Determining heat flux through area

[mizr3en]

Hi,

I have been struggling to determine heat fluxes through select areas in ANSYS 12.1 with a 3D model. I was unable to find a tutorial/example other than "VM161: Heat Flow From Insulated Pipe" in a document released by Ansys titled "ANSYS Mechanical APDL Verification Manual." My model is quite a bit different than the geometry used in this verification. If someone has a GUI-based thorough tutorial I would appreciate it if I could see it. Otherwise, I'll explain where I am:
What I ended up doing to produce a preliminary result was select the nodes on an area as seen in the top image in the attachment using:

Utility Menu>Select>Entities>(Elements By Num/Pick From Full OK)>"box" radio button selected

Then I went to General Postproc>list results>nodal solution>thermal flux>(select any direction)

All flux values in x,y,z directions (and sum) show up in a list. I copy this list to Excel and analyze the data there. The only thing I can verify is when a temperature gradient is constant on the top surface (as seen in the top figure of attached file). The heat flux on each node equals the heat flux in from the five cylinders on the bottom because every other exterior surface is insulated (flux=0). This seemed logical to me, because flux is in W/m^2. When I changed my BC's to let convection be on the cylinder walls from the shoulder to the top with top insulated (as seen in the second figure in attached file), I followed the same process and tried to take the average of the flux sum for each node (~262 nodes for these areas) but got a value that was 64% lower than the flux in from the cylinders. Please let me know (in detail) if there's a way to use the element table or FSUM as seen in xansys ("THERM: Integrating Heat Flux over Surface Boundarie" and "Calculating heat flow across convective surfaces" respectively).

Thanks!

 

[mizr3en]

Attached is the answer to the above question with explanation.

 

[flash3780]

I'd recommend using surface effect elements (SURF152) to apply your convective boundary conditions when building your model, and RAD252 radiosity elements if you need to apply radiation in a cavity. You can retrieve the ETABLE data through the surface effect elements. Check the RSURF and ESURF commands.

//signed//
Christopher K. Hubley
Mechanical Engineer
Sunpower Incorporated
Athens, Ohio
--

http://engineeringliberty.wordpress.com

 

[mizr3en]

Thanks I will look into using the SURF152 elements. I was able to verify a simple case of constant temperature on the top flat surface and convection on the curved sides using SURF87 elements throughout but I had to refine the mesh at the interface between the two faces. My energy out was 0.7% greater than my energy in. I will also look into the RSURF and ESURF commands and post any significant findings.

Nick