Large Gas Bubbles Research Articles

Main Composition and Visual Appearance of Milk Kefir Beverages Obtained from Four Consecutive 24- and 48-h Batch Subcultures

Nowadays, there has been a significant rise in the consumption of kefir, a functional beverage touted for its perceived health benefits. To offer a high-quality beverage to consumers, it is imperative to scrutinize and fine-tune the fermentation process. This study seeks to investigate the impact of fermentation time and the number of subcultures on the physicochemical, microbiological, and volatile composition, as well as the visual appearance, of kefir beverages obtained from four consecutive 24- or 48-h batch subcultures. All fermented beverages exhibited low lactose, ethanol and acids levels, with counts of viable probiotic lactic acid bacteria and yeast exceeding 106 colony forming units/mL. The four kefir beverages from the 48-h batch subcultures notably showed the lowest total concentrations of volatile compounds, likely due to overfermentation and over-acidification of the beverages. This caused the separation of the whey and curd, along with the formation of large gas bubbles, negatively affecting the visual appearance of the products. These findings emphasize the importance of fine-tuning the fermentation process to ensure the production of high-quality kefir beverages that align with consumer preferences. The four beverages from the 24-h batch subcultures exhibited high microbiological and physicochemical stability during storage at 4 °C for 28 days.

Bubble ascent and rupture in mud volcanoes.

Large gas bubbles can reach the surface of pools of mud and lava where they burst, often through the formation and expansion of circular holes. Bursting bubbles release volatiles and generate spatter, and hence play a key role in volcanic degassing and volcanic edifice construction. Here, we study the ascent and rupture of bubbles using a combination of field observations at Pâclele Mici (Romania), laboratory experiments with mud from the Imperial Valley (California, USA), numerical simulations and theoretical models. Numerical simulations predict that bubbles ascend through the mud as elliptical caps that develop a dimple at the apex as they impinge on the free surface. We documented the rupture of bubbles in nature and under laboratory conditions using high-speed video. The bursting of mud bubbles starts with the nucleation of multiple holes, which form at a near-constant rate and in quick succession. The quasi-circular holes rapidly grow and coalesce, and the sheet evolves towards a filamentous structure that finally falls back into the mud pool, sometimes breaking up into droplets. The rate of expansion of holes in the sheet can be explained by a generalization of the Taylor-Culick theory, which is shown to hold independent of the fluid rheology.

Maximum entropy model of chaotic explosion and implosion of a large gas bubble in liquid

A mathematical model for the chaotic explosion of a large gas bubble in a liquid is presented in which there is a maximum increase in entropy. It is shown that this requires that the acoustic radiation during the chaos must be minimal and that the spherical surface at the end of the chaos must be stable. Also, a model including the acoustic radiation is developed for the spherical phases of the explosion and implosion of the bubble during which there is no change in entropy. The (final) chaotic phase of the implosion is also modeled so that there is a maximum increase in entropy. There might be additional periods of the bubble during which the bubble explodes and implodes in a similar fashion as the first period. The calculations using this model are shown to agree reasonably well with the data. In particular, these calculations determined that the ratio of the duration of the second period of the bubble to the first period imply that the energy lost in the first period during its implosion is about 2/3 of the energy of the first period. Also, these calculations determine that only about 30% of the total energy is radiated and the rest is absorbed by the water for a total of about 2/3 of the total energy. This also agrees with the data. Furthermore, the data appear to scale with initial total energy as in the calculations using this chaos model.

