Accurate determination of bubble size, morphology, and spatial distribution is essential for quantitative analysis of gas-liquid two-phase flows, such as bubble columns and water electrolyzers. While deep learning has shown strong potential for bubble image analysis, most methods require large annotated datasets. In this paper, we adapt pretrained neural network models from Cellpose, originally developed for cell segmentation, for efficient bubble recognition using limited training data. Quantitative analysis shows that for millimeter-scale single bubbles, the Cyto model achieves a Dice coefficient over 0.9 and an average relative error of about 3% in equivalent diameter, enabling accurate trajectory tracking. For micrometer-scale overlapping bubbles, the Cpsam model trained on just 60 samples reaches over 90% in Dice coefficient, precision and recall, with bubble count deviation within +/- 5 and diameter error below 5%. Trained on only 15 images, it also segments bubbles well in complex scenarios like bubble columns and alkaline water electrolysis for hydrogen production. These results demonstrate that the proposed Cellpose-based approach enables accurate and efficient bubble image analysis without extensive labeled datasets or complex hardware, providing a robust tool for quantitative characterization of gas-liquid two-phase flow systems.

Liquid volatility is a fundamental property of gas-liquid systems and is particularly relevant in high-temperature processes, yet its hydrodynamic implications in bubble columns remain largely unexplored. In this work, we investigate the impact of liquid volatility on gas holdup and flow regime transition in a bubble column by employing n-pentane, n-hexane, and their binary mixtures, which share comparable viscosity and surface tension but different saturated vapor pressures. We found that increasing volatility significantly enhances gas holdup in the homogeneous regime, which is well described by corrected superficial gas velocity, Ug,vapor= Ug* Pa Pa-Pv, accounting for vapor generation based on Dalton's law. More importantly, this work demonstrates that higher volatility induces an earlier regime transition from homogeneous to heterogeneous flow. As the saturated vapor pressure increases from 19 to 58 kPa, the critical gas velocity Ug,trans decreases from 3.39 cm/s to 1.27 cm/s. Bubble dynamics analysis indicates that, although the intrinsic bubble coalescence efficiency remains essentially unchanged, increased volatility intensifies the lateral oscillations of rising bubbles. This may enhance bubble-bubble encounter probability and promote the early formation of large, fast-rising bubbles, thereby determining the flow regime. These findings establish a direct link between liquid volatility and flow regime stability in bubble columns, provide guidance for industrial bubble column operation involving high-temperature or volatile-liquid conditions.

Bubble detachment from solid surfaces governs heat, mass, and charge transport across technologies vital to clean energy, including high-current-density water electrolysis and boiling thermal management. At high gas fluxes, however, bubbles remain trapped at active surfaces despite immense buoyancy, severely restricting mass transfer and increasing energy losses. Here, we show that this unexpected surface retention originates from cascade coalescence between unequal-sized bubbles. High-speed observations around microelectrodes demonstrate that when a rising bubble merges with a smaller surface-attached successor, its trajectory abruptly reverses, accelerating toward the substrate at nearly two orders of magnitude above its rising speed. Direct numerical simulations and scaling analysis reveal that asymmetric interfacial retraction during merging generates non-canceling viscous stresses, producing a net downward impulse toward the smaller bubble. Repeated cascade coalescence events accumulate these transient impulses into a steady, time-averaged retaining force capable of opposing buoyancy three to four orders of magnitude beyond quasistatic limits. Our findings establish bubble coalescence as a previously unrecognized mechanism that dynamically sustains bubble retention under high gas flux.

Carbon underpins global energy and industry, and its efficient reuse is pivotal for advancing a circular economy and reducing environmental burden. A CO2-mediated flotation strategy based on coupled bubble dynamics and surface chemistry reconstruction was developed for efficient carbon recovery from low-rank coal and carbonaceous solid wastes. Compared with conventional flotation, CO2-mediated flotation generated finer and more stable microbubbles, enhancing bubble dispersion, collision probability, and bubble–particle attachment stability. Interfacial characterization demonstrated that CO2 treatment suppressed hydrophilic oxygen-containing functionalities, reduced surface polarity, and increased the contact angle of long-flame coal (LFC) from 21.88° to 49.30°, thereby improving hydrophobicity. Under optimized conditions, combustible recovery reached 88.49%. Density functional theory calculations demonstrated preferential CO2 adsorption onto oxygen-containing sites, promoting hydrophobic surface reconstruction and stable three-phase contact formation. Life-cycle assessment confirmed reduced environmental impacts. This work provides a sustainable strategy for low-impact carbon resource recovery.

