Discharge In Mixture Research Articles

Kinetic analysis of an optically pumped rare gas lasing medium with a nanosecond repetitively pulsed discharge in Ar-He mixture

A kinetic model of a lasing medium for an optically pumped rare gas laser (OPRGL) was developed that accounts for the production of excited argon atoms Ar* in a nanosecond repetitively pulsed discharge (NRPD). Analytical formulas were derived for the frequency of Ar* radiation losses, population of the energy levels involved in the laser cycle and specific powers for pump absorption and lasing in the limit of bleaching of pump and lasing transitions. The formulas use the kinetic constants of the model as parameters and Ar* number density as the independent variable. Periodic solutions for number density of plasma components, pump absorption and small signal gain, specific pump absorption and lasing were obtained numerically. Mean over the NRPD period values of Ar* number density, specific pump absorption and lasing were calculated as the functions of the preset peak values of the reduced electric field E/N. Triangular electric field pulses of 80 ns FWHM duration and 200 kHz frequency were considered. Optical pumping increases Ar* loss by more than a factor of 10, due to excess spontaneous emission from Ar* levels that populates the 1s4 state of argon, resulting in a reduced NRPD plasma ionization and Ar* production. As a result, without auxiliary optical pumping from the 1s4 state that compensates this loss, the averaged across the discharge period Ar* number density decreases by a factor of 30. Moreover, the average specific heat release in plasma becomes almost equal to the specific lasing power in the acceptable operating modes, making auxiliary optical pumping mandatory for scaling of an OPRGL. The sensitivity of the results to the values of kinetic constants in the model is analyzed.

Formation of Black Silicon in a Process of Plasma Etching with Passivation in a SF6/O2 Gas Mixture.

This article discusses a method for forming black silicon using plasma etching at a sample temperature range from -20 °C to +20 °C in a mixture of oxygen and sulfur hexafluoride. The surface morphology of the resulting structures, the autocorrelation function of surface features, and reflectivity were studied depending on the process parameters-the composition of the plasma mixture, temperature and other discharge parameters (radical concentrations). The relationship between these parameters and the concentrations of oxygen and fluorine radicals in plasma is shown. A novel approach has been studied to reduce the reflectance using conformal bilayer dielectric coatings deposited by atomic layer deposition. The reflectivity of the resulting black silicon was studied in a wide spectral range from 400 to 900 nm. As a result of the research, technologies for creating black silicon on silicon wafers with a diameter of 200 mm have been proposed, and the structure formation process takes no more than 5 min. The resulting structures are an example of the self-formation of nanostructures due to anisotropic etching in a gas discharge plasma. This material has high mechanical, chemical and thermal stability and can be used as an antireflective coating, in structures requiring a developed surface-photovoltaics, supercapacitors, catalysts, and antibacterial surfaces.

Laboratory and astronomical discovery of cyanothioketene, NCCHCS, in the cold starless core TMC-1

We present the detection of cyanothioketene, NCCHCS, in the laboratory and toward TMC-1. This transient species was produced through a discharge of a gas mixture of CH2CHCN and CS2 using argon as carrier gas, and its rotational spectrum between 9 and 40 GHz was characterized using a Balle-Flygare narrowband-type Fourier-transform microwave spectrometer. A total of 21 rotational transitions were detected in the laboratory, all of them exhibiting hyperfine structure induced by the spin of the N nucleus. The spectrum for NCCHCS was predicted in the domain of our line surveys using the derived rotational and distortion constants. The detection in the cold starless core TMC-1 was based on the QUIJOTE1 line survey performed with the Yebes 40 m radio telescope. Twenty-three lines were detected with Ka = 0, 1, and 2 and Ju = 9 up to 14. The derived column density is (1.2 ± 0.1)×1011 cm−2 for a rotational temperature of 8.5 ± 1.0 K. The abundance ratio of thioketene and its cyano derivative, H2CCS/NCCHCS, is 6.5 ± 1.3. Although ketene is more abundant than thioketene by ∼15 times, its cyano derivative NCCHCO surprisingly is not detected with a 3σ upper level to the column density of 3.0 × 1010 cm−2, which results in an abundance ratio H2CCO/NCCHCO > 430. Hence, the chemistry of CN derivatives seems to be more favored for S-bearing than for O-bearing molecules. We carried out chemical modeling calculations and found that the gas-phase neutral-neutral reactions CCN + H2CS and CN + H2CCS could be a source of NCCHCS in TMC-1.

