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• Novel comparative numerical study of non-Newtonian fluid mixing has been performed using efficient chaotic micromixers. • The TLCCM micromixer has shown its dominance due to its complex structure which generates more intense secondary flows compared to other micromixers. • High mixing index has been obtained using TLCCM micromixer, which exceeds 0.96 for all values of Reynolds number and power-law index. • The TLCCM micromixer has shown the lower pressure drops (Po/MI) compared to other considered micromixers. • Very low values of mixing energy cost (MEC) have been obtained using TLCCM micromixer. High-performances micromixers are widely used in various industrial applications. Mixing in the laminar regime and at low Reynolds numbers is of major importance in some processes. Implementing the physical phenomenon of chaotic advection to improve the mixing efficiency is a well-established technique, therefore, the secondary flows resulting from this technique are very intense and act at the microscopic level on homogenization. This study aims to compare different configurations of passive micromixers. The four examined micromixers are: Two-Layer Crossing Channels Micromixer (TLCCM), Semicircular Serpentine Micromixer (SCSM-90), Curved micromixer with Grooves (CG), and C-Shape micromixer. All micromixer geometries have the same hydraulic diameter and the equivalent unfolded length. The numerical simulations have been carried out at low Reynolds numbers using the CFD Fluent code to solve the 3D momentum equations, the continuity equation, and the species transport equation. The employed non-Newtonian shear-thinning fluids are the CMC solutions which are modeled by the power-law model with power-law index range from 0.73 to 1 and the generalized Reynolds number varies between 0.1 and 50. The mixing efficiency has been evaluated by calculating the mixing index (MI) based on the standard deviation of the mass fraction in different cross-sections. To examine the obtained results, the mass fraction distributions, the velocity profiles, and the mixing energy cost (MEC) have been presented. The results show that the TLCCM micromixer has a high mixing index which exceeds 0.96 for all the generalized Reynolds number values and the considered power-law index, it also has a lower mixing energy cost compared to other studied micromixers. [Display omitted] [ABSTRACT FROM AUTHOR]