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Sample records for air-water bubbly flow

  1. Gas and liquid measurements in air-water bubbly flows

    SciTech Connect

    Zhou, X.; Doup, B.; Sun, X.

    2012-07-01

    Local measurements of gas- and liquid-phase flow parameters are conducted in an air-water two-phase flow loop. The test section is a vertical pipe with an inner diameter of 50 mm and a height of 3.2 m. The measurements are performed at z/D = 10. The gas-phase measurements are performed using a four-sensor conductivity probe. The data taken from this probe are processed using a signal processing program to yield radial profiles of the void fraction, bubble velocity, and interfacial area concentration. The velocity measurements of the liquid-phase are performed using a state-of-the-art Particle Image Velocimetry (PIV) system. The raw PIV images are acquired using fluorescent particles and an optical filtration device. Image processing is used to remove noise in the raw PIV images. The statistical cross correlation is introduced to determine the axial velocity field and turbulence intensity of the liquid-phase. Measurements are currently being performed at z/D = 32 to provide a more complete data set. These data can be used for computational fluid dynamic model development and validation. (authors)

  2. A model for sound velocity in a two-phase air-water bubbly flow

    SciTech Connect

    Chung, N.M.; Lin, W.K.; Pei, B.S.; Hsu, Y.Y. )

    1992-07-01

    In this paper, wave propagation in a homogeneous, low void fraction, two-phase air-water bubbly flow is analyzed through the compressibility of a single bubble to derive a P({rho}) relation; the dispersion relation is then derived by a homogeneous model. The phase velocity and attenuation calculated from the model are compared with existing data and are in good agreement. The momentum transfer effect is considered through the virtual mass term and is significant at a higher void fraction. The interfacial heat transfer between phases is significant at low frequency, while bubble scattering effects are important at high frequency (near resonance). Bubble behavior at both low and high frequency is derived based on the isothermal and the adiabatic cases, respectively. The phase velocity occurs at the limiting condition in both cases. Furthermore, resonance is present in the model, and the resonant frequency is determined.

  3. Study of interfacial area transport and sensitivity analysis for air-water bubbly flow

    SciTech Connect

    Kim, S.; Sun, X.; Ishii, M.; Beus, S.G.

    2000-09-01

    The interfacial area transport equation applicable to the bubbly flow is presented. The model is evaluated against the data acquired by the state-of-the-art miniaturized double-sensor conductivity probe in an adiabatic air-water co-current vertical test loop under atmospheric pressure condition. In general, a good agreement, within the measurement error of plus/minus 10%, is observed for a wide range in the bubbly flow regime. The sensitivity analysis on the individual particle interaction mechanisms demonstrates the active interactions between the bubbles and highlights the mechanisms playing the dominant role in interfacial area transport. The analysis employing the drift flux model is also performed for the data acquired. Under the given flow conditions, the distribution parameter of 1.076 yields the best fit to the data.

  4. Interfacial structures of confined air-water two-phase bubbly flow

    SciTech Connect

    Kim, S.; Ishii, M.; Wu, Q.; McCreary, D.; Beus, S.G.

    2000-08-01

    The interfacial structure of the two-phase flows is of great importance in view of theoretical modeling and practical applications. In the present study, the focus is made on obtaining detailed local two-phase parameters in the air-water bubbly flow in a rectangular vertical duct using the double-sensor conductivity probe. The characteristic wall-peak is observed in the profiles of the interracial area concentration and the void fraction. The development of the interfacial area concentration along the axial direction of the flow is studied in view of the interfacial area transport and bubble interactions. The experimental data is compared with the drift flux model with C{sub 0} = 1.35.

  5. Structure of Air-Water Bubbly Flow in a Vertical Annulus

    SciTech Connect

    Rong Situ; Takashi Hibiki; Ye Mi; Mamoru Ishii; Michitsugu Mori

    2002-07-01

    Local measurements of flow parameters were performed for vertical upward bubbly flows in an annulus. The annulus channel consisted of an inner rod with a diameter of 19.1 mm and an outer round tube with an inner diameter of 38.1 mm, and the hydraulic equivalent diameter was 19.1 mm. Double-sensor conductivity probe was used for measuring void fraction, interfacial area concentration, and interfacial velocity, and Laser Doppler anemometer was utilized for measuring liquid velocity and turbulence intensity. The mechanisms to form the radial profiles of local flow parameters were discussed in detail. The constitutive equations for distribution parameter and drift velocity in the drift-flux model, and the semi-theoretical correlation for Sauter mean diameter namely interfacial area concentration, which were proposed previously, were validated by local flow parameters obtained in the experiment using the annulus. (authors)

  6. Application of the ultrasonic technique and high-speed filming for the study of the structure of air-water bubbly flows

    SciTech Connect

    Carvalho, R.D.M.; Venturini, O.J.; Tanahashi, E.I.; Neves, F. Jr.; Franca, F.A.

    2009-10-15

    Multiphase flows are very common in industry, oftentimes involving very harsh environments and fluids. Accordingly, there is a need to determine the dispersed phase holdup using noninvasive fast responding techniques; besides, knowledge of the flow structure is essential for the assessment of the transport processes involved. The ultrasonic technique fulfills these requirements and could have the capability to provide the information required. In this paper, the potential of the ultrasonic technique for application to two-phase flows was investigated by checking acoustic attenuation data against experimental data on the void fraction and flow topology of vertical, upward, air-water bubbly flows in the zero to 15% void fraction range. The ultrasonic apparatus consisted of one emitter/receiver transducer and three other receivers at different positions along the pipe circumference; simultaneous high-speed motion pictures of the flow patterns were made at 250 and 1000 fps. The attenuation data for all sensors exhibited a systematic interrelated behavior with void fraction, thereby testifying to the capability of the ultrasonic technique to measure the dispersed phase holdup. From the motion pictures, basic gas phase structures and different flows patterns were identified that corroborated several features of the acoustic attenuation data. Finally, the acoustic wave transit time was also investigated as a function of void fraction. (author)

  7. Air-water flow in subsurface systems

    NASA Astrophysics Data System (ADS)

    Hansen, A.; Mishra, P.

    2013-12-01

    Groundwater traces its roots to tackle challenges of safe and reliable drinking water and food production. When the groundwater level rises, air pressure in the unsaturated Vadose zone increases, forcing air to escape from the ground surface. Abnormally high and low subsurface air pressure can be generated when the groundwater system, rainfall, and sea level fluctuation are favorably combined [Jiao and Li, 2004]. Through this process, contamination in the form of volatile gases may diffuse from the ground surface into residential areas, or possibly move into groundwater from industrial waste sites. It is therefore crucial to understand the combined effects of air-water flow in groundwater system. Here we investigate theoretically and experimentally the effects of air and water flow in groundwater system.

  8. Effect of surfactants on bubble collisions with an air-water interface

    NASA Astrophysics Data System (ADS)

    Wang, Shiyan; Guo, Tianqi; Dabiri, Sadegh; Vlachos, Pavlos P.; Ardekani, Arezoo M.

    2016-11-01

    Collisions of bubbles on an air-water interface are frequently observed in natural environments and industrial applications. We study the coefficient of restitution of a bubble colliding on an air-water interface in the presence of surfactants through a combination of experimental and numerical approaches. In a high concentration surfactant solution, bubbles experience perfectly inelastic collisions, and bubbles are arrested by the interface after the collision. As the surfactant concentration decreases, collisions are altered to partially inelastic, and eventually, elastic collisions occur in the pure water. In a high concentration surfactant solution, the reduced bouncing is attributed to the Marangoni stress. We identify the Langmuir number, the ratio between absorption and desorption rates, as the fundamental parameter to quantify the Marangoni effect on collision processes in surfactant solutions. The effect of Marangoni stress on the bubble's coefficient of restitution is non-monotonic, where the coefficient of restitution first decreases with Langmuir number, and then increases.

  9. Numerical Modeling of Flow Dynamics in The Aluminum Smelting Process: Comparison Between Air-Water and CO2-Cryolite Systems

    NASA Astrophysics Data System (ADS)

    Zhao, Zhibin; Feng, Yuqing; Schwarz, M. Philip; Witt, Peter J.; Wang, Zhaowen; Cooksey, Mark

    2016-12-01

    Air-water models have been widely applied as substitutes for CO2-cryolite systems in the study of the complex bubble dynamics and bubble-driven flow that occurs in the molten electrolyte phase in the aluminum electrolytic process, but the detailed difference between the two systems has not been studied. This paper makes a numerical comparison between the bubble dynamics for the two systems. Simulations of both single bubble and continuous bubbling were conducted using a three-dimensional computational fluid dynamics (3D CFD) modeling approach with a volume of fluid (VOF) method to capture the phase interfaces. In the single bubble simulations, it was found that bubbles sliding under an anode in a CO2-cryolite system have a smaller bubble thickness and a higher sliding velocity than those in the air-water system for bubbles of the same volume. Dimensionless analysis and numerical simulation show that contact angle is the dominant factor producing these differences; the effects of kinematic viscosity, surface tension, and density are very small. In the continuous bubbling simulations, the continuous stream of air bubbles detaches from the anode sidewall after a period of climbing, just as it does in the single bubble simulation, but bubbles have less tendency to migrate away from the wall. Quasi-stable state flow characteristics, i.e., time-averaged bath flow pattern, turbulence kinetic energy, turbulence dissipation rate, and gas volume fraction, show a remarkable agreement between the two systems in terms of distribution and magnitude. From the current numerical comparisons, it is believed that the air-water model is a close substitutive model for studying bubble-driven bath flow in aluminum smelting processes. However, because of the difference in bubble morphologies between the two systems, and also the reactive generation and growth of bubbles in the real system, there will likely be some differences in bubble coverage of the anode in the anode-cathode gap.

  10. Numerical Modeling of Flow Dynamics in The Aluminum Smelting Process: Comparison Between Air-Water and CO2-Cryolite Systems

    NASA Astrophysics Data System (ADS)

    Zhao, Zhibin; Feng, Yuqing; Schwarz, M. Philip; Witt, Peter J.; Wang, Zhaowen; Cooksey, Mark

    2017-04-01

    Air-water models have been widely applied as substitutes for CO2-cryolite systems in the study of the complex bubble dynamics and bubble-driven flow that occurs in the molten electrolyte phase in the aluminum electrolytic process, but the detailed difference between the two systems has not been studied. This paper makes a numerical comparison between the bubble dynamics for the two systems. Simulations of both single bubble and continuous bubbling were conducted using a three-dimensional computational fluid dynamics (3D CFD) modeling approach with a volume of fluid (VOF) method to capture the phase interfaces. In the single bubble simulations, it was found that bubbles sliding under an anode in a CO2-cryolite system have a smaller bubble thickness and a higher sliding velocity than those in the air-water system for bubbles of the same volume. Dimensionless analysis and numerical simulation show that contact angle is the dominant factor producing these differences; the effects of kinematic viscosity, surface tension, and density are very small. In the continuous bubbling simulations, the continuous stream of air bubbles detaches from the anode sidewall after a period of climbing, just as it does in the single bubble simulation, but bubbles have less tendency to migrate away from the wall. Quasi-stable state flow characteristics, i.e., time-averaged bath flow pattern, turbulence kinetic energy, turbulence dissipation rate, and gas volume fraction, show a remarkable agreement between the two systems in terms of distribution and magnitude. From the current numerical comparisons, it is believed that the air-water model is a close substitutive model for studying bubble-driven bath flow in aluminum smelting processes. However, because of the difference in bubble morphologies between the two systems, and also the reactive generation and growth of bubbles in the real system, there will likely be some differences in bubble coverage of the anode in the anode-cathode gap.

  11. Water temperature effect on upward air-water flow in a vertical pipe: Local measurements database using four-sensor conductivity probes and LDA

    NASA Astrophysics Data System (ADS)

    Monrós-Andreu, G.; Chiva, S.; Martínez-Cuenca, R.; Torró, S.; Juliá, J. E.; Hernández, L.; Mondragón, R.

    2013-04-01

    Experimental work was carried out to study the effects of temperature variation in bubbly, bubbly to slug transition. Experiments were carried out in an upward air-water flow configuration. Four sensor conductivity probes and LDA techniques was used together for the measurement of bubble parameters. The aim of this paper is to provide a bubble parameter experimental database using four-sensor conductivity probes and LDA technique for upward air-water flow at different temperatures and also show transition effect in different temperatures under the boiling point.

  12. The effect of bubbles on air-water oxygen transfer in the breaker zone

    NASA Astrophysics Data System (ADS)

    Kakuno, Shohachi; Moog, Douglas B.; Tatekawa, Tetsuya; Takemura, Kenji; Yamagishi, Tatsuya

    The effect of bubbles entrained in the breaker zone on air-water oxygen transfer is examined. First, the area of bubbles entrained by breakers generated on a sloping bottom in a wave tank is analyzed using a color image sensor which can count the pixel number of a specific color in a frame. It was found that the time-averaged pixel number over a wave period has a strong relationship to the energy dissipation rate per unit mass of the breaker. The time-averaged pixel number is then incorporated with some modification into an equation proposed by Eckenfelder for the calculation of the mass transfer coefficient from bubble surfaces in an aeration tank. The coefficient resulting from the modified equation shows a strong relationship between the mass transfer coefficient and the dissipation rate.

  13. Development of Interfacial Structure in a Confined Air-Water Cap-Turbulent and Churn-Turbulent Flow

    SciTech Connect

    X. Sun; S. Kim; L. Cheng; M. Ishii; S.G. Beus

    2001-10-31

    The objective of the present work is to study and model the interfacial structure development of air-water two-phase flow in a confined test section. Experiments of a total of 9 flow conditions in a cap-turbulent and churn-turbulent flow regimes are carried out in a vertical air-water upward two-phase flow experimental loop with a test section of 20-cm in width and 1-cm in gap. The miniaturized four-sensor conductivity probes are used to measure local two-phase parameters at three different elevations for each flow condition. The bubbles captured by the probes are categorized into two groups in view of the two-group interfacial area transport equation, i.e., spherical/distorted bubbles as Group 1 and cap/churn-turbulent bubbles as Group 2. The acquired parameters are time-averaged local void fraction, interfacial velocity, bubble number frequency, interfacial area concentration, and bubble Sauter mean diameter for both groups of bubbles. Also, the line-averaged and area-averaged data are presented and discussed. The comparisons of these parameters at different elevations demonstrate the development of interfacial structure along the flow direction due to bubble interactions.

  14. Development of Interfacial Structure in a Confined Air-Water Cap-Turbulent and Churn-Turbulent Flow

    SciTech Connect

    Xiaodong Sun; Seungjin Kim; Ling Cheng; Mamoru Ishii; Beus, Stephen G.

    2002-07-01

    The objective of the present work is to study and model the interfacial structure development of air-water two-phase flow in a confined test section. Experiments of a total of 9 flow conditions in cap-turbulent and churn-turbulent flow regimes are carried out in a vertical air-water upward two-phase flow experimental loop with a test section of 200-mm in width and 10-mm in gap. Miniaturized four-sensor conductivity probes are used to measure local two-phase parameters at three different elevations for each flow condition. The bubbles captured by the probes are categorized into two groups in view of the two-group interfacial area transport equation, i.e., spherical/distorted bubbles as Group 1 and cap/churn-turbulent bubbles as Group 2. The acquired parameters are time-averaged local void fraction, interfacial velocity, bubble number frequency, interfacial area concentration, and bubble Sauter mean diameter for both groups of bubbles. Also, the line-averaged and area-averaged data are presented and discussed. The comparisons of these parameters at different elevations demonstrate the development of interfacial structure along the flow direction due to bubble interactions. (authors)

  15. Forced convective flow and heat transfer of upward cocurrent air-water slug flow in vertical plain and swirl tubes

    SciTech Connect

    Chang, Shyy Woei; Yang, Tsun Lirng

    2009-10-15

    This experimental study comparatively examined the two-phase flow structures, pressured drops and heat transfer performances for the cocurrent air-water slug flows in the vertical tubes with and without the spiky twisted tape insert. The two-phase flow structures in the plain and swirl tubes were imaged using the computerized high frame-rate videography with the Taylor bubble velocity measured. Superficial liquid Reynolds number (Re{sub L}) and air-to-water mass flow ratio (AW), which were respectively in the ranges of 4000-10000 and 0.003-0.02 were selected as the controlling parameters to specify the flow condition and derive the heat transfer correlations. Tube-wise averaged void fraction and Taylor bubble velocity were well correlated by the modified drift flux models for both plain and swirl tubes at the slug flow condition. A set of selected data obtained from the plain and swirl tubes was comparatively examined to highlight the impacts of the spiky twisted tape on the air-water interfacial structure and the pressure drop and heat transfer performances. Empirical heat transfer correlations that permitted the evaluation of individual and interdependent Re{sub L} and AW impacts on heat transfer in the developed flow regions of the plain and swirl tubes at the slug flow condition were derived. (author)

  16. Bubbly Cavitation Flows.

    DTIC Science & Technology

    1991-03-31

    and 12. Comparison is also made with analytical predictions based on the Rayleigh - Plesset equations. In addition to the single bubble studies, the...bubble maximum size distributions and those predicted using the measured nuclei number distribution and the Rayleigh - Plesset model for the bubble dyna...tions 7, 9, 11, 12, 13 examined travelling bubble cavitation on two classic axisymmetric headforms (a Schiebe body and the ITTC headform) and, with the

  17. Interfacial area transport in bubbly flow

    SciTech Connect

    Ishii, M.; Wu, Q.; Revankar, S.T.

    1997-12-31

    In order to close the two-fluid model for two-phase flow analyses, the interfacial area concentration needs to be modeled as a constitutive relation. In this study, the focus was on the investigation of the interfacial area concentration transport phenomena, both theoretically and experimentally. The interfacial area concentration transport equation for air-water bubbly up-flow in a vertical pipe was developed, and the models for the source and sink terms were provided. The necessary parameters for the experimental studies were identified, including the local time-averaged void fraction, interfacial area concentration, bubble interfacial velocity, liquid velocity and turbulent intensity. Experiments were performed with air-water mixture at atmospheric pressure. Double-sensor conductivity probe and hot-film probe were employed to measure the identified parameters. With these experimental data, the preliminary model evaluation was carried out for the simplest form of the developed interfacial area transport equation, i.e., the one-dimensional transport equation.

  18. Dynamics of surfactant sorption at the air/water interface: continuous-flow tensiometry.

    PubMed

    Svitova, T F; Wetherbee, M J; Radke, C J

    2003-05-01

    Dynamic interfacial tensiometry, gauged by axisymmetric drop shape analysis of static drops or bubbles, provides useful information on surfactant adsorption kinetics. However, the traditional pendant-drop methodology is not readily amenable to the study of desorption kinetics. Thus, the question of sorption reversibility is difficult to assess by this technique. We extend classical pendant/sessile drop dynamic tensiometry by immersing a sessile bubble in a continuously mixed optical cell. Ideal-mixed conditions are established by stirring and by constant flow through the cell. Aqueous surface-active-agent solutions are either supplied to the cell (loading) or removed from the cell by flushing with water (washout), thereby allowing study of both adsorption and desorption kinetics. Well-mixed conditions and elimination of any mass transfer resistance permit direct identification of sorption kinetic barriers to and from the external aqueous phase with time constants longer than the optical-cell residence time. The monodisperse nonionic surfactant ethoxy dodecyl alcohol (C(12)E(5)), along with cationic cetyltrimethyl ammonium bromide (CTAB) in the presence of added salt, adsorbs and desorbs instantaneously at the air/water interface. In these cases, the experimentally observed dynamic-tension curves follow the local-equilibrium model precisely for both loading and washout. Accordingly, these surfactants below their critical micelle concentrations (CMC) exhibit no detectable sorption-activation barriers on time scales of order a min. However, the sorption dynamics of dilute CTAB in the absence of electrolyte is markedly different from that in the presence of KBr. Here CTAB desorption occurs at local equilibrium, but the adsorption rate is kinetically limited, most likely due to an electrostatic barrier arising as the charged surfactant accumulates at the interface. The commercial, polydisperse nonionic surfactant ethoxy nonylphenol (NP9) loads in good agreement with

  19. Fluorescence light microscopy of pulmonary surfactant at the air-water interface of an air bubble of adjustable size.

    PubMed

    Knebel, D; Sieber, M; Reichelt, R; Galla, H-J; Amrein, M

    2002-07-01

    The structural dynamics of pulmonary surfactant was studied by epifluorescence light microscopy at the air-water interface of a bubble as a model close to nature for an alveolus. Small unilamellar vesicles of dipalmitoylphosphatidylcholine, dipalmitoylphosphatidylglycerol, a small amount of a fluorescent dipalmitoylphosphatidylcholine-analog, and surfactant-associated protein C were injected into the buffer solution. They aggregated to large clusters in the presence of Ca(2+) and adsorbed from these units to the interface. This gave rise to an interfacial film that eventually became fully condensed with dark, polygonal domains in a fluorescent matrix. When now the bubble size was increased or decreased, respectively, the film expanded or contracted. Upon expansion of the bubble, the dark areas became larger to the debit of the bright matrix and reversed upon contraction. We were able to observe single domains during the whole process. The film remained condensed, even when the interface was increased to twice its original size. From comparison with scanning force microscopy directly at the air-water interface, the fluorescent areas proved to be lipid bilayers associated with the (dark) monolayer. In the lung, such multilayer phase acts as a reservoir that guarantees a full molecular coverage of the alveolar interface during the breathing cycle and provides mechanical stability to the film.

  20. Statistical equilibrium of bubble oscillations in dilute bubbly flows

    PubMed Central

    Colonius, Tim; Hagmeijer, Rob; Ando, Keita; Brennen, Christopher E.

    2008-01-01

    The problem of predicting the moments of the distribution of bubble radius in bubbly flows is considered. The particular case where bubble oscillations occur due to a rapid (impulsive or step change) change in pressure is analyzed, and it is mathematically shown that in this case, inviscid bubble oscillations reach a stationary statistical equilibrium, whereby phase cancellations among bubbles with different sizes lead to time-invariant values of the statistics. It is also shown that at statistical equilibrium, moments of the bubble radius may be computed using the period-averaged bubble radius in place of the instantaneous one. For sufficiently broad distributions of bubble equilibrium (or initial) radius, it is demonstrated that bubble statistics reach equilibrium on a time scale that is fast compared to physical damping of bubble oscillations due to viscosity, heat transfer, and liquid compressibility. The period-averaged bubble radius may then be used to predict the slow changes in the moments caused by the damping. A benefit is that period averaging gives a much smoother integrand, and accurate statistics can be obtained by tracking as few as five bubbles from the broad distribution. The period-averaged formula may therefore prove useful in reducing computational effort in models of dilute bubbly flow wherein bubbles are forced by shock waves or other rapid pressure changes, for which, at present, the strong effects caused by a distribution in bubble size can only be accurately predicted by tracking thousands of bubbles. Some challenges associated with extending the results to more general (nonimpulsive) forcing and strong two-way coupled bubbly flows are briefly discussed. PMID:19547725

  1. Interfacial characteristic measurements in horizontal bubbly two-phase flow

    NASA Astrophysics Data System (ADS)

    Wang, Z.; Huang, W. D.; Srinivasmurthy, S.; Kocamustafaogullari, G.

    1990-10-01

    Advances in the study of two-phase flow increasingly require detailed internal structure information upon which theoretical models can be formulated. The void fraction and interfacial area are two fundamental parameters characterizing the internal structure of two-phase flow. However, little information is currently available on these parameters, and it is mostly limited to vertical flow configurations. In view of the above, the internal phase distribution of concurrent, air-water bubbly flow in a 50.3 mm diameter transparent pipeline has been experimentally investigated by using a double-sensor resistivity probe. Liquid and gas volumetric superficial velocities ranged from 3.74 to 5.60 m/s and 0.25 to 1.59 m/s, respectively, and average void fractions ranged from 2.12 to 22.5 percent. The local values of void fractions, interfacial area concentration, mean bubble diameter, bubble interface velocity, bubble chord-length and bubble frequency distributions were measured. The experimental results indicate that the void fraction interfacial area concentration and bubble frequency have local maxima near the upper pipe wall, and the profiles tend to flatten with increasing void fraction. The observed peak void fraction can reach 0.65, the peak interfacial area can go up to 900 approximately 1000 sq m/cu m, and the bubble frequency can reach a value of 2200 per s. These ranges of values have never been reported for vertical bubbly flow. It is found that either decreasing the liquid flow rate or increasing the gas flow would increase the local void fraction, the interfacial area concentration and the bubble frequency.

  2. Coalescence of protein-stabilized bubbles undergoing expansion at a simultaneously expanding planar air-water interface.

    PubMed

    Murray, Brent S; Dickinson, Eric; Lau, Cathy Ka; Nelson, Phillip V; Schmidt, Estelle

    2005-05-10

    A novel design of apparatus is described that allows observation of the coalescence stability of bubbles at a planar interface when the planar interface and the bubble surface both expand. Bubbles are introduced beneath the planar air-water interface contained within a square barrier made of perfluorocarbon rubber. The bubbles are then expanded by reducing the air pressure above the interface, while at the same time the rubber barrier is mechanically expanded, maintaining its square shape, to give the same rate and extent of expansion of the planar interface. The area can typically be increased by a factor of three over time scales as short as 0.2 s. This arrangement has been designed to mimic the behavior of aerated products when they exit from a pressurized aeration unit or product dispenser. Compared to results obtained via a previous technique, where it was only possible to expand the bubbles but not the planar interface, the bubbles are less stable. The apparatus has been used to compare the stabilizing effects of ovalbumin, beta-lactoglobulin, whey protein isolate, and sodium caseinate, in a model aqueous food system thickened with 40% invert sugar. Stability improved with increasing concentration of all the proteins and with a decrease in expansion rate, but considerable instability remained even at protein concentrations as high as 4 to 6 wt % and also at very low expansion rates, though the systems were stable in the absence of expansion. However, the stability was greatly improved by the replacement of the above proteins by the hydrocolloids gelatine or polypropylene glycol alginate. Detailed analysis revealed that the coalescence of individual bubbles in clusters of bubbles were not strongly correlated in distance or time, but larger bubbles and bubbles toward the outside of a cluster were found to be, on average, less stable than smaller bubbles and bubbles located more toward the interior of a cluster. The different degrees of stability are discussed

  3. Propagation of density disturbances in air-water flow

    NASA Technical Reports Server (NTRS)

    Nassos, G. P.

    1969-01-01

    Study investigated the behavior of density waves propagating vertically in an atmospheric pressure air-water system using a technique based on the correlation between density change and electric resistivity. This information is of interest to industries working with heat transfer systems and fluid power and control systems.