Surface modification of natural leather using RF plasma discharge

Radiofrequency (RF) low-pressure plasma has been applied to improve natural leather's wettability and water absorption. The plasma was generated using RF discharge of the Ar-He gas mixture at 60 and 120 W power using different treatment times (30, 60, 120, 180, and 300s). Before and after treatment, the contact angle, surface free energy, and water absorption ratio were measured. It was observed that a 300s plasma treatment time and plasma power 60 and 120 W is enough to decrease the water contact angle from 83.56 for an untreated sample to 0°. The surface-free energy and the water absorption ratio increase with an increase in the treatment time and plasma power. The findings demonstrate that plasma treatment increases the wettability of the surface of leather samples. In addition, the change in leather properties was analyzed by scanning electron microscopy, X-ray diffraction, and differential scanning calorimetry, Fourier transform infrared spectroscopy.

Source of High-Efficiency Radiation in the Lyman and Werner Bands of a Pulse Discharge in Mixtures of Hydrogen and Helium

Source of High-Efficiency Radiation in the Lyman and Werner Bands of a Pulse Discharge in Mixtures of Hydrogen and Helium

Effect of Erosion on Surface Roughness and Hydromechanical Characteristics of Abrasive-Jet Machining

The article contains the fundamental results of the experimental and numerical investigations for pneumo-abrasive unit nozzles with different geometries. The research was purposed by the pressing need to develop an inexpensive and effective working nozzle design of the air-abrasive unit which can be applied for surface processing before some technological processes are performed, as well as for surface coating, descaling after thermal treatment, processing of hollow holes of the crankshafts, smoothing of the inner surfaces of the narrow channels between the impeller blades after electric discharge machining for ultrahigh-pressure combination compressors. Several designs were considered, ranging from the simplest to those with a complicated inner channel geometry. The impact of the nozzle material and challenging inner surface application on its characteristics has also been studied. The research was done using the application of modern CFD complexes for numerical modeling of the air-abrasive mixture discharge from the working nozzle of the pneumo-abrasive unit. In addition, physical experimentation was provided. The methods applied in the research allow for profound, systematic research of spraying units operating on the air-abrasive mixture within a wide range of geometrical and mode parameters. The novelty of the gained results lies in the development of the mathematical model of the pneumo-abrasive nozzle operating process, the working out of a cheaper nozzle design, getting information about air-abrasive mixture distribution along the nozzle length, giving practical recommendations for calculation and designing a working nozzle for the jet-abrasive unit.

Comparative investigation on organosilicon film growth by cyclonic plasma using hexamethyldisilazane and hexamethyldisilazane/nitrogen gas mixture

This study aimed to discover the surface characteristics of cyclonic plasma‐deposited films and the effect of nitrogen gas addition. The influence of nitrogen gas addition on the surface characteristics of organosilicon films in hexamethyldisilazane (HMDSN) and HMDSN/nitrogen (HMDSN/N2) cyclonic plasmas at atmospheric pressure was evaluated. It was found that the addition of nitrogen gas is a crucial factor affecting organosilicon film growth in the plasma cyclone in one atmosphere. SEM, AFM, and ATR‐FTIR results indicated that on adding nitrogen gas, the surface morphology became rougher, the peak corresponding to the Si–O–Si group was detected at approximately 1050 cm−1, the degree of porosity was relatively low, and the proportion of the SiCHx group decreased. In general, the surface energies of the films deposited in the HMDSN discharge and the HMDSN/N2 gas mixture discharge exhibited similar features. SEM and AFM evaluations showed high roughness values of 44.5 nm for the film formation in the HMDSN/N2 gas mixture discharge, while the films grown in the HMDSN discharge exhibited a relatively flat surface with a roughness of 24.5 nm. Based on ATR‐FTIR detection, cyclonic plasma‐deposited films deposited in the HMDSN discharge obtained organic moieties, while the films generated in the HMDSN/N2 gas mixture discharge exhibited strong Si–O–Si absorption signals. A possible nano‐organosilicon film growth that prevails in atmospheric pressure plasma deposition is proposed based on atmospheric‐pressure plasma chemistry, nitrogen gas addition, and experimental observations.

