Modeling of batch and continuous twin rotor mixers, widely used in polymer processing is a challenging computational problem. One approach to understand the mechanics of flow in twin rotor mixers is to simplify the geometry, of the rotors bq: using cylindrical rotors. This geometry is referred to as the double-Couette geometry. Advantages of the double-Couette geometry are a simple symmetrical mesh design and no time-dependent flow boundaries. In this work, we used the double Couette geometry to study the mechanics of flow and mixing efficiency in laminar and turbulent flow regimes. Flow visualization experiments utilizing a flourescent dye were carried out in a transparent flow cell. A fluid dynamics analysis package-FIDAP, based on the finite element method, was used for the flow simulations in laminar and turbulent flow regimes. Numerical results showed good agreement with the experimental data. We attempted a qualitative comparison for distributive mixing efficiency in laminar and turbulent flow regimes in light of the spreading of a tracer. line (dye) in the matrix. The analysis pointed out to differences in the mixing mechanisms encountered in different flow regimes.