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Consumption of species

Posted 14.03.2015, 08:47 GMT-4 Chemical Reaction Engineering Version 5.2 8 Replies

Mika Haber
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Hello everyone,

I have a question because I'm not quite sure how to model it. I have a reactor (square) which contains a chemical component A. A can react to B with the help of a catalyst. I want to simulate the consumption on the right side of the reactor (lets say A can diffuse in the whole reactor) with respect to the generation of B.

I'm not quite sure which modules to use. I tried with the diluted species (and maybe surface reaction modul?); But I don't know how I can set this up with the diluted species module.

Thanks for you help. I appreciate it.

regards Mika
8 Replies Last Post 12.05.2016, 23:36 GMT-4
Lasse Murtomäki
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Posted: 10 years ago 14.03.2015, 09:00 GMT-4
Add a reaction term to the diffusion equation:

dcA/dt = DA*nabla^2 cA + R

R = -k*cA

or whatever reaction term that is pertinent to your reaction.

br
Lasse
Add a reaction term to the diffusion equation: dcA/dt = DA*nabla^2 cA + R R = -k*cA or whatever reaction term that is pertinent to your reaction. br Lasse
Mika Haber
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Posted: 10 years ago 14.03.2015, 09:42 GMT-4
Hi Lasse,

thank you for your fast reply.

But I still have an understanding problem. i know that I can add a reaction term for my diffusion but how does COMSOL know that the consumption only takes place at a certain domain? Can I implement this in any way?

Thanks for your help
Hi Lasse, thank you for your fast reply. But I still have an understanding problem. i know that I can add a reaction term for my diffusion but how does COMSOL know that the consumption only takes place at a certain domain? Can I implement this in any way? Thanks for your help
Lasse Murtomäki
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Posted: 10 years ago 15.03.2015, 04:10 GMT-4
When you define the reaction term, you must click the domain where you want it to take place. Otherwise it won't have any effect on the calculation.

Lasse
When you define the reaction term, you must click the domain where you want it to take place. Otherwise it won't have any effect on the calculation. Lasse
Mika Haber
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Posted: 10 years ago 15.03.2015, 04:38 GMT-4
Hi Lasse,

I did a mistake in my last answer, I wanted to say boundary instead of domain, sorry.
I know that I have to select the domain and that's where I have trouble because my reactor is a square. Is there a possibility to select a boundary where the reaction takes place? Or do I have to create a square reactor with four seperate lines which form a square and then select one domain?

Thanks for your help.
Hi Lasse, I did a mistake in my last answer, I wanted to say boundary instead of domain, sorry. I know that I have to select the domain and that's where I have trouble because my reactor is a square. Is there a possibility to select a boundary where the reaction takes place? Or do I have to create a square reactor with four seperate lines which form a square and then select one domain? Thanks for your help.
Lasse Murtomäki
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Posted: 10 years ago 15.03.2015, 04:44 GMT-4
OK, now I see.

If a reaction takes place on the boundary, then it is not written as a reaction term in the diffusion equation, but as a flux boundary condition.

Inward flux: -k*cA

but now notice that the units of k, the reaction rate constant, is m/s in order to have flux in mol/(m^2*s).

BR
Lasse
OK, now I see. If a reaction takes place on the boundary, then it is not written as a reaction term in the diffusion equation, but as a flux boundary condition. Inward flux: -k*cA but now notice that the units of k, the reaction rate constant, is m/s in order to have flux in mol/(m^2*s). BR Lasse
Mika Haber
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Posted: 10 years ago 15.03.2015, 06:26 GMT-4
Thank you Lasse, really appreciate your help.

So if I understood it correctly. For the species B which gets created at the boundary I can just do the same with an inward flux, right?
Thank you Lasse, really appreciate your help. So if I understood it correctly. For the species B which gets created at the boundary I can just do the same with an inward flux, right?
Lasse Murtomäki
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Posted: 10 years ago 15.03.2015, 09:30 GMT-4
Yes, +k*cA.
Yes, +k*cA.
Zhenguo Wang
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Posted: 9 years ago 12.05.2016, 23:36 GMT-4
Hi, I am solving the coupling of poisson equation and current continuity equations in the Transport of Diluted Species, However, what I am confused is that whether the right source term of the continuity equation can be represented by the reaction rate term in the module .

the equations are in the attached file.
Thanks!
Hi, I am solving the coupling of poisson equation and current continuity equations in the Transport of Diluted Species, However, what I am confused is that whether the right source term of the continuity equation can be represented by the reaction rate term in the module . the equations are in the attached file. Thanks!

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