Collision, and coalescence of bubbles in turbulence

Bubble coalescence in turbulence plays a pivotal role in determining the bubble size spectrum, holding significant importance in various natural phenomena and industrial applications. Despite numerous proposed models and hypotheses, their experimental validation has been limited due to inherent challenges in measuring the process. This study addresses these challenges by introducing an advanced 3D Lagrangian bubble tracking algorithm. Leveraging this method, we can precisely track closely spaced bubble pairs and acquire sufficient statistical data to characterize the approach velocity at which two bubbles collide. From the results, we also measure the contact time, which directly affects the bubble coalescence efficiency. The experimental results revealed the relationship between the bubble approach velocity with the bubble size, which exhibits a scaling law that deviates from the classical model based solely on Kolmogorov theories. This difference was explained by the biased sampling of bubbles in eddies of similar sizes.