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convection-diffusion with chemical reactions

Posted Oct 19, 2010, 12:27 p.m. EDT 2 Replies

Daniil Marinov
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Dear Friends,

i am working on a model of plasma jet with several reactive species. Hydrodinamic part is compressible Navier-Stokes, and then i aply convection - diffusion model.
The problem is that reaction equations are coupled and the solver is not able to converge.

Even when i solve 1 chemical equation but it contains square of concentrations - model fails.


Could you please advise me the right way of solving this problem?


Thank you in advance!
Daniil
2 Replies Last Post Oct 19, 2010, 5:37 p.m. EDT
Daniil Marinov
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Posted: 1 decade ago Oct 19, 2010, 12:29 p.m. EDT
And one more question for specialists:

does anybody know how to state boundary condition for convection/reaction/diffusion with partial reflection of impinging species (in order to take into account surface reactions).

thank you in advance
And one more question for specialists: does anybody know how to state boundary condition for convection/reaction/diffusion with partial reflection of impinging species (in order to take into account surface reactions). thank you in advance
Danial Tz
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Posted: 1 decade ago Oct 19, 2010, 5:37 p.m. EDT

Dear Friends,

i am working on a model of plasma jet with several reactive species. Hydrodinamic part is compressible Navier-Stokes, and then i aply convection - diffusion model.
The problem is that reaction equations are coupled and the solver is not able to converge.

Even when i solve 1 chemical equation but it contains square of concentrations - model fails.


Could you please advise me the right way of solving this problem?


Thank you in advance!
Daniil


It can be many reasons, but generally speaking you may have very sharp gradients around your reaction zone, so probably will need much finer mesh, or addition of high artificial diffusion. Also, try separating your solvers into segregated solvers (since fluid does not depend on C, in simple case). Also, make sure you have enough tolerance set for concentrations.


--
Comsol 4.0a
Ubuntu 10.04.1
[QUOTE] Dear Friends, i am working on a model of plasma jet with several reactive species. Hydrodinamic part is compressible Navier-Stokes, and then i aply convection - diffusion model. The problem is that reaction equations are coupled and the solver is not able to converge. Even when i solve 1 chemical equation but it contains square of concentrations - model fails. Could you please advise me the right way of solving this problem? Thank you in advance! Daniil [/QUOTE] It can be many reasons, but generally speaking you may have very sharp gradients around your reaction zone, so probably will need much finer mesh, or addition of high artificial diffusion. Also, try separating your solvers into segregated solvers (since fluid does not depend on C, in simple case). Also, make sure you have enough tolerance set for concentrations. -- Comsol 4.0a Ubuntu 10.04.1

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