Single-bubble fragmentation in a mechanically stirred liquid bath under trailing vortex conditions.

• Bubble fragmentation in a stirred vessel is categorized into three types: collision with a blade, boundary layer ahead of blade, and vortex-induced viscous shear stress. • Six-types fragmentation was observed according to the interaction between trailing vortices and bubble. • The bubble is fragmented by a single trailing vortex according to the two mechanisms: a trailing vortex cuts-off and a rotational flow of trailing vortex. • The bubble can be fragmented by several trailing vortices at the gap between them. We investigated the mechanism of single-bubble fragmentation during mechanical stirring under different trailing vortex conditions. Experiments and numerical simulations using the LES-VOF method were carried out under different bubble sizes and locations of bubble injection. We found that the following three phenomena can cause bubble fragmentation: collision with impeller blade; shear stress in the boundary layer ahead of the impeller blade; and interaction between trailing vortices and the bubble. In the last case, the mechanism of fragmentation can be categorized into six types, which are determined by the relationship between the bubble behavior and the trailing vortices. Thus, we clarified the relationship between trailing vortices and bubble fragmentation for the first time in a stirred vessel. [ABSTRACT FROM AUTHOR]