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