Polyatomic Gas Mixtures Research Articles

Kinetic theory for mixtures of polyatomic gases of rough spherical molecules

A kinetic theory for a mixture of ν-polyatomic gases of perfectly rough, perfectly elastic, and rigid spherical molecules is developed. A macroscopic state of the mixture is characterized by 16ν+1 fields of partial densities, partial velocities, partial pressure tensors, partial translational heat fluxes, partial rotational heat fluxes, and temperature of the mixture. The generalized laws of Fick, Fourier, and Navier–Stokes are obtained from an iteration method akin to the Maxwellian procedure. As an application, the transport coefficients for binary mixtures of CH4–CF4, CH4–CD4, and CD4–CF4 are determined.

Statistical fluctuations in the ionisation yield of low-energy photons absorbed in polyatomic gases

The statistical fluctuations of the number of ion pairs created by monoenergetic photons in several polyatomic gases and gas mixtures were derived by iterative deconvolution of measured pulse height spectra obtained by means of the proportional counter. The response of the proportional counter to the unit charge (the single-electron spectrum) has been determined precisely, making possible the measurement of the number of electrons created per absorbed photon. W values (mean energy per ion pair), generalised Fano factors and primary ion pair distribution characteristics have been derived as functions of incident photon energy for ten polyatomic gases, mostly alkanes, and two tissue-equivalent gas mixtures. Monoenergetic photons having an energy equal to 0.277 keV (carbon Kalpha line), 1.49 keV (aluminium Kalpha line) and 5.89 keV (55Fe) have been used throughout the experiment. It is shown that the primary distribution of ion pairs in all investigated gases and gas mixtures is asymmetrical and more peaked than the Gaussian distribution for low-energy incident photons, approaching the Gaussian shape for 6 keV photons.

Kinetic theory for the volume viscosity in binary mixtures of polyatomic and noble gases

A kinetic expression for the volume viscosity of binary mixtures of polyatomic and noble gases in terms of effective collision cross sections is derived within the framework of first order Chapman-Enskog theory using an inverse operator method. It is shown that the rotational relaxation rate, which is directly related to the volume viscosity, depends linearly on the composition of the mixture if it is assumed that coupling to higher order polynomials in internal and translational energy may be neglected. This result agrees with earlier predictions.

Thermal conductivity of methane with carbon monoxide

The paper reports the results of new measurements of the thermal conductivity of CH 4-CO mixtures at 27.5°C and up to a pressure of 12 MPa. This further contribution to a growing body of data on the thermal conductivity of binary mixtures of polyatomic gases is analyzed in the same way as was done by the present group in several earlier publications with essentially identical conclusions.

Thermal conductivity of mixtures of polyatomic gases at low and moderate density

The paper discusses the prediction of the thermal conductivity of gas mixtures containing polyatomic components at low and moderate density. The prediction scheme adopted is based upon the rigorous kinetic theory of gases and makes use of other thermophysical properties of the pure gases and binary mixtures in the evaluation of the thermal conductivity. Comparisons with accurate experimental data indicate that only for systems in which the mass ratio of the species is near unity and for which inelastic collisions are rare, is a reliable prediction of the mixture thermal conductivity at low density possible. On the other hand, the density dependence of the thermal conductivity is quite accurately represented for most systems.

Analytical solutions for infrared-laser-driven diffusion in polyatomic gas mixtures

Analytical solutions for infrared-laser-driven diffusion in polyatomic gas mixtures

Vibrational relaxation times in polyatomic gas mixtures on the validity of the linear mixture rule

The vibrational relaxation times in SO 2Ar and CH 4Ar mixtures have been estimated in the temperature range 300–2000 K. following the SSH-Tanczos method. The inverse relaxation times are found to be non-linear in concentration of the relaxing gas and the deviation from linearity is more pronounced at high temperatures. It is argued that the intramolecular vibration-vibration energy transfer is responsible for such non-linear dependence on concentration.

The thermal conductivity of mixtures of nitrogen with four noble gases at room temperature

The paper presents new, absolute measurements of the thermal conductivity of binary mixtures of nitrogen with four monatomic gases, He, Ne, Ar and Kr. The measurements have been performed at 27.5°C as a function of density within the pressure range 0.9–17 MPa. The experimental data have an estimated accuracy of ±0.3%. The experimental results are interpreted with the aid of the kinetic theory expressions of Monchick, Pereira and Mason for the thermal conductivity of polyatomic gas mixtures. These first-order formulae prove to be adequate to describe the experimental data within their uncertainty provided that empirical adjustments are made to the rotational relaxation collision numbers and collision integral ratios occuring in them. It is suggested that more accurate kinetic theory formulae would allow such quantities to be derived with greater precision and physical signifincance.

