The tubes form passages for flow of the hot gaseous mixture in heat exchange contact with the gaseous fluid through {HEAD ~ the heat} exchanging {TAIL ~ chamber}, thereby preheating the gaseous fluid prior to reaction with the fuel 
exchanging
The tubes form passages for flow of the hot gaseous mixture in heat exchange contact with the gaseous fluid through { HEAD ~ the heat } exchanging { TAIL ~ chamber } , thereby preheating the gaseous fluid prior to reaction with the fuel
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 OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH