### V0056: Diffusively-growing gas bubble coalescence

###### Authors
• Álvaro Moreno Soto, Physics of Fluids, Universiteit Twente
• Tom Maddalena, Physics of Fluids, Universiteit Twente & Département de Mécanique de l'École Polytechnique
• Arjan Fraters, Physics of Fluids, Universiteit Twente
• Devaraj van der Meer, Physics of Fluids, Universiteit Twente
• Detlef Lohse, Physics of Fluids, Universiteit Twente
DOI: https://doi.org/10.1103/APS.DFD.2016.GFM.V0056

The coalescence of two $$\mathrm{CO_2}$$ microbubbles in water has been followed at a frame rate of 60,000 fps. Starting from the diffusive growth of the bubbles, we study in detail the evolution of the collapsing process. First of all, we compare the formation of the collapsing neck between both bubbles for different bubble radius, concluding that its dynamics is universal. Afterwards, we characterise the propagating deformation along the surface, measuring its radial evolution. We also run a simulation using a boundary integral code, which is simplified by assuming that the coalescing bubbles are positioned in an infinite bulk, with no presence of the substrate. The comparison with the experiments is extremely precise for the early coalescence at the upper half of the system, not so for the lower half. We quantify the time scales of every phenomenon, concluding that the whole coalescence is only driven by capillarity, without remarkable influence of gravity or viscosity.