sensing the temperature of {HEAD ~ reaction products} at {TAIL ~ said outlet side} of said tube bundle; and 
at
sensing the temperature of { HEAD ~ reaction products } at { TAIL ~ said outlet side } of said tube bundle ; and
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH