Articoli di riviste: "Bubble breakup"

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Zhang, Zheng, Yi Zhang, Guanmin Zhang e Maocheng Tian. "The bubble breakup process and behavior in T-type microchannels". Physics of Fluids 35, n. 1 (gennaio 2023): 013319. http://dx.doi.org/10.1063/5.0131748.

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A double T-type microchannel consisting of two T-junctions is used as the base unit of tree-like microchannels. Studying the breakup process and behavior of bubbles in T-type microchannels can help enhance the capability of microfluidic systems and microchannel heat exchangers. In this study, the bubble breakup process in a double T-type microchannel was simulated using a volume of fluid model via numerical simulation. The simulation results show a total of five regimes of bubble breakup with capillary numbers between 0.001 and 0.008 and dimensionless bubble lengths between 1 and 9, which are the non-breakup, “tunnel” breakup, obstructed breakup, merging symmetric breakup, and merging non-breakup. These five breakup regimes were studied in detail. At a high velocity of the gas phase and with a small size of the generated bubble, the bubble does not break up. Symmetric breakup regimes can be divided into two regimes: tunnel breakup and obstructed breakup. Shear force plays a significant role in the tunnel breakup regime. The obstructed breakup regime is mainly caused by the increase in pressure at the T-junction, which elongates and makes the bubble break up. In the merging symmetrical breakup regime, the bubble has a tunnel breakup process at the beginning. The shear force is small and cannot break up the bubble. The merged bubble breaks up under the action of the obstructed breakup regime. Bubbles are in the merging non-breakup regime mainly because they are too long to break up.

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Pan, Wen-Tao, Lin Wen, Shan-Shan Li e Zhen-Hai Pan. "Numerical study of asymmetric breakup behavior of bubbles in Y-shaped branching microchannels". Acta Physica Sinica 71, n. 2 (2022): 024701. http://dx.doi.org/10.7498/aps.71.20210832.

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Microfluidic technology based on microchannel two-phase flow has been widely used. The precise control of the bubble or droplet size in the channel plays a crucial role in designing the microfluidic systems. In this work, the bubble breakup behavior in Y-shaped microchannel is reconstructed based on the volume of fluid method (VOF), and the effects of bubble dimensionless size (1.2–2.7), outlet flow ratio (1–4) and main channel Reynolds number (100–600) on the bubble breakup behavior are systematically investigated. The bubble asymmetric breakup process is found to be divided into three stages: extension stage, squeeze stage, and rapid pinch-off stage. In the case of small initial bubble size or relatively high outlet flow rate, the bubble does not break, but only experiences the extension stage and the squeezing stage. Four flow patterns of bubble breakup are further revealed for the bubbles with different sizes and outlet flow ratios: tunnel-tunnel breakup, obstruction-obstruction breakup, tunnel-obstruction breakup, and non-breakup. With the increase of outlet flow ratio, the breakup process of the bubble gradually becomes asymmetrical, and the flow pattern shifts along the tunnel-tunnel breakup and the obstruction-obstruction breakup, gradually turns toward the tunnel-obstruction breakup and non-breakup. On this basis, the critical flow ratio of bubble breakup and the variation of daughter bubble volume ratio with outlet flow ratio are obtained for different Reynolds numbers and initial bubble sizes, and the corresponding criterion correlation equation is refined, which can provide theoretical guidance for accurately regulating the daughter bubble size after breakup.

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Chen, Huiting, Shiyu Wei, Weitian Ding, Han Wei, Liang Li, Henrik Saxén, Hongming Long e Yaowei Yu. "Interfacial Area Transport Equation for Bubble Coalescence and Breakup: Developments and Comparisons". Entropy 23, n. 9 (25 agosto 2021): 1106. http://dx.doi.org/10.3390/e23091106.

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Bubble coalescence and breakup play important roles in physical-chemical processes and bubbles are treated in two groups in the interfacial area transport equation (IATE). This paper presents a review of IATE for bubble coalescence and breakup to model five bubble interaction mechanisms: bubble coalescence due to random collision, bubble coalescence due to wake entrainment, bubble breakup due to turbulent impact, bubble breakup due to shearing-off, and bubble breakup due to surface instability. In bubble coalescence, bubble size, velocity and collision frequency are dominant. In bubble breakup, the influence of viscous shear, shearing-off, and surface instability are neglected, and their corresponding theory and modelling are rare in the literature. Furthermore, combining turbulent kinetic energy and inertial force together is the best choice for the bubble breakup criterion. The reviewed one-group constitutive models include the one developed by Wu et al., Ishii and Kim, Hibiki and Ishii, Yao and Morel, and Nguyen et al. To extend the IATE prediction capability beyond bubbly flow, two-group IATE is needed and its performance is strongly dependent on the channel size and geometry. Therefore, constitutive models for two-group IATE in a three-type channel (i.e., narrow confined channel, round pipe and relatively larger pipe) are summarized. Although great progress in extending the IATE beyond churn-turbulent flow to churn-annual flow was made, there are still some issues in their modelling and experiments due to the highly distorted interface measurement. Regarded as the challenges to be addressed in the further study, some limitations of IATE general applicability and the directions for future development are highlighted.

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Wang, Ziyue, Liansheng Liu, Runze Duan e Liang Tian. "The aerobreakup of bubbles in continuous airflow". Physics of Fluids 34, n. 4 (aprile 2022): 043317. http://dx.doi.org/10.1063/5.0086604.

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Floating soap bubbles usually break up owing to gravitational drainage, surface evaporation, environmental disturbances, and collisions with objects. If a gust of wind blows into a bubble, does the bubble break, and, if so, how does it do so? This study reports experiments that use a high-speed camera to examine the dynamic behaviors of a suspended bubble that is suddenly exposed to continuous airflow. Specifically, the behaviors and mechanisms of the aerobreakup of bubbles are explored. The suspended bubble undergoes shedding and deformation under aerodynamic force and flows with airflow. As the Weber number ( We) increases, the parameter of Taylor deformation ( DT) first increases and then decreases. At a higher Reynolds number, K–H waves appear on the surface of the film owing to the strong shear of airflow on the liquid film. Most such bubbles break due to the shear of the wake vortices on the leeward surface or surface waves on the windward surface, both of which are shearing. The aerobreakup of the bubbles becomes more severe with an increase in We, and they successively exhibit modes of wind-flowing, leeward breakup, windward breakup, and multihole breakup.

