Free Bubbles Research Articles

Evolutionary mechanism of Y-branches in acoustic Lichtenberg figures just below the water surface

The acoustic Lichtenberg figure (ALF) in an ultrasonic cleaner with a frequency of 28 kHz at different power levels was observed using high-speed photography. The nonlinear response of the cavitation structure was analyzed by the entropy spectrum in the ALF images, which showed the modulation influence of the primary acoustic field, exhibiting the fluctuations of the bubble distribution with time. Typical Y-branches predict the paths by which surrounding bubbles are attracted and converge into the structure, the branches are curved due to bubble-bubble interactions, and the curvature increases as the bubbles are approaching the main chain. The average travelling speed of bubbles along the branches is about 1.1 m/s, almost independent of power level of the ultrasonic cleaner. A theoretical model consisting of free bubbles and a straight bubble chain of finite length was developed to explore the evolutionary mechanism of branching. It was found that the bubble trajectories showed a bending tendency similar to the experimentally observed Y-branches, and the stationary straight bubble chain parallel to the main chain could evolve into a curved chain and eventually become a branch of the main chain. The theoretical predictions agree well with the experimental results, verifying the evolutionary mechanism of Y-branches in ALF.

Photochemistry of Photoinduced-Reaction Generated Bubbles.

UV light can create and grow bubbles (herein referred to as PIRGBs for photoinduced-reaction generated bubbles) at liquid/solid interfaces through photoinduced reactions that produce gases. Unlike the simple experience of blowing water bubbles through a straw, in which the bubbles quickly move away from their nucleation sites, not only can a deep UV laser beam create PIRGBs in liquid acetone, but also can hold and grow them. Free bubbles could be attracted to the excitation region from millimeters away, indicating that the reactions cause radial inward flow on the liquid surface. The radial flow can be due to imbalanced surface tensions at the interfaces. Raman measurements reveal that the gases in the PIRGBs include C2H6, CO, and H2, and in liquid acetone, sp2-carbon species are detected upon the UV excitation. Time series Raman measurement discloses a photocarbonization process in which small acyclic carbon species gradually form small clusters with carbon rings and eventually produce a large piece of amorphous carbon at the top of a PIRGB in pure liquid acetone. The photocarbonization may open new avenues for development of carbonaceous materials. Using PIRGB, miniature or microscale gas production reactors can be developed for producing gases.

New cold seep sites on the continental slope southwest to Svalbard

We discovered seafloor features such as bacterial mats and carbonate crusts typical for active methane seeps on the continental slope southwest of Svalbard. These features are associated with two main northwest-southeast trending morphological structures that are oriented parallel to the regional continental slope. Both structures occur at c. 800 m water depth, at the boundary between the Storfjorden trough mouth fan to the south and the Hornsund trough mouth fan to the north, which suggests a loading related fluid seepage. The main structure displays depressions and ridges forming a crater in its center. Other occurring features include small sediment mounds, domes often covered by bacterial mats, and hummocky seafloor colonized by siboglinid tubeworms. Free gas bubbles were spotted close to the centre and plumes along the rims of the structure. Thick carbonate crusts indicate a long seepage history in the center of the structure and on top of the ridges. The sources of the seeps are likely to be Miocene old organic-rich deposits, or Paleocene hydrocarbon reservoirs.

Dynamic behaviors of concrete gravity dam against combined blast wave and bubble pulsation of underwater explosion

Underwater explosion process mainly includes the preceding blast wave and the succeeding bubble pulsation, while the effect of bubble pulsation on hydraulic structures is always neglected. This paper aims to numerically study the dynamic behaviors of prototype concrete gravity dam against underwater explosion, considering the combined effects of blast wave and bubble pulsation. Firstly, a finite element analysis (FEA) approach for predicting the underwater explosion loadings, as well as the damage evolution and dynamic responses of dam against underwater explosions was proposed, in which the hydrostatic pressure of reservoir and the dead load of dam were considered. Based on Cole's formula and the existing underwater explosion tests, the reliability of FEA approach, including the mesh sizes, material models and the corresponding parameters, as well as the mapping, Fluid-Structure Interaction and contact algorithms, was comprehensively validated. Secondly, to realize the simulation of the prototype gravity dam impeded by the validated small Lagrange mesh size, a mesh transition strategy was proposed based on the equivalence of dam damage modes and total eroded element mass. Finally, the dynamic behaviors of a typical 120 m-height concrete gravity dam against underwater explosion, i.e., 1 t of TNT equivalence detonated at a depth of 35 m and standoff distances of 4–16 m, were examined. The dimensionless distance λR, i.e., the ratio of the standoff distance to the maximum bubble radius, was introduced to quantitatively evaluate the underwater explosion loadings and dynamic behaviors of the dam. It indicates that, the blast wave firstly leads to the local compressive damage on the upstream surface, as well as the tensile damage on the downstream folded slope and dam heel. The succeeding free vibration and bubble pulsation will further aggravate the damage degree, resulting in the cracking of dam neck and heel. Especially for the scenarios when λR ≤ 1.22, the overall sliding of dam is highly prone to occur.

