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Laminar Flow +Chemical Reaction

Posted May 7, 2013, 11:26 a.m. EDT Low-Frequency Electromagnetics Version 4.0 6 Replies

Romani Patel
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Hi,

Can anyone please help me with my model and guide me as to where I am going wrong. I am trying to simulate a simple chemical reaction A+B-->C in a pipe filled with water flowing at laminar velocity. I create a laminar flow profile using Laminar physics which I used as my input velocity to the Transport of Diluted Species physics. I verified that the Laminar and Transport physics are coupled.

When I plot the concentration profile, there is no change in the reactant or products concentrations. They remain the same, meaning there is no reaction.

I have defined the reactions rates in the variables section of the model. I dont know if I am plotting it wrong or what is the issue.

Please Please help. I dont know where I am going wrong. I cleared all solutions and meshes as I was not able to upload the file with them due to size limit

Thanks,
Romani
6 Replies Last Post May 8, 2013, 12:12 p.m. EDT
Romani Patel
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Posted: 1 decade ago May 8, 2013, 9:23 a.m. EDT
Anyone please help
Anyone please help
Josh Thomas Certified Consultant
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Posted: 1 decade ago May 8, 2013, 10:05 a.m. EDT
Romani-

I made a minor change to your solver set-up and was able to get non-zero concentrations. See attached screenshot.

First, solve for the laminar flow study then when you solve for the species transport, click the "Values of variables NOT solved for" check box and use the final time step from the laminar flow study solution. Make sure to uncheck the "Laminar Flow" physics under the section "Physics and Variables Selection" for the transport of species study. You do NOT need to re-solved for the laminar flow because of the sequentially coupled (one-way) nature of the multi-physics problem.

See attached mph file. I, too, cleared the meshes and solution to save space.

Best regards,
Josh Thomas
AltaSim Technologies
Romani- I made a minor change to your solver set-up and was able to get non-zero concentrations. See attached screenshot. First, solve for the laminar flow study then when you solve for the species transport, click the "Values of variables NOT solved for" check box and use the final time step from the laminar flow study solution. Make sure to uncheck the "Laminar Flow" physics under the section "Physics and Variables Selection" for the transport of species study. You do NOT need to re-solved for the laminar flow because of the sequentially coupled (one-way) nature of the multi-physics problem. See attached mph file. I, too, cleared the meshes and solution to save space. Best regards, Josh Thomas AltaSim Technologies
Josh Thomas Certified Consultant
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Posted: 1 decade ago May 8, 2013, 10:23 a.m. EDT
Oops...just realized that the magnitudes are on the order of 1e-7. So, still no reaction to the cC concentration. Hmmm... I'll look a little bit more.

But, still it was worth pointing out that you don't need to re-solve for laminar flow.
Oops...just realized that the magnitudes are on the order of 1e-7. So, still no reaction to the cC concentration. Hmmm... I'll look a little bit more. But, still it was worth pointing out that you don't need to re-solve for laminar flow.
Romani Patel
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Posted: 1 decade ago May 8, 2013, 11:17 a.m. EDT
Thank you Josh for letting me know that I do not need to solve the laminar physics again. I did not know that.

If you could please guide me as to why I dont see the reactions happening, I will really appreciate it. I have been stuck with this problem past 2 weeks. I verified that I am using the right reaction, BCs..I just cant figure out why I dont see any reactions happening and change in the reactants/products concentrations.

Romani




Oops...just realized that the magnitudes are on the order of 1e-7. So, still no reaction to the cC concentration. Hmmm... I'll look a little bit more.

But, still it was worth pointing out that you don't need to re-solve for laminar flow.


Thank you Josh for letting me know that I do not need to solve the laminar physics again. I did not know that. If you could please guide me as to why I dont see the reactions happening, I will really appreciate it. I have been stuck with this problem past 2 weeks. I verified that I am using the right reaction, BCs..I just cant figure out why I dont see any reactions happening and change in the reactants/products concentrations. Romani [QUOTE] Oops...just realized that the magnitudes are on the order of 1e-7. So, still no reaction to the cC concentration. Hmmm... I'll look a little bit more. But, still it was worth pointing out that you don't need to re-solve for laminar flow. [/QUOTE]
Josh Thomas Certified Consultant
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Posted: 1 decade ago May 8, 2013, 11:23 a.m. EDT
Romani-

Okay. I believe I figured it out. If you increase your k2 reaction rate variable to a value of 3 you can see a good amount of reaction. I believe you had it set to many orders of magnitude less than this. I believe the reaction is happening in the other case, only it is so slow that you don't see it happening in the few seconds it takes for the fluid to pass through the domain.

Best regards,
Josh Thomas
AltaSim Technologies
Romani- Okay. I believe I figured it out. If you increase your k2 reaction rate variable to a value of 3 you can see a good amount of reaction. I believe you had it set to many orders of magnitude less than this. I believe the reaction is happening in the other case, only it is so slow that you don't see it happening in the few seconds it takes for the fluid to pass through the domain. Best regards, Josh Thomas AltaSim Technologies

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Romani Patel
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Posted: 1 decade ago May 8, 2013, 12:12 p.m. EDT
Hi Josh,

Thank you so much for your guidance and help. I will run the model as you suggested.

Thanks a million,
Romani
Hi Josh, Thank you so much for your guidance and help. I will run the model as you suggested. Thanks a million, Romani

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