Gas Bubbles Research Articles

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.

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.

A hybrid Phase field - Volume of fluid method for the simulation of three-dimensional binary solidification in the presence of gas bubble

A hybrid Phase field - Volume of fluid method for the simulation of three-dimensional binary solidification in the presence of gas bubble

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.

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.

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.

Superaerophobic polymer objects prototyped via liquid crystal display (LCD)-based 3D printing: one-step post-surface-treatment and application in underwater bubble manipulation

ABSTRACT Underwater superaerophobic surface is of great significance for controllable manipulation of gas bubbles in scientific research and practical applications. However, the fabrication of arbitrary-shaped superaerophobic solid surfaces through a simple and low-cost approach is still hard. Herein, superaerophobic 3D objects were manufactured via liquid crystal display (LCD)-based 3D printing (vat photopolymerisation-based additive manufacturing) combined with one-step post-surface-treatment in sodium hydroxide (NaOH) solution. The influences of NaOH concentration, reaction temperature and time on the wettability of the polymer surface were systematically investigated. After a suitable alkali-treatment, the object surface obtained a bubble contact angle of 159° with extremely low bubble adhesion, featuring the underwater superaerophobicity. Morphology and composition characterisation demonstrated that a hydrophilic gel layer was produced on the printed sheet after the alkali-treatment, which is explained as the main mechanism of the superwetting transition from aerophobicity to superaerophobicity. Interestingly, spontaneously formed surface microgrids (size in xy direction: ∼50 μm) during 3D printing accelerated the alkali-treatment. Further, a superaerophobic 3D tweezer was designed, fabricated, and successfully applied in a toxic nitric oxide (NO) bubble reaction underwater for gas purity detection. The one-step post-surface-treatment method is also suitable for other commercial photosensitive resins and digital-light-processing (DLP) 3D printing.

Gasified acid solution in pre-transition state for well stimulation

In this paper, a new class of fluids is considered, which are single-phase gas-liquid mixtures in the pre-transition state. The mentioned single-phase mixture is a liquid with precritical gas bubbles of nanometer size. The stability of nanobubbles can be increased by introducing surfactants into the gas-liquid mixture. The rheology of a gasified acid solution in a pre-transition has been studied. Based on the conducted research, the method of treating the wellbore zone with a gasified acid solution in a pre-transition state is proposed in order to increase the efficiency of acid treatment. The introduction of a cationic surfactant (0.1%) promotes hydrophobization of the pore walls and slows down the reaction between rock and acid. Improved filtration of single-phase gasified acid solution in pre-transition state increases liquid flow rate at constant pressure drop and reduces the consumption of gaseous agent. The effective viscosity of the gasified acid solution in the pre-transition state is 10 times lower than that of the non-carbonated acid solution. The resulting gasified acid solution flows uniformly into zones of varying permeability, increasing the treatment coverage through both the formation thickness and its depth. Compared to existing acid treatment technologies, such as the use of foam acid and viscoelastic surfactant-based systems, the gasified acid solution in the pre-transition state has a penetration capacity of 40-70% and a coverage factor of 100% higher. In order to reveal the effect of gasified acid solution in pre-transition state on the porous medium, the COMSOL Multiphysics simulation was used.

Methylene Blue degradation using plasma: A comparative study between the microwave plasma jet over water surface and the nanosecond pulsed discharge in gas bubbles in water

In this paper investigates the Methylene Blue degradation using two common reactors: the nanosecond pulsed discharge in oxygen bubbles and the Argon Microwave plasma jet above the treated solution. The aim of this study is to compare the evolution of the reactors' performance when the electrical conductivity increases. In deionized water, the Methylene Blue degradation and the energy efficiency in the nanosecond pulsed discharge configuration were significantly higher than the Argon microwave plasma jet. However, when the solution electrical conductivity is increased, the energy efficiency of the nanosecond pulsed discharge drops significantly by ~82%, whereas the performance of the microwave plasma jet reactors decreases by ~37% only for a greater variation of the electrical conductivity of the solution. Under these conditions, the efficiency of both reactors becomes comparable, suggesting the necessity to consider various parameters to compare the reactors' efficiency.