Spontaneous cecal perforation in a cat diagnosed with ultrasonography.

An 8-year-old cat was presented for an acute history of anorexia, marked abdominal pain, and hyperthermia. Ultrasonography showed a cecal perforation with focal steatitis and adjacent free gas bubbles, consistent with focal peritonitis. Surgery confirmed the imaging findings. An enterectomy was performed with the removal of the cecum and ileocolic valve, and anastomosis between the ileum and colon was performed. Histology revealed transmural enteritis and chronic severe pyogranulomatous peritonitis with intralesional plant fragments.

Comparison of the Behavior of the Free Bubble and the One Located on the Electrode at AC Action

Comparison of the Behavior of the Free Bubble and the One Located on the Electrode at AC Action

Outcomes of initially nonoperative management of diverticulitis with abscess formation in immunosuppressed patients. DIPLICAB study COLLABORATIVE group.

Management of diverticulitis with abscess formation in immunosuppressed patients (IMS) remains unclear. The main objective of the study was to assess short- and long-term outcomes between IMS and immunocompetent patients (IC). The secondary aim was to identify risk factors for emergency surgery. A nationwide retrospective cohort study was performed at 29 Spanish referral centres between 2015-2019 including consecutive patients with first episode of diverticulitis classified as modified Hinchey Ib or II. IMS included immunosuppressive therapy, biologic therapy, malignant neoplasm with active chemotherapy and chronic steroid therapy. A multivariate analysis was performed to identify independent risk factors to emergency surgery in IMS. A total of 1395 patients were included; 118 IMS and 1277 IC. There were no significant differences in emergency surgery between IMS and IC (19.5% and 13.5%, p = 0.075) but IMS was associated with higher mortality (15.1% vs. 0.6%, p < 0.001). Similar recurrent episodes were found between IMS and IC (28% vs. 28.2%, p = 0.963). Following multivariate analysis, immunosuppressive treatment, p = 0.002; OR: 3.35 (1.57-7.15), free gas bubbles, p < 0.001; OR: 2.91 (2.01-4.21), Hinchey II, p = 0.002; OR: 1.88 (1.26-2.83), use of morphine, p < 0.001; OR: 3.08 (1.98-4.80), abscess size ≥5 cm, p = 0.001; OR: 1.97 (1.33-2.93) and leucocytosis at third day, p < 0.001; OR: 1.001 (1.001-1.002) were independently associated with emergency surgery in IMS. Nonoperative management in IMS has been shown to be safe with similar treatment failure than IC. IMS presented higher mortality in emergency surgery and similar rate of recurrent diverticulitis than IC. Identifying risk factors to emergency surgery may anticipate emergency surgery.

Sound scattering and radiation suppression by pressurized spherical shells.

Thin-shell models offer important insights into the complex process of sound-structure interaction but are found to be inconsistent with the rigorous thick-shell theory for fluid-loaded spherical shells. Here, linearized equations of motion of fluid-loaded, thin, spherical shells are re-derived from the first principles. The shell may be prestressed due to the difference in the static pressures in the internal and external fluids. Differences in the fluid-loading terms from previously proposed ad hoc models are identified and their significance is analyzed. Analytic solutions are derived of the problems of spherical sound wave scattering by a fluid-filled, prestressed spherical shell and resonant vibrations of the shell. The results reduce to a number of known exact and asymptotic solutions in appropriate limiting cases. The mathematical model of the shell vibrations is applied to characterize the influence of the shell's material properties and the prestress on passive suppression of low-frequency underwater sound radiation due to diffraction on an acoustically compliant sphere, such as an encapsulated gas bubble. Using soft rubber as the encapsulating membrane is found to preserve the sound suppression qualities of the free gas bubble.

