Numerical Study of Geometric Characteristics and Coalescence and Breakup Behavior during the Rise of Multiple Parallel Bubbles

The characterization of multiple bubbles in gas–liquid two-phase flow is a critical yet unresolved issue in both science and industry. Utilizing the volume of fluid (VOF) numerical simulation technique and high-speed visualization of bubble flow, the coalescence and breakup behaviors among multiple bubbles were examined in detail for three, four, and five bubbles with different initial bubble diameters (4, 6, 8, and 10 mm) and different initial bubble spacings (0.8–16 mm), respectively. As the initial bubble diameter increased, the deformation trend of sub-bubbles after the coalescence of three bubbles diminished, the holding time of large bubbles and the size of breakup sub-bubbles increased after the coalescence of four bubbles, and the trend of secondary coalescence between sub-bubbles in five bubbles decreased. With the increase of initial bubble spacing, the interaction of the surrounding flow field and the effect of bubble wake weakened, reducing the trend of bubble coalescence. Differences in the number of bubbles can also have a marked effect on the way that the coalescence between bubbles behaves. This study compensates the gap of small number of bubbles in the field of multibubble coalescence, lays the foundation for predictability in the design of gas–liquid equipment, and deepens the understanding of the mechanism of bubble coalescence and interaction.