Abstract Summary (Max 250 words)
Confined impinging jets (CIJs) mixers are a class of efficient mixing devices known for their ability to achieve rapid mixing at the micro-scale. These devices are widely explored in the chemical industry, particularly in processes involving non-Newtonian fluids, such as reaction injection molding (RIM) and emulsification. However, fundamental studies addressing the flow behavior of non-Newtonian fluids in CIJ configurations remain limited. In this work, Computational Fluid Dynamics (CFD) simulations were performed to study the hydrodynamics of a shear-thinning fluid described by a power-law model, with a flow behavior index n=0.8229 and a consistency index K=0.0849 Pa s^n. A 2D model corresponding to an axial section of the 3D chamber was used to assess the conditions for the onset of chaotic mixing regimes. Reynolds numbers in the range 300-500 were analyzed, leading to the identification of two flow regimes: steady and chaotic. The critical Reynolds number that marks the transition between the two flow regimes occurs at 400-500, where a self-sustained chaotic flow regime characterized by the formation of vortices is observed, which is the main factor for the efficient mixing of fluids in CIJs. The validation of the 2D CFD model was done by comparison with fully resolved 3D CFD simulations. Furthermore, a spectral analysis was carried out to examine the characteristic jet oscillations at different locations within the chamber, demonstrating that the 2D model can accurately predict the main flow features when a corrective factor accounting for geometric differences is applied.
