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Continuous delivery in transport and surface reaction model

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Hi all,

I am doing modelling with trasport and surface reaction in a flat micro-channel (L:W:H= 800um, 300um and 10um). In this model, one reaction solution is delivered into the channel in with laminar flow continuously. The reaction material will be adsorbed onto a square reaction spot (50um x 50um) in the botton of channel.
So I am modelling this with three physics, Transport of diluted species (chds), Laminar flow (spf) and Surface reaction (chsr) (shown in the attachment). After modelling, I have got some problems;

(1) As to my target, material is delivered continuously with constant initial concentration. But the result shows that the concentration from inlet varies all the time.

(2) The reaction spot (50um x 50 um) should be saturated with materials, but the results shows that it is changing all the time but never saturated even after long term.

Could anybody please help me on this? Any help and suggestion is massively appreciated.

Thank you.


5 Replies Last Post 21 ago 2012, 07:51 GMT-4

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Posted: 1 decade ago 30 mag 2012, 10:41 GMT-4
Can anybody help me on this??
Can anybody help me on this??

Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 31 mag 2012, 02:03 GMT-4
Hi

not evident what to say, from my side, chemistry is not ma everyday business
what puzzles me a bit is the velocity profile after the stationary study, you have a drastical slow up over your reaction patch, this is partially due to the no-slip condition building up there but not on the rest of the surface. Maybe you should remove the "symmetry condition on the lower wall which changes drastically the velocity profile.

Then remains the question about boundary mesh or not on the no-slip wall

suggestion: plot rather c/c0 than just c its easier to see the "oscillations"

You seem to have a wave of higher concentration flowing by, that takes > 10 seconds to pass, If I take the diffusivity D of 1000 [um^2/s] and your time stepping in seconds you have a delta_x of about 33um and a meshing of 30 um so the mesh is for me too rough but that's easily fixed, try the default physics induced mesh

Remains to find out if this rapid inrush and 50% concentration increas wave flowing by is physical or numerical. I'm not sure what to conclude there, but I would appreciate to hear from you if you observe it ;)

for me diffusion PDE equation could not make " stading waves" but here its a transient, if you solve for 30 sec it dies away

Interesting model anyhow

--
Good luck
Ivar
Hi not evident what to say, from my side, chemistry is not ma everyday business what puzzles me a bit is the velocity profile after the stationary study, you have a drastical slow up over your reaction patch, this is partially due to the no-slip condition building up there but not on the rest of the surface. Maybe you should remove the "symmetry condition on the lower wall which changes drastically the velocity profile. Then remains the question about boundary mesh or not on the no-slip wall suggestion: plot rather c/c0 than just c its easier to see the "oscillations" You seem to have a wave of higher concentration flowing by, that takes > 10 seconds to pass, If I take the diffusivity D of 1000 [um^2/s] and your time stepping in seconds you have a delta_x of about 33um and a meshing of 30 um so the mesh is for me too rough but that's easily fixed, try the default physics induced mesh Remains to find out if this rapid inrush and 50% concentration increas wave flowing by is physical or numerical. I'm not sure what to conclude there, but I would appreciate to hear from you if you observe it ;) for me diffusion PDE equation could not make " stading waves" but here its a transient, if you solve for 30 sec it dies away Interesting model anyhow -- Good luck Ivar

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Posted: 1 decade ago 3 giu 2012, 06:26 GMT-4
thank you very much. I am trying to do this with your suggestions.

thank you very much. I am trying to do this with your suggestions.

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Posted: 1 decade ago 24 lug 2012, 09:52 GMT-4
why u have symmetry in all directions..
why u have symmetry in all directions..

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Posted: 1 decade ago 21 ago 2012, 07:51 GMT-4
Thank you for your suggestions, I have changed the settings, but the flow concentration profile still seams not good for me so far. So have you got any further suggestions?
Thank you for your suggestions, I have changed the settings, but the flow concentration profile still seams not good for me so far. So have you got any further suggestions?

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