Gas Bubbles Research Articles

Inertial collapse of a gas bubble in a shear flow near a rigid wall

Inertial collapse of a gas bubble in a shear flow near a rigid wall

Minimizing Product Back Reactions with Inert Carrier Gas Bubbling for Photoelectrochemical Water Splitting with H2/O2 Coevolution

Minimizing Product Back Reactions with Inert Carrier Gas Bubbling for Photoelectrochemical Water Splitting with H₂/O₂ Coevolution

Experimental Optimization of a Venturi-Type Fine Bubble Generation System Based on Gas Absorption Rate

Fine bubbles (FBs) are defined by the ISO/TC 281 as gas bubbles with a diameter of less than 100 μm, and they have interesting properties such as high surface-to-volume ratio, low buoyancy, long residence time, electric charge, and self-pressurization effect. Typically, FBs are characterized in terms of size distribution, concentration, and zeta potential through specialized microscopic and nanoscopic measuring devices. This work proposes a multi-objective optimization problem to find the optimal conditions to generate FBs from experimental macroscopic measurements in terms of dissolved oxygen (DO). Then, detailed microscopic measurements in terms of size distribution and zeta potential are conducted. Additionally, two venturi-type Fine Bubble Generators (FBGs) were 3D-printed in-house to evaluate the relationship between the internal structure and the generation of FBs. The best FBGs have an obstacle in the diverging section that promotes FB generation under the evaluated experimental conditions. Under the best operating conditions, FBs were stable over 7 days with a size distribution between 60 and 90 nm and with an average of −21 mV.

Cold gas bubble inflated by a low-luminosity radio jet

Cold gas bubble inflated by a low-luminosity radio jet

Evidence of pockmarks and seafloor gas venting in the northwestern Arabian Sea

Marine gas seeps are common along tectonically active margins, but they have not been previously observed along the Arabian continental margin. Here we present evidence of gas escape structures, pockmarks, and active gas seeps in the Gulf of Oman. Multibeam bathymetry, water column backscatter and physical parameters, and two-dimensional seismic reflection data were used to map active seafloor seeps and pockmarks. Circular and crescent-shaped pockmarks and complex pockmark strings were identified. These features are confined to regions shoreward of the shelf break. Thirty-five active gas bubble trains were observed, mostly not coincident with the mapped pockmarks. With progressive gas release, the gas seeps are anticipated to lead to development of pockmarks over time. Bright spots on the seismic data indicate shallow subsurface gas accumulation alongside normal fault and fracture conduits, strongly correlated to the presence of pockmarks. These findings suggest an important carbon flux into the Arabian Sea and atmosphere.

Decompression venous gas formation intensity scale

Relevance. Severe decompression sickness is the most common diving disorder; therefore, its diagnosis and prevention is considered important aspects of hyperbaric physiology and diving medicine. Diver’s susceptibility to gas bubble formation under decompression is most critical for decompression sickness prevention. Doppler bubble detection is the most common procedure to identify divers who are most susceptible to gas bubble formation under decompression; nevertheless, a more comprehensive examination including pulse pressure and 2D visualization of gas bubbles provide valuable advantages.The objective is to provide justify the implementation of the decompression risk and venous gas bubble formation scale.Methods. The study enrolled 42 divers who were examined for tolerance to gas bubble formation under decompression; gas bubbles were visualized using Doppler ultrasound. Next, the developed decompression risk and venous gas bubble formation scale was used to verify its efficiency and practical value.Results and discussion. After hyperbaric exposure, 2D gas bubble visualization data were analyzed showing that 6 subjects (14.3 %) had no decompression-caused gas bubble formation (0 points); 9 subjects (21.4 %) scored up to 5 points, showing a small amount of gas bubbles during exercise; 22 subjects (52.4 %) scored between 6 and 15; whereas the remaining 5 subjects presented with gas bubbles at rest and a sharp increase in bubble formation during mild exercise. The obtained data suggest that the examined diver cohort included 13 subjects (31 %) with very high tolerance to gas bubble formation, 21 divers (50 %) showing average tolerance and 8 highly susceptible subjects (19 %).Conclusion. During decompression, venous gas bubble formation scale has significant diagnostic value providing a tool to measure individual diver’s susceptibility to gas bubble formation. The scale allows to reduce the hyperbaric load by decreasing exposure on the ground at threshold pressure (0.4 MPa) and thus reduce the decompression time, based on sufficient evidence regarding individual susceptibility to gas bubble formation under decompression

