Binary Mixtures Of Noble Gases Research Articles

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.

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.

Emission of noble gases and their mixtures with lithium excited by the products of the 6Li(n,α)3H nuclear reaction

AbstractResearch results of luminescence spectra of noble gases and Ar–Xe, Ar–Kr, and Kr–Xe mixtures under the excitation by products of nuclear reaction in the core of a stationary nuclear reactor with 0.87 × 1014 n/cm2s thermal neutron flux are described in the article. The emission spectra of noble gases are similar to the obtained spectrum under the excitation by the 40Ar+7 ion beam from the DC-60 accelerator. Bands in spectra of the binary mixtures of noble gases are connected with the radiation on heteronuclear ion molecule transitions. The appearance of the lines of alkali metal atoms at the temperature increase of gas chamber is explained by sputtering of the lithium layer via nuclear reaction products as well as ionized and excited particles of the buffer gas.

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.

Adsorption and separation of binary mixtures of noble gases on single-walled carbon nanotube bundles

Adsorption and separation of binary mixtures of noble gases including Argon (Ar), Krypton (Kr), and Xenon (Xe) on (10,10) single-walled carbon nanotube (SWCNT) bundles is simulated by extensive equilibrium molecular dynamics (MD). Adsorption energies, diffusion coefficients, activation energies, and radial distribution functions (RDFs) were calculated to address the thermodynamics, transport and structural properties of adsorption process. The simulation results of exposing Ar–Kr, Ar–Xe, and Kr–Xe mixtures on (10,10) SWCNT bundles at temperatures of 75, 150, and 300 K, show that amount of adsorption is strongly influenced by the applied temperature. On the other hand, RDF plots show obviously that separation of binary gaseous mixture is occurred, where the heavier noble gas is adsorbed more than the lighter one in a selective manner by bundle. It is seen that the increase in the applied temperature results in more separation. These findings provide us a possible application of carbon nanotubes (CNTs) as efficient nanomaterials for separation and storage of gas mixtures.

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.

Gaseous mixture flow between two parallel plates in the whole range of the gas rarefaction

The flow of binary gaseous mixtures between two parallel plates driven by gradients of pressure, temperature and concentration is studied, based on the McCormack model of the Boltzmann equation. The coupled kinetic equations are solved numerically by the discrete velocity method. The mass flow, the heat flux and the diffusion flux, which are the mixture quantities of practical importance, are expressed in terms of the so-called thermodynamic fluxes. The latter are written in a form that allows us to verify the Onsager–Casimir reciprocity relations. In addition, analytical expressions for these quantities are derived in the limit case of the hydrodynamic regime. Thus, the numerical solution together with these expressions provides the solution in the whole range of the gas rarefaction. The influence of the intermolecular interaction potential is also investigated by comparing the results for the rigid sphere model with those for a realistic potential. Numerical results are presented for two binary mixtures of noble gases (Ne–Ar and He–Xe) for various values of the molar concentrations.

Shock structure near a wall in pure inert gas and in binary inert-gas mixtures

The shock-wave structure close to a wall in pure argon and binary mixtures of noble gases (argon–helium, xenon–helium) is investigated experimentally and numerically in the shock-wave Mach-number range 2·24 ≤ Ms ≤ 9.21. Measured and calculated density profiles are compared, and some conclusions are drawn about the accommodation at the wall and the intermolecular force potential.For binary gas mixtures only a few results are presented. Weak argon signals of the electron-beam-luminescence method on the experimental side and the computer time needed for the numerical simulation allowed the treatment of a few parameter combinations only.

Index of authors and papers

A new set of isotopic thermal diffusion factors for Ar, Kr and Xe is reported. The data have been obtained from thermal diffusion column measurements in a column previously calibrated with Ne gas, and complete the αT data for the binary mixtures of noble gases given previously. The results lead to the conclusion that the thermal diffusion properties of the noble gases and their mixtures are well described by the law of corresponding states first proposed by Kestin, Ro and Wakeham. It is also concluded that the calibration technique used makes the thermal diffusion column a valuable instrument for the determination of the thermal diffusion factors of isotopic and non-isotopic dilute gas mixtures.

Photon-echo studies of collisional relaxation in weakly ionized noble-gas mixtures

Photon-echo relaxation rates are measured in weakly ionized plasmas of binary mixtures of noble gases, in which the photon echo generated on a transition in one noble-gas species is damped primarily by atoms of the second species. The special cases of pure krypton and xenon are extensions of previous work in pure helium, neon, and argon. With the exception of mixtures with helium as the perturber, measured relaxation rates are consistent with collisional line-broadening calculations.

Variational theory of phase separation in binary liquid mixtures

It is shown that a double Yukawa potential provides a good physical representation for pair potentials in molecular fluids and that its use greatly simplifies variational calculations based on the Percus–Yevick hard-sphere reference system. The calculations show that for this reference fluid the virial hard-sphere equation of state is preferred to the semiempirical Carnahan–Starling expression. The variational procedure is used to calculate the fluid phase diagrams for two binary noble-gas mixtures.

Isotopic thermal diffusion factors of the noble gases

A new set of isotopic thermal diffusion factors for Ar, Kr and Xe is reported. The data have been obtained from thermal diffusion column measurements in a column previously calibrated with Ne gas, and complete the α T data for the binary mixtures of noble gases given previously. The results lead to the conclusion that the thermal diffusion properties of the noble gases and their mixtures are well described by the law of corresponding states first proposed by Kestin, Ro and Wakeham. It is also concluded that the calibration technique used makes the thermal diffusion column a valuable instrument for the determination of the thermal diffusion factors of isotopic and non-isotopic dilute gas mixtures.

Diffusion coefficients of noble-gas mixtures between 300 K and 1400 K

The diffusion coefficients of all the binary noble-gas mixtures, except Kr-Xe, were measured as a function of temperature between 300 K and 1400 K starting from the cataphoretic segregation in a dc discharge. A discharge tube of quartz glass was developed for this purpose. The measurements were performed mass-spectrometrically. The parameters in two models for the interatomic potential were determined from the temperature dependence of the diffusion coefficient. An excellent fit for both the Lennard-Jones model and the (exp-6) model was obtained over the entire temperature range from 100 K to 1400 K (with an exception for He-Ne); the values of the diffusion coefficient between 100 K and 300 K were determined by Van Heyningen. A value higher than 15 for the parameter α in the (exp-6) model was obtained for all considered gas mixtures.