Study of free‐surface and solids suspension in top‐sealed tanks stirred by pitched blade turbine impellers through DEM‐VOF method

A coupled method of discrete element method (DEM) and volume of fluid (VOF) is applied to study the particle suspension in top‐sealed solid–liquid tanks with a free‐surface. VOF is used to track the gas–liquid free‐surface, and DEM is used to calculate the movement and interaction of particles. As the air between the cover and free‐surface in a sealed tank is very limited, the free‐surface evolution process that a big vortex is generated quickly and then shrinks to a smaller one in sealed stirred tanks is reported first in this paper. In addition, the effects of pitched blade turbine (PBT) with different blade pitched angles (including 30°, 45°, 60°, 75°, and 90°) on solid suspension, free‐surface, and power number are investigated. Finally, the relationships between particle motion and fluid flow during the stirring are studied carefully. Fluid flow plays a dominant role during the start‐up of the stirring; and then, due to the contact of particles, some particles could obtain the larger velocity than the fluid. The results obtained here are helpful to design the sealed stirred tanks with PBT.