{HEAD ~ Channel} shaped {TAIL ~ fluid bed devices}, preferably subdivided into several zones, are preferred 
shaped
{ HEAD ~ Channel } shaped { TAIL ~ fluid bed devices } , preferably subdivided into several zones , are preferred
HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH