Pulsed Discharge In Water Research Articles

Electron transport characteristics in water under electrostrictive effect

The transport characteristics of electrons are crucial for the initiation and development of pulse discharge in water. In this work, we develop a physical model of electron transport that consides elastic and inelastic collision cross sections. The purpose of this study is to investigate frequency variations of elastic collisions, ionization and excitation collisions with different initial electron energy values, and to explore the characteristic of electron energy loss in water. The Monte Carlo method is employed to track structure characteristics of electron transmission and scattering under varying energy values. The results show that the electrons of lower energy (~20 eV) are significantly impacted by the water molecule scattering, hence their transmission capacities are weakened. When the incident energy of electron reaches 100 eV, the scattering deviation distance is roughly equivalent to the transmission depth, about 6–8 nm, and the maximum deviation angle <i>θ</i><sub>shift</sub> ~ 60°. When the electron incident energy is in a range of 10–1000 eV, the number of elastic collisions is much greater than the number of excitation and ionization collisions, and the number of ionization collisions and excitation collisions increases significantly with the increase of electron energy. The higher the electron incident energy, the greater the energy loss is. However, the energy loss decreases sharply with the extension of penetration distance. For the ionization collision, the average ionization energy loss, <i>W</i>, decreases rapidly with the increase of electron energy, and ultimately maintains at a level of 20–30 eV, which is consistent with the experimental results reported.

An improved resistance model of positive subsonic plasma channels in water

The subsonic plasma channel and water can be regarded as series resistors in the pre-breakdown stage of sub-millisecond pulsed discharge in conductive water. An improved resistance model of the positive subsonic plasma channel is proposed. The gap resistance and the morphology of the bubble cluster and the plasma channel inside it are obtained from the electrical measurement and optical observation, respectively. The resistance of the plasma channel in the strong-ionization stage is calculated using the small-current arc resistance model. The improved model of the water resistance is established by analyzing the relationship between its equivalent cross-sectional area and its length in an uneven electric field. The resistance of the plasma channel in the weak-ionization stage is calculated. The resistance, voltage, and energy in the gap are analyzed based on the improved resistance model. The plasma channel's resistance is far less than the water resistance. The low voltage drop in the plasma channel leads to a high electric potential in the plasma channel's head, which is conducive to the plasma channel's development. 97% of the total energy in the pre-breakdown stage is consumed by the water resistor. The improved resistance model is helpful to supplement the development mechanism of the sub-millisecond pulsed discharge in water.

Identification of Pulse Discharge Parameters in Water for Reservoir Resonance Transform Device

The reservoir resonance transform device is applied to unconventional shale gas stimulation. To achieve the purpose of resonance stimulation, the discharge frequency is dynamically corresponding to the natural frequency of the reservoir. However, the discharge parameters under the same conditions differ in the resonance process. It is hard to analyze the real-time change of reservoir frequency precisely. Therefore, the identification of pulse discharge parameters in water is extremely important. In this paper, an equivalent circuit model of pulse discharge in water is established to analyze the time-varying resistance. The Kalman filter makes the discrete resistance data continuous and reduces the interference caused by the random discharge. Meanwhile, the data error analysis is carried out. The results show that the variance of pulse discharge resistance in water based on the Kalman filter is less than 0.528 compared with the experiment value, so the identified resistance obtained by this method can be used in the study of resonant discharge in the same frequency.

Delay Correction for Pre-Breakdown Phase of Subsonic Stream Discharge in Water

Shock waves generated by streamer discharge in water have huge application value to improve unconventional reservoirs. In this paper, experiment platform for high-voltage pulse discharge in water, which beneficial to research the pre-breakdown phase of subsonic streamer discharge in water of high-frequency discharge application scenarios is established. The mechanism of stream discharge and the importance of polarization process were analysed by high voltage theory. The initial time of flow column development was determined based on the time-varying characteristics, and the time of pre-breakdown phase was corrected by using the lightning shock intercept analysis theory. The results show that the polarization process should be incorporated into the pre-breakdown phase. Meanwhile, the initial development time of the flow column is the 3μs of the experimental data. After modification, the polarization process is shortened by 0.9372μs and the delay correction ratio is 24.57% after modification.

