Shallow liquid layers enhance jet drop ejection from bursting bubbles

Bubble bursting and the resulting jet drop ejection mediate mass exchange across liquid-air interfaces in a wide range of natural and industrial processes. Prior research focused on bubble bursting in deep pools, yet many practical applications involve shallow liquid layers with geometric confinement. For instance, bubbles generated during drop impacts and by electrolysis in liquid films are in proximity to solid substrates. Here, we use direct numerical simulations to investigate how the confinement of a bubble near a bottom wall influences jet dynamics and droplet formation. We show that bubble bursting in shallow layers can produce jet drops that are significantly smaller and ejected with faster velocities compared to those in deep pools. By varying the Ohnesorge number and the dimensionless layer thickness, we establish a regime map describing conditions where jet drops are ejected. Surprisingly, shallow layers expand the Ohnesorge number range for jet drop production despite an expected increase in dissipation, demonstrating how confinement modifies mass transport by bubble bursting jets. This work advances our understanding of bubble bursting under confinement and may inform strategies to control aerosolization in pesticide delivery and respiratory droplet generation.