## Fluids

#### (in surface body) how to specify heat transfer coefficient in boundary condition

• Vsing
Subscriber

I am trying to simulate convection over a finned surface.

For this I made a 2-D geometry, by using Face Split tool in Design Modeler, to split a surface into the different zones(namely air, hot plate, fins, insulation, etc.).However, when I go to the Boundary Conditions section of the Setup to specify the Heat Transfer Coefficient for the convection between air and the finned surface, only 3 modes show up, the mixed, radiation, modes don't show up, hence i am unable to specify the heat transfer coefficient for my problem.

What could I be doing wrong? Suggestions are welcome.

Thanks,

Vsing

• DrAmine
Ansys Employee

Can you add screenshot: please insert and do not attach.

Do you want to prescribe the input into the domain by using HTC and Temperature of outside air?

• Vsing
Subscriber

abenhadj,

Yes, I want to input HTC and Free-stream Temperature(which isn't all that free in my case)

the following image describes my problem, this is the longitudinal section of a finned cylinder(cylider=1, fins=2), with a melting/solidifying substance(). 2 and 3 forms a convective boundary with 4(which is air, which in turn is in contact with another metal 5, which gets heated/cooled according to the heat give/taken by cylinder 1). The thing is I want 1, 2, and 3 to be COUPLED amongst each other, Meanwhile, in between (2,3) and 4 is to be a boundary condition with CONVECTION mode. 4 and 5 are to be coupled. The thing is that Ansys is treating the boundary between (2,3) and 4 as a kind of interior, even though I can turn it to a Wall, only coupled, temperature and heat flux modes appear for thermal boundary conditions. It just doesn't fit in with the system Ansys is using in the background. Is there a way to get around this issue. Only the outermost boundaries, of the surfaces, can be specified with convection kind of B.C.s, I get that. And I have figured that eliminating Domain 5, and 4 altogether, makes the boundary (2,3)-4, an eligible boundary for convection, and then inserting a UDF for free-stream Temperature could work as a substitution for the heat source/sink, that 5 is. But, I don't want to do that, please tell what am I naive about here?

• Rob
Ansys Employee

Do you have mesh in the "4" region?  If there are cells on both sides of the wall you'll get Coupled (and usually leave it that way). The mixed, radiation etc are only available on external walls (cells on one side only) as they're an approach for when you're not modelling the other side of a wall.

• Vsing
Subscriber
I realised that. Is there any way I can use these modes of B.C.s when I want to model both sides of the wall?
• DrAmine
Ansys Employee
No. Only though UDF might be possible.
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