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1
Zhang, Peng-li, and Shu-yu Lin. "Study on Bubble Cavitation in Liquids for Bubbles Arranged in a Columnar Bubble Group." Applied Sciences 9, no. 24 (December 4, 2019): 5292. http://dx.doi.org/10.3390/app9245292.
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In liquids, bubbles usually exist in the form of bubble groups. Due to their interaction with other bubbles, the resonance frequency of bubbles decreases. In this paper, the resonance frequency of bubbles in a columnar bubble group is obtained by linear simplification of the bubbles’ dynamic equation. The correction coefficient between the resonance frequency of the bubbles in the columnar bubble group and the Minnaert frequency of a single bubble is given. The results show that the resonance frequency of bubbles in the bubble group is affected by many parameters such as the initial radius of bubbles, the number of bubbles in the bubble group, and the distance between bubbles. The initial radius of the bubbles and the distance between bubbles are found to have more significant influence on the resonance frequency of the bubbles. When the distance between bubbles increases to 20 times the bubbles’ initial radius, the coupling effect between bubbles can be ignored, and after that the bubbles’ resonance frequency in the bubble group tends to the resonance frequency of a single bubble’s resonance frequency. Fluent software is used to simulate the bubble growth, shrinkage, and collapse of five and seven bubbles under an ultrasonic field. The simulation results show that when the bubble breaks, the two bubbles at the outer field first begin to break and form a micro-jet along the axis line of the bubbles. Our methods and conclusions will provide a reference for further simulations and indicate the significance of the prevention or utilization of cavitation.
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Zhao, Zhi Xin, Jian Hua Niu, Lan Huang, and Huan Ran Wang. "Simulation of the Motion of Two Bubbles in Aluminum Foams Produced Process by Using Level Set Method." Applied Mechanics and Materials 757 (April 2015): 13–17. http://dx.doi.org/10.4028/www.scientific.net/amm.757.13.
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In this paper, the three-dimensional motion of two bubbles in melt Aluminum was simulated by using level set method. Through changing the positions and sizes of two bubbles, the influence of bubbles wake flow and their interaction are considered. Our numerical simulations demonstrate the bubbles characteristic behavior such as distortion, attraction, and repulsion. The velocity field around the bubbles reveals the interaction between the wakes of two bubbles in fluid dynamics. For the two bubbles placed horizontally or vertically, it is found that the coalescence of bubbles may happen when 50% of the below bubble’s projected area enters the wake zone of the upper bubble.
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Bettaieb, Afef, Nabila Filali, Taoufik Filali, and Habib Ben Aissia. "An efficient algorithm for overlapping bubbles segmentation." Computer Optics 44, no. 3 (June 2020): 363–74. http://dx.doi.org/10.18287/2412-6179-co-605.
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Image processing is an effective method for characterizing various two-phase gas/liquid flow systems. However, bubbly flows at a high void fraction impose significant challenges such as diverse bubble shapes and sizes, large overlapping bubble clusters occurrence, as well as out-of-focus bubbles. This study describes an efficient multi-level image processing algorithm for highly overlapping bubbles recognition. The proposed approach performs mainly in three steps: overlapping bubbles classification, contour segmentation and arcs grouping for bubble reconstruction. In the first step, we classify bubbles in the image into a solitary bubble and overlapping bubbles. The purpose of the second step is overlapping bubbles segmentation. This step is performed in two subsequent steps: at first, we classify bubble clusters into touching and communicating bubbles. Then, the boundaries of communicating bubbles are split into segments based on concave point extraction. The last step in our algorithm addresses segments grouping to merge all contour segments that belong to the same bubble and circle/ellipse fitting to reconstruct the missing part of each bubble. An application of the proposed technique to computer generated and high-speed real air bubble images is used to assess our algorithm. The developed method provides an accurate and computationally effective way for overlapping bubbles segmentation. The accuracy rate of well segmented bubbles we achieved is greater than 90 % in all cases. Moreover, a computation time equal to 12 seconds for a typical image (1 Mpx, 150 overlapping bubbles) is reached.
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Cai, Runze, Jiao Sun, and Wenyi Chen. "Experimental Investigation on the Dynamic Characteristics of Bubble-in-Chain Near a Vertical Wall." Applied Sciences 14, no. 14 (July 12, 2024): 6076. http://dx.doi.org/10.3390/app14146076.
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The motion of near-wall bubble-in-chain, which is a crucial aspect of the study of near-wall bubble flows, involves not only the wall effect but also the interactions between bubbles. However, there have been few studies on this topic. In this study, we investigated the motion of near-wall bubble-in-chain using a dual-camera orthogonal shadow method and tracked bubbles using image processing and feature matching techniques. Considering both the wall effect and bubble generation frequency, we discussed the statistical characteristics, motion modes, dynamic characteristics, and energy evolution of bubbles. The results demonstrate that an increase in bubble generation frequency leads to a greater deviation of bubble trajectories from the wall and an increase in trajectory amplitude while weakening the suppression of bubble speed by the wall. Furthermore, changes in both bubble equivalent diameter and drag coefficient reveal how bubble generation frequency affects their shape stability during motion as well as regulation by the wall effect. The drag coefficient decreases with increasing Reynolds number for bubbles; however, an increase in bubble generation frequency broadens its distribution range. Additionally, it is evident that the wall effect significantly impacts drag characteristics for bubbles: uncollided bubbles experience increased drag coefficients with greater distance from the wall while collided bubbles exhibit decreased drag coefficients. In cases of high generation frequency, the conversion of kinetic energy to surface energy during bubble collisions, especially the enhancement of the peak of surface energy, indicates an increase in the bubble’s energy storage capacity and energy conversion efficiency. The findings not only enhance comprehension of behavior exhibited by near-wall bubbles but also offer a novel perspective for regulating near-wall bubble flows in industrial applications.
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Noguchi, Ryo, Ayako Yano, and Kenji Amagai. "Behaviors of Bubbles Trapped in Film Coating during Spray Gun Coating and Its Influences on Coating Defects." Coatings 13, no. 11 (October 30, 2023): 1860. http://dx.doi.org/10.3390/coatings13111860.
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In this paper, we investigated the behaviors of bubbles entrained in a film coating during spray coating. Air bubbles that remain in a film coating after diluent evaporation cause coating defects called bubbling defects, including fish-eye and crater defects. In this study, the visualization of a film coating revealed that smaller bubbles in the film shrank slowly and disappeared, while larger bubbles remained. These remaining bubbles grew during the heating process for the drying of the film coating. The shrinking phenomenon was explained using bubble dynamics based on the Young–Laplace equation of a bubble’s inner pressure and Henry’s law for bubble gas dissolution into the film coating. This shrinking model is often used in studies on microbubble dynamics. The results suggested the importance of avoiding the entrainment of large bubbles during the spraying process and enhancing the release of air bubbles from the film coating’s surface through the appropriate usage of defoaming agents.
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Meernik, P. R., and M. C. Yuen. "An Optical Method for Determining Bubble Size Distributions—Part I:Theory." Journal of Fluids Engineering 110, no. 3 (September 1, 1988): 325–31. http://dx.doi.org/10.1115/1.3243551.
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A new optical technique is developed to determine the size distribution of bubbles in a two-phase flow. Implementation involves passing a narrow beam of light through the bubbly flow and monitoring the transmitted light intensity. The basic units of data are the rate at which each bubble blocks off the beam and the duration of blockage. Adding the hypothesis that the distance of closest approach between a bubble’s center and the beam axis is randomly distributed, a statistical analysis yields the bubble size distribution.
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Han, Rui, Jiayi Chen, and Taikun Guo. "A Modified Phase-Transition Model for Multi-Oscillations of Spark-Generated Bubbles." Inventions 8, no. 5 (October 23, 2023): 131. http://dx.doi.org/10.3390/inventions8050131.