Gas bubble evolution during water electrolysis governs bubble-mediated interfacial transport, active-site availability, and voltage stability in gas-evolving electrochemical systems. Although microelectrodes are widely used as model platforms for probing electrochemical bubble dynamics, how electrode geometry regulates bubble evolution and the resulting electrochemical instability remains insufficiently understood. Here, platinum microelectrodes with diameters of 100, 200, and 500 μm are employed as well-defined model electrodes to investigate hydrogen bubble dynamics during the hydrogen evolution reaction (HER) in acidic electrolyte under galvanostatic conditions. By combining electrochemical measurements with high-speed imaging, we show that individual bubble growth follows an apparent Faradaic gas-production-limited scaling, dbt=βt1/3, within the experimentally resolved growth window across all electrode sizes. In contrast, the bubble growth coefficient β, bubble lifetime, detachment diameter, coalescence behavior, and potential response exhibit strong geometry dependence. Larger electrodes provide broader active areas with more nucleation sites and frequent bubble coalescence, leading to higher apparent β values, shorter bubble lifetimes, smaller detachment diameters, and delayed onset of periodic voltage oscillations at a given current. Conversely, smaller electrodes confine gas generation into single-bubble-dominated regimes, resulting in larger detachment sizes and earlier periodic bubble-induced voltage oscillations. Notably, the critical current density required to trigger periodic oscillations increases systematically with electrode size, while the dominant detaching bubble becomes comparable in size to the electrode at the transition. These findings provide a quantitative basis for selecting electrode feature size and operating current-density windows to mitigate bubble-induced voltage instability in water electrolysis systems.

Gas bubble evolution during water electrolysis governs bubble-mediated interfacial transport, active-site availability, and voltage stability in gas-evolving electrochemical systems. Although microelectrodes are widely used as model platforms for probing electrochemical bubble dynamics, how electrode geometry regulates bubble evolution and the resulting electrochemical instability remains insufficiently understood. Here, platinum microelectrodes with diameters of 100, 200, and 500 μm are employed as well-defined model electrodes to investigate hydrogen bubble dynamics during the hydrogen evolution reaction (HER) in acidic electrolyte under galvanostatic conditions. By combining electrochemical measurements with high-speed imaging, we show that individual bubble growth follows an apparent Faradaic gas-production-limited scaling,d_b(t)=βt^(1/3) , within the experimentally resolved growth window across all electrode sizes. In contrast, the bubble growth coefficient β, bubble lifetime, detachment diameter, coalescence behavior, and potential response exhibit strong geometry dependence. Larger electrodes provide broader active areas with more nucleation sites and frequent bubble coalescence, leading to higher apparent β values, shorter bubble lifetimes, smaller detachment diameters, and delayed onset of periodic voltage oscillations at a given current. Conversely, smaller electrodes confine gas generation into single-bubble-dominated regimes, resulting in larger detachment sizes and earlier periodic bubble-induced voltage oscillations. Notably, the critical current density required to trigger periodic oscillations scales linearly with electrode size, establishing a quantitative link between electrode geometry, bubble detachment dynamics, and electrochemical instability. These findings provide a quantitative basis for selecting electrode feature size and operating current-density windows to mitigate bubble-induced voltage instability in water electrolysis systems.

Improving mass transfer is critical for enhancing the efficiency of electrochemical devices, such as liquid flow batteries and water electrolyzers. However, the typical parallel-plate design of these devices, characterized by confined flow channels that aim to increase the reaction area, complicates the enhancement of mass transfer and makes it energy-intensive. This study proposes the use of rising bubbles as an effective strategy for improving mass transfer in a vertical plate electrochemical reactor with a confined 6-mm electrode gap. We measured mass transfer coefficients based on the limiting current and estimated equivalent diffusion layer thicknesses during ferricyanide reduction. Key experiments demonstrate that bubbles introduced at a flow rate of 10 ml/min achieve a mass transfer enhancement comparable to electrode rotation at 529 rad/min. This enhancement even surpasses the improvement observed the improvement observed with forced liquid convection at 1800 ml/min. Furthermore, single-bubble synchronization experiments and numerical simulations reveal quantitative relationships between bubble-induced convection and mass transfer enhancement. These experiments systematically uncover the underlying mechanisms, which are attributed to shear flow at the front of the bubble and the wake at the bubble's tail. This work clearly demonstrates the potential of using bubble-induced convection as a highly efficient strategy for enhancing mass transfer in confined electrochemical systems.