Impact of Solid Particle Concentration and Liquid Circulation on Gas Holdup in Counter-Current Slurry Bubble Columns

In this study, in a three-phase reactor with a rectangular cross-section, the effects of liquid circulation rates and solid particle concentration on gas holdup and bubble size distribution (BSD) were investigated. Air, water, and glass beads were used as the gas, liquid, and solid phases, respectively. Different liquid circulation velocities and different solid loads were applied. The results demonstrate that increasing solid content from 0% to 6% can decrease gas holdup by 50% (due to increased slurry phase viscosity and promotion of bubble coalescence). Also, increasing the liquid circulation rate showed a weak effect on gas holdup, although a slight incremental effect was observed due to the promotion of bubble breakup and the extension of bubble residence time. The gas holdup in counter-current slurry bubble columns (CCSBCs) was predicted using a novel correlation that took into account the combined effects of solid concentration and liquid circulation rate. These findings are crucial for the design and optimization of the three-phase reactors used in industries such as mining and wastewater treatment.

Electrodeposited Nitrate-Intercalated NiFeCe-Based (Oxy)hydroxide Heterostructure as a Competent Electrocatalyst for Overall Water Splitting.

Electrochemical water splitting is a promising method for the generation of "green hydrogen", a renewable and sustainable energy source. However, the complex, multistep synthesis processes, often involving hazardous or expensive chemicals, limit its broader adoption. Herein, a nitrate (NO3-) anion-intercalated nickel-iron-cerium mixed-metal (oxy)hydroxide heterostructure electrocatalyst is fabricated on nickel foam (NiFeCeOxHy@NF) via a simple electrodeposition method followed by cyclic voltammetry activation to enhance its surface properties. The NiFeCeOxHy@NF electrocatalyst exhibited a low overpotential of 72 and 186 mV at 10 mA cm-2 for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, in 1.0 M KOH. In a two-electrode system, the NiFeCeOxHy@NF obtained a low voltage of 1.47 V at 10 mA cm-2 in 1.0 M KOH with robust stability. Results revealed that the notable activity of the NiFeCeOxHy@NF catalyst is primarily due to (i) hierarchical nanosheet morphology, which provides a large surface area and abundant active sites; (ii) NO3- anion intercalation enhances electrode stability and eliminates the need for binders while simultaneously promoting a strong catalyst-substrate adhesion, resulting in decreased electrode resistance and accelerated reaction kinetics; and (iii) the unique superhydrophilic surface properties facilitate electrolyte penetration through capillary action and minimize gas bubble formation by reducing interfacial tension.

A TVD WAF scheme based on an accurate Riemann solver to simulate compressible two-phase flows

PurposeThis study aims to propose a robust total variation diminishing (TVD) weighted average flux (WAF) finite volume scheme for investigating compressible gas–liquid mixture flows.Design/methodology/approachThis study considers a two-phase flow composed of a liquid containing dispersed gas bubbles. To model this two-phase mixture, this paper uses a homogeneous equilibrium model (HEM) defined by two mass conservation laws for the two phases and a momentum conservation equation for the mixture. It is assumed that the velocity is the same for the two phases, and the density of phases is governed by barotropic laws. By applying the theory of hyperbolic equations, this study establishes an exact solution of the Riemann problem associated with the model equations, which allows to construct an exact Riemann solver within the first-order upwind Godunov scheme as well as a robust TVD WAF scheme.FindingsThe ability and robustness of the proposed TVD WAF scheme is validated by testing several two-phase flow problems involving different wave structures of the Riemann problem. Simulation results are compared against analytical solutions and other available numerical methods as well as experimental data in the literature. The proposed approach is much superior to other strategies in terms of the accuracy and ability of reconstruction.Originality/valueThe novelty of this work lies in its methodical extension of a TVD WAF scheme implementing an exact Riemann solver developed for compressible two-phase flows. Furthermore, other novelty lies on the quantitative calculation of different Riemann problem two-phase flows. Simulation results involve the verification of the constructed methods on the exact solutions of HEM without any restriction of variables.