Copper catastrophic oxidation: Theory and mechanisms

Copper and its alloys with transition metals (as good conductors of electricity and heat) are extensively used in electrical industry, electronics, and cooling systems and can be the subject of surface degradation by oxidation. In certain circumstances, surface degradation of copper occurs catastrophically. Predicting catastrophic oxidation kinetics and developing protective technology require understanding the mass transfer mechanisms in the solid/liquid/gas composite scale formed on the copper surface during catastrophic degradation. However, these mechanisms are not clear enough. The role of capillary forces in the mass transport process in the composite scale with a high density of solid/liquid and liquid/gas interfaces has not been established. Here, we show the significant contribution of both electrochemical and solutocapillary forces to mass transfer and suggest the mechanisms, involving selective transport of ions, gas bubbles, and liquid, and their relationships with the microstructure of the composite scale. The bubble nucleation is discussed.

Strontium-based additive for enhanced aluminum A356-reinforced Al2O3 composite mechanical properties and microstructures

A stir-casting process has produced aluminum alloy A356 reinforced with Al2O3 metal matrix composites (MMCs). The strontium was added into molten Al A356 to improve the mechanical properties of composites. The strontium used varied from 0.046 wt.% to 0.070 wt.%, while Al2O3 was kept constant at 10 vf-%. This research aims to study the effect of Sr on the microstructure and mechanical properties of Al A356/Al2O3 composite. The A356 was melted at 800 °C and mixed with Al-5TiB, Al-5Sr, and Mg as a master alloy of the matrix, then flushed with argon to remove all the gas bubbles from liquid aluminum and stirred for 2 min afterward, it was poured with Al2O3 particles and stirred again for 3 min to distribute the Al2O3 particles in molten Al matrix. The composites produced then characterized both microstructural analysis and mechanical properties. The maximum strength, elongation, and hardness of composites were achieved at 0,046 wt.% Sr with the value of 185 MPa, 4.00%, and 45.3 HRB, while strength, elongation, and hardness of unreinforced were 101 MPa, 2,72%, and 40 HRB respectively and further addition of Sr mechanical properties decreased. The increase in the strength is due to the refinement of Mg2Si primary in the matrix.

A simple approach to quantifying whole‐lake methane ebullition and sedimentary methane production, and its application to the Canadian Lake Pulse dataset

AbstractAquatic sediments represent a key component for understanding CH4 dynamics and emission to the atmosphere. Once produced in the sediments, CH4 is released either by diffusion at the sediment–water interface or by bubbling out to the atmosphere when total gas pressure in the sediment exceeds local ambient pressure due to high CH4 production. Although bubbling is one of the dominant CH4 emission pathways in lakes, direct measurements of this flux are hampered by its high spatiotemporal variability and methodological limitations. Here, we develop a conceptual approach to quantify CH4 production in lake sediments and particularly its release as bubbles based on simple measurements of bubble gas content and depth. Its main assumptions were empirically tested using > 200 long‐term bubble trap deployments collected from 4 temperate lakes. We then applied the developed methodology to a suite of 408 Canadian lakes to produce the first standardized large‐scale assessment of lakes CH4 ebullitive flux during summer. Our results show that lake sediments produced CH4 at a median rate of 3.3 mmol m−2 d−1 (ranged from 0.2 to 11.8 mmol m−2 d−1), releasing 33% via ebullition to the atmosphere. These rates are remarkably similar in magnitude to other regional estimates in the literature. Moreover, our approach revealed that catchment slope was an important determinant of both the lake‐wide ebullitive fluxes and the fraction of sediment CH4 production released as bubbles.

AC Plasmas Directly Excited in Liquid-Phase Hydrocarbons for H2 and Unsaturated C2 Hydrocarbon Production.

AC plasmas directly excited within liquid hydrocarbons were investigated for the production of hydrogen and unsaturated C2 hydrocarbon in a recirculating liquid "jet" flow configuration. Arc discharges were excited at two different frequencies (60 Hz and 17.3 kHz) in C6-C8 hydrocarbons (hexane, cyclohexane, benzene, toluene, and xylene) to produce H2, C2H4, C2H2, and CH4, along with liquid and solid carbon byproducts. AC frequency was seen to modify the plasma properties and gas bubble formation dynamics, significantly influencing the efficiency and reaction pathway. Higher discharge frequency increased energy efficiency more than 2-fold by minimizing thermal losses and favored the production of hydrogenated compounds due to shorter reactant-plasma contact times. Further optimization of hexane conversion was achieved by introducing fluid flow around the plasma electrodes, which led to competitively low specific energy requirements (SERs) of 3.2 kWh/kg C2H4, 4.9 kWh/kg C2H2, and 24.3 kWh/kg H2. The effect of hydrocarbon feed chemistry was analyzed, showing that hexane and cyclohexane are preferable for C2 hydrocarbon syntheses, whereas aromatic hydrocarbons produce more H2. Gas bubble dynamics and liquid/solid products were analyzed using high-speed imaging, optical emission spectroscopy (OES), gas chromatography-mass spectrometry (GC-MS), scanning electron microscopy/transmission electron microscopy (SEM/TEM), and Raman spectroscopy. This work contributes to the understanding of plasma conversion mechanisms within liquids and demonstrates the potential for the energy-efficient transformation of hydrocarbons with plasma in unique reaction environments.