The inelastic contributions to transport collision integrals in the infinite-order sudden approximation

The transport collision integrals of the Wang Chang and Uhlenbeck kinetic theory of polyatomic gases have been evaluated for an anisotropic intermolecular pair potential model for the He-CO2 interaction. The calculations have made use of the infinite-order sudden approximation to evaluate the state-to-state differential cross-sections, but otherwise involve no approximations. The results indicate that some earlier approximate methods for the evaluation of the collision integrals are quantiatively correct, although they are given a new interpretation. In particular, the simplifications introduced by Mason and Monchick are shown to yield essentially the same collision integral for viscosity as the more exact treatment. On the other hand, several long established procedures for treating the transport properties of polyatomic gases and gas mixtures are shown to be significantly in error. Specifically the diffusion coefficient for internal energy is some 10 per cent higher than the diffusion coefficient for ma...

Kinetic modeling of polyatomic gas mixtures

Abstract A generalized Gross-Jackson procedure for constructing linearized kinetic models is proposed for polyatomic gas mixtures. These models are examined from the point of view of the consistency with the conservation laws, the H-theorem and hydrodynamics. It is shown that a third-order collision model, which takes the relaxation of momentum and energy fluxes into account, is necessary for a consistent hydrodynamic description. A simple non-linear BGK model, which satisfies the conservation laws and takes account of the velocity and energy relaxation processes is also proposed. Its linearized version is shown to be contained in the second-order collision description obtained by the Gross-Jackson procedure.

The Thermal Conductivity of Mixtures of Hydrogen with the Monatomic Gases

AbstractThe paper presents experimental results for the thermal conductivity of hydrogen with the three monatomic gases: neon, argon, and krypton. The measurements have been carried out in a transient hot‐wire apparatus at 35°C within the pressure range 2–9 MPa. The accuracy of the thermal conductivity data is estimated as one of ± 0.2%. — Intermodular pair potentials for the interaction of hydrogen with the monatomic gases, obtained from molecular beam and spectroscopic studies, provide only a moderately good representation of the experimental data in the limit of zero density. The discrepancies are attributed in part to the limitations of the available kinetic theory formulae for the thermal conductivity of polyatomic gas mixtures. The density dependence of the thermal conductivity of the mixtures is well described by a calculation scheme based on the modified Enskog theory.

Waldmann-Snider Collision Integrals for Mixtures of Polyatomic Gases Exact and Approximate Relations

Collision brackets of the linearized Waldmann-Snider collision superoperator are studied for mixtures of polyatomic gases. Properties following f r om symmetries of molecular interaction and collisional conservation laws are discussed. For a complete system of expansion tensors bracket symbol expressions for effective cross sections are given which generalize the Chapman-Cowling Ω-integrals. Exact relations between effective cross sections are derived. Approximate relations which hold for molecules with small nonsphericity and elastic scattering are also given

Composition dependence of the thermal conductivity of dense gas mixtures

In this paper we present a method for predicting the composition dependence of the thermal conductivity of dense gas mixtures. The method requires the knowledge of the thermal conductivities of the pure component gases at high density, of the zero-density values of the thermal conductivities both of the pure components and of one binary mixture, and of the virial coefficients Bij and their derivatives dBijdT. The Thorne-Enskog hard-sphere theory, after a minor correction for consistency with the Onsager reciprocal relations, is then used as an interpolating formula between the end points. An extension of the method to mixtures of dense polyatomic gases is also provided. For these gases, the transport of internal energy is assumed to be entirely kinetic (diffusion mechanism). The method has been applied to the three binary monatomic systems He-Ne, Ne-Ar and He-Ar at 30°C and up to a pressure of 20 MPa. The calculated values of the thermal conductivity of these systems agree with the best available experimental data to within the uncertainty of the latter (about 2%). No comparison was performed for the polyatomic species owing to the unavailability of reliable experimental data.

