Bubble Size Research Articles

Hydrophobicity of Benzene-Based Surfactants and Its Effect on Bubble Coalescence Inhibition.

Bubble coalescence plays a critical role in optimizing biological and industrial processes, impacting efficiency in areas such as fermentation, wastewater treatment, and foaming control. While the relationship between chemical structure and bubble coalescence has been thoroughly explored for inorganic ions, limited data exist on organic ions and surfactants, despite their widespread use in these industries. This study addresses this gap by investigating the effects of surfactant hydrophobicity and bubble size on coalescence behavior at a flat air-liquid interface and within a bubble column. Surface tension measurements were employed to assess surfactant hydrophobicity, while bubble size and coalescence time were analyzed to determine their respective influences. The results reveal a novel quantitative relationship between surfactant hydrophobicity and the half-coalescence inhibition concentration (HCIC), a new variable introduced in this study. This relationship demonstrates that as hydrophobicity increases, the HCIC also rises, providing a new relationship between surfactant hydrophobicity and bubble coalescence. While it is well-known that more hydrophobic molecules delay coalescence, this is the first time a direct, proportional relationship has been established with HCIC, offering a new parameter for predicting and controlling coalescence phenomena.

High stability enhanced ultrasonic microfluidic structure with flexible tip coupled bubbles

Ultrasonic microfluidic technology is a technique that couples high-frequency ultrasonic excitation to microfluidic chips. To improve the issues of poor disturbance effects with flexible tip structures and the susceptibility of bubbles to thermal deformation, we propose an enhanced ultrasonic microchannel structure that couples flexible tips with bubbles aiming to improve the disturbance effects and the stability duration. Firstly, we used finite element analysis to simulate the flow field distribution characteristics of the flexible tip, the bubble, and the coupling structure and obtained the steady-state distribution characteristics of the velocity field. Next, we fabricated ultrasonic microfluidic chips based on these three structures, employing 2.8 μm polystyrene microspheres as tracers to analyze the disturbance characteristics of the flow field. Additionally, we analyzed the bubble size and growth rate within the adhering bubbles and coupling structures. Finally, we verified the applicability of the coupling structure for biological samples using human red blood cells (RBCs). Experimental results indicated that, compared to the flexible tip and adhering bubble structures, the flow field disturbance range of the coupling structure increased by 439.53% and 133.48%, respectively; the bubble growth rate reduced from 14.4% to 3.3%. The enhanced ultrasonic microfluidic structure proposed in this study shows great potential for widespread applications in micro-scale flow field disturbance and particle manipulation.

Computational Analysis of Flow Around Two Wall-Mounted Trapezoidal Bluff Bodies Arranged in Tandem Position

Abstract Flow around two identical wall-mounted trapezoidal bluff bodies, arranged in tandem, is numerically investigated at a Reynolds number of 750,000. The investigation employs Reynolds-averaged Navier–Stokes (RANS) equations and the k–ω SST turbulence model. The effect due to the change of the angular orientation of the inclined faces (α) of this bluff body and the pitch distance (L/D) on hydrodynamic quantities and turbulence quantities is investigated. Furthermore, the drag coefficient and Strouhal number have also been evaluated to understand the vortex shedding and flow pattern-related phenomena. For d and intermediate types of bluff bodies, the streamwise mean velocity, cross-stream mean velocity, turbulence kinetic energy, and recirculation length decrease with the increase of α or L/D. Significant changes are also observed in the case of Strouhal number. Reduction in drag coefficient and recirculation length is observed with increased L/D at a constant α for d-type bluff bodies. The change of α and L/D also creates the formation of a periodic von Kármán vortex street at downstream of the second bluff body in the case of L/D = 7, making the flows more complex and unstable. The maximum size of the recirculation bubble occurs in the case of L/D = 10 at α = 30 deg. The investigation provides valuable insight into the complex dynamics of tandem configurations of wall-mounted bluff bodies.