  4. Two-phase air-water stratified flow measurement using ultrasonic techniques

    SciTech Connect

    Fan, Shiwei; Yan, Tinghu; Yeung, Hoi

    2014-04-11

    In this paper, a time resolved ultrasound system was developed for investigating two-phase air-water stratified flow. The hardware of the system includes a pulsed wave transducer, a pulser/receiver, and a digital oscilloscope. The time domain cross correlation method is used to calculate the velocity profile along ultrasonic beam. The system is able to provide velocities with spatial resolution of around 1mm and the temporal resolution of 200μs. Experiments were carried out on single phase water flow and two-phase air-water stratified flow. For single phase water flow, the flow rates from ultrasound system were compared with those from electromagnetic flow (EM) meter, which showed good agreement. Then, the experiments were conducted on two-phase air-water stratified flow and the results were given. Compared with liquid height measurement from conductance probe, it indicated that the measured velocities were explainable.

  5. Numerical and experimental study of dissociation in an air-water single-bubble sonoluminescence system.

    PubMed

    Puente, Gabriela F; Urteaga, Raúl; Bonetto, Fabián J

    2005-10-01

    We performed a comprehensive numerical and experimental analysis of dissociation effects in an air bubble in water acoustically levitated in a spherical resonator. Our numerical approach is based on suitable models for the different effects considered. We compared model predictions with experimental results obtained in our laboratory in the whole phase parameter space, for acoustic pressures from the bubble dissolution limit up to bubble extinction. The effects were taken into account simultaneously to consider the transition from nonsonoluminescence to sonoluminescence bubbles. The model includes (1) inside the bubble, transient and spatially nonuniform heat transfer using a collocation points method, dissociation of O2 and N2, and mass diffusion of vapor in the noncondensable gases; (2) at the bubble interface, nonequilibrium evaporation and condensation of water and a temperature jump due to the accommodation coefficient; (3) in the liquid, transient and spatially nonuniform heat transfer using a collocation points method, and mass diffusion of the gas in the liquid. The model is completed with a Rayleigh-Plesset equation with liquid compressible terms and vapor mass transfer. We computed the boundary for the shape instability based on the temporal evolution of the computed radius. The model is valid for an arbitrary number of dissociable gases dissolved in the liquid. We also obtained absolute measurements for R(t) using two photodetectors and Mie scattering calculations. The robust technique used allows the estimation of experimental results of absolute R0 and P(a). The technique is based on identifying the bubble dissolution limit coincident with the parametric instability in (P(a),R0) parameter space. We take advantage of the fact that this point can be determined experimentally with high precision and replicability. We computed the equilibrium concentration of the different gaseous species and water vapor during collapse as a function of P(a) and R0. The

  6. Numerical and experimental study of dissociation in an air-water single-bubble sonoluminescence system

    NASA Astrophysics Data System (ADS)

    Puente, Gabriela F.; Urteaga, Raúl; Bonetto, Fabián J.

    2005-10-01

    We performed a comprehensive numerical and experimental analysis of dissociation effects in an air bubble in water acoustically levitated in a spherical resonator. Our numerical approach is based on suitable models for the different effects considered. We compared model predictions with experimental results obtained in our laboratory in the whole phase parameter space, for acoustic pressures from the bubble dissolution limit up to bubble extinction. The effects were taken into account simultaneously to consider the transition from nonsonoluminescence to sonoluminescence bubbles. The model includes (1) inside the bubble, transient and spatially nonuniform heat transfer using a collocation points method, dissociation of O2 and N2 , and mass diffusion of vapor in the noncondensable gases; (2) at the bubble interface, nonequilibrium evaporation and condensation of water and a temperature jump due to the accommodation coefficient; (3) in the liquid, transient and spatially nonuniform heat transfer using a collocation points method, and mass diffusion of the gas in the liquid. The model is completed with a Rayleigh-Plesset equation with liquid compressible terms and vapor mass transfer. We computed the boundary for the shape instability based on the temporal evolution of the computed radius. The model is valid for an arbitrary number of dissociable gases dissolved in the liquid. We also obtained absolute measurements for R(t) using two photodetectors and Mie scattering calculations. The robust technique used allows the estimation of experimental results of absolute R0 and Pa . The technique is based on identifying the bubble dissolution limit coincident with the parametric instability in (Pa,R0) parameter space. We take advantage of the fact that this point can be determined experimentally with high precision and replicability. We computed the equilibrium concentration of the different gaseous species and water vapor during collapse as a function of Pa and R0 . The model

  7. Gravity driven flows of bubble suspensions.

    NASA Astrophysics Data System (ADS)

    Zenit, Roberto; Koch, Donald L.; Sangani, Ashok K.

    1999-11-01

    Experiments on vertical and inclined channels were performed to study the behavior of a mono-dispersed bubble suspension for which the dual limit of large Reynolds number and small Weber number is satisfied. A uniform stream of 1.5 mm diameter bubbles is produced by a bank of identical capillaries and coalescence is inhibited by addition of salt to the water. Measurements of the liquid velocity and bubble-probe collision rate are obtained with a hot wire anemometer. The gas volume fraction, bubble velocity, velocity variance and chord length are measured using a dual impedance probe. Image analysis is used to quantify the distributions of bubble size and aspect ratio. For vertical channels the bubble velocity is observed to decrease as the bubble concentration increases in accord with the predictions of Spelt and Sangani (1998). The bubble velocity variance arises largely due to bubble-wall and bubble-bubble collisions. For inclined channels, the strength of the shear flow is controlled by the extent of bubble segregation and the effective viscosity of the bubble phase. The measurements are compared with solutions of the averaged equations of motion for a range of gas volume fractions and channel inclination angles.

  8. Viscoelastic Drag Forces and Crossover from No-Slip to Slip Boundary Conditions for Flow near Air-Water Interfaces

    NASA Astrophysics Data System (ADS)

    Maali, A.; Boisgard, R.; Chraibi, H.; Zhang, Z.; Kellay, H.; Würger, A.

    2017-02-01

    The "free" water surface is generally prone to contamination with surface impurities, be they surfactants, particles, or other surface active agents. The presence of such impurities can modify flow near such interfaces in a drastic manner. Here we show that vibrating a small sphere mounted on an atomic force microscope cantilever near a gas bubble immersed in water is an excellent probe of surface contamination. Both viscous and elastic forces are exerted by an air-water interface on the vibrating sphere even when very low doses of contaminants are present. The viscous drag forces show a crossover from no-slip to slip boundary conditions while the elastic forces show a nontrivial variation as the vibration frequency changes. We provide a simple model to rationalize these results and propose a simple way of evaluating the concentration of such surface impurities.

  9. Effects of flow on insulin fibril formation at an air/water interface

    NASA Astrophysics Data System (ADS)

    Posada, David; Heldt, Caryn; Sorci, Mirco; Belfort, Georges; Hirsa, Amir

    2009-11-01

    The amyloid fibril formation process, which is implicated in several diseases such as Alzheimer's and Huntington's, is characterized by the conversion of monomers to oligomers and then to fibrils. Besides well-studied factors such as pH, temperature and concentration, the kinetics of this process are significantly influenced by the presence of solid or fluid interfaces and by flow. By studying the nucleation and growth of a model system (insulin fibrils) in a well-defined flow field with an air/water interface, we can identify the flow conditions that impact protein aggregation kinetics both in the bulk solution and at the air/water interface. The present flow system (deep-channel surface viscometer) consists of an annular region bounded by stationary inner and outer cylinders, an air/water interface, and a floor driven at constant rotation. We show the effects of Reynolds number on the kinetics of the fibrillation process both in the bulk solution and at the air/water interface, as well as on the structure of the resultant amyloid aggregates.

  10. Buoyancy Driven Shear Flows of Bubble Suspensions

    NASA Astrophysics Data System (ADS)

    Hill, R. J.; Zenit, R.; Chellppannair, T.; Koch, D. L.; Spelt, P. D. M.; Sangani, A.

    1998-11-01

    In this work the gas volume fraction and the root-mean-squared fluid velocity are measured in buoyancy driven shear flows of bubble suspensions in a tall, inclined, rectangular channel. The experiments are performed under conditions where We << 1 and Re >> 1 , so that the bubbles are relatively undeformed and the flow is inviscid and approximately irrotational. Nitrogen is introduced through an array of capillaries at the base of a .2x.02x2 m channel filled with an aqueous electrolyte solution (0.06 molL-1 MgSO_4). The rising bubbles generate a unidirectional shear flow, where the denser suspension at the lower surface of the channel falls, while the less dense suspension at the upper surface rises. Hot-film anemometry is used to measure the resulting gas volume fraction and fluid velocity profiles. The bubble collision rate with the sensor is related to the gas volume fraction and the mean and variance of the bubble velocity using an experimentally measured collision surface area for the sensor. Bubble collisions with the sensor are identified by the characteristic slope of the hot-film anemometer signal when bubbles collide with the sensor. It is observed that the steady shear flow develops a bubble phase pressure gradient across the channel gap as the bubbles interchange momentum through direct collisions. The discrete phase presssure gradient balances the buoyancy force driving bubbles toward the upper surface resulting in a steady void fraction profile across the gap width. The strength of the shear flow is controlled by the extent of bubble segregation and by the effective viscosity of the bubble phase. The measurements are compared with solutions of the averaged equations of motion (Kang et al. 1997; Spelt and Sangani, 1998), for a range of gas volume fractions and channel inclination angles.

  11. Measurement of air distribution and void fraction of an upwards air-water flow using electrical resistance tomography and a wire-mesh sensor

    NASA Astrophysics Data System (ADS)

    Olerni, Claudio; Jia, Jiabin; Wang, Mi

    2013-03-01

    Measurements on an upwards air-water flow are reported that were obtained simultaneously with a dual-plane electrical resistance tomograph (ERT) and a wire-mesh sensor (WMS). The ultimate measurement target of both ERT and WMS is the same, the electrical conductivity of the medium. The ERT is a non-intrusive device whereas the WMS requires a net of wires that physically crosses the flow. This paper presents comparisons between the results obtained simultaneously from the ERT and the WMS for evaluation and calibration of the ERT. The length of the vertical testing pipeline section is 3 m with an internal diameter of 50 mm. Two distinct sets of air-water flow rate scenarios, bubble and slug regimes, were produced in the experiments. The fast impedance camera ERT recorded the data at an approximate time resolution of 896 frames per second (fps) per plane in contrast with the 1024 fps of the wire-mesh sensor WMS200. The set-up of the experiment was based on well established knowledge of air-water upwards flow, particularly the specific flow regimes and wall peak effects. The local air void fraction profiles and the overall air void fraction were produced from two systems to establish consistency for comparison of the data accuracy. Conventional bulk flow measurements in air mass and electromagnetic flow metering, as well as pressure and temperature, were employed, which brought the necessary calibration to the flow measurements. The results show that the profiles generated from the two systems have a certain level of inconsistency, particularly in a wall peak and a core peak from the ERT and WMS respectively, whereas the two tomography instruments achieve good agreement on the overall air void fraction for bubble flow. For slug flow, when the void fraction is over 30%, the ERT underestimates the void fraction, but a linear relation between ERT and WMS is still observed.

  12. Bubble Generation in a Continuous Liquid Flow Under Reduced Gravity Conditions

    NASA Technical Reports Server (NTRS)

    Pais, Salvatore Cezar

    1999-01-01

    The present work reports a study of bubble generation under reduced gravity conditions for both co-flow and cross-flow configurations. Experiments were performed aboard the DC-9 Reduced Gravity Aircraft at NASA Glenn Research Center, using an air-water system. Three different flow tube diameters were used: 1.27, 1.9, and 2.54 cm. Two different ratios of air injection nozzle to tube diameters were considered: 0.1 and 0.2. Gas and liquid volumetric flow rates were varied from 10 to 200 ml/s. It was experimentally observed that with increasing superficial liquid velocity, the bubbles generated decreased in size. The bubble diameter was shown to increase with increasing air injection nozzle diameters. As the tube diameter was increased, the size of the detached bubbles increased. Likewise, as the superficial liquid velocity was increased, the frequency of bubble formation increased and thus the time to detach forming bubbles decreased. Independent of the flow configuration (for either single nozzle or multiple nozzle gas injection), void fraction and hence flow regime transition can be controlled in a somewhat precise manner by solely varying the gas and liquid volumetric flow rates. On the other hand, it is observed that uniformity of bubble size can be controlled more accurately by using single nozzle gas injection than by using multiple port injection, since this latter system gives rise to unpredictable coalescence of adjacent bubbles. A theoretical model, based on an overall force balance, is employed to study single bubble generation in the dynamic and bubbly flow regime. Under conditions of reduced gravity, the gas momentum flux enhances bubble detachment; however, the surface tension forces at the nozzle tip inhibits bubble detachment. Liquid drag and inertia can act either as attaching or detaching force, depending on the relative velocity of the bubble with respect to the surrounding liquid. Predictions of the theoretical model compare well with performed

  13. Drag reductions and the air-water interface stability of superhydrophobic surfaces in rectangular channel flow

    NASA Astrophysics Data System (ADS)

    Zhang, Jingxian; Yao, Zhaohui; Hao, Pengfei

    2016-11-01

    Flow in a rectangular channel with superhydrophobic (SH) top and bottom walls was investigated experimentally. Different SH surfaces, including hierarchical structured surfaces and surfaces with different micropost sizes (width and spacing) but the same solid fraction, were fabricated and measured. Pressure loss and flow rate in the channel with SH top and bottom walls were measured, with Reynolds number changing from 700 to 4700, and the corresponding friction factor for the SH surface was calculated. The statuses of the air plastron on different SH surfaces were observed during the experiment. In our experiment, compared with the experiment for the smooth surface, drag reductions were observed for all SH surfaces, with the largest drag reduction of 42.2%. It was found that the hierarchy of the microstructure can increase the drag reduction by decreasing the solid fraction and enhancing the stability of the air-water interface. With a fixed solid fraction, the drag reduction decreases as the post size (width and spacing) increases, due to the increasing curvature and instability effects of the air-water interface. A correlation parameter between the contact angle hysteresis, the air-water interface stability, and the drag reduction of the SH surfaces was found.

  14. Drag reductions and the air-water interface stability of superhydrophobic surfaces in rectangular channel flow.

    PubMed

    Zhang, Jingxian; Yao, Zhaohui; Hao, Pengfei

    2016-11-01

    Flow in a rectangular channel with superhydrophobic (SH) top and bottom walls was investigated experimentally. Different SH surfaces, including hierarchical structured surfaces and surfaces with different micropost sizes (width and spacing) but the same solid fraction, were fabricated and measured. Pressure loss and flow rate in the channel with SH top and bottom walls were measured, with Reynolds number changing from 700 to 4700, and the corresponding friction factor for the SH surface was calculated. The statuses of the air plastron on different SH surfaces were observed during the experiment. In our experiment, compared with the experiment for the smooth surface, drag reductions were observed for all SH surfaces, with the largest drag reduction of 42.2%. It was found that the hierarchy of the microstructure can increase the drag reduction by decreasing the solid fraction and enhancing the stability of the air-water interface. With a fixed solid fraction, the drag reduction decreases as the post size (width and spacing) increases, due to the increasing curvature and instability effects of the air-water interface. A correlation parameter between the contact angle hysteresis, the air-water interface stability, and the drag reduction of the SH surfaces was found.

  15. Air-water two-phase flow in a 3-mm horizontal tube

    NASA Astrophysics Data System (ADS)

    Chen, Ing Youn; Chang, Yu-Juei; Wang, Chi-Chung

    2000-01-01

    Two-phase flow pattern and friction characteristics for air-water flow in a 3.17 mm smooth tube are reported in this study. The range of air-water mass flux is between 50 to 700 kg/m2.s and gas quality is between 0.0001 to 0.9. The pressure drop data are analyzed using the concept of the two-phase frictional multipliers and the Martinelli parameter. Experimental data show that the two-phase friction multipliers are strongly related to the flow pattern. Taitel & Dukler flow regime map fails to predict the stratified flow pattern data. Their transition lines between annular-wavy and annular-intermittent give fair agreement with data. A modified correlation from Klimenko and Fyodoros criterion is able to distinguish the annular and stratified data. For two-phase flow in small tubes, the effect of surface tension force should be significantly present as compared to gravitational force. The tested empirical frictional correlations couldn't predict the pressure drop in small tubes for various working fluids. It is suggested to correlate a reliable frictional multiplier for small horizontal tubes from a large database of various working fluids, and to develop the flow pattern dependent models for the prediction of two-phase pressure drop in small tubes. .

  16. Buoyancy Driven Shear Flows of Bubble Suspensions

    NASA Technical Reports Server (NTRS)

    Koch, D. L.; Hill, R. J.; Chellppannair, T.; Zenit, R.; Zenit, R.; Spelt, P. D. M.

    1999-01-01

    In this work the gas volume fraction and the root-mean-squared fluid velocity are measured in buoyancy driven shear flows of bubble suspensions in a tall, inclined, rectangular channel. The experiments are performed under conditions where We << 1a nd Re >> 1, for which comparisons are made with kinetic theory and numerical simulations. Here Re = gamma(a(exp 2)/nu is the Reynolds number and We = rho(gamma(exp 2))a(exp 3)/sigma is the Weber number; gamma is the shear rate, a is the bubble radius, nu is the kinematic viscosity of the liquid, rho is the density of the liquid, and sigma is the surface tension of the gas/liquid interface. Kang et al. calculated the bubble phase pressure and velocity variance of sheared bubble suspensions under conditions where the bubbles are spherical and the liquid phase velocity field can be approximated using potential flow theory, i.e. We= 0 and Re >> 1. Such conditions can be achieved in an experiment using gas bubbles, with a radius of O(0.5mm), in water. The theory requires that there be no average relative motion of the gas and liquid phases, hence the motivation for an experimental program in microgravity. The necessity of performing preliminary, Earth based experiments, however, requires performing experiments where the gas phase rises in the liquid, which significantly complicates the comparison of experiments with theory. Rather than comparing experimental results with theory for a uniform, homogeneous shear flow, experiments can be compared directly with solutions of the averaged equations of motion for bubble suspensions. This requires accounting for the significant lift force acting on the gas phase when the bubbles rise parallel to the average velocity of the sheared suspension. Shear flows can be produced in which the bubble phase pressure gradient, arising from shear induced collisions amongst the bubbles, balances a body force (centrifugal or gravitational) on the gas phase. A steady, non-uniform gas volume fraction

  17. A criterion for the onset of slugging in horizontal stratified air-water countercurrent flow

    SciTech Connect

    Chun, Moon-Hyun; Lee, Byung-Ryung; Kim, Yang-Seok

    1995-09-01

    This paper presents an experimental and theoretical investigation of wave height and transition criterion from wavy to slug flow in horizontal air-water countercurrent stratified flow conditions. A theoretical formula for the wave height in a stratified wavy flow regime has been developed using the concept of total energy balance over a wave crest to consider the shear stress acting on the interface of two fluids. From the limiting condition of the formula for the wave height, a necessary criterion for transition from a stratified wavy flow to a slug flow has been derived. A series of experiments have been conducted changing the non-dimensional water depth and the flow rates of air in a horizontal pipe and a duct. Comparisons between the measured data and the predictions of the present theory show that the agreement is within {plus_minus}8%.

  18. Time-resolved fast-neutron radiography of air-water two-phase flows in a rectangular channel by an improved detection system

    SciTech Connect

    Zboray, Robert; Dangendorf, Volker; Bromberger, Benjamin; Tittelmeier, Kai; Mor, Ilan

    2015-07-15

    In a previous work, we have demonstrated the feasibility of high-frame-rate, fast-neutron radiography of generic air-water two-phase flows in a 1.5 cm thick, rectangular flow channel. The experiments have been carried out at the high-intensity, white-beam facility of the Physikalisch-Technische Bundesanstalt, Germany, using an multi-frame, time-resolved detector developed for fast neutron resonance radiography. The results were however not fully optimal and therefore we have decided to modify the detector and optimize it for the given application, which is described in the present work. Furthermore, we managed to improve the image post-processing methodology and the noise suppression. Using the tailored detector and the improved post-processing, significant increase in the image quality and an order of magnitude lower exposure times, down to 3.33 ms, have been achieved with minimized motion artifacts. Similar to the previous study, different two-phase flow regimes such as bubbly slug and churn flows have been examined. The enhanced imaging quality enables an improved prediction of two-phase flow parameters like the instantaneous volumetric gas fraction, bubble size, and bubble velocities. Instantaneous velocity fields around the gas enclosures can also be more robustly predicted using optical flow methods as previously.

  19. Gas transfer in a bubbly wake flow

    NASA Astrophysics Data System (ADS)

    Karn, A.; Gulliver, J. S.; Monson, G. M.; Ellis, C.; Arndt, R. E. A.; Hong, J.

    2016-05-01

    The present work reports simultaneous bubble size and gas transfer measurements in a bubbly wake flow of a hydrofoil, designed to be similar to a hydroturbine blade. Bubble size was measured by a shadow imaging technique and found to have a Sauter mean diameter of 0.9 mm for a reference case. A lower gas flow rate, greater liquid velocities, and a larger angle of attack all resulted in an increased number of small size bubbles and a reduced weighted mean bubble size. Bubble-water gas transfer is measured by the disturbed equilibrium technique. The gas transfer model of Azbel (1981) is utilized to characterize the liquid film coefficient for gas transfer, with one scaling coefficient to reflect the fact that characteristic turbulent velocity is replaced by cross-sectional mean velocity. The coefficient was found to stay constant at a particular hydrofoil configuration while it varied within a narrow range of 0.52-0.60 for different gas/water flow conditions.

  20. Micro-bubbles seeding for flow characterization

    NASA Astrophysics Data System (ADS)

    Aumelas, V.; Lecoffre, Y.; Maj, G.; Franc, J.-P.

    2016-11-01

    Micro-bubbles injection has long been used in hydrodynamic facilities for the control of dissolved and free air. In some cavitation tunnels [9], very large quantities of microbubbles (billions per second) are injected for rapid degassing and, in smaller quantities (millions per second), for cavitation nuclei seeding. Micro-bubbles can also be used as tracers for optical measurements including visualization, LDV or PIV. For these applications, bubbles must be sufficiently small to faithfully follow the flow. Depending on the quality and spatial characteristics of the micro-bubbles seeding, several optical methods can be applied: simple visualization gives access to semi-quantitative information on the behaviour of flows; LASER velocimetry provides information on the mean velocity and other temporal local characteristics of the flow. This paper presents some new micro-bubbles seeding devices recently developed by YLEC Consultants. These devices have been designed to fulfill specific requirements related to integration into cavitation tunnels and permit optical velocimetry measurement techniques such as Particle Image Velocimetry (PIV). The LEGI cavitation tunnel is the first tunnel which has been equipped with these microbubbles seeding systems dedicated to optical velocimetry. This paper presents the final integration schemes selected for micro-bubbles seeding into LEGI tunnel and discuss about practical concerns related to the use of the injection system for optical velocimetry.

  1. Interfacial Area Transport of Vertical Upward Bubbly Flow in an Annulus

    SciTech Connect

    Takashi Hibiki; Ye Mi; Rong Situ; Mamoru Ishii; Michitsugu Mori

    2002-07-01

    In relation to the development of the interfacial area transport equation, hydrodynamic separate tests without phase change were performed in an adiabatic air-water bubbly flow in a vertical annulus to identify the effect of bubble coalescence and breakup on the interfacial area transport. A total of 20 data sets on axial developments of local void fraction, interfacial area concentration, and interfacial velocity were acquired by using the double-sensor conductivity probe method in an extensive bubbly flow region. The detailed discussion was given for the mechanism of the axial development of the local flow parameters. The one-dimensional interfacial area transport equation could reproduce proper trends of the interfacial area concentration change along the flow direction and good agreement between predicted and measured interfacial area concentration was obtained with an average relative deviation of {+-}8.96 %. (authors)

  2. Bubble transport in subcooled flow boiling

    NASA Astrophysics Data System (ADS)

    Owoeye, Eyitayo James

    Understanding the behavior of bubbles in subcooled flow boiling is important for optimum design and safety in several industrial applications. Bubble dynamics involve a complex combination of multiphase flow, heat transfer, and turbulence. When a vapor bubble is nucleated on a vertical heated wall, it typically slides and grows along the wall until it detaches into the bulk liquid. The bubble transfers heat from the wall into the subcooled liquid during this process. Effective control of this transport phenomenon is important for nuclear reactor cooling and requires the study of interfacial heat and mass transfer in a turbulent flow. Three approaches are commonly used in computational analysis of two-phase flow: Eulerian-Lagrangian, Eulerian-Eulerian, and interface tracking methods. The Eulerian- Lagrangian model assumes a spherical non-deformable bubble in a homogeneous domain. The Eulerian-Eulerian model solves separate conservation equations for each phase using averaging and closure laws. The interface tracking method solves a single set of conservation equations with the interfacial properties computed from the properties of both phases. It is less computationally expensive and does not require empirical relations at the fluid interface. Among the most established interface tracking techniques is the volume-of-fluid (VOF) method. VOF is accurate, conserves mass, captures topology changes, and permits sharp interfaces. This work involves the behavior of vapor bubbles in upward subcooled flow boiling. Both laminar and turbulent flow conditions are considered with corresponding pipe Reynolds number of 0 -- 410,000 using a large eddy simulation (LES) turbulence model and VOF interface tracking method. The study was performed at operating conditions that cover those of boiling water reactors (BWR) and pressurized water reactors (PWR). The analysis focused on the life cycle of vapor bubble after departing from its nucleation site, i.e. growth, slide, lift-off, rise

  3. Velocity and phase distribution measurements in vertical air-water annular flows

    SciTech Connect

    Vassallo, P.

    1997-07-01

    Annular flow topology for three air-water conditions in a vertical duct is investigated through the use of a traversing double-sensor hot-film anemometry probe and differential pressure measurements. Near wall measurements of mean and fluctuating velocities, as well as local void fraction, are taken in the liquid film, with the highest turbulent fluctuations occurring for the flow condition with the largest pressure drop. A modified law-of-the-wall formulation for wall shear is presented which, using near wall values of mean velocity and kinetic energy, agrees reasonably well with the average stress obtained from direct pressure drop measurements. The linear profile using wall coordinates in the logarithmic layer is preserved in annular flow; however, the slope and intercept of the profile differ from the single-phase values for the annular flow condition which has a thicker, more turbulent, liquid film.

  4. Air/water two-phase flow test tunnel for airfoil studies

    NASA Astrophysics Data System (ADS)

    Ohashi, H.; Matsumoto, Y.; Ichikawa, Y.; Tsukiyama, T.

    1990-02-01

    A test tunnel for the study of airfoil performances under air/water two-phase flow condition has been designed and constructed. This facility will serve for a better understanding of the flow phenomena and characteristics of hydraulic machinery under gas/ liquid two-phase flow operating conditions. At the test section of the tunnel, a two-dimensional isolated airfoil or a cascade of airfoils is installed in a two-phase inlet flow with a uniform velocity (up to 10 m/s) and void fraction (up to 12%) distribution. The details of the tunnel structure and the measuring systems are described and the basic characteristics of the constructed tunnel are also given. As an example of the test results, void fraction distribution around a test airfoil is shown.

  5. Air/water two-phase flow test tunnel for airfoil studies

    NASA Astrophysics Data System (ADS)

    Ohashi, H.; Matsumoto, Y.; Ichikawa, Y.; Tsukiyama, T.

