voltage electrical discharges (HVED), mild temperature (20–60°C) and ethanol addition in water (0–25%) on the extraction of total polyphenols and lignans from whole and crushed flaxseed cake. HVED noticeably enhanced the aqueous and hydro-ethanolic extractions of total polyphenols from both crushed and non crushed flaxseed cake. The addition of ethanol had a synergic effect and increased the extraction efficiency. For the uncrushed cakes, the diffusivity of total polyphenols from the untreated samples was in the range of 1.1–1.8×10−9m2/s (without ethanol) and 3.2–5.9×10−10m2/s (with ethanol). The diffusivity of polyphenols from the HVED-treated samples was higher: 2.6–2.7×10−9m2/s (without ethanol) and 3.0–4.2×10−9m2/s (with ethanol). However, the results obtained for lignan extraction were lower than those found in the literature (around 20mg SDG/g defatted flaxseed).

Experimental Study on Food Seasoning Treatment by High Voltage Electrical Discharge with Shock Wave Food Processor

In recent years, a method of food processing using underwater shock wave has been investigated. The underwater shock wave is generated by high voltage and large current gap discharge in water, and it is used for food processing in the present investigation. When the underwater shock wave is loaded on the food, the food cells are momentarily broken. Therefore, the food becomes soft, and possible to squeeze water easily. Also, seasonings can be penetrated inside of the food. The improvement of absorbing seasonings for the shock processed foods mainly on Japanese radish is reported in this paper.

Experimental Study of the Underwater Shock Wave on the High-Voltage Electric Discharge by Carbon Fiber

Carbon fiber is employed to induce underwater shock wave by the high-voltage electric discharge. By the release of an energy 10 kJ stored in a high-capacity condenser bank, carbon fiber was exploded showing the evidence inducing underwater shock wave effectively to a thin plate to be formed.

Ear damage by high voltage electrification in a mexican worker

Introduction: Altered hearing has been reported in persons who received electrical discharge by lightning. Case report: The case of a Mexican worker electrified by a high voltage (23 kV) electrical current is described as having hearing loss, absent otoacoustic emissions, and increased latency of all waves and interwave intervals of auditory evoked potentials of the brainstem. The worker showed permanent hearing loss post high voltage electrocution (23 kV), with progressive sensorineural hearing loss and perturbed neural conduction of the auditory nerve, and disturbed neuroconduction of the auditory nerve following to a high voltage electrical discharge. Conclusion: Given the implications in rehabilitation and the social and legal consequences patients should be fully evaluated, including a complete hearing study.

The peculiarities of spectral manifestations of high-voltage electric discharge in different phase states of ion systems

The effects of high-voltage pulsed discharge (HVPD activation) on vibrational spectra of ion salt systems have been studied. The peculiarities of spectral display of HVPD in ion melts and aqueous solutions of electrolytes, in ion-conducting phases of crystalline and glassy salt systems have been investigated.After HVPD a salt system is in non-equilibrium activated state. In the activated state of a salt system, the relaxation time of the vibrational excited states of molecular ions is shorter than in the equilibrium state if the vibrational relaxation rate increases with temperature in the system. For those systems for which the relaxation rate decreases at elevated temperatures, the relaxation time of the vibrational excited states of molecular ions is longer than in the equilibrium state.HVPD activation of a salt system can change the configuration of the electron shell of molecular ions. Therefore, the lifetime values of activated state of salt systems are abnormally large.

Initiation of detonation by a high-voltage discharge in powdered explosives with nanosize inert admixtures

It is shown that admixtures of a copper nanopowder in a high-disperse low-sensitivity explosive of the FOX-7 type sharply increase the sensitivity of the mixture to the action of a high-voltage electric discharge and facilitate detonation. The percolation model of propagation of the electric breakdown over a powdered mixture with nanosize admixtures and the model of initiation of detonation by a high-voltage discharge in the mixture of a brisant explosive with an inert admixture are developed. These models are in qualitative and quantitative agreement with experimental data.