Совершенствование проточной части газосепараторов с использованием мультифазного коэффициента относительной скорости движения дискретных частиц

The paper analyzes features of the flowing formation fluid that contains free gas bubbles in the flow part of a vortex-type separator with the movable screw. Expressions are derived for a dimensionless multiphase coefficient of the discrete particles relative separation rate and the multiphase similarity criterion, which are making it possible to evaluate the gas separator efficiency, design and develop new devices based on the previously created highly efficient models. The derived equations allow determining the main geometric dimensions of the gas separator flow part based on the given radial dimensions, nominal flow rate and permissible content of free gas at the inlet. For the obtained geometric dimensions of the gas separator flow part, it becomes possible to construct dependences of the separation coefficient and the permissible amount of free gas at the inlet on the rotor rotation speed, flow rate and physical properties of the multiphase mixture.

Совершенствование проточной части мультифазных ступеней с использованием мультифазного коэффициента относительной скорости движения дискретных частиц

Equations are derived to design and develop the multiphase stages flow path in a diagonal form using the dimensionless multiphase coefficient of the discrete particles relative speed. An analysis was made of the formation fluid flow containing free gas bubbles in the serial multiphase stages flow path of axial and axis-diagonal types in comparison with the developed diagonal-type stages and with inclined-cylindrical and helical blades. It is shown that, compared to the axial and axis-diagonal type stages, multiphase stages of the diagonal type with the inclined-cylindrical and helical blades have higher pressure when operating on the gas-liquid mixtures, especially in the multi-stage design. When operating on water without free gas, pressure and efficiency of the multiphase stages exceed characteristics of the best analogues, which makes it possible to manufacture the full-size pumps operating efficiently on liquid without gas and on the gas-liquid mixture.

Evidence of laser-induced nanobubble formation mechanism in water

Principles of laser-induced nanobubble formation in water are studied and presented. Nanobubbles were generated by laser light at intensities below threshold for laser-induced breakdown and subsequently expanded by a rarefaction wave to facilitate their observation and analysis. Different methods were used to study nanobubble formation and characteristics. Firstly, probability of nanobubble formation as a function of water sample purity was examined. Secondly, relation between laser fluence at different wavelengths and the number of generated nanobubbles was investigated. Thirdly, measurements of nanobubble lifetime were conducted indicating a contradiction to the Epstein-Plesset equation-based prediction of free bubble dissociation. Accumulated evidence suggests that the presence of physical impurities is a prerequisite for nanobubble formation. Consequently, a lack of impurities results in the absence of nanobubbles in contrast to assumptions by existing studies. The findings presented in this paper provide new insights into the fundamental properties of laser-induced nanobubbles in water.

Совершенствование проточной части десендеров циклонного типа с использованием мультифазного коэффициента относительной скорости движения дискретных частиц

In the oil producing wells with high content of mechanical impurities and free gas, efficiency of the electric centrifugal pump is increased by installing the cyclone-type desenders at its inlet. Desender protects the submersed pump from mechanical impurities entering it by separation and collecting them in a special container. At the same time, the problem of free gas bubbles enlargement is being solved to facilitate their separation into the annulus and thus reduce the free gas content at the pump inlet. Analysis was made of specifics of the formation fluid flow containing mechanical impurities and free gas in the flow path of a cyclone-type separator with the fixed screw. Expressions were derived to determine the dimensionless multiphase coefficient of the discrete particles relative separation rate and of the multiphase similarity criterion. They allow evaluating efficiency of the mechanical impurity separators and developing new highly efficient structures based on the previously created ones. Recommendations are provided for development of the new highly efficient structures.

How heterogeneous wettability enhances boiling

For super-heated water on a substrate with hydrophobic patches immersed in a hydrophilic matrix, one can choose the temperature so that micro-bubbles will form, grow and merge on the hydrophobic patches and not on the hydrophilic matrix. Until covering a patch, making a pinned macro-bubble, a bubble has a contact angle π−θ2, where θ2 is the receding contact angle of water on the patch material. This pinned macro-bubble serves as the initial condition of a quasi-static growth process, leading to detachment through the formation of a neck, so long as depinning and dewetting of the hydrophilic matrix was avoided during the growth of the pinned bubble: the bubble contact angle should not exceed π−θ1, where θ1 is the receding contact angle of water on the matrix material. The boiling process may then enter a cycle of macro-bubbles forming and detaching on the patches; the radii of these patches can be optimized for maximizing the heat transfer for a given substrate area. For this analysis to become quantitative, we revisit the Young–Laplace quasi-static evolution of key physical quantities, such as bubble energy, as functions of bubble growing volume, when gravity is either significative or negligible: this concerns both pinned bubbles on a fixed circular footprint (Dirichlet boundary conditions) and free un-pinned bubbles with a fixed contact angle (Neumann boundary conditions).

