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Transport of dilute species module

Posted Feb 18, 2015, 9:23 p.m. EST 3 Replies

Jayarama Krishna J V
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Respected Sir,
I want to know how a group of bulk reactions and a group of surface reactions can be written.I am hereby attaching the file.
I will be greatly indebted if any one can help me.
Thank you

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3 Replies Last Post Feb 19, 2015, 2:33 a.m. EST
Lasse Murtomäki
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Posted: 10 years ago Feb 19, 2015, 1:52 a.m. EST
Hi

Bulk reactions make reaction terms in the transport equation, i.e. Fick's law. Thus, add 5 reactions in your Transport of Diluted Species node.

Surface reactions make Flux boundary conditions; thus 5 Flux BCs.

I have been struggling with equilibrium reactions in numerical calculus and found it almost impossible. My solution is today to write kinetic equations for reactions and give arbitrary but very high values for the rate constants, so that the ratio of forward and backward rate constant is equal to the equilibrium constant. For example

kf = 10^8 and kb =kf/K where K is the equilibrium constant (all with proper units, naturally).

br
Lasse
Hi Bulk reactions make reaction terms in the transport equation, i.e. Fick's law. Thus, add 5 reactions in your Transport of Diluted Species node. Surface reactions make Flux boundary conditions; thus 5 Flux BCs. I have been struggling with equilibrium reactions in numerical calculus and found it almost impossible. My solution is today to write kinetic equations for reactions and give arbitrary but very high values for the rate constants, so that the ratio of forward and backward rate constant is equal to the equilibrium constant. For example kf = 10^8 and kb =kf/K where K is the equilibrium constant (all with proper units, naturally). br Lasse
Jayarama Krishna J V
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Posted: 10 years ago Feb 19, 2015, 2:15 a.m. EST
Thanx a lot sir.I will definitely try it.
Thanx a lot sir.I will definitely try it.
Lasse Murtomäki
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Posted: 10 years ago Feb 19, 2015, 2:33 a.m. EST
One question: Do the species adsorb on the surface before/after reaction? That would complicate things a lot, i.e. the adsorption kinetics should also be taken into account. In the surface reactions, silicon surface is involved, and if there is adsorption, it must be taken into account via the fraction of free surface. If there is no adsorption Si does not need to appear in the equations at all, because the activity of pure solid substance is 1 by definition.

Lasse
One question: Do the species adsorb on the surface before/after reaction? That would complicate things a lot, i.e. the adsorption kinetics should also be taken into account. In the surface reactions, silicon surface is involved, and if there is adsorption, it must be taken into account via the fraction of free surface. If there is no adsorption Si does not need to appear in the equations at all, because the activity of pure solid substance is 1 by definition. Lasse

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