Noble Gas Mixtures Research Articles

Theoretical investigation of ZIFs as adsorbents or membranes for separating noble gas mixtures: applying a newer method for predicting performances

Zeolitic imidazolate frameworks (ZIFs) possess similar topological structures with zeolites, however a number of characteristic properties of the ZIFs, such as easy incorporation of desired linkers to their structures, tunable pore sizes, high porosities, and large surface areas make them better option for targeted engineering applications. In this respect, cheaper, highly efficient, and selective separation of syngas mixtures using ZIFs has been already shown in the literature. Separation and purification of noble gases, on the other hand, have been achieved using energy demanding cryogenic distillation of air and currently we know little about noble gas separation performances of the ZIFs. Replacing energy intensive gas separation techniques with adsorbent and/or membrane based separation technologies, indeed, have been motivated for decreasing the operational costs, price of the pure noble gases, as well as opening new application areas for the noble gases. In this respect, we theoretically investigate Xe/Kr and Xe/Ar separation performances of eight ZIFs, namely ZIF-6, ZIF-11, ZIF-60, ZIF-67, ZIF-69, ZIF-78, ZIF-79, and ZIF-81 using Grand Canonical Monte Carlo and Molecular Dynamics simulations and calculate Xe permeability and permeation selectivity using a newer method suggested previously by our group. While ZIF-11 shows significant Xe uptake from the noble gas mixtures, ZIF-81 and ZIF-79 show exceptional Xe adsorption selectivities for two gas mixtures at low pressures, 22.5 and 21 for the Xe/Kr and 128 and 120 for the Xe/Ar mixture, respectively. ZIF-69 and ZIF-79 show high Xe permeability (4. $$2\times 1$$ 0 $$^5$$ and 3. $$2\times 1$$ 0 $$^5$$ Barrers) as well as high Xe permeation selectivity (17.35 and 15.85) for the Xe/Ar mixture at 2 bar feed gas pressure. For the Xe/Kr mixture, on the other hand, we observe high Xe permeability and moderate Xe permeation selectivity, especially at low pressures. Comparing with the limited literature available, these ZIFs show promise for selective separation of Xe from its binary mixtures of Kr and Ar at room temperature. We also compare the permeability and permeation selectivity predictions using different approaches, namely the new method and the approximate approach which is commonly used in the literature. Results reveal significant deviations of the approximate approach with respect to the new method, especially for the permeability calculations. Thus, using the new method for determining membrane performances is highly suggested.

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.

Gas mixture flow, diffusion, and heat transfer in a long tube at moderately small Knudsen numbers

The binary gas mixture flow, diffusion, and heat transfer through a long tube in the near-continuum regime (moderately small Knudsen numbers) are analyzed. The system of linearized third-order moment equations, obtained by Grad’s method, is used. An expression for the total mass flux of a binary gas mixture is deduced by using the extension of the procedure, proposed in the work by Zhdanov [“Slip and barodiffusion phenomena in slow flows of a gas mixture,” Phys. Rev. E 95, 033106 (2017)] for the study of slip phenomena in slow flows of a gas mixture. Relations for diffusion and heat fluxes are determined from the initial system of moment equations, averaged over the channel cross section, and supplied with several moments of the distribution function at the channel wall found with the modified Maxwell method. Analytical formulas for kinetic coefficients of the Onsager matrix, which connect averaged fluxes and gradients of the corresponding thermodynamic quantities, are obtained. It is shown that the employed approach automatically ensures the validity of the reciprocal relations for the cross terms in the Onsager matrix. The results of calculations of the derived kinetic coefficients for several binary mixtures of noble gases (He–Ar, Ne–Ar, and He–Xe) are presented and compared with numerical data found by the discrete velocity method on the basis of the linearized Boltzmann equation with the McCormack model.

BGK models for inert mixtures: Comparison and applications

<p style='text-indent:20px;'>Consistent BGK models for inert mixtures are compared, first in their kinetic behavior and then versus the hydrodynamic limits that can be derived in different collision-dominated regimes. The comparison is carried out both analytically and numerically, for the latter using an asymptotic preserving semi-Lagrangian scheme for the BGK models. Application to the plane shock wave in a binary mixture of noble gases is also presented.</p>

Transport coefficients of isotopic mixtures of noble gases based on ab initio potentials.

The transport coefficients such as viscosity, thermal conductivity, diffusion and thermal diffusion of neon, argon, krypton, and xenon are computed for a wide range of temperatures taking into consideration their real isotopic compositions. A new concept of isotopic thermal diffusion factor is introduced and calculated. The Chapman-Enskog method based on the 10th order approximation with respect to the Sonine polynomial expansion is applied. Ab initio potentials of interatomic interactions are employed to compute the transport cross-sections as they are part of the coefficient expressions. To study the influence of the isotopic composition, the same transport coefficients have been calculated for the single gases having an average atomic mass. The estimated numerical error of the present results is a function of the temperature and is different for each coefficient. At the room temperature, the relative numerical error of viscosity, thermal conductivity and diffusion coefficient is on the order of 10-6. The numerical error of the thermal diffusion factor affects the fifth decimal digit. The influence of the isotopic composition on viscosity and thermal conductivity depends on the gas species. It is negligible for argon and significant (about 0.02%) for xenon, while neon and krypton are weakly affected by the isotopic composition. The diffusion coefficient for each pair of isotopes differs from the corresponding self-diffusion coefficient by about 3%. The thermal diffusion factor of each isotope differs from the thermal self-diffusion factor in the third decimal digit.

Influence of Vortex Electron Currents on Transport Processes in 2-D Photoplasma of Sodium–Noble Gas Mixtures

This study has been performed for a 2-D fluid model of sodium photoplasma with noble gas mixtures in two-chamber cells. A source of photoexcitation of sodium resonance levels is located in the first (source) chamber. In contrast, plasma in the second (diffusion) chamber is formed due to the transport of charges from the first chamber. The created photoplasma at different excitation rate, gas type, and pressure have been studied. Unlike previous investigations of photoplasma based on the study of the temporal and spatial distributions of plasma parameters, in this research, the transport processes also have been investigated explicitly. The different flux components throughout the cell and the corresponding variations of electron temperature gradient affect the fluxes magnitude and, consequently, the electromotive force (EMF). Generally speaking, the findings from the model contribute to that, for the optimization of photoplasma cells, the study of transport processes must be focused.

Non-equilibrium phenomena in gas mixture flow through a plane channel in near-continuum regime

Non-equilibrium phenomena in the flow of a binary gas mixture between two parallel plates, driven by gradients of the pressure, temperature and concentration, are studied. The phenomenological relationships that describe the energy and mass transfer in the flow of a gas mixture through a channel are analyzed by using methods of the non-equilibrium thermodynamics of discontinuous systems. The solution of the linearized moment equations in the 13-moments approximation of the Grad’s method and the relation for the slip velocity previously found in Zhdanov (Phys. Rev. E95 (2017), 033106) are applied to deduce the expression for the mass-average velocity of the mixture flowing in a plane channel in the near-continuum regime. Expressions for the diffusion and heat fluxes are determined from the initial third-order moment equations for the gas mixture, averaged over the channel cross-section, with the subsequent evaluation of several moments of the distribution function at the channel wall by using the modified Maxwell method. It is shown that the employed approach automatically ensures the validity of the reciprocal relations for the cross terms in the Onsager matrix. Analytical formulas for kinetic coefficients of the Onsager matrix, expressed in terms of known transport coefficients of the gas mixture and slip coefficients at the channel wall, are obtained. The results of calculations of the matrix coefficients for several binary mixtures of noble gases (Ne–Ar and He–Xe) and their comparison with the results of the numerical calculations on the basis of the linearized Boltzmann equation with the McCormack model are presented.

2D simulation of solar/lamp two-chamber photoelectric converter with different sodium–noble gas mixtures

This work is devoted to the numerical analysis of the opportunity to obtain a steady generation of electromotive force (EMF) in a two-chamber gas cell exposed to concentrated solar/lamp radiation. For this purpose, we have carried out 2D simulations of the low-pressure photoplasma in the mixtures of sodium atom vapor and different noble gases and their pressures at different values of photoexcitation rate of resonance levels of Na. Herewith plasma chemistry and transfer of charges and radiation in the volume have been taken into account. It has been established that argon is a better candidate to be used as a buffer gas for photoplasma electric converter based on the obtained plasma parameters and commercial aspects. A parametric study has been carried out for the Na–Ar mixture to investigate the effect of increasing homogeneous photoexcitation rate in the small chamber on plasma parameters and obtained EMF. Another parametric study has been conducted to calculate the output current and electric power at a loaded chain. The results show that EMF could be obtained using the photovoltaic effect in photoplasma for the two-chamber cell. The present paper gives a key to the understanding of the effect of different processes (radiation, chemical, and electric) in the cell with these gas mixtures. The obtained results can be used in projecting a solar photoelectric converter based on a two-chamber device with a mixture of sodium and noble gases.

Transport coefficients of multicomponent mixtures of noble gases based on ab initio potentials: Diffusion coefficients and thermal diffusion factors

Diffusion coefficients and thermal diffusion factors of binary, ternary, and quaternary mixtures of helium, neon, argon, and krypton at low density are computed for wide ranges of temperatures and molar fractions, applying the Chapman–Enskog method. Two definitions of the diffusion coefficients are discussed, and a general relation between them is obtained. Ab initio interatomic potentials are employed in order to calculate the omega-integrals being part of the expression of the reported quantities. The relative numerical errors of the diffusion coefficients do not exceed the value of 5 × 10−5 being even smaller in some cases. The uncertainties of diffusion coefficients due to the interatomic potential vary between 4 × 10−4 and 6 × 10−3. The numerical error and uncertainty due to the potential of the thermal diffusion factors are estimated as 10−4 and 3 × 10−3, respectively. It is shown that the present results for binary mixtures are more accurate than any other available in the literature, while the results for ternary and quaternary mixtures are reported for the first time.

Calculation of fuel temperature profile for heavy water moderated natural uranium oxide fuel using two gas mixture conductance model for noble gas Helium and Xenon

A model for calculation of fuel temperature profile using binary gas mixture of Helium and Xenon for gap gas conductance is proposed here. In this model, the temperature profile of a fuel pencil from fuel centreline to fuel surface has been calculated by taking into account the dilution of Helium gas filled during fuel manufacturing due to accumulation of fission gas Xenon. In this model an explicit calculation of gap gas conductance of binary gas mixture of Helium and Xenon has been carried out. A computer code Fuel Characteristics Calculator (FCCAL) is developed for the model. The phenomena modelled by FCCAL takes into account heat conduction through the fuel pellet, heat transfer from pellet surface to the cladding through the gap gas and heat transfer from cladding to coolant. The binary noble gas mixture model used in FCCAL is an improvement over the parametric model of Lassmann and Pazdera. The results obtained from the code FCCAL is used for fuel temperature calculation in 3-D neutron diffusion solver for the coolant outlet temperature of the core at steady operation at full power. It is found that there is an improvement in calculation time without compromising accuracy with FCCAL.

Runaway dynamics in the DT phase of ITER operations in the presence of massive material injection

A runaway avalanche can result in a conversion of the initial plasma current into a relativistic electron beam in high-current tokamak disruptions. We investigate the effect of massive material injection of deuterium–noble gas mixtures on the coupled dynamics of runaway generation, resistive diffusion of the electric field and temperature evolution during disruptions in the deuterium–tritium phase of ITER operations. We explore the dynamics over a wide range of injected concentrations and find substantial runaway currents, unless the current quench time is intolerably long. The reason is that the cooling associated with the injected material leads to high induced electric fields that, in combination with a significant recombination of hydrogen isotopes, leads to a large avalanche generation. Balancing Ohmic heating and radiation losses provides qualitative insights into the dynamics; however, an accurate modelling of the temperature evolution based on energy balance appears crucial for quantitative predictions.

Design Optimization and Analysis of Thermoacoustic Refrigerators

Thermoacoustic refrigeration, a novel technology, uses eco-friendly gases like helium, air or the mixture of noble gases as working substances in the absence of moving parts. The design, optimization and analysis of thermoacoustic refrigerators using helium and air as oscillating gases are discussed. Pure helium is chosen since it is proven as the best and economical working gas compared to the alternate pure or the mixture of noble gases. Air is chosen since it is abundant in nature and the least cost of the pressurized dry air cylinders. The design optimization strategies discussed in this paper serve as a guide for aspiring researchers in the design and development of thermoacoustic coolers. Cooling power as a function of stack diameter is discussed. Theoretical results of the optimized coolers are compared with DeltaEC simulation results for validation and are in agreement with each other.

Transport coefficients of multi-component mixtures of noble gases based on ab initio potentials: Viscosity and thermal conductivity

The viscosity and thermal conductivity of binary, ternary, and quaternary mixtures of helium, neon, argon, and krypton at low density are computed for wide ranges of temperatures and molar fractions, applying the Chapman–Enskog method. Ab initio interatomic potentials are employed in order to calculate the omega-integrals. The relative numerical errors of the viscosity and thermal conductivity do not exceed 10−6 and 10−5, respectively. The relative uncertainty related to the interatomic potential is about 0.1%. A comparison of the present data with results reported in other papers available in the literature shows a significant improvement of accuracy of the transport coefficients considered here.

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.

УСТАНОВЛЕНИЕ НОРМАТИВОВ ДОПУСТИМЫХ ВЫБРОСОВ СМЕСИ НЕСКОЛЬКИХ РАДИОНУКЛИДОВ В АТМОСФЕРНЫЙ ВОЗДУХ ПРИ НОРМАЛЬНОЙ ЭКСПЛУАТАЦИИ АЭС

The article is focused on the description of the existing order for regulations of standards for permissible and maximum permissible discharges of radioactive pollutants into atmospheric air and (on) discussion of an alternative method for regulations of standards for permissible and maximum permissible discharges, basing on establishment of these standards for a mixture of radioactive materials and not for every radionuclide individually. This method is based on using the radionuclide vector concept and allows to significantly facilitate arrangements of radiation monitoring, to abandon spectrometric methods and to use more simple, cheap and speedy radiometric methods for discharge control. This result corresponds to internationally recognized ALARA principle. The procedure of the establishment of permissible discharge of noble gases mixture for atmospheric discharge of Rostov NPP site is shown in the article as an example. The results of the analysis of noble gases atmospheric discharges of 47 European NPPs with WWER and PWR power units, creation of nuclide vector and application of this vector for calculation of permissible discharge of noble gases mixture for the Rostov NPP are demonstrated.

