Bubble Discharge Research Articles

Plasma-Driven Reactive Species Production and Transport in a 2-D Discharge Cell

A 2-D cell was employed to study the plasma–liquid interface. Chemical probes were used to compare the chemical reactivity induced by both air and argon plasma discharges in bubbles. Methyl orange and potassium iodide-starch solutions were used to visualize the propagation of acidic and oxidative fronts into the bulk liquid beyond the interface. Acidic and oxidative fronts were observed for both air and argon plasmas, indicating that charge exchange and electron impact processes at the interface are crucial to plasma-induced reactivity in liquids. Absorption spectrophotometry of indigo trisulfonate was performed to measure the transport of oxidative species, primarily aqueous ozone, and hydroxyl radicals, from plasma to the liquid region. Chemical reactivity at the interface can be transported far into the bulk liquid region due to plasma-induced fluid flow.

Registration and simulation of partial discharges in free bubbles at AC voltage

Partial discharges in free bubbles in transformer oil are investigated both experimentally and theoretically. Optical, electric and optoelectronic registration are performed to obtain a picture of partial discharge. The time duration of electrical and optoelectronic signals is practically the same, 50 ns. Much longer time is needed for bubble deformation and its breaking, approximately several milliseconds. Electric properties obtained in experiments are confirmed by the simulation of the electrical field, “true” and “apparent” charges of partial discharge. Hydrodynamic behavior in experiments corresponds well to the simulation with the lattice Boltzmann method.

THE MICRO- AND NANOSECOND DISCHARGES IN GAS BUBBLES FOR WATER DISINFECTION AND PURIFICATION

Purpose. Comparison of electrical circuits of experimental plants for obtaining micro- and nanosecond discharges in gas bubbles in water and comparing the experimental results obtained for disinfecting water using such discharges. Methodology. To obtain high-voltage pulses on the load in the form of a gas bubbles and a layer of water with a frequency of more than 2000 pulses per second, a method of generating micro- and nanosecond pulses using high-voltage pulse generators based on a pulse transformer (PT) according to Tesla, with a transistor opening switch IGBT in the low-voltage part of the circui . A current-limiting resistor with a resistance Rcl = 24 kW is used to protect the transistor switch at microsecond discharges. At nanosecond discharges, a multi-gap spark gap is used to sharpen the front of high-voltage pulses. We used a capacitive voltage divider with a division factor of Kd = 7653 to measure voltage pulses, a shunt with a resistance of Rs = 2.5 W for measuring current pulses. RIGOL DS1102E digital oscilloscope with a 100 MHz bandwidth was used as a recording device. Results. The effect of micro- and nanosecond discharges in gas bubbles on microorganisms was experimentally investigated. It was possible to reduce the biochemical oxygen consumption of water during microsecond discharges, reduce the turbidity of water, and improve its organoleptic qualities. The energy released in a single pulse with microsecond discharges Wµ ≈ 17 mJ, with nanosecond discharges Wn ≈ 7.95 mJ. At nanosecond discharges, complete inactivation of E.coli bacteria was achieved. The disinfecting and purifying action of nanosecond pulses is better compared to microsecond pulses due to an increase in the amplitude of the pulsed voltage up to 30 kV, and a pulsed current of up to 35 A. Originality. The possibility of effective microbiological disinfection of water using nanosecond discharges in gas bubbles at low specific energy consumption has been experimentally shown. Practical value. The obtained experimental results on water disinfection using micro- and nanosecond discharges offer the prospect of industrial application of installations using such discharges for disinfecting and purification wastewater, swimming pools, and post-treatment of tap water.

Characteristics of a Nanosecond Pulsed Bubble Discharge in N2/O2 Atmospheres

Nanosecond pulse power is employed to excite a N2/O2 bubble discharge using hollow needle electrode underwater at atmospheric pressure. The discharge images, waveforms of applied voltage and discharge current, and optical emission spectra are recorded to investigate plasma characteristics and diagnose the active species in the discharge region with varying O2/N2 proportion, and the spectrophotometry is applied to measure the H2O2 concentration in the liquid phase. A glow-like discharge is obtained with bubbling N2, whereas the discharge transfers to a filament mode when mixing O2, and obvious filament regime is built when the volume proportion of O2 is above 80%. With the increase of O2 proportion, the emission intensity of O increases rapidly but that of OH decreases sharply. The effects of pulse voltage and pulse repetition on emission intensity are studied to optimize discharge parameters. The liquid pH values have an uptrend within plasma treatment for 30 s and then decrease with increasing treatment time.

