Binary gas diffusion

If Fick s equation is used and the diffusivities of the ion pair DAb and DBa are assumed to be equal, as for binary gas diffusivities, predicted exchange rates are the same, regardless of direction of diffusion. Thus, the newer theory taking into account the electric potential is clearly an improvement over the Fick s law approach. However, if an empirical view of this simple theory is used, allowing each diffusivity to assume a... 

Diffusion in the bulk gas is also a random walk process, and the similarity is brought out by the following approximate equation for binary gas diffusion ... 

Wilhelm and Battino have extended their measurements of binary gas diffusion coefficients using the Stefan technique to mixtures of SF with four aliphatic hydrocarbons. Jaster and Kosky have completed a series of measurements of the solubility of SF, in four commercially-available fluorocarbon mixtures and Pierotti has published a recent review on the application of scaled-particle theory to the estimation of gas solubilities. 

The Lx)schmidt diffusion cell is used to experimentally determine binary gas diffusivity. For ideal gases, the transport equation, for the hollow cylindrical cells, is Pick s second law of diffusion... 

Maxwell Binary gas diffusivity model in porous media... 

Table 3.1.10 Binary gas diffusion coefficients (and selected self-diffusion coefficients) at 1 bar comparison of experimental values (Baernseta/., 2006) and estimations by Eqs. (3.1.78a) and (3.1.78b).

Another frequently used equation for binary gas diffusion coefficients is derived based on kinetic theory and experimental data (Bird et al., 2002 Slattery and Bird, 1958) as... 

Fuller s equation, applied for the estimation of the coefficient of diffusion of a binary gas mixture, at a pressure greater than 10 bar, predicts values that are too high. As a first approximation, the value of the coefficient of diffusion can be corrected by multiplying it by the compressibility of the gas /... 

Mass Transport. An expression for the diffusive transport of the light component of a binary gas mixture in the radial direction in the gas centrifuge can be obtained directly from the general diffusion equation and an expression for the radial pressure gradient in the centrifuge. For diffusion in a binary system in the absence of temperature gradients and external forces, the general diffusion equation retains only the pressure diffusion and ordinary diffusion effects and takes the form... 

Gas Diffusivity For prediction of the gas diffusivity of binary hydrocarbon-hyarocarbon gas systems at low pressures (below about 500 psia [3.5 MPa]) the method of Gilliland given by Eq. (2-150) is recommended. 

In the late 1800s, the development of the kinetic theory of gases led to a method for calculating mmticomponent gas diffusion (e.g., the flux of each species in a mixture). The methods were developed simnlta-neonsly by Stefan and Maxwell. The problem is to determine the diffusion coefficient D, . The Stefan-Maxwell equations are simpler in principle since they employ binary diffnsivities ... 

In a binary gas mixture, the diffusion coefficient of the species i at a mole fraction jc, widr respect to tlrat of the species j is given after evaluating the constants by tire equation... 

Bailey, R. G. and Chen. H. T., Predicting Diffusion Coefficients In Binary Gas Systems," Chemical Engineering, March 17, 1975, p. 86. 

Table 10.5. Values of thermal diffusion factor (a) for binary gas mixtures (A is the heavier component, which moves towards the cooler end)...

Diffusivity Estimation Method for Binary Gas Mixtures from Treybal, Mass-Transfer Operations, 3rd Edition... 

When the mean free path is small compared with pore diameter, the dominating experience of molecules is that of collision with other molecules in the gas phase. In that respect, the situation is much the same as that which exists in the bulk gas. The appropriate diffusion coefficient Dm may be obtained from published experimental values, or calculated from a theoretical expression. For molecular diffusion in a binary gas, the Chapman and Enskog equation may be used, as discussed by Bird, Stewart and Lightfoot(32). This takes the form ... 

Figure 52. Effect of binary gas-phase diffusion on the impedance characteristics of porous mixed-conducting electrodes at low Por (a) zero-bias impedance of LSC on rare-earth-doped ceria at 1 atm and 750 °C as a function of Pq using concentrations and balance gases as indicated. (Reprinted with permission from ref 350. Copyright 2000 Elsevier B.V.) (b) Zero-bias impedance of SSC x= 0.5) on SDC at 800 °C and P02 — 9-91 a function of total...

Locate or calculate the binary-component diffusivity or self-diffusion coefficient for a gas, dilute solute, or melt. 

At moderate pressures the diffusion coefficient of a binary gas mixture of molecules i and j is well described by the Chapman-Enskog theory, discussed in Section 12.4 ... 

The sorption and diffusion behaviour of gas mixtures is of particular interest from the point of view of membrane gas separation, which is steadily gaining in importance by virtue of its low energy requirements. On the basis of the dual mode sorption model, one may reasonably expect that sorption of a binary gas mixture A, B in the polymer matrix will exhibit little gas-gas interaction and hence will tend to occur essentially additively. In the Langmuir-like mode of sorption, on the other hand, there will be competition between A and B for the limited number of available sites. These considerations led 67) to the following reformulation of Eqs. (8) and (9)... 

Bulk diffusion coefficients in binary gas mixture are almost independent of the ratio of components of the mixture. Therefore, it was supposed that if diffusion in the measurements described above is of the bulk type, i.e., the free path of molecules is much lesser than the diameter of pores, then the first gas diffuses into the second gas at the same rate as the second gas diffuses into the first. 

The explanation of Graham s law given by Hoogschagen is not complete, as subsequent authors (17,18) stated. However, the attempts of these authors to give a more complete explanation for the law are not convincing. It is known that at conventional measurements of diffusion coefficients in binary gas mixtures using wide capillaries, equal velocities of counterdiffusion of the components are observed. From the considerations developed... 

Fuller E.N., Schettler P.D., Giddings J.C. (1966) A new method for prediction of binary gas-phase diffusion coefficients. Industrial and Engineering Chemistry 58, 19-27. 

P 21] The mixing of gaseous methanol and oxygen was simulated. The equations applied for the calculation were based on the Navier-Stokes (pressure and velocity) and the species convection-diffusion equation [57]. As the diffusivity value for the binary gas mixture 2.8 x 10 m2 s 1 was taken. The flow was laminar in all cases adiabatic conditions were applied at the domain boundaries. Compressibility and slip effects were taken into account The inlet temperature was set to 400 K. The total number of cells was —17 000 in all cases. 

J. C. Giddings, A new method for prediction of binary gas-phase diffusion coefficients, Ind. 

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