Experimental Study of the Structural Damage to Coal Treated by a High-Voltage Electric Pulse Discharge in Water

Experimental Study of the Structural Damage to Coal Treated by a High-Voltage Electric Pulse Discharge in Water

Pulsed high-current discharge in water: adiabatic model of expanding plasma channel and acoustic wave

This paper presents the results of a theoretical and experimental study of the use of a pulsed discharge in water to obtain a strong acoustic wave in a liquid medium. A discharge with a current amplitude of 10 kA, a duration of 400 ns, and an amplitude pulsed power of 280 MW in water at atmospheric pressure created an expanding acoustic wave with an amplitude of more than 100 MPa. To describe the formation of the discharge channel, an isothermal plasma model has been developed, which made it possible to calculate both the expansion dynamics of a high-current channel and the strong acoustic wave generated by it. Our calculations show that the number density of plasma in the channel reaches 1020 cm–3, while the degree of water vapor ionization is about 10%, and the channel wall extends with a velocity of 500 m s−1. The calculations for the acoustic wave are in good agreement with measurements.

Multiphysics analysis of thermal fluid in quasi-DC discharge in water

In the process of microsecond and millisecond pulsed discharge in water, a liquid low-density region will be formed by the effect of Joule heating. Then, thermal fluid is formed. Thermal fluid can influence the flow field and temperature distribution; and thus, it will affect the development of discharge. In this paper, the schlieren technology is used to observe the development of thermal fluid. The temperature field around the thermal fluid is calculated by the quantitative schlieren method. Finite element analysis is used to simulate the development of thermal fluid. Results show that the development of thermal fluid involves the coupling of electric fields, flow fields, and thermal fields. When there is an electric field, the movement of thermal fluid is mainly driven by the electric force, and it conforms to electrohydrodynamics. When the electric field disappears, the movement of thermal fluid is mainly driven by pressure. Due to Rayleigh–Taylor instability in the thermal fluid's head, the thermal fluid takes on a mushroom shape. The change in the thermal fluid's development direction on the side of the electrode leads to a short increase in the equivalent resistance of the gap. The study of thermal fluid is helpful to qualitatively understand quasi-DC discharge in water.

Temperature measurement of initiation process of microsecond pulsed discharge in water by quantitative schlieren method

In the initiation process of microsecond pulsed discharge in water, Joule heating is believed to be responsible for the formation of a low-density region. Then, electron avalanche can be easily induced in this low-density region. The aim of this paper is to study the feasibility of the quantitative schlieren method in the temperature measurement of water in the initiation process of microsecond pulsed discharge. A lens-type schlieren system was applied in the measurement of the radial temperature around the tip of the electrode. Finite element analysis was used to simulate the electric field and temperature during the discharge. Measurement results of the schlieren quantitative schlieren method are compared with the simulation results of finite element analysis in terms of temperature and energy conversion. The comparison shows that most electrical energy is consumed in Joule heating of water in the initiation process of microsecond pulsed discharge. In the region with no thermal fluid, the temperature distributions obtained by the quantitative schlieren method and finite element analysis are in good agreement. This work is helpful in the quantitative study of the role of Joule heating in the initiation of the streamer in water.

Analysis of cavities characteristics of underwater pulsed current discharge

In order to analyze the motion characteristics of pulsed discharge cavities in water, the process of cavities motion were obtained by a combining shadow method and high-speed camera. Through detailed data analysis and calculation, the theoretical motion process of cavities in water is obtained by the Rayleigh–Plesset model. The comparison between the theoretical results and the experimental data shows that the model can reproduce the motion process of cavities well. The variation trend of pressure and temperature in cavities is given, and the characteristics of the cavitiy motion period, radius and initial energy under different voltages are analyzed. Finally, the mass diffusion and heat transfer are calculated quantitatively. The results provide a basis for analyzing the generation process of secondary shock waves and perfecting the theoretical system of pulsed discharge in water.

Time-resolved analysis of negative pulsed discharges in water: streamer initiation and propagation modes

Analyses of the initiation and propagation-mode transitions of negative streamers are essential to develop a thorough understanding of underwater pulsed discharges. This paper presents experimental observations of negative streamers in deionized water performed using time-resolved visualization and electrical measurements. Based on the distributions of discharge inception delay and quantitative calculations of the ionization initiation fields, a streamer initiation model combining Zener ionization and field emission processes is proposed to account for discharges with short inception delays (<200 ns). Joule heating is the main mechanism responsible for discharges with an inception delay on the order of microseconds. The evolutions of bushy streamer morphology show that streamers exhibit more uniform structures under higher voltages, as most of the streamer branches grow simultaneously. A large-area discharge of bushy streamers is observed and is speculated to be closely related to the charge dynamics at the gas/liquid interface. The propagation of filamentary streamers and the transitions from filamentary to bushy streamers are presented. The redistribution of deposited charge and mitigation of the electric field during branching are the main causes for the mode transitions of streamers.

