Research on the Characteristics of the Solid–Liquid Two-Phase Flow Field of a Submersible Mixer Based on CFD-DEM

Submersible mixers are widely used in the sewage treatment process in various fields, such as agriculture and industry. They are mainly responsible for pushing flow and mixing activated sludge particles in a pool. Based on the CFD-DEM coupling method under the Euler–Lagrange framework, the solid–liquid two-phase flow of a submersible mixer was simulated in this paper, and the motion characteristics and distribution laws of particles in the pool were studied in axial, horizontal, and lateral directions, respectively. An evaluation method of distribution uniformity was proposed to analyze the velocity distribution of the flow field, the velocity distribution of particles, and the mixing uniformity of particles. The results show that the movement process of activated sludge particles in the pool can be roughly divided into three stages: the horizontal development stage, absorption–injection stage, and reflux-mixing stage, in which the reflux-mixing stage is the main stage for the uniform distribution of particles in the whole flow field. Particle accumulation occurs mainly in the dead zones of the flow field. Distribution of particles in the axial direction has the most homogeneous extent. Vortices can be generated near pool walls, causing accumulation of particles. This method can be a good guide for engineering practice.