The burner is a gas fired burner whose flame is encapsulated in {HEAD ~ a layer} of cool air due to {TAIL ~ the effect} of the induction blower drawing air through the tube bundle from the exhaust outlet, so that the flame does not melt or burn through the tubes 
due to
The burner is a gas fired burner whose flame is encapsulated in { HEAD ~ a layer } of cool air due to { TAIL ~ the effect } of the induction blower drawing air through the tube bundle from the exhaust outlet , so that the flame does not melt or burn through the tubes
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH