Thermal Chaotic Mixing of Non-Newtonian Fluids in a Two Rod Mixer

We investigate the mixing and heat transfer enhancement in a two rod mixer for highly viscous non-Newtonian fluids. The mixer is composed of two circular rods maintained vertically in a cylindrical tank. Chaotic flows are obtained by imposing temporal modulations of the rotational velocities of the walls. We study the effect of different stirring protocols leading to non-chaotic and chaotic flows on the efficiency of mixing and heat transfer for three different rheological fluid behaviors: shear-thinning, Newtonian and shear thickening. For this purpose we use statistical indicators characterizing the mean value of fluid temperature and its homogenization. We find that chaotic mixing is suitable for shear-thickening fluids for which we observe a manifest enhancement of the thermal mixing (heat extraction and homogenization). This is due to the increase of apparent fluid viscosity in the vicinity of the rotating walls. This aspect confirms the relevance of chaotic mixing for highly viscous fluids.