    1994-01-01

    A test tunnel for the study of airfoil performances under air/water two-phase flow condition has been designed and constructed. This facility will serve for a better understanding of the flow phenomena and characteristics of hydraulic machinery under gas/ liquid two-phase flow operating conditions. At the test section of the tunnel, a two-dimensional isolated airfoil or a cascade of airfoils is installed in a two-phase inlet flow with a uniform velocity (up to 10 m/s) and void fraction (up to 12%) distribution. The details of the tunnel structure and the measuring systems are described and the basic characteristics of the constructed tunnel are also given. As an example of the test results, void fraction distribution around a test airfoil is shown.

  6. An investigation of channel flow with a smooth air-water interface

    NASA Astrophysics Data System (ADS)

    Madad, Reza; Elsnab, John; Chin, Cheng; Klewicki, Joseph; Marusic, Ivan

    2015-06-01

    Experiments and numerical simulation are used to investigate fully developed laminar and turbulent channel flow with an air-water interface as the lower boundary condition. Laser Doppler velocimetry measurements of streamwise and wall-normal velocity components are made over a range of Reynolds number based upon channel height and bulk velocity from 1100 to 4300, which encompasses the laminar, transitional and low Reynolds numbers turbulent regimes. The results show that the airflow statistics near the stationary wall are not significantly altered by the air-water moving interface and reflect those found in channel flows. The mean statistics on the water interface side largely exhibit results similar to simulated Poiseuille-Couette flow (PCF) with a solid moving wall. For second-order statistics, however, the simulation and experimental results show some discrepancies near the moving water surface, suggesting that a full two-phase simulation is required. A momentum and energy transport tubes analysis is investigated for laminar and turbulent PCFs. This analysis builds upon the classical notion of a streamtube and indicates that part of the energy from the pressure gradient is transported towards the stationary wall and is dissipated as heat inside the energy tubes, while the remainder is transmitted to the moving wall. For the experiments, the airflow energy is transmitted towards the water to overcome the drag force and drive the water forward; therefore, the amount of energy transferred to the water is higher than the energy transferred to a solid moving wall.

  7. Measurement of the Shear Lift Force on a Bubble in a Channel Flow

    NASA Technical Reports Server (NTRS)

    Nahra, Henry K.; Motil, Brian; Skor, Mark

    2005-01-01

    Two-phase flow systems play vital roles in the design of some current and anticipated space applications of two-phase systems which include: thermal management systems, transfer line flow in cryogenic storage, space nuclear power facilities, design and operation of thermal bus, life support systems, propulsion systems, In Situ Resource Utilization (ISRU), and space processes for pharmaceutical applications. The design of two-phase flow systems for space applications requires a clear knowledge of the behaviors of the dispersed phase (bubble), its interaction with the continuous phase (liquid) and its effect on heat and mass transfer processes, The need to understand the bubble generation process arises from the fact that for all space applications, the size and distribution of bubbles are extremely crucial for heat and mass transfer control. One important force in two-phase flow systems is the lift force on a bubble or particle in a liquid shear flow. The shear lift is usually overwhelmed by buoyancy in normal gravity, but it becomes an important force in reduced gravity. Since the liquid flow is usually sheared because of the confining wall, the trajectories of bubbles and particles injected into the liquid flow are affected by the shear lift in reduced gravity. A series of experiments are performed to investigate the lift force on a bubble in a liquid shear flow and its effect on the detachment of a bubble from a wall under low gravity conditions. Experiments are executed in a Poiseuille flow in a channel. An air-water system is used in these experiments that are performed in the 2.2 second drop tower. A bubble is injected into the shear flow from a small injector and the shear lift is measured while the bubble is held stationary relative to the fluid. The trajectory of the bubble prior, during and after its detachment from the injector is investigated. The measured shear lift force is calculated from the trajectory of the bubble at the detachment point. These

  8. Probing Effect of Salinity and pH on Surface Interactions between Air Bubbles and Hydrophobic Solids: Implications on Colloidal Assembly at Air/Water Interface.

    PubMed

    Cui, Xin; Shi, Chen; Zhang, Shuo; Xie, Lei; Liu, Jing; Jiang, Dazhi; Zeng, Hongbo

    2017-04-05

    In this work, bubble probe atomic force microscope (AFM) was employed to quantify the interactions between two air bubbles and between an air bubble and an octadecyltrichlorosilane (OTS)-hydrophobized mica under various aqueous conditions. The key parameters (e.g. surface potentials, decay length of hydrophobic attraction) were obtained by analyzing the measured forces through a theoretical model based on Reynolds lubrication theory and augmented Young-Laplace equation by including effect of disjoining pressure. The bubble-OTS hydrophobic attraction with a decay length of 1.0 nm was found to be independent of solution pH and salinity. These parameters were further used to predict the attachment of OTS-hydrophobized particles onto air/water interface, demonstrating that particle attachment driven by hydrophobic attraction could be facilitated by suppressing electrical double-layer repulsion at low pH or high salinity condition. This facile methodology can be readily extended to quantify interactions of many other colloidal particles with gas/water and oil/water interfaces, with implications on colloidal assembly at different interfaces in many engineering applications.

  9. Bubble Eliminator Based on Centrifugal Flow

    NASA Technical Reports Server (NTRS)

    Gonda, Steve R.; Tsao, Yow-Min D.; Lee, Wenshan

    2004-01-01

    The fluid bubble eliminator (FBE) is a device that removes gas bubbles from a flowing liquid. The FBE contains no moving parts and does not require any power input beyond that needed to pump the liquid. In the FBE, the buoyant force for separating the gas from the liquid is provided by a radial pressure gradient associated with a centrifugal flow of the liquid and any entrained bubbles. A device based on a similar principle is described in Centrifugal Adsorption Cartridge System (MSC- 22863), which appears on page 48 of this issue. The FBE was originally intended for use in filtering bubbles out of a liquid flowing relatively slowly in a bioreactor system in microgravity. Versions that operate in normal Earth gravitation at greater flow speeds may also be feasible. The FBE (see figure) is constructed as a cartridge that includes two concentric cylinders with flanges at the ends. The outer cylinder is an impermeable housing; the inner cylinder comprises a gas-permeable, liquid-impermeable membrane covering a perforated inner tube. Multiple spiral disks that collectively constitute a spiral ramp are mounted in the space between the inner and outer cylinders. The liquid enters the FBE through an end flange, flows in the annular space between the cylinders, and leaves through the opposite end flange. The spiral disks channel the liquid into a spiral flow, the circumferential component of which gives rise to the desired centrifugal effect. The resulting radial pressure gradient forces the bubbles radially inward; that is, toward the inner cylinder. At the inner cylinder, the gas-permeable, liquid-impermeable membrane allows the bubbles to enter the perforated inner tube while keeping the liquid in the space between the inner and outer cylinders. The gas thus collected can be vented via an endflange connection to the inner tube. The centripetal acceleration (and thus the radial pressure gradient) is approximately proportional to the square of the flow speed and

  10. On the stability of an accelerated coupled air-water flow.

    NASA Astrophysics Data System (ADS)

    Veron, Fabrice; Ierley, Glenn; Melville, W. Kendall

    2000-11-01

    We present the results of a study of the stability of the interface of an accelerated coupled air-water flow. We develop a general solution of the two-layer, laminar parallel flow driven by a pressure gradient in the air. The velocity profiles in both fluids are given by analytical functions for pressure gradients that can be represented as power series in time. The stability of the coupled flow is then examined by solving the two layer Orr-Sommerfeld equations allowing for linear displacements of the interface. In the simple case of the linearly accelerating flow, we find that the flow is always stable for an air velocity below 0.6 m s-1. Instabilities first appear in the form of surface waves with a phase speed of approximately 30 cm s-1 and a wavenumber of O(1) cm-1. In cases when the flow in the air is turbulent, and represented by a continuously differentiable analytical approximation of the log-linear mean velocity profile, we find that the flow is rapidly unstable to surface waves. Comparisons are made with the previous computations of Kawai (1979) and Wheless and Csanady (1993), and with the measurements of Veron and Melville (2000).

  11. Bubble Generation in a Flowing Liquid Medium and Resulting Two-Phase Flow in Microgravity

    NASA Technical Reports Server (NTRS)

    Pais, S. C.; Kamotani, Y.; Bhunia, A.; Ostrach, S.

    1999-01-01

    The present investigation reports a study of bubble generation under reduced gravity conditions, using both a co-flow and a cross-flow configuration. This study may be used in the conceptual design of a space-based thermal management system. Ensuing two-phase flow void fraction can be accurately monitored using a single nozzle gas injection system within a continuous liquid flow conduit, as utilized in the present investigation. Accurate monitoring of void fraction leads to precise control of heat and mass transfer coefficients related to a thermal management system; hence providing an efficient and highly effective means of removing heat aboard spacecraft or space stations. Our experiments are performed in parabolic flight aboard the modified DC-9 Reduced Gravity Research Aircraft at NASA Lewis Research Center, using an air-water system. For the purpose of bubble dispersion in a flowing liquid, we use both a co-flow and a cross-flow configuration. In the co-flow geometry, air is introduced through a nozzle in the same direction with the liquid flow. On the other hand, in the cross-flow configuration, air is injected perpendicular to the direction of water flow, via a nozzle protruding inside the two-phase flow conduit. Three different flow conduit (pipe) diameters are used, namely, 1.27 cm, 1.9 cm and 2.54 cm. Two different ratios of nozzle to pipe diameter (D(sub N))sup * are considered, namely (D(sub N))sup * = 0.1 and 0.2, while superficial liquid velocities are varied from 8 to 70 cm/s depending on flow conduit diameter. It is experimentally observed that by holding all other flow conditions and geometry constant, generated bubbles decrease in size with increase in superficial liquid velocity. Detached bubble diameter is shown to increase with air injection nozzle diameter. Likewise, generated bubbles grow in size with increasing pipe diameter. Along the same lines, it is shown that bubble frequency of formation increases and hence the time to detachment of a

  12. Interfacial area transport equation for bubbly to cap-bubbly transition flows

    NASA Astrophysics Data System (ADS)

    Worosz, Theodore S.

    To fully realize the benefit of the two-group interfacial area transport equation (IATE) as a constitutive model for the interfacial area concentration in the two-fluid model, it is imperative that models be developed to dynamically transition from one-group to two-group flows. With this in mind, the two-group IATE is derived in detail to establish new expansion source terms that correctly account for the effects of intergroup bubble transport. In addition to this theoretical effort, the state-of-the-art four-sensor conductivity probe is used to establish a reliable experimental database of local two-phase flow parameters to characterize one-group to two-group transition flows and to support model development. The experiments are performed in verticalupward air-water two-phase flow in a 5.08cm pipe. Additionally, the local conductivity probe is improved through systematic studies into: 1) signal "ghosting" electrical interference among probe sensors, 2) sampling frequency sensitivity, 3) measurement duration sensitivity, and 4) probe sensor orientation. Wake-dominated bubble transport characterizes the transition from onegroup to two-group flows. Therefore, the necessary intergroup and intragroup wake entrainment source terms that are required for two-group interfacial area transport in transition flows are developed. Furthermore, an approach is developed to initiate the shearing-off source and reduce the one-group interaction mechanisms as an established two-group flow develops. The new interfacial area transport model for one-group to two-group transition flows is evaluated against the experimental database. The model accurately captures the exchange of void fraction and interfacial area concentration between group-I and group-II in transition flows. Overall, the group-I void fraction and interfacial area concentration are predicted within +/-6% and +/-4%, respectively, of the experimental data. The group-II void fraction and interfacial area concentration are

  13. Bifurcations of a creeping air-water flow in a conical container

    NASA Astrophysics Data System (ADS)

    Balci, Adnan; Brøns, Morten; Herrada, Miguel A.; Shtern, Vladimir N.

    2016-10-01

    This numerical study describes the eddy emergence and transformations in a slow steady axisymmetric air-water flow, driven by a rotating top disk in a vertical conical container. As water height Hw and cone half-angle β vary, numerous flow metamorphoses occur. They are investigated for β =30°, 45°, and 60°. For small Hw, the air flow is multi-cellular with clockwise meridional circulation near the disk. The air flow becomes one cellular as Hw exceeds a threshold depending on β . For all β , the water flow has an unbounded number of eddies whose size and strength diminish as the cone apex is approached. As the water level becomes close to the disk, the outmost water eddy with clockwise meridional circulation expands, reaches the interface, and induces a thin layer with anticlockwise circulation in the air. Then this layer expands and occupies the entire air domain. The physical reasons for the flow transformations are provided. The results are of fundamental interest and can be relevant for aerial bioreactors.

  14. Multiscale Modeling of Cavitating Bubbly Flows

    NASA Astrophysics Data System (ADS)

    Ma, J.; Hsiao, C.-T.; Chahine, G. L.

    2013-03-01

    Modeling of cavitating bubbly flows is challenging due to the wide range of characteristic lengths of the physics at play: from micrometers (e.g., bubble nuclei radius) to meters (e.g., propeller diameter or sheet cavity length). To address this, we present here a multiscale approach which integrates a Discrete Bubble Model for dispersed microbubbles and a level set N-S solver for macro cavities, along with a mesoscale transition model to bridge the two. This approach was implemented in 3DYNAFScopyright and used to simulate sheet-to-cloud cavitation over a hydrofoil. The hybrid model captures well the full cavitation process starting from free field nuclei and nucleation from solid surfaces. In low pressure region of the foil small nuclei are seen to grow large and eventually merge to form a large scale sheet cavity. A reentrant jet forms under the cavity, travels upstream, and breaks it, resulting in a bubble cloud of a large amount of microbubbles as the broken pockets shrink and travel downstream. This is in good agreement with experimental observations based of sheet lengths and frequency of lift force oscillation. DOE-SBIR, ONR (monitored by Dr. Ki-Han Kim)

  15. Towards numerical simulation of bubbly flows in complex geometries

    NASA Astrophysics Data System (ADS)

    Mattson, Michael; Mahesh, Krishnan

    2008-11-01

    We are developing the LES capability for bubbly flows in complex geometries using unstructured grids and an Euler--Lagrangian methodology. Two Lagrangian bubble models are considered: (i) the bubbles are treated as a dispersed phase in the carrier fluid, and individual bubbles are point particles governed by an equation for bubble motion and (ii) the force coupling method by Maxey et al. [Fluid Dyn. Res., 32 (1997), 143-156]. The evolution of the bubble radius (assuming spherical bubbles) is governed by the Rayleigh--Plesset equation and integrated using a Runge--Kutta integrator with adaptive time-stepping. The talk will discuss numerical issues and contrast results between the two methodologies. Numerical results ranging from the motion of individual bubbles in channels and around bodies to drag reduction by bubbles in turbulent channel flow will be presented.

  16. Predictions of bubbly flows in vertical pipes using two-fluid models in CFDS-FLOW3D code

    SciTech Connect

    Banas, A.O.; Carver, M.B.; Unrau, D.

    1995-09-01

    This paper reports the results of a preliminary study exploring the performance of two sets of two-fluid closure relationships applied to the simulation of turbulent air-water bubbly upflows through vertical pipes. Predictions obtained with the default CFDS-FLOW3D model for dispersed flows were compared with the predictions of a new model (based on the work of Lee), and with the experimental data of Liu. The new model, implemented in the CFDS-FLOW3D code, included additional source terms in the {open_quotes}standard{close_quotes} {kappa}-{epsilon} transport equations for the liquid phase, as well as modified model coefficients and wall functions. All simulations were carried out in a 2-D axisymmetric format, collapsing the general multifluid framework of CFDS-FLOW3D to the two-fluid (air-water) case. The newly implemented model consistently improved predictions of radial-velocity profiles of both phases, but failed to accurately reproduce the experimental phase-distribution data. This shortcoming was traced to the neglect of anisotropic effects in the modelling of liquid-phase turbulence. In this sense, the present investigation should be considered as the first step toward the ultimate goal of developing a theoretically sound and universal CFD-type two-fluid model for bubbly flows in channels.

  17. Performance of a combined three-hole conductivity probe for void fraction and velocity measurement in air-water flows

    NASA Astrophysics Data System (ADS)

    Borges, João Eduardo; Pereira, Nuno H. C.; Matos, Jorge; Frizell, Kathleen H.

    2010-01-01

    The development of a three-hole pressure probe with back-flushing combined with a conductivity probe, used for measuring simultaneously the magnitude and direction of the velocity vector in complex air-water flows, is described in this paper. The air-water flows envisaged in the current work are typically those occurring around the rotors of impulse hydraulic turbines (like the Pelton and Cross-Flow turbines), where the flow direction is not known prior to the data acquisition. The calibration of both the conductivity and three-hole pressure components of the combined probe in a rig built for the purpose, where the probe was placed in a position similar to that adopted for the flow measurements, will be reported. After concluding the calibration procedure, the probe was utilized in the outside region of a Cross-Flow turbine rotor. The experimental results obtained in the present study illustrate the satisfactory performance of the combined probe, and are encouraging toward its use for characterizing the velocity field of other complex air-water flows.

  18. Surfactant-Induced Flow in Unsaturated Porous Media: Implications for Air-Water Interfacial Area Determination

    NASA Astrophysics Data System (ADS)

    Costanza-Robinson, M. S.; Zheng, Z.; Estabrook, B.; Henry, E. J.; Littlefield, M. H.

    2011-12-01

    Air-water interfacial area (AI) in porous media is an important factor governing equilibrium contaminant retention, as well as the kinetics of interphase mass transfer. Interfacial-partitioning tracer (IPT) tests are a common technique for measuring AI at a given moisture saturation (SW), where AI is calculated based on the ratio of arrival times of a surfactant and a non-reactive tracer. At surfactant concentrations often used, the aqueous surface tension of the interfacial tracer solution is ~30% lower than that of the resident porewater in the system, creating transient surface tension gradients during the IPT measurement. Because surface tension gradients create capillary pressure gradients, surfactant-induced unsaturated flow may occur during IPT tests, a process that would violate fundamental assumptions of constant SW, of steady-state flow, and of nonreactive and surfactant tracers experiencing the same transport conditions. To examine the occurrence and magnitude of surfactant-induced flow, we conducted IPT tests for unsaturated systems at ~84% initial SW using surfactant input concentrations that bracket concentrations commonly used. Despite constant boundary conditions (constant inlet flux and outlet pressure), the introduction of the surfactant solution induced considerable transience in column effluent flowrate and SW. Real-time system mass measurements revealed drainage of 20-40% SW, with the amount of drainage and the maximum rate of drainage proportional to the influent surfactant concentration, as would be expected. Because AI is inversely related to SW, the use of higher surfactant concentrations should yield larger AI estimates. Measured AI values, however, showed no clear relationship to surfactant concentration or the time-averaged SW of the system. These findings cast doubt on the reliability of IPT for AI determination.

  19. The existence of longitudinal vortices in the flow of air above an air/water interface

    NASA Astrophysics Data System (ADS)

    Kou, J.; Saylor, J. R.

    2009-11-01

    Many researchers have observed the formation of longitudinal vortices in boundary layers developing over heated solid surfaces. In the present work, such vortices were observed in an air boundary layer developing over a heated water surface. The existence of these vortices was documented via infrared imaging of the water surface, which showed a consistent pattern of hot and cold streaks, coinciding with the vortex position. These vortices were also visualized through smoke injected into the air-side flow. The onset position Xc and lateral vortex spacing λ were investigated for a range of wind speeds (0.1 - 1 m/s) and air/water temperature differences (26 - 42 ^oC). Plots of Xc/λ versus the Reynolds number exhibit power-law behavior similar to that of prior work on boundary layers over heated solid surfaces. However, plots of Xc/λ versus the Grashof number show significant differences from the power-law behavior observed for heated solid plates. A theory explaining the similarity and difference between the present results and those for heated solid plates is discussed which is based on differences in the thermal boundary conditions.

  20. Time-evolving bubbles in two-dimensional stokes flow

    NASA Technical Reports Server (NTRS)

    Tanveer, Saleh; Vasconcelos, Giovani L.

    1994-01-01

    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 behavior in the sense that for essentially arbitrary initial shapes the bubble will asymptote an expanding circle. Contracting bubbles, on the other hand, can develop narrow structures ('near-cusps') on the interface and may undergo 'break up' before all the bubble-fluid is completely removed. The mathematical structure underlying the existence of these exact solutions is also investigated.

  1. Photothermally controlled Marangoni flow around a micro bubble

    SciTech Connect

    Namura, Kyoko Nakajima, Kaoru; Kimura, Kenji; Suzuki, Motofumi

    2015-01-26

    We have experimentally investigated the control of Marangoni flow around a micro bubble using photothermal conversion. Using a focused laser spot acting as a highly localized heat source on Au nanoparticles/dielectric/Ag mirror thin film enables us to create a micro bubble and to control the temperature gradient around the bubble at a micrometer scale. When we irradiate the laser next to the bubble, a strong main flow towards the bubble and two symmetric rotation flows on either side of it develop. The shape of this rotation flow shows a significant transformation depending on the relative position of the bubble and the laser spot. Using this controllable rotation flow, we have demonstrated sorting of the polystyrene spheres with diameters of 2 μm and 0.75 μm according to their size.

  2. The cultivation of Anabaena variabilis in a bubble column operating under bubbly and slug flows.

    PubMed

    Yoon, Jong Hyun; Choi, Shin Sik; Park, Tai Hyun

    2012-04-01

    In a bubble column reactor with an inner diameter of 6cm and a height of 63cm for the culture of cyanobacteria two different shapes of bubbles can be generated, resulting in bubbly flow or slug flow. Growth of Anabaena variabilis under slug flow (1.9g/l/day) was 1.73 times higher than that under bubbly flow (1.1g/l/day) when the specific irradiation rate was maintained above 10μmol/s/g dry cell. Although a stepwise increase in superficial gas velocity enhanced the average cell growth rate under bubbly flow by 1.57 times, the average cell growth rate during the deceleration phase under bubbly flow (1.98g/l/day) was 0.61 times smaller than that under slug flow (3.22g/l/day). These results demonstrate that the bubble shape in the slug flow was advantageous in regards to the radial circulation of cells.

  3. Influence of bubble size, diffuser width, and flow rate on the integral behavior of bubble plumes

    NASA Astrophysics Data System (ADS)

    Fraga, Bruño.; Stoesser, Thorsten

    2016-06-01

    A large-eddy simulation based Eulerian-Lagrangian model is employed to quantify the impact of bubble size, diffuser diameter, and gas flow rate on integral properties of bubble plumes, such as the plume's width, centerline velocity, and mass flux. Calculated quantities are compared with experimental data and integral model predictions. Furthermore, the LES data were used to assess the behavior of the entrainment coefficient, the momentum amplification factor, and the bubble-to-momentum spread ratio. It is found that bubble plumes with constant bubble size and smaller diameter behave in accordance with integral plume models. Plumes comprising larger and non-uniform bubble sizes appear to deviate from past observations and model predictions. In multi-diameter bubble plumes, a bubble self-organisation takes place, i.e., small bubbles cluster in the center of the plume whilst large bubbles are found at the periphery of the plume. Multi-diameter bubble plumes also feature a greater entrainment rate than single-size bubble plumes, as well as a higher spread ratio and lower turbulent momentum rate. Once the plume is fully established, the size of the diffuser does not appear to affect integral properties of bubble plumes. However, plume development is affected by the diffuser width, as larger release areas lead to a delayed asymptotic behavior of the plume and consequently to a lower entrainment and higher spread ratio. Finally, the effect of the gas flow rate on the integral plume is studied and is deemed very relevant with regards to most integral plume properties and coefficients. This effect is already fairly well described by integral plume models.

  4. The initial generation of waves in an accelerated coupled air-water flow.

    NASA Astrophysics Data System (ADS)

    Veron, Fabrice; Ierley, Glenn; Melville, Ken

    2001-11-01

    The initial generation of surface waves over the ocean has a long been a problem of great interest. With the globally averaged wind speed in the range 6-7 m/s, and 40 % of the time below 6 m/s, much of the air-sea interface is in a low wind speed regime, and therefore the initial generation of waves under these conditions is of special interest. There is also a transition in the surface heat flux and surface cool skin at these low wind speeds when gravity capillary waves are first generated. We present the results of laboratory and field experiments, and numerical studies, on the stability of a wind-driven water surface to the initial generation of surface waves. Using modern quantitative flow visualization techniques, we show that the classical wave generation problem, where the wind is linearly accelerated over a still water surface, leads to the generation of a two-dimensional wave field. At this stage, the flow in the water phase has been observed to be sub-critical. These results are compared with numerical solutions of the stability of the coupled air-water problem obtained by solving both the linear and non-linear Orr-Sommerfeld coupled equations. The effects of non-linearity will be discussed. In addition, we show that the wave generation problem is accompanied by the turbulent transition of the water surface boundary layer through the formation and dislocation of Langmuir circulations. Field data suggest that this transition, rather than microscale breaking waves, first disrupt the cool skin. We show that this turbulent transition also marks the change from a two- to three-dimensional surface wave field as the coherent sub-surface velocities modulate the waves. This rapid evolution from 2D to 3D surface wave patterns in the early stages of the wave generation implies that 2D models for wind-wave generation might only apply in the very early stages of wave growth. This will be discussed in light of linear and non-linear wave generation models.

  5. Gas Bubble Formation in Stagnant and Flowing Mercury

    SciTech Connect

    Wendel, Mark W; Abdou, Ashraf A; Riemer, Bernie; Felde, David K

    2007-01-01

    Investigations in the area of two-phase flow at the Oak Ridge National Laboratory's (ORNL) Spallation Neutron Source (SNS) facility are progressing. It is expected that the target vessel lifetime could be extended by introducing gas into the liquid mercury target. As part of an effort to validate the two-phase computational fluid dynamics (CFD) model, simulations and experiments of gas injection in stagnant and flowing mercury have been completed. The volume of fluid (VOF) method as implemented in ANSYS-CFX, was used to simulate the unsteady two-phase flow of gas injection into stagnant mercury. Bubbles produced at the upwards-oriented vertical gas injector were measured with proton radiography at the Los Alamos Neutron Science Center. The comparison of the CFD results to the radiographic images shows good agreement for bubble sizes and shapes at various stages of the bubble growth, detachment, and gravitational rise. Although several gas flows were measured, this paper focuses on the case with a gas flow rate of 8 cc/min through the 100-micron-diameter injector needle. The acoustic waves emitted due to the detachment of the bubble and during subsequent bubble oscillations were recorded with a microphone, providing a precise measurement of the bubble sizes. As the mercury flow rate increases, the drag force causes earlier bubble detachment and therefore smaller bubbles.

  6. Transport of micro-bubbles in turbulent shear flows

    NASA Astrophysics Data System (ADS)

    Gualtieri, P.; Battista, F.; Casciola, C. M.

