Abstract
Because of their practical importance and complex underlying physics, the thin liquid films formed between colliding bubbles or droplets have long been the subject of experimental investigations and theoretical modeling. Here, we examine the possibility of accurately predicting the dynamics of the thin liquid film drainage using numerical simulations when compared to an experimental investigation of millimetric bubbles free-rising in pure water and colliding with a flat glass interface. A high-speed camera is used to track the bubble bounce trajectory, and a second high-speed camera together with a pulsed laser is used for interferometric determination of the shape and evolution of the thin liquid film profile during the bounce. The numerical simulations are conducted with the open source Gerris flow solver. The simulation reliability was first confirmed by comparison with the experimental bubble bounce trajectory and bubble shape evolution during the bounce. We further demonstrate that the simulation predicted time evolution for the shape of the thin liquid film profiles is in excellent agreement with the high-speed interferometry measured profiles for the entire experimentally accessible film size range. Finally, we discuss the implications of using numerical simulation together with theoretical modeling for resolving the complex processes of high velocity bubble and droplet collisions.
Highlights
Interactions involving bubbles and droplets are ubiquitous in many naturally occurring and biological processes as well as in industrial processes and products.[1]
The comparison of the bounce from the interface trajectory is used to evaluate the general consistency between the experiment and the Gerris numerical simulation (GNS)
In our latest study of water bubbles bouncing from free mobile and immobile water interfaces, we demonstrate that the force balance model prediction could deviate significantly from the experimental bubble bounce trajectory.[16]
Summary
Interactions involving bubbles and droplets are ubiquitous in many naturally occurring and biological processes as well as in industrial processes and products.[1] When bubbles or droplets collide or approach an interface, a thin liquid film is formed between the two bubbles or the bubble and the interface due to the deformability of the liquid interface. The draining dynamics of the thin liquid film determines the behavior of many practically important gas or droplet emulsion systems. We have examined the interface mobility effect on the dynamics of free-rising bubble collisions with various liquid interfaces.[14−17] A clean liquid−air interface is tangentially mobile, whereas contamination or the presence of surfactant can immobilize the interface due to Marangoni effects.[18,19] Bubbles with mobile interfaces are expected to coalesce much faster than bubbles with immobile interfaces because of the lower hydrodynamic resistance to the drainage of the thin liquid between the colliding bubbles.[11,14] Together with the expected fast coalescence, our experiments demonstrated that mobile interface bubbles could bounce back much stronger from a mobile liquid interface compared to an immobile liquid interface.[15,16] The general explanation of the stronger bounce is in the lower viscous dissipation during collisions involving mobile liquid interfaces compared to immobile liquid interfaces
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