Reducing hydrogen-in-oxygen (HTO) to mitigate the explosive hazard is critical for the renewable energy powered alkaline water electrolysis (AWE). However, the role of trans-diaphragm convection in influencing HTO remains poorly characterized. In this study, we employ a home-designed AWE experimental system with separated liquid circulation circuits for the hydrogen side and oxygen side, respectively, which facilitates the precise measurement of trans-diaphragm flow rates and their effects on HTO. Experimental results reveal a persistent liquid convection carrying dissolved hydrogen from the hydrogen compartment to the oxygen compartment. This convection flowrate increases with both the electrolysis current and the electrolyte circulation rate, constituting 10-15% of the circulation flow rate on the hydrogen side. Through theoretical modeling, we established a linear correlation between the dissolved hydrogen crossover rate (QH2 ) and the liquid crossover rate (Qlc), demonstrating that the dissolved hydrogen in the liquid exceeds saturation levels by approximately 0.36 times. Importantly, reducing liquid crossover by modulating electrolyte circulation resulted a remarkable reduction in HTO from 0.6% to below 0.1% at the same electrolysis current-an approximately 80% decrease. These findings offer critical insights into the origin of HTO and provide actionable strategies for optimizing AWE operation, paving the way for safer and more efficient large-scale green hydrogen production.

Bubble column reactors are widely used in industrial applications due to their excellent mass and heat transfer capabilities, where the critical parameter gas holdup is significantly influenced by interactions between bubbles of different sizes. This study investigates the effect of dual-sized bubble interaction on gas holdup in coalescence-inhibited systems. A quantitative comparison between dual-sized and single-sized systems reveals that micrometer-sized bubbles primarily contribute to gas holdup. A non-monotonic trend in system gas holdup is observed when millimeter-sized bubbles are gradually introduced into a fixed micro-bubble system. To explain the phenomenon, a coupled drift-flux model is developed to relate the intermediate decline in gas holdup to the enhanced velocity of micro-bubbles through dual-sized bubble interactions. These findings provide new insights for optimizing bubble column systems, particularly in applications requiring high gas flux and improved gas-liquid mass transfer, such as in wastewater oxidation, 1,4-Butanediol synthesis, and electrolysis processes.

Electrochemical CO2 reduction reaction (CO2RR) is a promising technique to address the excess CO2 emissions for closing the global carbon cycle. However, challenges remain to break the trade-off between high Faradaic efficiencies and high current densities. Herein, we synthesize Ag nano-foams (Ag NFs) featuring sufficient gas channels by a facile wet-chemical method. It is revealed that the gaseous products can be rapidly released from Ag NFs with the presence of nanochannels, profiting from the exposure of active sites and their further access to CO2. COMSOL simulation verifies the uniform distribution of low-pressure drop and thus promotes local mass transfer within the catalyst layers. Benefiting from the improved transport features, the Ag NFs achieve excellent CO Faradaic efficiencies (FECO > 90.9

The adhesion and growth of gas bubbles during water electrolysis increase overpotential and energy loss, and their behavior is strongly influenced by electrolyte composition. In this study, a 500 mu m-diameter platinum microelectrode was used to investigate bubble detachment behavior and electrolysis current in six electrolyte systems under constant potential conditions. The results reveal that, even at identical applied potentials and proton concentrations, both bubble detachment size and electrolysis current vary significantly with electrolyte type. In coalescence-prone electrolytes (e.g., H2SO4 and HNO3), large single bubbles form and detach at high potentials (up to similar to 1000 mu m at -5.34 V), supporting higher electrolysis currents. In contrast, coalescence-inhibiting electrolytes (e.g., HClO4 and Na2SO4) produced smaller, multiple bubbles (as low as 187 mu m) and exhibited substantially lower currents-up to 52 % lower at more negative potential. These findings highlight electrolyte-regulated bubble coalescence as a critical and often overlooked factor in gas-evolving electrochemical systems. Designing electrolytes or electrode structures that promote moderate bubble coalescence offers a promising strategy for improving energy efficiency in high-rate water electrolysis and related industrial applications.