VUV lasing in diffuse discharges formed by runaway electrons

The parameters of stimulated emission in diffuse discharges formed in a sharply inhomogeneous electric field by runaway electrons in mixtures of rare gases with the addition of H2 and F2 at pressures up to 10 atm are studied. Efficient VUV lasing was obtained at wavelengths from 148 to 193 nm on the transitions of H2, F2 and exciplex ArF* molecules. It was shown that the addition of He buffer gas increases the pulse duration, while Ne addition improves the output energy of the VUV laser on the H2 Lyman band. A laser pulse duration over 10 ns and an output of 0.12 mJ were obtained. The diffuse discharge in mixtures of He with F2 was found to form as a result of successive ionization waves. It was shown that the laser pulse at 157 nm has three peaks, which correspond to the maxima of the diffuse discharge current. Therewith, the first or second peak of the laser radiation has the maximum intensity, depending on the amplitude of the conduction current in the primary ionization wave. A maximal F2* laser electrical efficiency of η 0 = 0.18% and an output of Q 157 = 3.8 mJ were obtained in a He–F2 gas mixture at pressure of 10 atm, which exceeds the efficiency of lasers of this type pumped by transverse volume discharges with UV preionization. Long-pulse operation of the ArF* laser was achieved in a He–Ne–Ar–F2 gas mixture. Lasing at 193 nm continued during two periods of the diffuse discharge current. The total duration of the laser pulse was as long as 40 ns, and the radiation energy at 193 nm was as high as 2 mJ from an active volume of 20 cm3.

Simulation of Light Intensity of VUV Lamp Based on Inductively Coupled Plasma Discharge in Low-pressure Kr-He Mixture

Simulation of Light Intensity of VUV Lamp Based on Inductively Coupled Plasma Discharge in Low-pressure Kr-He Mixture

Laboratory and astronomical discovery of the cyanovinyl radical H2CCCN

We report the first laboratory and interstellar detection of the α-cyano vinyl radical (H2CCCN). This species was produced in the laboratory by an electric discharge of a gas mixture of vinyl cyanide, CH2CHCN, and Ne. Its rotational spectrum was characterized using a Balle-Flygare narrowband-type Fourier-transform microwave spectrometer operating in the frequency region of 8–40 GHz. The observed spectrum shows a complex structure due to tunneling splittings between two torsional sublevels of the ground vibronic state, 0+ and 0−, derived from a large-amplitude inversion motion. In addition, the presence of two equivalent hydrogen nuclei makes it necessary to discern between ortho- and para-H2CCCN. A least-squares analysis reproduces the observed transition frequencies with a standard deviation of ca. 3 kHz. Using the laboratory predictions, this radical was detected in the cold dark cloud TMC-1 using the Yebes 40 m telescope and the QUIJOTE1 line survey. The 40, 4-30, 3 and 50, 5-40, 4 rotational transitions, composed of several hyperfine components, were observed in the 31.0–50.4 GHz range. Adopting a rotational temperature of 6 K, we derived a column density of (1.4±0.2)×1011 cm−2 and (1.1±0.2)×1011 cm−2 for ortho-H2CCCN and para-H2CCCN, respectively. The reaction of C + CH3CN emerges as the most likely route to H2CCCN in TMC-1, and possibly that of N + CH2CCH as well.

A phenomenological model for plasma-assisted combustion with NRP discharges in methane-air mixtures: PACMIND

The recent advances in plasma-assisted combustion must now be strengthened through high-fidelity numerical simulations. However, detailed plasma-combustion coupled simulations in complex geometry and turbulent flow involving hundreds of discharges are still unaffordable due to prohibitive computational costs. In this work, a Plasma-Assisted Combustion phenoMenological modelIng for Non-equilibrium Discharges (PACMIND) is proposed. The model aims to avoid computing in detail the plasma phase and consists of incorporating the leading order plasma effects on the reactive compressible Navier–Stokes equations. It consists of two ultra-fast effects with radical productions and gas heating, as well as a slower gas heating due to vibrational energy relaxation. Based on detailed kinetic simulations, the model has been applied to air and methane-air mixtures and contains respectively 5 species, 3 reactions and 12 species, 7 reactions. The model has been validated against experiments in air and detailed plasma-assisted combustion ignition simulations in methane-air at various equivalence ratios and reduced electric fields. Significant improvements regarding ignition delay times have been observed by comparison with an existing model. In addition, the model accounts for NOx production by plasma discharge and covers the full range of conditions encountered in a premixed flame. Hence, it opens the way to the simulation of realistic 3D turbulent configurations with minimal over-costs.

