{HEAD ~ Air} is forced through {TAIL ~ the tube bundle} by either a draft induction blower located at the outlet end of the tube bundle or a forced draft blower located at the inlet 
{ HEAD ~ Air } is forced through { TAIL ~ the tube bundle } by either a draft induction blower located at the outlet end of the tube bundle or a forced draft blower located at the inlet
HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL 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