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Old   September 24, 2001, 05:07
Default about thermal conditions for two-sided walls
  #1
Devy
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Hi,Fluent Users:

I am simulating combustion of gas,and the flame temperature is about 3500k. I also define a wall zone which have a fluid or solid region on each side.And I want to couple the two sides of the wall,so I select the coupled options under thermal condition.

When I get convegenced solution and I plot surface heat flux on the two-sided walls,I find the result is nearly zero.

Would you give me some advice?Any ansnwer wiil be welcome.

Thank you.

Devy

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Old   September 24, 2001, 05:53
Default Re: about thermal conditions for two-sided walls
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passer-by
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I think "nearly zero Flux on interface" means that at least heat is penetrating from fluid zone to solid zone" That means, solver solved that heat transfer problem. (I think you can polt the temperature contour and see the temperature distribution around the interface)

So, how about considering your physical phenomena again?(for example, checking solid conductiity)

P.S. Did your solver split your wall boundary to wall and wall_shadow successfully when you read the mesh file?
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Old   September 24, 2001, 19:45
Default Re: about thermal conditions for two-sided walls
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Devy
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Hi,

Thank you for your reply.

Yes,My solver split your wall boundary to wall and wall_shadow successfully.

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Old   September 25, 2001, 10:39
Default Re: about thermal conditions for two-sided walls
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AJ
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Devy, If there is any heat transfer from the wall after coupling the two walls it should show the value of heat transferred. If these walls are not coupled then it will show zero HT. Bye AJ
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Old   September 25, 2001, 21:37
Default Re: about thermal conditions for two-sided walls
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Devy
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Hi,

Thank you for reply.

I define a wall zone which has a fluid or solid region on each side in gambit. When I read this grid with this type of wall zone into FLUENT, a ``shadow'' zone is automatically created.

In the Wall panel,I choose Coupled option under Thermal Conditions. I also define zero wall wall thickness and heat generation rate. And I only change material type as my material (density:950,Cp:1260,K:0.1554).

But it show the zero value of heat transferred. Would you give me some advice?Any ansnwer wiil be welcome.

Thank you

Devy 2001.8.26

.
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Old   September 26, 2001, 01:41
Default Re: about thermal conditions for two-sided walls
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passer-by
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I think you set your wall condition well. According to your solid property, thermal conductovity value is 0.1554. If you see the thermal conductivity of wood in material database in solver, the value would be about 0.17.

I think your heat flux problem is probably a natural phenomenon unless the value is exactly zero.
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Old   September 26, 2001, 03:37
Default Re: about thermal conditions for two-sided walls
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AJ
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1)For zero wall thickness the material should not matter, because the thermal resistance across the wall is zero. 2) Fluent calculates thermal resistance based on simple 1d calculation. Only in 3D you can swich on planar-conduction ON and get 2D heat transfer from wall with finite thickness. 3)Is your problem 2D or 3d? 4) Try doing simple convection/conduction HT analysis to check whether HT is taking place or not... Bye AJ
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Old   September 26, 2001, 06:59
Default Re: about thermal conditions for two-sided walls
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Devy
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Hi,

Thank you for your reply.

My problrm is in 2D
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Old   September 26, 2001, 12:42
Default Re: about thermal conditions for two-sided walls
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Lanre
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The resultant heat flux through an interior coupled wall with no heat source is zero.

Heat IN = Heat OUT

The flux value on the wall would be positive or negative, depending on the temperature difference between the cell zones on either side of the wall. The heat flux through the shadow would carry the reverse sign of the heat flux through the wall.
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