Optimization of impeller blades for laminar flow mixing of food-grade non-Newtonian fluids in a stirred tank without baffles

In this study, the triangular fractal impeller (TF impeller) was introduced to instigate structural instability of the IMRs. The mixing performance was evaluated by investigating the power consumption characteristics, fluid mixing time, and the visual structure of IMRs via experimental methods. Numerical simulations were employed to analyze the flow field characteristics by assessing the velocity distribution, strain rate distribution, Poincaré maps, and trajectories of massless particles. The findings demonstrated that TF impeller decreased power consumption and power number, shortened the mixing time, and reduced the dimension of the IMRs. Moreover, TF impeller could also improve the fluid velocity and strain rate while enlarging the size of the CMRs. The impacts became more significant as iteration count of TF impeller increased. In addition, the Poincaré section revealed the existence of IMRs and CMRs in the flow field, which was observed in the visual experimentation. The Poincaré section showed that fluid particles in the IMRs exhibited quasi-periodic motion confined to their respective regions. It was also found that the structure design of TF impeller could facilitate the fluid particles escape from the IMRs into the CMRs, enhance their continuous stretching and folding, and improve interregional material exchange and mixing homogeneity.