Revealing the Impact of Cell Conditioning on PEMWE Catalyst Layer Morphology

Polymer electrolyte membrane (PEM) water electrolysis is a promising green hydrogen generation technology to mitigate the effects of anthropogenic climate change. To achieve stable cell voltages, a conditioning procedure is typically required, where current or voltage cycling is applied until stable performance is achieved. Previous studies have demonstrated that a decrease in voltage occurs within the first few hours of operation [1], but this conditioning period has not been extensively studied for PEM electrolyzers, despite a variety of standard conditioning protocols available for PEM fuel cells in the literature. Previous works additionally suggest that changes in performance may be induced due to structural changes in the anode catalyst layer (CL) caused by large gas bubble evolution during the first few hours of operation [2]. However, to establish and optimize a conditioning procedure for PEMWEs, the specific structural changes caused by conditioning on the anode CL must be elucidated and correlated with the electrochemical performance parameters.In this work, we applied scanning transmission X-ray microscopy (STXM) to PEMWE catalyst layers to reveal pore and ionomer distributions in pristine and conditioned commercial CL samples. Prior to imaging, CL samples were embedded in epoxy and cut to 50 nm thick slices using an ultramicrotome. Using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, Carbon 1s and Fluorine 1s absorption edges were probed to reveal pore and ionomer distributions, respectively. After image acquisition, the image stacks were processed to obtain the ionomer and epoxy spectra to enable spectral fitting and thresholding. Through this analysis, we quantified various morphological properties of catalyst layers (including CL thickness, porosity, pore size distribution, agglomerate distribution, and ionomer content) and compared these properties to those of pristine CLs to explain changes in cell performance. The insights gained from this work will aid in the development of efficient conditioning protocols and identify optimal post-conditioned anode CL morphology to inform the design of next-generation catalyst materials. A. Weiß et al., J Electrochem Soc, 166, F487–F497 (2019).O. Panchenko et al., Mater Today Energy, 16, 100394 (2020).

Critical review and experimental validation of radiative transfer models for semitransparent media containing large gas bubbles

Many materials manufacturing, photobiochemical, and photoelectrochemical processes involve radiation transfer through foams and bubbly fluids. Controlling and optimizing these processes require accurate predictions of radiation transfer through semitransparent media. Previously developed models treated the heterogeneous media as homogeneous plane-parallel slabs with some effective radiation characteristics while radiation transfer was governed by the one-dimensional radiative transfer equation (RTE). Unfortunately, their accuracy and range of validity remains unclear for lack of comparison with one another or against the same set of experimental data. This study aims to critically review and assess the validity of these models both numerically and experimentally. First, predictions of the transmittance and reflectance of heterogeneous slabs containing large randomly distributed bubbles were compared with those obtained from Monte Carlo ray-tracing (MCRT) method based on geometric optics. A new hybrid model was proposed that predicts the effective scattering coefficient and asymmetry factor using the Lorenz–Mie theory and the effective absorption coefficient as the volume-weighted sum of the bubbles and medium absorption coefficients and solves the RTE using the Monte Carlo method. Its predictions showed excellent agreement with those by the MCRT method for a wide range of bubble volume fractions (0%–30%) as well as slab thicknesses (2–40 mm) and medium absorption coefficients (0.1–100 m−1). Second, microcomputed X-ray tomography scans were performed on a fused silica sample containing bubbles with mean radius of 480 μm to retrieve the exact locations, diameters, and total volume fraction of bubbles. Here also, predictions of the hybrid model using the retrieved data agreed well with experimental measurements of the spectral normal-hemispherical reflectance and transmittance of the sample for wavelengths between 0.4 and 3 μm when silica ranges from weakly absorbing to absorbing.

Steroidal saponins PPI/CCRIS/PSV induce cell death in pancreatic cancer cell through GSDME-dependent pyroptosis

