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Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: chenginst on July 01, 2019, 02:29:10 AM

Can anyone please suggest a formula to calculate the diffusion coefficient of water vapor in a gas mixture of N_{2}, CO_{2} ,O_{2}, and H_{2}O at 1 atm and 0 to 200 °C.
I found this formula.
D'_{A} = (1  Y_{A})/(Y_{B}/D_{AB} + Y_{C} /D_{AC} + ..)
where D'_{A} is the diffusion coefficient of the component A in the mixture with B, C, ..., Y_{A}, Y_{B}, Y_{C} are the molar fractions of the appropriate components; and D_{AB} and D_{AC} are the diffusion coefficients in the AB and AC binary systems, respectively.
But to use that I need experimental data of the diffusion coefficient of water vapor at pure N_{2}, O_{2} and CO_{2}.
Can anyone please mention a reliable source to get the experimental values or mention another theoretical equation to derive a formula ?

Your gas mixture is basically air, and you can find experimental diffusion constants for water vapor in air at different temperatures: e.g., https://www.engineeringtoolbox.com/airdiffusioncoefficientgasmixturetemperatured_2010.html
There are some binary diffusion constants of gases in the CRC, and you may also seek out Marrero TR and Mason EA, J Phys Chem Ref Data 1, 1, 1972, which provides some more information on how they are determined and where they are applicable.
With the exception of water, at those temperatures and pressures most of these gases probably behave nearly ideally, so the primary difference in their diffusion behavior will be determined by their molecular radii. But we're not talking huge differences here, so you could probably get a fairly decent estimate by just treating all the gases in the medium as identical.

Thanks for your reply. Actually the gas is not air. It is flue gas after burning hydrocarbons.
I found Fuller, Schettler, and Giddings Correlation
http://www.umich.edu/~elements/fogler&gurmen/html/course/lectures/eleven/exam4.htm
It can calculate the diffusion coefficient of water vapor in pure N_{2}, O_{2} and CO_{2} and then using the previous equation I can find the diffusion coefficient of water vapor in the gas mixture. Hope this is right.