I work in the biopharmaceutical industry and wanted to make a small model bioreactor. This bioreactor has a cutaway that allows you to see the inside. This is printed as 4 separate parts which allows the impellor to move. 

Supports are only needed for the impellor, all other pieces print without supports. 

The tolerances for the impellor are tight so if you find it doesn't fit, just scale down a bit. 

A model for the bioreactor is also available as a single piece if you want to print all together (i have not tested this one).