Rubber-like elasticity in laser-driven free surface flow of a Newtonian fluid

The energy needed to deform an elastic solid may be recovered, while in Newtonian fluids, like water and glycerol, deformation energy dissipates on timescales of the intermolecular relaxation time [Formula: see text] . For times considerably longer than [Formula: see text] the existence of shear elasticity requires long-range correlations, which challenge our understanding of the liquid state. We investigated laser-driven free surface bubbles in liquid glycerol by analyzing their expansion and bursting dynamics, in which we found a flow-dominating, rubber-like elasticity unrelated to surface tension forces. In extension to findings of a measurable liquid elasticity at even very low deformation frequencies [L. Noirez, P. Baroni, J. Mol. Struct. 972, 16-21 (2010), A. Zaccone, K. Trachenko, Proc. Natl. Acad. Sci. U.S.A. 117, 19653-19655 (2020)], that is difficult to access under increased strain, we find a robust, strain rate driven elasticity. The recovery of deformation energy allows the bursting bubble to reach Taylor-Culick velocities 20-fold higher than expected. The elasticity is persistent for microseconds, hence four orders of magnitude longer than [Formula: see text] . The dynamic shows that this persistence cannot originate from the far tail of a distribution of relaxation times around [Formula: see text] but must appear by frustrating the short molecular dissipation. The longer time should be interpreted as a relaxation of collective modes of metastable groups of molecules. With strain rates of 106 s-1, we observe a metastable glycerol shell exhibiting a rubber-like solid behavior with similar elasticity values and characteristic tolerance toward large strains, although the molecular interaction is fundamentally different.

Pneumatosis cystoides intestinalis: when the location of the air may be a pitfall

Pneumatosis cystoides intestinalis (PCI) is a rare and generally benign condition characterized by air within the walls of the small intestines or colon. Moreover, it may be a cause of free air in peritoneum. To correctly manage this entity when found at CT, it is of crucial importance for the radiologist to recognize and distinguish it from life-threatening causes of pneumatosis intestinalis or pneumoperitoneum. This differentiation may be challenging and the absence of additional findings (bowel wall thickening, altered contrast mucosal enhancement, fat stranding, dilated bowel, ascites, and the presence of portal venous gas) may be very helpful in suggesting the diagnosis. In this short communication we present a case of PCI in an asymptomatic 60-year old woman with a history of uterine carcinoma. The patient underwent a colonoscopy after a positive result of fecal occult blood test; the colonoscopy showed the presence of multiple grape-like nodules in the splenic flexure of the colon and biopsies were performed to exclude malignity of the findings. Then, a CT was conducted and it showed the presence of multiple, thin-walled, air-filled submucosal cysts in the splenic flexure of the colon. The endoscopic and CT findings, together with the absence of abdominal symptoms and altered laboratory test, allowed to establish the diagnosis of PCI. The patient was managed conservatively. Moreover, some free air bubbles were found in the pneumoperitoneum at one-year and two-year follow-up CTs, without abdominal symptoms.

Experimental study on flow fields and bubble entrainments by the water droplet impact using 3D PIV tests

The phenomenon of a water droplet impact on a free surface is studied to understand the physics of free surface bubble entrainment. Particle image velocimetry (PIV) and high-speed image system are used to analyse the flow structure evolutions in the droplet impact cavity period and bubble entrainment cavity period, respectively. The photographic results show that the entrapped surface of the impact cavity remains intact and continuous, and individual bubble entrainment occurs during the secondary entrainment cavity evolution. The instantaneous distributions of velocity fields in the longitudinal and lateral directions are uniform and independent of the approaching impact velocity. For the entrainment cavity evolution, the transverse diffusion intensity is higher than that for the impact cavity period. An individual bubble forms during the transverse velocity penetration across the droplet impact area. Consequently, for the droplet impact on a water surface, the present study implies the presence of a mechanism by which the interior flow field plays a key role in the bubble entrainment.

Ultrasonic Traveling Waves for Near-Wall Positioning of Single Microbubbles in a Flowing Channel.

