CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > FLUENT

Convection with Shell Conduction

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   November 17, 2008, 08:35
Default Convection with Shell Conduction
  #1
Corentin
Guest
 
Posts: n/a
Hi!

I have a few questions about the shell conduction. I am calculating the air temperature in a room. I am doing unsteady calculations and I would like to consider the heat mass of the walls. I am using shell conduction. There is convection on both sides of the wall but how can I deal with that? In Fluent, in the convection panel, I can put only ONE convection coefficient. I don't understand how this works. I cannot specify the convection on each side? What if the coefficients are different? All in all, what coefficient Fluent is expecting? The inner one (close to fluid)? The outer one (external)?

Thanks!
  Reply With Quote

Old   November 17, 2008, 23:38
Default Re: Convection with Shell Conduction
  #2
JSM
Guest
 
Posts: n/a
Hi Corentin,

The heat transfer coefficient you are applying in the wall is only for external surface. For internal wall, fluent will automatically calculate the heat transfer coefficient depends upon temperature difference.

Hope it will help

with regards, JSM
  Reply With Quote

Old   November 18, 2008, 01:04
Default Re: Convection with Shell Conduction
  #3
Corentin
Guest
 
Posts: n/a
Ok, thank you. So, I don't have to worry about the internal convection coefficient. I just have to compute the external one.

Now, I want to calculate this external coefficient through a UDF.

It should be this :

h=1.31*abs(T_wall_ext-T_ext)^0.33

T_ext is the external temperature of the environment, not modeled.

I am using the WALL_TEMP_INNER(f,t) function to get T_wall_ext. It seems strange to use the "INNER" word to obtain the outer (external) wall temperature, but it seems to be the thing to do.

Am I correct?

Regards, Corentin.
  Reply With Quote

Old   November 21, 2008, 04:58
Default Re: Convection with Shell Conduction
  #4
JSM
Guest
 
Posts: n/a
Hi Corentin,

If you want to calculate the heat transfer coefficient by using some function, UDF is the only way.

From your last reply, I understand that the thickness of the wall is not modeled for simulation. If wall thickness is not modeled, then there is no inner wall and outer wall concept. Fluent takes this as zero thickness wall. You can take the temperature value at this wall for heat transfer coefficient calculation in UDF.

If you think the thickness really affect the heat transfer coefficient, the thickness of the wall also should be modeled.

Hope it will help U

With regards, JSM
  Reply With Quote

Old   November 21, 2008, 05:58
Default Re: Convection with Shell Conduction
  #5
Corentin
Guest
 
Posts: n/a
Hi!

I am using shell conduction with NON-zero thickness (because I want to consider the effect of the wall mass inertia on the temperature in unsteady calculations).

That is why i have TWO wall temperatures : interior (contact with modeled fluid) and exterior (contact with outside air, not modeled, free stream temperature).

I am using a UDF to compute the exterior convection coefficient which is :

h = 1.31 * abs [ ( T_wall_ext - T_ext ) ]

That is why I need to get the value of T_wall_ext.

To do so, I am using the WALL_TEMP_INNER(f,t) function.

The Fluent Guide is not very clear on this point, and I think this is strange because the exterior wall temperature should logically be named OUTER but from what I understood I should type WALL_TEMP_INNER instead of WALL_TEMP_OUTER to get the exterior wall temperature (isn't that strange?).

Anyway, could you confirm that WALL_TEMP_INNER will give me the EXTERIOR wall temperature?

About the INTERIOR convection coefficient, you told me that Fluent is dealing with it, so I don't have to worry about that.

Is it still the case?

Anyway, with shell conduction activated and non-zero thickness, Fluent only ask for ONE convection coefficient. Not two.

So I assume Fluent is expecting the exterior one (wich I compute with a UDF) and I guess Fluent is automatically taking care of the interior one.

Am I correct?

Thanks a lot

  Reply With Quote

Old   November 24, 2008, 00:17
Default Re: Convection with Shell Conduction
  #6
JSM
Guest
 
Posts: n/a
Hi,

Yes. You are correct. If you are modeling the thickness of wall, convection coefficient is applied on the exterior wall.

With shell ocnduction, the names given in Fluent is different. Outer wall means that it is modeled in preprocessing. Inner wall means that it is the imaginary wall with the thickness you specified. This wall is in contact with atmosphere. So take the inner wall temperature for convection heat transfer coefficient UDF.

with regards, JSM
  Reply With Quote

Old   November 24, 2008, 02:13
Default Re: Convection with Shell Conduction
  #7
Corentin
Guest
 
Posts: n/a
Ok, thank you very much JSM, you were of a great help
  Reply With Quote

Old   January 30, 2012, 13:12
Default
  #8
Member
 
arjun
Join Date: Oct 2011
Location: Tokyo, JAPAN
Posts: 66
Rep Power: 5
arjun3020 is on a distinguished road
Hi,
Could you please let me know that up to what thikness i can use shell conduction.?

i have model with only surface for flow analysis, if i want to know the heat transfer from model using shell conduction without modeling the thickness,
actual model have 5 mm thickness.
please help.
arjun3020 is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
shell conduction (urgent) muhittin FLUENT 4 September 24, 2013 03:30
Shell Conduction Corentin FLUENT 1 November 12, 2008 05:54
Shell conduction with VOF ??? Asghari FLUENT 0 May 31, 2006 11:38
Shell conduction and Conjugate problem RBM FLUENT 1 October 24, 2005 12:20
Baffle and shell conduction B.N.LOO CD-adapco 1 August 2, 2000 21:08


All times are GMT -4. The time now is 13:16.