air region not closed?
 

I'm trying to model a block that sits in an air duct. Inside the block there is a small cylindrical hole coming up from the bottom that will have a heat flux. The purpose is to simulate a cartridge heater being placed inside the block.

When I create the geometry, I do an extrude to create the duct. Then I extrude another block inside the duct and imprint it. Then I extrude cut a cylinder into that block.

The problem is when I split the surfaces and define regions, when I try to mesh it says the air region is not closed. I'm guesing this is because of the hole, because when I suppress that extrude cut I am able to mesh. The only way I can put this hole in the block is to do an extrude cut up into the duct from the bottom where the block sits. How can I define this in another way so I don't have this problem?

EDIT: I tried creating the block with the cylindrical hole first, and then extruding the duct over it so that I did not have to extrude cut up into the duct, but now I cannot boolean imprint to get the two seperate bodies.

Can you provide a picture of the part as you want it to be (i.e. the one that is giving you the not closed error)? It is hard for me, and maybe others, to follow a text description of geometry creation.

Thanks

I recommend you to separately, generate the block with the cylinder inside and then export it. Then generate the air duct and export it.
Open new STAR-CCM file and then import both files as surface meshes and set them as regions. Then translate the block inside the duct by Translate function to sit in the proper place.
Finally combine two regions.
Good luck