Efficient mixing of yield-pseudoplastic fluids at low Reynolds numbers in the chaotic SMX static mixer

Abstract

Complex rheology of non-Newtonian fluids often leads to non-homogenous mixing due to the spatial viscosity gradients. The non-intrusive electrical resistance tomography (ERT) technique was employed to study the mixing of non-Newtonian fluids in a chaotic SMX static mixer. For the first time, the effect of the rheology of the yield-pseudoplastic fluids on the quality of distributive mixing was explored in this study. The non-Newtonian fluid used in this study was the xanthan gum solution, which is a yield-pseudoplastic fluid obeying the Herschel-Bulkley model and its rheological parameters change as the solution mass concentration increases. The tomography images were utilized to investigate the efficacy of the distributive mixing of two different types of the secondary streams (Newtonian and non-Newtonian) in the primary stream of xanthan gum solutions (0.5wt%, 1.0wt%, and 1.5wt%). Experiments were conducted for three different primary flow rates ranging from 3.5L/min to 12.5L/min while keeping the center-line injection of secondary stream fixed at 100mL/min for all experiments. Our results revealed that the Newtonian secondary stream favored effective axial mixing over the non-Newtonian secondary stream. However, interestingly, for both types of the secondary streams, a more effective radial mixing was observed as the xanthan gum mass concentration increased at low Reynolds numbers.