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Zhang, Chengbin, Xuan Zhang, Qianwen Li e Liangyu Wu. "Numerical Study of Bubble Breakup in Fractal Tree-Shaped Microchannels". International Journal of Molecular Sciences 20, n. 21 (5 novembre 2019): 5516. http://dx.doi.org/10.3390/ijms20215516.

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Hydrodynamic behaviors of bubble stream flow in fractal tree-shaped microchannels is investigated numerically based on a two-dimensional volume of fluid (VOF) method. Bubble breakup is examined in each level of bifurcation and the transition of breakup regimes is discussed in particular. The pressure variations at the center of different levels of bifurcations are analyzed in an effort to gain further insight into the underlying mechanism of bubble breakup affected by multi-levels of bifurcations in tree-shaped microchannel. The results indicate that due to the structure of the fractal tree-shaped microchannel, both lengths of bubbles and local capillary numbers decrease along the microchannel under a constant inlet capillary number. Hence the transition from the obstructed breakup and obstructed-tunnel combined breakup to coalescence breakup is observed when the bubbles are flowing into a higher level of bifurcations. Compared with the breakup of the bubbles in the higher level of bifurcations, the behaviors of bubbles show stronger periodicity in the lower level of bifurcations. Perturbations grow and magnify along the flow direction and the flow field becomes more chaotic at higher level of bifurcations. Besides, the feedback from the unequal downstream pressure to the upstream lower level of bifurcations affects the bubble breakup and enhances the upstream asymmetrical behaviors.

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MARTÍNEZ-BAZÁN, C., J. L. MONTAÑÉS e J. C. LASHERAS. "On the breakup of an air bubble injected into a fully developed turbulent flow. Part 1. Breakup frequency". Journal of Fluid Mechanics 401 (25 dicembre 1999): 157–82. http://dx.doi.org/10.1017/s0022112099006680.

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The transient evolution of the bubble-size probability density functions resulting from the breakup of an air bubble injected into a fully developed turbulent water ow has been measured experimentally using phase Doppler particle sizing (PDPA) and image processing techniques. These measurements were used to determine the breakup frequency of the bubbles as a function of their size and of the critical diameter Dc defined as Dc = 1.26 (σ/ρ)3/5ε−2/5, where ε is the rate of dissipation per unit mass and per unit time of the underlying turbulence. A phenomenological model is proposed showing the existence of two distinct bubble size regimes. For bubbles of sizes comparable to Dc, the breakup frequency is shown to increase as (σ/ρ)−2/5ε−3/5 √D/Dc−1, while for large bubbles whose sizes are greater than 1.63Dc, it decreases with the bubble size as ε1/3D−2/3. The model is shown to be in good agreement with measurements performed over a wide range of bubble sizes and turbulence intensities.

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ENTOV, VLADIMIR, e PAVEL ETINGOF. "On the breakup of air bubbles in a Hele-Shaw cell". European Journal of Applied Mathematics 22, n. 2 (21 dicembre 2010): 125–49. http://dx.doi.org/10.1017/s095679251000032x.

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We study the problem of breakup of an air bubble in a Hele-Shaw cell. In particular, we propose some sufficient conditions of breakup of the bubble, and ways to find the contraction points of its parts. We also study regulated contraction of a pair of bubbles (in which the rates of air extraction from the bubbles are controlled) and study various asymptotic questions (such as the asymptotics of contraction of a bubble to a degenerate critical point, and asymptotics of contraction of a small bubble in the presence of a big bubble)

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Ekambara, K., R. Sean Sanders, K. Nandakumar e J. H. Masliyah. "CFD Modeling of Gas-Liquid Bubbly Flow in Horizontal Pipes: Influence of Bubble Coalescence and Breakup". International Journal of Chemical Engineering 2012 (2012): 1–20. http://dx.doi.org/10.1155/2012/620463.

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Modelling of gas-liquid bubbly flows is achieved by coupling a population balance equation with the three-dimensional, two-fluid, hydrodynamic model. For gas-liquid bubbly flows, an average bubble number density transport equation has been incorporated in the CFD code CFX 5.7 to describe the temporal and spatial evolution of the gas bubbles population. The coalescence and breakage effects of the gas bubbles are modeled. The coalescence by the random collision driven by turbulence and wake entrainment is considered, while for bubble breakage, the impact of turbulent eddies is considered. Local spatial variations of the gas volume fraction, interfacial area concentration, Sauter mean bubble diameter, and liquid velocity are compared against experimental data in a horizontal pipe, covering a range of gas (0.25 to 1.34 m/s) and liquid (3.74 to 5.1 m/s) superficial velocities and average volume fractions (4% to 21%). The predicted local variations are in good agreement with the experimental measurements reported in the literature. Furthermore, the development of the flow pattern was examined at three different axial locations ofL/D= 25, 148, and 253. The first location is close to the entrance region where the flow is still developing, while the second and the third represent nearly fully developed bubbly flow patterns.

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Solsvik, Jannike, e Hugo A. Jakobsen. "Single Air Bubble Breakup Experiments in Stirred Water Tank". International Journal of Chemical Reactor Engineering 13, n. 4 (1 dicembre 2015): 477–91. http://dx.doi.org/10.1515/ijcre-2014-0154.

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Abstract Single gas bubbles have been injected into an stirred liquid tank and the eventual breakup process of the bubbles was examined through high-speed imaging. Experimental observations of the breakup probability, breakup time, number of daughter bubbles and daughter bubble size distribution have been collected. The occurrence of non-equal-size breakup events dominated over equal-size breakup events. The frequency of binary and multiple breakup events was about equal. The largest uncertainty is associated with the determination of the breakup time because the bubbles take continuously altering deformed shapes already from the point of injection into the tank. The present experimental data do not support the standard model assumption regarding the number of daughter particles. The active breakup zone in the stirred tank was in the large velocity field close to the radial impeller. It is not evident whether the breakup events are due to time average shear or pressures and velocity fluctuations.

