Neon Argon Research Articles

Numerical study of microdevice with surface acoustic waves for separation of gas mixtures

Recently, it was shown that traveling surface acoustic waves (SAWs) can affect gas flow in microchannels. The effect of SAWs was studied in free-molecular flow regime, and it was shown that SAWs can induce separation of gas mixtures. In the present work, this effect is studied for denser flow regimes, which are more interesting from a practical point of view. The problem is studied numerically using own modification of the direct simulation Monte Carlo method on the example of a neon–argon mixture. The main finding is that SAWs still enhance separation of gas mixtures outflowing into vacuum through a microchannel under all studied rates of gas rarefaction up to Kn≈0.1. Another important practical result is that effect is present for wave speeds typical for existing SAWs (≈1000 m/s) and in a wide range of SAW amplitude to channel height ratios. Influence of other practical aspects, such as channel length, masses of species, and available magnitudes of material surface speed, are also briefly discussed.

Separation of binary gas mixture in a microchannel with oscillating barriers

The time-dependent flow of a neon–argon mixture in a microchannel interrupted by a row of oscillating barriers is numerically studied using the Direct Simulation Monte Carlo method in a range of Knudsen numbers from 0.1 to 10 and in a wide range of oscillation frequencies. The emphasis of the study is on the effect of mixture separation. It is demonstrated that in addition to a mid-frequency (“resonance”) regime, as discovered in the author's previous works [Kosyanchuk et al., “Numerical simulation of novel gas separation effect in microchannel with a series of oscillating barriers,” Microfluid. Nanofluid. 21, 116 (2017) and Kosyanchuk and Pozhalostin, “Non-stationary rarefied gas flow in a plane channel with a series of oscillating barriers,” Eur. J. Mech.-B/Fluids 92, 90–99 (2022)], two other enhanced separation regimes at very low and at very high oscillation frequencies are present. It is also demonstrated that the effect in the mid-frequency regime degrades with decreasing Knudsen number and is almost absent for Kn values around 0.1. The effect in the high-frequency regime is shown to be dictated both by the high frequency of barrier oscillations and by the high speed of barrier motion, and it is shown that with decreasing Knudsen number, the impact of barriers speed becomes dominant. The effect in the low-frequency regime is present for all Knudsen numbers and significantly depends on the phases of barrier motion, which is not observed in other regimes. The separation factor in the low-frequency regime also increases with the number of barriers but only up to the level of molecular diffusion. It was also shown that in the low-frequency regime, there is a trade-off between the separation factor and the gas flow rate.

Simulation of Electron Beam Emission in Argon–Neon Mixture Pinch Using the Nonrelativistic 6-D Valsov–Maxwell System Solved by the Forward Semi-Lagrangian Approach

The 6-D Vlasov–Maxwell equations in the cylindrical coordinates have been solved to calculate the electron beam emission from mixtures of argon and neon. The forward semi-Lagrangian approach was used for solutions. The simulation of the electron velocity field has shown that at the early stage of the pinch evolution of a 4-mbar 90% Ar–10% Ne mixture, the sausage instabilities began to develop from the top parts of the pinch due to bigger $B_{\theta }$ with respect to $B_{z}$ . In the turbulence regions, the electrons could accelerate up to speeds of $905 \times 10^{5}$ and $2387.5 \times 10^{5} \,\,{\text {m}}/{\text {s}}$ at 90.9 and 181.82 ns, respectively. It has been observed that in the high turbulence region, $E_{z}=-2.04\times {10}^{7}\,\,{\text {V}}/{\text {m}}$ , while in the weak turbulence region, $E_{z}=-1.46\times {10}^{7}\,\,\text {V}/{\text {m}}$ . Increasing the neon percentage in the mixture changed the turbulence regions and the upstream and downstream emissions.

