Thanks to ppemawm user at FreeCAD forum, who pointed out that the design is known for ages. It is called "screw-type labyrinth seal" or "labyrinth pump". The internet is definitely not full of pictures of this design.

See ppemawm's post here: http://forum.freecadweb.org/viewtopic.php?f=24&t=13507&p=108132#p108125