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Yang, Weidong, Zhiguo Luo, Nannan Zhao e Zongshu Zou. "Numerical Analysis of Effect of Initial Bubble Size on Captured Bubble Distribution in Steel Continuous Casting Using Euler-Lagrange Approach Considering Bubble Coalescence and Breakup". Metals 10, n. 9 (27 agosto 2020): 1160. http://dx.doi.org/10.3390/met10091160.

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A mathematic model considering the bubble coalescence and breakup using the Euler-Lagrange approach has been developed to study the effect of the initial bubble size on the distribution of bubbles captured by the solidification shell. A hard sphere model was applied for dealing with the bubble collision. Advanced bubble coalescence and breakup models suitable for the continuous casting system and an advanced bubble captured criteria have been identified established with the help of user-defined functions of FLUENT. The predictions of bubble behavior and captured bubble distribution agree with the water model and plant measurements well respectively. The results show that the number of small bubbles captured by solidification shell is much higher than that of large bubbles. What is more, the number of captured bubbles at the sidewalls decreases with the distance from the meniscus. For the case of large gas flow rate (gas flow fraction of 8.2%), the initial size of bubbles has little effect on bubble captured distribution under various casting speeds. When the gas flow rate is small (gas flow fraction of 4.1%), the number density of captured bubbles increases as the initial bubble size increases, and the effect of initial bubbles size on captured bubble number density is amplified when the casting speed decreases. The average captured bubble diameter is about 0.12–0.14 mm. Additionally, for all cases, the initial bubble size hardly affects the average size of captured bubbles.

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Tao, Sijia, Guangtai Shi, Yexiang Xiao, Zongliu Huang e Haigang Wen. "Effect of Operating Parameters on the Coalescence and Breakup of Bubbles in a Multiphase Pump Based on a CFD-PBM Coupled Model". Journal of Marine Science and Engineering 10, n. 11 (8 novembre 2022): 1693. http://dx.doi.org/10.3390/jmse10111693.

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When the multiphase pump is running, the internal medium often exists as bubble flow. In order to investigate the bubble occurrence characteristics in the pressurization unit of the multiphase pump more accurately, this paper couples computational fluid dynamics (CFD) with a population balance model (PBM) to investigate the bubble size distribution law of the multiphase pump under different operating conditions, taking into account the bubble coalescence and breakup. The research shows that the mean bubble size in the impeller domain gradually decreases from 1.7013 mm at the inlet to 0.6179 mm at the outlet along the axis direction; the average bubble diameter in the diffuser domain fluctuates around 0.60 mm. The bubbles in the impeller region gradually change from the trend of coalescence to the trend of breakup along the axial and radial directions, and the bubbles in the diffuser tend to be broken by the vortex entrainment. The bubble size development law is influenced by the inlet gas volume fraction (IGVF) and the rotational speed, showing a more obvious rule, where the gas phase aggregation phenomenon enhanced by the increase in IGVF promotes the trend of bubble coalescence and makes the bubble size gradually increase. The increased blade shearing effect with the increase in rotational speed promotes the trend of bubble breakup, which gradually reduces the size of the bubbles. In addition, increasing the bubble coalescence probability is a key factor leading to changes in bubble size; the bubble size development law is not very sensitive to changes in flow, and the bubble size is at its maximum under design conditions. The research results can accurately predict the performance change of the multiphase pump and provide technical guidance for its safe operation and optimal design.

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MOCHIZUKI, Warjito Osamu, e Masaru KIYA. "B218 Single Bubble Breakup". Journal of the Visualization Society of Japan 20, n. 2Supplement (2000): 229–32. http://dx.doi.org/10.3154/jvs.20.2supplement_229.

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Kálal, Zbyněk, Milan Jahoda e Ivan Fořt. "Modelling of the Bubble Size Distribution in an Aerated Stirred Tank: Theoretical and Numerical Comparison of Different Breakup Models". Chemical and Process Engineering 35, n. 3 (1 settembre 2014): 331–48. http://dx.doi.org/10.2478/cpe-2014-0025.

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Abstract The main topic of this study is the mathematical modelling of bubble size distributions in an aerated stirred tank using the population balance method. The air-water system consisted of a fully baffled vessel with a diameter of 0.29 m, which was equipped with a six-bladed Rushton turbine. The secondary phase was introduced through a ring sparger situated under the impeller. Calculations were performed with the CFD software CFX 14.5. The turbulent quantities were predicted using the standard k-ε turbulence model. Coalescence and breakup of bubbles were modelled using the MUSIG method with 24 bubble size groups. For the bubble size distribution modelling, the breakup model by Luo and Svendsen (1996) typically has been used in the past. However, this breakup model was thoroughly reviewed and its practical applicability was questioned. Therefore, three different breakup models by Martínez-Bazán et al. (1999a, b), Lehr et al. (2002) and Alopaeus et al. (2002) were implemented in the CFD solver and applied to the system. The resulting Sauter mean diameters and local bubble size distributions were compared with experimental data.

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MARTÍNEZ-BAZÁN, C., J. L. MONTAÑÉS e J. C. LASHERAS. "On the breakup of an air bubble injected into a fully developed turbulent flow. Part 2. Size PDF of the resulting daughter bubbles". Journal of Fluid Mechanics 401 (25 dicembre 1999): 183–207. http://dx.doi.org/10.1017/s0022112099006692.

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Based on energy principles, we propose a statistical model to describe the bubble size probability density function of the daughter bubbles resulting from the shattering of a mother bubble of size D0 immersed in a fully developed turbulent water flow. The model shows that the bubble size p.d.f. depends not only on D0, but also on the value of the dissipation rate of turbulent kinetic energy of the underlying turbulence of the water, ε. The phenomenological model is simple, yet it predicts detailed experimental measurements of the transient bubble size p.d.f.s performed over a range of bubble sizes and dissipation rates ε in a very consistent manner. The agreement between the model and the experiments is particularly good for low and moderate bubble turbulent Weber numbers, Wet = ρΔu2(D0)D0/σ where the assumption of the binary breakup is shown to be consistent with the experimental observations. At larger values of Wet, it was found that the most probable number of daughter bubbles increases and the assumption of tertiary breakup is shown to lead to a better fit of the experimental measurements.