Oscillatory Couette flow of rarefied binary gas mixtures

The oscillatory Couette flow of binary gas mixtures is numerically investigated on the basis of the McCormack model. The dependence of the velocity and shear stress amplitudes and the penetration depth on the gas rarefaction and the oscillation parameters is studied numerically. Two typical mixtures of noble gases, i.e., a neon–argon (Ne–Ar) mixture with a molecular mass ratio less than 2 and a helium–xeon (He–Xe) mixture with a molecular mass ratio of about 32, are considered to explore the influences of the molecular mass ratio and molar concentration. It is found that the Ne–Ar mixture exhibits similar behavior with a single gas, while significant deviations can be observed between a single gas and the He–Xe mixture. Particularly when the gases are in the transitional and near-continuum regimes and the oscillation frequency is high, the amplitudes of velocity and shear stress for the He–Xe mixture vary non-monotonically between the plates as the molar concentration of the light species He exceeds 50% due to the oscillation superposition of the two species. These findings are helpful to design the structure of micro-electromechanical devices.

Equations of State for the Thermodynamic Properties of Binary Mixtures for Helium-4, Neon, and Argon

Based on the conceptual design reports for the Future Circular Collider cryogenic system, the need for more accurate thermodynamic property models of cryogenic mixtures of noble gases was identified. Both academic institutes and industries have identified the lack of a reliable equation of state for mixtures used at very low temperatures. Detailed cryogenic architecture modeling and design cannot be carried out without accurate fluid properties. Therefore, the helium–neon equation was the first goal of this work, and it was further extended to other fluids beneficial for scientific and industrial applications beyond the particle physics needs. The properties of the noble gas mixtures of helium–neon, neon–argon, and helium–argon are accurately modeled with the equations of state explicit in the Helmholtz energy.

Investigation of E–H mode transition in magnetic-pole-enhanced inductively coupled neon–argon mixture plasma

In this paper, E–H mode transition in magnetic-pole-enhanced inductively coupled neon–argon mixture plasma is investigated in terms of fundamental plasma parameters as a function of argon fraction (0%–100%), operating pressure (1 Pa, 5 Pa, 10 Pa and 50 Pa), and radio frequency (RF) power (5–100 W). An RF compensated Langmuir probe and optical emission spectroscopy are used for the diagnostics of the plasma under study. Owing to the lower ionization potential and higher collision cross-section of argon, when its fraction in the discharge is increased, the mode transition occurs at lower RF power; i.e. for 0% argon and 1 Pa pressure, the threshold power of the E–H mode transition is 65 W, which reduces to 20 W when the argon fraction is increased. The electron density increases with the argon fraction at a fixed pressure, whereas the temperature decreases with the argon fraction. The relaxation length of the low-energy electrons increases, and decreases for high-energy electrons with argon fraction, due to the Ramseur effect. However, the relaxation length of both groups of electrons decreases with pressure due to reduction in the mean free path. The electron energy probability function (EEPF) profiles are non-Maxwellian in E-mode, attributable to the non-local electron kinetics in this mode; however, they evolve to Maxwellian distribution when the discharge transforms to H-mode due to lower electron temperature and higher electron density in H-mode. The tail of the measured EEPFs is found to deplete in both E- and H-modes when the argon fraction in the discharge is increased, because argon has a much lower excitation potential (11.5 eV) than neon (16.6 eV).

Observation and Investigation of “Reverse Breakdown” in a Discharge Tube

A discharge operating in a 80-cm-long discharge tube with an inner diameter of 15 mm, filled with a 3 : 1 neon–argon mixture at a pressure of 1 Torr, was investigated experimentally. Square voltage pulses with a period of 1 s were supplied to one of the tube electrodes, the second electrode being ungrounded. The initial stage of breakdown—the primary breakdown between the high-voltage (active) electrode and the tube wall, accompanied by the propagation of the prebreakdown ionization wave—was the same as in the conventional scheme with a grounded low-voltage electrode. Since the discharge gap was not closed, the discharge was not ignited. An essentially new effect was observed after the end of the voltage pulse. After a certain time interval, voltage spikes of opposite polarity, the amplitude and shape of which were close to those observed during the primary breakdown, appeared in the voltage and current waveforms of the active electrode. Simultaneously, a radiation pulse from the region adjacent to the active electrode was observed and an ionization wave began to propagate toward the second electrode. This work is dedicated to investigating this effect (which was named “reverse breakdown”) and analyzing its mechanism. A conclusion is made on the similarity of this phenomenon to the processes occurring in atmospheric-pressure dielectric barrier discharges.

