chtMultiRegionFoam and two independent diffusion equations

Lada · December 8, 2011, 08:12

I use chtMultiRegionFoam to simulate heat transfer through building walls. What I need to include into the simulation is an extra transport equation to solve water vapour diffusion through the wall as well so I could evaluate where condensation happens within the wall.
I guess I need to rewrite the solver but I am afraid I am not so skilled yet to do so.
Could you give me a hint where to start and what to look for, or if rewriting is the way?

unnikrsn · September 20, 2012, 11:32

Hi Lada...

I am also planning to work on the same solver... ChtMultiregionFoam for Condensation...

Do you have any information for moving forward... Atleast a few hints on what to do???

Regards
Unnikrishnan.

Lada · September 21, 2012, 09:15

Hi Unnikrishnan,
I am sorry to say that I have not made any progress regarding the solver as other things drew my attention to them. I have developed a simple model sufficient for my needs with the use of octave environment though, and I am still planning to do the more advanced version by modifying ChtMultiRegionFoam or so.
If you or me find anything useful I would be happy to share it.
Good luck to both of us.

Lada

Linse · September 23, 2012, 08:02

At the moment I am working on something that might be helpful for both of you. Bare with me for another two weeks or so and I might be able to give you part of what you need!

In the meantime I would suggest to exactly find out about the formulas you want to use. Changing an equation within chtMultiRegionFoam for one region in my opinion should not be the problem. The more important thing probably will be to find the way how the steam goes through the solid and how the temperature is influenced inside the solid.

Maybe the solvers for porous materials give a hint on that? Maybe you could check what the porous solvers do and if they - at least in part - cooperate with the major infrastructure within chtMultiRegionFoam?
My hint for that: Changing the solver for the fluid region happens within /chtMultiRegionFoam/fluid/solveFluid.H, changing for the solid region within /chtMultiRegionFoam/solid/solveSolid.H. ;-)

Lada · September 24, 2012, 09:08

The extra differential equation is essentially the same as for the thermal diffusion
fvm::ddt(rho, u) - fvm::laplacian(delta(u), p)
where u stands for moisture content in kg_water /kg_dry_material, delta - vapour permeability and p is the water vapour pressure.
The equation does not account for condensation. It can be further simplified by treating delta as a constant. Another simplification is the independence of this equation on the thermal diffusion equation - thermal diffusion coefficient (conductivity) not affected by moisture content.

Thank you Bernhard for your concern.

December 8, 2011, 08:12	chtMultiRegionFoam and two independent diffusion equations	#1
Lada New Member vladimir krejci Join Date: Mar 2009 Location: Czech Republic Posts: 20 Rep Power: 17	I use chtMultiRegionFoam to simulate heat transfer through building walls. What I need to include into the simulation is an extra transport equation to solve water vapour diffusion through the wall as well so I could evaluate where condensation happens within the wall. I guess I need to rewrite the solver but I am afraid I am not so skilled yet to do so. Could you give me a hint where to start and what to look for, or if rewriting is the way?

September 20, 2012, 11:32		#2
unnikrsn New Member Unnikrishnan Mohankumar Join Date: Apr 2011 Posts: 29 Rep Power: 15	Hi Lada... I am also planning to work on the same solver... ChtMultiregionFoam for Condensation... Do you have any information for moving forward... Atleast a few hints on what to do??? Regards Unnikrishnan.

September 21, 2012, 09:15		#3
Lada New Member vladimir krejci Join Date: Mar 2009 Location: Czech Republic Posts: 20 Rep Power: 17	Hi Unnikrishnan, I am sorry to say that I have not made any progress regarding the solver as other things drew my attention to them. I have developed a simple model sufficient for my needs with the use of octave environment though, and I am still planning to do the more advanced version by modifying ChtMultiRegionFoam or so. If you or me find anything useful I would be happy to share it. Good luck to both of us. Lada

September 23, 2012, 08:02		#4
Linse Senior Member Bernhard Linseisen Join Date: May 2010 Location: Heilbronn Posts: 183 Blog Entries: 1 Rep Power: 16	At the moment I am working on something that might be helpful for both of you. Bare with me for another two weeks or so and I might be able to give you part of what you need! In the meantime I would suggest to exactly find out about the formulas you want to use. Changing an equation within chtMultiRegionFoam for one region in my opinion should not be the problem. The more important thing probably will be to find the way how the steam goes through the solid and how the temperature is influenced inside the solid. Maybe the solvers for porous materials give a hint on that? Maybe you could check what the porous solvers do and if they - at least in part - cooperate with the major infrastructure within chtMultiRegionFoam? My hint for that: Changing the solver for the fluid region happens within /chtMultiRegionFoam/fluid/solveFluid.H, changing for the solid region within /chtMultiRegionFoam/solid/solveSolid.H. ;-)

September 24, 2012, 09:08		#5
Lada New Member vladimir krejci Join Date: Mar 2009 Location: Czech Republic Posts: 20 Rep Power: 17	The extra differential equation is essentially the same as for the thermal diffusion fvm::ddt(rho, u) - fvm::laplacian(delta(u), p) where u stands for moisture content in kg_water /kg_dry_material, delta - vapour permeability and p is the water vapour pressure. The equation does not account for condensation. It can be further simplified by treating delta as a constant. Another simplification is the independence of this equation on the thermal diffusion equation - thermal diffusion coefficient (conductivity) not affected by moisture content. Thank you Bernhard for your concern.