The hydrodynamics performance of a coaxial mixing system operating in the laminar regime has been experimentally studied by flow visualization. A Rushton turbine was used in combination with an anchor in both co- and counter-rotating modes to mix viscous Newtonian and non-Newtonian fluids. Image analysis of a discoloration reaction was used to quantify the mixing evolution in the tank. The mixing curves generated by this method were used to reveal the presence of flow compartmentalization and dead zones. It was shown that the co-rotating mode is better to avoid flow compartmentalization