Convection into enclosure in Ansys Workbench/Mechanical
Convection into enclosure in Ansys Workbench/Mechanical
(OP)
Good morning,
I'm using Ansys Mechanical 12.1 (although I just got 13.0), and I'm trying to model convection in an enclosure in my model. I don't want to run a full CFD analysis, but I want to be sure that my energy balances (i.e. that the heat going into the enclosure plus the heat leaving the enclosure equal zero). However, using surface-based convection elements, I'm unable to have Ansys solve for the temperature of the air in the enclosure. Sure, I could model the air as a solid, but it would be difficult to capture the proper convective coefficients.
What I've seen people do in the past is to create convective link elements from the nodes along the surface of the enclosure to a single thermal mass element representing the air in the enclosure. The problem is, I can't find any examples showing me how to do that.
I asked the guys from Ansys and their first response was "we can't do that" but when I pressed them, they simply stated, "You'll have to use command objects". Great. I'm not a pro at APDL syntax, so without an example to go by, I'm stuck. I'm thinking that I can use the "E" command to create the link elements, and the EL command to assign their type? From there would I specify the convective coefficient as a function of the temperatures with the KEYOPT command? Uugh... I'm a bit frustrated at the moment. Any help would be greatly appreciated.
I'm using Ansys Mechanical 12.1 (although I just got 13.0), and I'm trying to model convection in an enclosure in my model. I don't want to run a full CFD analysis, but I want to be sure that my energy balances (i.e. that the heat going into the enclosure plus the heat leaving the enclosure equal zero). However, using surface-based convection elements, I'm unable to have Ansys solve for the temperature of the air in the enclosure. Sure, I could model the air as a solid, but it would be difficult to capture the proper convective coefficients.
What I've seen people do in the past is to create convective link elements from the nodes along the surface of the enclosure to a single thermal mass element representing the air in the enclosure. The problem is, I can't find any examples showing me how to do that.
I asked the guys from Ansys and their first response was "we can't do that" but when I pressed them, they simply stated, "You'll have to use command objects". Great. I'm not a pro at APDL syntax, so without an example to go by, I'm stuck. I'm thinking that I can use the "E" command to create the link elements, and the EL command to assign their type? From there would I specify the convective coefficient as a function of the temperatures with the KEYOPT command? Uugh... I'm a bit frustrated at the moment. Any help would be greatly appreciated.





RE: Convection into enclosure in Ansys Workbench/Mechanical
If I get something working, I'll post it on here. It boggles my mind that ANSYS doesn't have any examples set up for modeling enclosures in a thermal model. It's not supported by the GUI in their Workbench platform, and they're not encouraging people to use Classic.
I'm not out in left field to say that this is the proper way to model an enclosure, am I? Energy in = energy out?
RE: Convection into enclosure in Ansys Workbench/Mechanical
I've attached a picture of the geometry that I'm using to test my script and the script for adding the convective links (a square tube). I've yet to make the HTC tabular with temperature (*DIM, I assume) and I'm having trouble getting ANSYS to determine the area represented by the LINK34s (ARNODE command?).
Mesh
Result
I got some help from the guys at ANSYS to put together the script below, but it still isn't quite working. Anyone have any suggestions?
CODE
*GET,n_max,node,,num,max ! Get the maximum node number
nc = n_max+1 ! Set the number of the center node
n,nc,0,0,0 ! Create node at 0,0,0 to tie convective elements to
cmsel,s,inside_surface ! Select convective surface
*GET,nn,node,,count ! Get number of nodes along surface
nsel,a,node,,nc ! Also select node representing enclosure (eg. air)
et,99,34 ! Set element type 99 to link34
r,99,5 ! Set area of element type 99
mp,hf,99,5000 ! Set heat flux for element type 99
type,99 ! Set element type to 99
mat,99 ! Set element material to 99 (i.e. HTC=5000)
real,99 ! Set element area to 5
*do,i,1,nn,1 ! Loop through nodes on convective surface
*GET,n1,node,,num,min ! Get min node number in set
nodearea=arnode(n1) ! Get area per node for link34s (not working)
r,99,nodearea ! Set area of link 34 elements
e,nc,n1 ! Create element from center node to minimum node in set
nsel,u,node,,n1 ! Unselect minimum node in set
*enddo
elist
allsel
/solu
RE: Convection into enclosure in Ansys Workbench/Mechanical
There's a lot of great information on SURF152 elements and all other things ANSYS on Sheldon Imaoka's page at: http://ans
I hope that this helps someone out there.