Bubble plume effects on the flotation kinetics of nonmetallic inclusions based on experimental observations

AbstractSteelmaking has shown an increasing concern toward nonmetallic inclusions, leading to new technologies in the secondary metallurgy of steel. Although the typical inclusion removal procedure is by injecting inert gas into the ladle, this vessel does not fulfill all the requirements to accept a porous structure tailored to produce “clean steels.” Consequently, the spotlight has moved to the tundish, the last vessel before solidification, in which gas injection can continuously operate. Therefore, this work focuses on understanding the influence of typical gas flow rates (10–60 NL/min) on the kinetics of inclusion flotation, considering two bubble diameters (0.6 and 1.1 mm). For this purpose, experimental measurements were conducted in a water model, where glass hollow spheres played the role of inclusions, and their concentration was fitted by an exponential decay. In general, injecting bubbles into the system contributed positively to a faster and greater flotation of particles. The smaller bubbles led to a higher maximum efficiency, whereas the larger ones allowed a shorter time scale (i.e., a faster removal), defining a trade‐off to tune the bubble size. Regarding the gas flow rate, the results indicate an optimum range to decrease the time scale, and suggestions for bubble curtains in tundishes are drawn.

Optimizing flotation froth image segmentation via parallel branch network and hybrid loss supervision

Flotation is a crucial technology for fine coal separation, and accurately acquiring bubble size information during the flotation process is essential for monitoring flotation conditions and achieving intelligent control. However, existing semantic segmentation models encountered issues with boundary disconnection when segmenting flotation bubbles, resulting in deviations between the extracted bubble sizes and their true values. To address the aforementioned challenges, a semantic segmentation model was proposed to maintain high-resolution feature maps throughout the network by designing a parallel branch network structure. Additionally, a ConvTranspose module was proposed to preserve the detailed feature information of images while gradually enhancing the resolution of feature maps. In the model training phase, a hybrid loss function combining pixel classification loss with shape similarity loss was proposed to alleviate the sample imbalance problem caused by the substantial difference in the number of pixels between bubble boundaries and the interior of bubbles. Moreover, since traditional semantic segmentation evaluation metrics, such as MIoU, lack a mechanism for measuring bubble boundary continuity and cannot effectively penalize the problem of boundary disconnection, this paper proposed a new evaluation method for assessing the segmentation performance of flotation froth images. To comprehensively evaluate the effectiveness of the proposed method, this paper conducted tests using flotation froth images collected from actual production processes. Compared with existing methods, the segmentation model proposed in this paper exhibited clear superiority in mitigating the problem of bubble boundary disconnection. The prediction error for the number of bubbles was 6.38 %, which is significantly better than other methods.

Enhancement of critical current density using micro-porous structure in a low-temperature water electrolysis

The critical current density (CCD), which limits the hydrogen production rate was measured by forming micro-porous structures on the cathode electrode in a low-temperature water electrolysis. Several micro-porous structures were formed by the electrodeposition method varying the current density during the deposition. A maximum 54% enhancement of the CCD was recorded compared to the plain surface. With the micro-porous structures, the superior capillary wicking effect allowed the electrolyte to penetrate the structure, resulting in the increased number of hydrogen nucleation sites. The increased hydrogen nucleation sites led to the decreased hydrogen bubble size and increased departed bubble density, which delayed formation of the hydrogen film leading to the CCD. The surface morphology revealed that the multiple pore layers with the interconnected pores exhibited superior capillary wicking effect compared to the open type single pore layer. It is expected that the results of present work stimulate further research regarding electrode surface design in the low-temperature water electrolysis.

Experimental study on flow boiling heat transfer in rigid-tail rib-channel under rolling motion conditions

