Discussion Groups

Simulation CFD

Reply
Active Member
Rycosso
Posts: 7
Registered: ‎05-11-2011

Thermal Analysis Heat Flux Through Walls

534 Views, 7 Replies
04-22-2013 01:22 PM

I am modeling walls to test thermal performance, and I have found that as my model gets more complex the difference between the interior and exterior heat flux gets larger. I applied a film coefficient boundary condition on the interior and exterior of the wall, and on all the edges I put a heat flux boundary 0.

 Heat Flux and FC.JPG

 

At first I thought it was meshing, but I still had the issue when I made the mesh as small as the software allows. The problem also goes away if I apply the same material to all layers of the system.

 

Why am I getting a different heat flux on the interior and exterior of my model? 

 

Heat Flux and FC2.JPG

 

Please use plain text.
Product Support
Royce_adsk
Posts: 565
Registered: ‎08-24-2011

Re: Thermal Analysis Heat Flux Through Walls

04-22-2013 02:42 PM in reply to: Rycosso
Try running with tight convergence with ADV5. Let us know if that helps!

-Royce


Royce Abel
Please use plain text.
Active Member
Rycosso
Posts: 7
Registered: ‎05-11-2011

Re: Thermal Analysis Heat Flux Through Walls

04-22-2013 03:43 PM in reply to: Royce_adsk
I turned the convergence to the tightest that the slider would go, and changed the Advection to ADV5, and my results did not change at all.
Please use plain text.
Product Support
apolo.vanderberg
Posts: 296
Registered: ‎08-31-2011

Re: Thermal Analysis Heat Flux Through Walls

04-30-2013 11:23 AM in reply to: Rycosso

Rycosso,

  As your model gets more complex, be sure that the mesh quality through the thickness (of each material) remains at a similar mesh quality. It is possible that your more simplistic models had a better quality mesh through the material thicknesses such that we were able to maintain an energy balance more easily.

 

There is no need to assign a Heat Flux of 0W on the sides/edges, we automatically assume that an exterior wall without any thermal boundary condition will be treated as adiabatic.

 

Apolo

Please use plain text.
Active Member
Rycosso
Posts: 7
Registered: ‎05-11-2011

Re: Thermal Analysis Heat Flux Through Walls

05-03-2013 11:46 AM in reply to: apolo.vanderberg
Thank you Apolo for the suggestion. I have reduced the mesh in the model to the lowest the software will allow, and the change in the result is negligible. I have also tried the adaptive mesh options, and they do not resolve the issue either.

Thank you for the Adiabatic tip, that will help speed up the model making process.
Please use plain text.
Active Member
Rycosso
Posts: 7
Registered: ‎05-11-2011

Re: Thermal Analysis Heat Flux Through Walls

05-16-2013 03:25 PM in reply to: Rycosso

I have even tried the simple wall below to show that meshing could not be the issue. I made this super simplified wall model with 1" thick studs with the settings you described above, and I am still getting different heat fluxes on the interior and exterior.

1in stud.PNG

Wall Calc.PNG

 

Please use plain text.
Product Support
Royce_adsk
Posts: 565
Registered: ‎08-24-2011

Re: Thermal Analysis Heat Flux Through Walls

05-16-2013 03:35 PM in reply to: Rycosso
That is a 3.6% error which is typically regarded as a reasonable error.

-Royce


Royce Abel
Please use plain text.
Member
megmac
Posts: 3
Registered: ‎11-20-2013

Re: Thermal Analysis Heat Flux Through Walls

07-29-2014 10:53 AM in reply to: Rycosso

Hi there.

 

Please see my post here: http://forums.autodesk.com/t5/Simulation-CFD/Wall-Calculator-Heat-Flux-in-AutoDesk-Simulation-CFD/m-...

 

I believe I am having a similar problem (i.e., interior surface fluxes do not equal boundary fluxes at steady state).

 

Did you ever find a resolution to this problem?

 

Thanks!

Please use plain text.