Pancreatic cancer is highly aggressive and lethal, and treatment options for it are limited. Gasdermin E (GSDME) is highly expressed in pancreatic cancer and can induce pyroptosis. In this type of programmed cell death, cells swell and emit large gas bubbles through their plasma membranes. Hence, GSDME induction is potentially an efficacious therapeutic approach against pancreatic cancer.In the present study, we found that the steroidal saponins polyphyllin I (PPI), collettiside III (CCRIS), and paris saponin V (PSV) significantly inhibited PANC-1, AsPC-1, and BxPC-3 cell proliferation. PPI/CCRIS/PSV altered the morphology of PANC-1 cells and induced the release of lactate dehydrogenase (LDH) from them. Therefore, these three constituents caused PANC-1 cells to undergo pyroptosis. This conclusion was confirmed by propidium iodide (PI) staining and flow cytometry assays. The present work also revealed that PPI/CCRIS/PSV induced pyroptosis via GSDME rather than gasdermin D (GSDMD). Whereas PPI/CCRIS/PSV induced caspase-3 to cleave GSDME, it had no such effect on GSDMD. We also established a PANC-1 xenograft tumor model in BALB/c nude mice and administered CCRIS to them as this compound demonstrated the most substantial pyroptotic effect in the in vitro experiments. This treatment significantly inhibited tumor growth in the mice by activating GSDME-dependent pyroptosis.This research demonstrates demonstrate that pyroptosis induction by PPI/CCRIS/PSV has important implications in basic science and clinical medicine. Future investigations should endeavor to determine the benefits and risks associated with the administration of these steroidal saponins as anti-PDAC therapy.

Immediate subretinal fluid displacement from the buoyant force of a small gas bubble in pneumatic retinopexy: Insights into the potential mechanism of retinal displacement following retinal detachment repair.

To demonstrate how a small gas bubble injected into the vitreous cavity in pneumatic retinopexy (PnR) for rhegmatogenous retinal detachment (RRD) causes immediate displacement of subretinal fluid and to gain insights into the potential mechanism of retinal displacement.Methods: Three patients with RRD who underwent PnR were enrolled and prospectively followed. All patients underwent ultra-widefield fundus photography at baseline and at 1-2 minutes after intravitreal gas injection. In all cases, the ultra-widefield fundus photograph demonstrated immediate displacement of subretinal fluid, suggesting that the buoyant force applied to the retina by the bubble was responsible for the displacement of subretinal fluid. The results were extrapolated to determine the buoyant force applied by a small and large gas bubble as in PnR and pars plana vitrectomy (PPV). We determined that the buoyant force applied with a larger bubble in PPV was substantially greater and this may lead to retinal displacement. Intravitreal gas applies significant buoyant force to the detached retina and subretinal fluid which leads to substantial and rapid displacement of subretinal fluid. Understanding the impact of the buoyant force of the gas bubble on the detached retina can provide insight into possible mechanisms of retinal displacement.

Capillary driven fragmentation of large gas bubbles in turbulence

Bubble fragmentation drives up to 40% of the CO2 transfer from the atmosphere to the ocean. However, the small size bubble distribution, mainly responsible for gas dissolution, is still poorly understood. Combining experimental and numerical calculations, we find that capillary effects set small bubble production rate which physically explains the origin of their size distribution.

Wetting Transition of Active Brownian Particles on a Thin Membrane.

We study nonequilibrium analogues of surface phase transitions in a minimal model of active particles in contact with a purely repulsive potential barrier that mimics a thin porous membrane. Under conditions of bulk motility-induced phase separation, the interaction strength ϵ_{w} of the barrier controls the affinity of the dense phase for the barrier region. We uncover clear signatures of a wetting phase transition as ϵ_{w} is varied. In common with its equilibrium counterpart, the character of this transition depends on the system dimensionality: a continuous transition with large density fluctuations and gas bubbles is uncovered in 2D while 3D systems exhibit a sharp transition absent of large correlations.

Modeling of nonstationary gas outflow at breaks of subsea gas pipelines

Numerical modeling of the outflow of an air jet into water with a guillotine rupture of a pipeline by the VOF method using k-ε and k-ω SST turbulence models was carried out. The calculations were carried out in the axisymmetric approximation. The following phases of the outflow process were calculated: the formation of a large gas bubble at the place of the rupture, its growth, the separation of the bubble from the place of rupture, and the formation of a gas jet behind the bubble. It is shown that the rate of bubble detachment in the calculations by the k-ω SST model is higher than that in the calculation by the k-ε model.

