Heat flux surface integral

[MechMick1]

Hi,

I have solved a heat transfer problem in ANSYS workbench, with internal heat generation and some heat flux into the system (representing Joule heating). The heat is dissipated via convection and radiation on various surfaces.

I am wanting to see how much heat is lost through each surface. I assume I need to integrate the heat flux over each surface to give me the total heat being dissipated over that surface. I would of thought this would be common (and easy), but I haven't had much luck finding examples and help on this.

I have practically no experience with ANSYS classic and have made and solved the model in workbench, and exported the input file to be opened in classic because I believe I can't do the surface integration in workbench. Is this true?

Are there any good examples of how to do this? Or is it something that can be explained in a forum post?

I have tried using the FSUM command, but I get the warning "No element nodal forces available. The FSUM command is ignored". Why is this?

Do I need to export individual values for heat flux as nodal/element values in table format and manually integrate in another program (e.g. excel/matlab)? I have seen this recommended to people in posts that are 10+ years old, and I'm hoping this isn't still the standard way to compute heat loss?

Thank you for any assistance,
Mick.

 

[MechMick1]

Hi again,

So an update on my problem: I believe I have it worked out.

I need to use the command "outres,all,all" before solving, then it will solve with the needed variables. And I can use selection groups from workbench to select and then 'fsum' to get the heat flow from that surface.

I haven't had a chance to check this thoroughly yet, but hopefully it is correct.

-Mick.

 

[rickfischer51]

You can do this all in Workbench. In Solution, add a Probe, Reaction to the surface of interest.

If you want to do this in Classic, I think the best way is to apply SURF152 elements to the surface of interest, then select those elements and use the ETABLE command to get the total heat flow HFCTOT which is SMISC,2 for those elements. Then, use SSUM to get the total for the surface.

FSUM sums forces. There are no forces in a thermal analysis.

Rick Fischer
Principal Engineer
Argonne National Laboratory