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The main composition within a spark-generated bubble primarily consists of vapor, accompanied by a minor presence of noncondensable gases. The phase transition exerts a substantial influence on bubble dynamics throughout various stages, a facet that has been frequently overlooked in prior research. In this study, we introduce a modified theoretical model aimed at accurately predicting the multiple oscillations of spark-generated bubbles. Leveraging the Plesset equation, which integrates second-order corrections for compressibility and non-equilibrium evaporation, we further incorporate the thermal boundary layer approximation for bubbles, as proposed by Zhong et al. We employ an adjusted phase transition duration tailored to the unique characteristics of spark-generated bubbles. Furthermore, we meticulously ascertain initial conditions through repeated gas content measurements within the bubble. Our proposed theoretical model undergoes rigorous validation through quantitative comparisons with experimental data, yielding commendable agreement in modeling the dynamic behavior of bubbles across multiple cycles. Remarkably, we uncover that the condensation rate significantly governs the behavior of spark bubbles during their initial two cycles. Finally, we investigate the dependence of spark-generated bubble dynamics on the phase transition and the presence of air. Air content exhibits a minimal impact on bubble motion prior to the initial bubble collapse, but plays a role in the bubble’s rebound thereafter.
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Zhou, Ge. "THE SPIRIT OF CAPITALISM AND RATIONAL BUBBLES." Macroeconomic Dynamics 20, no. 6 (June 30, 2015): 1432–57. http://dx.doi.org/10.1017/s1365100514000972.
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This study provides an infinite-horizon model of rational bubbles in a production economy. A bubble can arise when the pursuit of status is modeled explicitly, capturing the notion of “the spirit of capitalism.” Using a parameterized model, I demonstrate the specific conditions for the existence of bubbles and their implications. Bubbles crowd out investment, stimulate consumption, and slow economic growth. I also discuss a stochastic bubble that bursts with an exogenous probability. I show that there could be multiple stochastic bubbly equilibria. Moreover, I suggest that taxing wealth properly can eliminate bubbles and achieve the social optimum.
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Prakash, Vivek N., J. Martínez Mercado, Leen van Wijngaarden, E. Mancilla, Y. Tagawa, Detlef Lohse, and Chao Sun. "Energy spectra in turbulent bubbly flows." Journal of Fluid Mechanics 791 (February 15, 2016): 174–90. http://dx.doi.org/10.1017/jfm.2016.49.
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We conduct experiments in a turbulent bubbly flow to study the nature of the transition between the classical $-5/3$ energy spectrum scaling for a single-phase turbulent flow and the $-3$ scaling for a swarm of bubbles rising in a quiescent liquid and of bubble-dominated turbulence. The bubblance parameter (Lance & Bataille J. Fluid Mech., vol. 222, 1991, pp. 95–118; Rensen et al., J. Fluid Mech., vol. 538, 2005, pp. 153–187), which measures the ratio of the bubble-induced kinetic energy to the kinetic energy induced by the turbulent liquid fluctuations before bubble injection, is often used to characterise bubbly flow. We vary the bubblance parameter from $b=\infty$ (pseudoturbulence) to $b=0$ (single-phase flow) over 2–3 orders of magnitude (0.01–5) to study its effect on the turbulent energy spectrum and fluctuations in liquid velocity. The probability density functions (PDFs) of the fluctuations in liquid velocity show deviations from the Gaussian profile for $b>0$, i.e. when bubbles are present in the system. The PDFs are asymmetric with higher probability in the positive tails. The energy spectra are found to follow the $-3$ scaling at length scales smaller than the size of the bubbles for bubbly flows. This $-3$ spectrum scaling holds not only in the well-established case of pseudoturbulence, but surprisingly in all cases where bubbles are present in the system ($b>0$). Therefore, it is a generic feature of turbulent bubbly flows, and the bubblance parameter is probably not a suitable parameter to characterise the energy spectrum in bubbly turbulent flows. The physical reason is that the energy input by the bubbles passes over only to higher wavenumbers, and the energy production due to the bubbles can be directly balanced by the viscous dissipation in the bubble wakes as suggested by Lance & Bataille (1991). In addition, we provide an alternative explanation by balancing the energy production of the bubbles with viscous dissipation in the Fourier space.
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Loisy, Aurore, Aurore Naso, and Peter D. M. Spelt. "Buoyancy-driven bubbly flows: ordered and free rise at small and intermediate volume fraction." Journal of Fluid Mechanics 816 (March 3, 2017): 94–141. http://dx.doi.org/10.1017/jfm.2017.64.
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Various expressions have been proposed previously for the rise velocity of gas bubbles in homogeneous steady bubbly flows, generally a monotonically decreasing function of the bubble volume fraction. For suspensions of freely moving bubbles, some of these are of the form expected for ordered arrays of bubbles, and vice versa, as they do not reduce to the behaviour expected theoretically in the dilute limit. The microstructure of weakly inhomogeneous bubbly flows not being known generally, the effect of microstructure is an important consideration. We revisit this problem here for bubbly flows at small to moderate Reynolds number values for deformable bubbles, using direct numerical simulation and analysis. For ordered suspensions, the rise velocity is demonstrated not to be monotonically decreasing with volume fraction due to cooperative wake interactions. The fore-and-aft asymmetry of an isolated ellipsoidal bubble is reversed upon increasing the volume fraction, and the bubble aspect ratio approaches unity. Recent work on rising bubble pairs is used to explain most of these results; the present work therefore forms a platform of extending the former to suspensions of many bubbles. We adopt this new strategy also to support the existence of the oblique rise of ordered suspensions, the possibility of which is also demonstrated analytically. Finally, we demonstrate that most of the trends observed in ordered systems also appear in freely evolving suspensions. These similarities are supported by prior experimental measurements and attributed to the fact that free bubbles keep the same neighbours for extended periods of time.
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Martin, Alberto, and Jaume Ventura. "Economic Growth with Bubbles." American Economic Review 102, no. 6 (October 1, 2012): 3033–58. http://dx.doi.org/10.1257/aer.102.6.3033.
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We develop a stylized model of economic growth with bubbles in which changes in investor sentiment lead to the appearance and collapse of macroeconomic bubbles or pyramid schemes. These bubbles mitigate the effects of financial frictions. During bubbly episodes, unproductive investors demand bubbles while productive investors supply them. These transfers of resources improve economic efficiency thereby expanding consumption, the capital stock and output. When bubbly episodes end, there is a fall in consumption, the capital stock and output. We argue that the stochastic equilibria of the model provide a natural way of introducing bubble shocks into business cycle models. (JEL E22, E23, E32, E44, O41)
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Battistella, Alessandro, Sander Aelen, Ivo Roghair, and Martin van Sint Annaland. "Euler–Lagrange Modeling of Bubbles Formation in Supersaturated Water." ChemEngineering 2, no. 3 (August 24, 2018): 39. http://dx.doi.org/10.3390/chemengineering2030039.
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Phase transition, and more specifically bubble formation, plays an important role in many industrial applications, where bubbles are formed as a consequence of reaction such as in electrolytic processes or fermentation. Predictive tools, such as numerical models, are thus required to study, design or optimize these processes. This paper aims at providing a meso-scale modelling description of gas–liquid bubbly flows including heterogeneous bubble nucleation using a Discrete Bubble Model (DBM), which tracks each bubble individually and which has been extended to include phase transition. The model is able to initialize gas pockets (as spherical bubbles) representing randomly generated conical nucleation sites, which can host, grow and detach a bubble. To demonstrate its capabilities, the model was used to study the formation of bubbles on a surface as a result of supersaturation. A higher supersaturation results in a faster rate of nucleation, which means more bubbles in the column. A clear depletion effect could be observed during the initial growth of the bubbles, due to insufficient mixing.
13
Lu, Jiacai, and Gretar Tryggvason. "Dynamics of nearly spherical bubbles in a turbulent channel upflow." Journal of Fluid Mechanics 732 (August 30, 2013): 166–89. http://dx.doi.org/10.1017/jfm.2013.397.
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AbstractThe dynamics of bubbles in upflow, in a vertical channel, is examined using direct numerical simulations (DNS), where both the flow and the bubbles are fully resolved. Two cases are simulated. In one case all the bubbles are of the same size and sufficiently small so they remain nearly spherical. In the second case, some of the small bubbles are coalesced into one large bubble. In both cases lift forces drive small bubbles to the wall, removing bubbles from the channel interior until the two-phase mixture is in hydrostatic equilibrium, and forming a bubble-rich wall layer. The same evolution has been seen in earlier DNS of bubbly upflows, but here the friction Reynolds number is higher (${\mathit{Re}}^{+ } = 250$). In addition to showing that the overall structure persists at higher Reynolds numbers, we show that the bubbles in the wall layer form clusters. The mechanism responsible for the clustering is explained and how bubbles move into and out of the wall layer is examined. The dynamics of the bubbles in the channel core is also compared with results obtained in fully periodic domains and found to be similar. The presence of the large bubble disrupts the wall layer slightly, but does not change the overall picture much, for the parameters examined here.
