Reply To: How to define side walls, inner walls, and outer walls in a pipe using ANSYS Flu

[Hemantg_17]

Hello Anas Al Rafin, 
You can directly create the required surfaces in CAD model and  create the appropriate Named Selection that can be imported in Ansys Fluent. Also you can provide wall thickness (in Thermal tab) to your geometry and create the shadows where you can assign different boundary/wall conditions. 
For more information please refere to following links :
Creating interior surfaces (ansys.com)
Domains, Cell zone conditions and Boundary conditions (ansys.com)
How to use Thin Walls with Thermal boundary conditions? - Ansys Knowledge

Thank you, 
Hemant G