Stirred Tank Reactors are extensively used in chemical industries. It is common to use either jackets or internal coils when the reaction inside these reactors is highly exothermic. Both arrangements have positive influence and drawbacks in controling the bulk temperature. The design of coiled vessels today follows very much the geometry by Oldshue and Gretton [4] which has been criticized since it affects the flow. Street and McGreavy [6, 5] and Nunhez and McGreavy [3, 7, 2] indicated that if coils are placed in the same height of the impeller blades, internal flow circulation is restricted, even though there is an excellente local heat transfer in the impeller region. This work aims to show by simulating the momentum, mass and energy equations inside the reactor, that there is great gain in performance if small alterations in the internals location are made. The idea is to simulate the flow for both the experimental apparatus cited above and some proposed geometries to indicate how internal flow can be improved. Preliminary simulations have already shown that there is great gain by avoiding to place any coil at the impeller height.433649651Kuncewicz, C., Three-dimensional model of laminar liquid flow for paddle impellers and flat-blade turbines (1992) Chem. Eng. Sci., 47 (15-16), pp. 3959-3967Nunhez, J.R., (1994) The Influence of Geometric Factors on the Optimum Design of Stirred Tank Reactors, , PhD thesis, The University of Leeds, in preparationNunhez, J.R., McGreavy, C., A comparison of the heat transfer in helical coils and jacketed stirred tank reactors (1995) Brazilian Journal of Chemical Engineering, 12 (1)Oldshue, J.Y., Gretton, A.T., Helical coil heat transfer in mixing vessels (1954) Chem. Eng. Progress, 50 (12), pp. 615-621Street, D.A., (1991) Computational Modelling of Stirred Reaction Vessels, , PhD thesis, The University of LeedsStreet, D.A., McGreavy, C., A model of the heat transfer in internally cooled reaction vessels (1991) Heat Exchange Engineering, 2, pp. 279-302. , E. A. Foumeny and P. J. Heggs, editors, Ellis Horwood LtdTatterson, G., Industrial Mixing Technology: Chemical and Biological Applications. Title of the Chapter: The Influence of Geometric Factors on the Optimum Design of Stirred Tank Reactors (1994) AIChE Symposium Series, 89. , AIChEUhl, V., Gray, (1966) Mixing: Theory and Practice, 1. , Academic Press, London