I would like to specify my hex mesh with different domain names in order to initialize my 2 phase calculation correct in FLUENT. How do I set up the mesh in ICEM so I in FLUENT will have 2 domains, just lige the tutorial no. 20 in fluent?

You can re-assign the blocks to a new part. By default the blocks belong to the part SOLID, so you can create a new part called SOLID2, for example, and add the blocks to that. Then when you set up the boundary conditions, define the two volume parts as separate fluid or solid domains.

Ok Thanks for your help. I'm getting the picture. I have now created what i call LIVE and LIVE2. But how do I actually specify them as two separate fluid domains? Fluent crashes when i read in the mesh.

Try saving the two domains as separate unstructured meshes, and reading them separately into Fluent, so that you can see where it crashes.

they both crash.... I've attached a plot of the 2D case, maybe that gives a better overview. LIVE2 (purple) should be sand and LIVE (red) air in my fluent multiphase case.