A high pressure reactor calorimeter was developed to study chem. reactions in supercrit. fluids. Non-dimensional anal. of the heat transfer mechanism in the calorimeter verifies the application of the Nusselt correlation in scCO2. The reactor's cover and flange were modified to be fully temp. controlled and their contribution to the dynamic response of the calorimeter is investigated. Finally, the esterification of methanol with acetic anhydride was chosen as a model reaction and the role of heat transfer in chem. reactions in supercrit. fluids is discussed.