激光辅助水中脉冲放电生成等离子体的数值模拟

激光辅助水中脉冲放电生成等离子体的数值模拟

Experimental Study on Pressure Wave Characteristics of High-Voltage Discharge in Water With Hemispherical Electrodes

High-voltage pulse discharge in water is a promising technology to enhance the permeability of coal seam and rock mass by generating fractures within them. With the aim of improving the stability and efficiency of this technology, a high voltage electric pulse experiment system was constructed. The discharge electrodes in the experiment was hemispherical. The positive and negative electrodes were arranged on the same axis with adjustable spacing. Five sets of experiments were undertaken with the electrode spacing of 1mm, 2mm, 3mm, 4mm, and 5mm, respectively. In the experiments, an oscilloscope was used to analyze the voltage, current, and pressure wave signals. The experimental results of two typical voltage-current curves indicate that the peak pressure of plasma shock wave follows a parabolic trend with the electrode spacing, and there is an optimal electrode spacing for a given discharge voltage. The peak pressure of plasma shock wave tends to increase linearly with the increase of discharge voltage. The greater the electrode spacing, the greater the sensitivity of shock wave peak pressure to the discharge voltage. The shock wave peak pressure sensitivity of 5 mm discharge spacing is 4.7 times that of 1 mm discharge spacing. The experimental results for the voltages of 9 kV, 12 kV, and 24 kV with the optimal electrode spacing show that a power function is the best fit for the attenuation of the peak pressure of shock wave with its propagation distance.

Damage characteristics and laws of micro-crack of underwater electric pulse fracturing coal-rock mass

The purpose of this study is to study the mechanism of crack initiation, the damage characteristics and the propagation law of high-voltage pulse hydraulic fracturing coal so as to evaluate the fracturing effect of coal-rock mass. Based on the mechanism of high-voltage discharge fracturing in water, crack fracture and propagation, the numerical calculation and experiment of high-voltage pulse discharge (3 kV, 5 kV) based on a water pressure (3 MPa) were carried out. The CT scanning technique and PCAS image processing program were used to study the crack initiation and propagation of coal-rock mass. From the results, it is shown that under the action of high-voltage pulse discharge in water, the crack of coal-rock mass is dominated by the I-II composite crack and its damage type is mainly the tensile-shear damage; The periodic oscillation of the shock wave in the water causes the stress at the tip of the coal body to have an oscillating variation. The crack growth rate is related to the Rayleigh wave speed, and the growth of the crack length is unstable; The crack propagation and extension in the coal-rock mass are related to the preset angle of crack, the peak pressure of water shock wave and the direction of the maximum principal stress. Specifically, with the same voltage, the larger the pre-crack angle, the smaller the crack length, and the larger the crack width, area, and cracking rate; with the same crack angle, the higher the discharge voltage, the larger the cracking rate, length, width and area of crack. Compared with the 3 kV high-voltage discharge, the crack propagation pattern is more complicated under the condition of 5 kV discharge. The more the number of cracks, the larger the crack length, width, area and cracking rate, and the better the fracturing effect of coal-rock mass.

Determination of the Electrical Circuit Equivalent to a Pulsed Discharge in Water: Assessment of the Temporal Evolution of Electron Density and Temperature

Pulsed electrical discharges in dielectric liquids are intensively studied due to the wide range of applications in which they are implicated. Despite the simplicity of the experimental manipulation of these discharges, the underlying fundamental physics is relatively complex. In this study, we use the electrical characteristics, voltage and current, of pulsed discharges in water (various applied voltage and pulse width conditions) to determine the equivalent electrical circuit of the plasma. Based on a Mayr-type model, the plasma resistance is time-dependent, but the inductance is not. Considering that plasma resistivity also depends on electron density and temperature (Spitzer formula), the temporal evolution of these two parameters was also determined.

Analysis of Shockwave Front-Time Characteristics based On Pulse Discharge in Water

Analysis of Shockwave Front-Time Characteristics based On Pulse Discharge in Water

Chemistry in nanosecond plasmas in water

AbstractDischarges in liquids are the basis of a range of applications in electrochemistry, wastewater treatment, or plasma medicine. One advantage of discharges in water is their ability to produce radicals and molecules directly inside liquid with a high conversion efficiency. In this study, H2O2 production in a 10 ns pulsed discharge in water is investigated. The dynamic of these discharges is based on plasma ignition directly inside liquid followed by the formation of a bubble that expands in time before it eventually collapses. This sequence can be well described by cavitation theory. H2O2 is produced using different plasma conditions varying the treatment time, the pulse frequency between 1 and 100 Hz, and the applied voltage in a range from 15–30 kV. The resulting H2O2 concentration is measured using absorption spectroscopy ex situ based on a colorimetry method. The results indicate that the main parameter controlling the H2O2 production constitutes the applied voltage. The measured concentrations are compared with a global chemistry model simulating the chemistry involved during a single pulse using pressures and temperatures from the cavitation model. In addition, a global chemical equilibrium model for H2O2 creation is evaluated as well. The models show a good agreement with the data. The energy efficiency for the production of H2O2 reaches values up to 2 g/kWh.