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Wang, HanBin, Yang Xu, and Jinjun Wang. "Experimental Study On Bubble Pairs And Induced Flow Fields Using Tomographic Particle Image Velocimetry." Proceedings of the International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics 21 (July 8, 2024): 1–10. http://dx.doi.org/10.55037/lxlaser.21st.147.
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Gas-liquid two-phase flows, such as bubbly flows, are widely used across various engineering and military applications due to their distinctive fluid dynamics. This study utilizes advanced imaging techniques, including shadowgraphy and laser-induced fluorescence tomographic particle image velocimetry (LIF-TPIV), to provide a quantitative analysis of bubble motions and the resulting flow fields. We systematically investigate the effects of orifice distances (s) set at 10, 15, 20, and 25 mm to assess the impact of spacing on bubble behavior and interactions. Our findings indicate that at orifice distances of 20 mm or less, the proximity of bubbles facilitates interactions, promoting dynamic bubble behaviors. In contrast, at distances greater than 25 mm, interactions become markedly weaker, leading to increased separation between bubbles during their free oscillation stages. This weak interaction directly influences the characteristics of bubble-induced flow fields. As orifice spacing increases, there is a noticeable decrease in the velocity of the flow field between bubbles, particularly noticeable at spacings of 20 mm and above. At these larger spacings, a low-velocity zone develops between the bubbles at higher heights, which, according to Bernoulli's principle, corresponds to a high-pressure area. This high pressure contributes to a reduction in bubble volume with increasing orifice spacing. Furthermore, the intensity of wake vortices between two bubbles is observed to be highest at the smallest spacing of 10 mm, closely resembling the flow structure characteristic of a single rising bubble. For spacings of 15 and 20 mm, the induced flow fields of the bubbles continue to interact significantly. However, at a spacing of 25 mm, the flow fields appear to function independently, suggesting a threshold beyond which bubble interactions stop to significantly affect their surrounding fluid environments. These findings are helpful for comprehending the two-phase flow dynamics, particularly in multi-orifices bubbly flow.
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Chen, Yong, Tao Wu, and Jian-Ping Lin. "Numerical Study on the Influence of Bubble Defection on the Bond Strength of Externally Bonded Fiber-Reinforced Polymer-to-Concrete Joints." Buildings 13, no. 10 (September 29, 2023): 2479. http://dx.doi.org/10.3390/buildings13102479.
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The influences of bubble defects on the bond strengths of externally bonded fiber-reinforced polymer (EB-FRP) concrete joints were investigated using numerical method in this research. Studies of the influences of increasing bubble defect areas on interfacial bonding performance were first conducted. It was observed that the influence of a bubble deficiency located in the middle of the bond region is not significant when the size of the bubble area is less than 2.5% of the effective bond area. Then, further investigation was conducted on the influences of the distances between the bubble and the loaded end, as well as the distance between the bubble and the side of the FRP, the ratio of the bubble’s width to the width of the FRP, the number of bubbles with a fixed total area and the distribution of multiple bubbles. It was found that the distances of the bubble to the loaded end and different numbers of bubbles distributed within a fixed area do not significantly affect the bond strength. When the bubble is positioned closer to the side of the FRP, a decrease in load capacity tends to occur earlier, and the amount of decrease also slightly increases. The bond capacity can be influenced by the shapes of the bubbles, and as the bubble width in the lateral direction increases while keeping the bubble areas constant, the load capacity decreases.
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Wang, Yi-Chun. "Effects of Nuclei Size Distribution on the Dynamics of a Spherical Cloud of Cavitation Bubbles." Journal of Fluids Engineering 121, no. 4 (December 1, 1999): 881–86. http://dx.doi.org/10.1115/1.2823550.
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The nonlinear dynamics of a spherical bubble cloud with nuclei size distribution are studied numerically. The spectrum of nuclei is assumed uniform initially. The simulations employ a nonlinear continuum bubbly mixture model with consideration of the presence of bubbles of different sizes. This model is then coupled with the Rayleigh-Plesset equation for the dynamics of bubbles. A numerical method based on the integral representation of the mixture continuity and momentum equations in the Lagrangian coordinates is developed to solve this set of integro-differential equations. Computational results show that the nuclei size distribution has significant effects on the cloud dynamics in comparison to the results for a single bubble size. One important effect is that the bubble collapse is always initiated near the surface of the cloud, even if the cloud has a very small initial void fraction. This effect has an important consequence, namely that the geometric focusing of the bubbly shock wave is always a part of the nonlinear dynamics associated with the collapse of a spherical cloud with nuclei size distribution. The strength of the shock and the oscillation structure behind the shock front are suppressed due to the effects of multiple bubble sizes. Far-field acoustic pressures radiated by two bubble clouds, one of equal-size bubbles and the other with bubble size distribution, are also compared. It is found that the cloud containing bubbles of different sizes emits a larger noise than the cloud of identical bubbles. Explanations for this effect are also presented.
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Reeder, D. Benjamin, John E. Joseph, Thomas A. Rago, Jeremy M. Bullard, David Honegger, and Merrick C. Haller. "Acoustic spectrometry of bubbles in an estuarine front: Sound speed dispersion, void fraction, and bubble density." Journal of the Acoustical Society of America 151, no. 4 (April 2022): 2429–43. http://dx.doi.org/10.1121/10.0009923.
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Estuaries constitute a unique waveguide for acoustic propagation. The spatiotemporally varying three-dimensional front between the seawater and the outflowing freshwater during both flood and ebb constitutes an interfacial sound speed gradient capable of supporting significant vertical and horizontal acoustic refraction. The collision of these two water masses often produces breaking waves, injecting air bubbles into the water column; the negative vertical velocities of the denser saltwater often subduct bubbles to the bottom of these shallow waveguides, filling the water column with a bubbly mixture possessing a significantly lower effective sound speed. A field experiment was carried out in the mouth of Mobile Bay, Alabama in June 2021 to characterize estuarine bubble clouds in terms of their depth-dependent plume structure, frequency-dependent sound speed and attenuation, bubble size distribution, bubble number density, and void fraction. Results demonstrate that sound speed in the bubbly liquid consistently falls below the intrinsic sound speed of bubble-free water; specifically, the bubbly liquid 1.3 m below the surface in a front in this environment possesses effective sound speeds, void fractions, and bubble number densities of approximately 750 m/s, 0.001%, and 2 × 106 bubbles/m3, respectively.
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Van Liew, Hugh D., and Soumya Raychaudhuri. "Stabilized bubbles in the body: pressure-radius relationships and the limits to stabilization." Journal of Applied Physiology 82, no. 6 (June 1, 1997): 2045–53. http://dx.doi.org/10.1152/jappl.1997.82.6.2045.
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Van Liew, Hugh D., and Soumya Raychaudhuri. Stabilized bubbles in the body: pressure-radius relationships and the limits to stabilization. J. Appl. Physiol.82(6): 2045–2053, 1997.—We previously outlined the fundamental principles that govern behavior of stabilized bubbles, such as the microbubbles being put forward as ultrasound contrast agents. Our present goals are to develop the idea that there are limits to the stabilization and to provide a conceptual framework for comparison of bubbles stabilized by different mechanisms. Gases diffuse in or out of stabilized bubbles in a limited and reversible manner in response to changes in the environment, but strong growth influences will cause the bubbles to cross a threshold into uncontrolled growth. Also, bubbles stabilized by mechanical structures will be destroyed if outside influences bring them below a critical small size. The in vivo behavior of different kinds of stabilized bubbles can be compared by using plots of bubble radius as a function of forces that affect diffusion of gases in or out of the bubble. The two ends of the plot are the limits for unstabilized growth and destruction; these and the curve’s slope predict the bubble’s practical usefulness for ultrasonic imaging or O2 carriage to tissues.
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Su, Chi-Wei, Lu Liu, and Kai-Hua Wang. "Do Bubble Behaviors Exist in Chinese Film Stocks?" SAGE Open 10, no. 4 (October 2020): 215824402098330. http://dx.doi.org/10.1177/2158244020983300.