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Branger, Annette B., e David M. Eckmann. "Accelerated Arteriolar Gas Embolism Reabsorption by an Exogenous Surfactant". Anesthesiology 96, n. 4 (1 aprile 2002): 971–79. http://dx.doi.org/10.1097/00000542-200204000-00027.

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Background Cerebrovascular gas embolism can cause profound neurologic dysfunction, and there are few treatments. The authors tested the hypothesis that an exogenous surfactant can be delivered into the bloodstream to alter the air-blood interfacial mechanics of an intravascular gas embolism and produce bubble conformations, which favor more rapid bubble absorption. Methods Microbubbles of air were injected into the rat cremaster microcirculation after intravascular administration of either saline (control, n = 5) or Dow Corning Antifoam 1510US (surfactant, n = 5). Embolism dimensions and dynamics were directly observed after entrapment using intravital microscopy. Results To achieve embolization, the surfactant group required twice as many injections as did controls (3.2 +/- 1.3 vs. 1.6 +/- 0.9; P < 0.05). There was no difference in the initial lodging configuration between groups. After bubble entrapment, there was significantly more local vasoconstriction in the surfactant group (24.2% average decrease in diameter) than in controls (3.4%; P < 0.05). This was accompanied by a 92.7% bubble elongation in the surfactant group versus 8.2% in controls (P < 0.05). Embolism shape change was coupled with surfactant-enhanced breakup into multiple smaller bubbles, which reabsorbed nearly 30% more rapidly than did parent bubbles in the control group (P < 0.05). Conclusions Intravascular exogenous surfactant did not affect initial bubble conformation but dramatically increased bubble breakup and rate of reabsorption. This was evidenced by both the large shape change after entrapment and enhancement of bubble breakup in the surfactant group. These dynamic surfactant-induced changes increase the total embolism surface area and markedly accelerate bubble reabsorption.

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Tian, Yushi, Pengzhao Shi, Lijun Xu, Shengtao Qiu e Rong Zhu. "Numerical Modeling of Transient Two-Phase Flow and the Coalescence and Breakup of Bubbles in a Continuous Casting Mold". Materials 15, n. 8 (12 aprile 2022): 2810. http://dx.doi.org/10.3390/ma15082810.

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The multiphase flow and spatial distribution of bubbles inside a continuous casting (CC) mold is a popular research issue due to its direct impact on the quality of the CC slab. The behavior of bubbles in the mold, and how they coalesce and break apart, have an important influence on the flow pattern and entrapment of bubbles. However, due to the limitations of experiments and measurement methods, it is impossible to directly observe the multiphase flow and bubble distribution during the CC process. Thus, a three-dimensional mathematical model which combined the large eddy simulation (LES) turbulent model, VOF multiphase model, and discrete phase model (DPM) was developed to study the transient two-phase flow and spatial distribution of bubbles in a continuous casting mold. The interaction between the liquid and bubbles and the coalescence, bounce, and breakup of bubbles were considered. The measured meniscus speed and bubble diameter were in good agreement with the measured results. The meniscus speed increased first and then decreased from the nozzle to the narrow face, with a maximum value of 0.07 m/s, and appeared at 1/4 the width of the mold. The current mathematical model successfully predicted the transient asymmetric two-phase flow and completely reproduced the coalescence, bounce, and breakup of bubbles in the mold. The breakup mainly occurred near the bottom of the submerged entry nozzle (SEN) due to the strong turbulent motion of the molten steel after hitting the bottom of the SEN. The average bubble diameter was about 0.6 mm near the nozzle and gradually decreased to 0.05 mm from the nozzle to the narrow face. The larger bubbles floated up near the SEN due to the effect of their greater buoyancy, while the small bubbles were distributed discretely in the entire mold with the action of the molten steel jet. Overall, the bubbles were distributed in a fan shape. The largest concentration of bubbles was in the lower part of the SEN and the upper edge of the SEN outlet.

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Mhawesh, Anas Malik, Basim O. Hasan e Hussein Znad. "Hydrodynamics of Stirred Tank and Bubble Breakup Behavior Induced by Rushton Turbine". Al-Nahrain Journal for Engineering Sciences 25, n. 1 (3 aprile 2022): 35–43. http://dx.doi.org/10.29194/njes.25010035.

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The hydrodynamics of stirred tanks and bubble breakup are crucial in gas-liquid flows, yet this system has not been well characterized for different operating conditions. In this work, the numerical method was used to investigate the hydrodynamics of six- flat blades impeller (Rushton turbine) and the results were employed to understand the bubble breakup behavior in the stirred tank. Simulation results of predicted flow pattern, power number, and the distribution of turbulence energy generated were performed with COMSOL Multiphysics. Numerical results showed good agreement with the experimental literature. The effect of rotational speed on bubble breakup behavior, such as breakage probability, the average number of daughter bubbles, and the breakage time was investigated using the high-speed imaging method. The main finding is that the breakage process occurs in the high energy area of high turbulence intensity, which is located within a distance equal to the blade width of a radius of (15-35 mm). The breakage probability (Bp) was found to be increased by 12.61 percent for a mother bubble of 4 mm at 340 rpm, with an average fragmentation of up to 22 fragments. Furthermore, the bubble breakage time was found to decrease with increasing impeller rotational speed, with an average value of 19.8 ms.

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Tanveer, Saleh, e Giovani L. Vasconcelos. "Time-evolving bubbles in two-dimensional Stokes flow". Journal of Fluid Mechanics 301 (25 ottobre 1995): 325–44. http://dx.doi.org/10.1017/s0022112095003910.

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A general class of exact solutions is presented for a time-evolving bubble in a two-dimensional slow viscous flow in the presence of surface tension. These solutions can describe a bubble in a linear shear flow as well as an expanding or contracting bubble in an otherwise quiescent flow. In the case of expanding bubbles, the solutions have a simple behaviour in the sense that for essentially arbitrary initial shapes the bubble its asymptote is expanding circle. Contracting bubbles, on the other hand, can develop narrow structures (‘near-cusps’) on the interface and may undergo ‘breakup’ before all the bubble fluid is completely removed. The mathematical structure underlying the existence of these exact solutions is also investigated.