Effect of a new synthetic bubble model on forces in simulations of two-phase flows in tube bundles

In this paper, the influence of the phase distribution imposed as an inlet boundary condition in a two-phase flow simulation is investigated. Firstly, a new inlet model is proposed which defines a transient inlet boundary condition to be applied in a subsequent Eulerian simulation, more specifically using the Volume-Of-Fluid method. This inlet model is aimed at generating large gas bubbles, making a Lagrangian approach less applicable. The new model, which is coined the “Synthetic Bubble Model” (SBM), generates a transient inlet condition with large gas bubbles such that there is no need for bubble creation through break-up of a continuous gas jet in a long inlet region upstream of the region of interest, which results in a smaller computational mesh. This model is applied on a 5-by-3 tube bundle subjected to an axially flowing air/water mixture and compared to a simulation with a precursor-domain in which bubbles are created by break-up of air jets imposed at the inlet. Compared to the precursor domain simulations, the SBM is both faster and more or equally accurate. Secondly, a tube bundle subjected to two-phase cross-flow is modelled. It is shown that the SBM yields better correspondence with the experimental force data than a steady inlet condition, in this case without addition of a precursor-domain (yielding a similar computational time for both simulations).

Gas Bubble Evolution in Polycrystalline UMo Fuels Under Elastic-Plastic Deformation: A Phase-Field Model With Crystal-Plasticity

In monolithic UMo fuels, the interaction between the Al cladding and large gas bubble volumetric swelling causes both elastic-plastic and creep deformation. In this work, a phase-field model of gas bubble evolution in polycrystalline UMo under elastic-plastic deformation was developed for studying the dynamic interaction between evolving gas bubble/voids and deformation. A crystal plasticity model, which assumes that the plastic strain rate is proportional to resolved shear stresses of dislocation slip systems on their slip planes, was used to describe plastic deformation in polycrystalline UMo. Xe diffusion and gas bubble evolution are driven by the minimization of chemical and deformation energies in the phase-field model, while evolving gas bubble structure was used to update the mechanical properties in the crystal plasticity model. With the developed model, we simulated the effect of gas bubble structures (different volume fractions and internal gas pressures) on stress-strain curves and the effect of local stresses on gas bubble evolution. The results show that 1) the effective Young’s modulus and yield stress decrease with the increase of gas bubble volume fraction; 2) the hardening coefficient increases with the increase of gas bubble volume fraction, especially for gas bubbles with higher internal pressure; and 3) the pressure dependence of Xe thermodynamic and kinetic properties in addition to the local stress state determine gas bubble growth or shrinkage. The simulated results can serve as a guide to improve material property models for macroscale fuel performance modeling.

Gas Bubble Anatomy During Laser Lithotripsy: An Experimental In Vitro Study of a Pulsed Solid-State Tm:YAG and Ho:YAG Device.

Purpose: To examine gas bubbles generated by two laser lithotripsy devices, a pulsed thulium solid-state laser and a holmium:yttrium-aluminum-garnet (Ho:YAG) device, and their possible effects in lithotripsy. Materials and Methods: We investigated two Dornier laser devices, a Medilas H Solvo 35 and a pulsed solid-state thulium laser evaluation model (Dornier MedTech Laser GmbH, Wessling, Germany). Our setup consisted of a water-filled glass tank heated to 37/60/70°C. Different laser power/frequency settings and short/long pulses were examined for both laser devices. We analyzed the impact of degraded, cut, and broken fibers on gas bubble anatomy. Furthermore, high-speed recordings of BegoStone ablation were analyzed. For all recordings, we used a Photron Nova S12 camera. Results: These two devices produced differently shaped gas bubbles under different fiber conditions, temperatures, power settings, and short and long pulse settings, which explain the differing repulsive force and pressure values. Inside the gas bubble, a cone was visible whose angle correlates with the protruding jet. We observed turbulences and swirls moving back and forth the fiber tip. During fragmentation, sparks are generated that demonstrate the photothermal effect, and we recorded stone fragments being pulled toward the fiber. Both devices showed comparable results with differences mainly due to pulse lengths. Conclusion: The shapes of the vapor bubbles formed during laser lithotripsy depend on several factors. Excessive transoperative fiber cleavage seems to be unnecessary. Due to the large gas bubbles observed and because of the amount of potential pressure generated, only low energies should be applied in the ureter.

