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