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The different flow regimes of two‐phase gas‐in‐liquid flow—as it occurs in the shallow conduit of basaltic volcanoes—are characterized by distinct frequency‐size distributions of the liquid and gaseous slugs. Assuming that the ascent of gaseous bubbles is indicated by seismic events, we explore the possibility of inferring the flow regime from the frequency distributions of magnitudes and interevent times. Our data set consists of 20,000 volcanic seismic events recorded in early March 2012 at Villarrica Volcano (Chile), which are commonly attributed to Strombolian activity. One crucial factor is the completeness of the catalog in terms of detectable amplitudes, which we assess using a stochastic simulation of the network output based on statistical properties of the ambient seismicity. Magnitudes, at which we consider the catalog complete, show an exponential occurrence. Yet, the simulation approach indicates that low magnitude events occur indeed more sparsely than expected for an exponential distribution, and that the magnitude distribution does not obey the Gutenberg‐Richter law. Interevent times are log‐normally distributed, which implies a preferred recurrence interval. The distributions are consistent with a slug flow regime. They correlate weakly with the preceding magnitude, suggesting that slugs coalesce while ascending. Plain Language Summary: A common type of volcanic seismic events at Villarrica is thought to result from gas bubbles, which ascend through the liquid magma in the conduit and produce mild volcanic explosions at the surface. We investigated the statistical occurrence of the time between these events and of their size. In contrast to normal earthquakes, the events recur more periodically and the number of smaller events does not increase exponentially, hence confirming their different nature. Laboratory experiments showed that bubbles flowing in a liquid develop characteristic patterns of size and distance between them, which depend on the gas supply rate and the flow ability of the liquid. We qualitatively compared the statistical distributions of event sizes to bubble sizes and the time between the events to the distance between gas bubbles. The result suggests a flow pattern where the gas bubbles span the entire width of the conduit and are several times longer than wide. Such batches of gas are known to produce the typical volcanic activity of Villarrica. Key Points: Seismic transient events are commonly seen as ascending gas slugs but other mechanisms, for example, brittle failure, are conceivableAmplitudes and time between events are approximately log‐normally distributed and thus different from tectonic earthquakesComparison with slug size distributions in gas‐in‐liquid flow suggests a sustained slug flow regime [ABSTRACT FROM AUTHOR]

Bubble bursting is a primary source of marine aerosols, yet little is known about particle emissions due to the bubble bursting in slicks containing oil‐dispersant mixtures. In this study, bubbles with mode sizes of 86 μm (denoted as small), 178 μm (medium), and 595 μm (large) are injected into a seawater column covered by slicks of crude oil, pure dispersant, and dispersant premixed with oil at a ratio of 1:25. The aerosol size distributions are monitored in the 0.5‐ to 20‐μm and 10‐ to 380‐nm ranges both in clean and ambient air environments. In ambient air, a tenfold increase in submicron particle concentration occurs when large bubbles burst on slicks of 500‐μm dispersant premixed with oil at a ratio of 1:25 oil or 50‐μm pure dispersant. Yet, in multiple tests performed at different ambient particle concentrations, the elevated size distributions persistently maintain the same shape as that of the ambient air. In contrast, smaller bubbles and tests not involving dispersants do not cause such an increase. Nanodroplets are also generated by large bubbles in particle‐free air, but their concentrations are much lower. All plumes generate micron‐sized aerosols, but trends vary. For the same contaminant, the microdroplet concentration decreases with increasing slick thickness. Particularly striking is a reduction of 2 orders of magnitude in the microdroplet concentration when medium and small bubbles burst on 500‐μm crude oil slicks. Chemical analysis of air and particulates collected from filters sampling the particles confirms the presence of airborne oil above the slicks. Key Points: Bursting of bubbles in slicks containing crude oil and dispersant mixtures aerosolizes the oil, generating microdroplets and nanodropletsIn ambient air, a tenfold increase in submicron particle concentration occurs when large bubbles burst on slicks containing dispersantsMicrodroplets are generated for all bubble plumes and slick types, but their concentration decreases with increasing slick thickness [ABSTRACT FROM AUTHOR]

Gas–liquid phase separation under microgravity conditions or in small‐scale fluidic systems represents a challenge for two‐phase liquid‐continuous systems. In this study, capillary channels formed by 3‐mm diameter stretched stainless‐steel springs coated with a commercial superhydrophobic coating are used to remove air bubbles from water. A single channel is capable of absorbing a stream of 3.7‐mm diameter bubbles impinging on a small area of the channel at a rate of over 50 bubbles/s. High‐permeability walls lead to fast individual absorption events (4 ms for 2.5‐mm bubbles) where bubble collapse time is limited by the inertia of the surrounding liquid. A horizontal three‐channel array has been shown capable of absorbing impinging bubbles from a sparger at superficial gas velocities of 0.03 m/s. The ultimate capacity of the 3‐mm diameter channel is predicted to be much higher than what could be measured with the existing apparatus. © 2018 American Institute of Chemical Engineers AIChE J, 65: 1340–1354, 2019 [ABSTRACT FROM AUTHOR]

The fundamental aspects of rising argon bubbles in molten metal for a laminar flow were investigated by numerical simulations. The Volume-of-Fluid (VOF) model was used to track the interface between argon and liquid metal. The process of a bubble rising in the molten metal includes two steps, one is the bubble rising inside the liquid, and the other one is the bubble rising across the liquid surface. The bubbling dynamics inside the liquid phase was studied in terms of the bubble's trajectory, shape and terminal velocity over a wide range of bubble diameters. It shows that ≈3-10mm bubbles rise in a spiral way with strong instabilities by changing their instantaneous shapes, while ≈10-20mm bubbles rise rectilinearly and their shapes are kept almost steady. All these bubbles' terminal velocities are around 0.3 m s−1, which are in accordance with literature data. For a bubble with a specific size, small metal droplets can be formed due to the bubble bursting on the free surface. In a situation when the top surface of the bubble is ruptured, the remains of the bubble will collapse and jet droplets can be formed. Simulations of jet droplets were qualitatively analyzed. It shows that when the surface tension is 1.4 N m−1, the critical bubble size is 9.3 mm. Also, the ejection is found to increase with an increased surface tension value, unless a critical bubble size is reached. [ABSTRACT FROM AUTHOR]