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This article investigates bubbles in the Chinese film industry to reveal the industry’s boom and bust process that influences employment, citizen’s livelihoods, and even economic growth. We adopt the film stock index to reflect the industry’s trajectory and employ the generalized and backward sup augmented Dickey–Fuller tests to detect bubble periods. Empirical results indicate that there are three positive bubbles in 2007, 2013, and 2015, indicating that the film market continues to expand after temporary frustrations. Meanwhile, one negative bubble is found in 2019, which demonstrates that the bubble’s negative impacts persist and the film industry is still having problems such as declining industrial output. Economic growth, film quality, and industrial policies are common factors for all bubbles. The global financial crisis, capital in- and outflows, internet giants’ entry and sky-high remuneration are reasons for certain bubble behaviors. Hence, market practitioners should actively recognize bubbles and observe their evolution, which will favor industrial stabilization. A perfect legal system, moderate industrial policies, a competitive market environment, and other measures are needed to confront the opportunities and challenges.
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Zhao, Mengke, Jianjun Zhou, Willem A. Baan, Yue Hu, A. Lazarian, Xindi Tang, Jarken Esimbek, et al. "Magnetic Field of Molecular Gas Measured with the Velocity Gradient Technique. II. Curved Magnetic Field in kpc-scale Bubble of NGC 628." Astrophysical Journal 967, no. 1 (May 1, 2024): 18. http://dx.doi.org/10.3847/1538-4357/ad3a62.
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Abstract We report the detection of the ordered alignment between the magnetic field and kpc-scale bubbles in the nearby spiral galaxy, NGC 628. Applying the Velocity Gradient Technique on CO spectroscopic data from the ALMA-PHANGS, the magnetic field of NGC 628 is measured at the scale of 191 pc (∼4″). The large-scale magnetic field is oriented parallel to the spiral arms and curves around the galactic bubble structures in the mid-infrared emission observed by the James Webb Space Telescope. A total of 21 bubble structures have been identified at the edges of spiral arms with scales over 300 pc, which includes two kpc-scale structures. These bubbles are caused by supernova remnants and prolonged star formation and are similar to the outflow chimneys found in neutral hydrogen in galactic disks. At the edge of the bubbles, the shocks traced by the O iii emission present a curved magnetic field that parallels the bubble’s shell. The magnetic field follows the bubble expansion and binds the gas in the shell to trigger further star formation. By analyzing the larger sample of 1694 bubbles, we found a distinct radial-size distribution of bubbles in NGC 628 indicating the star formation history in the galaxy.
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Mundhra, Raghav, Rajaram Lakkaraju, Prasanta Kumar Das, Maksim A. Pakhomov, and Pavel D. Lobanov. "Effect of Wall Proximity and Surface Tension on a Single Bubble Rising near a Vertical Wall." Water 15, no. 8 (April 17, 2023): 1567. http://dx.doi.org/10.3390/w15081567.
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Path instability of a rising bubble is a complex phenomenon. In many industrial applications, bubbles encounter walls, and the interactions between the bubbles and the wall have a significant impact on flow physics. A single bubble rising near a vertical wall was experimentally observed to follow a bouncing trajectory. To investigate the near-wall dynamics of rising bubbles, 3D numerical simulations were performed based on the volume of fluid (VOF) method using the open source solver OpenFOAM. The effect of wall proximity and surface tension on the bubble trajectory was investigated. Previous studies have focused on the near-wall rising dynamics of bubbles for higher Eotvos numbers (Eo) and varied the Galilei number (Ga). The physical properties of the flow were chosen such that the free-rising bubble lies in the rectilinear regime. The Ga number was fixed and the Eo number was varied to analyze its effect on the bubble’s rising trajectory. It was found that the presence of the wall increases the drag experienced by the bubble and induces an early transition from rectilinear to a planar zigzagging regime. We identify the maximum wall distance and the critical Eo number for the bubble to follow a bouncing trajectory. The amplitude, frequency and wavelength of the bouncing motion are independent of the initial wall distance, but they decrease with decreasing surface tension.
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Wang, Chuanxi, Yashar Mehmani, and Ke Xu. "Capillary equilibrium of bubbles in porous media." Proceedings of the National Academy of Sciences 118, no. 17 (April 19, 2021): e2024069118. http://dx.doi.org/10.1073/pnas.2024069118.
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In geologic, biologic, and engineering porous media, bubbles (or droplets, ganglia) emerge in the aftermath of flow, phase change, or chemical reactions, where capillary equilibrium of bubbles significantly impacts the hydraulic, transport, and reactive processes. There has previously been great progress in general understanding of capillarity in porous media, but specific investigation into bubbles is lacking. Here, we propose a conceptual model of a bubble’s capillary equilibrium associated with free energy inside a porous medium. We quantify the multistability and hysteretic behaviors of a bubble induced by multiple state variables and study the impacts of pore geometry and wettability. Surprisingly, our model provides a compact explanation of counterintuitive observations that bubble populations within porous media can be thermodynamically stable despite their large specific area by analyzing the relationship between free energy and bubble volume. This work provides a perspective for understanding dispersed fluids in porous media that is relevant to CO2 sequestration, petroleum recovery, and fuel cells, among other applications.
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DELALE, C. F., G. H. SCHNERR, and J. SAUER. "Quasi-one-dimensional steady-state cavitating nozzle flows." Journal of Fluid Mechanics 427 (January 25, 2001): 167–204. http://dx.doi.org/10.1017/s0022112000002330.
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Quasi-one-dimensional cavitating nozzle flows are considered by employing a homogeneous bubbly liquid flow model. The nonlinear dynamics of cavitating bubbles is described by a modified Rayleigh–Plesset equation that takes into account bubble/bubble interactions by a local homogeneous mean-field theory and the various damping mechanisms by a damping coefficient, lumping them together in the form of viscous dissipation. The resulting system of quasi-one-dimensional cavitating nozzle flow equations is then uncoupled leading to a nonlinear third-order ordinary differential equation for the flow speed. This equation is then cast into a nonlinear dynamical system of scaled variables which describe deviations of the flow field from its corresponding incompressible single-phase value. The solution of the initial-value problem of this dynamical system can be carried out very accurately, leading to an exact description of the hydrodynamic field for the model considered.A bubbly liquid composed of water vapour–air bubbles in water at 20 °C for two different area variations is considered, and the initial cavitation number is chosen in such a way that cavitation can occur in the nozzle. Results obtained, when bubble/bubble interactions are neglected, show solutions with flow instabilities, similar to the flashing flow solutions found recently by Wang and Brennen. Stable steady-state cavitating nozzle flow solutions, either with continuous growth of bubbles or with growth followed by collapse of bubbles, were obtained when bubble/bubble interactions were considered together with various damping mechanisms.
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Bogatko, Tatiana V., Aleksandr V. Chinak, Ilia A. Evdokimenko, Dmitriy V. Kulikov, Pavel D. Lobanov, and Maksim A. Pakhomov. "The Effect of a Backward-Facing Step on Flow and Heat Transfer in a Polydispersed Upward Bubbly Duct Flow." Water 13, no. 17 (August 24, 2021): 2318. http://dx.doi.org/10.3390/w13172318.
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The experimental and numerical results on the flow structure and heat transfer in a bubbly polydispersed upward duct flow in a backward-facing step are presented. Measurements of the carrier fluid phase velocity and gas bubbles motion are carried out using the PIV/PLIF system. The set of RANS equations is used for modeling the two-phase bubbly flow. Turbulence of the carrier fluid phase is predicted using the Reynolds stress model. The effect of bubble addition on the mean and turbulent flow structure is taken into account. The motion and heat transfer in a dispersed phase is modeled using the Eulerian approach taking into account bubble break-up and coalescence. The method of delta-functions is employed for simulation of distributions of polydispersed gas bubbles. Small bubbles are presented over the entire duct cross-section and the larger bubbles mainly observed in the shear mixing layer and flow core. The recirculation length in the two-phase bubbly flow is up to two times shorter than in the single-phase flow. The position of the heat transfer maximum is located after the reattachment point. The effect of the gas volumetric flow rate ratios on the flow patterns and maximal value of heat transfer in the two-phase flow is studied numerically. The addition of air bubbles results in a significant increase in heat transfer (up to 75%).