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Kálal, Zbyněk, Milan Jahoda e Ivan Fořt. "CFD Prediction of Gas-Liquid Flow in an Aerated Stirred Vessel Using the Population Balance Model". Chemical and Process Engineering 35, n. 1 (1 marzo 2014): 55–73. http://dx.doi.org/10.2478/cpe-2014-0005.

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Abstract The main topic of this study is the experimental measurement and mathematical modelling of global gas hold-up and bubble size distribution in an aerated stirred vessel using the population balance method. The air-water system consisted of a mixing tank of diameter T = 0.29 m, which was equipped with a six-bladed Rushton turbine. Calculations were performed with CFD software CFX 14.5. Turbulent quantities were predicted using the standard k-ε turbulence model. Coalescence and breakup of bubbles were modelled using the homogeneous MUSIG method with 24 bubble size groups. To achieve a better prediction of the turbulent quantities, simulations were performed with much finer meshes than those that have been adopted so far for bubble size distribution modelling. Several different drag coefficient correlations were implemented in the solver, and their influence on the results was studied. Turbulent drag correction to reduce the bubble slip velocity proved to be essential to achieve agreement of the simulated gas distribution with experiments. To model the disintegration of bubbles, the widely adopted breakup model by Luo & Svendsen was used. However, its applicability was questioned.

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TOMITA, Y., T. SAITO e S. GANBARA. "Surface breakup and air bubble formation by drop impact in the irregular entrainment region". Journal of Fluid Mechanics 588 (24 settembre 2007): 131–52. http://dx.doi.org/10.1017/s0022112007007483.

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Drop impact on a water surface can be followed by underwater sounds originating not at the drop impact but when the entrained bubbles oscillate. Although the sound mechanism in the regular bubble entrainment region is well-known, there is less knowledge on the impact phenomena in the irregular bubble entrainment region where various situations can exist, such as many types of bubble formation or even no bubble generation under some conditions. In the present study, the aim is to clarify the dynamics of the water surface after the impact of a primary drop, mainly with diameter 5.2, 5.7 and 6.2mm, each of which is accompanied by a single satellite drop. Special attention was paid to the breakup behaviour of the water surface for Froude number Fr < 300. It was found that three underwater sounds were generated for a single drop impact, besides the sound due to impact itself. The first two were audible to the human ear, but the third one was almost inaudible. The first underwater sound resulted from the oscillation of a single air bubble formed as a result of the satellite drop impact on the bottom of the contracting cavity, and the second sound was due to the oscillation of air bubbles generated during the collapse of the water column. The formation of these air bubbles strongly depends on the Froude number, Weber number (or Bond number) and the aspect ratio of the drop at impact, although involving probability characteristics. Furthermore it is suggested that an air bubble entrapped in a water column plays an important role in increasing the probability of contact between the column surface and the curved free surface. A Japanese Suikinkutsu was introduced as an application of drop-impact-induced sounds. Using an open-type Suikinkutsu an additional experiment was carried out with larger drops with average diameters of 6.2, 7.2 and 7.8, mm.

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Yamashita, Fukuji. "Superficial Rate of Bubble Breakup in a Bubble Column." JOURNAL OF CHEMICAL ENGINEERING OF JAPAN 27, n. 5 (1994): 682–85. http://dx.doi.org/10.1252/jcej.27.682.

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Chen, Jingbo, Wen Du, Bo Kong, Zhiguo Wang, Jun Cao, Weiran Wang e Zhe Yan. "Numerical Investigation on the Symmetric Breakup of Bubble within a Heated Microfluidic Y-Junction". Symmetry 14, n. 8 (11 agosto 2022): 1661. http://dx.doi.org/10.3390/sym14081661.

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This study numerically investigated the symmetric breakup of bubble within a heated microfluidic Y-junction. The established three-dimensional model was verified with the results in the literature. Two crucial variables, Reynolds number (Re) and heat flux (q), were considered. Numerical results demonstrated that the bubble breakup was significantly affected by phase change under the heated environment. The “breakup with tunnel” and “breakup with obstruction” modes respectively occurred at the low and high q. The breakup rate in pinch-off stage was much larger than that in squeezing stage. As Re increased, the bubble broke more rapidly, and the critical neck thickness tended to decrease. The bubble annihilated the vortices existing in the divergence region and made the fluid flow more uniform. The heat transfer was enhanced more drastically as Re was decreased or q was increased, where the maximum Nusselt number under two-phase case was 6.53 times larger than single-phase case. The present study not only helps understanding of the physical mechanisms of bubble behaviors and heat transfer within microfluidic Y-junction, but also informs design of microfluidic devices.

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Shi, Fengyan, Gangfeng Ma e James T. Kirby. "NUMERICAL MODELING OF OPTICAL PROPERTIES INSIDE THE SURFZONE". Coastal Engineering Proceedings 1, n. 32 (29 gennaio 2011): 51. http://dx.doi.org/10.9753/icce.v32.currents.51.

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This paper provides a review of our recent developments in numerical models for predicting physical processes related to optical properties inside the surfzone. Model components in the developments include the bubble entrainment model, 2D and 3D multiphase two-fluid models for modeling quiescent phase of bubbles, turbulence models with influences of bubbles, bubble coalescence and breakup models used in the two-fluid models, and foam model for predicting foam patch generation and evolution inside the surfzone. The paper summarizes theories used in the model components and shows some numerical results from model tests.

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24

Ivashnyov, Oleg E., e Marina N. Ivashneva. "Bubble breakup simulation in nozzle flows". Journal of Fluid Mechanics 710 (23 agosto 2012): 72–101. http://dx.doi.org/10.1017/jfm.2012.352.

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AbstractExperiments on high-pressure vessel decompression have shown that vaporization occurs in ‘boiling shocks’ moving with a velocity of ${\ensuremath{\sim} }10~\mathrm{m} ~{\mathrm{s} }^{\ensuremath{-} 1} $. To explain this phenomenon, a model accounting for bubble breakup was suggested (Ivashnyov, Ivashneva & Smirnov, J. Fluid. Mech., vol. 413, 2000, pp. 149–180). It was shown that the explosive boiling was caused by chain bubble fragmentation, which led to a sharp increase in the interface area and instantaneous transformation of the mixture into an equilibrium state. In the present study, this model is used to simulate nozzle flows with no change in the free parameters chosen earlier for modelling a tube decompression. It is shown that an advanced model ensures the best correspondence to experiments for flashing flows in comparison with an equilibrium model and with a model of boiling at a constant number of centres. It is also shown that the formation of a boiling shock in a critical nozzle flow leads to autovibrations.

