Bubble puzzles

With their ubiquitous occurrence in a multitude of fluid systems, bubbles occupy an important place in contemporary science and technology. One can readily cite several examples: the production and transport of oil, in which bubbles are purposely injected to help lift heavy oil to the surface; energy generation, in which boiling is the key process in producing the steam to drive turbines; the chemical industry, in which gas–liquid reactors rely on bubbles to increase the contact area between the phases; the oceans, in which bubbles generated by breaking waves are important sinks for atmospheric carbon dioxide; piezoelectric ink-jet printing, in which they are just disturbing; and bubble chambers in high-energy physics, in which they used to signal the traces of energetic particles.