Production of extended plasma channels in atmospheric air by amplitude-modulated UV radiation of GARPUN-MTW Ti : sapphire – KrF laser. Part 2. Accumulation of plasma electrons and electric discharge control

The problem of the production of extended () plasma channels is studied in atmospheric air by amplitude-modulated laser pulses of UV radiation, which are a superposition of a subpicosecond USP train amplified in a regenerative KrF amplifier with an unstable confocal resonator and a quasi-stationary lasing pulse. The USPs possess a high () peak power and efficiently ionise oxygen molecules due to multiphoton ionisation, and the quasi-stationary lasing pulse, which has a relatively long duration (), maintains the electron density at a level by suppressing electron attachment to oxygen. Experiments in laser triggering of high-voltage electric discharges suggest that the use of combined pulses results in a significant lowering of the breakdown threshold and enables controlling the discharge trajectory with a higher efficiency in comparison with smooth pulses. It was shown that controlled breakdowns may develop with a delay of tens of microseconds relative to the laser pulse, which is many orders of magnitude greater than the lifetime of free electrons in the laser-induced plasma. We propose a mechanism for this breakdown, which involves speeding-up of the avalanche ionisation of the air by negative molecular oxygen ions with a low electron binding energy () and a long lifetime (), which are produced upon cessation of the laser pulse.

Variation in the particle size of FE–TI–B4C powders induced by high-voltage electrical discharge

The effect of high-voltage electrical discharge (ED) on the particle size of Fe–Ti–B4C powders in a hydrocarbon liquid is studied. It is shown that high-voltage ED allows significant refinement of the powders. The important factors are integral processing energy and pressure in the discharge channel. A relationship between the integral processing energy and decrease in the average diameter of micropowder particles is found. It is shown that the average particle size monotonically decreases up to a certain value of integral processing energy. The use of high-voltage ED for the refinement of micropowders permits significant reduction in time and energy needed to reach the desired particle size compared with other methods.

Scale-up of high voltage electrical discharges for polyphenols extraction from grape pomace: Effect of the dynamic shock waves

Abstract This work aims at producing high dynamic shock waves by high voltage electrical discharges (HVED) in a water suspension in order to increase polyphenols extraction from grape pomace. Experiments at the laboratory (1 L) and pilot (35 L) scales were compared. The total specific energy input was varied up to 800 kJ/kg. The intensification of the extraction of total polyphenols was increased 7 times from grape pomace, seeds, skins and stems treated by HVED at both laboratory and pilot scales. However, higher treatment energies are required at the pilot scale to obtain equivalent polyphenols rates. The pressure of the shock wave generated during HVED was measured. When applying the same specific energy input per pulse ( E Bm = 0.53 kJ/kg) at both scales, the entire volume of both treatment chambers is treated by shock waves of similar pressures values (≥ 100 bars). Below this pressure value, the shock waves seem to have no effect on the polyphenols extraction. Industrial relevance: This paper presents relevant information for the design of generating electrical discharges treatment. The study also addresses a specific case of use of by-products and shows the effectiveness of such technology at the laboratory and pilot scale.

Influence of metal nanopowders on the sensitivity of explosives to a high-voltage electric discharge. A fractal-percolation approach

The initiation of detonation in pressed finely dispersed explosives by a high-voltage electric discharge is studied. It is shown that this type of initiation can be greatly simplified by adding to the explosive metal (conductive) additives with a high specific heat capacity and thermal conductivity. It is established that the parameters of the initiating electric discharge depend on the fractal structure of the nanocrystalline explosive.