Droplet menisci recognition by deep learning for digital microfluidics applications

AbstractThis paper demonstrates the use of deep learning, specifically the U‐Net model, to recognize the menisci of droplets in an electrowetting‐on‐dielectric (EWOD) digital microfluidic (DMF) device. Accurate recognition of droplet menisci would enable precise control over the movement of droplets to improve the performance and reliability of an EWOD DMF system. Furthermore, important information such as fluid properties, droplet characteristics, spatial position, dynamic behavior, and reaction kinetics of droplets during DMF manipulation can be understood by recognizing the menisci. Through a convolutional neural network utilizing the U‐Net architecture, precise identification of droplet menisci is achieved. A diverse dataset is prepared and used to train and test the model. As a showcase, details of training and the optimization of hyperparameters are described. Experimental validation demonstrated that the trained model achieves a 98% accuracy rate and a 0.92 Dice score, which confirms the model's high performance. After the successful recognition of droplet menisci, post‐processing techniques are applied to extract essential information such as the droplet and bubble size and volume. This study shows that the trained U‐Net model is capable of discerning droplet menisci even in the presence of background image interference and low‐quality images. The model can detect not only simple droplets, but also compound droplets of two immiscible liquids, droplets containing gas bubbles, and multiple droplets of varying sizes. Finally, the model is shown to detect satellite droplets as small as 2% of the size of the primary droplet, which are byproducts of droplet splitting.

Industrial Investigations of S355 Steel-Grade Homogenization in a 100-Tonne Ladle Furnace.

The paper presents the results of industrial research and numerical simulations of the chemical homogenization of liquid steel. The research object was a ladle furnace with a working capacity of the ladle of 100 t at the steel plant of Huta Częstochowa, currently Liberty Częstochowa Sp. z o.o. Industrial research was carried out under standard production conditions of the steelworks. The research included automatic steel sampling, measurement of the bath temperature, controlled measurement of argon flow at a given intensity, and the determination of the concentration of elements in steel samples using a spectrometric analyser. The element introduced in the form of a ferroalloy (FeMn and FeSiMn) played the role of a marker in the study of changes in the chemical composition during the process of dissolution and mixing of the alloying additive. Monitoring changes in the chemical composition of steel after the introduction of the marker was carried out by taking metal samples. The initial and boundary parameters of the modelled processes necessary to perform numerical simulations were determined successively through industrial measurements or determined on the basis of empirical relationships. A two-equation k-ε turbulence model was used to assess the flow inside the tested ladle furnace, and a discrete phase model was used to model gas bubbles. The mixing characteristics of the steel bath after introducing the alloying additive to it were determined. The comparison of the results of numerical simulations with experimental data was based on the analysis of the chemical homogenization process.

Interaction of light with gas-liquid interfaces: influence on photon absorption in continuous-flow photoreactors.

Light interacts with gas bubbles in various ways, potentially leading to photon losses in gas-liquid photochemical applications. Given that light is a valuable 'reagent', understanding these losses is crucial for optimizing reactor efficiency. In this study, we address the challenge of quantifying these interactions by implementing a method that separately determines the photon flux and utilizes actinometric experiments to determine the effective optical path length, a key descriptor of photon absorption. The results reveal the unexpected impact of gas phase introduction in continuous-flow photoreactors. Notably, photon absorption, and consequently the throughput of a photoreactor, can be increased by the introduction of a gas phase. This enhancement arises from the reflection and refraction effects of gas bubbles, which can intensify light intensity in the liquid volume and thereby offset any loss in residence time. The photon absorption losses that were observed were associated with large bubbles and were less significant than anticipated. In contrast, the introduction of small bubbles was found to increase photon absorption, suggesting it is a potential strategy to optimize photoreactor performance.

