Session F01: Bubbles: Acoustics and General (3:55pm - 4:40pm CST)

Lateral Spreading of Gas Bubbles on Submerged Horizontal Wettability-confined Tracks

While the spreading of liquid droplets on wettability-confined paths has been widely studied in the past decade, a quantitative study of the inverse scenario of a gas bubble spreading on a submerged, wettability-confined track has rarely been investigated in the scientific literature. In the present study, an experimental investigation of the spreading of millimetric gas bubbles on horizontally-submerged, textured, wettability-confined straight tracks is carried out. After gently dispensing a bubble at one end of the track, the spreading dynamics of the gas bubble is studied. The effects of varying bubble diameter, track width, and ambient liquid properties are investigated. After contact, the gas bubble spreads laterally with a constant velocity of $O$(0.5 m/s), while remaining pinned at the starting point. The experimentally-observed spreading dynamics is described accurately by an inertio-capillary force balance.   

Air Bubbles Rise through Carbopol Water Two-layer System

We have conducted laboratory experiments, injecting air bubbles into a layer of Carbopol capped by a layer of water, to mimic ebullition in aquatic systems where bubbles rise through sediment and overlaying waterbodies. In a single experiment, around 60 bubbles rise through the two-layer system. A variety of behaviors has been observed. The first bubble creates a path inside the Carbopol layer, which is utilized by the following bubbles. Due to the passage of bubbles, a tube will gradually develop inside Carbopol, and overlaying water will flow into this tube. Inside the tube, the shape of the rising bubble resembles Taylor bubbles. However, its rise speed is much greater than Taylor bubbles and greater than its speed in water cap. When rising bubbles go through the Carbopol-water interface, bubble tails can be pinched off, leaving small bubbles beneath the interface. The pinched-off small bubble can sometimes increase the speed of the next bubble inside the tube by about 20{\%}.   

Haines jumps of bubble in constricted capillary tube

When gas bubble passes the narrowest part of constricted tube, the bubble could present impulsive motion. This bursting event is called Haines jump. Even though the Haines jump of bubble in porous media is observed through kinds of advanced imaging approaches, the mathematical model of Haines jump is highly in demand. In this study, a mathematical model is proposed to describe the dynamic motion of bubble passing through constricted capillary tube. A moving-boundary control volume concept is used to establish the dynamics of upstream and downstream incompressible fluids. In this way, the dynamics of bubble can be quantified by the trajectory of two menisci. The mathematical model highlights the importance of Ohnesorge number, bubble length and injected capillary number on the extent of Haines jump. The crossover between spontaneous and slow Haines jump is identified in the analytical model. In spontaneous Haines jump, bubble exhibits impulsive motion and overshoots its equilibrium position. The inertia force dominates in this regime. In slow Haines jump, bubble exhibit oozing motion and sluggishly pass the constriction. The viscous force dominates in this regime. In addition, this theory is compared with existing method and shows remarkable advances. The mathematical model is validated with experiments at constant flow rate boundary condition as well. This theory advances the understanding of Haines jump of bubble and provide insights on controlled flow for targeted delivery in porous media.   

Gas column oscillation inside a closed-end hole and its expelling by irradiating an acoustic wave

Filling the small and high aspect holes with liquid is a fundamental process for both cleaning and painting. However, due to the presence of surface tension, it is challenging to expel the gas through small holes with closed ends. Here we show a new method of expelling gas from a hole by acoustic wave irradiation. We used two acoustic waves, constant frequency sinusoidal waves, and time-varying frequency waves, i.e., sweeping waves. The acoustic wave could discharge only a part of the gas with a constant frequency, but the sweeping wave entirely expelled the gas. We also observed the expelling process using a high-speed video camera. As a result, the gas expelling consists of three stages. At these stages, the natural frequencies of the gas column and bubbles were critical. In the first stage, the entire air column oscillates, and in the second stage, the gas column in the hole was divided into multiple bubbles. Then, the bubbles were discharged by its oscillating motion.   

Quantitative Measurement of Bubble Bifurcation in a Vibrated, Enclosed Cylinder Using High-Speed Imaging

When an enclosed cylinder partially filled with viscous liquid is exposed to certain vibration conditions, the gas bubble normally contained in the upper region will undergo breakup. Bubbles entrained within the liquid will migrate downward due to Bjerknes forces. Within a range of conditions, bubbles will sink to a specific depth that is a function of the vibration conditions and rapidly accelerate to the bottom if this depth is exceeded. Bubbles remaining steady at the bottom of the cylinder can coalesce, so that the gas occupying the cylinder bifurcates into two separate regions encasing the liquid. High-speed visible-light imaging is used to characterize the resulting bubble size and velocity distributions as the bubbles migrate to the bottom of the cylinder. The parameters investigated include oscillation frequency and initial gas volume fraction in the cylinder. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. SAND2020-7749 A   

Steady streaming induced by a trapped oscillating microbubble

A sessile micro bubble oscillating under the influence of an ultrasound field creates strong steady microstreaming vortices. These induced vortices have been exploited by researchers in particle trapping, micro-pumping, micro-mixing and particle separation. Analytical studies in the past have been conducted assuming the sessile bubble to be semi-cylindrical. However, experiments with applications in micro-mixing and micro-pumping often encounter an oscillating bubble interface which is relatively flat at steady state. Our focus in this study is to obtain an analytical solution to the steady two-dimensional flow field induced by an oscillating trapped interface of a slug in a micro channel. We consider three different boundary layers i.e., two close to the enclosing wall and one close to the oscillating gas-liquid interface separately, as Reynolds stresses are high in these regions. We obtain a composite solution to the flow using matched asymptotics.