Synthesis of nano titanium oxide with controlled oxygen content using pulsed discharge in water

Different titanium oxide nanoparticles were formed through pulsed discharge of Ti wires in distilled water and H2O2 solution. The recovered samples were characterized by various techniques, such as XRD, SEM and TEM. The results confirm the presence of various titanium oxide nanoparticles including TiO2 phases (anatase and rutile) and various nonstoichiometric TiO2−x in recovered samples owing to the oxygen deficient circumstance through pulsed discharge. The titanium oxide nanoparticles exhibit a spherical shape with a size of 10–300 nm. The results show that the energy input adjusted by charging voltage is one major factor to control the phases of titanium oxide and the overall oxygen content of recovered samples. In addition, the H2O2 content in distilled water also affects the oxygen content of recovered samples. The sample recovered from 10% H2O2 solution is pure TiO2 consisting of anatase and rutile without nonstoichiometric TiO2−x. Moreover, the UV–Vis absorption spectra of recovered samples show their intensive visible light absorption and the correlation between the visible light absorption and the experimental conditions (charging voltage and H2O2 content).

Recycling experimental investigation on end of life photovoltaic panels by application of high voltage fragmentation

With the rapid development of photovoltaic industry, the recycling of waste solar photovoltaic (PV) panels is becoming a critical and global challenge. Considering PV panels recycling is significantly effective and worthwhile to save natural resources and reduce the cost of production, how to selectively recycle valuable components of PV panels is the hot and dominant topic. Different from current mechanical crushing, heat treatment and chemical operation processes, novel and environment-friendly recycling approaches by using high voltage pulse discharge in water, called high voltage fragmentation (HVF), was discussed under different discharge conditions. The results showed that discharging across surface and interior of PV panels produced ablation round holes, sputter metal particles and dendritic channels. The average particle size decreased with the ascent of pulse number and voltage amplitude. Considering the energy consumption, the optimal condition of HVF in this paper was 160 kV for 300 pulses with the energy consumption of 192.99 J/g, crushing the PV panels into particles of 4.1 mm in average (13.7% of the initial size). More particle was distributed among the 0.1–2 mm size fractions as the energy increased. Selective fragmented products, such as Cu, Al, Pb, Ag and Sn, are concentrated on the fractions under 1 mm. Finally, hybrid crushing energy consumption model combined with fractal theory was discussed, which presented close relationship between energy and average particle size. Walker’s model (n = 2.047 determined by fractal theory) had the best fitting effect.

Acoustic Effects of Underwater Plasma Pulsed Sound Source under Different Electrical Parameters

Methods of pulse discharge in water were studied under different voltage and conductivity parameters. The voltage and current data in the experiment were collected and analyzed. Then the mechanism of the two discharge modes was briefly discussed (the initial mechanism of the corona mode is still unclear compared to the thermal process mechanism of the arc mode). Finally, two kinds of discharge methods were compared and analyzed from the aspects of experimental phenomena, production mechanism and application prospects. The experiment found that the acoustic effect of corona discharge in water under large solution conductivity is obvious, which provides a new idea for the design of underwater plasma sound source.

Direct impact characteristics of magnesite fragmentation by pulsed discharge in water

To clarify direct impact characteristics (pressure and position) of middle-grade magnesite fragmentation by pulsed discharge in water, this work uses pressure film to accomplish passive measurement through pulsed discharge experiment and obtain the pressure. The impact position is determined by image analysis of fragmentation product morphology, crack edge and discharge channel. Then, pressure load on magnesite surface is numerically analyzed based on the measured pressure obtained from the film. Results indicate that, at 10 mm discharge gap, the impact pressure increases with the discharge voltage, and the discharge voltage to disintegrate magnesite is −40 kV. The impact position is normally in the boundary among different mineral components. Simulation analysis indicates that, the pressure load applied directly on magnesite surface is approximately 142.5 MPa at −40 kV and greater than the compressive strength of magnesite, thus leading to the fragmentation.