Carbon microflowers

Micro- or nanoflowers are self-organized, planar or 3D microstructures similar to macroscopic flowers. The interest in microflowers has increased in recent years because of many potential applications of microflowers, due to their high specific surface area. The analysis of the morphology of carbon flower-like microstructures produced in low-current plasma, generated by high voltage electrical discharge in a mixture of cyclohexane with argon as the carrier gas has been presented in the paper. It was shown that various carbon microstructures, including microfibers and microflowers of different pattern, can be synthesized on the electrodes by the same plasma method, at various process parameters.

Thermal processes during high-voltage electric discharge consolidation of powder materials

The results of a simulation of the thermal processes occurring within interparticle contacts of powder materials under high-voltage electric discharge consolidation are presented. The thermal processes in the contacts between powder particles are characterized by significant spatial inhomogeneity and time dependence. The determination of the behavior of the interparticle contact zones enables optimization of the pulse electrical current parameters. A good correlation between the modeling and experimental data for compacted iron and heat-resistant steel powders is demonstrated.

Application of electrical treatments in alcoholic solvent for polyphenols extraction from grape seeds

The polyphenols extraction from grape seeds was studied. In order to increase the polyphenols yield and the extraction kinetics, three different pre-treatments were applied on grape seeds: pulsed electric fields (PEF) (8–20 kV/cm, 0–20 ms), high-voltage electrical discharges (HVED) (10 kA/40 kV, 1 ms) and grinding (180 W, 40 s). These electrical treatments can damage cell membranes (PEF/HVED) and cell walls (HVED) thus accelerating the compounds extraction but have different effects on the product fragmentation. The diffusion was then performed after pre-treatment with a mixture of water and ethanol. The PEF efficiency was improved when the treatment was performed at 50 °C in the presence of ethanol. PEF-assisted diffusion was then compared to HVED-assisted diffusion and to diffusion of ground grape seeds. These two pre-treatments increased both the extraction kinetics and the maximum polyphenols yield. For both cases, the final polyphenols content was 9 g GAE/100 g DM after 15 min of extraction with grinding and after 60 min with HVED. When PEF were applied in a suspension containing ethanol, the maximum polyphenols yield was also reached after 60 min. The subsequent solid–liquid separation was faster with PEF as compared to ground and HVED-treatments.

Space observations of comets during solar flares: A possible explanation for comet brightness outbursts

Problems connected with mechanisms for comet brightness outbursts as well as for gamma-ray bursts remain open. Meantime, calculations show that irradiation of a certain class of comet nuclei, having high specific electric resistance, by intense fluxes of energetic protons and positively charged ions with kinetic energies more than 1 MeV/nucleon, ejected from the Sun during strong solar flares, can produce a macroscopic high-voltage electric double layer with positive charge in the subsurface zone of the nucleus, during irradiation times of the order of 10–100 h at heliocentric distances around 1–10 AU. The maximum electric energy accumulated in such layer will be restricted by the electric discharge potential of the layer material. For comet nuclei with typical radii of the order of 1–10 km the accumulated energy of such natural electric capacitor is comparable to the energy of large comet outbursts that are estimated on the basis of ground based optical observations. The impulse gamma and X-ray radiation together with optical burst from the comet nucleus during solar flares, anticipated due to high-voltage electric discharge, may serve as an indicator of realization of the processes above considered. Multi-wavelength observations of comets and pseudo-asteroids of cometary origin, having brightness correlation with solar activity, using ground based optical telescopes as well as space gamma and X-ray observatories, during strong solar flares, are very interesting for the physics of comets as well as for high energy astrophysics.

