CFD-DEM study on circulation pattern and particle suspension dynamics in PBT solid–liquid stirred tank

Abstract

The stirred tank is widely used in industrial processes for efficient material mixing. In this work, a multi-scale numerical model suitable for dense particle flow is established based on the CFD-DEM approach. After verifying the reliability of the model by comparing with experiments, the solid–liquid two-phase behaviors in a single-layer unbaffled pitched blade turbine (PBT) stirred tank under transitional flow regime are investigated at different stirring speeds. The chain effect of stirring speed- discharge stream-suspension dynamics and the hindering mechanism of isolated mixing zone in solid–liquid system are revealed. Results show that the discharge stream caused by the pitched blades, which is directly affected by the stirring speed dominates the formation of two main circulation structures and the isolated mixing regions (IMRs). Notably, when the stirring speed exceeds a threshold, which lies between 350 rpm and 450 rpm, the enhancement of suspension is significantly diminished. To elucidate the underlying mechanism responsible for this phenomenon in the transitional flow regime, this study employs a multi-scale and multi-physics analysis. The outcomes of this study present insights into solid–liquid flow dynamics and provide a theoretical basis for optimizing stirred tank performance.