For reactions m nomsothermal systems, the thermal tune dlstnbubon IS the analog of the residence tie dlstibution If the reaction can be characterrzed by a smgle activation energy, knowledge of the thermal tnne dtstnbution based on thus activation energy can be used to predict the yield of a tist order reaction umquely and to closely bound the yield for reactions of order other than first Thermal tie &stnbutions are a useful conceptual and analmcal tool for reaction engmeenng, particularly m systems where the temperature and velocity profiles are not strongly coupled to the extent of reaction Thus situation frequently occurs m the processmg of polymer melts, for example m the actwatton of blowmg agents or m chenucal mod&ahon of the polymer &am Slmphfied flow models of heat exchange and extrusion eqmpment are used to tiustrate the apphcation of thermal tune dlstnbutions and to show that they often Mer slgmficantly from the residence tune &stnbution m the same device In fixed wall heat exchangers, the thermal tune dlstrtbution shows less umform reaction con&tions than would be true for an isothermal reaction governed by the residence tnne Qstnbution In extruders, and particularly for those where VISCOUS Qsslpation IS the major energy mput, tlus situation IS dramattcally reversed vvlth a reaction envuonment very sun&u to that for piston flow and substantiy better than would occur m the same eqmpment operated Isothermally