Separation of Noble-Gas Isotope Mixtures Using Low-Temperature Adsorption

Separation of noble-gas isotope mixtures by low-temperature adsorption was considered. The proposed conceptual diagram of an experimental pressure-swing adsorption unit included a vacuum-insulated vessel for maintaining cryogenic temperatures, temperature- and pressure-control systems, and vacuum equipment. The directions of applied research performed on the unit were defined. Experimental methodology for studying activated carbon adsorbents and adsorption parameters was proposed. The gasmixture isotopic composition was monitored by mass spectrometry during the adsorption.

Strong enhancement of electron-ion recombination induced by free-bound and bound-bound resonance transitions

SynopsisThe role of free-bound and bound-bound resonant nonadiabatic transitions on electron-ion recombination in plasma of noble gas mixtures is studied. A kinetic model of recombination is proposed which includes the energy relaxation in collisions with electrons, resonant and non-resonant electron capture to Rydberg states through collisions of atomic ions with neutral particles, and resonant n → n’ transitions. It is shown that the resonant processes considered may strongly enhance total recombination coefficient even at relatively high degrees of ionization of plasma.

The Role of Clathrate Formation in Europa’s Ocean Composition

Abstract We use a thermodynamic statistical model to evaluate how the composition of Europa’s internal ocean may have been affected by clathrate hydrate formation. Assuming an input of the observed O2 and CO2 from the surface into a mildly acidic ocean (pH < 6), and considering the possibility of contributions by reduced (with CH4 and H2S) or oxidized (CO2-bearing) hydrothermal fluids, we calculate the fractional occupancies in clathrate and deduce the effect on the ocean’s composition. The structure of the clathrate formed, and therefore its density and composition is influenced by the relative amount of O2 compared to the other compounds present. We also include a mixture of noble gases—argon, krypton, and xenon—based on cometary abundances measured at comet 67P and find that the Ar/Kr ratio can be affected by almost two orders of magnitude. In most cases, the formed clathrate is likely to become part of the icy crust, with guest molecules possibly accessible to future in situ measurements by the Europa Clipper and JUICE missions.

Effects of aqueous alteration on primordial noble gases and presolar SiC in the carbonaceous chondrite Tagish Lake

AbstractEffects of aqueous alteration on primordial noble gas carriers were investigated by analyzing noble gases and determining presolar SiC abundances in insoluble organic matter (IOM) from four Tagish Lake meteorite (C2‐ung.) samples that experienced different degrees of aqueous alteration. The samples contained a mixture of primordial noble gases from phase Q and presolar nanodiamonds (HL, P3), SiC (Ne‐E[H]), and graphite (Ne‐E[L]). The second most altered sample (11i) had a ~2–3 times higher Ne‐E concentration than the other samples. The presolar SiC abundances in the samples were determined from NanoSIMS ion images and 11i had a SiC abundance twice that of the other samples. The heterogeneous distribution of SiC grains could be inherited from heterogeneous accretion or parent body alteration could have redistributed SiC grains. Closed system step etching (CSSE) was used to study noble gases in HNO3‐susceptible phases in the most and least altered samples. All Ne‐E carried by presolar SiC grains in the most altered sample was released during CSSE, while only a fraction of the Ne‐E was released from the least altered sample. This increased susceptibility to HNO3 likely represents a step toward degassing. Presolar graphite appears to have been partially degassed during aqueous alteration. Differences in the 4He/36Ar and 20Ne/36Ar ratios in gases released during CSSE could be due to gas release from presolar nanodiamonds, with more He and Ne being released in the more aqueously altered sample. Aqueous alteration changes the properties of presolar grains so that they react similar to phase Q in the laboratory, thereby altering the perceived composition of Q.

Calculation of scalar nuclear spin-spin coupling in a noble-gas mixture

Indirect spin-spin interactions between nuclei bound in a molecule are well-known in nuclear magnetic resonance, but such interactions between unbound atoms are less well studied and are often assumed to be zero. We present the first precision calculation of this interaction between 129Xe and 3He nuclei in a gas. Relativistic, state-of-the-art electronic structure theory is used to compute the scalar coupling constant J(R) and the interatomic potential energy function, V(R), as functions of the Xe-He internuclear distance R. Using virial expansion we find the nuclear spin enhancement factor kappa = -0.0105 +/- 0.0015 in excellent agreement with recent experiments. This interaction is particularly important for precision measurements using nuclear spin co-magnetometers.