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25

Naveen, S., T. Sriram, S. Prithvi Raj e M. Venkatesan. "Hydrodynamic Study of Bubbles in a Bubble Column Reactor Part I – Image Processing". Applied Mechanics and Materials 813-814 (novembre 2015): 1018–22. http://dx.doi.org/10.4028/www.scientific.net/amm.813-814.1018.

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The study of bubble column reactors has its significance in applications such as multiphase reactors, aerators and in industrial waste-water treatment. Extensive works has been done in studying the hydrodynamics of a single gas bubble flowing through stationary liquid phase. The natural breakup of bubble during its motion has been studied in the past. In the Part I of the present work, hydrodynamics of an air bubble after its artificial splitting using a stainless steel mesh is experimentally studied using image processing and high speed photography. The significance of bubble splitting is that it increases the surface area of contact between stationery and moving fluid which in turn increases the rate of reaction desired during the process. The motion of the bubble is captured during its release and after splitting using High-Speed Camera. The velocity, area and diameter of the bubble before and after splitting are calculated by applying Image processing technique on the high speed photograph. The splitting of the bubble is found to vary with the superficial gaseous velocity. The splitting of bubbles into two bubbles of nearly equal size is considered and its hydrodynamic characteristics are studied.

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26

Liao, Yixiang, Roland Rzehak, Dirk Lucas e Eckhard Krepper. "Baseline closure model for dispersed bubbly flow: Bubble coalescence and breakup". Chemical Engineering Science 122 (gennaio 2015): 336–49. http://dx.doi.org/10.1016/j.ces.2014.09.042.

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27

HAMEED, M., M. SIEGEL, Y. N. YOUNG, J. LI, M. R. BOOTY e D. T. PAPAGEORGIOU. "Influence of insoluble surfactant on the deformation and breakup of a bubble or thread in a viscous fluid". Journal of Fluid Mechanics 594 (14 dicembre 2007): 307–40. http://dx.doi.org/10.1017/s0022112007009032.

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The influence of surfactant on the breakup of a prestretched bubble in a quiescent viscous surrounding is studied by a combination of direct numerical simulation and the solution of a long-wave asymptotic model. The direct numerical simulations describe the evolution toward breakup of an inviscid bubble, while the effects of small but non-zero interior viscosity are readily included in the long-wave model for a fluid thread in the Stokes flow limit.The direct numerical simulations use a specific but realizable and representative initial bubble shape to compare the evolution toward breakup of a clean or surfactant-free bubble and a bubble that is coated with insoluble surfactant. A distinguishing feature of the evolution in the presence of surfactant is the interruption of bubble breakup by formation of a slender quasi-steady thread of the interior fluid. This forms because the decrease in surface area causes a decrease in the surface tension and capillary pressure, until at a small but non-zero radius, equilibrium occurs between the capillary pressure and interior fluid pressure.The long-wave asymptotic model, for a thread with periodic boundary conditions, explains the principal mechanism of the slender thread's formation and confirms, for example, the relatively minor role played by the Marangoni stress. The large-time evolution of the slender thread and the precise location of its breakup are, however, influenced by effects such as the Marangoni stress and surface diffusion of surfactant.

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28

Elghobashi, Said. "Direct Numerical Simulation of Turbulent Flows Laden with Droplets or Bubbles". Annual Review of Fluid Mechanics 51, n. 1 (5 gennaio 2019): 217–44. http://dx.doi.org/10.1146/annurev-fluid-010518-040401.

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This review focuses on direct numerical simulations (DNS) of turbulent flows laden with droplets or bubbles. DNS of these flows are more challenging than those of flows laden with solid particles due to the surface deformation in the former. The numerical methods discussed are classified by whether the initial diameter of the bubble/droplet is smaller or larger than the Kolmogorov length scale and whether the instantaneous surface deformation is fully resolved or obtained via a phenomenological model. Also discussed are numerical methods that account for the breakup of a single droplet or bubble, as well as multiple droplets or bubbles in canonical turbulent flows.

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29

Gatapova, Elizaveta Ya, e Kyunney B. Gatapova. "Bubble dynamics in thin liquid films and breakup at drop impact". Soft Matter 16, n. 46 (2020): 10397–404. http://dx.doi.org/10.1039/d0sm01882a.

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A bubble layer forms in a thin liquid film at drop impact on a hot surface. Bubble coalescence and instability generated by a wave are the reason for irreversible bubble bursting, leading to film breakup at contact boiling.

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30

Guo, Jinglan, e Siyuan Wang. "Multiphase Flow Coupling Behavior of Bubbles Based on Computational Fluid Dynamics during AFP Process: The Behavior Characteristics of Bubbles during AFP Process". Advances in Materials Science and Engineering 2021 (31 luglio 2021): 1–12. http://dx.doi.org/10.1155/2021/3237713.

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To investigate the mechanism of the effect of process parameters on bubble flow behavior during automated fiber placement (AFP) and the relationship between the bubble and voids, mechanical properties of laminates, this paper analyzes the multiphase flow coupling behavior of the bubble and fiber formation using computational fluid dynamics (CFD) and finite element (FE) method under different AFP process parameters. The effects of AFP process parameters on bubble characteristics and fiber deformation are then discussed, respectively, including bubble displacement, maximum cross-sectional area, the lowest internal temperature of the bubble, bubble breakup, and maximum deformation of the fiber. Furthermore, the AFP and corresponding test experiments are performed to investigate the relationships between different bubble characteristics and void content, mechanical properties, mainly interlaminar shear strength (ILSS) and flexural strength (FS). The results show that the maximum cross-sectional area of bubbles is closely related to the AFP process parameters. The FS and ILSS are positively correlated with the maximum cross-sectional area. With the increase of bubble displacement and fiber maximum deformation, FS and ILSS are first increased and then decreased.