This study proposes a novel addition of rigid filamentous tail structure at the trailing edge of the ribs to enhance the heat transfer performance of flow boiling in mini-channel under rolling conditions. The flow boiling heat transfer characteristics of Novec649 in both rib-channel and rigid-tail rib-channel are experimentally investigated. Heat flux, inlet flow velocity, rolling angle and rolling period are considered as the variable parameters, which are 50 – 300 kW·m−2, 0.3 – 0.9 m·s−1, 0 – 15°, 10 – 20 s, respectively. The experimental results show that the rigid-tail structure improves the heat transfer performance of the channels within the entire range of thermal parameters, while increasing the pressure drop at high heat flux and/or high velocity. Compared with rib-channel, the rigid-tail structure exhibits the strongest enhancement in flow boiling heat transfer performance under high heat flux of qeff = 300 kW·m−2 and high flow velocity of vin = 0.9 m·s−1, and the heat transfer coefficient can be increased by 6.93 % at most. And increasing the rolling angle or decreasing the rolling period will decrease the average wall temperature by a maximum of 1.94 °C and increase the heat transfer performance factor j by a maximum of 8 % at vin = 0.3 m·s−1, qeff = 200 – 300 kW·m−2 for the rigid-tail rib-channel. Furthermore, the addition of a rigid-tail structure helps maintain smaller bubble sizes and a more uniform distribution in the mainstream region of the two-phase flow.

Study on the mechanism of laser-induced breakdown and damage performance of internal defects in transparent materials through local optical field modulation

This paper establishes a photothermal damage model for bubble impurities affecting laser optical field modulation based on Mie scattering theory and incorporates the effects of optical field modulation. This model elucidates the evolution mechanism of synergistic damage in fused silica, with simulation results validated through experimental verification. A novel characterization of optical breakdown due to bubble impurities is proposed, occurring on a millisecond timescale through the dynamic evolution of combustion waves. The model delineates the influence of bubble size and spacing on optical field distribution, temperature, stress distribution, and their evolutionary behaviors. The modulation of the optical field due to double bubble impurities creates a localized “hot spot,” resulting in a differential transverse contraction stress at the edges of the bubble impurities, thereby reducing the damage threshold of fused silica. The spacing of 1.1 λ represents the enhancement node for optical field modulation by double bubble impurities. Furthermore, localized oscillations in the optical field arise when the spacing between the double bubbles exceeds 1.1 λ, attributed to changes in the refractive index at the bubble defects and resonance oscillations generated by optical field modulation. This study not only enhances our understanding of the optical field modulation processes occurring at 1064 nm in the presence of bubble defects but also establishes a theoretical foundation for detecting internal defects at this wavelength without inducing surface damage.

On the reliability of image analysis for bubble size distribution measurements in electrolyte solutions in stirred reactors

The translation of chemical processes from laboratory to industrial scale is crucial for the effective and sustainable implementation of new technologies. This transition presents significant challenges, particularly in multiphase systems where variations in physical chemistry can complicate scale-up efforts. A key aspect of this challenge is understanding bubble dynamics in gas-liquid systems, which are pivotal in processes such as hydrogen production and CO2 absorption. Bubble size significantly influences mass transfer rates and process efficiency, necessitating accurate measurement methods. A factorial design approach was employed to assess the sensitivity of results to key parameters. The findings provide quantitative guidelines for optimizing image analysis techniques and improving the accuracy of bubble size measurements in diverse operational conditions. This work advances the understanding of bubble dynamics in gas-liquid systems and offers practical insights for refining measurement techniques, ultimately supporting more effective scale-up of chemical processes.

Insights into kinetic and transfer mechanisms for alkaline decoupled water electrolysis based on distribution of relaxation times

Electrochemical water splitting is crucial for the decarbonization of industrial processes and the coupling of renewable energy sources. Evaluation of individual HER and OER contributions to the transfer process is essential for optimizing electrolysis system performance. This study uses nickel-cobalt layered double hydroxide (NiCo-LDH) as a solid-state redox mediator (SRM), achieving efficient H2 and O2 separation. This study provides an in-depth analysis of kinetic and ion/charge/mass transfer mechanisms linked to various characteristic impedances in alkaline decoupled water electrolysis (DWE) system by integrating Electrochemical Impedance Spectroscopy (EIS) and Distribution of Relaxation Times (DRT) methods. The characteristic frequency evolution is consistent with the charge-discharge state of SRM and mass transfer frequency is related to the bubble size and gas diffusion rate of electrocatalysts at different current densities. The charge transfer Rct dominates the total polarization impedance in decoupled HER, and mass transfer Rm decreases remarkably in decoupled OER. OER shows lower Rct with Fe species existence and lower total polarization impedance than HER. Rm in decoupled HER increases by 38.24% and OER by 29.82% during prolonged decoupled test. This study provides valuable insights into the impedance contributions and kinetic mechanisms through novel electrolysis approaches, guiding further optimization of decoupled electrolyzer and electrode.

Nanobubble Formation and Coverage during High Current Density Alkaline Water Electrolysis.

Gas bubbles are a necessary byproduct of water electrolysis whereby hydrogen and oxygen are produced from water. These attached gases reduce the electrode's active area, which necessitates a deep understanding of the bubble life cycle starting from nanobubbles. Synchronized with the electrochemistry, the time evolution of the surface nanobubble size and coverage is resolved using grazing incidence small-angle X-ray scattering (GISAXS) and correlated with optical microscopy and theoretical calculations to show that a significant portion of the surface is covered in nanobubbles after larger micron-sized bubbles are observed. These nanobubbles increase in number and decrease in size, toward 2 nm diameter, with the charge passed. The trend in size and number is consistent with an increase in supersaturation, which reduces the nascent bubble size. Altogether, this study suggests a significant portion of the surface contains nanobubbles and that strategies to reduce the dissolved hydrogen would be effective at reducing the nanobubble surface coverage.

Development of emulsion foams based on healthier oleogels and their application as low-fat replacers for whipped cream

This study aimed to develop emulsion foams (I: 1:1 flaxseed oil to coconut oil; II: 1:2 flaxseed oil to coconut oil; III: 2:1 flaxseed oil to coconut oil) based on the formation of an air-in-water-in oleogel as a healthy substitute for whipped cream.The developed emulsion foamswere assessed for their physicochemical properties and fatty acid composition. They were also characterized through Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), polarized light microscopy (PLM), and differential scanning calorimetry (DSC). Based on the results, emulsion foamII demonstrated a higher overrun percentage (90%) thanI and III (80 and 70%, respectively).The serum leakage values for all formulations were zero after 24 h at 5 °C. While, hardness values for emulsion foams I, II, and III were 0.40 ± 0.03, 0.50 ± 0.10, and 0.30 ± 0.04 N, respectively. The emulsion foamIII had higher unsaturated fatty acids than I and II (54.67% vs. 41.50% and 28.72%). Theemulsion foamsI and II showed more packed air bubbles than the emulsion foamIII.In emulsion foams I, II, and III, the average size of air bubbles was 36, 25.09, and 15.09 μm, respectively. Moreover, the thermal stability of the emulsion foam II is enhancedby increasing the coconut oilratio.

Impact of Wettability on CO2 Dynamic Dissolution in Three-Dimensional Porous Media: Pore-Scale Simulation Using the Lattice Boltzmann Method.

Understanding the dissolution behavior of supercritical CO2 (scCO2) in porous media is crucial for efficient CO2 storage. However, the precise modeling of dynamic dissolution behavior at this pore scale remains a huge challenge, and the impact of wettability on this process still needs to be clarified. In this study, the influence of rock wettability on CO2 dynamic dissolution in the three-dimensional porous media is investigated using the lattice Boltzmann method (LBM). The LBM is coupled with scCO2-water two-phase flow, solute transport, and heterogeneous and homogeneous reactions. The size, number, and dissolution pattern of scCO2 bubbles during the dissolution process are observed under strongly water-wet, weakly water-wet, intermediate-wet, and mixed-wet conditions. The CO2(aq) concentration and pH are investigated, followed by a quantitative investigation of the impact of wettability on the specific interface area and the mass transfer coefficient. An empirical relationship between the specific interface area and scCO2 saturation is established. The findings reveal that under weakly water-wet and intermediate-wet conditions, the sizes of scCO2 clusters and monomers are small and mostly distributed at the dead end of the pores. In contrast, under strongly water-wet and mixed-wet conditions, the clusters are larger and interconnected, and distributed in the center of the pore. This results in a greater scCO2-water interface area, consequently enhancing the dissolution rate. Furthermore, a strong linear correlation is observed between scCO2 saturation and specific interface area. It is noted that as the hydrophilicity of the rock increases, the mass transfer coefficient initially rises and then declines.

