This paper shows the results of flow visualization and residence time distribution experiments in a Taylor-Poiseuille vortex flow apparatus. It is the first of a series that starts with the identification of flow patterns inside the device and goes up to the assessment of its performance as an enzymatic reactor. Our approach is to study in depth one single geometric configuration (radius ratio "0.677 and aspect ratio "18.30), adequate for use as a heterogeneous reactor and/or adsorption system in bio-processes, rather than spanning a range of geometries and proposing empirical expressions for mass transport coefficients. The range of rotations and axial flow rates used here correspond to low/moderate rotational Reynolds numbers (Re F from 130 to 615, with 1.6(Re F /Re FA (7.7) and low axial ones (Re from 0.172 to 1.067). An unusual behavior of the system was noted in this operational region: the vortex drift velocities are less than one, and decrease continuously with increasing rotations, until a full stop. Except for Re F close to the critical value, the downstream displacement of vortices is slower than the mean axial velocity. The implications of this fact on the reactor performance are discussed.