One or more outlet apertures are formed between {HEAD ~ the two inner shells} for {TAIL ~ passage} of the gaseous fluid out of the heat exchanging chamber 
One or more outlet apertures are formed between { HEAD ~ the two inner shells } for { TAIL ~ passage } of the gaseous fluid out of the heat exchanging chamber
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH