The goal of this work was the study of the flow in a square-sectioned torus reactor, in both batch and continuous conditions. A characterization of hydrodynamics in the reactor by computational fluids dynamics (CFD) using Fluent software (R) is presented. Results obtained in batch conditions for the mean bulk velocity as a function of the impeller rotation speed are studied and are compared to a correlation available for a circular-sectioned torus reactor. Mixing time is also investigated. The study is next extended to the case of the continuous regime. After validation of the residence time distribution (RTD) by experimental determination, the influence of the inlet-outlet flowrate on the hydrodynamic characteristics is established, emphasizing a possible modification of mixing performance of the reactor when conducted in continuous mode, depending on the ratio of the circulation time to the mean residence time. (c) 2007 Elsevier B.V. All rights reserved.