Numerical simulation of solid-liquid suspension in a stirred tank with a dual punched rigid-flexible impeller

- A new type of dual punched rigid-flexible impeller was proposed.
- Dual punched rigid-flexible impeller was optimized by CFD simulation.
- Dual punched rigid-flexible impeller can improve the solid suspension quality.
- Dual punched rigid-flexible impeller can reduce power consumption.

The hydrodynamics of solid-liquid suspension process in a stirred tank with a dual rigid impeller, a dual rigid-flexible impeller, and a dual punched rigid-flexible impeller were investigated using computational fluid dynamics (CFD) simulation. A classical Eulerian-Eulerian approach coupled with standard k-ε turbulence model was employed to simulate solid-liquid turbulent flow in the stirred tank. The multiple reference frame (MRF) approach was used to simulate impeller rotation. The effects of impeller type, impeller speed, flexible connection piece width/length of dual rigid-flexible impeller, aperture size/ratio of dual punched rigid-flexible impeller, particle diameter, and liquid viscosity on the homogeneity degree of solid-liquid system were investigated. Results showed that the homogeneity degree of solid-liquid system increased with an increase in impeller speed. A long and wide flexible connection piece was conductive to solid particles suspension process. Larger particle diameter resulted in less homogenous distribution of solid particles. An increase in liquid viscosity was beneficial to maintain solid particles in suspension state. The optimum aperture ratio and aperture diameter were 12% and 8 mm, respectively, for solid particles suspension process. It was found that dual punched rigid-flexible impeller was more efficient in terms of solid particles suspension quality compared with dual rigid impeller and dual rigid-flexible impeller under the same power consumption.

Dual punched rigid-flexible impeller consists of two rigid impellers and six silicone flexible connection pieces. There are a certain number of holes on the surface of the flexible connection pieces of dual punched rigid-flexible impeller. The flexible connection pieces are under the interaction of agitating shaft and flowing medium, which can cause a series of disturbances on the flowing medium and generate a series of high-speed jet flows. Dual punched rigid-flexible impeller can improve solid particles suspension degree compared with dual rigid impeller and dual rigid-flexible impeller under the same power consumption.40