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Binary gas diffusion in microchannel

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Old   August 11, 2014, 02:57
Post Binary gas diffusion in microchannel
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Hello everyone,
I'm new to CFX (and never used any CFD software before), but my case seems quite simple.
I'd like to mix two gases, methanol and oxygen in a microchannel (2 inlets and 1 outlet). I've searched lots of discussion related to my case and tried so many boundary condition settings, but still can't get a reasonable result.

Here are my BCs, hoping someone can tell me where is the error from.
Steady State
Laminar flow
Isothermal, fluid temp.=400 [k]
No-slip wall
Interfase Len. Scale = 1e-20 [m]
Drag coefficient = 0
Oxygen - ideal gas
I set CH3OH as an additional variable(specific), kinematic diffusivity (for O2) = 2.78e-5 [m^2s^-1] (Should I set the same value for CH3OH itself? )

Inlet1
volume fraction of CH3OH=1, O2=0
mass flow rate = 4.99e-8[kg s^-1]
AV Value = 0 [kg s^-1]

Inlet2
volume fraction of CH3OH=0, O2=1
mass flow rate = 4.39e-8[kg s^-1]
AV Value = 0 [kg s^-1]

Outlet
Outlet Relative Pressure = 0 [Pa] AV Value = 0 [kg s^-1]

In the simulation result, mixing length is too long compared to other people's research, and the volume fraction cross the mixing channel is strange. Changing the kinematic diffusivity or interfase len. scale wasn't much help.

Sorry for such a long description, if I can provide further detail please let me know.
Thanks!
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