Impact of Electric Pulse Treatment on Selective Extraction of Intracellular Compounds from Saccharomyces cerevisiae Yeasts

Treatments by high-voltage electrical discharges (HVED, needle-plate electrode geometry, U = 40 kV, tp ≈ 0.5 μs) and pulsed electric field (PEF, plate–plate electrode geometry, E = 5–40 kV/cm, tp ≈ 8.3 μs) were evaluated as tools for selective extraction of different intracellular components from the wine Saccharomyces cerevisiae (bayanus) yeasts in a 0.5% (w/w) aqueous suspension. The pulses in the form of damped oscillations and exponential decay were applied in HVED and PEF modes of treatment, respectively. The extraction efficiency results obtained using HVED and PEF techniques were compared with those for high-pressure homogenization technique. The HVED and PEF treatments always resulted in incomplete damage of yeast cells, though efficiency of HVED was higher than that of PEF. The high selectivity of extraction of ionic substances, proteins, and nucleic acids was demonstrated; e.g., electric pulse treatments at E = 40 kV/cm and N = 500 allowed extraction of ≈80% and ≈70% of ionic substances, ≈4% and ≈1% of proteins and ≈30% and ≈16% of nucleic acids in cases of HVED and PEF modes, respectively.

Intensification of polyphenols extraction from grape seeds by high voltage electrical discharges and extract concentration by dead-end ultrafiltration

Grape seed is a rich source of polyphenols. In this study, the high voltage electrical discharges (HVED) were used as alternative method for polyphenols extraction from grape seeds. The extraction efficiency was evaluated by conductivity disintegration index Z and polyphenols concentration in extracts. It was shown that HVED treatment permits effective extraction of polyphenols from grape seeds. The maximal concentration of extracted polyphenols reached 8.3 g GAE/100 w db after 300 discharges. The extraction of polyphenols was satisfactorily described by the Peleg’s model ( R 2 > 0.995). Extracts obtained with HVED were then concentrated using membranes with different molecular weight cut off (0.15 μm, 150 and 50 kDa). The dead-end filtration of obtained extracts followed the cake filtration mechanism with membranes UP150 (150 kDa) and UV050 (50 kDa), and the combined mechanism (standard pore blocking/cake filtration) with FSM0, 15PP membrane (0.15 μm). The polyphenols content and physico-chemical properties of the permeates and retentates were evaluated. The polyphenols rejection of 87% and 91% were achieved with UP150 and UV050 membranes, respectively.

Control of extended high-voltage electric discharges in atmospheric air by UV KrF-laser radiation

Experiments in the commutation of extended (∼1-m long) high-voltage (up to 390 kV) electric discharges were carried out with the aid of 100-ns long UV pulses of the GARPUN KrF laser, in which we demonstrated a one-and-a-half-fold lengthening of the discharge gap broken down in the presence of laser illumination. Total control of discharge trajectory along the direction of the laser beam was observed for a radiation energy of ∼300 mJ (the corresponding intensity I = 5×108 W cm-2 and its attendant initial electron density Ne ∼ 1011 cm-3) and partial control for an energy of 40 mJ (I = 7×107 W cm-2, Ne ∼ 8×109 cm-3) with a 100% probability of breakdown. We discuss the advantages of employing a UV laser for active lightning protection in comparison with IR lasers and ultrashort-pulse laser systems.

Valorisation of grape pomace by the extraction of phenolic antioxidants: Application of high voltage electrical discharges

The aim of this study was to optimise the electrically assisted extraction in order to obtain grape pomace extracts with high polyphenols content, which would be potentially interesting for applications as natural antioxidants. High voltage electrical discharges (HVED) were applied for intensification of the extraction. The effects of the energy input, the electrodes distance gap and the liquid-to-solid ratio were studied. Diffusion was then carried out in different mixtures of water and ethanol for one hour at 20, 30, 40 and 60°C. The most efficient extraction was (i) an HVED pre-treatment at 80kJ/kg with an electrodes distance of 5mm in a liquid-to-solid ratio of 5 followed by (ii) a diffusion with 30% ethanol in water at 60°C for 30min. The highest total polyphenols content reached 2.8±0.4gGAE/100gDM with a corresponding antioxidant activity of 66.8±3.1gTEAC/kgDM. The polyphenols extraction rate increased with temperature in accordance to an Arrhenius type of relationship: activation energy of 21.5±1.1kJ/mol for HVED treated systems against 0.5±0.2kJ/mol for untreated ones.