    2015-12-01

    The dynamics of micro-bubbles, which are typical in many industrial applications, is addressed by means the Direct Numerical Simulations (DNS) of two prototypal flows, namely a homogeneous shear flow and a fully developed pipe flows. This preliminary study has a two-fold purpose. The homogenous turbulent shear flow is useful to characterize the bubble dynamics in terms of their eventual clustering properties which is expected to be controlled by the Stokes number. The time history of the fluid pressure experienced by the bubbles during their evolution is recorded and successively employed to force the Rayleigh-Plesset equation [1]. The ensuing data are used to address a posteriori the bubble diameter statistics in view of bubble collapse induced by strong and intermittent turbulent pressure fluctuations. The turbulent pipe flow simulations serve to address the bubble dynamics in wall bounded flows. Here the bubbles are observed to accumulate in the near-wall region with different intensity depending on the bubble dimensions.

  7. Flow through an Array of Superhydrophopic Pillars: The Role of the Air-Water Interface Shape on Drag Reduction

    NASA Astrophysics Data System (ADS)

    Kim, Jeong-Hyun; Rothstein, Jonathan

    2016-11-01

    In this study, measurements of the pressure drop and the velocity fields associated with the flow of water through a regular array of superhydrophobic pillars were systematically performed to investigate the role of the air-water interface shape on drag reduction. A microfluidic channel was created with circular and superhydrophobic apple-core-shaped pillars bridging across the entire channel. The apple-core-shaped pillars were designed to trap an air pocket along the side of the pillars. The shape of the interface was systematically modified from concave to convex by changing the static pressure within the microchannel. For superhydrophobic pillars having a circular cross section, D /D0 = 1.0, a drag reduction of 7% and a slip velocity of 20% the average channel velocity along the air-water interface were measured. At large static pressures, the interface was driven into the pillars resulting in a decrease in the effective size of the pillars, an increase in the effective spacing between pillars and a pressure drop reduction of as much as 18% when the interface was compressed to D /D0 = 0.8. At low static pressures, the pressure drop increased significantly even as the slip velocity increased as the expanding air-water interface constricted flow through the array of pillars. This research was supported by the National Science Foundation under Grant CBET-1334962.

  8. Bubbly flows around a two-dimensional circular cylinder

    NASA Astrophysics Data System (ADS)

    Lee, Jubeom; Park, Hyungmin

    2016-11-01

    Two-phase cross flows around a bluff body occur in many thermal-fluid systems like steam generators, heat exchangers and nuclear reactors. However, our current knowledge on the interactions among bubbles, bubble-induced flows and the bluff body are limited. In the present study, the gas-liquid bubbly flows around a solid circular cylinder are experimentally investigated while varying the mean void fraction from 5 to 27%. The surrounding liquid (water) is initially static and the liquid flow is only induced by the air bubbles. For the measurements, we use the high-speed two-phase particle image velocimetry techniques. First, depending on the mean void fraction, two regimes are classified with different preferential concentration of bubbles in the cylinder wake, which are explained in terms of hydrodynamic force balances acting on rising bubbles. Second, the differences between the two-phase and single-phase flows (while matching their Reynolds numbers) around a circular cylinder will be discussed in relation to effects of bubble dynamics and the bubble-induced turbulence on the cylinder wake. Supported by a Grant (MPSS-CG-2016-02) through the Disaster and Safety Management Institute funded by Ministry of Public Safety and Security of Korean government.

  9. Numerical Simulation of Bubble Formation in Co-Flowing Mercury

    SciTech Connect

    Abdou, Ashraf A; Wendel, Mark W; Felde, David K; Riemer, Bernie

    2008-01-01

    In this work, we present computational fluid dynamics (CFD) simulations of helium bubble formation and detachment at a submerged needle in stagnant and co-flowing mercury. Since mercury is opaque, visualization of internal gas bubbles was done with proton radiography (pRad) at the Los Alamos Neutron Science Center (LANSCE2). The acoustic waves emitted at the time of detachment and during subsequent oscillations of the bubble were recorded with a microphone. The Volume of Fluid (VOF) model was used to simulate the unsteady two-phase flow of gas injection in mercury. The VOF model is validated by comparing detailed bubble sizes and shapes at various stages of the bubble growth and detachment, with the experimental measurements at different gas flow rates and mercury velocities. The experimental and computational results show a two-stage bubble formation. The first stage involves growing bubble around the needle, and the second follows as the buoyancy overcomes wall adhesion. The comparison of predicted and measured bubble sizes and shapes at various stages of the bubble growth and detachment is in good agreement.

  10. Study of a downward bubbly flow in a vertical pipe

    SciTech Connect

    Gorelik, R.S.; Kashinskii, O.N.; Nakoryakov, V.E.

    1987-07-01

    This paper reports on an experimental study of downward bubble-diffused concurrent flow in a vertical pipe. Two-phase flow was induced by introducing gas into a liquid with a special mixer which made it possible to obtain a gas-liquid flow with consistent bubble size. Visualization was performed by photography and flow rate was monitored by friction transducers. Shear stress and hydraulic conductivity were determined for various flow rates and Reynolds numbers. It was found that the stabilizing effect of the gas phase is determined by the fact that the flow rate pulsations introduced into the liquid flow have a negative sign; that the flow rate of the liquid near the bubbles, in other words, is lower than the mean flow rate of the liquid. This effect is not seen in ascending flows.

  11. Bubble-induced damping in displacement-driven microfluidic flows.

    PubMed

    Lee, Jongho; Rahman, Faizur; Laoui, Tahar; Karnik, Rohit

    2012-08-01

    Bubble damping in displacement-driven microfluidic flows was theoretically and experimentally investigated for a Y-channel microfluidic network. The system was found to exhibit linear behavior for typical microfluidic flow conditions. The bubbles induced a low-pass filter behavior with a characteristic cutoff frequency that scaled proportionally with flow rate and inversely with bubble volume and exhibited a minimum with respect to the relative resistances of the connecting channels. A theoretical model based on the electrical circuit analogy was able to predict experimentally observed damping of fluctuations with excellent agreement. Finally, a flowmeter with high resolution (0.01 μL/min) was demonstrated as an application of the bubble-aided stabilization. This study may aid in the design of many other bubble-stabilized microfluidic systems.

  12. Thermocapillary Flow and Aggregation of Bubbles on a Solid Wall

    NASA Technical Reports Server (NTRS)

    Kasumi, Hiroki; Solomentsev, Yuri E.; Guelcher, Scott A.; Anderson, John L.; Sides, Paul J.

    2000-01-01

    During the electrolytic evolution of oxygen bubbles forming on a vertically oriented transparent tin oxide electrode, bubbles were found to be mutually attractive. The mechanism of the aggregation had never been explained satisfactorily until Guelcher et al. attributed it to thermocapillary flow. The gradient of surface tension of the liquid at the bubble's surface, which was established because of reaction heat and ohmic heat loss at the electrode wall, drives flow of the liquid adjacent to each bubble; the bubble "pumps" fluid along its surface away from the wall. Fluid flows toward the bubble to conserve mass and entrains nearby bubbles in the flow pattern. The same logic would apply when two bubbles of equal size are adjacent to each other on a warm wall. Each bubble drives thermocapillary flow and hence entrains the other in its flow pattern, which drives the aggregation. Our objective here is to perform experiments where the temperature gradient at the wall is well known and controlled. The theory can be quantitatively tested by studying aggregation of bubble pairs of equal size, and by varying system parameters such as temperature gradient, bubble size and fluid viscosity. The results are then compared with the theory in a quantitatively rigorous manner. We demonstrate that the theory without adjustable parameters is capable of quantitatively modeling the rate of aggregation of two bubbles. The equations governing the thermocapillary flow around a single stationary bubble on a heated or cooled wall in a semi-infinite domain were solved. Both Reynolds number and Marangoni number were much less than unity. The critical result is that liquid in the vicinity of a warm wall flows toward a stationary collector bubble. Consequently the thermocapillary flow around the stationary bubble entrains another bubble toward itself. The bubbles undergo hindered translation parallel to the wall with velocity U while the fluid flow field is described with u. Two velocities

  13. Phase Distribution Characteristics of Bubbly Flow in Mini Pipes Under Normal and Microgravity Conditions

    NASA Astrophysics Data System (ADS)

    Hazuku, Tatsuya; Takamasa, Tomoji; Hibiki, Takashi

    2015-03-01

    The axial development of the void fraction, interfacial area concentration and Sauter mean bubble diameter profiles of adiabatic air-water bubbly flows in 5.0 and 3.0 mm-diameter pipes were measured using a stereo image processing method under two gravity conditions, vertical upward (normal gravity) and microgravity. The flow measurements were performed at four axial locations. The axial distances from the pipe inlet ( z) normalized by the pipe diameter ( D) were z/ D = 5.5, 34, 72 and 110 for 5.0 mm-diameter pipe and z/ D = 15, 62, 120 and 188 for 3.0 mm-diameter pipe. Data were collected for superficial gas and liquid velocities respectively in the ranges of 0.00434-0.0500 m/s and 0.205-0.754 m/s. The effect of gravity on the radial distribution of bubbles and the axial development of two-phase flow parameters is discussed in detail, based on the obtained database. The phase distributions in pipe cross-sections were classified into 3 basic patterns: core peak, intermediate peak and wall peak distributions, based on two normalized parameters: a normalized void peak position and a normalized void peak intensity. Phase distribution pattern maps under normal and microgravity conditions were generated for bubbly flows in 5.0 and 3.0 mm-diameter pipes. The data obtained in the current experiment are expected to contribute to the benchmarking of CFD simulation of void fraction and interfacial area concentration distribution patterns in forced convective pipe flow under microgravity conditions.

  14. Measurements of Gas Bubble Size Distributions in Flowing Liquid Mercury

    SciTech Connect

    Wendel, Mark W; Riemer, Bernie; Abdou, Ashraf A

    2012-01-01

    ABSTRACT Pressure waves created in liquid mercury pulsed spallation targets have been shown to induce cavitation damage on the target container. One way to mitigate such damage would be to absorb the pressure pulse energy into a dispersed population of small bubbles, however, measuring such a population in mercury is difficult since it is opaque and the mercury is involved in a turbulent flow. Ultrasonic measurements have been attempted on these types of flows, but the flow noise can interfere with the measurement, and the results are unverifiable and often unrealistic. Recently, a flow loop was built and operated at Oak Ridge National Labarotory to assess the capability of various bubbler designs to deliver an adequate population of bubbles to mitigate cavitation damage. The invented diagnostic technique involves flowing the mercury with entrained gas bubbles in a steady state through a horizontal piping section with a glass-window observation port located on the top. The mercury flow is then suddenly stopped and the bubbles are allowed to settle on the glass due to buoyancy. Using a bright-field illumination and a high-speed camera, the arriving bubbles are detected and counted, and then the images can be processed to determine the bubble populations. After using this technique to collect data on each bubbler, bubble size distributions were built for the purpose of quantifying bubbler performance, allowing the selection of the best bubbler options. This paper presents the novel procedure, photographic technique, sample visual results and some example bubble size distributions. The best bubbler options were subsequently used in proton beam irradiation tests performed at the Los Alamos National Laboratory. The cavitation damage results from the irradiated test plates in contact with the mercury are available for correlation with the bubble populations. The most effective mitigating population can now be designed into prototypical geometries for implementation into

  15. Verification and Validation of Numerical Models for Air/Water Flow on Coastal and Navigation Fluid-Structure Interaction Applications

    NASA Astrophysics Data System (ADS)

    Kees, C. E.; Farthing, M.; Dimakopoulos, A.; DeLataillade, T.

    2015-12-01

    Performance analysis and optimization of coastal and navigation structures is becoming feasible due to recent improvements in numerical methods for multiphase flows and the steady increase in capacity and availability of high performance computing resources. Now that the concept of fully three-dimensional air/water flow modelling for real world engineering analysis is achieving acceptance by the wider engineering community, it is critical to expand careful comparative studies on verification,validation, benchmarking, and uncertainty quantification for the variety of competing numerical methods that are continuing to evolve. Furthermore, uncertainty still remains about the relevance of secondary processes such as surface tension, air compressibility, air entrainment, and solid phase (structure) modelling so that questions about continuum mechanical theory and mathematical analysis of multiphase flow are still required. Two of the most popular and practical numerical approaches for large-scale engineering analysis are the Volume-Of-Fluid (VOF) and Level Set (LS) approaches. In this work we will present a publically available verification and validation test set for air-water-structure interaction problems as well as computational and physical model results including a hybrid VOF-LS method, traditional VOF methods, and Smoothed Particle Hydrodynamics (SPH) results. The test set repository and test problem formats will also be presented in order to facilitate future comparative studies and reproduction of scientific results.

  16. A numerical simulation of flows around a deformable gas bubble

    NASA Astrophysics Data System (ADS)

    Sugano, Minoru; Ishii, Ryuji; Morioka, Shigeki

    1991-12-01

    A numerical simulation of flows around a (deformable) gas bubble rising through an incompressible viscous fluid was carried out on a supercomputer Fujitsu VP2600 at Data Processing Center of Kyoto University. The solution algorithm is a modified Marker And Cell (MAC) method. For the grid generation, an orthogonal mapping proposed by Ryskin and Leal was applied. it is assumed that the shape of the bubble and the flow field are axisymmetric.

  17. Numerical and physical modelling of bubbly flow phenomena

    SciTech Connect

    Sangani, A.S.

    1991-01-01

    The objective of this study is to develop theoretical tools -- analytical as well as numerical -- for understanding how the flows of bubbly liquids are affected by its microstructure, i.e., the detailed spatial, size, and velocity distribution of bubbles, and how the microstructure, in turn, is affected by the flow. This report describes the progress made to date on the several problems that are being studied. The first problem is concerned with the molecular-dynamics type simulations of monodispersed bubbly liquids under equilibrium and homogeneous conditions and their application to slightly inhomogeneous flows. The Reynolds number is large and the Weber and Froud numbers are small in these simulations. The second problem is concerned with the simulations of flows of bubbly liquids undergoing small amplitude oscillatory motion. Both the cases of bubbles with rigid (due to impurities) and stress-free interfaces are examined. The results are related to the added mass, Basset, and viscous drag coefficients. The third problem is concerned with the acoustic wave propagation in bubbly liquids at frequencies above natural frequency of the bubbles. The second problem is completed as of this writing. Work on the other two problems is currently in progress. A summary of the work to be carried out during the period 1/91 to 6/92 is given in the last section. 4 figs.

  18. Experiments performed with bubbly flow in vertical pipes at different flow conditions covering the transition region: simulation by coupling Eulerian, Lagrangian and 3D random walks models

    NASA Astrophysics Data System (ADS)

    Muñoz-Cobo, José; Chiva, Sergio; El Aziz Essa, Mohamed; Mendes, Santos

    2012-08-01

    Two phase flow experiments with different superficial velocities of gas and water were performed in a vertical upward isothermal cocurrent air-water flow column with conditions ranging from bubbly flow, with very low void fraction, to transition flow with some cap and slug bubbles and void fractions around 25%. The superficial velocities of the liquid and the gas phases were varied from 0.5 to 3 m/s and from 0 to 0.6 m/s, respectively. Also to check the effect of changing the surface tension on the previous experiments small amounts of 1-butanol were added to the water. These amounts range from 9 to 75 ppm and change the surface tension. This study is interesting because in real cases the surface tension of the water diminishes with temperature, and with this kind of experiments we can study indirectly the effect of changing the temperature on the void fraction distribution. The following axial and radial distributions were measured in all these experiments: void fraction, interfacial area concentration, interfacial velocity, Sauter mean diameter and turbulence intensity. The range of values of the gas superficial velocities in these experiments covered the range from bubbly flow to the transition to cap/slug flow. Also with transition flow conditions we distinguish two groups of bubbles in the experiments, the small spherical bubbles and the cap/slug bubbles. Special interest was devoted to the transition region from bubbly to cap/slug flow; the goal was to understand the physical phenomena that take place during this transition A set of numerical simulations of some of these experiments for bubbly flow conditions has been performed by coupling a Lagrangian code, that tracks the three dimensional motion of the individual bubbles in cylindrical coordinates inside the field of the carrier liquid, to an Eulerian model that computes the magnitudes of continuous phase and to a 3D random walk model that takes on account the fluctuation in the velocity field of the

  19. Evolution of energy in flow driven by rising bubbles.

    PubMed

    Mazzitelli, Irene M; Lohse, Detlef

    2009-06-01

    We investigate by direct numerical simulations the flow that rising bubbles cause in an originally quiescent fluid. We employ the Eulerian-Lagrangian method with two-way coupling and periodic boundary conditions. In order to be able to treat up to 288000 bubbles, the following approximations and simplifications had to be introduced, as done before, e.g., by Climent and Magnaudet, Phys. Rev. Lett. 82, 4827 (1999). (i) The bubbles were treated as point particles, thus (ii) disregarding the near-field interactions among them, and (iii) effective force models for the lift and the drag forces were used. In particular, the lift coefficient was assumed to be 1/2, independent of the bubble Reynolds number and the local flow field. The results suggest that large-scale motions are generated, owing to an inverse energy cascade from the small to the large scales. However, as the Taylor-Reynolds number is only in the range of 1, the corresponding scaling of the energy spectrum with an exponent of -5/3 cannot develop over a pronounced range. In the long term, the property of local energy transfer, characteristic of real turbulence, is lost and the input of energy equals the viscous dissipation at all scales. Due to the lack of strong vortices, the bubbles spread rather uniformly in the flow. The mechanism for uniform spreading is as follows. Rising bubbles induce a velocity field behind them that acts on the following bubbles. Owing to the shear, those bubbles experience a lift force, which makes them spread to the left or right, thus preventing the formation of vertical bubble clusters and therefore of efficient forcing. Indeed, when the lift is artificially put to zero in the simulations, the flow is forced much more efficiently and a more pronounced energy that accumulation at large scales (due to the inverse energy cascade) is achieved.

  20. Volume Displacement Effects in Bubble-laden Flows

    NASA Astrophysics Data System (ADS)

    Cihonski, Andrew; Finn, Justin; Apte, Sourabh

    2012-11-01

    When a few bubbles are entrained in a traveling vortex ring, it has been shown that even at extremely low volume loadings, their presence can significantly affect the structure of the vortex core (Sridhar & Katz 1999). A typical Euler-Lagrange point-particle model with two-way coupling for this dilute system, wherein the bubbles are assumed subgrid and momentum point-sources are used to model their effect on the flow, is shown to be unable to accurately capture the experimental trends of bubble settling location and vortex distortion for a range of bubble parameters and vortex strengths. The bubbles experience a significant amount of drag, lift, added mass, pressure, and gravity forces. However, these forces are in balance of each other, as the bubbles reach a mean settling location away from the vortex core. Accounting for fluid volume displacement due to bubble motion, using a model termed as volumetric coupling, experimental trends on vortex distortion and bubble settling location are well captured. The fluid displacement effects are studied by introducing a notion of a volumetric coupling force, the net force on the fluid due to volumetric coupling, which is found to be dominant even at the low volume loadings investigated here.

  1. Transient Flow Dynamics in Optical Micro Well Involving Gas Bubbles

    NASA Technical Reports Server (NTRS)

    Johnson, B.; Chen, C. P.; Jenkins, A.; Spearing, S.; Monaco, L. A.; Steele, A.; Flores, G.

    2006-01-01

    The Lab-On-a-Chip Application Development (LOCAD) team at NASA s Marshall Space Flight Center is utilizing Lab-On-a-Chip to support technology development specifically for Space Exploration. In this paper, we investigate the transient two-phase flow patterns in an optic well configuration with an entrapped bubble through numerical simulation. Specifically, the filling processes of a liquid inside an expanded chamber that has bubbles entrapped. Due to the back flow created by channel expansion, the entrapped bubbles tend to stay stationary at the immediate downstream of the expansion. Due to the huge difference between the gas and liquid densities, mass conservation issues associated with numerical diffusion need to be specially addressed. The results are presented in terms of the movement of the bubble through the optic well. Bubble removal strategies are developed that involve only pressure gradients across the optic well. Results show that for the bubble to be moved through the well, pressure pulsations must be utilized in order to create pressure gradients across the bubble itself.

  2. Contactless Inductive Bubble Detection in a Liquid Metal Flow

    PubMed Central

    Gundrum, Thomas; Büttner, Philipp; Dekdouk, Bachir; Peyton, Anthony; Wondrak, Thomas; Galindo, Vladimir; Eckert, Sven

    2016-01-01

    The detection of bubbles in liquid metals is important for many technical applications. The opaqueness and the high temperature of liquid metals set high demands on the measurement system. The high electrical conductivity of the liquid metal can be exploited for contactless methods based on electromagnetic induction. We will present a measurement system which consists of one excitation coil and a pickup coil system on the opposite sides of the pipe. With this sensor we were able to detect bubbles in a sodium flow inside a stainless steel pipe and bubbles in a column filled with a liquid Gallium alloy. PMID:26751444

  3. Using DNS and Statistical Learning to Model Bubbly Channel Flow

    NASA Astrophysics Data System (ADS)

    Ma, Ming; Lu, Jiacai; Tryggvason, Gretar

    2015-11-01

    The transient evolution of laminar bubbly flow in a vertical channel is examined by direct numerical simulation (DNS). Nearly spherical bubbles, initially distributed evenly in a fully developed parabolic flow, are driven relatively quickly to the walls, where they increase the drag and reduce the flow rate on a longer time scale. Once the flow rate has been decreased significantly, some of the bubbles move back into the channel interior and the void fraction there approaches the value needed to balance the weight of the mixture and the imposed pressure gradient. A database generated by averaging the DNS results is used to model the closure terms in a simple model of the average flow. Those terms relate the averaged lateral flux of the bubbles, the velocity fluctuations and the averaged surface tension force to the fluid shear, the void fraction and its gradient, as well as the distance to the nearest wall. An aggregated neural network is used for the statistically leaning of unknown closures, and closure relationships are tested by following the evolution of bubbly channel flow with different initial conditions. It is found that the model predictions are in reasonably good agreement with DNS results. Supported by NSF.

  4. Effect of surface active materials on bubble dynamics in two-phase flow

    NASA Astrophysics Data System (ADS)

    Johnson, Bruce D.

    1992-12-01

    Our goal in this research is to relate bubble performance in processes such as bubble breaking, dissolution, coalescence, and breakup to bubble interfacial characteristics, including surface tension, surface charge, and surface rheological properties. This fiscal year we have studied bubble dissolution rates in clean fresh water and in sea water samples representing a wide range of biological activities. Previous measurements of bubble dissolution have used water that was equilibrated with a known atmosphere a process that takes many hours and results in alteration of chemical and biological properties. We have used a novel gas tension method to determine O2 and N2 partial pressures in the water phase. Our results indicate that mass transfer rates for dissolution in fresh water coincide with theoretical predictions, but those for sea water are always significantly less and especially at low Reynolds Numbers. Bubble coalescence and breaking of bubbles at the air-water interface were observed in fresh water and sea water samples. Both process were observed to produce satellite bubbles. For example, millimeter-size bubbles breaking at the air-water interface each produced 20 or more bubbles of greater than 30 microns in diameter.

  5. Direct and Continuous Numerical Simulations of Bubbly Flows

    NASA Astrophysics Data System (ADS)

    Lu, Tianshi; Samulyak, Roman; Glimm, James

    2003-11-01

    We have studied numerically the propagation of linear and nonlinear waves in bubbly flows using direct and continuous approaches. The direct method represents a mixture of gas bubbles in a liquid as a system of one phase domains separated by free interfaces. FronTier, a front tracking hydro code was used for numerical simulations. It is capable of tracking simultaneously a large number of interfaces and resolving their topological changes (the breakup and merger of bubbles) in two- and three-dimensional spaces. The continuous method describes a bubbly fluid as a homogeneous system or pseudofluid that obeys an equation of state of single-component flow. Homogeneous equation of state models based on the Rayleigh-Plesset equation have been developed for the FronTier code. We have compared results of our numerical simulations with theoretical predictions and experimental data on the propagation of shocks and linear sound waves in bubbly fluids. The two methods can be applied to estimate the efficiency of gas bubble mitigation in reducing the cavitation erosion of the container of the Spallation Neutron Source liquid mercury target.

  6. Surfactant-induced flow compromises determination of air-water interfacial areas by surfactant miscible-displacement.

    PubMed

    Costanza-Robinson, Molly S; Henry, Eric J

    2017-03-01

    Surfactant miscible-displacement (SMD) column experiments are used to measure air-water interfacial area (AI) in unsaturated porous media, a property that influences solute transport and phase-partitioning. The conventional SMD experiment results in surface tension gradients that can cause water redistribution and/or net drainage of water from the system ("surfactant-induced flow"), violating theoretical foundations of the method. Nevertheless, the SMD technique is still used, and some suggest that experimental observations of surfactant-induced flow represent an artifact of improper control of boundary conditions. In this work, we used numerical modeling, for which boundary conditions can be perfectly controlled, to evaluate this suggestion. We also examined the magnitude of surfactant-induced flow and its impact on AI measurement during multiple SMD flow scenarios. Simulations of the conventional SMD experiment showed substantial surfactant-induced flow and consequent drainage of water from the column (e.g., from 75% to 55% SW) and increases in actual AI of up to 43%. Neither horizontal column orientation nor alternative boundary conditions resolved surfactant-induced flow issues. Even for simulated flow scenarios that avoided surfactant-induced drainage of the column, substantial surfactant-induced internal water redistribution occurred and was sufficient to alter surfactant transport, resulting in up to 23% overestimation of AI. Depending on the specific simulated flow scenario and data analysis assumptions used, estimated AI varied by nearly 40% and deviated up to 36% from the system's initial AI. We recommend methods for AI determination that avoid generation of surface-tension gradients and urge caution when relying on absolute AI values measured via SMD.

  7. Shearing flow from transient bubble oscillations in narrow gaps

    NASA Astrophysics Data System (ADS)

    Mohammadzadeh, Milad; Li, Fenfang; Ohl, Claus-Dieter

    2017-01-01

    The flow driven by a rapidly expanding and collapsing cavitation bubble in a narrow cylindrical gap is studied with the volume of fluid method. The simulations reveal a developing plug flow during the early expansion followed by flow reversal at later stages. An adverse pressure gradient leads to boundary layer separation and flow reversal, causing large shear stress near the boundaries. Analytical solution to a planar pulsating flow shows qualitative agreement with the CFD results. The shear stress close to boundaries has implications to deformable objects located near the bubble: Experiments reveal that thin, flat biological cells entrained in the boundary layer become stretched, while cells with a larger cross section are mainly transported with the flow.

  8. Scalewise investigation of two-phase flow turbulence in upward turbulent bubbly pipe flows

    NASA Astrophysics Data System (ADS)

    Lee, Jun Ho; Kim, Hyunseok; Park, Hyungmin

    2015-11-01

    In the present study, the two-phase flow turbulence in upward turbulent bubbly pipe flows (at the Reynolds number of 5300) is invesgitated, especially focusing on the changes in flow structures with bubbles depending on the length scales. For the scalewise investigation, we perform the wavelet multi-resolution analysis on the velocity fields at three streamwise locations, measured with high-speed two-phase particle image velocimetry technology. While we intentaionlly introduce asymmetrically distributed bubbles at the pipe inlet, the mean volume void fraction is varied from from 0.3% to 1.86% and the considered mean bubble diameter is roughly maintained at 3.8 mm. With the present condition, turbulence enhancement is achieived for most cases but the turbulent suppression is also captured near the wall for the smallest void fraction case. Comparing the scalewise energy contribution, it is understood that the flow structures with length scales between bubble radius and bubble wake size are enhanced due to bubbles, resulting in the turbulence enhancement. On the other hand, flow structure with smaller length scales (mostly existing near the wall) may decrease depending on the bubble condition, which may be one of the explanations in turbulence suppression with bubbles. Supported by the NRF grant funded by the Korea government (NRF-2012M2A8A4055647) via SNU-IAMD.