Internal morphological changes during metamorphosis in the sheep nasal bot fly, Oestrus ovis.

During the larval stage, oestrid flies (Diptera: Oestridae) are obligate parasites, whereas during the adult stage they are free-living and do not feed. Like other cyclorrhaphous flies, oestrids undergo metamorphosis inside an opaque puparium, formed by the contracted and hardened cuticle of the third-instar larva. The present study documents the internal morphological changes taking place during metamorphosis of the sheep nasal bot fly, Oestrus ovis L., using non-invasive, micro-CT-based virtual histology and provides quantitative data of volumetric changes in specific organs. Virtual histological sections allowed visualisation of the progression and completion of the apolyses, which delimit the different intra-puparial stages, and the connection to the tracheal system of a large gas bubble, which plays an essential role during early metamorphosis. Overall, our results show that the sequence of morphological and volumetric changes in tissues and organs is similar to those found in other cyclorrhaphous flies, but they also reveal developmental differences that result in an adult vestigial digestive tract. Future studies could develop non-invasive, reliable methods for aging the intra-puparial forms of different oestrid species of veterinary importance, based on both qualitative and quantitative markers, thus improving our knowledge of their development and the efficiency of control strategies.

Investigation of two-phase flow hydrodynamics under SGTR severe accident conditions

The international EU-SGTR and ARTIST projects investigated the transport of fission products in the form of aerosols during SGTR severe accidents. The major finding of the two projects was that there was significant retention of aerosols in the steam generator secondary side, and that the retention was increased by more than an order of magnitude if the secondary side of the steam generator was flooded with water. Furthermore, the experiments with the flooded secondary side showed that the aerosol particle retention was significantly increased due to the presence of submerged structures, i.e., the tube bundle, as compared to an empty pool. The increased aerosol retention was attributed to the interactions of the high velocity gas jet discharged from the tube break with the dense bundle of the steam generator tubes. Under these conditions, the two-phase flow is very complex due to the high gas velocities and complicated geometry of the steam generator secondary side.To determine the effect of the tube bundle on aerosol retention, hydrodynamic characteristics of an empty pool and a flooded steam generator secondary side were measured in a facility equipped with wire-mesh sensors. The facility was equipped with either a tube bundle consisting of 221 steam generator tubes, or with a single tube in the center of the facility. The flow development could be followed by making the measurements at different distances between the gas injection and the measurement point, and using different flow rates. The facility was operated at close to ambient conditions.Void fraction, bubble size distributions, gas phase velocity as well as interfacial area concentration were determined based on the wire-mesh sensor data. In addition, the penetration depth of the initial large gas bubble into the channel was studied for the closest break-sensor distances. The investigations show distinct differences between the flow characteristics in the single tube geometry and in the tube bundle. As compared to the single tube, the flow was more confined in the tube bundle due to the interactions of the flow with the tubes. The interfacial area between the liquid and gas phase is larger with the tube bundle than with the single tube and also the bubble size distributions show distinct differences between the two geometries.

Electrochemistry of nanobubbles

Abstract Gas bubble formation is a common phenomenon in numerous electrochemical processes, such as water splitting, chloralkaline process, and fuel cells. Many efforts have been made to understand the behaviors of microsized or larger gas bubbles in electrochemical systems in the past few decades. It was not until recent years that the electrochemistry of nanosized gas bubbles (nanobubbles) has begun receiving attention. In this short review, we summarize recent advances in the field of electrochemistry of nanobubbles, ranging from new fundamental understandings of nanobubble behaviors to the development of novel bubble-based applications inspired by the basic research of nanobubble electrochemistry.

