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heat and mass transfer coupling

Posted Oct 14, 2010, 11:23 a.m. EDT 7 Replies

Roopesh Mohandas Syamaladevi
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Hi,
I am doing some heat and mass transfer coupling on food (drying of food). for heat transfer, the boundary conditions are heat flux continuity and temperature continuity. but in comsol, either i can select temperature or heat flux. I can't select both together. for mass transfer, the B.C are mass flux and thermodynamic equilibrium. I can't select mass flux and concentration together in comsol as B.C. Is there any way for this?

Thanks,
Roopesh
7 Replies Last Post Nov 29, 2010, 10:19 a.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Oct 17, 2010, 5:08 a.m. EDT
Hi

for me if you fix a temperature, then you ask COMSOL to adapt the heat flux such to maintain the temperature, therefore you cannot also add a heat flux.
But you can always consider the heat flux COMSOL finds it needs to control the temperature, and offset this value by your fixed value if you that makes more sens for you.

I believe the same applies to your second question too. I do not really catch the physical sens of what you are asking for

--
Good luck
Ivar
Hi for me if you fix a temperature, then you ask COMSOL to adapt the heat flux such to maintain the temperature, therefore you cannot also add a heat flux. But you can always consider the heat flux COMSOL finds it needs to control the temperature, and offset this value by your fixed value if you that makes more sens for you. I believe the same applies to your second question too. I do not really catch the physical sens of what you are asking for -- Good luck Ivar
Roopesh Mohandas Syamaladevi
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Posted: 1 decade ago Oct 17, 2010, 3:58 p.m. EDT
Sorry, I did not quite understand your reply. In my coupling model, in the air-food interface, I can select continuity, temperature or flux discontinuity. The BC are heat flux continuity and temperature continuity. A latent heat term is involved in the heat flux continuity expn. If I select temperature as my BC, where I will express the heat flux continuity in Comsol? please see the attachment for the BCs.

Could you please explain this?
Sorry, I did not quite understand your reply. In my coupling model, in the air-food interface, I can select continuity, temperature or flux discontinuity. The BC are heat flux continuity and temperature continuity. A latent heat term is involved in the heat flux continuity expn. If I select temperature as my BC, where I will express the heat flux continuity in Comsol? please see the attachment for the BCs. Could you please explain this?

Attachments:

Roopesh Mohandas Syamaladevi
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Posted: 1 decade ago Oct 17, 2010, 3:58 p.m. EDT
Sorry, I did not quite understand your reply. In my coupling model, in the air-food interface, I can select continuity, temperature or flux discontinuity. The BC are heat flux continuity and temperature continuity. A latent heat term is involved in the heat flux continuity expn. If I select temperature as my BC, where I will express the heat flux continuity in Comsol? please see the attachment for the BCs.

Could you please explain this?
Sorry, I did not quite understand your reply. In my coupling model, in the air-food interface, I can select continuity, temperature or flux discontinuity. The BC are heat flux continuity and temperature continuity. A latent heat term is involved in the heat flux continuity expn. If I select temperature as my BC, where I will express the heat flux continuity in Comsol? please see the attachment for the BCs. Could you please explain this?
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Oct 18, 2010, 2:08 a.m. EDT
Hi

In v3.5 all fields are shown but some might not be changed (greyed) due to the BC you select:

continuity means the normal flux is matched (internally by COMSOL nothing to do)

Temperature means you decide the Temperature, but nothing else (others are greyed) etc

--
Good luck
Ivar
Hi In v3.5 all fields are shown but some might not be changed (greyed) due to the BC you select: continuity means the normal flux is matched (internally by COMSOL nothing to do) Temperature means you decide the Temperature, but nothing else (others are greyed) etc -- Good luck Ivar
Roopesh Mohandas Syamaladevi
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Posted: 1 decade ago Oct 21, 2010, 11:18 a.m. EDT
Thank you Ivar for your help. I figured it out.

Roopesh
Thank you Ivar for your help. I figured it out. Roopesh
Ganesh Samdani
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Posted: 1 decade ago Nov 29, 2010, 4:48 a.m. EST
Hi Roopesh,

Can you please tell me how u did it??

I mean: temperature continuity and heat flux @ a boundary

--
Ganesh Samdani
Hi Roopesh, Can you please tell me how u did it?? I mean: temperature continuity and heat flux @ a boundary -- Ganesh Samdani
Roopesh Mohandas Syamaladevi
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Posted: 1 decade ago Nov 29, 2010, 10:19 a.m. EST
Actually I did not continue the model the way I described in the question. But i can suggest you to make two physics for each sub domain. for instance, make one heat transfer and mass transfer physics for one sub domain and let it be active in that domain. Let this heat and mass transfer physics not active in the other sub domain. Similarly add another heat and mass transfer physics for the second sub domain and let it be not active in the first sub domain. Now you get the needed BCs.

Hope this helps.
Roopesh
Actually I did not continue the model the way I described in the question. But i can suggest you to make two physics for each sub domain. for instance, make one heat transfer and mass transfer physics for one sub domain and let it be active in that domain. Let this heat and mass transfer physics not active in the other sub domain. Similarly add another heat and mass transfer physics for the second sub domain and let it be not active in the first sub domain. Now you get the needed BCs. Hope this helps. Roopesh

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