Measurement of reactive species in different solutions of bubble discharge with varying O2/N2 proportion in Ar: Analysis of reaction pathways

The generation of species in gas phase and long‐lived species in deionized water and d‐mannitol solution of a bubble discharge in dependence on bubbled gas atmosphere with different O 2/N 2 proportion are studied. Argon is mixed to enhance the discharge. The optical emission spectra and Fourier‐transform infrared spectroscopy are used to diagnose gaseous species and exhaust gas components, and study the effects of O 2/N 2 proportion on the species intensities. The aqueous species and OH radical are measured by chemical probes to reveal the role of OH radical on the formation of long‐lived species. The liquid species and exhaust gas are also analyzed varying with O 2/N 2 proportion to demonstrate the effect of O 2‐based radicals on the formation of long‐lived species.

Preparation and synthesis of carbon nanomaterials from 1-hexanol by solution plasma process with Ar/O2 gas bubbles

This study presents the simple and catalyst-free methods for synthesizing carbon nanomaterials from 1-hexanol alcohol by using stable solution plasma process by varying the argon (Ar), oxygen (O2), and Ar and O2 mixtures plasma working gas bubble. The structural characteristics of carbon nanomaterials are measured by transmission electron microscopy, Raman spectroscopy, and X-ray diffraction. The discharge characteristics are examined based on the discharge voltage, current, and optical emission spectrometer (OES) techniques. By using the external Ar gas bubble discharge during solution plasma process, the size of carbon nanoparticle and discharge voltage are decreased compared to the no gas case and the discharge current is increased, which would be due to the increase of plasma energy and enhancement of the square of plasma-liquid contact to plasma volume. By using the external O2 gas bubble discharge during solution plasma process, whereas, the size of carbon nanoparticle is increased compared to the no gas case and the discharge voltage and current are decreased, which would be due to the production of relatively high amounts of oxygen radicals, resulting in the flame synthesis. Raman spectra results show that the degree of graphitization of the carbon nanomaterials synthesized with external Ar 150 and O2 50 standard cubic centimeter per minutes (sccm) mixtures gas bubble during solution plasma process is observed to be greater than that of the carbon nanomaterials synthesized with the only Ar or O2 gas bubble. This solution plasma process by varying the plasma working gas mixtures can potentially be used for the precise nanomaterial synthesis.

Controlling of reactive species in atmospheric Ar bubble discharge by adding N2/O2a

An underwater Ar bubble discharge is excited by nanosecond pulsed power, and the effects of adding N2/O2 in Ar discharge on products are investigated. This work focus on regulating species concentration in plasma activated water (PAW), and then seeking specific concentrations for future application. The optical emission spectra (OES) and colorimetric chemical probes are used to diagnose and measure active species in plasma region or liquid phase. The H2O2 energy yield with Ar bubble can be up to 3.04 g kWh−1. The emission intensity characteristics of Ar (4p‐4s), OH (A‐X), Hα, and O (3p‐3s) in plasma region, and the concentrations of H2O2, , and in liquid are investigated with adding varying N2/O2 proportion in Ar bubble discharge.

Proteomic analysis of Saccharomyces cerevisiae response to plasma treatment

Food safety is one of the main issues for the food industry. Regarding the increased reports of food-associated infections new non-thermal technologies are rapidly developing and improving. The aim of this research was to define the inactivation, recovery and stress response of Saccharomyces cerevisiae ATCC 204508 cells after the treatment by high voltage gas phase plasma and liquid phase plasma discharges in bubbles. Variations of the plasma frequency (60, 90 and 120 Hz), input gas (air or argon) and processing time (5 and 10 min) have been used to define plasma effects on S. cerevisiae cells. Complete inactivation's by liquid plasma in bubbles were determined as well as recovery of treated samples. Transmission electron microscopy figures showed cells with the normal cell shape and intact inner and outer membrane after the plasma treatments. Proteomic analyses indicated overexpressed proteins which contributed in cell defense mechanisms to overcome stress conditions. S. cerevisiae ATCC 204508 cells were under the stress, but with the proven ability to recover its metabolic activity.

