To improve static and continuous mixers, several methods have been proposed inthe literature. Herein, two well-known passive intensification configurations wereapplied to an annular laminar flow and numerically studied. Residence time distributions(RTDs) and Poincare´ sections were examined to investigate the dispersionof the particles. These two approaches show that geometric perturbations ofthe walls improve the mixing level for all Reynolds numbers investigated. AboveRe = 300, the increase in mixing can be attributed to chaotic advection within theflow. Finally, a general reactor model that allows the RTD in the annular tube tobe predicted with high confidence is proposed.