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Steady state solution in chtMultiRegionSimpleFoam depends on kappa (t. conductivity)?

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Old   May 7, 2014, 09:56
Default Steady state solution in chtMultiRegionSimpleFoam depends on kappa (t. conductivity)?
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Hello

I use chtMultiRegionSimpleFoam solver. My case is very simple. I have a box 1x1x2m with two aeras (hot and cold air) and baffle. I want to have steady state solution, and I think there is only one solition for my case (heat flow through baffle until temperatures in two aeras are the same).

But if I change the value of kappa in thermophysicalProperties for solid I have different final temperature in my box (!)
hotair >>> 400 K
cold air >>> 300 K

kappa=80 >>> T_final~310
kappa=8 >>> T_final~340
kappa=800 >>> T_final~300

Does anyone can help? Why kappa (thermal conductivity) change my steady-state solution? Other variables in thermophysicalProperties does not influence on solution...

Case is very simple and small (1 Mb), ready to run:
http://speedy.sh/4mGcf/my-case.zip
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Old   May 7, 2014, 12:50
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Andrew Somorjai
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Quote:
Originally Posted by karoltomek View Post
Hello

I use chtMultiRegionSimpleFoam solver. My case is very simple. I have a box 1x1x2m with two aeras (hot and cold air) and baffle. I want to have steady state solution, and I think there is only one solition for my case (heat flow through baffle until temperatures in two aeras are the same).

But if I change the value of kappa in thermophysicalProperties for solid I have different final temperature in my box (!)
hotair >>> 400 K
cold air >>> 300 K

kappa=80 >>> T_final~310
kappa=8 >>> T_final~340
kappa=800 >>> T_final~300

Does anyone can help? Why kappa (thermal conductivity) change my steady-state solution? Other variables in thermophysicalProperties does not influence on solution...

Case is very simple and small (1 Mb), ready to run:
http://speedy.sh/4mGcf/my-case.zip
So what you want is for the hotter side to stay constant while the cooler side warms up, that would be steady state. Were these the final temps of both sides or just the side with lower initial temperature?

kappa=80 >>> T_final~310
kappa=8 >>> T_final~340
kappa=800 >>> T_final~300
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Old   May 7, 2014, 15:12
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Quote:
Originally Posted by massive_turbulence View Post
So what you want is for the hotter side to stay constant while the cooler side warms up, that would be steady state. Were these the final temps of both sides or just the side with lower initial temperature?

kappa=80 >>> T_final~310
kappa=8 >>> T_final~340
kappa=800 >>> T_final~300
Final temperature >>> temperature of both sides

I want to solve this problem:
at begining I have two fluids with different temperatures
- 400 K >>> hotter side
- 300 K >>> cooler side
and the baffle between them
the heat can flow only through the baffle

at the end I want to have the same temperatures on the both sides (this is my steady state solution), the temperature of hotter side decreases and the tepmerature of coller side increases until the temperatures are different

the problem is:
final temperature (the same in both sides) depends on kappa value and I don't undestand why... The final temperature must be always the same...
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Old   May 8, 2014, 01:54
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This screenshots shows my solutions.
When kappa=0 heat can't flow through the baffle, the temperatures don't change and this is ok.
Attached Images
File Type: jpg time_0.jpg (25.0 KB, 10 views)
File Type: png solution_kappa=8.png (81.0 KB, 11 views)
File Type: png solution_kappa=40.png (74.9 KB, 10 views)
File Type: png solution_kappa=80.png (62.9 KB, 10 views)
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