Two faces at interfaces after volume subtraction
 

Hi pals,
I have a problem when creating geometries in GAMBIT. As you know, volume subtraction command is a useful command in making complex geometries. The problem is when, for example, you subtract two cylinders to build an annulus, GAMBIT creates two faces at the interface! This is undesired, because when you want to set boundary conditions in FLUENT, you can not use coupled for temperature of the interface (This means that you want to specify that the temperatures of solid and fluid phases are similar at the interface).
I usually avoid using volume subtraction in GAMBIT. I mean that I make points, then edges, then faces and then volumes. However this method is very tedious for complex geometries.
One solution is that you delete extra faces one by one. But this method is very exhaustive too! Sometimes you have to select and delete over 100s of faces!
Is there any way to solve this problem? To set GAMBIT in a way that it doesn't create extra faces at interfaces?!
I appreciate your useful comments.

If you substract your in-cylinder from the other you are not suppose tho get the inner cylinder anymore.
Can you reproduce your issue with a simple .dbs and post the journal file here.
I will try to check where the problem is