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