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To jump or not to jump: Adhesion and viscous dissipation dictate the detachment of coalescing wall-attached bubbles

Çayan Demirkır, Rui Yang, Aleksandr Bashkatov, and Vatsal Sanjay

Detlef Lohse

Dominik Krug*

  • *Contact author: d.krug@aia.rwth-aachen.de
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Phys. Rev. Fluids 10, 123602 – Published 8 December, 2025

DOI: https://doi.org/10.1103/nq3w-57gg

Abstract

Bubble coalescence can promote bubble departure at much smaller bubble sizes than those required for buoyancy-driven detachment. This can critically enhance the efficiency of gas-evolving electrochemical processes, such as water electrolysis. In this study, we integrate high-speed imaging experiments and direct numerical simulations to dissect how and under which conditions bubble coalescence on surfaces leads to detachment. Our transparent electrode experiments provide insights into contact line dynamics, demonstrating that the bubble neck generally does not contact the surface during coalescence. We reveal that whether coalescence leads to bubble departure or not is determined by the balance between surface energy, adhesion forces, and viscous dissipation. For the previously unexplored regime at low effective Ohnesorge number, a measure of viscosity that incorporates the effect of asymmetry between the coalescing bubbles, we identify a critical dimensionless adhesion energy threshold of ≈15% of the released surface energy, below which bubbles typically detach. We develop a global energy balance model that successfully predicts coalescence outcomes across diverse experimental conditions.

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Phys. Rev. Fluids 10, 123602– Published 8 December, 2025
  • Received 9 January 2025
  • Accepted 27 October 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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