Gas-Liquid-Solid Three-Phase Boundary in Scanning Electrochemical Cell Microscopy.

The gas-liquid-solid interface plays a crucial role in various electrochemical energy conversion devices, including fuel cells and electrolyzers. Understanding the effect of gas transfer on the electrochemistry at this three-phase interface is a grand challenge. Scanning electrochemical cell microscopy (SECCM) is an emerging technique for mapping the heterogeneity in electrochemical activity; it also inherently features a three-phase boundary at the nanodroplet cell. Herein, we quantitatively analyze the role of the three-phase boundary in SECCM involving gas via finite element simulation. Oxygen reduction reaction is used as an example for reaction with a gas reactant, which shows that interfacial gas transfer can enhance the overall mass transport of reactant, allowing measuring current density of several A/cm2. The hydrogen evolution reaction is used as an example for reaction with a gas product, and fast interfacial gas transfer kinetics can significantly reduce the concentration of dissolved gas near the electrode. This helps to measure electrode kinetics at a high current density without the complication of gas bubble formation. The contribution of interfacial gas transfer can be understood by directly comparing its kinetics to the mass transfer coefficient from the solution. Our findings aid the quantitative application of SECCM in studying electrochemical reactions involving gases, establishing a basis for investigating electrochemistry at the three-phase boundary.

Electric Field-Based Ozone Nanobubbles in Tandem with Reduced Ultraviolet Light Exposure for Water Purification and Treatment: Aquaculture and Beyond

Micro- and nanobubbles are tiny gas bubbles that are smaller than 100 μm and 1 μm, respectively. This study investigated the impact of electric field ozone nanobubbles (EF-ONBs) on the purification of both deionised and aquaculture water bodies, finding that heightened reactive oxygen species (ROS) production and oxygen reduction potential (ORP) are correlated to a higher production of EF-ONBs. In particular, it was found that there were substantially reduced ultraviolet light requirements for aquaculture when using EF-ONBs to maintain aquaculture purification standards. It is clear that the approximately exponential decay is slowed down by almost ten times by EF-ONBs even without UV applied, and that it is still roughly six times longer than the ‘control’ case of standard O3 sparging in water (i.e., meso- and macro-bubbles with no meaningful level of dispersed-phase, bubble-mediated dissolution beyond the standard Henry’s law state—owing mostly to rapid Stokes’ law rising speeds). This has very positive implications for, inter alia, recirculation aeration systems featuring an ozonation cycle, as well as indoor agriculture under controlled-light environments and malting, where ozonation cycles are also often used or contemplated in process redesign strategies. Such promising results for EF-ONBs offer, inter alia, more sustainable aquaculture, water sterilisation, indoor farming, and malting.

Integrated portable gas dispersion device

ABSTRACT This paper proposes a new portable device for gas dispersion investigations based on the simultaneous measurements of gas holdup and bubble size in an integrated system. The aim of developing this device is to acquire a better understanding of the interdependence of flotation hydrodynamic parameters mainly: gas holdup (ϵg), bubble size, represented in this study as Sauter mean bubble diameter (D32), superficial gas velocity (Jg), frother type and frother concentration. Utilisation of the device can extend from laboratory to plant processes for investigating the effect of naturally occurring and residual surfactants as well as salts in process water on bubble size and gas holdup using dilution and frother equivalent techniques. Additionally, conventional methods of frother classification such as critical coalescence concentration determination of frothers can be determined as well. Lastly, a preliminary investigation into the use of bubble size and gas holdup for frother classification is explored. Experiments were performed in two-phase batch tests at varying superficial gas velocities of 0.5 cm s−1 and 1 cm s−1 and the frothers used were MIBC (methyl isobutyl carbinol), Flottec F140 (commercial frother blend of aldehydes and ketones) and Flottec F150 (polypropylene glycol). The results show the practicality and versatility of the device.