Combined diffusion coefficient for gas mixture

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Thread starter Snow_buggy
Start date Oct 26, 2023
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Plasma physics

Oct 26, 2023

Snow_buggy

TL;DR Summary: Is the diffusion direction from high concentration to low concentration and from high temperature to low temperature?

Hi. I am starting to do a gas mixture simulation. I learn the fundamentals from a paper. (doi: 10.1088/0022-3727/43/2/022001)
For a gas mixture (Fe vapor in Argon), the mole fraction of Fe vapor is calculated by,

and the diffusion flux JFe is given by,

x_ar is the mole fraction of Argon; T is the temperature; P is the pressure; E is the electric field.
It seems like Fe vapor diffuses from high concentration of Fe vapor to low concentration (grad x_Ar) and from high temperature to low temperature (- grad T).

If we calculates the mole fraction of Argon not Fe vapor, this paper (doi: 10.1007/BF01459700) says these coefficients follow this rule,

I don't understand why the temperature diffusion coefficient change the sign? Does it mean the argon diffuses from low temperature to high temperature?

What is the combined diffusion coefficient for a gas mixture?

The combined diffusion coefficient for a gas mixture is a measure of how quickly the gas molecules in the mixture spread out and mix with each other. It takes into account the individual diffusion coefficients of each gas in the mixture.

How is the combined diffusion coefficient calculated?

The combined diffusion coefficient for a gas mixture is calculated using a formula that takes into account the individual diffusion coefficients of each gas in the mixture, as well as the mole fractions of each gas. The formula is D = Σ(xiDi), where D is the combined diffusion coefficient, xi is the mole fraction of gas i, and Di is the diffusion coefficient of gas i.

What factors affect the combined diffusion coefficient for a gas mixture?

The combined diffusion coefficient for a gas mixture is affected by several factors, including the diffusion coefficients of the individual gases in the mixture, the temperature, pressure, and composition of the mixture, as well as the size and shape of the container in which the mixture is contained.

Why is the combined diffusion coefficient important in gas mixtures?

The combined diffusion coefficient is important in gas mixtures because it helps to predict how quickly the gases in the mixture will mix and spread out. This information is crucial in various industrial processes, such as chemical reactions, air pollution control, and gas separation techniques.

Can the combined diffusion coefficient be experimentally determined?

Yes, the combined diffusion coefficient for a gas mixture can be experimentally determined using various techniques, such as the Taylor dispersion method, the chromatographic method, or the dusty gas model. These experimental methods help to measure the diffusion coefficients of individual gases in the mixture and calculate the combined diffusion coefficient accordingly.