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