This article investigates ways of modeling the homogenization mechanism occurring when mixing highly viscous Newtonian fluids with a planetary mixer. In particular, an arrangement of ideal reactors containing a perfect-mixed zone sweeping out a torus reactor is proposed to represent the dynamics of the mixing process. The originality of the arrangement of ideal reactors developed is due to the time-dependent location of the perfect-mixed zone in the torus which mimics the periodic revolution motion of the agitator around the vertical and central axis in the vessel. To ascertain the reliability of the method proposed, tracer injections were carried out with a planetary mixer named TRIAXE (R) system. It is shown that modeling results are in close agreement with experimental ones on the whole range of impeller revolution speeds tested. The model proposed captures well the physical mixing phenomena. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 1678-1683, 2011