The lifespan of clusters in confined bubbly liquids

A nearly monodispersed bubbly flow in a Hele-Shaw type channel was studied, for large but finite Reynolds numbers. Experiments were carried out with millimetre-sized Nitrogen bubbles rising through water-glycerin mixtures.The velocities, geometry and other flow characteristics were measured by means of a high speed camera and an image processing routine, in order to validate this experimental set-up with previous results from the literature and shed some light on the cluster formation, timespan and breakup mechanisms. The timespan of clusters was estimated by tracing the clusters trajectories. The results show that clustering occurs, but the bubble aggregates breakup rapidly due to hydrodynamic effects. Scaling arguments were used to obtain an estimate for the lifespan, which is compared to experiments. This estimate does not take into account wake effects, so it can be interpreted as a lower bound of clusters lifespan in an homogeneous bubbly flow.