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Ren, Zhong-Fu, Fang-Zhi Kong, Fei-Yan Wang, and Gui-Fang Hu. "Effect of bubble size on nanofiber diameter in bubble electrospinning." Thermal Science 20, no. 3 (2016): 845–48. http://dx.doi.org/10.2298/tsci1603845r.
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Polymer bubbles are widely used for fabrication of nanofibers. Bubble size affects not only bubble's surface tension, but also fiber's morphology. A mathematical model is established to reveal the effect of bubble size on the spinning process, and the experiment verification shows the theoretical analysis is reliable.
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Yoon, Dongik, Hyun Jin Park, Yuji Tasaka, and Yuichi Murai. "Lift coefficient of bubble sliding inside turbulent boundary layers in an inclinable channel flow." Physics of Fluids 34, no. 5 (May 2022): 053301. http://dx.doi.org/10.1063/5.0086777.
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The behavior of bubbles traveling in the proximity of a tilted wall is studied experimentally to understand the fundamental sliding motion of bubbles inside turbulent boundary layers along an inclined wall. The qualitative visualization of sliding bubbles confirms the contribution of bubble buoyancy on the sliding motion for negative and positive inclinations of the channel. An opto-acoustic combined measurement technique is adopted to explore the sliding motion. Liquid velocity profiles in the bubbly flow and the distance between the wall and bottom of the bubble are obtained using the ultrasound pulsed Doppler method, while the bubble diameters and velocities are obtained from particle-tracking type image processing. The combined measurements reveal that the velocity of bubbles decreases under the negative slope condition and increases under the positive slope condition due to opposite buoyancy effects. In addition, the distance between the wall and bottom of the bubble increases with an increase in negative inclination. The lift coefficient is derived from the measured variables using a force–balance equation among the buoyancy, lift, and surface tension. Finally, we propose modeling equations for the lift coefficient expressed in terms of the Reynolds, Weber, and Bond numbers, which apply to the bubbles inside boundary layers.
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Nguyen, Van Luc, Tomohiro Degawa, and Tomomi Uchiyama. "Numerical simulation of the interaction between a vortex ring and a bubble plume." International Journal of Numerical Methods for Heat & Fluid Flow 29, no. 9 (September 2, 2019): 3192–224. http://dx.doi.org/10.1108/hff-12-2018-0734.
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Purpose This paper aims to provide discussions of a numerical method for bubbly flows and the interaction between a vortex ring and a bubble plume. Design/methodology/approach Small bubbles are released into quiescent water from a cylinder tip. They rise under the buoyant force, forming a plume. A vortex ring is launched vertically upward into the bubble plume. The interactions between the vortex ring and the bubble plume are numerically simulated using a semi-Lagrangian–Lagrangian approach composed of a vortex-in-cell method for the fluid phase and a Lagrangian description of the gas phase. Findings A vortex ring can transport the bubbles surrounding it over a distance significantly depending on the correlative initial position between the bubbles and the core center. The motion of some bubbles is nearly periodic and gradually extinguishes with time. These bubble trajectories are similar to two-dimensional-helix shapes. The vortex is fragmented into multiple regions with high values of Q, the second invariant of velocity gradient tensor, settling at these regional centers. The entrained bubbles excite a growth rate of the vortex ring's azimuthal instability with a formation of the second- and third-harmonic oscillations of modes of 16 and 24, respectively. Originality/value A semi-Lagrangian–Lagrangian approach is applied to simulate the interactions between a vortex ring and a bubble plume. The simulations provide the detail features of the interactions.
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Bulatova, A. Z., O. A. Solnyshkina, and N. B. Fatkullina. "Numerical study of single bubble mobility in triangular and deltoid microchannels using the boundary element method." Journal of Physics: Conference Series 2057, no. 1 (October 1, 2021): 012042. http://dx.doi.org/10.1088/1742-6596/2057/1/012042.
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Abstract The study of bubbly liquid dynamics in microchannels of unconventional shapes is of great importance for different fields of science and industry. This work investigates the dynamics of the incompressible single bubbles in the slow periodic flow of viscous liquid in a triangular channel with a variable pressure gradient. The numerical approach used in this research is based on the boundary element method (BEM). This method is widely used for solving three-dimensional problems and problems in areas with complex geometry. The influence of the bubble’s initial position relative to the channel centerline on the bubble deformation, the relative velocity of the bubble, and its center of mass displacement in the channel are considered.
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Yang, Zhi Yong, Jian Dong Li, and Guo Hua Zhang. "Numerical Simulation of Bubble Coalescence Based on VOF Method." Applied Mechanics and Materials 148-149 (December 2011): 814–17. http://dx.doi.org/10.4028/www.scientific.net/amm.148-149.814.
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This paper takes bubbles of bubble shell as research object, mainly studies two bubbles arranged in a vertical position. Applying VOF (volume of fluid) method to simulate interaction between two bubbles, analyses the effect of center distances and diameters on deformation and coalescence of bubbles. Results show that coalescence time of two bubbles with same diameters increases as the center distance increases. To two bubbles with different diameters, when the bigger bubble located beneath at the initial time, the smaller bubble moves upward first and then moves downward before two bubbles coalesce. When the smaller bubble located beneath at the initial time, bubble coalescence cannot happen. This paper is the basis of bubble group research, it is of positive significance to the bubble group research and performance improvement of bubble shell.
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Jia, Zheng, Mingjun Pang, and Ruipeng Niu. "Numerical Investigation on Effect of Bubbles Arrangement and Volume Fraction on Apparent Viscosity of Bubbly Suspensions." Recent Innovations in Chemical Engineering (Formerly Recent Patents on Chemical Engineering) 16, no. 4 (August 2023): 285–304. http://dx.doi.org/10.2174/0124055204268474230922054143.
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Background:: Bubbly suspensions can be often run into in natural and industrial processes. The addition of bubbles with different sizes can lead to a significant change in the rheological properties of a matrix liquid. It is extremely significant to fully understand the rheological properties of bubbly suspensions for improving process efficiencies and optimizing productive processes. background: Bubbly suspensions can be often run into in natural and industrial processes. The addition of bubbles of different sizes can greatly change the rheological properties of matrix liquid. It is extremely significant to fully understand the rheological properties of bubbly suspensions for improving process efficiencies and optimizing productive processes. Objective:: The objective of this study is to explore qualitatively the physical law and internal mechanism of the apparent viscosity of suspensions formed by a Newtonian liquid containing different bubbles. Methods:: Based on the parallel plate model of shear flow, the volume of fluid method (VOF) was used to investigate the effect of bubble arrangement and volume fraction on the apparent viscosity of bubbly suspensions at low volume fractions. The piecewise linear interface calculation (PLIC) method was applied to reconstruct the interface based on the phase function. Results:: The present results show that the relative viscosity (ηr) of bubbly suspensions shows a nonlinear change with an increase in bubble volume fraction (ϕ). When the capillary number (Ca) is less than 0.6, ηr shows a nonlinear increase with an increase in ϕ (ηr increases from 1 to 1.03 with an increase in ϕ from 0 to 2.94% at Ca=0.1). However, Ca is greater than or equal to 0.6, ηr shows a nonlinear decrease with an increase in ϕ (ηr decreases from 1 to 0.92 with an increase in ϕ from 0 to 2.94% at Ca=2.5). Even if ϕ is the same, different arrangements of bubbles can lead to different magnitudes of apparent viscosity of bubbly suspensions Conclusion:: As ϕ increases, the region of low shear rate increases, which leads to a non−linear decrease in the relative viscosity. When ϕ is the same, the different arrangements of bubbles can lead to different effects on bubble dynamics and flow fields. This results in different viscous dissipation in bubbly suspensions. Thus, the apparent viscosity of bubbly suspensions is different. other: Nothing
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Truby, J. M., S. P. Mueller, E. W. Llewellin, and H. M. Mader. "The rheology of three-phase suspensions at low bubble capillary number." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 471, no. 2173 (January 2015): 20140557. http://dx.doi.org/10.1098/rspa.2014.0557.