The micro-nanobubbles (MNBs) technology provides an innovative theoretical basis and application prospect for solving the problem of water treatment. However, the fabrication of bubble generators with high MNBs generation efficiency has always been challenging. Herein, we developed a new hydrodynamic cavitation bubble generator by equipping the multi-jet reactor to enhance the shear breakage effect of bubbles. The breakup behavior of bubbles with different diameters and velocities in jet orifices was investigated by numerical simulation. At the same time, the turbulent model of two-phase flow in the Venturi gas-liquid mixer was established to analyze the internal flow field under different intake rates. The bubble size and dissolved oxygen (DO) concentration of bulk MNBs water were determined through image analysis and a DO sensor, respectively. The results showed that the cavitation generator produced bubbles with diameters no larger than 27.85 mu m. Moreover, the MNBs generator exhibited a superior oxygen-dissolving capability, which was 1.48 times that of general aerated water. This study has deepened the comprehension of the bubble breakup mechanism, providing a reference for designing and developing of MNBs generation technology.

Gas–liquid two‐phase flow in alkaline water electrolysis critically influences current density and efficiency, yet quantitative insights remain limited. This work examines gas holdup and bubble size distribution in a custom‐designed 1.5‐m high‐electrolytic cell, mimicking an industrial press‐filter design. Results reveal that gas holdup increases with cell height and current density due to cumulative gas production, while higher electrolyte flow velocity reduces holdup by accelerating bubble transport. The average electrolytic bubble size d 43 evolves significantly from ~100 μm near the bottom to ~300 μm at the top of the cell, driven by coalescence and influenced by electrolysis current. A one‐dimensional drift‐flux model identified cell height, current density, electrolyte circulation rate, and bubble size as critical determinants of gas holdup. Theoretical predictions demonstrate that increasing d 43 from 130 to 270 μm can halve gas holdup, highlighting bubble size regulation as a key strategy for reducing gas holdup to enhance electrolyzer performance.

Gas evolution during the hydrogen evolution reaction (HER) induces complex interfacial dynamics and can lead to oscillations in potential. However, the real-time coupling between bubble behavior and overpotential response remains poorly understood. In this study, we report a previously unrecognized delay phenomenon during constant-current HER: the minimum in overpotential does not coincide with the moment of bubble detachment, but instead occurs tens of milliseconds later-after a new bubble has already formed and grown to several hundred microns on the electrode surface. Using synchronized high-speed imaging and time-resolved electrochemical measurements, we show that the delay time increases consistently with current density and bubble detachment size. Statistical analysis across multiple cycles confirms strong correlations among detachment size, oscillation amplitude, and delay time. Notably, in rare cases involving successive bubble detachments, both the delay and amplitude are further amplified. Complementary CFD simulations confirm that bubble wake generates transient interfacial convection, which significantly enhances local mass transfer and temporarily reduces the concentration overpotential, thereby delaying the recovery of reaction potential even as a surface new bubble begins to grow on electrode. These findings unveil a previously unrecognized dynamic feedback mechanism in which gas bubble evolution actively modulates interfacial mass transfer, offering new insight into gas-involved electrochemical processes and a potential strategy for optimizing multiphase electrochemical systems.

An eddy deep leaching technology was developed in this paper to address the challenge of treating heavy metal contaminants in industrial mining areas. The desorption effect of As, Cd, Sb and Pb was investigated utilizing chemical leaching and physical eddy techniques. It was found that the heavy metals concentration increased with decreasing particle size. The highest proportion of Cd in the form distribution of soil was in the bound to iron and manganese oxides, while the maximum proportion of As, Sb and Pb were in the residual. The optimal solid-liquid ratio of the hydrocyclone was 1:20, and the corresponding separation efficiency and flow rate were 84.7% and 1.76 m3/hr, respectively. The grade efficiency of soil particle separation increases with particle size and exceeds 99% for particles above 1,000 µm. Leaching experiments have revealed that oxalic acid (OA) and a combination of oxalic acid and EDTA (OAPE) were more efficient than citric acid (CA) and a combination of citric acid and EDTA (CAPE) for the desorption of heavy metals, respectively. The comparison of OAPE and eddy leaching found that the latter improved the desorption efficiency by 9.4%, 7.5%, 7.2% and 7.8% for As, Cd, Sb and Pb compared to the former, respectively. The results demonstrated that the eddy leaching technique could further enhance the desorption efficiency of heavy metals. It is expected to provide technical support for soil remediation with reduced usage of leaching agents.

