## Fluids

#### How can I set two diff. heat transf.coeff. on either sides of a virtually thickened wall in wall BC?

• soumitra2102
Subscriber

Hi,

How can I set two different heat transfer coefficients on either sides of a wall boundary face if I use thickness option in wall boundary condition definition?

I have single fluid domain (pipe) surrounded a another fluid domain separated by a solid domain. I don't want to model the solid domain due to its very thin thickness and surrounding fluid domain due to its constant temperature.

Can I provide separate momentum and thermal properties on either side of the separating domain without actually modelling (/meshing) it?

• DrAmine
Ansys Employee
If it is a internal solid located between two fluids you can use shell conduction assign thickness and leave thermal tab as coupled. Convection boundary condition applies rather if external boundary
• soumitra2102
Subscriber

Did you mean 'System Coupling'?

If so, I do not see Shell Conduction option there.

Also, is it possible to to apply two different heat transfer coefficient on either side of the face selected for wall boundary condition with (virtual) thickness applied?

Or maybe, is modeling/meshing a thick-solid-domain mesh for wall thickness is mandatory to do so?

P.S. Although I have three domains (fluid1-solid-fluid2) in real life, I have defined only fluid1 domain in the simulation setup. Fluid2 domain is just for a constant temperature source. And the solid domain is in-between the two domains for conjugate heat transfer.

• Rob
Ansys Employee

Heat transfer from the fluid to a wall is calculated by Fluent. You only set a HTC for the outside of a domain where we don't have cells.

• soumitra2102
Subscriber

Okay, got it!

So you mean, if I want to assign two different  HTCs on either side, I will have to model the wall thickness, right?

Thanks

• DrAmine
Ansys Employee
Again if it is internal wall everything is done by Fluent. You keep the default option to coupled (You can modify that and overwrite what Fluent is doing but you need some expert knowledge hete). (Not talking about system coupling). If the wall has no cells at one side you might that kind of boundary.
• soumitra2102
Subscriber

That means I have to create mesh on other side (even though it has constant (temperature and pressure) conditions) if I want to see the Coupling option.

By the way, I am interested in the manual HTC assigning option because I do have a correlation which I want to test.

Thank You.

• Rob
Ansys Employee

Coupled means we have cells on both sides: heat can pass through the wall.  If you want to alter the  Fluent fluid-wall heat transfer models you'll need to write a wall function UDF: I don't recommend it given the questions you're asking and won't be helping on here beyond suggesting you attend training.

In Fluent we use the wall function models (there are several) to calculate the heat transfer from the fluid to the wall. This flux can then be used in equations to determine an HTC: in Fluent we have a few different definitions. Note the HTC is a derived value used to compare things in engineering, where flux and temperature may vary between cases.