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We develop a model for the rheology of a three-phase suspension of bubbles and particles in a Newtonian liquid undergoing steady flow. We adopt an ‘effective-medium’ approach in which the bubbly liquid is treated as a continuous medium which suspends the particles. The resulting three-phase model combines separate two-phase models for bubble suspension rheology and particle suspension rheology, which are taken from the literature. The model is validated against new experimental data for three-phase suspensions of bubbles and spherical particles, collected in the low bubble capillary number regime. Good agreement is found across the experimental range of particle volume fraction ( 0 ≤ ϕ p ≲ 0.5 ) and bubble volume fraction ( 0 ≤ ϕ b ≲ 0.3 ). Consistent with model predictions, experimental results demonstrate that adding bubbles to a dilute particle suspension at low capillarity increases its viscosity, while adding bubbles to a concentrated particle suspension decreases its viscosity. The model accounts for particle anisometry and is easily extended to account for variable capillarity, but has not been experimentally validated for these cases.
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Lu, Tianshi, Roman Samulyak, and James Glimm. "Direct Numerical Simulation of Bubbly Flows and Application to Cavitation Mitigation." Journal of Fluids Engineering 129, no. 5 (October 25, 2006): 595–604. http://dx.doi.org/10.1115/1.2720477.
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The direct numerical simulation (DNS) method has been used to the study of the linear and shock wave propagation in bubbly fluids and the estimation of the efficiency of the cavitation mitigation in the container of the Spallation Neutron Source liquid mercury target. The DNS method for bubbly flows is based on the front tracking technique developed for free surface flows. Our front tracking hydrodynamic simulation code FronTier is capable of tracking and resolving topological changes of a large number of interfaces in two- and three-dimensional spaces. Both the bubbles and the fluid are compressible. In the application to the cavitation mitigation by bubble injection in the SNS, the collapse pressure of cavitation bubbles was calculated by solving the Keller equation with the liquid pressure obtained from the DNS of the bubbly flows. Simulations of the propagation of linear and shock waves in bubbly fluids have been performed, and a good agreement with theoretical predictions and experiments has been achieved. The validated DNS method for bubbly flows has been applied to the cavitation mitigation estimation in the SNS. The pressure wave propagation in the pure and the bubbly mercury has been simulated, and the collapse pressure of cavitation bubbles has been calculated. The efficiency of the cavitation mitigation by bubble injection has been estimated. The DNS method for bubbly flows has been validated through comparison of simulations with theory and experiments. The use of layers of nondissolvable gas bubbles as a pressure mitigation technique to reduce the cavitation erosion has been confirmed.
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Sun, T. Y., R. N. Parthasarathy, and G. M. Faeth. "Structure of Bubbly Round Condensing Jets." Journal of Heat Transfer 108, no. 4 (November 1, 1986): 951–59. http://dx.doi.org/10.1115/1.3247040.
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A theoretical and experimental study of turbulent bubbly condensing jets is reported. Tests involved initially monodisperse carbon dioxide bubbles in water (∼ 1 mm diameter bubbles with initial gas volume fractions of 2.4 and 4.8 percent) injected vertically upward in still water. Measurements were made of mean and fluctuating phase velocities, mean bubble diameters, mean bubble number intensities, and mean concentrations of dissolved carbon dioxide. Three theoretical methods were used to interpret the measurements: (1) locally homogeneous flow analysis, assuming infinitely fast interphase transport rates; (2) deterministic separated flow analysis, where finite interphase transport rates are considered but bubble/turbulence interactions are ignored; and (3) stochastic separated-flow analysis where both finite interphase transport rates and bubble/turbulence interactions are considered using random-walk methods. Both finite interphase transport rates and the turbulent dispersion of bubbles were important for present test conditions; therefore, only the stochastic separated flow analysis provided reasonable agreement with measurements.
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Lelouvetel, J., T. Tanaka, Y. Sato, and K. Hishida. "Transport mechanisms of the turbulent energy cascade in upward/downward bubbly flows." Journal of Fluid Mechanics 741 (February 13, 2014): 514–42. http://dx.doi.org/10.1017/jfm.2014.24.
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AbstractThe turbulent energy cascade in an upward or downward bubbly pipe flow with a Reynolds number of 1.5 × 104 was experimentally investigated in order to examine the effects of the flow direction on the turbulence modifications by bubbles. The bubble diameter was approximately 1 mm. The combination of a particle tracking velocimetry (PTV) system with Kolmogorov-order spatial and temporal resolutions and a shape projection imaging (SPI) system was used to simultaneously capture the liquid and bubble motions. The physical mechanisms of turbulence modification at each length scale, or in wavenumber space, were investigated by introducing a filtering-based scaling analysis, in which the filtering techniques derived from large eddy simulation (LES) were applied to the PTV measurements. The analysis can be used to examine the turbulent kinetic energy (TKE) exchange between bubbles and flows at each wavenumber. We observed significant differences in the flow statistics and turbulent energy budget of upward and downward flows, which are due to the sign of the relative velocity of bubbles. A negative relative velocity (downward flow) induces greater modifications in the energy budget than a positive relative velocity (upward flow), which suggests that the bubble-transport term of the turbulent energy is greater when the flow has to push down the bubbles. The flow provides more energy to the bubbles when it pushes them in the downward direction. The flow will also receive and dissipate more energy from the bubbles in a downward flow compared with an upward flow due to the greater transverse motion of the bubbles. The analysis introduced in the present study shows that the energy transfer from large to small scales is decreased in an upward flow and is increased in a downward flow. Similarly, the sign of the bubble term indicates that turbulent flow receives energy from bubbles in an upward flow, while it transfers energy to bubbles in a downward flow. We also observed that this energy transport is approximately 10 times larger in a downward flow than in an upward flow.
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THO, PAUL, RICHARD MANASSEH, and ANDREW OOI. "Cavitation microstreaming patterns in single and multiple bubble systems." Journal of Fluid Mechanics 576 (March 28, 2007): 191–233. http://dx.doi.org/10.1017/s0022112006004393.
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Cavitation microstreaming is a well-known phenomenon; however, few flow visualizations or measurements of the velocity fields have been conducted. In this paper micro-PIV (particle image velocimetry) measurements and streak photography were used to study the flow field around a single and two oscillating bubbles resting on a solid boundary. The mode of oscillation of the bubble was also measured in terms of the variation in the radius of the bubble and the movement of the bubble's centroid so that the streaming flow field could be accurately related to the bubble's oscillatory motion. The mode of oscillation was found to vary primarily with the applied acoustic frequency. Several modes of oscillation were investigated, including translating modes where the bubble's centroid moves along either a single axis, an elliptical orbit or a circular orbit. The flow field resulting from these oscillation modes contains closed streamlines representing vortical regions in the vicinity of the bubble. The translating modes were observed to occur in sequential order with the acoustic excitation frequency, changing from a translation along a single axis, to an elliptical orbit and finally to a circular orbit, or vice versa. Following this sequence, there is a corresponding transformation of the streaming pattern from a symmetrical flow structure containing four vortices to a circular vortex centred on the bubble. Despite some inconsistencies, there is general agreement between these streaming patterns and those found in existing theoretical models. Volume and shape mode oscillations of single bubbles as well as several different cases of multiple bubbles simultaneously oscillating with the same frequency and phase were also investigated and show a rich variety of streaming patterns.
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Ban, Zhen Hong, Kok Keong Lau, and Mohd Sharif Azmi. "Bubble Nucleation and Growth of Dissolved Gas in Solution Flowing across a Cavitating Nozzle." Applied Mechanics and Materials 773-774 (July 2015): 304–8. http://dx.doi.org/10.4028/www.scientific.net/amm.773-774.304.
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Computational modelling of dissolved gas bubble formation and growth in supersaturated solution is essential for various engineering applications, including flash vaporisation of petroleum crude oil. The common mathematical modelling of bubbly flow only caters for single liquid and its vapour, which is known as cavitation. This work aims to simulate the bubble nucleation and growth of dissolved CO2 in water across a cavitating nozzle. The dynamics of bubble nucleation and growth phenomenon will be predicted based on the hydrodynamics in the computational domain. The complex interrelated bubble dynamics, mass transfer and hydrodynamics was coupled by using Computational Fluid Dynamics (CFD) and bubble nucleation and growth model. Generally, the bubbles nucleate at the throat of the nozzle and grow along with the flow. Therefore, only the region after the throat of the nozzle has bubbles. This approach is expected to be useful for various types of bubbly flow modelling in supersaturated condition.