Physical proprieties of DC glow discharges in a neon–argon gas mixture

This paper reports a detailed study of 90% Ne – 10% Ar gas mixture DC glow discharge at low pressure, wherein 15 chemical reactions are considered. The second-order fluid model is used. The parameters of particle transport and their rate coefficients strictly depend on mean electron energy. In the framework of the local electric field approximation, we have developed an analytical expression of the drift velocity of positive argon ions in a neon gas [Formula: see text], which is in good agreement with the experimental results, and serves to give best results than the results obtained using [Formula: see text] that exist in the literature. The results show that the argon ion density is more important than the neon ion density despite the presence of more constant background neon gas density in the mixture. The current density reaches 0.1729 mA/cm2 for 250 V applied potential under 2 Torr pressure in a gas mixture. The spatio-temporal evolution of both electric and energetic characteristics, as well as their spatial distribution in the steady state, are shown and discussed. The maximum value of the neon metastable atom density is 4.54957 × 108 cm−3, and for argon metastable atom density is 5.4689 × 108 cm−3. The model is verified experimentally and theoretically in the particular case.

Validation of the van der Waals broadening method for the determination of gas temperature in microwave discharges sustained in argon–neon mixtures

Gas temperature is a key parameter to understand the processes that take place in a plasma because this temperature is related to the energy of the heavy plasmas particles which participate in the atomization of molecules and the formation of radicals from the substances introduced into the discharges. The method for the measurement of gas temperature in argon-helium plasma at atmospheric pressure, using the van der Waals broadening of spectral atomic lines, is adapted for the case of argon–neon mixtures. The Ar I lines 425.9 nm and 603.2 nm are determined as recommendable for such measurements, especially when the use of OH radicals is difficult or the contribution of these radicals to the plasma pollution is to be avoided.

Binary Diffusion Coefficient Data of Various Gas Systems Determined Using a Loschmidt Cell and Holographic Interferometry

The paper reports on binary diffusion coefficient data for the gaseous systems argon–neon, krypton–helium, ammonia–helium, nitrous oxide–nitrogen, and propane–helium measured using a Loschmidt cell combined with holographic interferometry between (293.15 and 353.15) K as well as between (1 and 10) bar. The investigations on the noble gas systems aimed to validate the measurement apparatus by comparing the binary diffusion coefficients measured as a function of temperature and pressure with theoretical data. In previous studies, it was already shown that the raw concentration-dependent data measured with the applied setup are affected by systematic effects if pure gases are used prior to the diffusion process. Hence, the concentration-dependent measurement data were processed to obtain averaged binary diffusion coefficients at a mean mole fraction of 0.5. The data for the molecular gas systems complete literature data on little investigated systems of technical interest and point out the capabilities of the applied measurement apparatus. Further experimental data are reported for the systems argon–helium, krypton–argon, krypton–neon, xenon–helium, xenon–krypton, nitrous oxide–carbon dioxide, and propane–carbon dioxide at 293.15 K, 2 bar, and a mean mole fraction of 0.5.

Measurement of Binary Diffusion Coefficients for Neon–Argon Gas Mixtures Using a Loschmidt Cell Combined with Holographic Interferometry

The paper reports on experimental binary diffusion coefficient data of neon–argon gas mixtures. Measurements were performed in the temperature range between 293.15 K and 333.15 K and for pressures between 1 bar and 10 bar over almost the whole composition range using a Loschmidt diffusion cell combined with holographic interferometry. The thermostated Loschmidt cell is divided into two half-cells, which can be separated and connected by a sliding plate. Prior to the measurements, two different pure gases are filled into the two half-cells. After starting the diffusion process, the temporal change of the partial molar densities, or rather of the refractive index of the gases, is detected in both half-cells using two holographic interferometers. With this apparatus, the temperature, pressure, and concentration dependence of the binary diffusion coefficient can be determined. The relative uncertainty of a diffusion measurement is between 0.4 % and 1.4 % depending on the pressure. The experimental data are compared with data from the literature and with new theoretical data based on quantum-mechanical ab initio calculations combined with the kinetic theory of gases. Due to a systematic error, the concentration dependence determined in the upper half-cell shows deviations from the theoretical values and from most of the literature data. The concentration, temperature, and pressure dependence obtained from the data from the lower half-cell, however, are in very good agreement with available data. The product of the binary gas diffusion coefficient and the molar density of the gas mixture shows no significant dependence on pressure for the studied neon–argon noble gas system.

Kinetic and thermodynamic treatments of a neutral binary gas mixture affected by a nonlinear thermal radiation field

In the present study, the kinetic and the irreversible thermodynamic properties of a binary gas mixture, under the influence of a thermal radiation field, are presented from the molecular viewpoint. In a frame comoving with the fluid, the Bhatnagar–Gross–Krook model of the kinetic equation is analytically applied, using the Liu–Lees model. We apply the moment method to follow the behavior of the macroscopic properties of the binary gas mixture, such as the temperature and the concentration. The distinction and comparisons between the perturbed and equilibrium distribution functions are illustrated for each gas mixture component. From the viewpoint of the linear theory of irreversible thermodynamics we obtain the entropy, entropy flux, entropy production, thermodynamic forces, and kinetic coefficients. We verify the second law of thermodynamics and celebrated Onsager’s reciprocity relation for the system. The ratios between the different contributions of the internal energy changes, based upon the total derivatives of the extensive parameters, are estimated via Gibbs’ formula. The results are applied to the argon–neon binary gas mixture, for various values of both the molar fraction parameters and radiation field intensity. Graphics illustrating the calculated variables are drawn to predict their behavior and the results are discussed.

A Loschmidt cell combined with holographic interferometry for binary diffusion experiments in gas mixtures including first measurements on the argon–neon system

A new variant of the Loschmidt technique has been developed for measuring binary diffusion coefficients in gas mixtures in a temperature range from 10 to 80 °C and for pressures between 0.1 and 1 MPa. The two half cells of the thermostatted diffusion cell have a rectangular cross section and are fixed one upon the other. They can be connected and separated by means of a sliding plate provided with a pneumatically operated seal. The concentration in both half cells is determined simultaneously during the diffusion process using an optical system for holographic interferometry for each. The change in the refractive index results in an interference pattern which is recorded as a function of time. The concentrations of the diffusing components are derived by means of the Lorentz–Lorenz equation. The binary diffusion coefficients are calculated via the integrated ideal diffusion equation for the complete mole fraction range performing only a unique diffusion experiment. The performance of the apparatus is demonstrated on first measurements on the argon–neon system at 293.15 K. Separate refractive index measurements are carried out leading to values for the first refractivity virial coefficient of the pure gases with an estimated uncertainty of ±0.1%. This low uncertainty is required for the aimed uncertainty of ±0.5…1% for the diffusion measurements to determine the concentration and density dependences of the binary diffusion coefficient.

Calculations of the thermophysical properties of binary mixtures of noble gases at low density from ab initio potentials

Interaction potentials determined ab initio from quantum mechanics were used to calculate the thermophysical properties of six binary mixtures of noble gases: helium–neon, helium–argon, helium–krypton, neon–argon, neon–krypton and argon–krypton. From the ab initio potentials, the second pressure virial coefficient, the binary diffusion coefficient and the thermal diffusion factor were computed for the considered binary mixtures at low density in the temperature range 100–5000 K employing well-established formulas in statistical thermodynamics and the kinetic theory of dilute gases. In all cases, while not as good as that for pure noble gases, close agreement between experimental data and the theoretically calculated values shows that ab initio potentials are reliable for the calculation of accurate thermophysical properties of binary mixtures of noble gases over a wide temperature range.

Excitation dynamics of micro-structured atmospheric pressure plasma arrays

The spatial dynamics of the optical emission from an array of 50 times 50 individual microcavity plasma devices is investigated. The array is operated in argon and argon–neon mixtures close to atmospheric pressure with an ac voltage. The optical emission is analysed with phase and space resolution. It has been found that the emission is not continuous over the entire ac period, but occurs once per half period. Each of the observed emission phases shows a self-pulsing of the discharge, with several bursts of emission of fixed width and repetition rate. The number of emission bursts depends on applied voltage and frequency. Spatially resolved measurements prove that the emission bursts are formed by overlapping emission pulses from single discharge cavities. Intensity differences between positive and negative half-wave can be interpreted through spatially resolved measurements of single discharge cavities.

Prediction of transport properties of pure noble gases and some of their binary mixtures by ab initio calculations

The ab initio potentials of kinetic theory are used to calculate viscosity and thermal conductivity of pure helium-4, neon, argon, krypton, and xenon over the temperature range from 100 K to 5000 K at zero-density. The viscosity and thermal conductivity of binary mixtures of noble gases like helium–neon, helium–argon, neon–argon, argon–krypton, and argon–xenon are also obtained by ab initio calculations for temperature between 100 K and 5000 K at zero-density. The results of viscosity and thermal conductivity, both for pure noble gases and their binary mixtures are in good agreement with that of the literature. It is concluded that the ab initio calculations lead to a quantitative prediction of viscosity and thermal conductivity of pure noble gases and their binary mixtures.

Infrared spectra, structure and bonding in the LiO2, LiO2Li, LiO and Li2O molecules in solid neon

Laser-ablated lithium atoms react with oxygen molecules, as do thermal lithium atoms, to form the LiO2 and LiO2Li ionic molecules. In addition excess energy associated with the laser ablation process fosters the endothermic reaction to give LiO and ultimately Li2O, which form in higher yield from the analogous N2O reactions. The subject molecules were trapped in solid neon and identified by isotopic shifts, comparison with earlier argon and nitrogen matrix results, and DFT frequency calculations. The observed neon–argon matrix shifts follow the molecular polarities. Molecular orbitals from theoretical analysis show the highly ionic nature of the electron distribution in the LiO2 and LiO2Li molecules.

Molecular dynamic simulations of some thermodynamic properties of mixtures of argon with neon, krypton, and xenon using two-body and three-body interaction potentials

Molecular dynamics (MD) has been performed to compute the pressure and internal energy of binary mixtures of argon–neon, argon–krypton, and argon–xenon at different temperatures and compositions using two-body Hartree–Fock dispersion-like (HFD-like), total (two-body + three-body) HFD-like, and Lennard–Jones (LJ) potentials. The results are in a good overall agreement with the experimental data. To elucidate the role of three-body interactions on the thermodynamic properties of the studied mixtures, we have incorporated Wang and Sadus method into MD simulations performed using density-dependent two-body HFD-like potentials. Much better results for pressure have been obtained at high densities using the effective LJ potential. For the second virial coefficient, the HFD-like potential is a better choice. Since a little attention has been paid to the qualitative analysis of RDF in the liquid mixtures so far, we have also analyzed the variation of radial distribution function (RDF) of the mixtures with density and composition.

Heat flux between parallel plates through a binary gaseous mixture over the whole range of the Knudsen number

The heat flux problem for a binary gaseous mixture confined between two parallel plates with different temperatures is studied on the basis of the McCormack kinetic model equation, which was solved by the discrete velocity method. The calculations were carried out for three mixtures of noble gases: neon–argon, helium–argon and helium–xenon. The heat flux and distributions of temperature, density and concentration were calculated for several values of rarefaction in the range from 0.01 to 40 and for three values of the concentration: 0.1 , 0.5 and 0.9 . The numerical data together with an analytical solution based on the temperature jump boundary condition cover the whole range of the gas rarefaction beginning from the free-molecular regime to the hydrodynamic one. It was shown that the heat flux significantly depends on the intermolecular interaction law.

Measurements of Stark widths and shifts of Ne I lines using degenerate four-wave mixing and Thomson scattering methods

We report on measurements of Stark widths and shifts of four prominent Ne I lines of the 3s,3s′-3p transition arrays. The measurements were performed in an atmospheric-pressure arc discharge operated in argon–neon gas mixture. Sub-Doppler degenerate four-wave mixing technique was used to measure the line profiles, while Thomson scattering yielded the plasma parameters: electron density, n e = (0 .53–1 .33) × 10 23 m − 3 , and electron temperature, T e = 10,200–20,900 K. The measured profiles are symmetric within the uncertainty limits. The experimental Stark widths and shifts are compared with results of other experiments and theoretical calculations.