Although microbubbles are used primarily in the medical industry as ultrasonic contrast agents, they can also be manipulated by acoustic waves for targeted drug delivery, sonothrombolysis and sonoporation. Acoustic waves can also potentially remove microbubbles from tubing systems (e.g., in hemodialysis) to prevent the negative effects associated with circulating microbubbles. A deeper understanding of the interactions between the acoustic radiation force, the microbubble and the channel wall could greatly benefit these applications. In this study, single air-filled microbubbles were injected into a flowing (polydimethylsiloxane) channel and monitored by a high-speed camera while passing through a pulsed ultrasonic wave zone (0.5 MHz). This study compared various bubble sizes, flow rates and acoustic pressure amplitudes to better understand the three physical regimes observed: free bubble translation (away from the wall); on-wall translation; and bubble-wall attachment. Comparison with a theoretical model revealed that the acoustic radiation force needs to exceed the combined repulsive forces (shear lift, wall lubrication and repulsive Van der Waal forces) for the dead state of bubble-wall attachment. The bubble dynamics revealed through this investigation provide an opportunity for efficient positioning of microbubbles in a channel flow, for either in vivo manipulation or removal in biological applications.

Spherical alveolar shapes in live mouse lungs

Understanding how the alveolar mechanics work in live lungs is essential for comprehending how the lung behaves during breathing. Due to the lack of appropriate imaging tools, previous research has suggested that alveolar morphologies are polyhedral rather than spherical based on a 2D examination of alveoli in fixed lungs. Here, we directly observe high-resolution 3D alveoli in live mice lungs utilizing synchrotron x-ray microtomography to show spherical alveolar morphologies from the live lungs. Our measurements from x-ray microtomography show high sphericity, low packing density, big alveolar size, and low osmotic pressure, indicating that spherical alveolar morphologies are natural in living lungs. The alveolar packing fraction is quite low in live lungs, where the spherical alveoli would behave like free bubbles, while the confinement of alveolar clusters in fixed lungs would lead to significant morphological deformations of the alveoli appearing polyhedral. Direct observations of the spherical alveolar shapes will help understand and treat lung disease and ventilation.

Effective medium modeling of acoustic propagation in a seagrass meadow

Seagrasses are foundation species in many coastal ecosystems, but these environments are declining globally due to climate change and other anthropogenic impacts. Ballard et al. [J. Acoust. Soc. Am. 147, 2020] established the efficacy of acoustic remote sensing techniques for seagrass monitoring by exploiting acoustic sensitivity to gas bubbles produced by photosynthesis and gas channels within the seagrass leaves. However, the effects of seagrass on acoustic propagation are not understood with sufficient quantitative detail, and an improved model describing propagation through a mixture of seagrass leaves, free gas bubbles, and seawater is needed to aid in integrating acoustic methods into conservation efforts. This talk provides an overview of developments in the modeling of acoustic propagation through a Thalassia testudinum meadow using a homogeneous effective medium approach to represent the seagrass leaves and seawater. The model accounts for the complex microstructure of seagrass leaves including the encapsulated gas channels and the elastic properties of the seagrass tissue. The model is intended for use in geoacoustic inference algorithms for the overall goal of providing estimates of seagrass productivity and biomass. Candidate effective medium models include 2D cylindrical seagrass leaves and a micromechanical model of a seagrass leaf cross-section. [Work supported by NSF.]

High-speed imaging of degassing kinetics of CO2–water mixtures

The exsolution of gas molecules from gas–liquid mixtures plays a significant role in a wide range of applications from industrial processes such as metal casting to subsurface flow of oil or geothermal waters. This study aims to improve the understanding of the conditions under which free gas bubbles start forming in CO2–water mixtures. The bubble point pressure was determined under various different conditions like the temperature and initial pressure of the mixture along with other parameters such as the bubble growth rate. A series of depressurization experiments at high pressure and temperature (up to 100 bar and 100 °C) is performed using a pressure cell that allows for visual monitoring of the degassing process. Bubble formation during the depressurization process is recorded using a high-speed camera paired with a uniform light source along with a pressure transducer and thermocouple. Image analysis allows for the determination of the bubble point pressure and rate of bubble formation. For CO2 in its gaseous state and at moderate temperatures, decent agreement between experimental results and the theoretical bubble point pressure is found, although significant deviations are observed at elevated temperatures. More pronounced differences in bubble point are observed for mixtures starting out at high pressures where CO2 is a supercritical fluid, which lead to lower than expected bubble point pressures.