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thermal Diffusion Coefficient or Thermodiffusion

Posted 01.08.2012, 12:07 GMT-4 Version 4.3 4 Replies

Ziad Saghir
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Hi all

I am trying to solve a problem of a binary system for the moment using Comsol version 4.3 to study thermal diffusion or thermodiffusion. It consist of solving beside the fluid flow and heat transfer equations, the mass transfer equation and themass flux contain usually two terms one for the molecular diffusion multiplied by the concentration gradient and the second term is thermal diffusion coefficient multiplied by the temperature gradient. Surpsingly in comsol there is a third term relation to mass fraction gradient!I have no clue where this term come from.My question did anyone know what is this term and whether someone has an input file for me to read to see how this part is handled.

Thank you for replying

Regards
4 Replies Last Post 20.08.2012, 12:56 GMT-4
Suresh Seetharam
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Posted: 1 decade ago 01.08.2012, 19:27 GMT-4
Hi,


Which module you are referring to? Is there a built in thermo-diffusion model? If you give a screen shot of the equation, may be I can help.


Suresh
Hi, Which module you are referring to? Is there a built in thermo-diffusion model? If you give a screen shot of the equation, may be I can help. Suresh
Ziad Saghir
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Posted: 1 decade ago 06.08.2012, 00:06 GMT-4
Dear Suresh

I am referering to the mass transfer module. I read DT in the left hand side of the equation but I tried to solve a simple problem to test the thermal diffusion model with no luck sofar. Take a square cavity filled with a binary fluid having concentration o.5 for constitutuent A and 0.5 for B. Assume no buoyancy and apply a lateral temperature gradient. Assume zero mass flux in the 4 walls(i.e. Dm*concentration gradient+DT*temperature gradient).If thermal diffusion is working I expect a linear concentration distribution with one component migrating to the hot side and the other one to the cold side. Also i expect a linear temperature distribution. Can you help me model this simple problem. The linear concentration distribution is due to the thermal diffusion coefficient.

I hope you can help

Ziad
Dear Suresh I am referering to the mass transfer module. I read DT in the left hand side of the equation but I tried to solve a simple problem to test the thermal diffusion model with no luck sofar. Take a square cavity filled with a binary fluid having concentration o.5 for constitutuent A and 0.5 for B. Assume no buoyancy and apply a lateral temperature gradient. Assume zero mass flux in the 4 walls(i.e. Dm*concentration gradient+DT*temperature gradient).If thermal diffusion is working I expect a linear concentration distribution with one component migrating to the hot side and the other one to the cold side. Also i expect a linear temperature distribution. Can you help me model this simple problem. The linear concentration distribution is due to the thermal diffusion coefficient. I hope you can help Ziad
Semen Semenov
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Posted: 1 decade ago 17.08.2012, 10:24 GMT-4
Hi Ziad,
I cannot find any mass transport module, there is only the heat transport module. Had I overlooked it?
Semen.
Hi Ziad, I cannot find any mass transport module, there is only the heat transport module. Had I overlooked it? Semen.
Suresh Seetharam
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Posted: 1 decade ago 20.08.2012, 12:56 GMT-4
Hi,


Sorry I cannot be of any help, because you seem to have a module that I don't. I have subsurface module and I don't find any mass transfer module. Unless, it is in chemical engineering, in which case, I do not have the license.

You can easily set up two transport equations for the two chemicals and a temperature equation and input the thermal diffusion coupling term yourself for the two transport equations and see whether you end up with the same problem. I guess you will not consider the Dufour effect.


Suresh

Hi, Sorry I cannot be of any help, because you seem to have a module that I don't. I have subsurface module and I don't find any mass transfer module. Unless, it is in chemical engineering, in which case, I do not have the license. You can easily set up two transport equations for the two chemicals and a temperature equation and input the thermal diffusion coupling term yourself for the two transport equations and see whether you end up with the same problem. I guess you will not consider the Dufour effect. Suresh

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