Study of partial discharges in bubbles and microsphere in transformer oil

Partial discharges in free bubbles floating in transformer oil and in a glass sphere are studied both experimentally and theoretically. Optical, electrical and optoelectronic registration was performed to obtain partial discharge pattern. The time duration of electrical and optoelectronic signals were practically the same and equaled to 50 ns. PDs in bubbles were rare events even at the electric field two times higher than required by Pashen’s law. In the case of rigid sphere the voltage of PD inception was practically the same as the value given by Pashen’s law. Simulations of PD gave the values of “true” and the “apparent” charges close to those measured at the experiments. Simultaneous PDs in bubble and closely situated sphere were not recorded.

Measuring the Amount of Substance Evaporated from the Surface of a Viscous Dielectric Liquid during Nanosecond Barrier Discharge

The amount of substance evaporated from the surface of a viscous dielectric liquid during nanosecond barrier discharge has been measured for the first time using a method based on the creation of a gas microbubble in the volume of liquid and subsequent generation of discharge in the bubble. By measuring increase in the bubble radius during discharge, it is possible to determine the amount of substance evaporated from the microbubble walls. It is established that millijoule energy deposition in discharge leads to the evaporation of several nanomoles of substance, and this amount grows with the deposited electric energy.

Special issue: Plasma and Liquids

Special issue: Plasma and Liquids

Rapid Formation of Diamond-Like Nano-Carbons in a Gas Bubble Discharge in Liquid Ethanol

This work demonstrates that diamond-like nano-carbons can be rapidly grown at atmospheric pressure and near ambient temperature in Ar gas bubble discharge in liquid ethanol. The method uses a discharge between point-to-plate electrodes immersed in ethanol, with plasma being generated inside Ar gas bubbles introduced through the needle electrode. The ethanol was dissociated at the liquid/gas interface into reactive species such as C2 and CH, which are the primary species responsible for diamond formation. A mixture of lonsdaleite nano-diamonds, amorphous carbon nano-spheres, and a graphitic carbon network, was formed. The rapid bubble movement distributes the reaction products almost immediately into the liquid phase, ensuring that nucleation of new material continues throughout the process. This simple, inexpensive and fast process avoids the elevated temperatures and extreme pressures of current methods.

Plasma treated water – A promising electrolyte to produce nanoporous titanium dioxide nanotubes

Plasma‐treated water is used as an environmentally friendly electrolyte for the synthesis of nanoporous titanium dioxide nanotubes by anodization of titanium. The possible mechanism of nanotube formation in the process is studied. The reactive species hydrogen peroxide and nitrate can be selectively produced in a gas bubble discharge in liquid using argon plasma or air plasma, respectively. It is observed that hydrogen peroxide enhances only the formation of an oxide layer, while nitrate forms pores on this oxide layer. It is proposed that the nitrate determines the formation of nanoporous nanotubes, while hydrogen peroxide enhances the oxidation.

Development of a capillary plasma pump with vapour bubble for water purification: experimental and theoretical investigation

This paper describes the development of a small-sized reactive plasma pump driven by capillary bubble discharge for the purification of treated water. The apparatus we developed decomposes the pollutants in the water by using chemical species generated by the plasma discharge. The resulting stream of bubbles obviates the need for an external gas supply or pump to transport the water. A high-speed camera was used to investigate the bubble dynamics responsible for the pumping effect, which is achieved by selecting the shape of the capillary such that the bubble ejections within enhance the ‘self-repetition’ action required for the pumping motion. Our experiments showed that optimal bubble generation requires a consumed power of 17.8 W. A theoretical model was developed to investigate the pumping mechanism. We solve the problems associated with liquid oscillations in the U-shaped water reservoir by employing a non-uniform cross-sectional area in our model. The chemical reactivity of the device was confirmed by using emission spectroscopy of OH radical and by measuring the decomposition of methylene blue.

