A study of the two-bulb method for measuring diffusion coefficients of binary gas mixtures

The concentration dependences of the binary diffusion coefficients of the systems He-Ar and He-O₂ are reported at 300 K and 1 atm pressure. Two independent sets of data, obtained with a two-bulb cell and a shearing-cell of Loschmidt design, agree within the error of measurement. The data for the two-bulb cell were obtained at pressures where Knudsen effects are important. It was found necessary to improve the extrapolation procedure of van Heijningen et al. by using the results of the dusty-gas model as described by Mason et al.     

Mutual (isothermal) diffusion in binary hard-sphere mixtures: The effects of the Onsager reciprocity relations

The mutual diffusion coefficients of the Revised Enskog Theory of van Beijeren and Ernst and the Standard Theory of Thorne are compared. The former theory is consistent with the Onsager Reciprocity Relations while the latter is not. The diffusion constant of the Revised Theory is found to be as much as 30% larger than that predicted by the Standard Theory.     

Unsteady mass and energy transfer in binary gas mixtures

Thermodynamic analysis and a theory of unsteady-state process of thermal diffusion and diffusional thermal effect in gas mixtures are presented. A mathematical model for unsteady mass transfer process in gas mixtures is developed.     

Flow birefringence in binary para hydrogen-noble gas mixtures

Experimental flow birefringence data for para hydrogen-noble gas mixtures at 293 K are presented. The consistency with available data on depolarized Rayleigh line broadening is discussed. The results disagree with recent close coupled calculations by McCourt.     

Kinetic boundary layers in gas mixtures: Systems described by nonlinearly coupled kinetic and hydrodynamic equations and applications to droplet condensation and evaporation

We consider a mixture of heavy vapor molecules and a light carrier gas surrounding a liquid droplet. The vapor is described by a variant of the Klein-Kramers equation, a kinetic equation for Brownian particles moving in a spatially inhomogeneous background; the gas is described by the Navier-Stokes equations; the droplet acts as a heat source due to the released heat of condensation. The exchange of momentum and energy between the constituents of the mixture is taken into account by force terms in the kinetic equation and source terms in the Navier-Stokes equations. These are chosen to obtain maximal agreement with the irreversible thermodynamics of a gas mixture. The structure of the kinetic boundary layer around the sphere is then determined from the self-consistent solution of this set of coupled equations with appropriate boundary conditions at the surface of the sphere. For this purpose the kinetic equation is rewritten as a set of coupled moment equations. A complete set of solutions of these moment equations is constructed by numerical integration inward from the region far away from the droplet, where the background inhomogeneities are small. A technique developed in an earlier paper is used to deal with the severe numerical instability of the moment equations. The solutions so obtained for given temperature and pressure profiles in the gas are then combined linearly in such a way that they obey the boundary conditions at the droplet surface; from this solution source terms for the Navier-Stokes equation of the gas are constructed and used to determine improved temperature and pressure profiles for the background gas. For not too large temperature differences between the droplet and the gas at infinity, self-consistency is reached after a few iterations. The method is applied to the condensation of droplets from a supersaturated vapor, where small but significant corrections to an earlier, not fully consistent version of the theory are found, as well as to strong evaporation of droplets under the influence of an external heat source, where corrections of up to 40 % are obtained.     

Thermal conduction and thermal diffusion in dilute polyatomic gas mixtures

A novel theoretical basis for the evaluation of the thermal conductivity and the thermal diffusion ratios of dilute polyatomic gas mixtures is derived within the semi-classical isotropic kinetic theory. New expressions for species diffusion coefficients, thermal diffusion coefficients, and thermal diffusion ratios are also obtained by using an expansion vector based upon the total energy of the molecules. Finally, practical and accurate expressions for the thermal conductivity and the thermal diffusion ratios are derived by using the recent theory of iterative transport algorithms, as developed by the authors. The resulting expressions can be used in either theoretical calculations or computational models of multicomponent flows.     

Benchmark values for the Soret,thermal diffusion and diffusion coefficients of three binary organic liquid mixtures

With the aim of providing reliable benchmark values, we have measured the Soret, diffusion and thermal diffusion coefficients of the three binary mixtures of dodecane, isobutylbenzene and 1,2,3,4 tetrahydronaphthalene for a concentration of 50 wt% at a temperature of 25C. The experimental techniques applied by the five participating laboratories are transient holographic gratings, annular and parallelepipedic thermogravitational columns, and vertical parallelepipedic columns with velocity amplitude determination by laser doppler velocimetry. The systems have also been studied in a annular thermogravitational column filled with a porous medium in the gap. There is a good agreement between the different experiments with deviations of the order of a few per cent in most cases (8.5% at most). The numerical values are tabulated in the paper.     

Diffusion and thermal diffusion in binary mixtures of sulphur hexafluoride with noble gases

Diffusion coefficients and thermal diffusion factors are reported for binary mixtures of sulphur hexafluoride with noble gases. The results are compared with theoretical values calculated by means of the Chapman-Enskog theory, spherical potentials for the like interactions and multi-parameter anisotropic potentials for the unlike interactions.     