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31

FUJIWARA, Akiko, Kazuhiro WATANABE, Shu TAKAGI e Yoichiro MATSUMOTO. "Mechanism of Bubble Breakup in Micro-bubble Generator Using Venturi Tube". Proceedings of the JSME annual meeting 2004.2 (2004): 83–84. http://dx.doi.org/10.1299/jsmemecjo.2004.2.0_83.

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32

Song, Yuchen, Dezhong Wang, Junlian Yin, Jingjing Li e Kangbei Cai. "Experimental studies on bubble breakup mechanism in a venturi bubble generator". Annals of Nuclear Energy 130 (agosto 2019): 259–70. http://dx.doi.org/10.1016/j.anucene.2019.02.020.

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33

Atkinson, Bruce W., Graeme J. Jameson, Anh V. Nguyen, Geoffrey M. Evans e Piotr M. Machniewski. "Bubble Breakup and Coalescence in a Plunging Liquid Jet Bubble Column". Canadian Journal of Chemical Engineering 81, n. 3-4 (19 maggio 2008): 519–27. http://dx.doi.org/10.1002/cjce.5450810325.

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34

Wei, Yi kun, Yuehong Qian e Hui Xu. "Lattice Boltzmann Simulations of Single Bubble Deformation and Breakup in a Shear Flow". Journal of Computational Multiphase Flows 4, n. 1 (marzo 2012): 111–17. http://dx.doi.org/10.1260/1757-482x.4.1.111.

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Lattice Boltzmann method (LBM) is used to simulate the deformation and breakup of single bubble in a shear flow. Numerical simulations of single bubble deformation are qualitatively compared with experimental results in a shear flow. Respectively the rotation angle θ is quantitatively compared with experimental results according to different capillary numbers ( Ca), which shows numerical simulations are in agreement with the experimental results and theoretical results. Finally, the breakup process of single bubble in a shear flow is simulated straightforwardly.

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35

Brandner, P. A., A. D. Henderson, K. L. de Graaf e B. W. Pearce. "Bubble breakup in a turbulent shear layer". Journal of Physics: Conference Series 656 (3 dicembre 2015): 012015. http://dx.doi.org/10.1088/1742-6596/656/1/012015.

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36

Liu, Xiangdong, Chengbin Zhang, Wei Yu, Zilong Deng e Yongping Chen. "Bubble breakup in a microfluidic T-junction". Science Bulletin 61, n. 10 (maggio 2016): 811–24. http://dx.doi.org/10.1007/s11434-016-1067-1.

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37

Tanveer, Saleh, e Giovani L. Vasconcelos. "Bubble Breakup in Two-Dimensional Stokes Flow". Physical Review Letters 73, n. 21 (21 novembre 1994): 2845–48. http://dx.doi.org/10.1103/physrevlett.73.2845.

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38

YU, WEI, LUYAO XU, SHUNJIA CHEN e FENG YAO. "NUMERICAL STUDY ON FLOW BOILING IN A TREE-SHAPED MICROCHANNEL". Fractals 27, n. 07 (novembre 2019): 1950111. http://dx.doi.org/10.1142/s0218348x19501111.

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A two-dimensional model is developed to numerically study the water flow boiling through a tree-shaped microchannel by VOF method. In this work, the bubble dynamics and flow patterns along the channel are examined. Additionally, the pressure drop, heat transfer performance and the effects of mass flow rate and heat flux on the heat transfer coefficient are analyzed and discussed. The numerical results indicate that, there are three main bubble dynamic behaviors at the wall, namely coalesce-lift-off, coalesce-slide and coalesce-reattachment. At the bifurcation in high branching level, the slug bubbles may coalesce or breakup. The flow patterns of bubbly, bubbly-slug flows occur at low branching level and slug flow occurs at high branching level. The passage of bubbles causes the increasing of fluid temperature and local pressure. Additionally, the pressure drop decreases with the branching level. The flow pattern and channel confinement effect play a vital role in heat transfer performance. The nucleate boiling dominant heat transfer is observed at low branching level, the heat transfer performance is enhanced with increasing branching level from [Formula: see text] to 2. While, at high branching level, the heat transfer performance becomes weaker due to the suppression of nucleate boiling. Moreover, the heat transfer coefficient increases with the mass flow rate and heat flux.

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39

Colli, A. N., e J. M. Bisang. "Current and Potential Distribution in Two-Phase (Gas Evolving) Electrochemical Reactors by the Finite Volume Method". Journal of The Electrochemical Society 169, n. 3 (1 marzo 2022): 034524. http://dx.doi.org/10.1149/1945-7111/ac5d90.

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A solver was developed and implemented in the OpenFOAM framework in order to predict the current distribution in gas evolving electrochemical reactors. The solver takes into account both liquid and gas flows under turbulent conditions and assumes a bubble population balance with a range of bubble sizes. The possibility of coalescence and breakup of bubbles is also considered. The comparison between experimental results of gas fraction and current distribution, from this research and from previous ones, demonstrates that the solver is able to predict the behavior of this kind of electrochemical systems. The model presented is supplied as a free source code.

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40

Karn, Ashish, Siyao Shao, Roger E. A. Arndt e Jiarong Hong. "Bubble coalescence and breakup in turbulent bubbly wake of a ventilated hydrofoil". Experimental Thermal and Fluid Science 70 (gennaio 2016): 397–407. http://dx.doi.org/10.1016/j.expthermflusci.2015.10.003.

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41

RISSO, FRÉDÉRIC, e JEAN FABRE. "Oscillations and breakup of a bubble immersed in a turbulent field". Journal of Fluid Mechanics 372 (10 ottobre 1998): 323–55. http://dx.doi.org/10.1017/s0022112098002705.

