Diffusion gas mixtures

The Maxwell-Stefan equations do not depend on choice of the reference velocity, and therefore they are a proper starting point for other descriptions of multicomponent diffusion. For ideal gas mixtures, diffusivities /, and D u are... 

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 /... 

The starting point for developing the model is the set of diffusion equations for a gas mixture in the presence of temperature, pressure and composition gradients, and under the influence of external forces." These take the following form... 

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... 

For prediction of the gas diffusivity of binary air-hydrocarbon or nonhydrocarbon gas mixtures at low pressures, the method of Fuller et al. given by Eq. (2-152) is recommended. 

TABLE 5-17 Relationships for Diffusivities of Multicomponent Gas Mixtures at Low Pressure... 

The generalized Stefan-Maxwell equations using binary diffusion coefficients are not easily applicable to hquids since the coefficients are so dependent on conditions. That is, in hquids, each Dy can be strongly composition dependent in binary mixtures and, moreover, the binaiy is strongly affected in a multicomponent mixture. Thus, the convenience of writing multicomponent flux equations in terms of binary coefficients is lost. Conversely, they apply to gas mixtures because each is practically independent of composition by itself and in a multicomponent mixture (see Taylor and Krishna for details). 

Figure 3.5 The apparent vapour pressure of gold in gas transportation measurements as a function of the gas flow rate. Low flow rates, which were used earlier to assure equilibrium, are now known to be too high as a result of thermal diffusion in the gas mixture which is saturated with gold vapour...

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... 

The dimensionless parameter Dpc / is called the Lewis number, which is the ratio of the diffusion coefficient of a gas through the mixture divided by the thermal diffusion coefficient of the gas mixture. 

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

Eagles T. E., McClung R. E. D. Rotational diffusion of spherical top molecules in liquids and gases. IV. Semiclassical theory and applications to the v3 and v4 band shapes of methane in high pressure gas mixtures, J. Chem. Phys. 61, 4070-82 (1974). 

How does a 1 2 mixture of O2 and He appear on the molecular level As O2 is added to the container, its molecules move throughout the volume and become distributed uniformly. Diffusion causes gas mixtures to become... 

Characterization. In-situ diffuse reflectance FTIR (DRIFT) experiments were carried out with undiluted samples of the zeolites in a Spectratech DRIFT cell and a Nicolet Magna 550 spectrometer. Most experiments were carried out in a flow mode, passing 0.84 ml/s of a gas mixture containing inert (He, Ar or N2) and N2O, NO, CO or mixtures of these gases continuously through the cell at atmospheric pressure. Each spectrum was recorded by addition of 256 scans and a resolution of 8 cm. ... 

Diffusion Systems The liquid whose vapor is to be the contaminant of the gas phase is contained in a reservoir maintained at a constant temperature. The liquid is allowed to evaporate and the vapor diffuses slowly through the capillary tube into a flowing gas stream. If the rate of diffusion of the vapor and the flow rate of the diluent gas are known, the vapor concentration in the resultant gas mixture can be calculated. 

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