On thermal diffusion in binary and ternary Lennard-Jones mixtures by non-equilibrium molecular dynamics

Molecular simulation appears to be an alternative to experiment for the estimation of transport and thermodynamics properties of fluid mixtures, which is of primary importance in the evaluation of the initial state of a petroleum reservoir. In this study, a non-equilibrium molecular dynamics algorithm has been applied to mixtures of Lennard-Jones spheres in order to compute the thermal diffusion process. The pertinence of such an approach to simple alkane mixtures is shown. The separate influences on the thermal diffusion of the molecular features in binary equimolar mixtures are then summarized. Simulations on binary non-equimolar mixtures have been performed as well. The results indicate an increase in the thermal diffusion process with increasing molar fraction of the lightest component. Moreover, this increase is enhanced with increasing difference in the number of carbons between the two alkanes. Then, a simple method, which yields results consistent with simulations, is proposed to predict thermal diffusion for the whole range of molar fractions starting only from the equimolar value. Finally, for ternary mixtures, the law of the corresponding states is shown to be valid when the appropriate mixing rules are applied, which allows the estimation of thermal diffusion in such mixtures from equivalent binary mixtures.     

Specific effects and deconvolution in submicrometre EPMA: application to binary diffusion

Electron probe (x‐ray) microanalysis (EPMA) is nowadays a classical and well‐established method for qualitative and (semi)quantitative evaluation of the elemental composition of the (near) surface of a sample on the micrometre scale. This technique can be used to determine concentration profiles due to (inter)diffusion in materials at submicrometre resolution if physical and geometrical effects that occur during the measurement process are accounted for. Standard phenomena are usually corrected by commercial software for a homogeneous elemental composition in the analysed area. However, in the case of a diffusion process on a small scale, the composition is no longer homogeneous and the effect of the hemispherical volume of the x‐ray emission on the spatial resolution of the concentration profiles, and consequently on the diffusion coefficients, has to be considered. A radial x‐ray distribution associated with the classical depth distribution, ?(z), allows for the definition of a 2D x‐ray emission function for medium to heavy materials. This enables one to study the effect of some geometrical parameters on the measured concentration profile and to propose a method of reconstructing the real weight fraction profile from the measured profile of the x‐ray intensities by using regularized deconvolution algorithms. Copyright © 2003 John Wiley & Sons, Ltd.     

Influence of difference in the atomic volumes of the components on the mutual diffusion in liquid binary alloys

Expressions relating the partial diffusion coefficients, macroscopic flow velocity, and mutual diffusion coefficient are obtained. Unlike the known Darken relations, the relations obtained take into account the difference in the atomic volumes of the solution components. The influence of the volume factor is more pronounced when the component concentrations are significantly different.     

Phase separation and super diffusion of binary mixtures of active and passive particles

Computer simulations were performed to study the dense mixtures of passive particles and active particles in two dimensions. Two systems with different kinds of passive particles(e.g., spherical particles and rod-like particles) were considered. At small active forces, the high-density and low-density regions emerge in both systems, indicating a phase separation. At higher active forces, the systems return to a homogeneous state with large fluctuation of particle area in contrast with the thermo-equilibrium state. Structurally, the rod-like particles accumulate loosely due to the shape anisotropy compared with the spherical particles at the high-density region. Moreover, there exists a positive correlation between Voronoi area and velocity of the particles. Additionally, a small number of active particles capably give rise to super-diffusion of passive particles in both systems when the self-propelled force is turned on.     

The viscosity and diffusion coefficients of the binary mixtures of xenon with the other noble gases

This paper presents new experimental data for the viscosity of binary mixtures of xenon with the remaining monatomic gases, helium, neon, argon, and krypton. The measurements have been performed in a high precision oscillating-disk viscometer at atmospheric pressure and within the temperature range 25–500°C. The data have an estimated uncertainty of ±0.1% at 25°C increasing to ±0.3% at 500°C. The collision integrals for the interactions of xenon with the other monatomic species conform to the extended law of corresponding states formulated by Kestin, Ro and Wakeham. For each binary interaction the scaling parameters σ_ij and ∈_ij have been obtained. The ensemble of experimental results can be correlated by means of the appropriate kinetic theory expressions reinforced by the extended law of corresponding states. The deviations do not exceed 0.5%. The binary diffusion coefficients were calculated from the measured mixture viscosity and compared with the available experimental results. The standard deviation was estimated as ±2% which is within the mutual uncertainty of the two sets.     

Second law of thermodynamics in volume diffusion hydrodynamics in multicomponent gas mixtures

We presented the thermodynamic structure of a new continuum flow model for multicomponent gas mixtures. The continuum model is based on a volume diffusion concept involving specific species. It is independent of the observer?s reference frame and enables a straightforward tracking of a selected species within a mixture composed of a large number of constituents. A method to derive the second law and constitutive equations accompanying the model is presented. Using the configuration of a rotating fluid we illustrated an example of non-classical flow physics predicted by new contributions in the entropy and constitutive equations.     

On the choice of correlations for calculating the heat transfer coefficient in binary gas mixtures

Analytical review of numerous Russian and foreign sources of information on convective heat transfer to single-phase flows in circular pipes and rod bundles is represented. Formulas for calculation of heat transfer in circular pipes and rod bundles for different flow regimes of a binary gas mixture are proposed.     

Acoustic non-linearity parameter B/A and related molecular properties of binary organic liquid mixtures

Acoustic non-linearity parameter B/A is calculated for binary mixtures using four different methods. The interactions in the liquid mixtures are explained on the basis of excess non-linearity parameter and excess adiabatic compressibility. Sehgal's relations for calculating molecular properties of pure liquids are extended to binary mixtures.