  9. Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume II. Chapters 6-10)

    SciTech Connect

    Guo, T.; Park, J.; Kojasoy, G.

    2003-03-15

    Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.

  10. Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume I. Chapters 1-5)

    SciTech Connect

    Guo, T.; Park, J.; Kojasoy, G.

    2003-03-15

    Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.

  11. Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume III. Chapters 11-14)

    SciTech Connect

    Guo, T.; Park, J.; Kojasoy, G.

    2003-03-15

    Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.

  12. Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume IV. Chapters 15-19)

    SciTech Connect

    Guo, T.; Park, J.; Kojasoy, G.

    2003-03-15

    Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.

  13. Heat transfer and fluid dynamics of air-water two-phase flow in micro-channels

    SciTech Connect

    Kaji, Masuo; Sawai, Toru; Kagi, Yosuke; Ueda, Tadanobu

    2010-05-15

    Heat transfer, pressure drop, and void fraction were simultaneously measured for upward heated air-water non-boiling two-phase flow in 0.51 mm ID tube to investigate thermo-hydro dynamic characteristics of two-phase flow in micro-channels. At low liquid superficial velocity j{sub l} frictional pressure drop agreed with Mishima-Hibiki's correlation, whereas agreed with Chisholm-Laird's correlation at relatively high j{sub l}. Void fraction was lower than the homogeneous model and conventional empirical correlations. To interpret the decrease of void fraction with decrease of tube diameter, a relation among the void fraction, pressure gradient and tube diameter was derived. Heat transfer coefficient fairly agreed with the data for 1.03 and 2.01 mm ID tubes when j{sub l} was relatively high. But it became lower than that for larger diameter tubes when j{sub l} was low. Analogy between heat transfer and frictional pressure drop was proved to hold roughly for the two-phase flow in micro-channel. But satisfactory relation was not obtained under the condition of low liquid superficial velocity. (author)

  14. An electrical impedance sensor for water level measurements in air-water two-phase stratified flows

    NASA Astrophysics Data System (ADS)

    Ko, Min Seok; Lee, Sung Yong; Lee, Bo An; Yun, Byong Jo; Kim, Kyung Youn; Kim, Sin

    2013-09-01

    We report a design of an optimized ring-type impedance sensor for water level measurements in air-water stratified flows through horizontal pipes. The ring-type sensor is optimized in view of the sensor linearity. In order to determine an optimal electrode and gap size of a ring-type sensor which generates a linear relationship between the impedance (resistance and/or reactance) and the water level, systematic numerical calculations are performed, and a ring-type impedance sensor of electrode width-to-diameter ratio 0.25 and gap-to-diameter ratio 0.2 has been selected as optimal. Lab-scale static experiments have been conducted to verify the sensor performance in terms of the linearity. Finally, this proposed sensor is installed in a horizontal loop 40 mm in diameter and roughly 5200 mm in length and measures water levels for various stratified flow conditions. The comparisons of water level measurements between the proposed sensor and the high-speed camera images post-processed by the edge detection scheme show that the maximum deviation in dimensionless water level is roughly 0.037, which corresponds to 1.5 mm over the range 40 mm.

  15. The effects of channel diameter on flow pattern, void fraction and pressure drop of two-phase air-water flow in circular micro-channels

    SciTech Connect

    Saisorn, Sira; Wongwises, Somchai

    2010-05-15

    Two-phase air-water flow characteristics are experimentally investigated in horizontal circular micro-channels. Test sections are made of fused silica. The experiments are conducted based on three different inner diameters of 0.53, 0.22 and 0.15 mm with the corresponding lengths of 320, 120 and 104 mm, respectively. The test runs are done at superficial velocities of gas and liquid ranging between 0.37-42.36 and 0.005-3.04 m/s, respectively. The flow visualisation is facilitated by systems mainly including stereozoom microscope and high-speed camera. The flow regime maps developed from the observed flow patterns are presented. The void fractions are determined based on image analysis. New correlation for two-phase frictional multiplier is also proposed for practical applications. (author)

  16. Flow pattern, void fraction and pressure drop of two-phase air-water flow in a horizontal circular micro-channel

    SciTech Connect

    Saisorn, Sira; Wongwises, Somchai

    2008-01-15

    Adiabatic two-phase air-water flow characteristics, including the two-phase flow pattern as well as the void fraction and two-phase frictional pressure drop, in a circular micro-channel are experimentally studied. A fused silica channel, 320 mm long, with an inside diameter of 0.53 mm is used as the test section. The test runs are done at superficial velocity of gas and liquid ranging between 0.37-16 and 0.005-3.04 m/s, respectively. The flow pattern map is developed from the observed flow patterns i.e. slug flow, throat-annular flow, churn flow and annular-rivulet flow. The flow pattern map is compared with those of other researchers obtained from different working fluids. The present single-phase experiments also show that there are no significant differences in the data from the use of air or nitrogen gas, and water or de-ionized water. The void fraction data obtained by image analysis tends to correspond with the homogeneous flow model. The two-phase pressure drops are also used to calculate the frictional multiplier. The multiplier data show a dependence on flow pattern as well as mass flux. A new correlation of two-phase frictional multiplier is also proposed for practical application. (author)

  17. Flow-induced molecular segregation in beta-casein-monoglyceride mixed films spread at the air-water interface.

    PubMed

    Sánchez, Cecilio Carrera; Rodríguez Patino, Juan M

    2004-07-20

    In this work, we have used different and complementary interfacial techniques (surface film balance, Brewster angle microscopy, and interfacial shear rheology) to analyze the static (structure, topography, reflectivity, miscibility, and interactions) and flow characteristics (surface shear characteristics) of beta-casein and monoglyceride (monopalmitin and monoolein) mixed films spread on the air-water interface. The structural, topographical, and shear characteristics of the mixed films depend on the surface pressure and on the composition of the mixed film. The surface shear viscosity (etas) varies greatly with the surface pressure. In general, the greater the surface pressure, the greater the values of etas. At higher surface pressures, collapsed beta-casein residues may be displaced from the interface by monoglyceride molecules with important repercussions on the shear characteristics of the mixed films. A shear-induced change in the topography of monoglyceride and beta-casein domains, on one hand, and a segregation between domains of the film-forming components, on the other hand, were also observed. The displacement of the beta-casein by the monoglycerides is facilitated under shear conditions, especially for beta-casein-monoolein mixed films.

  18. Well-posedness and convergence of cfd two-fluid model for bubbly flows

    NASA Astrophysics Data System (ADS)

    Vaidheeswaran, Avinash

    the presence of the wall boundaries need to be addressed in a CFD TFM. A near-wall modeling technique is proposed which takes into account the turbulent boundary conditions and void fraction distribution in the vicinity of the wall. An important consequence of using the proposed technique is that the need of wall force model, which is questionable when applied to air-water turbulent bubbly flows, is eliminated. Also the bubbly TFM near the wall becomes convergent. Finally, the well-posed CFD TFM developed in the present study is checked for grid convergence. Previous researchers have advocated the idea of fixing the minimum grid size based on bubble diameter. This has restricted a thorough verification exercise in the past. It is shown that the grid size criterion can be removed if the model is made well-posed, which also makes sense because a continuum model should be independent of grid size. It is observed that the solution from the coarse grid simulations is a limit cycle whereas upon grid refinement, the solution becomes chaotic which is characteristic of turbulent bubbly two-phase flows. Therefore the grid size restriction may have an unwanted consequence. FFT spectra and time averaged void fraction profiles are used to assess grid convergence since the solutions are chaotic. The energy spectra indicate the Kolmogorov -5/3 scaling commonly used to describe turbulent flows.

  19. Bubbly flow model for the dynamic characteristics of cavitating pumps

    NASA Technical Reports Server (NTRS)

    Brennen, C.

    1978-01-01

    The recent experimental transfer matrices obtained by Ng and Brennen (1978) for some axial flow pumps revealed some dynamic characteristics which were unaccounted for by any existing theoretical analysis; their visual observations suggested that the bubbly cavitating flow in the blade passages could be responsible for these effects. A theoretical model of the dynamic response of this bubbly blade-passage flow is described in the present paper. Void-fraction fluctuations in this flow result not only from pressure fluctuations but also because the fluctuating angle of attack causes fluctuations in the rate of production of bubbles near the leading edge. The latter causes kinematic waves which interact through the boundary conditions with the dynamic waves caused by pressure fluctuation. The resulting theoretical transfer functions which results are in good qualitative agreement with the experiments; with appropriate choices of two parameters good quantitative agreement is also obtained. The theoretical model also provides one possible explanation of the observation that the pump changes from an essentially passive dynamic element in the absence of cavitation to a progressively more active element as the extent of cavitation increases.

  20. Multiscale interactions of bubbles with free vortex flows

    NASA Astrophysics Data System (ADS)

    Finn, Justin; Shams, Ehsan; Apte, Sourabh

    2009-11-01

    We simulate bubble and particle interactions with several types of free vortex flows using both a Discrete Element Model (DEM) and a fully resolved approach. In the DEM approach, DNS is used with Lagrangian particle tracking to compute the motion of a subgrid scale dispersed phase. The volumetric displacement of the fluid by the dispersed phase is modeled along with interphase momentum-exchange for more realistic coupling of the dispersed phase to the flow. In the fully resolved approach, a fictitious domain technique is used with refined grids to directly compute the motion of the dispersed phase to obtain high fidelity solutions. First, both approaches are used to simulate bubble entrainment into a stationary Gaussian vortex [Oweis et al. 2005]. Next, bubble entrainment and interaction with a traveling vortex tube [Sridhar & Katz 1999] is simulated using the DEM approach. Finally, a viscous falling `blob' of particles is simulated [Walther & Koumoutsakos 2001, Mitts 1995], where the dispersed phase generates and interacts with a 3D vortex ring. The results show that the less expensive DEM approach with volumetric coupling is able to capture clustering induced flow distortion, while the fully resolved approach gives insight into dispersed phase scale interactions with the flow.

  1. Bubble Generation in a Flowing Liquid Medium and Resulting Two-Phase Flow in Microgravity

    NASA Technical Reports Server (NTRS)

    Kamotani, Yasuhiro

    1996-01-01

    An experimental and theoretical research program is described herein to study bubble generation in a liquid flow in a pipe under reduced gravity conditions. The objective of the work is to study the bubble size and frequency of the generation and the resulting two-phase flow but it also concerns the fluid mechanical aspects of boiling in forced flow in microgravity. By injecting a gas into a liquid flow in a pipe through a small hole in the pipe wall we will investigate how the bubble expands and detaches from the wall, without involving the complexities of boiling. The experiments will be conducted both under isothermal conditions and with heat transfer from the wall. In the experiments with heat transfer the effect of thermocapillarity on the bubble formation and detachment will be the main subject.

  2. A Study of Bubble and Slug Gas-Liquid Flow in a Microgravity Environment

    NASA Technical Reports Server (NTRS)

    McQuillen, J.

    2000-01-01

    The influence of gravity on the two-phase flow dynamics is obvious.As the gravity level is reduced,there is a new balance between inertial and interfacial forces, altering the behavior of the flow. In bubbly flow,the absence of drift velocity leads to spherical-shaped bubbles with a rectilinear trajectory.Slug flow is a succession of long bubbles and liquid slug carrying a few bubbles. There is no flow reversal in the thin liquid film as the long bubble and liquid slug pass over the film. Although the flow structure seems to be simpler than in normal gravity conditions,the models developed for the prediction of flow behavior in normal gravity and extended to reduced gravity flow are unable to predict the flow behavior correctly.An additional benefit of conducting studies in microgravity flows is that these studies aide the development of understanding for normal gravity flow behavior by removing the effects of buoyancy on the shape of the interface and density driven shear flows between the gas and the liquid phases. The proposal calls to study specifically the following: 1) The dynamics of isolated bubbles in microgravity liquid flows will be analyzed: Both the dynamics of spherical isolated bubbles and their dispersion by turbulence, their interaction with the pipe wall,the behavior of the bubbles in accelerated or decelerated flows,and the dynamics of isolated cylindrical bubbles, their deformation in accelerated/decelerated flows (in converging or diverging channels), and bubble/bubble interaction. Experiments will consist of the use of Particle Image Velocimetry (PIV) and Laser Doppler Velocimeters (LDV) to study single spherical bubble and single and two cylindrical bubble behavior with respect to their influence on the turbulence of the surrounding liquid and on the wall 2) The dynamics of bubbly and slug flow in microgravity will be analyzed especially for the role of the coalescence in the transition from bubbly to slug flow (effect of fluid properties and

  3. Bubbles

    NASA Astrophysics Data System (ADS)

    Prosperetti, Andrea

    2004-06-01

    Vanitas vanitatum et omnia vanitas: bubbles are emptiness, non-liquid, a tiny cloud shielding a mathematical singularity. Born from chance, a violent and brief life ending in the union with the (nearly) infinite. But a wealth of phenomena spring forth from this nothingness: underwater noise, sonoluminescence, boiling, and many others. Some recent results on a "blinking bubble" micropump and vapor bubbles in sound fields are outlined. The last section describes Leonardo da Vinci's observation of the non-rectlinear ascent of buoyant bubbles and justifies the name Leonardo's paradox recently attributed to this phenomenon.

  4. Numerical analysis of incompressible viscous flow around a bubble

    NASA Astrophysics Data System (ADS)

    Sugano, Minoru; Ishii, Ryuji; Morioka, Shigeki

    1992-12-01

    A numerical simulation of flows around a deformable gas bubble rising through an incompressible viscous fluid is carried out on a supercomputer Fujitsu VP-2600 at the Data Processing Center of Kyoto University. The solution algorithm is a modified MAC (Marker And Cell) method. For the grid generation, an orthogonal mapping proposed by Ryskin and Leal is applied. The numerical results are compared with Ryskin and Leal's results and previous experiments. It will be shown that a good agreement is obtained between them.

  5. Numerical and physical modelling of bubbly flow phenomena

    SciTech Connect

    Sangani, A.S.

    1992-02-01

    The objective of the proposed research is to develop a theoretical framework for analyzing various two-phase flows, with special emphasis on the flows, with special emphasis on the flows of gas- liquid dispersions. The macroscopic behavior of these flows depends on the details of the microstructure of the dispersion, and these details, in turn, depend on the nature of the flow. Given the very diverse nature of the flows and their complex dependence on the microstructure of the dispersion, it is unlikely that a single set of equations, similar to the Navier-Stokes equations for homogeneous fluids, will apply to all the different situations. What is possible, however, is to develop general methodologies that can be used to examine specific situations and a general understanding about different kinds of macroscopic flows. The aim of the proposed research is to develop efficient numerical techniques for carrying out dynamic simulations of flows of dispersions and to apply them to a carefully selected problems whose solutions would reveal important qualitative as well as quantitative insights into the complex interdependence of the microstructure and macroscopic properties of the flows. These numerical techniques are to be supplemented with the techniques of ensemble averaging and statistical physics to obtain results that could be used in modelling more complicated flows through a set of relatively simple equations. Two classes of macroscopic flows were analyzed in detail during the current funding period. The first is the oscillatory flows, as in the case of acoustic or pressure wave propagation through bubbly liquids, and the second is convective flows as in bubbles rising through a liquid. 20 refs.

  6. Numerical and physical modelling of bubbly flow phenomena. Progress report

    SciTech Connect

    Sangani, A.S.

    1992-02-01

    The objective of the proposed research is to develop a theoretical framework for analyzing various two-phase flows, with special emphasis on the flows, with special emphasis on the flows of gas- liquid dispersions. The macroscopic behavior of these flows depends on the details of the microstructure of the dispersion, and these details, in turn, depend on the nature of the flow. Given the very diverse nature of the flows and their complex dependence on the microstructure of the dispersion, it is unlikely that a single set of equations, similar to the Navier-Stokes equations for homogeneous fluids, will apply to all the different situations. What is possible, however, is to develop general methodologies that can be used to examine specific situations and a general understanding about different kinds of macroscopic flows. The aim of the proposed research is to develop efficient numerical techniques for carrying out dynamic simulations of flows of dispersions and to apply them to a carefully selected problems whose solutions would reveal important qualitative as well as quantitative insights into the complex interdependence of the microstructure and macroscopic properties of the flows. These numerical techniques are to be supplemented with the techniques of ensemble averaging and statistical physics to obtain results that could be used in modelling more complicated flows through a set of relatively simple equations. Two classes of macroscopic flows were analyzed in detail during the current funding period. The first is the oscillatory flows, as in the case of acoustic or pressure wave propagation through bubbly liquids, and the second is convective flows as in bubbles rising through a liquid. 20 refs.

  7. A study of the accuracy of neutrally buoyant bubbles used as flow tracers in air

    NASA Technical Reports Server (NTRS)

    Kerho, Michael F.

    1993-01-01

    Research has been performed to determine the accuracy of neutrally buoyant and near neutrally buoyant bubbles used as flow tracers in air. Theoretical, computational, and experimental results are presented to evaluate the dynamics of bubble trajectories and factors affecting their ability to trace flow-field streamlines. The equation of motion for a single bubble was obtained and evaluated using a computational scheme to determine the factors which affect a bubble's trajectory. A two-dimensional experiment was also conducted to experimentally determine bubble trajectories in the stagnation region of NACA 0012 airfoil at 0 deg angle of attack using a commercially available helium bubble generation system. Physical properties of the experimental bubble trajectories were estimated using the computational scheme. These properties included the density ratio and diameter of the individual bubbles. the helium bubble system was then used to visualize and document the flow field about a 30 deg swept semispan wing with simulated glaze ice. Results were compared to Navier-Stokes calculations and surface oil flow visualization. The theoretical and computational analysis have shown that neutrally buoyant bubbles will trace even the most complex flow patterns. Experimental analysis revealed that the use of bubbles to trace flow patterns should be limited to qualitative measurements unless care is taken to ensure neutral buoyancy. This is due to the difficulty in the production of neutrally buoyant bubbles.

  8. Bubbly flow velocity measurements near a heated cylindrical conductor

    SciTech Connect

    Canaan, R.E.; Hassan, Y.A. )

    1990-01-01

    The objective of this study is to apply recent advances and improvements in the digital pulsed laser velocimetry (DPLV) technique to the analysis of two-phase bubbly flow about a cylindrical conductor emitting a constant heat flux within a transparent rectangular enclosure. Pulsed laser velocimetry is a rapidly advancing fluid flow visualization technique that determines full-field instantaneous velocity vectors of a quantitative nature such that the flow field remains undisturbed by the measurement. The DPLV method offers several significant advantages over more traditional fluid velocity measurement techniques such as hot wire/film anemometry and laser Doppler anemometry because reliable instantaneous velocity data may be acquired over substantial flow areas in a single experiment.

  9. Shock Waves in Bubbly Cavitating Flows: Part I. Shock Waves in Cloud Cavitation. Part II. Bubbly Cavitating Flows Through a Converging-Diverging Nozzle.

    NASA Astrophysics Data System (ADS)

    Wang, Yi-Chun

    Two problems are considered in this thesis: the nonlinear dynamics of a cloud of cavitation bubbles, and bubbly cavitating flows through a converging-diverging nozzle. The focus of the first problem is to explore the characteristics of the growth and collapse of a spherical cloud of bubbles. This is typical of the transient behaviour exhibited by a bubble cloud as it passes a body or the blade of a ship propeller. The simulations employ the fully nonlinear, non-barotropic, homogeneous two-phase flow equations coupled with the Rayleigh-Plesset equation for the dynamics of individual bubbles. It was found that the collapse of the cloud is accompanied by the formation of an inward propagating bubbly shock wave. The focusing of the shock is responsible for the severe noise and damage potential in cloud cavitation. The second problem investigates the nonlinear behavior of bubbly cavitating flows through a converging -diverging nozzle. Two different flow regimes are found from steady state solutions: quasi-steady and quasi-unsteady. Bifurcation occurs as the flow transitions from one regime to the other. Unsteady solutions in a period of consecutive times are also presented. These solutions are characterized by large pressure pulses changing in both magnitude and location with time downstream of the throat. The characteristics of these pulses are similar to the shock pulses of the first problem and are produced by the local violent collapse of the bubbles in the flow.

  10. Measurements of Shear Lift Force on a Bubble in Channel Flow in Microgravity

    NASA Technical Reports Server (NTRS)

    Nahra, Henry K.; Motil, Brian J.; Skor, Mark

    2003-01-01

    Under microgravity conditions, the shear lift force acting on bubbles, droplets or solid particles in multiphase flows becomes important because under normal gravity, this hydrodynamic force is masked by buoyancy. This force plays an important role in furnishing the detachment process of bubbles in a setting where a bubble suspension is needed in microgravity. In this work, measurements of the shear lift force acting on a bubble in channel flow are performed. The shear lift force is deduced from the bubble kinematics using scaling and then compared with predictions from models in literature that address different asymptotic and numerical solutions. Basic trajectory calculations are then performed and the results are compared with experimental data of position of the bubble in the channel. A direct comparison of the lateral velocity of the bubbles is also made with the lateral velocity prediction from investigators, whose work addressed the shear lift on a sphere in different two-dimensional shear flows including Poiseuille flow.

  11. Numerical modeling of gravity-driven bubble flows with account of polydispersion

    NASA Astrophysics Data System (ADS)

    Chernyshev, A. S.; Schmidt, A. A.

    2016-10-01

    The present study is focused on the investigation of motion of bubble-liquid medium inside the bubble columns or vertical pipes with account of polydisperse phenomena by the means of numerical simulation. The underlying mathematical model is based on the Euler- Euler approach with interphase interaction described by the momentum and mass transfer between phases, along with the k-w-SST turbulence model which includes turbulence generation by the bubble motion and bubble path dispersion. Polydispersion is taken into account by the multi-class model with piecewise-constant distribution of bubble sizes per cell. Simulation of downward flow inside the straight vertical pipe resulted in maximum of the bubble void fraction close to the pipe center which is in good correlation with the experimental data. Simulation of multiphase flow inside rectangular bubble column with off-center sparger resulted in vertical bubble-liquid jet which is biased towards nearby wall with the correct prediction of attachment point location.

  12. The bubbly-slug transition in a boiling two-phase flow under microgravity

    NASA Technical Reports Server (NTRS)

    Kiper, Ali M.; Swanson, T. D.

    1993-01-01

    A theory is presented to describe, in reduced gravity flow boiling, the transition from bubbly two-phase flow to slug flow. It is shown that characteristics of the bubbly flow and the transition were controlled by the mechanism of vapor bubble growth dynamics. By considering in nucleate boiling, behavior of vapor bubbles at departure from a heated surface a condition required for transition was determined. Although required, this condition alone could not ensure coalescence of bubbles to cause the transition to slug two-phase flow. The condition leading to coalescence, therefore, was obtained by examining oscillations of vapor bubbles following their departure from the heated surface. The predicted transition conditions were compared with the prediction and test data reported for adiabatic reduced gravity two-phase flow, and good qualitative agreement was found.

  13. Bubble formation during horizontal gas injection into downward-flowing liquid

    NASA Astrophysics Data System (ADS)

    Bai, Hua; Thomas, Brian G.

    2001-12-01

    Bubble formation during gas injection into turbulent downward-flowing water is studied using high-speed videos and mathematical models. The bubble size is determined during the initial stages of injection and is very important to turbulent multiphase flow in molten-metal processes. The effects of liquid velocity, gas-injection flow rate, injection hole diameter, and gas composition on the initial bubble-formation behavior have been investigated. Specifically, the bubble-shape evolution, contact angles, size, size range, and formation mode are measured. The bubble size is found to increase with increasing gas-injection flow rate and decreasing liquid velocity and is relatively independent of the gas injection hole size and gas composition. Bubble formation occurs in one of four different modes, depending on the liquid velocity and gas flow rate. Uniform-sized spherical bubbles form and detach from the gas injection hole in mode I for a low liquid speed and small gas flow rate. Modes III and IV occur for high-velocity liquid flows, where the injected gas elongates down along the wall and breaks up into uneven-sized bubbles. An analytical two-stage model is developed to predict the average bubble size, based on realistic force balances, and shows good agreement with measurements. Preliminary results of numerical simulations of bubble formation using a volume-of-fluid (VOF) model qualitatively match experimental observations, but more work is needed to reach a quantitative match. The analytical model is then used to estimate the size of the argon bubbles expected in liquid steel in tundish nozzles for conditions typical of continuous casting with a slide gate. The average argon bubble sizes generated in liquid steel are predicted to be larger than air bubbles in water for the same flow conditions. However, the differences lessen with increasing liquid velocity.

  14. Vertical, Bubbly, Cross-Flow Characteristics over Tube Bundles

    NASA Astrophysics Data System (ADS)

    Iwaki, C.; Cheong, K. H.; Monji, H.; Matsui, G.

    2005-12-01

    Two-phase flow over tube bundles is commonly observed in shell and tube-type heat exchangers. However, only limited amount of data concerning flow pattern and void fraction exists due to the flow complexity and the difficulties in measurement. The detailed flow structure in tube bundles needs to be understood for reliable and effective design. Therefore, the objective of this study was to clarify the two-phase structure of cross-flow in tube bundles by PIV. Experiments were conducted using two types of models, namely in-line and staggered arrays with a pitch-to-diameter ratio of 1.5. Each test section contains 20 rows of five 15 mm O.D. tubes in each row. The experiment’s data were obtained under very low void fraction (α<0.02). Liquid and gas velocity data in the whole flow field were measured successfully by optical filtering and image processing. The structures of bubbly flow in the two different configurations of tube bundles were described in terms of the velocity vector field, turbulence intensity and void fraction.

  15. Bubble Formation from Wall Orifice in Liquid Cross-Flow Under Low Gravity

    NASA Technical Reports Server (NTRS)

    Nahra, Henry K.; Kamotani, Y.

    2000-01-01

    Two-phase flows present a wide variety of applications for spacecraft thermal control systems design. Bubble formation and detachment is an integral part of the two phase flow science. The objective of the present work is to experimentally investigate the effects of liquid cross-flow velocity, gas flow rate, and orifice diameter on bubble formation in a wall-bubble injection configuration. Data were taken mainly under reduced gravity conditions but some data were taken in normal gravity for comparison. The reduced gravity experiment was conducted aboard the NASA DC-9 Reduced Gravity Aircraft. The results show that the process of bubble formation and detachment depends on gravity, the orifice diameter, the gas flow rate, and the liquid cross-flow velocity. The data are analyzed based on a force balance, and two different detachment mechanisms are identified. When the gas momentum is large, the bubble detaches from the injection orifice as the gas momentum overcomes the attaching effects of liquid drag and inertia. The surface tension force is much reduced because a large part of the bubble pinning edge at the orifice is lost as the bubble axis is tilted by the liquid flow. When the gas momentum is small, the force balance in the liquid flow direction is important, and the bubble detaches when the bubble axis inclination exceeds a certain angle.

