Mixing enhancement of pseudoplastic fluids by multi‐stage fractal‐arranged perforated impellers

Abstract High‐viscosity pseudoplastic non‐Newtonian fluids readily form localized active‐flow caverns and stagnant regions during laminar agitation, which weakens bulk circulation and prolongs mixing time. In this work, the active‐flow cavern refers to an impeller‐induced intensified flow zone rather than a true yield cavern in a viscoplastic fluid. To address this problem, a multi‐stage fractal‐arranged perforated impeller (FAP impeller) was proposed. The effects of impeller stage number and blade pitch on the mixing characteristics of sodium carboxymethyl cellulose (CMC‐Na) solutions were investigated using computational fluid dynamics (CFD) simulations and experimental validation. Single‐ and double‐stage FAP impellers with straight blades (FAP‐SB) and pitched blades (FAP‐PB) were compared in terms of flow characteristics, power consumption, active‐flow cavern evolution, and mixing time. The results showed that the double‐stage configuration expanded the active‐flow cavern and reduced high‐viscosity stagnant regions. At Re ≈ 101–272, the mixing times of the double‐stage FAP impeller with straight blades (2S FAP‐SB) and the double‐stage FAP impeller with pitched blades (2S FAP‐PB) were reduced by approximately 15.21%–21.18% and 17.79%–27.16%, respectively, compared with the single‐stage FAP impeller with straight blades (1S FAP‐SB). Moreover, 2S FAP‐PB further shortened the mixing time by 3.03%–7.59% relative to 2S FAP‐SB. Overall, 2S FAP‐SB was more effective in enhancing local shear, enlarging the active‐flow cavern, and increasing the strain rate, whereas 2S FAP‐PB exhibited better bulk mixing performance. These findings provide guidance for impeller design and equipment retrofit in the agitation of high‐viscosity non‐Newtonian fluids.