Influence of bubble breakup on cavitation effect in vortex flow field

<sec>The liquid vortex flow field plays a crucial role not only in the transfer of matter and heat but also in significantly affecting the distribution of sound fields, which in turn influences the behavior of bubbles in the flow. This ultimately affects the phenomenon of acoustic cavitation. Based on the combination of the theory of bubble fragmentation and the theory of funnel-shaped vortex, in a three-dimensional vortex field. The effect of the vortex flow field (flow field generated by stirring) on the bubble breakup probability, as well as its modulation of acoustic cavitation, is investigated in this paper. In addition, the phenomena observed in experiments are explained. When the stirring speed reaches 1000 rad/min, the degradation effect no longer shows a monotonic increase, but instead begins to decline.</sec><sec>It is demonstrated that with the increase of stirring speed, the probability of bubble breakup increases significantly. For instance, when the stirring speed is 1000 rad/min, the probability of bubble breakup is about 0.17%. At a stirring speed of 1500 rad/min, the breakup probability rises to 23%, and at 2000 rad/min, it reaches 44%. Moreover, the critical radius for bubble breakup decreases. The critical radius, as defined in this study, refers to the bubble radius at which the probability of breakup becomes nonzero. Experimental data show that at 600 rad/min, the critical radius for bubble breakup is about 200 μm, while at 2000 rad/min, it shortens to 55.5 μm. This indicates that in a high-speed rotating vortex field, bubbles may rupture before reaching their maximum cavitation radius, thus losing their effective cavitation effect.</sec><sec>Further analysis shows that in the vortex flow field, for bubbles with an initial radius smaller than 22.5 μm, the temperature inside the bubbles upon collapse can reach as high as 2217.3 K (corresponding to an initial radius of 22.5 μm). For bubbles with an initial radius of 20 μm, the collapse temperature can even reach 2264.3 K. For bubbles with an initial radius of 40 μm, when the stirring speed does not exceed 1500 rad/min, the bubbles can still collapse under the action of the sound field, and the temperature inside the bubble upon collapse can reach 1659.6 K, which is sufficient to trigger off the cavitation effect. However, when the stirring speed exceeds 1500 rad/min, bubbles may break up too quickly and lose their cavitation capacity, thus failing to produce the expected cavitation effect.</sec><sec>Experimental results further verify that at moderate stirring speeds (600—1000 rad/min), the acoustic cavitation effect is most pronounced, while excessively high stirring speeds suppress the enhancement of the degradation effect. This phenomenon suggests that the introduction of the vortex flow field makes the factors affecting acoustic cavitation more complex. The optimization of the acoustic cavitation effect requires not only the consideration of the sound field distribution and mass transfer but also the comprehensive factors such as gas entrainment, bubble aggregation, and breakup. Therefore, a thorough analysis and regulation of these factors are crucial for the widespread application of acoustic cavitation technology in engineering, with important theoretical value and practical significance, providing scientific basis and direction for further optimizing the acoustic cavitation process.</sec>

Quantifying the relationship between bubble surface area and gas evolution rate

Quantifying the relationship between bubble surface area and gas evolution rate

Boosting energy efficiency and selectivity of glucose oxidation toward glucuronic acid in high-frequency ultrasound using multicavity CuO catalytic cavitation agents

Reactive oxygen species generated from the inertial collapse of a gas bubble trapped on the surface of an MC-CuO cavity selectively oxidize glucose into glucuronic acid.

Retrospective evaluation of a novel ultrasound-based imaging analysis software for predicting radiofrequency ablation areas.

This study aimed to introduce and evaluate a novel software-based system, BioTrace, designed for real-time monitoring of thermal ablation tissue damage during image-guided radiofrequency ablation for hepatocellular carcinoma (HCC). BioTrace utilizes a proprietary algorithm to analyze the temporo-spatial behavior of thermal gas bubble activity during ablation, as seen in conventional B-mode ultrasound imaging. Its predictive accuracy was assessed by comparing the ablation zones it predicted with those annotated by radiologists using contrast-enhanced computed tomography (CECT) 24 hours post-treatment, considered the gold standard. The study included 20 liver tumors. The median tumor measurement along the major axis was 1.2 cm. The median Dice coefficient, Sensitivity, and Precision between BioTrace and CECT were 0.90, 0.91, and 0.91, respectively. The intraclass correlation showed excellent agreement in volume size between BioTrace and CECT findings (0.98). BioTrace effectively generates an ablation damage prediction map based on real-time ultrasound imaging, accurately predicting the ablation zone as confirmed by 24-hour post-procedural CECT. This system has the potential to enhance the safety and efficacy of ablation procedures in clinical settings.

Functional nanocrystal as effective contrast agents for dual-mode imaging: Live-cell sonoluminescence and contrast-enhanced echography.

In the context of molecular imaging, the present work explores an innovative platform made of lipid-coated nanocrystals as contrast-enhanced agent for both ultrasound imaging and sonoluminescence. At first, the dynamics of gas bubbles generation and cavitation under insonation with either pristine or lipid-coated nanocrystals (ZnO-Lip) are described, and the differences between the two colloidal systems are highlighted. These ZnO-Lip show an unprecedented ability to assist cavitation, which is reflected in enhanced sonoluminescent light emission with respect to the pristine nanocrystals or the pure water. Highly defined and sharp sonoluminescent images of cultured cells are indeed obtained, for the first time, when ZnO-Lip are used. Furthermore, ZnO-Lip were adopted as a nanosized agent for contrast-enhanced ultrasound imaging, i.e. echography, first in solutions, and then on ex-vivo tissues. A prolonged over time and bright imaging effect is observed when adopting the developed nanoparticles. Furthermore, their nanometric size and potential targeting with biomolecules would allow ease extravasation and tissue or even cell penetration, achieving enhanced-contrast imaging. Finally, the stimuli-responsive therapeutic applications of ZnO-Lip against tumors is overviewed, aiming to achieve a fully theranostic approach.