Stability analysis of CO2 microbubble for CO2 sequestration and mobility control in enhanced oil recovery

This study addresses the challenge of CO2 microbubble stability in enhanced oil recovery (EOR), with a focus on the combined effects of surfactant concentration, brine concentration, brine-oil ratio, and gas flow rate. Microbubble destabilization, driven by phase separation and improper brine-oil ratios, is a critical issue in EOR. The novelty of this research lies in the use of Acacia concinna, a natural, non-ionic surfactant, to enhance microbubble stability sustainably. The study systematically investigates foamability, drainage kinetics, surface tension, rheology, and bubble size distribution to assess microbubble stability. The results showed that increasing surfactant concentration and brine-oil ratio significantly impacted foam stability and bubble size distribution, with optimal stability conditions observed at 2 wt% surfactant concentration (53.6 min), 5000 ppm brine concentration (47.6 min), a brine-oil ratio of 1:2 (52.4 min), and a CO2 gas flow rate of 1 lpm. Key findings also indicate that increasing NaCl concentration from 5000 to 20,000 ppm caused an increase in microbubble diameter, while higher gas flow rates reduced bubble size. The work introduces new empirical correlations for predicting bubble size distribution based on column diameter, surfactant and brine concentrations, viscosity, density, and gas superficial velocity. These correlations provide a more accurate means of optimizing EOR processes, improving oil recovery efficiency while enhancing CO2 sequestration, contributing to both energy production and environmental sustainability.

Two-phase flow properties for air sheets injected from rectangular slots in high-velocity crossflow

This work presents an experimental contribution towards the understanding of the two-phase jet dynamics in high-speed transverse flows, a field that is essential to many industrial applications. Four slot injectors are the subject of this investigation, which examines air flows as high as 0.05 m3/s and cross flows as high as 6 m/s. Using an invasive optical probe, the study reveals the presence of an air cavity surrounded by a two-phase mixing zone. Analysis of the spatial void fraction reveals counter-rotating vortices that direct bubbles towards their centers while larger bubbles rise to the top of the vein and form an upper zone with a maximum void fraction. The study also looks at the dynamic evolution of air sheet characteristics, which reveals an increasing trend in average void fraction along the flow. The comparison of bubble characteristics of different slots and conditions provides valuable insights into the impact of environment pressure and slot geometry on void fraction and bubble size in two-phase flows. Finally, correlations based on dimensionless numbers generalize the information on bubble characteristics for a wide range of conditions, assisting in estimation and validation in numerical simulations.

Development and validation of a 1D gas–liquid model for dissolved Mn(II) removal by oxidation process in a square bubble column

Modeling multiphase reactors requires an in-depth multidisciplinary analysis of various phenomena including the chemical kinetics, oxygen mass transfer, as well as the simulation of flows within these contactors. In this study, a 1D model of two-phase flow for Mn(II) removal from drinking water by aeration process is developed and validated. This model is based on the Eulerian description of two-phase gas–liquid flow with the comparison between a one-medium bubble size and a two-bubble class description to represent the bubble population in the heterogeneous flow regime. All the relevant chemical species are simulated by coupling hydrodynamics, gas–liquid mass transfer, and reaction kinetic. A pseudo-first-order model accounting for homogeneous and heterogeneous kinetics is considered for Mn(II) oxidation. The performance of the developed 1D model is compared and validated with experimental data. The 1D model was able to predict quantitatively Mn oxidation as a function of pH, initial Mn(II) and initial Mn(IV) concentrations.