On the theory of the viscomagnetic diffusion flux (bulk effect)

For a streaming polyatomic gas mixture in an external magnetic field, a diffusion flux arises perpendicular to both flow and field directions. The viscomagnetic diffusion flux is treated by extending the inverse operator technique previously used for the calculation of first order Chapman-Enskog effects to second order Chapman-Enskog effects. An expression for the transverse viscomagnetic concentration difference for a mixture of a polyatomic gas and a noble gas is given in terms of Waldmann-Snider collision integrals. For a N 2-Ar mixture the magnitude of the effect is estimated.

Prediction of propagating laminar flames in methane, oxygen, nitrogen mixtures

An unsteady-state, one-dimensional, flame propagation model was used to study the characteristics of methane oxygen and methane air flames. The transformed species and energy concervation equations were solved with a numerical computer solution proposed by Spalding [1]. The diffusion model employed is based on the Chapman-Enskog kinetic theory and the development of Mason, Monchick and co-workers [2–6] for polyatomic gas mixtures containing one polar component. A methane oxygen reaction mechanism consisting of 29 elementary reactions was used in the flame model. The effects of equivalence ratio, pressure, initial temperature, and transport coefficients on the flame velocity, flame thickness, temperature profile, and concentration profiles were investigated for a series of methane air flames. Many of the model predictions were compared with experimental data. Some of the chemical kinetic data were selected or slightly modified in order to improve the agreement between calculated and measured values, which was good, when the final set of rate coefficients was used. The relative importance of each of the 29 elementary reactions was examined. The concentrations of the radicals H and OH were major factors in determination of flame characteristics.

Thermal diffusion in binary mixtures of linear molecules

The composition dependence of the thermal diffusion factors alpha T of the binary gas mixtures NO-CO, N2-C2H2, NO-C2H2 and CO-C2H2 have been studied by the swing separator method. All these systems have the special feature that the gases involved are linear molecules so that interpretation of the data in terms of inelastic theories is feasible. Attempts have been made to interpret the data by using both elastic and inelastic theories of thermal diffusion. The results indicate the influence of inelastic collisions on thermal diffusion in polyatomic gas mixtures. However, the inelastic theories available cannot explain satisfactorily the experimental data. It has been suggested that a more sophisticated theory involving more rigorously defined inelastic cross sections will be necessary for a proper interpretation to be made of the effects of inelastic collisions on thermal diffusion.

Kinetic Theory of Thermal Diffusion in a Magnetic Field

A kinetic theory of thermal diffusion in binary mixtures of polyatomic gases in an external homogeneous magnetic field is presented. It is based on the transport-relaxation equations obtained from the linearized Waldmann-Snider equation with the moment method. Under the assumption that the Kagan polarization is the decisive nonequilibrium alignment an expression for the thermal diffusion tensor in terms of Waldmann-Snider collision integrals is derived. In particular, mixtures of linear molecules with noble gas atoms are treated and the mole fraction dependence of the transverse effect is studied. As examples, the mixtures N2-Ar and N2-Ne are considered. Finally the order of magnitude of the transverse Senftleben-Beenakker effect of diffusion is estimated

Statistical collision model for Monte Carlo simulation of polyatomic gas mixture

A formal derivation of the direct simulation technique of solution to the Boltzmann equation for a mixture of polyatomic gases is presented. A phenomenological model for binary collisions in a gas mixture having continuous internal energy is then developed. The model is based on the relaxation concept applied to individual collisions and interpreted statistically in a manner suitable to Monte Carlo simulation of rarefied flows. The model has a high degree of flexibility and requires little more computing time per collision than the hard-sphere model of monatomic gas. Sample calculations of a rotationally relaxing gas are compared to loaded-sphere and rough-sphere results.

Thermal diffusion in isotopic mixtures of polyatomic gases. I. The thermal diffusion coefficient

Perturbation techniques are used to derive an analytical expression for the thermal diffusion coefficient for isotopic, polyatomic gas mixtures. The expansions isolate the contributions to the thermal diffusion coefficient which are subject to isotopic variation and elucidate the effect of external fields on the phenomena.

Temperature and specie concentration measurements in a flow field

The Raman scattering technique and its application to the diagnostics of flow fields is discussed. It is shown experimentally that the technique is capable of providing not only specie concentration and their temperature in a quiescent mixture of polyatomic gases, but also in a flow field. It is further shown that due to the extremely fast Raman transition, utilizing the simple high laser power pulse technique, the existence of transient fluctuations in the flow field both in terms of specie concentration and temperature can easily be detected. Furthermore, average type data as obtained using the Chromatographie methods can also be obtained without difficulties.