Dynamic electroosmotic flow and solute dispersion through a nanochannel filled with an electrolyte surrounded by a layer of a dielectric and immiscible liquid.

The present article deals with the modulation of oscillatory electroosmotic flow (EOF) and solute dispersion across a nanochannel filled with an electrolyte solution surrounded by a layer of a dielectric liquid. The dielectric permittivity of the liquid layer adjacent to supporting rigid walls is taken to be lower than that of the electrolyte solution. Besides, the aforesaid liquid layer may bear additional mobile charges, e.g., free lipid molecules, charged surfactant molecules etc., which in turn lead to a nonzero charge along the liquid-liquid interface. Such a layer of a dielectric liquid resembles the membrane of various biological cells. An AC voltage is applied to generate the fluid motion. Note that among others, the major advantage of AC voltage is that it can suppress the formation of gas bubbles that are often very detrimental in flow through microdevices. Considering the combined impact of ion partitioning and ion steric effects, we have studied the EOF modulation and its impact on the dispersion of the solute band of given width placed initially at the middle of the channel. The full scale numerical results for flow modulation induced by an AC electric field and its impact on the solute transport are presented considering a wide range of pertinent parameters. It is observed that the molar concentration of additional charge present in the dielectric liquid layer and its thickness, interfacial charge, and concentration of the bulk electrolyte, ion partitioning and ion steric effects, frequency of oscillatory electric field, channel height etc., have a substantial impact on the flow modulation, effective dispersion coefficient as well as broadening of the solute band across the channel. We have further highlighted the impact of the Péclet number on the transport and dispersion of solutes. Along with the numerical results, several benchmark analytical results under various limits are deduced for electrostatic potential, flow velocity and various quantities associated with the dispersion process.

Methods to prevent or mitigate total dissolved gas supersaturation in the waterways downstream hydropower plants

Abstract Downstream hydropower plants, a change in water chemistry can lead to the occurrence of a widely unknown problem: total dissolved gas (TDG) supersaturation. It takes place when air is entrained in a water body and exposed to high pressures, which leads to gas dissolution in the water. Re-exposure to atmospheric pressure downstream the power plant results in TDG supersaturation. This is a potential danger for the aquatic environment living in these waters, as the increased saturation poses the risk of experiencing gas bubble disease (GBD). Studies about TDG supersaturation are found in North America (USA and Canada), China, Brazil, and Norway (minor studies include Austria, Germany, and Sweden). Yet, knowledge about the risk of the problem is not widespread, which leads to the repetition of mistakes. Moreover, shifting precipitation patterns induced by climate change are expected to lead to an increase in TDG supersaturation occurrences, as those are associated with flooding. An overview of methods to either prevent or mitigate the problem of TDG supersaturation downstream hydropower plants is presented and recent study results are disseminated. These include civil engineering, operational, and technical methods. Where hydropower plants are in a planning phase, this can contribute to preventing the occurrence of TDG supersaturation in the first place, while existing hydropower plants can implement different measures to reduce the risk of producing TDG supersaturation in the downstream waterways. This helps maintain the aquatic environment as well as local habitat for fish and invertebrates, and therefore counts towards hydropower taxonomy and increases social acceptance of hydropower.

Three-dimensional Modeling of the Interaction of a Bubble pair with a Rigid Wall using Boundary Integral Method

This study examines the three-dimensional dynamics of two gas bubbles near a horizontal rigid wall, focusing on how inter-bubble distance affects their shape, size, and jet formation. The Boundary Integral Method (BIM) with a novel local smoothing technique is employed. Critical parameters including jet velocity, bubble centroid movement, bubble radius, and collapse time are computed for each bubble to understand their interaction dynamics comprehensively. The velocity vector field and pressure distribution surrounding the bubbles are analyzed, providing detailed insights into the fluid dynamics. The findings demonstrate that inter-bubble distance significantly influences their interaction and overall behavior. These results advance the understanding of bubble dynamics near rigid boundaries, with potential applications across various scientific and engineering disciplines.