Error in geometry Fluent

[neder.thomas]

Hello, I'm a beginner in CFD and I want to do an axisymmetric simulation of a diffuser. I have 2 sketches, one is my control area where the fluid passes, in this case water, and the second sketch is a line that represents my diffuser. I generate the surface from my first sketch and a line from my second sketch. When I try to subtract one from the other, Ansys doesn't accept it, I believe because I'm trying to subtract a line from an area. Does anyone know how I can adjust this geometry to do this axisymmetric simulation of my diffuser?
P.S.: After I did this, I tried to open the mesh and it gave an error in the geometry that indicated that the diffuser line could not be there.

[neder.thomas]

I want to replicate this example

[NickFL]

Take a look here: https://innovationspace.ansys.com/forum/forums/topic/line-heat-source-in-a-2d-fluent-model/

You do not want to apply any heat transfer there, simply treat it as a wall.