Flow Regimes and Transition Criteria during Passage of Bubbles through a Liquid–Liquid Interface

Abstract

The passage of a single bubble or a stream of bubbles through a liquid-liquid interface is a highly dynamic process that can result in a number of different outcomes. Previous studies focused primarily on a single bubble and single flow regime, and very few investigations have considered bubble streams. In the present work, six different liquid combinations made up of water, ethanol, a perfluorocarbon liquid, PP1, and one of three different viscosity silicone oils are tested with air bubbles from 2 to 6 mm in diameter rising between 5 and 55 cm/s. Both single bubbles and bubble streams varying in frequency from 5 to 40 bubbles/s are tested. High-speed imaging is used to capture and classify the flow regimes associated with each flow type. Four different flow regimes are identified for single-bubble passage, and six are found for bubble stream passage. On the basis of theoretical considerations, nondimensional numbers are developed for characterizing the flow regimes and maps are generated that distinguish them and define flow regime transitions.

Particles, Drops, and Bubbles Moving Across Sharp Interfaces and Stratified Layers

“…In most cases, this column or tail lengthens as the body moves away from the interface until it pinches off at some point. Depending on the fluids properties, especially the viscosity and density contrasts and flow conditions prior to breakthrough, the tail may exhibit various geometries and dynamics (Maru et al 1971;Dietrich et al 2008Dietrich et al , 2011Bonhomme et al 2012;Emery et al 2018;Pierson & Magnaudet 2018a,b). The tailing configuration may take place under creeping flow conditions (Geller et al 1986, De Folter et al 2010, Jarvis et al 2019.…”

“…Hence the most significant differences with rigid bodies are found for large Bo 1 and Bo 2 and small λ s , i.e., with large bubbles. The various regimes discussed in Sections 4.1-4.3 are successively encountered as the drop or bubble size (i.e., Bo) increases, all else being equal (Bonhomme et al 2012, Emery et al 2018: Drops that do not satisfy Equation 4 (with = 0) or Equation 6 remain trapped at the interface, possibly after a bouncing sequence (Feng et al 2016, Singh et al 2017, while slightly larger drops cross the interface in a quasi-static manner. Once released in the second fluid, they remain encapsulated in a thin shell corresponding to the remains of the film or meniscus left by the drainage process or the snapping mechanism.…”

“…Pinch-off usually takes place as described in Section 4.4, and the resulting ligaments exhibit the same rich dynamics. However, with largeenough bubbles (λ s ≈ 0, Ar 1 1), tail pinch-off may be overtaken by film breakup at the bubble apex, which arises sooner (Uemura et al 2010, Emery et al 2018. In this case, the film first recedes along the bubble surface.…”

Numerical simulation of the crossing of a liquid-liquid interface by a droplet

“…It has been found that the volume entrained is also larger with such spherical cap bubble shapes since they offer a larger cross section to the interface than spheroidal bubbles, for a given gas volume. In the experiments of Emery et al [20], the crossing by a single bubble shows additionally that, in the tailing mode, the column of liquid entrained is longer in the case where the bubble velocity does not change much during the crossing of the interface; the tail is observed to remain connected a long time before its rupture, in some cases the liquid shell covering the bubble breaking before the column. The latter study has investigated the crossing of a stream of bubbles, giving a map of the different flow regimes with the possible formation of clusters.…”

Passage of a rising bubble through a liquid‐liquid interface: A flow map for different regimes

“…A nondimensional flow map can cover all possible regimes. Emery et al [30] presented a flow regime map for different flow regimes and transition criteria during the passage of bubbles through a liquid-liquid interface based on dimensionless numbers. They considered four flow regimes for the single bubble (including trapped, shell formation, long tail, and rupture) and six flow regimes for the bubble stream (including single equivalent, partial column, bubble cluster, stable column, unstable column, and churn flow).…”