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Liu 刘, Teng 腾., Andrea Merloni, Jeremy Sanders, Gabriele Ponti, Andrew Strong, Michael C. H. Yeung, Nicola Locatelli, et al. "Morphological Evidence for the eROSITA Bubbles Being Giant and Distant Structures." Astrophysical Journal Letters 967, no. 2 (May 22, 2024): L27. http://dx.doi.org/10.3847/2041-8213/ad47e0.
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Abstract There are two contradictory views of the eROSITA bubbles: either a 104 pc scale pair of giant bubbles blown by the Galactic center (GC), or a 102 pc scale local structure coincidentally located in the direction of GC. A key element of this controversy is the distance to the bubbles. Based on the 3D dust distribution in the Galactic plane, we found three isolated, distant (500–800 pc) clouds at intermediate Galactic latitudes. Their projected morphologies perfectly match the X-ray shadows on the defining features of the north eROSITA bubble, i.e., the North Polar Spur (NPS) and the Lotus Petal Cloud (LPC), indicating that both the NPS and LPC are distant, with a distance lower limit of nearly 1 kpc. In the X-ray-dark region between the NPS and LPC, we found a few polarized radio arcs and attributed them to the bubble’s shock front. These arcs match up perfectly with the outer border of the NPS and LPC and provide a way to define the bubble’s border. The border defined in this way can be well described by the line-of-sight tangent of a 3D skewed cup model rooted in the GC. We conclude that, instead of being two independent, distant features, the NPS and LPC compose a single, giant bubble, which therefore is most plausibly a 10 kpc scale bubble rooted at the GC.
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Ochiai, N., and J. Ishimoto. "Numerical investigation of multiple-bubble behaviour and induced pressure in a megasonic field." Journal of Fluid Mechanics 818 (April 6, 2017): 562–94. http://dx.doi.org/10.1017/jfm.2017.154.
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Clarifying the mechanism of particle removal by megasonic cleaning and multiple-bubble dynamics in megasonic fields is essential for removing contaminant particles during nanodevice cleaning without pattern damage. In particular, the effect of the interaction of multiple bubbles on bubble-collapse behaviour and impulsive pressure induced by bubble collapse should also be discussed. In this study, a compressible locally homogeneous model of a gas–liquid two-phase medium is used to numerically analyse the multiple-bubble behaviour in a megasonic field. The numerical results indicate that, for bubbles with the same equilibrium radius, the natural frequency of the bubble decreases, and bubbles with smaller equilibrium radii resonate with the megasonic wave as the number of bubbles increases. Therefore, the equilibrium radius of bubbles showing maximum wall pressure decreases with an increasing number of bubbles. The increase in bubble number also results in chain collapse, inducing high wall pressure. The effect of the configuration of bubbles is discussed, and the bubble–bubble interaction in the concentric distribution makes a greater contribution to the decrease in the natural frequency of bubbles than the interaction in the straight distribution.
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Chen, Junliang, Mao Lei, Shaobo Lu, Xiaolong Xiao, Mingxiu Yao, and Qiang Li. "Numerical simulation of single bubble motion fragmentation mechanism in Venturi-type bubble generator." Mechanics & Industry 25 (2024): 21. http://dx.doi.org/10.1051/meca/2024016.
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Microbubbles have been widely used in power, chemical, mining and petroleum applications to improve energy efficiency. The venture-type bubble generator can improve reaction efficiency in chemical engineering as an efficient bubble generation method. Studying the flow field and bubble bursting mechanism can enhance the bubble generation performance. The volume of fluid (VOF) multiphase flow model was used in the Open Field Operation and Manipulation (OpenFOAM) framework to study the deformation and fragmentation behaviour of a single bubble in a Quasi three-dimensional. The relationship between the mechanism of bubble breakup and the flow field in the diverging section of a Venturi-type bubble generator was revealed. The reasons for the uneven distribution of bubble size were analyzed and discussed. The numerical simulation result shows that the fragmentation of a single bubble injected by the converging section is more substantial than that injected by the throat in the axial direction. Bubble fragmentation occurs mainly in the diverging section. The bubble's trajectory is highly similar to the vortex trajectory of the diverging section. The size of sub-bubbles generated by single bubble fragmentation decreases with the diverging angle and liquid flow rate increase. The differential distribution of turbulent kinetic energy in the radial position directly leads to the uneven distribution of the bubble size of the broken bubbles. As the liquid Reynolds number increases, static and dynamic erosion breakup are more prominent. The size of the sub-bubbles is much smaller.
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CHEW, LUP WAI, BOO CHEONG KHOO, EVERT KLASEBOER, and SIEW-WAN OHL. "INTERACTION OF TWO DIFFERENTLY SIZED BUBBLES IN A FREE FIELD." International Journal of Modern Physics: Conference Series 19 (January 2012): 180–84. http://dx.doi.org/10.1142/s2010194512008720.
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The interaction between two different sized (spark created, non-equilibrium) bubbles is studied by using high speed photography. The bubble size ranges from 2 to 7 mm. The experimental results are compared to that of the similar sized bubbles reported in the literature. Interestingly, all the four major behaviors of bubble-bubble interactions (i.e. 'bubble-collapsed' induced liquid jets directed away from each other, liquid jets directed towards each other, bubble coalescence and the 'catapult' effect) are observed which bear much similarity to that found for similar sized bubbles' interaction. The main parameters studied/varied are the size of the bubbles, the dimensionless separation distance and the phase difference between the two bubbles. The results obtained are consistent with the cases of similar sized bubbles reported in the literature, with each type of behavior occupying a distinct region in the graphical plot. This indicates that the results for the (special) similar sized bubbles can be generalized to cases with different sized bubbles. Many of the real life applications such as cavitations corrosions often involve bubbles with significant size difference, thus the present findings are useful in predicting the behavior of multiple bubbles in many situations.
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van Lookeren Campagne, C., R. Nicodemus, G. J. de Bruin, and D. Lohse. "A Method for Pressure Calculation in Ball Valves Containing Bubbles." Journal of Fluids Engineering 124, no. 3 (August 19, 2002): 765–71. http://dx.doi.org/10.1115/1.1486220.
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A method of analyzing bubbly flow in a ball valve in a hydraulic circuit is presented. The dynamics of a single bubble can be well described by a quasi-static approximation of the Rayleigh-Plesset equation. Hence the presence of bubbles in low volume fractions can be modeled through an effective compressibility of the flow, which is easy to implement in commercial CFD packages. In the sample valve, a volume fraction of 4% air bubbles results in a mass flux reduction of up to 10%, as the bubbles expand due to the pressure drop in the valve and partly block it.
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Guo, Wenqi, Fulin Yu, Chao Su, Zhanquan Li, Fengguang Jia, and Yueying Gong. "Experimental Study on Multi Bubble Ice Breaking Under Layer Ice Boundary Conditions." Advances in Computer and Engineering Technology Research 1, no. 1 (December 8, 2023): 210. http://dx.doi.org/10.61935/acetr.1.1.2023.p210.
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Under certain conditions of bubble spacing and bubble to ice distance, the motion state and ice breaking effect of horizontal and vertical bubbles under ice plate boundary conditions were studied. Bubbles are generated through underwater discharge, and the generating device is placed horizontally or vertically below the ice plate, and the experimental phenomenon is observed through an ultra-high-speed camera. Firstly, the motion characteristics and ice breaking ability of two horizontal bubbles under an unperforated ice block were demonstrated. Then, the motion characteristics of two horizontal bubbles and two vertical bubbles under a porous ice block, the breaking effect of the ice block, and the water mound phenomenon on the free surface were observed. The experiment observed unique bubble behavior, including bubble fusion, bubble collapse, and oblique jet, as well as the influence of bubble-bubble and bubble-ice interactions on the morphology evolution and ice breaking effect of bubbles. The results indicate that the ice breaking effect of the interaction between bubbles and perforated ice plates is weaker than that of non-perforated ice plates, which may be more helpful for subsequent bubble ice breaking research.
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d’Agostino, Luca, and Fabio Burzagli. "On the Stability of Parallel Bubbly Cavitating Flows." Journal of Fluids Engineering 122, no. 3 (April 25, 2000): 471–80. http://dx.doi.org/10.1115/1.1287036.
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This paper illustrates the effects of the dynamics of bubbles with arbitrary vapor-gas contents on the inviscid and viscous stability of two-dimensional parallel bubbly flows of low void fraction. The linear perturbation equations derived for the stability analysis include the effects of bubble compressibility, inertia, and energy dissipation due to the viscosity of the liquid and the transfer of heat and mass as a consequence of compression/expansion of the noncondensable gas and evaporation/condensation of the vapor contained in the bubbles. Numerical solution of the spatial stability problem for two-dimensional inviscid shear layers and Blasius boundary layers confirms that the presence of the dispersed phase is generally in favor of stability. Significant deviations from the classical results for compressible and incompressible single phase fluids are observed, especially when the occurrence of large compliant and/or resonant oscillations of the bubbles greatly enhances their dynamic coupling with the perturbation field. More importantly, the present analysis points out some major differences in the stability of parallel flows with noncondensable gas bubbles with respect to cavitating flows containing bubbles with a dominant content of vapor. Unconditional stability is predicted in the travelling bubble cavitation limit for low pressures and high vapor mass fraction of the bubble contents. Results are shown to illustrate these effects for some representative flow configurations and conditions. [S0098-2202(00)00603-9]
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Yang, Weidong, Zhiguo Luo, Nannan Zhao, and 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, no. 9 (August 27, 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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Roshid, Mohammed M., and Richard Manasseh. "Passive acoustic measurement of bubble size and number from a bubble chain." Journal of the Acoustical Society of America 154, no. 4_supplement (October 1, 2023): A110. http://dx.doi.org/10.1121/10.0022953.
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Experiments and matching simulations are presented on the passive-acoustic emissions of a chain of bubbles, with the aim of deducing both the bubble size and number of bubbles from the emitted sound. It is well known that bubble-acoustic interactions cause shifts in frequency from those predicted for single bubbles, complicating the goal of measuring bubble size by measuring frequency, and also affecting the collective resonances of bubbles driven by ultrasound. A horizontal line of identical bubbles was held fixed in space, eliminating uncertainties in earlier studies due to the variable shape and location of freely rising bubbles. At one end of the line, a first, identical bubble naturally emitted a pulse of sound on formation from an underwater nozzle, exciting the rest of the bubbles into a coupled acoustic emission. It was found that a theoretically predicted relation between frequency and the number of bubbles, which can be derived from the coupled equations of motion, permitted an accurate fit to the data. Measurements of two independent spectral peaks unambiguously determined the two unknowns of bubble size and bubble number. However, experiments diverge from theory and simulations for greater than six bubbles, which are speculated may be explicable by network theory.
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Chen, Mengchi, Cheng Zhang, Wen Yang, Suyi Zhang, and Wenjun Huang. "End-to-End Bubble Size Distribution Detection Technique in Dense Bubbly Flows Based on You Only Look Once Architecture." Sensors 23, no. 14 (July 21, 2023): 6582. http://dx.doi.org/10.3390/s23146582.
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Accurate measurements of the bubble size distribution (BSD) are crucial for investigating gas–liquid mass transfer mechanisms and describing the characteristics of chemical production. However, measuring the BSD in high-density bubbly flows remains challenging due to limited image algorithms and high data densities. Therefore, an end-to-end BSD detection method in dense bubbly flows based on deep learning is proposed in this paper. The bubble detector locates the positions of dense bubbles utilizing objection detection networks and simultaneously performs ellipse parameter fitting to measure the size of the bubbles. Different You Only Look Once (YOLO) architectures are compared, and YOLOv7 is selected as the backbone network. The complete intersection over union calculation method is modified by the circumferential horizontal rectangle of bubbles, and the loss function is optimized by adding L2 constraints of ellipse size parameters. The experimental results show that the proposed technique surpasses existing methods in terms of precision, recall, and mean square error, achieving values of 0.9871, 0.8725, and 3.8299, respectively. The proposed technique demonstrates high efficiency and accuracy when measuring BSDs in high-density bubbly flows and has the potential for practical applications.
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Zhang, Xiaoxi, Can Cao, Nan Gui, Xiaoli Huang, Xingtuan Yang, Jiyuan Tu, Shengyao Jiang, and Qian Zhao. "A Particle-Scale Model of Surface Tension for Two-Phase Flow: Model Description and Validation." Energies 15, no. 19 (September 28, 2022): 7132. http://dx.doi.org/10.3390/en15197132.
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A particle-scale surface tension force model (STF) is proposed here to be incorporated in the smoothed hydrodynamics particle (SPH) method. This model is based on the identification of interface geometry and the gradient of densities across the interface. A square bubble of single-phase and a square bubble immersed in fluids are simulated by the STF model accompanied with a combined kernel in SPH to validate their suitability to simulate the immersed bubble motion. Two cases of rising bubbles, i.e., a single rising bubble and a pair of rising bubbles, are simulated for demonstration. The rising velocity, density, surface tension force, interfacial curvature, the power of the STF, and the smoothing length of the rising bubble and surrounding fluids are all computed by the current STF model to study the characteristics of immersed bubble’s motion and coalescence. The current model provides a way to capture the interfacial interactions in two-phase flows at particle scales.
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Wu, Yaorong, Weizhong Chen, Lingling Zhang, Yang Shen, Guoying Zhao, and Shaoyang Kou. "The left-right symmetrical and asymmetrical deformations in a three-bubble system." Journal of the Acoustical Society of America 152, no. 4 (October 2022): 2446–55. http://dx.doi.org/10.1121/10.0014905.
Full textAbstract:
This paper studies the simplest system that can possess left-right symmetrical and asymmetrical surroundings, three bubbles in a line. Assuming that the deformations are small, the surfaces of bubbles are described by a combination of the first three Legendre polynomials, that is, spherical symmetrical mode P0, L-R antisymmetrical mode P1, and symmetrical mode P2. A dynamical model is built to describe aspherical oscillations of central and two side bubbles. It is found that when three identical bubbles are separated uniformly, the central bubble only has a P2 component and P1 component tends to zero, while two side bubbles have both P1 and P2 components. When three identical bubbles are separated by different distances, they can be degenerated into a two-bubble system and a free bubble. The bubble deformations contain both P1 and P2 components in the two-bubble system, while both aspherical components P1 and P2 of the free bubble tend to zero. If side bubbles are different in ambient radii but located symmetrically on the left and right of the central bubble, the side bubble pulsated more strongly plays an important role on the deformation of the central one.
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Li, Jian, and Zhiguang Guo. "Patterned Slippery Surface for Bubble Directional Transportation and Collection Fabricated via a Facile Method." Research 2019 (November 5, 2019): 1–9. http://dx.doi.org/10.34133/2019/9139535.
Full textAbstract:
Directional manipulation of underwater bubbles on a solid surface has attracted much attention due to its large-scale applications such as electrocatalytic gas evolution reactions, wastewater remediation, and solar energy harvesting. In this work, the patterned slippery surface (PSS) is fabricated via a facile method where the patterned pathways are fabricated by means of etching the pristine copper sheet. These patterned surfaces consisted of pristine copper and modified oxide copper which exhibit different wettability for bubble and water. The superhydrophobic and aerophilic surface can efficiently capture bubbles, and the infused oil layer is beneficial for reducing the resistance during transportation. Furthermore, the bubble can move upward, downward, and horizontally. Hence, it is easy to realize the bubble’s transportation and collection on the functional surfaces.
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Brunnermeier, Markus, Simon Rother, and Isabel Schnabel. "Asset Price Bubbles and Systemic Risk." Review of Financial Studies 33, no. 9 (February 10, 2020): 4272–317. http://dx.doi.org/10.1093/rfs/hhaa011.
Full textAbstract:
Abstract We analyze the relationship between asset price bubbles and systemic risk, using bank-level data covering almost 30 years. Banks’ systemic risk already rises during a bubble’s buildup and even more so during its bust. The increase in risk strongly differs across banks and by bubble. It depends on bank characteristics (especially bank size) and bubble characteristics and can become very large: in a median real estate bust, systemic risk increases by almost 70% of the median for banks with unfavorable characteristics. These results emphasize the importance of bank-level factors in the buildup of financial fragility during bubble episodes. Authors have furnished an Internet Appendix, which is available on the Oxford University Press Web site next to the link to the final published paper online.