Structural evolution and stabilisation mechanism of foam fluids that contain cellulose nanofibres and cellulose nanocrystals: An experimental and theoretical study

Foam fluids are thermodynamically metastable systems, and they evolve over timescales comparable to their time of use, which makes the study of their destabilisation mechanisms crucial for many industrial applications. In our study, foams were made from fluids that contained cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs). We explored the effects of nanocelluloses and oils (n-heptane and n-dodecane) on foam stability, bubble coarsening and liquid drainage. Results show that the evolution of the bubble size is strongly slowed by the synergistic effect of CNCs and CNFs, and the structural evolution of foam is greatly impacted. The main responsible mechanism is an increase in local yield stresses due to the presence of CNCs in the foam. The jammed CNCs in foam produce a drainage delay, which makes the foam 50 % drainage time (t50%) of the experimental value deviate by up to 400 % from the classical theory value. When the bubbles coarsen and grow above a threshold size, liquid can drain out of the foam. Finally, a modified model for t50% that considers the drainage delay was proposed. The experimental results validated the proposed correlation and exhibited good reliability and predictive accuracy. The results enable us to elucidate the impact of CNCs and CNFs on the stability of foam fluids.

Effects of pressure depletion rate, solvent, and surfactant on non‐equilibrium reactions in foamy oil

AbstractThis research employed a visual method to explore the behaviour of foamy oil in heavy oil systems. A Hele‐Shaw cell was designed for observing the volumetric expansion of foamy oil as the system pressure decreased. This approach facilitated an examination of foamy oil's interface evolution under pressure depletion and an analysis of bubble sizes and their distribution. Using Minitab, 15 experiments were strategized, aimed at observing the distribution of bubbles and their stability during the foamy oil process. The investigation also extended to studying the influence of surfactants, solvent type, and pressure reduction rate on foamy oil. The findings suggest that a high concentration of surfactant, a high percentage of CO2 solvent, and a rapid pressure drop rate all contributed to the generation of microbubbles and enhanced volumetric expansion and stability of foamy oil. However, in light of the conducted energy analysis, a lower rate of pressure reduction is recommended. Finally, the conditions of the 15 experiments were applied to the CMG to derive two non‐equilibrium reactions for bubble generation and collapsing. The reaction rates are such that they relate bubble generation to the pressure reduction rate of the process and bubble resistance to collapsing to the surfactant concentration of the foamy oil.

Bubble characteristics in a novel microbubble gas-liquid-solid fluidized bed

The bubble characteristics are critical in gas-liquid-solid fluidized beds and microbubbles significantly enhance mass transfer in multiphase systems. In this work, a novel concept of microbubble gas-liquid-solid fluidized bed is proposed. Telecentric camera is employed to measure and analyze the microbubble characteristics including bubble size and gas holdup in this three-phase fluidized bed. Additionally, solid holdups in the fluidized bed are also examined. The results demonstrate that the bubble size adheres a lognormal distribution and is significantly influenced by superficial gas velocity. Bubble diameter exhibit a relatively uniform distribution in the radial direction. Bubbles exceeding than 1 mm substantially affect local gas holdup, and the microbubble flow promotes a more uniform distribution of local gas holdup in radial position. The average gas holdup deviation is less than 15 % compared to overall gas holdup obtained from pressure drop. Although microbubbles are more abundant, larger bubbles (> 1 mm) contribute more to solid particle fluidization. This paper introduces a methodology for assessing smaller-sized microbubbles in three-phase flow. The hydrodynamic analysis of the microbubble gas-liquid-solid fluidized bed establishes a foundational framework for enhancing gas-liquid mass transfer in fluidized bed.

Influence of the gas phase on a large-scale bubble column fluid dynamics: Gas holdup, flow regime transitions, and bubble size distributions

We present the results of an experimental study of a large-diameter bubble column operating in batch mode with air or CO2 as the gas phase and water as the liquid phase. The bubble column has an inner diameter of 0.24 m and is 5.3 m in height. The superficial gas velocity varied between 0.0037 m/s and 0.0233 m/s. The experimental investigation consists of gas holdup measurements and image analysis. Flow regime transitions were detected by gas holdup measurements, and image analysis was used to investigate the bubble size distributions. The results suggest that the homogeneous flow regime is stabilized when CO2 is used as the gas phase. The gas holdup is higher for the CO2-water system at fixed superficial gas velocity, especially in the heterogeneous flow regime. In the homogeneous flow regime, the mean bubble diameter and the fraction of large bubbles are lower for the CO2-water system, explaining the higher gas holdup.