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This work is an experimental study of the deformation and breakup of a bubble in a turbulent flow. A special facility was designed to obtain intense turbulence without significant mean flow. The experiments were performed under microgravity conditions to ensure that turbulence was the only cause of bubble deformation. A scalar parameter, characteristic of this deformation, was obtained by video processing of high-speed movies. The time evolution and spectral representation of this scalar parameter showed the dynamical characteristics of bubble deformation. The signatures of the eigenmodes of oscillation predicted by the linear theory were clearly observed and the predominance of the second mode was proved. In addition, numerical simulations were performed by computing the response of a damped oscillator to the measured turbulence forcing. Simulations and experiments were found to be in good agreement both qualitatively, from visual inspections of the signals, and quantitatively, from a statistical analysis. The role of bubble dynamics in the deformation process has been clarified. On the one hand, the time response of the bubble controls the maximum amount of energy which can be extracted from each turbulent eddy. On the other hand, the viscous damping limits the energy that the bubble can accumulate during its fluctuating deformation. Moreover, two breakup mechanisms have been identified. One mechanism results from the balance between two opposing dominant forces, and the other from a resonance oscillation. A new parameter, the mean efficiency coefficient, has been introduced to take into account the various aspects of bubble dynamics. Used together with the Weber number, this parameter allows the prediction of the occurrence of these two mechanisms. Finally, the influence of the residence time of the bubble on the statistics of the deformation has been analysed and quantified.

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42

Piccone, Ashley. "Bubbles generate their own kind of turbulence". Scilight 2022, n. 36 (2 settembre 2022): 361103. http://dx.doi.org/10.1063/10.0013892.

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Simulations of bubble-induced turbulence, while fundamentally different from those of classical homogeneous isotropic turbulence, do not need to account for bubble shape, topology, or breakup and coalescence.

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43

Gadallah, Aly H., e Kamran Siddiqui. "Bubble breakup in co-current upward flowing liquid using honeycomb monolith breaker". Chemical Engineering Science 131 (luglio 2015): 22–40. http://dx.doi.org/10.1016/j.ces.2015.03.028.

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44

Politano, M. S., P. M. Carrica e J. L. Baliño. "About bubble breakup models to predict bubble size distributions in homogeneous flows". Chemical Engineering Communications 190, n. 3 (marzo 2003): 299–321. http://dx.doi.org/10.1080/00986440302135.

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45

Chen, P., M. P. Dudukovi? e J. Sanyal. "Three-dimensional simulation of bubble column flows with bubble coalescence and breakup". AIChE Journal 51, n. 3 (2005): 696–712. http://dx.doi.org/10.1002/aic.10381.

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46

ESMAEELI, ASGHAR, e GRÉTAR TRYGGVASON. "Direct numerical simulations of bubbly flows. Part 1. Low Reynolds number arrays". Journal of Fluid Mechanics 377 (25 dicembre 1998): 313–45. http://dx.doi.org/10.1017/s0022112098003176.

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Direct numerical simulations of the motion of two- and three-dimensional buoyant bubbles in periodic domains are presented. The full Navier–Stokes equations are solved by a finite difference/front tracking method that allows a fully deformable interface between the bubbles and the ambient fluid and the inclusion of surface tension. The governing parameters are selected such that the average rise Reynolds number is O(1) and deformations of the bubbles are small. The rise velocity of a regular array of three-dimensional bubbles at different volume fractions agrees relatively well with the prediction of Sangani (1988) for Stokes flow. A regular array of two- and three-dimensional bubbles, however, is an unstable configuration and the breakup, and the subsequent bubble–bubble interactions take place by ‘drafting, kissing, and tumbling’. A comparison between a finite Reynolds number two-dimensional simulation with sixteen bubbles and a Stokes flow simulation shows that the finite Reynolds number array breaks up much faster. It is found that a freely evolving array of two-dimensional bubbles rises faster than a regular array and simulations with different numbers of two-dimensional bubbles (1–49) show that the rise velocity increases slowly with the size of the system. Computations of four and eight three-dimensional bubbles per period also show a slight increase in the average rise velocity compared to a regular array. The difference between two- and three-dimensional bubbles is discussed.

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47

Yamoah, S., Castro K. Owusu-Manu e Edward H. K. Akaho. "nNumerical investigation of bubble interaction mechanisms in gas-liquid bubbly flows: Harmonisation of bubble breakup and coalescence effects". International Journal of Multiphase Flow 144 (novembre 2021): 103781. http://dx.doi.org/10.1016/j.ijmultiphaseflow.2021.103781.

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48

Yuan, Fangyang, Zhengwei Cui e Jianzhong Lin. "Experimental and Numerical Study on Flow Resistance and Bubble Transport in a Helical Static Mixer". Energies 13, n. 5 (6 marzo 2020): 1228. http://dx.doi.org/10.3390/en13051228.

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Flow resistance and bubble transport in a helical static mixer were studied experimentally and numerically. The inline mixer increases the volume fraction of gas in liquids by breaking bubbles into smaller sizes with a micrometer size in the flow experiments. The gas–liquid flow was simulated by a combination of computational fluid dynamics and Taylor expansion methods of moments. The friction factor of the helical static mixer is much smaller than that of the Kenics static mixers. The pressure drop increases with the Reynolds number, and the increment is larger when the Reynolds number is higher. The equidistant pressure drop increases with the argument of Reynolds number, and increases when the pitch decreases from upstream to downstream. The energy expenditure increases significantly when the variable-pitch coefficient is too small. The bubble geometric mean diameter decreases and the geometric standard deviation increases when the gas–liquid fluid flows through the mixer. The variable pitch structure enhances the bubble breakup effectively. The change of the bubble size decreases with the argument of the Reynolds number. The effect of the mixer has a limitation on breaking the bubbles.

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49

Carneiro, Luiz Eduardo Marinho, Geniffer Stefany de Oliveira Martins, Atila Pantaleão Silva Freire, Cristian Mauricio Potosi Rosero, Isabela do Nascimento Pena e Isabela Garcia Do Carmo. "BUBBLE BREAKUP IN CENTRIFUGAL PUMPS: A PHENOMENOLOGICAL APPROACH". Rio Oil and Gas Expo and Conference 22, n. 2022 (26 settembre 2022): 117–18. http://dx.doi.org/10.48072/2525-7579.rog.2022.117.

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50

Wu, Zhao-Wei, Hui Zhao, Wei-Feng Li, Jian-Liang Xu, Sheng Wang e Hai-Feng Liu. "Effects of inner bubble on liquid jet breakup". Physics of Fluids 31, n. 3 (marzo 2019): 034107. http://dx.doi.org/10.1063/1.5074105.

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