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