  16. Effects of outlet blade angle of centrifugal pump on the pump performance under air-water two-phase flow conditions

    SciTech Connect

    Minemura, Kiyoshi; Kinoshita, Katsuhiko; Ihara, Masaru; Furukawa, Hironori; Egashira, Kazuyuki

    1995-12-31

    To establish the optimum design parameters of offshore oil well centrifugal pumps, which should deliver crude oil containing a large amount of gas, various shapes of pump impeller with different outlet blade angles, locations of leading-edge and numbers of impeller blades as the design parameters were tested with various rotating speeds and suction pressures under air-water two-phase flow conditions. The greater the outlet blade angle, the less the degradation of the pump performance becomes, showing the optimum blade angle approximately equals to 90{degree}.

  17. Experimental investigation of head resistance reduction in bubbly Couette-Taylor flow

    NASA Astrophysics Data System (ADS)

    Maryami, R.; Javadpoor, M.; Farahat, S.

    2016-12-01

    Small bubble experiments are carried out in a circulating vertical Couette-Taylor flow system to investigate the effect of air bubbles on head resistance. In the system with inner rotating cylinder and circulating flow, flow is combined with circumferential and axial flow. Moreover, the variation range of rotational Reynolds number is 7 × 103 ≤ {Re}_{ω } ≤ 70 × 103 and small bubbles are dispersed into fully turbulent flow which consists of Taylor vortices. The modification of head resistance is examined by measuring the pressure difference between two certain holes along the cylinders axis. The results show that head resistance is decreased in the presence of small bubbles and a head resistance reduction greater than 60 % is achieved in low {Re}_{ω } s and in all {Re}_{ax} s changing from 299.15 to 396.27. The effect of air bubbles on vortices could be possible reason for head resistance reduction. Since Taylor vortices are stable in this regime, bubbles decrease the momentum transfer by elongating vortices along the axis of cylinders and decreasing their numbers. The positive effect of air bubbles on head resistance reduction is diminished when {Re}_{ω } is increased. Moreover, in certain ranges of {Re}_{ω }, small bubbles enhance head resistance when {Re}_{ax} is increased. It is predicted that negative effect of small bubbles on head resistance reduction is due to flow turbulence enhancement when {Re}_{ω } and {Re}_{ax} are increased.

  18. Modeling and Measurements of Multiphase Flow and Bubble Entrapment in Steel Continuous Casting

    NASA Astrophysics Data System (ADS)

    Jin, Kai; Thomas, Brian G.; Ruan, Xiaoming

    2016-02-01

    In steel continuous casting, argon gas is usually injected to prevent clogging, but the bubbles also affect the flow pattern, and may become entrapped to form defects in the final product. To investigate this behavior, plant measurements were conducted, and a computational model was applied to simulate turbulent flow of the molten steel and the transport and capture of argon gas bubbles into the solidifying shell in a continuous slab caster. First, the flow field was solved with an Eulerian k- ɛ model of the steel, which was two-way coupled with a Lagrangian model of the large bubbles using a discrete random walk method to simulate their turbulent dispersion. The flow predicted on the top surface agreed well with nailboard measurements and indicated strong cross flow caused by biased flow of Ar gas due to the slide-gate orientation. Then, the trajectories and capture of over two million bubbles (25 μm to 5 mm diameter range) were simulated using two different capture criteria (simple and advanced). Results with the advanced capture criterion agreed well with measurements of the number, locations, and sizes of captured bubbles, especially for larger bubbles. The relative capture fraction of 0.3 pct was close to the measured 0.4 pct for 1 mm bubbles and occurred mainly near the top surface. About 85 pct of smaller bubbles were captured, mostly deeper down in the caster. Due to the biased flow, more bubbles were captured on the inner radius, especially near the nozzle. On the outer radius, more bubbles were captured near to narrow face. The model presented here is an efficient tool to study the capture of bubbles and inclusion particles in solidification processes.

  19. Two-way Interaction of Lagrangian Bubble Dynamics and Eulerian Mixture Flow Field

    NASA Astrophysics Data System (ADS)

    Choi, Jin-Keun; Hsiao, Chao-Tsung; Chahine, Georges

    2007-11-01

    Although under simple flow conditions a well dispersed bubble cloud in a liquid can be modeled with an Eulerian continuum model, the fine scale interactions between the two phases, the potential non-uniformities and high bubble concentrations in stiff gradient regions of complex flows can only be represented by more detailed numerical models such as Lagrangian tracking of individual bubbles. To meet both needs of describing individual bubbles and of including the collective effects in the two-phase continuum, we have developed a method coupling in a two-way fashion the two approaches. The bubble dynamics and tracking scheme is based on extensive studies on bubble dynamics and interactions at Dynaflow and is based on a Surface Averaged Pressure spherical model using a modified incompressible Rayleigh-Plesset equation or a modified compressible Gilmore equation. The bubbles presence in the Eulerian flow field is considered through a variable medium density formulation resulting from the instantaneous bubble population distribution in the field. The developed method is applicable to many practical flows in pipes, jets, pumps, propellers, ships, and the ocean. We present the method and its application to waterjet thrust augmentation by bubble injection.

  20. Direct Numerical Simulation of Insoluble Surfactant Effect on Turbulent Channel Bubbly Flows

    NASA Astrophysics Data System (ADS)

    Lu, Jiacai; Tryggvason, Gretar

    2016-11-01

    Direct Numerical Simulations (DNS) have been successfully used to obtain detailed data for turbulent channel bubbly flows. However, most of DNS that have been done so far remain problematic in comparing to most experiments. One of the major reasons is that real bubbly flows contain surfactants. The surfactants adhere to the interface, and produce an uneven distribution of the surfactant concentration due to the moving of bubbles and result in uneven surface tension over bubble surfaces. In this project, the effect of surfactants on the flow of many bubbles in an upward turbulent channel flow is studied by using of Direct Numerical Simulation with 3D Front-tracking method. The surfactant mass and the interfacial area are directly tracked in the method, and the surfactant mass remains conserved during the evolution. By using of different elasticity numbers in the non-linear equation of state which relates the surface tension to the surfactant concentration, the simulations show that the evolution of the turbulent channel bubbly flow are much different among the cases with contaminated bubbles and clean bubbles. Profiles of many parameters, such as streamwise velocity, shear stress and etc., are also compared at the statistically steady state for these cases. Research supported by DOE (CASL).

  1. Adsorption of Egg-PC to an Air/Water and Triolein/Water Bubble Interface: Use of the 2-Dimensional Phase Rule to Estimate the Surface Composition of a Phospholipid/Triolein/Water Surface as a Function of Surface Pressure

    PubMed Central

    Mitsche, Matthew A.; Wang, Libo; Small, Donald M.

    2010-01-01

    Phospholipid monolayers play a critical role in the structure and stabilization of biological interfaces including all membranes, the alveoli of the lung, fat droplets in adipose tissue, and lipoproteins. The behavior of phospholipids in bilayers and at an air-water interface is well understood. However, the study of phospholipids at oil-water interfaces is limited due to technical challenges. In this study, egg-phosphatidylcholine (EPC) was deposited from small unilamellar vesicles onto a bubble of either air or triolein (TO) formed in a low salt buffer. The surface tension (γ) was measured using a drop tensiometer. We observed that EPC binds irreversibly to both interfaces and at equilibrium exerts ~12 and 15 mN/m of pressure (Π) at an air and TO interface, respectively. After EPC was bound to the interface, the unbound EPC was washed out of the cuvette and the surface was compressed to study the Π/area relationship. To determine the surface concentration (Γ), which cannot be measured directly, compression isotherms from a Langmuir trough and drop tensiometer were compared. The air-water interfaces had identical characteristics using both techniques, thus Γ on the bubble can be determined by overlaying the two isotherms. TO and EPC are both surface active so in a mixed TO/EPC monolayer both molecules will be exposed to water. Since TO is less surface active than EPC, as Π increases the TO is progressively ejected. To understand the Π/area isotherm of EPC on a TO bubble, a variety of TO-EPC mixtures were spread at the air-water interface. The isotherms show an abrupt break in the curve caused by the ejection of TO from the monolayer into a new bulk phase. By overlaying the compression isotherm above the ejection point with a TO bubble compression isotherm, Γ can be estimated. This allows determination of Γ of EPC on a TO bubble as a function of Π. PMID:20151713

  2. Bubble velocity, diameter, and void fraction measurements in a multiphase flow using fiber optic reflectometer

    NASA Astrophysics Data System (ADS)

    Lim, Ho-Joon; Chang, Kuang-An; Su, Chin B.; Chen, Chi-Yueh

    2008-12-01

    A fiber optic reflectometer (FOR) technique featuring a single fiber probe is investigated for its feasibility of measuring the bubble velocity, diameter, and void fraction in a multiphase flow. The method is based on the interference of the scattered signal from the bubble surface with the Fresnel reflection signal from the tip of the optical fiber. Void fraction is obtained with a high accuracy if an appropriate correction is applied to compensate the underestimated measurement value. Velocity information is accurately obtained from the reflected signals before the fiber tip touches the bubble surface so that several factors affecting the traditional dual-tip probes such as blinding, crawling, and drifting effects due to the interaction between the probe and bubbles can be prevented. The coherent signals reflected from both the front and rear ends of a bubble can provide velocity information. Deceleration of rising bubbles and particles due to the presence of the fiber probe is observed when they are very close to the fiber tip. With the residence time obtained, the bubble chord length can be determined by analyzing the coherent signal for velocity determination before the deceleration starts. The bubble diameters are directly obtained from analyzing the signals of the bubbles that contain velocity information. The chord lengths of these bubbles measured by FOR represent the bubble diameters when the bubble shape is spherical or represent the minor axes when the bubble shape is ellipsoidal. The velocity and size of bubbles obtained from the FOR measurements are compared with those obtained simultaneously using a high speed camera.

  3. Numerical study of the influence of geometrical characteristics of a vertical helical coil on a bubbly flow

    NASA Astrophysics Data System (ADS)

    Saffari, H.; Moosavi, R.

    2014-11-01

    In this article, turbulent single-phase and two-phase (air-water) bubbly fluid flows in a vertical helical coil are analyzed by using computational fluid dynamics (CFD). The effects of the pipe diameter, coil diameter, coil pitch, Reynolds number, and void fraction on the pressure loss, friction coefficient, and flow characteristics are investigated. The Eulerian-Eulerian model is used in this work to simulate the two-phase fluid flow. Three-dimensional governing equations of continuity, momentum, and energy are solved by using the finite volume method. The k- ɛ turbulence model is used to calculate turbulence fluctuations. The SIMPLE algorithm is employed to solve the velocity and pressure fields. Due to the effect of a secondary force in helical pipes, the friction coefficient is found to be higher in helical pipes than in straight pipes. The friction coefficient increases with an increase in the curvature, pipe diameter, and coil pitch and decreases with an increase in the coil diameter and void fraction. The close correlation between the numerical results obtained in this study and the numerical and empirical results of other researchers confirm the accuracy of the applied method. For void fractions up to 0.1, the numerical results indicate that the friction coefficient increases with increasing the pipe diameter and keeping the coil pitch and diameter constant and decreases with increasing the coil diameter. Finally, with an increase in the Reynolds number, the friction coefficient decreases, while the void fraction increases.

  4. Bubble shapes in steady axisymmetric flows at intermediate Reynolds number

    NASA Technical Reports Server (NTRS)

    Ryskin, G.; Leal, L. G.

    1982-01-01

    The shape of a gas bubble which rises through a quiescent incompressible, Newtonian fluid at intermediate Reynolds numbers is considered. Exact numerical solutions for the velocity and pressure fields, as well as the bubble shape, are obtained using finite difference techniques and a numerically generated transformation to an orthogonal, boundary-fitted coordinate system. No restriction is placed on the allowable magnitude of deformation.

  5. Bubble-induced turbulence study in homogeneous turbulent flow using DNS approach

    NASA Astrophysics Data System (ADS)

    Feng, Jinyong; Bolotnov, Igor

    2015-11-01

    The effect of a single bubble on the energy transfer to a homogeneous turbulent flow using DNS approach is investigated for various conditions. The single-phase turbulence is numerically generated by pressure-gradient driven uniform flow through a fully resolved turbulence generating grid. The turbulent intensity measured is uniform normal to the flow direction. The decay rate of the turbulent kinetic energy is validated against analytical power law. The collected instantaneous velocity is used as inflow condition for single-bubble simulations to study the bubble-induced turbulence (BIT). In interface-resolved two-phase simulation the bubble is kept at fixed positions by using a proportional-integral-derivative controller. This simulation set allows estimating the turbulent kinetic energy before and after the bubble, quantifying the BIT. Effects of bubble deformability, velocity and turbulent intensity are separately studied. We observe that for a nearly spherical bubble, the bubble-induced turbulence is positive, increasing the level of turbulent kinetic energy in the liquid phase. BIT is influenced by the other studied parameters and the presented work will contribute to the closure BIT model development in multiphase computational fluid dynamics modeling. The work is supported by NSF-CBET-Fluid Dynamics, Award #1333993.

  6. μ-PIV measurements of the ensemble flow fields surrounding a migrating semi-infinite bubble.

    PubMed

    Yamaguchi, Eiichiro; Smith, Bradford J; Gaver, Donald P

    2009-08-01

    Microscale particle image velocimetry (μ-PIV) measurements of ensemble flow fields surrounding a steadily-migrating semi-infinite bubble through the novel adaptation of a computer controlled linear motor flow control system. The system was programmed to generate a square wave velocity input in order to produce accurate constant bubble propagation repeatedly and effectively through a fused glass capillary tube. We present a novel technique for re-positioning of the coordinate axis to the bubble tip frame of reference in each instantaneous field through the analysis of the sudden change of standard deviation of centerline velocity profiles across the bubble interface. Ensemble averages were then computed in this bubble tip frame of reference. Combined fluid systems of water/air, glycerol/air, and glycerol/Si-oil were used to investigate flows comparable to computational simulations described in Smith and Gaver (2008) and to past experimental observations of interfacial shape. Fluorescent particle images were also analyzed to measure the residual film thickness trailing behind the bubble. The flow fields and film thickness agree very well with the computational simulations as well as existing experimental and analytical results. Particle accumulation and migration associated with the flow patterns near the bubble tip after long experimental durations are discussed as potential sources of error in the experimental method.

  7. Multiscale computations of mass accumulation effect on mass transfer in bubbly flow

    NASA Astrophysics Data System (ADS)

    Aboulhasanzadeh, Bahman; Tryggvason, Gretar

    2014-11-01

    Mass transfer in bubbly flow generally takes place on a much smaller length and time scale than the length and time scale of the momentum flow, resulting in a thin mass boundary layer around the bubbles. We developed a multiscale model to solve a boundary layer equation for the mass boundary layer next to the bubble interface, assuming zero mass concentration in the far field, which couples with the rest of domain using a source/sink term. Here, we extend our model to account for non-zero concentration next to the mass boundary layer. Comparison of simple case studies in 1D and 2D problems show good agreement between the fully resolved solution and the solution on a much coarser grid using our model. We study the effect of mass accumulation in a domain and also the effect of bubble moving into the wake of another bubble on the mass transfer. This study was funded by NSF Grant CBET-1132410.

  8. Numerical Simulation of Turbulent Bubbly Flow in a Vertical Square Duct

    NASA Astrophysics Data System (ADS)

    Vanka, Pratap; Kumar, Purushotam; Jin, Kai

    2016-11-01

    We numerically investigate the dynamics of a large number of gas bubbles in a turbulent liquid flow in a confined vertical square duct, a problem of interest to many industrial equipment. The fluid flow is simulated by Direct Numerical Simulations and the motions of the bubbles are resolved by an accurate Volume of Fluid (VOF) technique. The flow is considered periodic in the streamwise direction with an imposed pressure gradient. The surface tension force is incorporated through a Sharp Surface Force (SSF) method that is observed to generate only very small spurious velocities at the interface. The algorithm has been programmed on a multiple-GPU computer in a data parallel mode. The turbulence driven secondary flows are first ensured to agree with previous DNS/LES by other researchers. A very fine grid with 192 x 192 x 768 control volumes is used to resolve the liquid flow as well as 864 bubbles using 12 grid points across each bubble in all directions. The computations are carried out to 1.5 million time steps. It is seen that the bubbles preferentially migrate to walls, starting from a uniform layout. We present instantaneous and time mean velocities, turbulence statistics and compare them with unladen flow as well as with a bubbly flow in a planar channel.

  9. The Terminal Velocity of a Bubble in an Oscillating Flow

    NASA Astrophysics Data System (ADS)

    Romero, L. A.; Kraynik, A. M.; Torczynski, J. R.

    2010-11-01

    A bubble in an acoustic field experiences a net "Bjerknes" force from the nonlinear coupling of its radial oscillations with the oscillating buoyancy force. It is typically assumed that the bubble's net terminal velocity can be found by considering a spherical bubble with the imposed "Bjerknes stresses". We have analyzed the motion of such a bubble using a rigorous perturbation approach and found that one must include a term involving an effective mass flux through the bubble that arises from the time average of the second-order nonlinear terms in the kinematic boundary condition. The importance of this term is governed by the dimensionless parameter α=R^2φ / R^2φ ν . - ν, where R is the bubble radius, φ is the driving frequency, and ν is the liquid kinematic viscosity. If α is large, this term is unimportant, but if α is small, this term is the dominant factor in determining the terminal velocity. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  10. Formation of bubbles in a simple co-flowing micro-channel

    NASA Astrophysics Data System (ADS)

    Xiong, Renqiang; Bai, Mo; Chung, Jacob N.

    2007-05-01

    Bubble generation in a simple co-flowing micro-channel with a cross-sectional area of 1.69 × 0.07 mm2 was experimentally and numerically investigated. Air and water were used as the gas and liquid, respectively. Mixtures of water-glycerol and water-Tween 20 were also used to obtain the effects of viscosity and surface tension. The experimental data show that the break-up process is periodic under certain operating conditions. The break-up dynamics are also examined using three-dimensional incompressible two-phase flow numerical simulation based on the volume of fluid (VOF) method. The simulation successfully predicts the flow behavior and provides a more detailed examination of the bubble shape. The physics can be further explained by the detailed micro-PIV measurements, which show that the bubble is formed due to the velocity component perpendicular to the gas flow created by the sudden change of the liquid velocity distribution around the barrier. The bubble length L is dependent on the liquid flow rate Ql and the gas flow rate Qg, and the ratio of L to the channel width w is a function of the ratio of gas and liquid flow rates Qg/Ql which is similar to that previously used in the T-junction case. The formulation of bubble frequency f is derived under current conditions and it shows a good agreement with the experimental data at the low frequency region. Different bubble shapes can be obtained at different liquid viscosities and surface tensions. The ratio L/w can still be predicted by a modified equation which uses the real bubble width wb or an equivalent bubble length Le.

  11. Research on the Conductivity-Based Detection Principles of Bubbles in Two-Phase Flows and the Design of a Bubble Sensor for CBM Wells

    PubMed Central

    Wu, Chuan; Wen, Guojun; Han, Lei; Wu, Xiaoming

    2016-01-01

    The parameters of gas-liquid two-phase flow bubbles in field coalbed methane (CBM) wells are of great significance for analyzing coalbed methane output, judging faults in CBM wells, and developing gas drainage and extraction processes, which stimulates an urgent need for detecting bubble parameters for CBM wells in the field. However, existing bubble detectors cannot meet the requirements of the working environments of CBM wells. Therefore, this paper reports findings on the principles of measuring the flow pattern, velocity, and volume of two-phase flow bubbles based on conductivity, from which a new bubble sensor was designed. The structural parameters and other parameters of the sensor were then computed, the “water film phenomenon” produced by the sensor was analyzed, and the appropriate materials for making the sensor were tested and selected. After the sensor was successfully devised, laboratory tests and field tests were performed, and the test results indicated that the sensor was highly reliable and could detect the flow patterns of two-phase flows, as well as the quantities, velocities, and volumes of bubbles. With a velocity measurement error of ±5% and a volume measurement error of ±7%, the sensor can meet the requirements of field use. Finally, the characteristics and deficiencies of the bubble sensor are summarized based on an analysis of the measurement errors and a comparison of existing bubble-measuring devices and the designed sensor. PMID:27649206

  12. Research on the Conductivity-Based Detection Principles of Bubbles in Two-Phase Flows and the Design of a Bubble Sensor for CBM Wells.

    PubMed

    Wu, Chuan; Wen, Guojun; Han, Lei; Wu, Xiaoming

    2016-09-17

    The parameters of gas-liquid two-phase flow bubbles in field coalbed methane (CBM) wells are of great significance for analyzing coalbed methane output, judging faults in CBM wells, and developing gas drainage and extraction processes, which stimulates an urgent need for detecting bubble parameters for CBM wells in the field. However, existing bubble detectors cannot meet the requirements of the working environments of CBM wells. Therefore, this paper reports findings on the principles of measuring the flow pattern, velocity, and volume of two-phase flow bubbles based on conductivity, from which a new bubble sensor was designed. The structural parameters and other parameters of the sensor were then computed, the "water film phenomenon" produced by the sensor was analyzed, and the appropriate materials for making the sensor were tested and selected. After the sensor was successfully devised, laboratory tests and field tests were performed, and the test results indicated that the sensor was highly reliable and could detect the flow patterns of two-phase flows, as well as the quantities, velocities, and volumes of bubbles. With a velocity measurement error of ±5% and a volume measurement error of ±7%, the sensor can meet the requirements of field use. Finally, the characteristics and deficiencies of the bubble sensor are summarized based on an analysis of the measurement errors and a comparison of existing bubble-measuring devices and the designed sensor.

  13. Thermocapillary Flow and Coalescences of Heterogeneous Bubble Size Diameter in a Rotating Cylinder: 3D Study

    NASA Astrophysics Data System (ADS)

    Alhendal, Yousuf; Turan, Ali

    2016-12-01

    Two dimensional axisymmetric and three-dimensional VOF simulations of gas/liquid transient flow were performed using a multiphase flow algorithm based on the finite-volume method. The results for motion of a multiple bubbles of a heterogeneous sizes aligned horizontally and perpendicular to a hot surface incorporating thermocapillary forces in a rotating liquid in a zero-gravity environment have been presented for the first time. No bubbles broke in any of the cases observed. The results also show that collision and agglomeration of bubbles of unequal sizes diameter are different from those of similar size diameters presented from earlier research work of Alhendal et al. Acta Astronaut. 117, 484-496 (2015). Different flow patterns such as thermocapillary bubble migration, collision, and stream function were observed and presented for the 2-D and 3-D models.

  14. Numerical Simulation of Bubbly Flows in an Aeration Tank with Biochemical Reactions

    NASA Astrophysics Data System (ADS)

    Noor Ul Huda, Khateeb; Shimizu, Kazuya; Gong, Xiaobo; Takagi, Shu

    2016-11-01

    For bubbly flow with biochemical reactions, all the analyses including overall fluid flow, bubble motion, bubble dissolution at local level and bacterial reactions/consumption of substrates are important. The developed system is provided by mixed Eulerian-Lagrangian formulation in which liquid media is represented in Eulerian system and bubbles are tracked individually. Murai and Matsumoto developed a model to track bubbles to predict plume structure in finely dispersed domain. Gong et al. developed the model further to include mass transfer, gas dissolution and mixing phenomenon entrained in this model. In this research we are using the model to include simulation of bacterial biochemical reactions for the purification of water and make it resemble as the wastewater purification tank. The gas bubble dissolution and mass transfer from gas to liquid phase is linked with biochemical reactions for an overall comprehensive study. The main area associated with this research is to incorporate all biochemical reactions in this bubbly flow based on situation of water and demand. In this particular study, various kinds of biomass and substrates are considered. A detailed model for biological wastewater purification involving reactions using bacteria's is developed and primary validation has been carried out based on experimental study. Finally, we tried to achieve physical optimization for this biochemical reactions.

  15. Two-Phase CFD Model of the Bubble-Driven Flow in the Molten Electrolyte Layer of a Hall-Héroult Aluminum Cell

    NASA Astrophysics Data System (ADS)

    Feng, Yuqing; Schwarz, M. Philip; Yang, William; Cooksey, Mark

    2015-08-01

    A two-phase computational fluid dynamics (CFD) model has been developed to simulate the time-averaged flow in the molten electrolyte layer of a Hall -Héroult aluminum cell. The flow is driven by the rise of carbon dioxide bubbles formed on the base of the anodes. The CFD model has been validated against detailed measurements of velocity and turbulence taken in a full-scale air-water physical model containing three anodes in four different configurations, with varying inter-anode gap and the option of slots. The model predictions agree with the measurements of velocity and turbulence energy for all configurations within the likely measurement repeatability, and therefore can be used to understand the overall electrolyte circulation patterns and mixing. For example, the model predicts that the bubble holdup under an anode is approximately halved by the presence of a slot aligned transverse to the cell long axis. The flow patterns do not appear to be significantly altered by halving the inter-anode gap width from 40 to 20 mm. The CFD model predicts that the relative widths of center, side, and end channels have a major influence on several critical aspects of the cell flow field.

  16. The growth of vapor bubble and relaxation between two-phase bubble flow

    NASA Astrophysics Data System (ADS)

    Mohammadein, S. A.; Subba Reddy Gorla, Rama

    2002-10-01

    This paper presents the behavior of the bubble growth and relaxation between vapor and superheated liquid. The growth and thermal relaxation time between the two-phases are obtained for different levels of superheating. The heat transfer problem is solved numerically by using the extended Scriven model. Results are compared with those of Scriven theory and MOBY DICK experiment with reasonably good agreement for lower values of superheating.

  17. Numerical Simulation of Bubble Cluster Induced Flow by Three-Dimensional Vortex-in-Cell Method.

    PubMed

    Chen, Bin; Wang, Zhiwei; Uchiyama, Tomomi

    2014-08-01

    The behavior of air bubble clusters rising in water and the induced flow field are numerically studied using a three-dimensional two-way coupling algorithm based on a vortex-in-cell (VIC) method. In this method, vortex elements are convected in the Lagrangian frame and the liquid velocity field is solved from the Poisson equation of potential on the Eulerian grid. Two-way coupling is implemented by introducing a vorticity source term induced by the gradient of void fraction. Present simulation results are favorably compared with the measured results of bubble plume, which verifies the validity of the proposed VIC method. The rising of a single bubble cluster as well as two tandem bubble clusters are simulated. The mechanism of the aggregation effect in the rising process of bubble cluster is revealed and the transient processes of the generation, rising, strengthening, and separation of a vortex ring structure with bubble clusters are illustrated and analyzed in detail. Due to the aggregation, the average rising velocity increases with void fraction and is larger than the terminal rising velocity of single bubble. For the two tandem bubble cluster cases, the aggregation effect is stronger for smaller initial cluster distance, and both the strength of the induced vortex structure and the average bubble rising velocity are larger. For the 20 mm cluster distance case, the peak velocity of the lower cluster is about 2.7 times that of the terminal velocity of the single bubble and the peak average velocity of two clusters is about 2 times larger. While for the 30 mm cluster distance case, both the peak velocity of the lower cluster and two clusters are about 1.7 times that of the terminal velocity of the single bubble.

  18. Thermocapillary bubble flow and coalescence in a rotating cylinder: A 3D study

    NASA Astrophysics Data System (ADS)

    Alhendal, Yousuf; Turan, A.; Al-mazidi, M.

    2015-12-01

    The process of thermocapillary bubbles rising in a rotating 3D cylinder in zero gravity was analysed and presented numerically with the aid of computational fluid dynamics (CFD) by means of the volume of fluid (VOF) method. Calculations were carried out to investigate in detail the effect of the rotational speed of the hosted liquid on the trajectory of both single and group bubbles driven by the Marangoni force in zero-gravity conditions. For rotational speeds from 0.25 to 2 rad/s, bubble displacement with angular motion was found to be directed between the hotter surface and the rotational axis. This is contrary to the conventional bubble flow from areas of high pressure to low pressure, radial direction, or from cold to hot regions, axial direction. The results demonstrate that for the ratio of rotational speeds to the thermocapillary bubble velocity larger than unity, the surface tension gradient is the dominant force and the bubble motion towards the hotter. On the other hand, for ratio less than 1, the bubble motion is dominated and is significantly affected by centrifugal force. As rotation speed increases, the amount of deflection increases and the Marangoni effect vanishes. The current study is novel in the sense that single- and multi-bubble motion incorporating thermocapillary forces in a rotating liquid in a zero-gravity environment has never been numerically investigated.

  19. The effects of geometric, flow, and boiling parameters on bubble growth and behavior in subcooled flow boiling

    NASA Astrophysics Data System (ADS)

    Samaroo, Randy

    Air bubble injection and subcooled flow boiling experiments have been performed to investigate the liquid flow field and bubble nucleation, growth, and departure, in part to contribute to the DOE Nuclear HUB project, Consortium for Advanced Simulation of Light Water Reactors (CASL). The main objective was to obtain quantitative data and compartmentalize the many different interconnected aspects of the boiling process -- from the channel geometry, to liquid and gas interactions, to underlying heat transfer mechanisms. The air bubble injection experiments were performed in annular and rectangular geometries and yielded data on bubble formation and departure from a small hole on the inner tube surface, subsequent motion and deformation of the detached bubbles, and interactions with laminar or turbulent water flow. Instantaneous and ensemble- average liquid velocity profiles have been obtained using a Particle Image Velocimetry technique and a high speed video camera. Reynolds numbers for these works ranged from 1,300 to 7,700. Boiling experiments have been performed with subcooled water at atmospheric pres- sure in the same annular channel geometry as the air injection experiments. A second flow loop with a slightly larger annular channel was constructed to perform further boiling experiments at elevated pressures up to 10 bar. High speed video and PIV measurements of turbulent velocity profiles in the presence of small vapor bubbles on the heated rod are presented. The liquid Reynolds number for this set of experiments ranged from 5,460 to 86,000. It was observed that as the vapor bubbles are very small compared to the injected air bubbles, further experiments were performed using a microscopic objective to obtain higher spatial resolution for velocity fields near the heated wall. Multiple correlations for the bubble liftoff diameter, liftoff time and bub- ble history number were evaluated against a number of experimental datasets from previous works, resulting in a

  20. Acoustic saturation in bubbly cavitating flow adjacent to an oscillating wall

    NASA Astrophysics Data System (ADS)

    Colonius, T.; d'Auria, F.; Brennen, C. E.

    2000-11-01

    Bubbly cavitating flow generated by the normal oscillation of a wall bounding a semi-infinite domain of fluid is computed using a continuum two-phase flow model. Bubble dynamics are computed, on the microscale, using the Rayleigh-Plesset equation. A Lagrangian finite volume scheme and implicit adaptive time marching are employed to accurately resolve bubbly shock waves and other steep gradients in the flow. The one-dimensional, unsteady computations show that when the wall oscillation frequency is much smaller than the bubble natural frequency, the power radiated away from the wall is limited by an acoustic saturation effect (the radiated power becomes independent of the amplitude of vibration), which is similar to that found in a pure gas. That is, for large enough vibration amplitude, nonlinear steepening of the generated waves leads to shocking of the wave train, and the dissipation associated with the jump conditions across each shock limits the radiated power. In the model, damping of the bubble volume oscillations is restricted to a simple "effective" viscosity. For wall oscillation frequency less than the bubble natural frequency, the saturation amplitude of the radiated field is nearly independent of any specific damping mechanism. Finally, implications for noise radiation from cavitating flows are discussed.

  1. Eulerian-Lagrangian Simulations of Bubbly Flows in A Vertical Square Duct

    NASA Astrophysics Data System (ADS)

    Liu, Rui; Vanka, Surya P.; Thomas, Brian G.

    2013-11-01

    We report results of Eulerian-Lagrangian simulations of developing upward and downward bubbly flows in a vertical square duct with a bulk Reynolds number of 5000. The continuous fluid is simulated with DNS, solving the Navier-Stokes equations by a second-order accurate finite volume fractional step method. Bubbles of sizes comparable to the Kolmogorov scale are injected at the duct entrance with a mean bulk volume fraction below 10-2. A two-way coupling approach is adopted for the interaction between the continuous fluid phase and dispersed bubble phase. The bubbles are tracked by a Lagrangian method including drag and lift forces due to buoyancy and Saffman lift. A in-house code, CU-FLOW, implemented on Graphic Processing Unit (GPU) is used for simulations in this work. The preferential distributions of bubbles and their impact on local turbulence structures and their effects on turbulent kinetic energy budgets are studied. Results between an upward flow and a downward flow with the bubbles are compared. Work Supported by Continuous Casting Consortium at UIUC.

  2. Compressible DNS study of separation bubbles for flow past a low pressure turbine blade

    NASA Astrophysics Data System (ADS)

    Ranjan, Rajesh; Deshpande, Suresh; Narasimha, Roddam

    2014-11-01

    A representative low pressure turbine blade T106A is subjected to a direct numerical simulation (DNS) study for low Reynolds Number (Re = 51831 based on inflow velocity and axial chord) and angle of incidence (45.5 deg from the axial chord). The DNS code used here solves the compressible Navier-Stokes equations and uses a semi-kinetic energy preserving scheme. A hybrid grid is used for the computational domain, with a very fine wall-bounded boundary layer grid near the surface of the blade and an unstructured grid for rest of the domain. Total grid size for the current simulation is around 160 million. In the mean flow, a long but shallow separation bubble is found near the trailing edge. However, the instantaneous flow reveals a train of bubbles at this location. These instantaneous bubbles continually break and merge in time. The presence of these separation bubbles make the flow very complicated, as the bubbles are responsible for tripping the otherwise laminar flow to a transitional state. Skin friction and heat transfer co-efficient are also computed over the blade to understand the effect of these bubbles on parameters of engineering importance. Supported by a GATET funded project on DNS of turbomachinery blading. The Param Yuva-II at CDAC was utilized for the simulations.

  3. 3-Dimensional numerical study of cooling performance of a heat sink with air-water flow through mini-channel

    NASA Astrophysics Data System (ADS)

    Majumder, Sambit; Majumder, Abhik; Bhaumik, Swapan

    2016-07-01

    The present microelectronics market demands devices with high power dissipation capabilities having enhanced cooling per unit area. The drive for miniaturizing the devices to even micro level dimensions is shooting up the applied heat flux on such devices, resulting in complexity in heat transfer and cooling management. In this paper, a method of CPU processor cooling is introduced where active and passive cooling techniques are incorporated simultaneously. A heat sink consisting of fins is designed, where water flows internally through the mini-channel fins and air flows externally. Three dimensional numerical simulations are performed for large set of Reynolds number in laminar region using finite volume method for both developing flows. The dimensions of mini-channel fins are varied for several aspect ratios such as 1, 1.33, 2 and 4. Constant temperature (T) boundary condition is applied at heat sink base. Channel fluid temperature, pressure drop are analyzed to obtain best cooling option in the present study. It has been observed that as the aspect ratio of the channel decreases Nusselt number decreases while pressure drop increases. However, Nusselt number increases with increase in Reynolds number.

  4. Parallel lattice Boltzmann simulation of bubble rising and coalescence in viscous flows

    NASA Astrophysics Data System (ADS)

    Shi, Dongyan; Wang, Zhikai

    2015-07-01

    A parallel three-dimensional lattice Boltzmann scheme for multicomponent immiscible fluids is proposed to simulate bubble rising and coalescence process in viscous flows. The lattice Boltzmann scheme is based on the free-energy model and is parallelized in the share-memory model by using the OpenMP. Bubble interface is described by a diffusion interface method solving the Cahn-Hilliard equation and both the surface tension force and the buoyancy are introduced in a form of discrete body force. To avoid the numerical instability caused by the interface deformation, the 18 point finite difference scheme is utilized to calculate the first- and second-order space derivative. The correction of the parallel scheme handling three-dimensional interfaces is verified by the Laplace law and the dynamic characteristics of an isolated bubble in stationary flows. Subsequently, effects of the initially relative position, accompanied by the size ratio on bubble-bubble interaction are studied. The results show that the present scheme can effectively describe the bubble interface dynamics, even if rupture and restructure occurs. In addition to the repulsion and coalescence phenomenon due to the relative position, the size ratio also plays an insignificant role in bubble deformation and trajectory.

  5. Bubbling at high flow rates in inviscid and viscous liquids (slags)

    NASA Astrophysics Data System (ADS)

    Engh, T. Abel; Nilmani, M.

    1988-02-01

    The behavior of gas discharging into melts at high velocities but still in the bubbling regime has been investigated in a laboratory modeling study for constant flow conditions. Air or helium was injected through a vertical tuyere into water, zinc-chloride, and aqueous glycerol solutions. High speed cinematography and pressure measurements in the tuyere have been carried out simultaneously. Pressure fluctuations at the injection point were monitored and correlated to the mode of bubble formation. The effects of high gas flow rates and high liquid viscosities have been examined in particular. Flow rates were employed up to 10-3 m3/s and viscosity to 0.5 Ns/m2. In order to attain a high gas momentum, the tuyere diameter was only 3 x 10-3 m. The experimental conditions and modeling liquids were chosen with special reference to the established practice of submerged gas injection to treat nonferrous slags. Such slags can be highly viscous. Bubble volume is smaller than that calculated from existing models such as those given by Davidson and Schüler10,11 due to the effect of gas momentum elongating the bubbles. On the other hand, viscosity tends to retard the bubble rise velocity, thus increasing volumes. To take elongation into account, a mathematical model is presented that assumes a prolate ellipsoidal shape of the bubbles. The unsteady potential flow equations for the liquid are solved for this case. Viscous effects are taken into account by noting that flow deviates from irrotational motion only in a thin boundary layer along the surface of the bubble. Thus, drag on the bubble can be obtained by calculating the viscous energy dissipation for potential flow past an ellipse. The time-dependent inertia coefficient for the ellipsoid is found by equating the vertical pressure increase inside and outside the bubble. This pressure change in the bubble is obtained by assuming that gas enters as a homogeneous jet and then calculating the stagnation pressure at the apex of

  6. A Mass Tracking Formulation for Bubbles in Incompressible Flow

    DTIC Science & Technology

    2012-10-14

    that the smaller bubbles remain spherical because of larger surface tension forces while the larger bubbles readily deform. 43 t = 0 s t = .075 s t...objects in a small computational domain. The effects of surface tension and viscosity are present. 44 t = 0 s t = .7 s t = 1 s t = 1.4 s Figure 34...and the inclusion of surface tension using jump conditions as proposed in [22, 18]. For large air bodies connected to the atmosphere, we use a free

  7. Study of bubble-induced turbulence in upward laminar bubbly pipe flows measured with a two-phase particle image velocimetry

    NASA Astrophysics Data System (ADS)

    Kim, Minki; Lee, Jun Ho; Park, Hyungmin

    2016-04-01

    In the present study, focusing on characterizing the bubble-induced agitation (turbulence), spatially varying flow statistics of gas and liquid phases in laminar upward bubbly flows (Reynolds number of 750) with varying mean void fraction are investigated using a two-phase high-speed particle image velocimetry. As the flow develops along the vertical direction, bubbles with small-to-moderate void fractions, which were intentionally distributed asymmetrically at the inlet, migrate fast and show symmetric distributions of wall or intermediate peaking. Meanwhile, the mean liquid velocity saturates relatively slowly to a flat distribution at the core region. Despite small void fractions considered, the bubbles generate a substantial turbulence, which increases with increasing mean void fraction. Interestingly, it is found that the mean vertical velocity, bubble-induced normal stress in radial direction, and Reynolds stress profiles match well with those of a single-phase turbulent flow at a moderate Reynolds number (e.g., 104), indicating the similarity between the bubble-induced turbulence and wall-shear-generated turbulence in a single-phase flow. Previously suggested scaling relations are confirmed such that the mean bubble rise velocity and bubble-induced normal stress (in both vertical and radial directions) scale with mean volume void fraction as a power of -0.1 and 0.4, respectively. Finally, based on the analysis of measured bubble dynamics (rise in an oscillating path), a theoretical model for two-phase turbulent (Reynolds) stress is proposed, which includes the contributions by the non-uniform distributions of local void fraction and relative bubble rise velocity, and is further validated with the present experimental data to show a good agreement with each other.

  8. Similarity between particles and bubbles as micro-additives in turbulent channel flow

    NASA Astrophysics Data System (ADS)

    Mito, Yoichi

    2015-11-01

    The acceleration of turbulent fluid flow in a vertical channel by the use of a uniform distribution of microparticles and of microbubbles has been examined by using a direct numerical simulation to calculate the fluid velocities seen by the additives. The flows considered are the downward gas flow to which solid particles of density ratio of 103 are added and the upward liquid flow to which bubbles of density ratio of 10-3 are added. Both additives, ranging in volume fraction up to 2 ×10-3 , are represented as solid spheres. The Froude numbers are chosen so as to have similar effects in both flows by the use of the same volume fraction of the additives. The fluid-phase momentum balance, integrated over the domain, is used to examine the changes in drag, wall friction and averaged feedback force of the non-stationary flow models. The feedback force per volume fraction is unchanged in the bubble flow. It decreases with increasing volume fraction and inertia of particles in the particle flow. Similarities between the two disperse flows are seen at small times for small volume fractions. Drag is reduced by both additives. The amount of reduced drag decreases with time at large times in the bubble flow, due to the increases in the accumulation of bubbles above walls. This work was supported by JSPS KAKENHI Grant Number 26420097.

  9. Acoustic wave propagation in bubbly flow with gas, vapor or their mixtures.

    PubMed

    Zhang, Yuning; Guo, Zhongyu; Gao, Yuhang; Du, Xiaoze

    2017-03-29

    Presence of bubbles in liquids could significantly alter the acoustic waves in terms of wave speed and attenuation. In the present paper, acoustic wave propagation in bubbly flows with gas, vapor and gas/vapor mixtures is theoretically investigated in a wide range of parameters (including frequency, bubble radius, void fraction, and vapor mass fraction). Our finding reveals two types of wave propagation behavior depending on the vapor mass fraction. Furthermore, the minimum wave speed (required for the closure of cavitation modelling in the sonochemical reactor design) is analyzed and the influences of paramount parameters on it are quantitatively discussed.

  10. A polydisperse two-fluid model for surf zone bubble simulation

    NASA Astrophysics Data System (ADS)

    Ma, Gangfeng; Shi, Fengyan; Kirby, James T.

    2011-05-01

    Wave breaking in the surf zone entrains large volumes of air bubbles into the water column, forming a two-phase bubbly flow field. Numerical study of bubbly flow is largely restricted by the lack of robust and comprehensive bubble entrainment models. In this paper, we propose a new model that connects bubble entrainment with turbulent dissipation rate at the air-water interface. The entrainment model as well as a polydisperse two-fluid model are incorporated into a 3-D volume of fluid code TRUCHAS. The bubbly flow model is first tested against laboratory experimental data for an oscillatory bubble plume. The calculated time-averaged liquid velocities and their fluctuations agree well with measurements, indicating that the model correctly reproduces dynamic interactions between the liquid phase and the continuum representation of the gas phase. Then, it is employed to study the bubbly flow under a laboratory surf zone breaking wave. Through the comparisons with experimental data, it is demonstrated that the model describes bubble entrainment and void fraction evolution reasonably well. The exponential decay of void fraction observed in the laboratory experiments is captured by the model. The kinematics of bubble plume as well as the vertical evolution of bubble size spectrum at any depth are investigated. Studies of bubble effects on liquid phase turbulence show that the presence of bubbles could suppress a large amount of turbulence under breaking waves.

  11. In situ visualization study of CO 2 gas bubble behavior in DMFC anode flow fields

    NASA Astrophysics Data System (ADS)

    Yang, H.; Zhao, T. S.; Ye, Q.

    This paper reports on a visual study of the CO 2 bubble behavior in the anode flow field of an in-house fabricated transparent Direct Methanol Fuel Cell (DMFC), which consisted of a membrane electrode assembly (MEA) with an active area of 4.0 × 4.0 cm 2, two bipolar plates with a single serpentine channel, and a transparent enclosure. The study reveals that at low current densities, small discrete bubbles appeared in the anode flow field. At moderate current densities, a number of gas slugs formed, in addition to small discrete bubbles. And at high current densities, the flow field was predominated by rather long gas slugs. The experiments also indicate that the cell orientation had a significant effect on the cell performance, especially at low methanol flow rates; for the present flow field design the best cell performance could be achieved when the cell was orientated vertically. It has been shown that higher methanol solution flow rates reduced the average length and the number of gas slugs in the flow field, but led to an increased methanol crossover. In particular, the effect of methanol solution flow rates on the cell performance became more pronounced at low temperatures. The effect of temperature on the bubble behavior and the cell performance was also examined. Furthermore, for the present flow field consisting of a single serpentine channel, the channel-blocking phenomenon caused by CO 2 gas slugs was never encountered under all the test conditions in this work.

  12. Shadow imaging in bubbly gas-liquid two-phase flow in porous structures

    NASA Astrophysics Data System (ADS)

    Altheimer, Marco; Häfeli, Richard; Wälchli, Carmen; Rudolf von Rohr, Philipp

    2015-09-01

    Shadow imaging is used for the investigation of bubbly gas-liquid two-phase flow in a porous structure. The porous structure is made of Somos WaterShed XC 11122, a clear epoxy resin used in rapid prototyping. Optical access is provided by using an aqueous solution of sodium iodide and zinc iodide having the same refractive index as the structure material (). Nitrogen is injected into the continuous phase at volumetric transport fractions in the range of resulting in a hold-up of . The obtained images of overlapping bubble shadows are processed to measure the bubble dimensions. Therefore, a new processing sequence is developed to determine bubble dimensions from overlapping bubble shadows by ellipse fitting. The accuracy of the bubble detection and sizing routine is assessed processing synthetic images. It is shown that the developed technique is suitable for volumetric two-phase flow measurements. Important global quantities such as gas hold-up and total interfacial area can be measured with only one camera. Operation parameters for gas-liquid two-phase flows are determined to improve mass and heat transfer between the phases.

  13. The Effect of Surface Induced Flows on Bubble and Particle Aggregation

    NASA Technical Reports Server (NTRS)

    Guelcher, Scott A.; Solomentsev, Yuri E.; Anderson, John L.; Boehmer, Marcel; Sides, Paul J.

    1999-01-01

    Almost 20 years have elapsed since a phenomenon called "radial specific coalescence" was identified. During studies of electrolytic oxygen evolution from the back side of a vertically oriented, transparent tin oxide electrode in alkaline electrolyte, one of the authors (Sides) observed that large "collector" bubbles appeared to attract smaller bubbles. The bubbles moved parallel to the surface of the electrode, while the electric field was normal to the electrode surface. The phenomenon was reported but not explained. More recently self ordering of latex particles was observed during electrophoretic deposition at low DC voltages likewise on a transparent tin oxide electrode. As in the bubble work, the field was normal to the electrode while the particles moved parallel to it. Fluid convection caused by surface induced flows (SIF) can explain these two apparently different experimental observations: the aggregation of particles on an electrode during electrophoretic deposition, and a radial bubble coalescence pattern on an electrode during electrolytic gas evolution. An externally imposed driving force (the gradient of electrical potential or temperature), interacting with the surface of particles or bubbles very near a planar conducting surface, drives the convection of fluid that causes particles and bubbles to approach each other on the electrode.

  14. Observations of Gas-Liquid Flows Through Contractions in Microgravity

    NASA Technical Reports Server (NTRS)

    McQuillen, John

    1996-01-01

    Tests were conducted for an air-water flow through two sudden contractions aboard the NASA DC-9 low gravity aircraft. Flow rate, residual accelerations, void fraction, film thickness, and pressure drop data were recorded and flow visualization at 250 images per second were recorded. Some preliminary results based on the flow visualization data are presented for bubbly, slug and annular flow.

  15. Bubble-free electrokinetic flow with propylene carbonate.

    PubMed

    Sritharan, Deepa; Chen, Abraham Simpson; Aluthgama, Prabhath; Naved, Bilal; Smela, Elisabeth

    2015-10-01

    For electroosmotic pumping, a large direct-current (DC) electric field (10+ V/cm) is applied across a liquid, typically an aqueous electrolyte. At these high voltages, water undergoes electrolysis to form hydrogen and oxygen, generating bubbles that can block the electrodes, cause pressure fluctuations, and lead to pump failure. The requirement to manage these gases constrains system designs. This article presents an alternative polar liquid for DC electrokinetic pumping, propylene carbonate (PC), which remains free of bubbles up to at least 10 kV/cm. This offers the opportunity to create electrokinetic devices in closed configurations, which we demonstrate with a fully sealed microfluidic hydraulic actuator. Furthermore, the electroosmotic velocity of PC is similar to that of water in PDMS microchannels. Thus, water could be substituted by PC in existing electroosmotic pumps.

  16. Using statistical learning to close two-fluid multiphase flow equations for a simple bubbly system

    NASA Astrophysics Data System (ADS)

    Ma, Ming; Lu, Jiacai; Tryggvason, Gretar

    2015-09-01

    Direct numerical simulations of bubbly multiphase flows are used to find closure terms for a simple model of the average flow, using Neural Networks (NNs). The flow considered consists of several nearly spherical bubbles rising in a periodic domain where the initial vertical velocity and the average bubble density are homogeneous in two directions but non-uniform in one of the horizontal directions. After an initial transient motion the average void fraction and vertical velocity become approximately uniform. The NN is trained on a dataset from one simulation and then used to simulate the evolution of other initial conditions. Overall, the resulting model predicts the evolution of the various initial conditions reasonably well.

  17. Bubble dynamics, two-phase flow, and boiling heat transfer in a microgravity environment

    NASA Technical Reports Server (NTRS)

    Chung, Jacob N.

    1994-01-01

    The two-phase bubbly flow and boiling heat transfer in microgravity represents a substantial challenge to scientists and engineers and yet there is an urgent need to seek fundamental understanding in this area for future spacecraft design and space missions. At Washington State University, we have successfully designed, built and tested a 2.1 second drop tower with an innovation airbag deceleration system. Microgravity boiling experiments performed in our 0.6 second Drop Tower produced data flow visualizations that agree with published results and also provide some new understanding concerning flow boiling and microgravity bubble behavior. On the analytical and numerical work, the edge effects of finite divergent electrode plates on the forces experienced by bubbles were investigated. Boiling in a concentric cylinder microgravity and an electric field was numerically predicted. We also completed a feasibility study for microgravity boiling in an acoustic field.

  18. Vapor Bubbles

    NASA Astrophysics Data System (ADS)

    Prosperetti, Andrea

    2017-01-01

    This article reviews the fundamental physics of vapor bubbles in liquids. Work on bubble growth and condensation for stationary and translating bubbles is summarized and the differences with bubbles containing a permanent gas stressed. In particular, it is shown that the natural frequency of a vapor bubble is proportional not to the inverse radius, as for a gas bubble, but to the inverse radius raised to the power 2/3. Permanent gas dissolved in the liquid diffuses into the bubble with strong effects on its dynamics. The effects of the diffusion of heat and mass on the propagation of pressure waves in a vaporous bubbly liquid are discussed. Other topics briefly touched on include thermocapillary flow, plasmonic nanobubbles, and vapor bubbles in an immiscible liquid.

  19. Bubble Formation in Yield Stress Fluids Using Flow-Focusing and T -Junction Devices

    NASA Astrophysics Data System (ADS)

    Laborie, Benoit; Rouyer, Florence; Angelescu, Dan E.; Lorenceau, Elise

    2015-05-01

    We study the production of bubbles inside yield stress fluids (YSFs) in axisymmetric T -junction and flow-focusing devices. Taking advantage of yield stress over capillary stress, we exhibit a robust break-up mechanism reminiscent of the geometrical operating regime in 2D flow-focusing devices for Newtonian fluids. We report that when the gas is pressure driven, the dynamics is unsteady due to hydrodynamic feedback and YSF deposition on the walls of the channels. However, the present study also identifies pathways for potential steady-state production of bubbly YSFs at large scale.

  20. Bubble and Slug Flow at Microgravity Conditions: State of Knowledge and Open Questions

    NASA Technical Reports Server (NTRS)

    Colin, C.; Fabre, J.; McQuillen, J.

    1996-01-01

    Based on the experiments carried out over the past decade at microgravity conditions, an overview of our current knowledge of bubbly and slug flows is presented. The transition from bubble to slug flow, the void fraction and the pressure drop are discussed from the data collected in the literature. The transition from bubble to slug flow may be predicted by introducing a critical void fraction that depends on the fluid properties and the pipe diameter; however, the role of coalescence which controls this transition is not clearly understood. The void fraction may be accurately calculated using a drift-flux model. It is shown from local measurements that the drift of the gas with respect to the mixture is due to non-uniform radial distribution of void fraction. The pressure drop happens to be controlled by the liquid flow for bubbly flow whereas for slug flow the experimental results show that pressure drops is larger than expected. From this study, the guidelines for future research in microgravity are given.

