CFD Online URL
[Sponsors]
Home > Forums > CFX

radiation in glass plate

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

Reply
 
LinkBack Thread Tools Display Modes
Old   June 25, 2013, 08:51
Default radiation in glass plate
  #1
Senior Member
 
Join Date: Jul 2010
Posts: 142
Rep Power: 6
keeper is on a distinguished road
Hello guys.

I have a problem with radiation simulation. I simulate flow in the winter garden including sun heat flux. I want to compare different types of glasses (three-plate vs. two-plate etc.).

If I use Discrete Transfer radiation model, everything is OK if I set radiation up only on fluid domain. But I want to simulate radiation through the windows so I suppose that I need to define radiation model also for solid domain so I have to use Monte Carlo for both domains. But as soon as I run the calculation with MC model, I get strange results (temperatures between -50 and 300C).

The radiation source is on grey wall with mesh displayed (600 W/m^-2).

I defined material properties (scattering and absorbtion ceoffs and refractive index) for glass and I left all the interfaces as a default. And this is what I don't know how to set up. Can anyone help me with that? Any idea could help...

Thanks in advance.

Best Regards
Attached Images
File Type: jpg model1.jpg (35.8 KB, 33 views)
keeper is offline   Reply With Quote

Old   June 25, 2013, 19:58
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 9,880
Rep Power: 78
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
I presume then you want to model transmission, reflection and absorption in the glass. I do not think the discrete transfer model can handle this, I think you will need the full Monte Carlo model to do this.

If the Monte Carlo model is giving strange results then I suspect it is not fully converged yet, or you do not have enough rays to accurately model the heat transfer.

Can you post your CCL?
ghorrocks is offline   Reply With Quote

Old   June 27, 2013, 02:10
Default
  #3
Senior Member
 
Join Date: Jul 2010
Posts: 142
Rep Power: 6
keeper is on a distinguished road
Thank you for reply.

Yes you are right that is what I want to define and check. And because MC is the only radiation model available for solids I have to use it. I attached CCL and two pictures to see what I obtained. The contours are identical, the only difference is in variable range (post1.png - user specified range, post2.png - local range). Just to see nonrealistic values.

In CCL please note that "okna" domain represents windows.

Thank you in advance for reply.

Best Regards
Attached Images
File Type: jpg post1.jpg (57.5 KB, 26 views)
File Type: jpg post2.jpg (47.0 KB, 23 views)
Attached Files
File Type: txt ccl_radiation.txt (83.8 KB, 12 views)
keeper is offline   Reply With Quote

Old   June 27, 2013, 02:16
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 9,880
Rep Power: 78
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
That is exactly what happens when the radiation model is too coarse. Try reducing the radiation ray tracing coarsening factor.
ghorrocks is offline   Reply With Quote

Old   June 27, 2013, 02:57
Default
  #5
Senior Member
 
Join Date: Jul 2010
Posts: 142
Rep Power: 6
keeper is on a distinguished road
Excuse me, what do you mean exactly? Where I can find it please? Cause I don't know what you mean exactly right now
keeper is offline   Reply With Quote

Old   June 27, 2013, 03:06
Default
  #6
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 9,880
Rep Power: 78
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
Code:
     THERMAL RADIATION CONTROL:
       Diagnostic Output Level = 1
       Iteration Interval = 3
       COARSENING CONTROL:
         Target Coarsening Rate = 32
       END
     END
Target coarsening rate - reduce it from 32, and maybe try a shorter iteration interval. Anything which look like it will make the radiation modelling more accurate.
ghorrocks is offline   Reply With Quote

Old   June 27, 2013, 03:07
Default
  #7
Senior Member
 
Join Date: Jul 2010
Posts: 142
Rep Power: 6
keeper is on a distinguished road
OK I'll try. Thank you very much Glenn.
keeper is offline   Reply With Quote

Old   June 27, 2013, 09:13
Default
  #8
Senior Member
 
Join Date: Jul 2010
Posts: 142
Rep Power: 6
keeper is on a distinguished road
So I tried to decrease coarsening rate to 8 and calculated radiation each 2 steps but it is still the same. What is wierd to me is that when I check radiation coarsening information just in partitioning it shows me that I get only 1 radiation element from 2.4M elements. Is it possible to force it somehow or just to have "power" to affect this coarsening? I know that there are few other options but I don't know which one could be appropriate.
keeper is offline   Reply With Quote

Old   June 27, 2013, 19:41
Default
  #9
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 9,880
Rep Power: 78
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
There are a lot of radiation options and to be honest I do not know them all well. But I can say the image you showed was typical of poor radiation resolution and/or accuracy, so it looks like adjusting the radiation defaults is required in your case. So I would adjust all relevant looking radiation controls and look at their impact.
ghorrocks 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
problem in glass radiation model (DO model) wunan805 FLUENT 0 October 10, 2012 06:06
Aluminium Plate Heated by Solar Radiation Allankey FLUENT 0 May 29, 2012 14:45
Radiation through: glass – air cavity – glass Yingchun CFX 7 February 27, 2012 17:46
radiation through glass amrjoao FLUENT 0 July 19, 2011 11:18
ACOUSTIC RADIATION behavior of a plate with mass distribution rickyben ANSYS 0 August 22, 2009 08:38


All times are GMT -4. The time now is 09:00.