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