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