NUMERICAL STUDY OF DETONATION INITIATION BY SPARK DISCHARGE IN A HYDROGEN-OXYGEN HIGH-PRESSURE GAS MIXTURE

The influence of the initial pressure of the combustible gas mixture on the processes that occur during the initiation of detonation by a spark discharge in a high-pressure hydrogen-oxygen mixture was estimated. A onedimensional gas-dynamic model in a chemically reacting gas with separation of the vibrational temperature of diatomic molecules from the kinetic temperature of the gas was used for the numerical study. It was simulated that an intensity of the shock wave causing the detonation initiation by a critical regime is below of the detonation wave intensity when the initial gas pressure is 1.013 MPa and the intensity of the shock wave exceeds the detonation wave intensity when the initial gas pressure is 0.304 MPa. It was found out that the process of the detonation initiation falling by a near-critical regime is more longitudinal when the gas pressure is low. Energy deposition history into the spark channel when detonation is initiated at different initial gas pressures was calculated.

Stability of breakdown phenomenon in N2, SF6, and their mixture under impulse voltages

In the self-breakdown experiment, it is demonstrated that the breakdown stability of 15% SF6/N2 was higher than that of pure SF6 and N2 in the non-uniform field under negative impulse voltages. In this paper, the stable breakdown phenomenon of the gas mixture is studied at the nanosecond scale. The corona process and streamer process of these three gases are investigated by using a high-speed framing camera. The stabilized corona and the abnormal streamer phenomena observed in the gas mixture discharge have a relation to the stable breakdown phenomenon. The stabilized corona is supposed to be the main reason that obstructs the development of negative steamer and stabilizes the supply of photons to the anode. Furthermore, the captured images of the streamer process in the gas mixture show that there is a negative ion sheath between the electrodes. The sheath keeps the corona stabilized near the cathode tip. In addition, photons emitted by the stabilized corona can ionize neutral particles near the anode. The generated photoelectrons and positive ions accumulate near the anode surface. The positive streamer occurs once the accumulation number reaches a certain value. In addition, the photon emission intensity and stability also have an influence on the stability of the positive streamer.

Macro-encapsulation of metal balls prepared by waste aluminum cans in ceramic capsules with reserved space

Phase change materials (PCMs) form the core of thermal energy storage (TES) for enhancing solar and industrial waste heat recovery. Metals have attracted growing attention due to their unique advantages, including high latent heat storage and high thermal conductivity. The application of metallic PCMs in TES is limited by the absence of appropriate packaging technology. Volume expansion during the solid-liquid phase can cause breakage of the protective coatings. This study proposes a “double-layer coating, recycling inner layer” method for the encapsulation of metallic PCMs. Waste aluminum cans (WACs) were selected as the PCM for cost reasons. The alloy balls prepared using the WACs were sequentially coated with an alkane mixture and ceramic slurry. The alkane mixture melts and discharges during the baking process, leaving a void for the phase-change volume expansion. The shell was gradually densified, and the metallic PCM was completely encapsulated after the heat treatment. The prepared MAEPCMs heat-treated at 1200 °C showed excellent mechanical properties, high heat storage capacity, and thermal cycle stability. The force required for compressive failure was approximately 2623 N. In addition, the total heat storage capacity reached approximately 198.6 kJ/kg at the temperature range of 600–700 °C, of which the latent heat accounted for more than 98.5%. There was no erosion between the alloy and the shell material, and the cumulative mass change was less than 8 wt. % after 600 thermal cycles. This study provides a structurally stable and low-cost technique for the preparation of durable macro-encapsulated PCMs with a high heat storage capacity and high thermal conductivity.

Chemical and Electrical Aspects of Homogeneous Discharge in an Argon-Oxygen Mixture for Ozone Generation

In this work, a dielectrics barriers discharge (DBD) in an Ar/O<sub>2</sub> gas mixture excited with sinusoidal applied voltage for ozone generation has been investigated in order to draw attention to the important role of the kinetic scheme of this gas mixture in the plasma discharge. The adopted model was based on argon-oxygen plasma chemistry, the external circuit, and the Boltzmann equations. This approach predicts the optimal operating conditions and can also describes the chemical and electrical aspects of the DBD reactor. The kinetic scheme of an Ar/O<sub>2</sub> gas mixture takes into account 15 species regrouped in 123 reactions. The time evolutions of kinetic and electric characteristics of plasma discharges, and the effect of the main discharge parameters on DBD behavior and ozone efficiency are analyzed and discussed.

Effect of Argon on Decomposition in Micro-Slit Sustained Glow Discharge Reactor

The microdischarge decomposition devices have the advantages of a simple structure and low energy consumption and thus have a very promising future in in-situ resource utilization technology for Mars missions. It was found that the addition of Ar increased the conversion rate of in a micro-slit sustained glow discharge reactor. The experimental results showed that the breakdown voltage of Ar was significantly lower than that of in the micro-slit discharge, which indicated that the discharge breakdown channel was more likely to be generated. Thus, the addition of Ar to resulted in a lower breakdown voltage, and the discharge energy could be more distributed for decomposition. Spectral intensity analyses showed that, for mixture discharges, the presence of high-energy Ar excited states was clearly observed. With increasing discharge voltage, an increase in the light intensity of active components such as , O, and CO was observed. Combined with the discharge parameters and spectral characterization, it can be concluded that the metastable species of Ar exist and accumulate during the discharge, which contributes to the conversion of .

A simple design method of dust explosion venting size at elevated static activation pressure

To develop the application of explosion venting technology in high-pressure vessels, a new model for the design of dust explosion venting size was presented, which took the physicochemical phenomenon deriving from the elevation of the static activation pressure into account. Firstly, for confined pressure rise, the wall quenching effect originating from the dust flame thickness was considered by adopting the three-zone model. Secondly, for the venting pressure rise, the energy loss due to the discharge of high-energy burnt mixture (quantified as the specific surface area loss of the flame) was taken into account and the induced turbulence factor was introduced. Thirdly, for the venting pressure drop, a dynamic pressure relief capability evaluation model which takes into account the flame morphology evolution (tear-shaped flame) and the proportion of discharged mixture (relative volume ratio) at elevated activation pressure was proposed. The predicted maximum reduced pressure and venting size were checked against the PMMA explosion experiments and a more great performance was obtained compared with standards.

Effect of atmospheric pressure pulsed discharge spatial inhomogeneity on Ar I and H I lines: Electron number density study

AbstractThe spatial inhomogeneity of pulsed atmospheric pressure discharge in argon is investigated using the electron number density Ne diagnostics procedure applied to asymmetrically broadened Ar I lines. A dedicated fitting procedure is used for describing Ar I 703.0 nm line shape recorded from argon gas discharge and H I (at 486.13 and 656.28 nm) lines recorded from Ar‐H2 gas mixture discharge. The results revealed the change in Ne in both axial and radial directions. The additional Ar I lines at 614.5, 710.7, 731.2, and 731.6 nm, recorded from integral spatial radiation, are analysed as well to confirm the results from the plasma column region. The possibility of using AlO (B2∑+–X2∑+) and CN (B2∑+–X2∑+) molecular bands for gas temperature Tg measurements in this type of gas discharge source is demonstrated and Tg used as an input parameter for the Ne diagnostics procedure. For the proper identification of molecular band spectral lines, the Fortrat parabolas are constructed. The results obtained from Ar I 703.0 nm line indicate three different Ne values, with Ne1 ≈ 0.6 × 1016 cm−3, Ne2 ≈ 3.6 × 1016 cm−3, and Ne3 ≈ 19 × 1016 cm−3 measured from the plasma column. These Ne values increase in the cathode and anode region.

Effective ionization coefficient in mixtures of Ar and O2 determined using the Townsend discharge

Precise knowledge of the fundamental ionization properties of gases, such as the effective ionization coefficient, is crucial for discharges in mixtures of Ar:O2, which are significant for a wide range of plasma applications. This study determined the effective ionization coefficient in electronegative gas mixtures of Ar:O2 in the pressure range of 10–800 Torr and reduced electric field strength E/N range of 40–1200 Td utilizing a steady-state non-self-sustaining Townsend discharge. The reduced effective ionization coefficient αe/N increased with E/N and decreased with increasing O2 content in the gas mixture. The experimental results were compared with a model which was based on calculating the ionization and attachment coefficients with BOLSIG+. The ion conversion of O− to O2−, detachment from O2−, and formation of O3 were accounted for similarly as has been done with N2:O2 mixtures. Reasonably good agreement between the measurements and the model calculations was achieved for Ar:O2 mixtures with the O2 content between 20% and 70%. A discrepancy of more than 20% between measurement and calculations was observed at low E/N values when the O2 content was below 20% and at high E/N values when the O2 content was above 70%. Several possible explanations were proposed for the observed discrepancy; however, more elaborate models are required. The reduced critical electric field E/Ncrit, where the apparent effective ionization coefficient is zero, was determined as a function of the O2 content in the Ar:O2 mixtures. E/Ncrit increased with increasing O2 content in the mixture.

Experimental characterization of the dimensionless momentum length for submerged jet discharges of air-steam mixtures into stagnant water

Welcome to the WIT Press eLibrary - the home of the Transactions of the Wessex Institute collection, providing on-line access to papers presented at the Institute's prestigious international conferences and from its State-of-the-Art in Science & Engineering publications.