passing said reactants at a known preselected concentration through said bundle of parallel tubes wherein the inlet temperature is high enough to initiate said {HEAD ~ catalytic conversion} throughout {TAIL ~ said volume} of catalyst 
passing said reactants at a known preselected concentration through said bundle of parallel tubes wherein the inlet temperature is high enough to initiate said { HEAD ~ catalytic conversion } throughout { TAIL ~ said volume } of catalyst
OTH OTH OTH OTH 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 TAIL OTH OTH