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Old   January 19, 2010, 09:25
Default Natural Convection BC
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YIP KOK SENG
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I'm doing my final year project on Natural Convection in fin array.. I investigate the Natural Convection of the air domain. I created 3D volume of air which partial of the face of that air volume is fin wall and base which temp constant, i set th BC as below:

Fin wall -Wall (constant temp 400K)
Fin base -Wall (constant temp 400K)
Other surface = Pressure inlet and outlet randomly (both oso "0" presure)

And

Operation Condition = 101325 pascal, 300K temp and tick gravity(y= -9.81)
Material = air with ideal gas
Solution Initialization = all zero value



Picture uploaded:
http://img210.imageshack.us/img210/357/fin2b.jpg
http://img402.imageshack.us/img402/5941/finmeshed.jpg

But i got error ms as:
----------------------------------------------------------------------
reversed flow in 650 faces on pressure-outlet 3.

reversed flow in 1248 faces on pressure-inlet 4.

reversed flow in 5000 faces on pressure-outlet 5.
10 2.6736e-01 2.8976e-05 5.2343e-02 2.4865e-02 3.7876e-08 0:00:00 0

No error handler available

Error: FLUENT received a fatal signal (SEGMENTATION VIOLATION).
Error Object: ()

Error message from graphics function Close_Segment:
Nothing open - can't Close a 'segment'

-------------------------------------------------------------------

Anyone tell me wat to do? I set the error bc?
thanks... I 'm a beginer here, hope ur help...

Last edited by yipseng; January 27, 2010 at 09:13.
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Old   January 23, 2010, 03:28
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No one reply me?
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Old   January 25, 2010, 01:07
Default natural convection BC
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Quote:
Originally Posted by yipseng View Post
I'm doing my final year project on Natural Convection in fin array.. I investigate the Natural Convection of the air domain. I created 3D volume of air which partial of the face of that air volume is fin wall and base which temp constant, i set th BC as below:

Fin wall -Wall (constant temp 400K)
Fin base -Wall (constant temp 400K)
Other surface = Pressure inlet and outlet randomly (both oso "0" presure)

And

Operation Condition = 101325 pascal, 300K temp and tick gravity
Material = air with ideal gas
Solution Initialization = all zero value

But i got error ms as:
----------------------------------------------------------------------
reversed flow in 650 faces on pressure-outlet 3.

reversed flow in 1248 faces on pressure-inlet 4.

reversed flow in 5000 faces on pressure-outlet 5.
10 2.6736e-01 2.8976e-05 5.2343e-02 2.4865e-02 3.7876e-08 0:00:00 0

No error handler available

Error: FLUENT received a fatal signal (SEGMENTATION VIOLATION).
Error Object: ()

Error message from graphics function Close_Segment:
Nothing open - can't Close a 'segment'

-------------------------------------------------------------------

Anyone tell me wat to do? I set the error bc?
thanks... I 'm a beginer here, hope ur help...
hey this is rahul .........
i think you should use boussinesq model instead of ideal gas in the material selection panel of for air and set the appropriate thermal expansion coefficient....
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Old   January 27, 2010, 04:19
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Thanks rahul.. But izit ideal gas more suitable to which has large temp diff?
thermal expansion coefficient what value i should set? I jus set default value..
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Old   January 27, 2010, 07:43
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Hi, yipseng

Let us see how are the fins oriented , Are they horizontal of vertical W.R.T. gravity.

Once this is clear. You can find out whether the natural convection flow is laminar or turbulent.

In many cases where the flow is turbulent in natural convection cases it is tough to converge.

In that case you can reduce you gravity to 100 times run it in stage to reach the value of 9.81 m^2/sec.

Let me know the exact errors you encountered.

Uday
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Old   January 27, 2010, 09:15
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Picture uploaded.. Anyone noe what the problem??
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Old   January 27, 2010, 11:08
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Daniele
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I've got a problem with natural convection, too. The suggestion to check if flow is turbolent or laminar is surely good! In case of turbolent flow i suggest to use K-eps models.
Hi!
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Old   February 2, 2010, 12:07
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any 1 know how to solve? Thanks
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Old   February 3, 2010, 08:36
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i know but it is you project, so you have to done it yourself.

best regards.
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Old   February 4, 2010, 00:46
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Dear Yapiseng, I happen to simulate the same model with you. But I set the fin base as heat flux and I consider the air-fin coupled domain. And I also set BC as symmetric and pressure-out. I did have solutions. I wonder if you have succeeded with a solution and what's the error. How much was that?
Maybe we could help each other.
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