The principle of fibrous coalescers is to induce the coalescence and growth of small oil droplets in oil-in-water emulsions to achieve oil-water separation. However, they are poorly adaptable to emulsions containing highviscosity oil. In this study, pressurized air is dissolved in the oil-in-water emulsion, microbubbles are released by reducing the pressure, and the emulsion is subsequently processed through a fibrous coalescer. Adding microbubbles altered the oil removal mechanism within the fibrous bed from oil droplet coalescence and growth to oil droplet-microbubble floc flotation, which significantly improved the emulsion separation efficiency of the fibrous bed, especially in complex emulsions containing surfactants and low salinity. Notably, the decrease in the interfacial energy of the oil droplet-microbubble floc caused oil droplets adhered to fibers to detach and renew quickly. Moreover, the curved interfacial tension increased oil droplet buoyancy and kinetic energy collectively drove the detachment of oil droplets from the fibrous bed. Effective, dynamic anti-fouling of the fibrous bed was able to maintain high throughput during long-term emulsion separation. This study provides a theoretical basis for the industrial application of fibrous coalescers for the treatment of oily wastewater produced during extraction high-viscosity crude oil.

Coarse particle flotation provides significant advantages in terms of reducing grinding costs and improving the throughput of the flotation process. However, the high probability of the detachment of coarse particles during flotation is a significant challenge. In this study, we explored the feasibility of using oily bubbles to reduce the detachment of coarse particles from the bubbles. Specifically, the effect of oily bubbles on the attachment stability of bubble???particle aggregates from the perspective of attachment force was theoretically analyzed and compared to that of air bubbles, and the effect of oily bubbles on the detachment probability of spherical glass beads with different contact angles was investigated experimentally using a home-built experimental system. Both the theoretical and experimental results proved that it is feasible to apply oily bubbles to reduce the detachment probability of coarse particles. However, there are limitations to this method. The influence of oily bubbles on the detachment behavior was mainly governed by changes in the contact angle and interfacial tension, which is not the case with air bubbles. Therefore, the oily bubbles were effective in reducing the detachment probability only for particles in which the influence of the increase in contact angle on the particle detachment exceeded that of the decrease in interfacial tension. The results of this study advance our understanding of the effect of oily bubbles on the detachment behavior of coarse particles, such as in the flotation separation of valuable minerals using oily bubbles.

Selective etching of Si3N4 is a critical process in the fabrication of 3D-NAND structures; however, it faces a by-product re-deposition problem that significantly deteriorates the remaining structure morphology. A recent study by Kim et al.[1] showed that generating CO2 bubbles during the etching process efficiently solves the re-deposition problem in the fabrication of a 128 multi-layer 3D-NAND structure. In this study, we numerically investigated the multiscale mass transport of byproducts in the etching process to reveal the underlying mechanism. We found that mass transport within the multilayer structures alone cannot contribute to the oxide re-deposition behavior. Macroscopic transport from the wafer-etchant interface to the bulk must be considered. This contributes to a high by-product concentration at the wafer-etchant surface, which further increases the concentration within the slits, leading to the re-deposition problem. The large bubbles generated from the reaction agitate the surrounding liquid and dramatically reduce the surface concentration by one order of magnitude, thereby solving the re-deposition problem. Our findings clearly explain the experimental results reported by Kim et al. and will further benefit the development of process-intensification technologies in wet etching.

The selective etching of SI3N4 is a critical process in the fabrication of the 3D-NAND structures but faces the by-product re-deposition problem that significantly worsens the remaining structure morphology. A recent work by Kim et al.[1] show that generating CO2 bubbles in the etching process can efficiently solve the re-deposition problem in fabricating a 128 multi-layer 3D-NAND structure. In this work, we numerically studied the multi-scale mass transport of by-products in the etching process to unveil the underlying mechanism. We found that mass transport within the multi-layer structures alone cannot contribute to the oxide re-deposition behavior. The macroscopic transport from the wafer-etchant interface to the bulk must be considered. It contributes to a high by-product concentration at the wafer-etchant surface, which further increases the concentration within the slits that leading to the re-deposition problem. The reaction-generated large bubbles agitated the surrounding liquid and dramatically reduced the surface concentration by one order of magnitude, solving the re-deposition problem. Our findings clearly explain the experimental results of Kim et al. and would benefit the further development of process intensification technologies in wet etching.