A reaction system comprising a reactor containing a reaction process medium and a heat exchanger providing a conduit through which flows a heat transfer fluid in which measurement of the flow rate and temperature change of the heat transfer fluid across the reaction is used to determine the heat generated or absorbed by the reaction system and that determination is used to monitor and control the reaction and the measurement instrumentation is calibrated by process specific calibration and the reaction system is calibrated by simulating the reaction conditions and the data from the two calibrations is used to set the monitoring and control means.