3D Elastoplastic Model for Fine-Grained Gassy Soil Considering the Gas-Dependent Yield Surface Shape and Stress-Dilatancy

AbstractFine-grained sediments containing large discrete gas bubbles are widely distributed in the five continents throughout the world. The presence of gas bubbles could either degrade or enhance ...

Constitutive modelling of fine‐grained gassy soil: A composite approach

SummaryFine‐grained marine sediments containing large undissolved gas bubbles are widely distributed around the world. Presence of the bubbles could degrade the undrained shear strength (su) of the soil, when the gas pressure ug is relatively high as compared with the effective stress in the saturated soil matrix. Meanwhile, the addition of bubbles may also increase su when the difference between ug and pore water pressure uw becomes smaller than the water entry value, causing partial water drainage from the saturated matrix into the bubbles (bubble flooding) during globally undrained shearing. A new constitutive model for describing the two competing effects on the stress‐strain relationship of fine‐grained gassy soil is proposed within the framework of critical state soil mechanics. The gassy soil is considered as a three‐phase composite material with compressible cavities, which allows water entry from the saturated matrix. Bubble flooding is modelled by introducing an additional positive volumetric strain increment of the saturated clay matrix, which is dependent on the difference between pore gas and pore water pressure based on experimental observations. A modified hardening law based on that of the modified Cam clay model is employed, which in conjunction with the expression for bubble flooding, can describe both the detrimental and beneficial effects of gas bubbles on soil strength and plastic hardening in shear. Only two extra parameters in addition to those in the modified Cam clay model are used. It is shown that the key features of the stress‐strain relationship of three fine‐grained gassy soils can be reproduced satisfactorily.

A study of the vibration of a horizontal U-bend subjected to an internal upwards flowing air–water mixture

U-bends are a common geometry in heat exchangers. In this paper, a U-bend in the vertical plane connected to horizontal straight pipes is considered. An initially stratified water/air flow moves upwards against gravity. The aim of this research is to investigate the internal flow profile and resulting force when the U-bend is subjected to a stratified air–water flow at the inlet. This is done numerically, i.e. by solving the unsteady Reynolds-averaged Navier–Stokes equations. For low mass flow rates, large gas bubbles are naturally formed at the entrance of the bend. The transient force on the tube allows to determine precisely the time instants of bubble initiation and thus to quantify the bubble frequency. Firstly, the tube is assumed to be rigid and the dependence of force oscillation on the inlet conditions is investigated. Secondly, the influence of the viscosity, wall wetting and the mass flow rate is analyzed. Finally, a fluid–structure interaction calculation is performed in order to quantify the vibration characteristics of the tube.

A thermodynamic model to simulate the thermo-mechanical behavior of fine-grained gassy soil

Fine-grained gassy soil is a special kind of unsaturated soil, with the gas in the form of discrete big bubbles within the saturated matrix. These gas bubbles are sealed and considerably larger than the normal particle size. Based on the conceptual model of soil containing large gas bubbles proposed by Wheeler (Geotechnique 38(3):389–397, 1988a) and the granular solid hydrodynamics (GSH) theory, a thermodynamic model is presented to describe the mechanical properties and temperature effect of fine-grained gassy soil in this paper. The model assumes that the gas pressure is related to total stress and pore water pressure of soil, and the behavior of saturated matrix is controlled by “quasi-effective stress.” In addition, the effect of gas on the plastic deformation of soil skeleton is considered. Comparing with the experimental results, the ability of the model to describe the consolidation and undrained shear properties of fine-grained gassy soil is verified. What is more, the effect of temperature on fine-grained gassy soil considering the various responses for different drainage conditions and overconsolidation ratios is discussed and simulated by the proposed model. It is concluded that for fine-grained gassy soil with different overconsolidation ratios, the increase of temperature can increase the compressibility and thermal contraction under drained conditions, as well as the pore water pressure under undrained conditions, while the temperature effect on undrained shear properties depends on the initial conditions.