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Transport of dilute species module

Posted Feb 10, 2015, 6:32 a.m. EST 3 Replies

Jayarama Krishna J V
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Respected Sir,
I am attaching my .mph file.It is working well when a>=1.For my case a=0.5 it is showing error.
Here 'a' is the power of the concentration.
I kindly request you to help me out with this problem.
Regards

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3 Replies Last Post Feb 10, 2015, 9:12 a.m. EST
Lasse Murtomäki
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Posted: 10 years ago Feb 10, 2015, 9:05 a.m. EST
Hi

I just remembered that you have to write the flux BC as

-kr*c1*(c2/C0+eps)^a/(1+K*(c1/C0))

"eps" is a machine constant, floating point accuracy, a very small number, 2^-52. Look at help with "eps".

Another thing: You do need two separate nodes of "Transport of Dilutes Species", you can have both variables c and c2 in the same node, just put the number of variables 2.

I usually do so that I first calculate the laminar flow at steady-state in its own Study, i.e. disabling all the other physics; let's call this Study 1. Then I calculate the rest of the physics in another Study 2, disabling Laminar Flow, and in the menu "Values of variables not solved for" I select "Study 1, Stationary". In the Transport of Diluted Species node I choose the velocity field "spf", not user defined u and v. Now Comsol understands that I am using the velocity field of the Laminar Flow node for which Comsol gives the default identifier "spf".

I tried with a = 0.5 with no problems.

Good luck
Lasse
Hi I just remembered that you have to write the flux BC as -kr*c1*(c2/C0+eps)^a/(1+K*(c1/C0)) "eps" is a machine constant, floating point accuracy, a very small number, 2^-52. Look at help with "eps". Another thing: You do need two separate nodes of "Transport of Dilutes Species", you can have both variables c and c2 in the same node, just put the number of variables 2. I usually do so that I first calculate the laminar flow at steady-state in its own Study, i.e. disabling all the other physics; let's call this Study 1. Then I calculate the rest of the physics in another Study 2, disabling Laminar Flow, and in the menu "Values of variables not solved for" I select "Study 1, Stationary". In the Transport of Diluted Species node I choose the velocity field "spf", not user defined u and v. Now Comsol understands that I am using the velocity field of the Laminar Flow node for which Comsol gives the default identifier "spf". I tried with a = 0.5 with no problems. Good luck Lasse
Lasse Murtomäki
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Posted: 10 years ago Feb 10, 2015, 9:08 a.m. EST
Attached my model if you have Comsol 5.
Attached my model if you have Comsol 5.

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Jayarama Krishna J V
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Posted: 10 years ago Feb 10, 2015, 9:12 a.m. EST
thanx a lot sir for guiding me..now i will try the way you told me
thanx a lot sir for guiding me..now i will try the way you told me

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