[saimen]

Dear CFD community

I have been struggling with a coupled heat transfer problem for quite a while now and tried to look for a solution in your forums but could not find any answer.

For simplicity, my model contains a tube (solid domain) with water (fluid domain) flowing on the inside at laminar conditions. I defined the geometries and created a contact between the inner tube surface and outer water surface before generating the mesh.
When I want to setup up my solution, I have a src and trg interface for both domains. I can make a coupled wall by selecting these two interfaces and ANSYS automatically creates 4 new boundary conditions:

- side1-wall-contact-src (wall) -> can choose BC
- side2-wall-contact-trg (wall) -> can choose BC
- wall1-1-1 (wall) -> coupled selected
- wall1-1-1-shadow (wall) -> coupled selected

My question now is, why does ANSYS create 4 new walls?
I would just like to have coupled heat transfer across the interfaces. However, I also have to set BCs for the src and trg walls but I only know the outside surface temperature of the pipe and have no information on the heat flux.

Does ANSYS need a HTC as input or can it calculate this value directly from correlations using flow conditions and thermal properties? In case I need to insert a HTC, which wall should I choose (src, trg or both)?

I would be very glad to have some answers. Maybe I got confused with some stuff and hope some of you could help me with the understanding.

Best Regards!
-saimen

[saimen]

I think I found the solution. Before creating the mesh, I have to select all bodies in the DesignModeler, right click and "form body". Now when I create the mesh and go to the setup procedure, I see a wall and shadow wall for both domains. They are already defined as coupled and this seems to work.

One other question: When I want to include S2S radiation, which wall do i have to choose for the view factor calculations, the shadow walls or normal walls? Because I can only change the emissivity in the shadow walls, so I used those for the view factor calculation.

Best,
saimen

[dvolkind]

Hi, Saimen!

S2S model works in fluid domains only, so you don't have to care about solid side of the coupled wall. But fluid side is not always "shadow" - that's geometry dependent. To tell which wall is which you can simply judge by available BC settings. There is also a text box in the BC menu, indicating its neighboring cell zone.

[saimen]

Hi dvolkind,

Thanks for your quick reply! I was thinking about the same thing, but someone posted a long time ago that you don't have to include shadow-walls.
But that is really geometry dependent!

Regards,
saimen

[scholar]

Dear Sir,

I have to calculate the inner heat transfer coefficient of a helical coil inside which cold water is flowing. I have created the geometry in Gambit. Kindly help me with the steps to carry out the heat transfer process in Fluent.

Thank you.

[tong6061]

Step 1. On mesh step, u should specify the connects. (automatically will connects,connects1, connects2...)
Step 2, On Setup/ solution.
if solid-fluid interface, it will have different name, like wall-1,wall-2,etc
Step 3, go to mesh interfaces, delete the old interfaces and create new interface, u should choose' coupled' or "mapped" (same thing, just mapped is more robust).
Step 4, it will automatically create 4 walls, (2 shadows and 2 normals), the two shadows u just need set as coupled, and 2 noramls set the bc (generally u dont need set anything to it, it will automatically calucalte, if zero thickness, it will perfect conduction).