Study on mixing characteristics of viscoplastic fluid in a rigid-flexible impeller stirred tank

The rigid-flexible impeller (RF impeller) was used in the mixing process of viscoplastic fluid, and the mixing performance of RF impeller was explored by using numerical simulation and experimental analysis. Results indicated that RF impeller could reduce the power consumption (P) and demonstrate the advantage of energy-saving compared with Rushton turbine (RT). RF impeller demonstrated a more pronounced force coupling effect between the impeller and surrounding fluid, and exhibited superior adaptability in the flow field compared with RT. Meanwhile, the utilization of RF impeller can effectively enhance the expansion of high velocity region, expand the cavern zone, and decrease the mixing efficiency number while maintaining constant P compared with RT, and the size of high velocity region and cavern zone could be increased with an increase in impeller speed. Moreover, the cavern structure was obtained through the visualization experiment, and the results were similar to that in the simulation. The findings suggested that incorporating rigid-flexible combination structure design of impeller blades could effectively expand the cavern zone, reduce the stagnant zone, and enhance the mixing efficiency in the viscoplastic fluid mixing process.