Kinetics and dynamics of nanosecond streamer discharge in atmospheric-pressure gas bubble suspended in distilled water under saturated vapor pressure conditions

We perform computational studies of nanosecond streamer discharges generated in helium bubbles immersed in distilled water under atmospheric pressure conditions. The model takes into account the presence of water vapor in the gas bubble for an accurate description of the discharge kinetics. We find that the dynamic characteristics of the streamer discharge are different at low and high positive trigger voltages with the axial streamer evolution dominant for low voltages and a surface hugging mode favored for high voltages. We also find a substantial difference in initiation, transition and evolution stages of discharge for positive and negative trigger voltages with the volumetric distribution of species in the streamer channel much more uniform for negative trigger voltages on account of the presence of multiple streamers. We observe that the presence of water vapor does not affect the breakdown voltage even for oversaturated conditions but significantly influences the composition of dominant species in the trail of the streamer as well as the flux of the dominant species on the bubble surface.

Pulsed electrical discharge in conductive solution

Electrical discharge in a conductive solution of isopropyl alcohol in tap water (330 S cm−1) has been studied experimentally applying high voltage millisecond pulses (rise time ∼0.4 , amplitude up to 15 kV, positive polarity) to a pin anode electrode. Dynamic current–voltage characteristics synchronized with high-speed images of the discharge were studied. The discharge was found to develop from high electric field region in the anode vicinity where initial conductive current with density ∼100 A cm−2 results in fast heating and massive nucleation of vapor bubbles. Discharges in nucleated bubbles then produce a highly conductive plasma region and facilitate overheating instability development with subsequent formation of a thermally ionized plasma channel. The measured plasma channel propagation speed was 3–15 m s−1. A proposed thermal model of plasma channel development explains the low observed plasma channel propagation speed.

高粘度絶縁油中における絶縁紙の直流部分放電特性と電荷挙動

In long-distance DC submarine cables, insulating oil depletion phenomenon occurs due to limitations in pressure transmission distance. Therefore, the high viscosity insulating oil such as high viscosity oil is promising. However, if the unexpected bubbles are occurred in the high viscosity oil, partial discharge in bubbles may reduce insulation performance of the cable. In addition, the partial discharge promote the degradation of insulating oil and insulating performance may reduce. In this paper, it is investigated DC partial discharge inception voltage and repetition rate of DC partial discharge occurrence of the kraft paper impregnated with the high viscosity insulating oil. Furthermore, the charge behavior was discussed.

Efficient and Selectable Production of Reactive Species Using a Nanosecond Pulsed Discharge in Gas Bubbles in Liquid

A plasma gas bubble‐in‐liquid method for high production of selectable reactive species using a nanosecond pulse generator has been developed. The gas of choice is fed through a hollow needle in a point‐to‐plate bubble discharge, enabling improved selection of reactive species. The increased interface reactions, between the gas‐plasma and water through bubbles, give higher productivity. H2O2 was the predominant species produced using Ar plasma, while predominantly and NO2 were generated using air plasma, in good agreement with the observed emission spectra. This method has nearly 100% selectivity for H2O2, with seven times higher production, and 92% selectivity for , with nearly twice the production, compared with a plasma above the water.

Evolution of electrical discharge channel in isopropyl alcohol solution

Evolution of the spark channel created by the high voltage pulse generator in 15% isopropyl alcohol solution in tap water was investigated experimentally. Fast camera images show the start of spark discharge channel with the anode region glowing, which is due to ionization-overheating instability near the surface of anode electrode. Measured propagation velocity is about 4 m/s and points to thermal process of channel evolution. Partial discharges in gas bubbles near the spark channel were observed. When the channel bridges the gap the cathode flash of lightning occurs which is much brighter than anode glowing and channel one. After destruction of the spark channel the cathode glowing stays for a longer period than anode one.

Understanding the plasma and power characteristics of a self-generated steam bubble discharge

Plasma formation in a self-generated steam bubble is studied using a coaxial discharge tube with an axial powered electrode (nominal peak operating voltage 2000 V) and an external ground lead without any gas flow. The discharge is potentially attractive for water purification applications in that the production of reactive nitrogen species and the associated water acidification is avoided. The discharge was found to form after a finite delay, which is attributed to the vapor bubble formation necessary for plasma ignition. Steam bubble composition was confirmed using emission spectra. Plasma properties and power dissipated in the self-generated steam bubble were characterized using emission spectroscopy and Lissajous methods. Discharge density and gas temperature were found to vary significantly over the applied ac voltage cycle. The power dissipated as inferred from the Lissajous method was found to scale inversely with frequency over the low frequency range investigated (4 kHz and 5 kHz).