  1. Bubble confinement in flow boiling of FC-72 in a ''rectangular'' microchannel of high aspect ratio

    SciTech Connect

    Barber, Jacqueline; Brutin, David; Tadrist, Lounes; Sefiane, Khellil

    2010-11-15

    Boiling in microchannels remains elusive due to the lack of full understanding of the mechanisms involved. A powerful tool in achieving better comprehension of the mechanisms is detailed imaging and analysis of the two-phase flow at a fundamental level. Boiling is induced in a single microchannel geometry (hydraulic diameter 727 {mu}m), using a refrigerant FC-72, to investigate the effect of channel confinement on bubble growth. A transparent, metallic, conductive deposit has been developed on the exterior of the rectangular microchannel, allowing simultaneous uniform heating and visualisation to be achieved. The data presented in this paper is for a particular case with a uniform heat flux applied to the microchannel and inlet liquid mass flowrate held constant. In conjunction with obtaining high-speed images and videos, sensitive pressure sensors are used to record the pressure drop across the microchannel over time. Bubble nucleation and growth, as well as periodic slug flow, are observed in the microchannel test section. The periodic pressure fluctuations evidenced across the microchannel are caused by the bubble dynamics and instances of vapour blockage during confined bubble growth in the channel. The variation of the aspect ratio and the interface velocities of the growing vapour slug over time, are all observed and analysed. We follow visually the nucleation and subsequent both 'free' and 'confined' growth of a vapour bubble during flow boiling of FC-72 in a microchannel, from analysis of our results, images and video sequences with the corresponding pressure data obtained. (author)

  2. Air/Water Purification

    NASA Technical Reports Server (NTRS)

    1992-01-01

    After 18 years of research into air/water pollution at Stennis Space Center, Dr. B. C. Wolverton formed his own company, Wolverton Environmental Services, Inc., to provide technology and consultation in air and water treatment. Common houseplants are used to absorb potentially harmful materials from bathrooms and kitchens. The plants are fertilized, air is purified, and wastewater is converted to clean water. More than 100 U.S. communities have adopted Wolverton's earlier water hyacinth and artificial marsh applications. Catfish farmers are currently evaluating the artificial marsh technology as a purification system.

  3. Effect of a bubble nucleation model on cavitating flow structure in rarefaction wave

    NASA Astrophysics Data System (ADS)

    Petrov, N.; Schmidt, A.

    2016-12-01

    This paper explains research examining processes accompanying underwater explosions near the free surface. Particular attention is paid to the effect of heterogeneous nucleation on cavitating flow induced by underwater explosions near the free surface. Variation of the size spectrum of produced bubbles and influence of this process on flow structure are studied. The cavitating liquid is considered as a two-phase bubbly medium described in the framework of the Euler-Lagrange approach treating the carrier phase (liquid) as a continuum and the dispersed phase (bubbles) as a set of test particles. More detailed descriptions of a mathematical model, numerical method, and algorithm validation are observed in the authors' previous paper [see, Petrov and Schmidt (Exp Thermal Fluid Sci 60:367-373, 2015)].

  4. The Constrained Vapor Bubble Experiment - Interfacial Flow Region

    NASA Technical Reports Server (NTRS)

    Kundan, Akshay; Wayner, Peter C., Jr.; Plawsky, Joel L.

    2015-01-01

    Internal heat transfer coefficient of the CVB correlated to the presence of the interfacial flow region. Competition between capillary and Marangoni flow caused Flooding and not a Dry-out region. Interfacial flow region growth is arrested at higher power inputs. 1D heat model confirms the presence of interfacial flow region. 1D heat model confirms the arresting phenomena of interfacial flow region Visual observations are essential to understanding.

  5. A one-way coupled, Euler-Lagrangian simulation of bubble coalescence in a turbulent pipe flow

    NASA Astrophysics Data System (ADS)

    Mattson, Michael; Mahesh, Krishnan

    2011-11-01

    A bubble coalescence model is developed using an Euler-Lagrangian approach for unstructured grids. The Eulerian carrier fluid is solved using large-eddy simulation (LES) and the Lagrangian particle motion is solved using one-way coupled equations relating the turbulent motion of the carrier fluid to the forces on each discrete bubble. The collision process is deterministic; bubble-bubble collisions are assumed to be binary and are modeled using a hard-sphere approach. A stochastic approach is used to model coalescence, with the probability of coalescence being a function of the bubble-bubble interaction timescale and the time to drain fluid between the colliding bubbles. Coalescence in a bubbly, turbulent pipe flow without buoyancy is simulated with conditions similar to a microgravity experiment by Colin, Fabre and Dukler [Int. J. Multiphase Flow (1991) 17:533-544] and excellent agreement of bubble size distribution is obtained between simulation and experiment. With increasing downstream distance, the number density of bubbles decreases due to coalescence and the average probability of coalescence decreases slightly due to an increase in overall bubble size. Supported by the U.S. Office of Naval Research under ONR Grant N00014-07-1-0420.

  6. Effects of Soluble Surfactant on Lateral Migration of a Bubble in a Shear Flow

    NASA Astrophysics Data System (ADS)

    Muradoglu, Metin; Tryggvason, Gretar

    2014-11-01

    Motivated by the recent experimental study of Takagi et al. (2008), direct numerical simulations are performed to examine effects of soluble surfactant on the lateral migration of a deformable bubble in a pressure-driven channel flow. The interfacial and bulk surfactant concentration evolution equations are solved fully coupled with the incompressible Navier-Stokes equations. A non-linear equation of state is used to relate interfacial surface tension to surfactant concentration at the interface. A multiscale method is developed to handle the mass exchange between the interface and bulk fluid at high Peclet numbers, using a boundary-layer approximation next to the bubble and a relatively coarse grid for the rest of the flow. It is found that the surfactant induced Marangoni stresses can dominate over the shear-induced lift force and thus alter the behavior of the bubble completely, i.e., the contaminated bubble drifts away from the channel wall and stabilizes at the center of the channel in contrast with the corresponding clean bubble that drifts toward the wall and stabilizes near the wall. The Scientific and Technical Research Council of Turkey (TUBITAK), Grant 112M181 and Turkish Academy of Sciences (TUBA).

  7. Two-Phase Flow in Packed Columns and Generation of Bubbly Suspensions for Chemical Processing in Space

    NASA Technical Reports Server (NTRS)

    Motil, Brian J.; Green, R. D.; Nahra, H. K.; Sridhar, K. R.

    2000-01-01

    For long-duration space missions, the life support and In-Situ Resource Utilization (ISRU) systems necessary to lower the mass and volume of consumables carried from Earth will require more sophisticated chemical processing technologies involving gas-liquid two-phase flows. This paper discusses some preliminary two-phase flow work in packed columns and generation of bubbly suspensions, two types of flow systems that can exist in a number of chemical processing devices. The experimental hardware for a co-current flow, packed column operated in two ground-based low gravity facilities (two-second drop tower and KC- 135 low-gravity aircraft) is described. The preliminary results of this experimental work are discussed. The flow regimes observed and the conditions under which these flow regimes occur are compared with the available co-current packed column experimental work performed in normal gravity. For bubbly suspensions, the experimental hardware for generation of uniformly sized bubbles in Couette flow in microgravity conditions is described. Experimental work was performed on a number of bubbler designs, and the capillary bubble tube was found to produce the most consistent size bubbles. Low air flow rates and low Couette flow produce consistent 2-3 mm bubbles, the size of interest for the "Behavior of Rapidly Sheared Bubbly Suspension" flight experiment. Finally the mass transfer implications of these two-phase flows is qualitatively discussed.

  8. Lagrangian coherent structures analysis of gas-liquid flow in a bubble column

    NASA Astrophysics Data System (ADS)

    Wu, Qin; Wang, GuoYu; Huang, Biao; Bai, ZeYu

    2014-06-01

    The objective of this paper is to apply a new identifying method to investigating the gas-liquid two-phase flow behaviors in a bubble column with air injected into water. In the numerical simulations, the standard k- ɛ turbulence model is employed to describe the turbulence phenomenon occurring in the continuous fluid. The Finite-Time Lyapunov Exponent (FTLE) and Lagrangian Coherent Structures (LCS) are applied to analyze the vortex structures in multiphase flow. Reasonable agreements are obtained between the numerical and experimental data. The numerical results show that the evolution of gas-liquid in the column includes initial and periodical developing stages. During the initial stage, the bubble hose is forming and extending along the vertical direction with the vortex structures formed symmetrically. During the periodical developing stage, the bubble hose starts to oscillate periodically, and the vortexes move along the bubble hose to the bottom of column alternately. Compared to the Euler-system-based identification criterion of a vortex, the FTLE field presents the boundary of a vortex without any threshold defined and the LCS represents the divergence extent of infinite neighboring particles. During the initial stage, the interfaces between the forward and backward flows are highlighted by the LCS. As for the periodical developing stage, the LCS curls near the vortex centers, providing a method of analyzing a flow field from a dynamical system perspective.

  9. Prediction of Bubble Diameter at Detachment from a Wall Orifice in Liquid Cross Flow Under Reduced and Normal Gravity Conditions

    NASA Technical Reports Server (NTRS)

    Nahra, Henry K.; Kamotani, Y.

    2003-01-01

    Bubble formation and detachment is an integral part of the two-phase flow science. The objective of the present work is to theoretically investigate the effects of liquid cross-flow velocity, gas flow rate embodied in the momentum flux force, and orifice diameter on bubble formation in a wall-bubble injection configuration. A two-dimensional one-stage theoretical model based on a global force balance on the bubble evolving from a wall orifice in a cross liquid flow is presented in this work. In this model, relevant forces acting on the evolving bubble are expressed in terms of the bubble center of mass coordinates and solved simultaneously. Relevant forces in low gravity included the momentum flux, shear-lift, surface tension, drag and inertia forces. Under normal gravity conditions, the buoyancy force, which is dominant under such conditions, can be added to the force balance. Two detachment criteria were applicable depending on the gas to liquid momentum force ratio. For low ratios, the time when the bubble acceleration in the direction of the detachment angle is greater or equal to zero is calculated from the bubble x and y coordinates. This time is taken as the time at which all the detaching forces that are acting on the bubble are greater or equal to the attaching forces. For high gas to liquid momentum force ratios, the time at which the y coordinate less the bubble radius equals zero is calculated. The bubble diameter is evaluated at this time as the diameter at detachment from the fact that the bubble volume is simply given by the product of the gas flow rate and time elapsed. Comparison of the model s predictions was also made with predictions from a two-dimensional normal gravity model based on Kumar-Kuloor formulation and such a comparison is presented in this work.

  10. Study of Critical Heat Flux Mechanism in Flow Boiling Using Bubble Crowding Model

    NASA Astrophysics Data System (ADS)

    Kinoshita, Hidetaka; Nariai, Hideki; Inasaka, Fujio

    Critical heat flux (CHF) of Subcooled Flow Boiling with water in a tube was investigated from the viewpoint of mechanistic models. The Weisman-Pei bubble crowding model was selected to predict CHF in a short tube and in a tube with an internal twisted tape under nonuniform heating conditions, Based on the results of bubble behavior observation and preliminary analysis. The original Weisman-Pei model was modified in order to explain the physical phenomena of CHF. The modified model predicted well CHF in a smooth tube including the very short tube and the tube with an internal twisted tape under uniform and nonuniform heating conditions.

  11. Interactive actuation of multiple opto-thermocapillary flow-addressed bubble microrobots

    PubMed Central

    Hu, Wenqi; Fan, Qihui; Ohta, Aaron T

    2014-01-01

    Opto-thermocapillary flow-addressed bubble (OFB) microrobots are a potential tool for the efficient transportation of micro-objects. This microrobot system uses light patterns to generate thermal gradients within a liquid medium, creating thermocapillary forces that actuate the bubble microrobots. An interactive control system that includes scanning mirrors and a touchscreen interface was developed to address up to ten OFB microrobots. Using this system, the parallel and cooperative transportation of 20-μm-diameter polystyrene beads was demonstrated. PMID:25678988

  12. Bubble and bubble cloud dynamics

    NASA Astrophysics Data System (ADS)

    Matsumoto, Yoichiro

    2000-07-01

    Cavitation bubbles are formed from small air bubbles, so-called nuclei, with the surrounding pressure reduction caused by the flow, and then, the bubbles shrink and collapse with the surrounding pressure rise. Such volumetric changes of bubbles are calculated in detail and it is found that they are significantly influenced by the internal phenomena, such as thermal diffusion, mist formation due to a homogeneous condensation, mass diffusion between vapor and noncondensable gas, heat and mass transfer through the bubble wall. The structure in cavitating flow interacts with the cavitation bubbles, and those bubbles form a cloud cavitation. It is well known that cloud cavitation is one of the most destructive forms. The behavior of bubble clouds is simulated numerically. An inward propagating shock wave is formed during the collapse of the bubble cloud, and the shock wave and its precursor are focused at the cloud center area. These phenomena associate high frequency pressure oscillations and violent bubble collapses. Those bubble collapses emit high pressure peaks, which are several hundreds times larger than that of a single bubble collapse.

  13. Detachment of colloids from a solid surface by a moving air-water interface.

    PubMed

    Sharma, Prabhakar; Flury, Markus; Zhou, Jun

    2008-10-01

    Colloid attachment to liquid-gas interfaces is an important process used in industrial applications to separate suspended colloids from the fluid phase. Moving gas bubbles can also be used to remove colloidal dust from surfaces. Similarly, moving liquid-gas interfaces lead to colloid mobilization in the natural subsurface environment, such as in soils and sediments. The objective of this study was to quantify the effect of moving air-water interfaces on the detachment of colloids deposited on an air-dried glass surface, as a function of colloidal properties and interface velocity. We selected four types of polystyrene colloids (positive and negative surface charge, hydrophilic and hydrophobic). The colloids were deposited on clean microscope glass slides using a flow-through deposition chamber. Air-water interfaces were passed over the colloid-deposited glass slides, and we varied the number of passages and the interface velocity. The amounts of colloids deposited on the glass slides were visualized using confocal laser scanning microscopy and quantified by image analysis. Our results showed that colloids attached under unfavorable conditions were removed in significantly greater amounts than those attached under favorable conditions. Hydrophobic colloids were detached more than hydrophilic colloids. The effect of the air-water interface on colloid removal was most pronounced for the first two passages of the air-water interface. Subsequent passages of air-water interfaces over the colloid-deposited glass slides did not cause significant additional colloid removal. Increasing interface velocity led to decreased colloid removal. The force balances, calculated from theory, supported the experimental findings, and highlight the dominance of detachment forces (surface tension forces) over the attachment forces (DLVO forces).

  14. A computational model for large eddy simulation of dilute bubbly turbulent flows

    NASA Astrophysics Data System (ADS)

    Hajit, Mohammad; Sotiropoulos, Fotis

    2013-11-01

    A mathematical formulation of filtered equations for two phase bubbly flows based on two-fluid method is presented. To remove high frequencies (noise), we extracted the filtered form of the equations in curvilinear coordinates, converting the microscopic governing equations to macroscopic equations via spatial averaging of solution variables. The set of equations describing the hydrodynamics in a gas-liquid system can be solved effectively if the solution procedure is decoupled so that an efficient iterative scheme can be employed. We propose a formulation for dilute bubbly flows in which the equations are converted to a loosely-coupled form. The resulting mathematical model is based on five distinct sets of equations, namely mixture momentum balance, pressure Poisson equation, Boyle's law and momentum and mass balances of gas phase. This mathematical formulation provides an efficient numerical procedure for two-way coupling of bubbly flows at low gas holdups. The subgrid-scale modeling is based on dynamic procedure of Germano for both phases. The formulation is validated for a fully turbulent bubble column test by comparing to available experimental results. This work is supported by the US department of energy (DE-EE0005416) and the Minnesota supercomputing institute.

  15. The effect of flow pattern around a bubble rising near a vertical wall, on the wall to liquid heat transfer

    NASA Astrophysics Data System (ADS)

    Bhuvankar, Pramod; Dabiri, Sadegh

    2016-11-01

    Two-phase flow is an effective means for heat removal due to the enhanced convective effect caused by bubbly flow and the usually high latent heat of vaporization of the liquid phase. We present a numerical study of the effect of flow patterns around a single bubble rising in shear flow near a vertical wall, on the wall-to-liquid heat transfer. The Navier-Stokes equations are solved in a frame of reference moving with the bubble, by using the front tracking method for interface tracking. Our simulations reveal an enhancement of heat transfer downstream of the bubble, and a less pronounced diminishment of heat transfer upstream of the bubble. We observe that in the range of 5 <= Re <= 40 for Reynolds number based on shear and bubble diameter, heat transfer first increases, attains a maximum and decreases as Re increases. The optimum Re depends on the Archimedes number. The heat transfer enhancement is attributed to flow reversal happening in a confined region of the shear flow, in the presence of a bubble. The analytical solution of 2 - D inviscid shear flow over a cylinder near a wall is used to identify two parameters of flow reversal namely 'reversal height' and 'reversal width'. These parameters are then used to qualitatively explain what we observe in 3 - D simulations.

  16. Large eddy simulation of dilute bubbly turbulent flows for aerating hydrofoils

    NASA Astrophysics Data System (ADS)

    Hajit, Mohammad; Sotiropoulos, Fotis

    2014-11-01

    We have proposed a formulation for the large eddy simulation of dilute bubbly flows by converting the governing equations to a more loosely-coupled form. This formulation provides an efficient numerical procedure for two-way coupling of bubbly flows at low gas holdups. Subgrid-scale turbulence modeling is based on the dynamic procedure of Germano for the liquid phase and the Jakobson approach for the gas phase. Wall-modeling is implemented using the method of Cabot & Moin. Our approach is employed to simulate flow over aerating hydrofoils at different angles of attack. A structured body-fitted C-grid is employed for domain discretization. Validation of our computational code, for C-grids, is carried out by simulating single-phase flows over a NACA0012 airfoil (20° AOA) with laminar flow and an E387 airfoil (6° AOA) with turbulent flow. Comparisons with available computational and experimental data in terms of time averaged drag coefficient, lift coefficient, separation bubble length, and reattachment point proves the validity of our computational code. The aerating hydrofoil simulation utilizes a NACA0015 hydrofoil, for which experiments were carried out at Saint Anthony Falls Laboratory. Comparisons between computational and experimental datasets show promising results. This work is supported by the U.S. Dept. of Energy and the Hydro Reasearch Foundation.

  17. Singular effective slip length for longitudinal flow over a dense bubble mattress

    NASA Astrophysics Data System (ADS)

    Schnitzer, Ory

    2016-09-01

    We consider the effective hydrophobicity of a periodically grooved surface immersed in liquid, with trapped shear-free bubbles protruding between the no-slip ridges at a π /2 contact angle. Specifically, we carry out a singular-perturbation analysis in the limit ɛ ≪1 where the bubbles are closely spaced, finding the effective slip length (normalized by the bubble radius) for longitudinal flow along the ridges as π /√{2 ɛ }-(12 /π ) ln2 +(13 π /24 ) √{2 ɛ }+o (√{ɛ }) , the small parameter ɛ being the planform solid fraction. The square-root divergence highlights the strong hydrophobic character of this configuration; this leading singular term (along with the third term) follows from a local lubrication-like analysis of the gap regions between the bubbles, together with general matching considerations and a global conservation relation. The O (1 ) constant term is found by matching with a leading-order solution in the outer region, where the bubbles appear to be touching. We find excellent agreement between our slip-length formula and a numerical scheme recently derived using a unified-transform method [Crowdy, IMA J. Appl. Math. 80, 1902 (2015), 10.1093/imamat/hxv019]. The comparison demonstrates that our asymptotic formula, together with the diametric dilute-limit approximation [Crowdy, J. Fluid Mech. 791, R7 (2016), 10.1017/jfm.2016.88], provides an elementary analytical description for essentially arbitrary no-slip fractions.

  18. Calculation of the virtual current in an electromagnetic flow meter with one bubble using 3D model.

    PubMed

    Zhang, Xiao-Zhang; Li, Yantao

    2004-04-01

    Based on the theory of electromagnetic induction flow measurement, the Laplace equation in a complicated three-dimensional (3D) domain is solved by an alternating method. Virtual current potentials are obtained for an electromagnetic flow meter with one spherical bubble inside. The solutions are used to investigate the effects of bubble size and bubble position on the virtual current. Comparisons are done among the cases of 2D and 3D models, and of point electrode and large electrode. The results show that the 2D model overestimates the effect, while large electrodes are least sensitive to the bubble. This paper offers fundamentals for the study of the behavior of an electromagnetic flow meter in multiphase flow. For application, the results provide a possible way to estimate errors of the flow meter caused by multiphase flow.

  19. Flow and Heat Flux Behavior of Micro-bubble Jet Flows Observed in Thin, Twisted-Wire, Subcooled Boiling in Microgravity

    NASA Astrophysics Data System (ADS)

    Munro, Troy R.; Ban, Heng

    2015-02-01

    Thin wire, subcooled boiling experiments were performed onboard an aircraft flying a parabolic trajectory to provide microgravity conditions for improved observation of jet flow phenomena and their behavior in the absence of buoyant forces. A new type of nucleation jet flow was observed in microgravity. This new micro-bubble jet flow is seen at medium to high heat fluxes and is characterized by a region of the wire that forms multiple jet columns which contain micro-bubbles. These columns flow together and penetrate tens of millimeters into the bulk fluid. Bubble behavior on the wire was observed to progress from a dominance of larger isolated bubbles on the wire to a dominance of micro-bubble jet flows on the wire as heat flux was increased. There was also a transient transition from a few large isolated bubbles to micro-bubble jet flow dominance for a set heat flux. A cross correlation calculation provided velocities of micro-bubbles in the flow, which were in the range of 4-14 mm/s. These velocities were used with convection correlations to show that fluid flows induced by jet flows are a significant contributor to the subcooled boiling heat transfer in microgravity, but are not the primary contributor. Additionally, a relative bubble area analysis approximates the direct contribution of these jet flows to the overall heat dissipation. These micro-bubble jet flows, which are only observed on thin wires (not flat surfaces), and the convection currents they induce, have the potential to allow for sustained fluid motion to occur in microgravity.

  20. Theoretical and pragmatic modeling of governing equations for two-phase flow in bubbly and annular flow regimes

    SciTech Connect

    Bottoni, M.; Ajuha, S.; Sengpiel, W.

    1994-12-31

    Starting from the rigorous formulation of the conservation equations for mass, momentum and enthalpy derived for a two-phase flow by volume-averaging microscopic balance equations over Eulerian control cells, the article discusses the formulation of the terms describing exchanges between the phases. Two flow regimes are taken into consideration; bubbly flow, applicable for small or medium void fractions, and annular flow, for large void fractions. When lack of knowledge of volume-averaged physical quantities makes the rigorously formulated terms useless for computational purposes, modeling of these terms is discussed.

  1. Theoretical and pragmatic modelling of governing equations for a two-phase flow in bubbly and annular flow regimes

    SciTech Connect

    Bottoni, M.; Sengpiel, W.

    1992-12-01

    Starting from the rigorous formulation of the conservation equations for mass, momentum and enthalpy, derived for a two-phase flow by volume averaging microscopic balance equations over Eulerian control cells, the article discusses the formulation of the terms describing exchanges between the phases. Two flow regimes are taken into consideration, bubbly flow, applicable for small or medium void fractions, and annular flow, for large void fractions. When lack of knowledge of volume-averaged physical quantities make the rigorously formulated terms useless for computational purposes, modelling of these terms is discussed. 3 figs., 15 refs.

  2. Theoretical and pragmatic modelling of governing equations for a two-phase flow in bubbly and annular flow regimes

    SciTech Connect

    Bottoni, M. . Materials and Components Technology Div.); Sengpiel, W. . Inst. fuer Reaktorsicherheit)

    1992-01-01

    Starting from the rigorous formulation of the conservation equations for mass, momentum and enthalpy, derived for a two-phase flow by volume averaging microscopic balance equations over Eulerian control cells, the article discusses the formulation of the terms describing exchanges between the phases. Two flow regimes are taken into consideration, bubbly flow, applicable for small or medium void fractions, and annular flow, for large void fractions. When lack of knowledge of volume-averaged physical quantities make the rigorously formulated terms useless for computational purposes, modelling of these terms is discussed. 3 figs., 15 refs.

  3. Observations of internal flow inside an evaporating nanofluid sessile droplet in the presence of an entrapped air bubble

    NASA Astrophysics Data System (ADS)

    Shin, Dong Hwan; Allen, Jeffrey S.; Lee, Seong Hyuk; Choi, Chang Kyoung

    2016-09-01

    Using a unique, near-field microscopy technique, fringe patterns and nanoparticle motions are visualized immediately following a nanofluid droplet deposition on a glass substrate in which an air bubble is entrapped. The nanofluid consists of DI-water, 0.10% Aluminum Oxide nanoparticles with an average diameter of 50 nm, and 0.0005% yellow-green polystyrene fluorescent particles of 1 μm diameter. High-speed, fluorescent-mode confocal imaging enables investigation of depth-wise sectioned particle movements in the nanofluid droplet inside which a bubble is entrapped. The static contact angle is increased when a bubble is applied. In the presence of the bubble in the droplet, the observed flow toward the center of the droplet is opposite to the flow observed in a droplet without the bubble. When the bubble is present, the evaporation process is retarded. Also, random motion is observed in the contact line region instead of the typical evaporation-driven flow toward the droplet edge. Once the bubble bursts, however, the total evaporation time decreases due to the change in the contact line characteristics. Moreover, the area of fringe patterns beneath the bubble increases with time. Discussed herein is a unique internal flow that has not been observed in nanofluid droplet evaporation.

  4. Observations of internal flow inside an evaporating nanofluid sessile droplet in the presence of an entrapped air bubble

    PubMed Central

    Shin, Dong Hwan; Allen, Jeffrey S.; Lee, Seong Hyuk; Choi, Chang Kyoung

    2016-01-01

    Using a unique, near-field microscopy technique, fringe patterns and nanoparticle motions are visualized immediately following a nanofluid droplet deposition on a glass substrate in which an air bubble is entrapped. The nanofluid consists of DI-water, 0.10% Aluminum Oxide nanoparticles with an average diameter of 50 nm, and 0.0005% yellow-green polystyrene fluorescent particles of 1 μm diameter. High-speed, fluorescent-mode confocal imaging enables investigation of depth-wise sectioned particle movements in the nanofluid droplet inside which a bubble is entrapped. The static contact angle is increased when a bubble is applied. In the presence of the bubble in the droplet, the observed flow toward the center of the droplet is opposite to the flow observed in a droplet without the bubble. When the bubble is present, the evaporation process is retarded. Also, random motion is observed in the contact line region instead of the typical evaporation-driven flow toward the droplet edge. Once the bubble bursts, however, the total evaporation time decreases due to the change in the contact line characteristics. Moreover, the area of fringe patterns beneath the bubble increases with time. Discussed herein is a unique internal flow that has not been observed in nanofluid droplet evaporation. PMID:27615999

  5. Measurement of Gas and Liquid Velocities in an Air-Water Two-Phase Flow using Cross-Correlation of Signals from a Double Senor Hot-Film Probe

    SciTech Connect

    B. Gurau; P. Vassalo; K. Keller

    2002-02-19

    Local gas and liquid velocities are measured by cross-correlating signals from a double sensor hot-film anemometer probe in pure water flow and air water two-phase flow. The gas phase velocity measured in two-phase flow agrees with velocity data obtained using high-speed video to within +/-5%. A turbulent structure, present in the liquid phase, allows a correlation to be taken, which is consistent with the expected velocity profiles in pure liquid flow. This turbulent structure is also present in the liquid phase of a two-phase flow system. Therefore, a similar technique can be applied to measure the local liquid velocity in a two-phase system, when conditions permit.

  6. Bursting the bubble on bacterial biofilms: a flow cell methodology

    PubMed Central

    Crusz, Shanika A.; Popat, Roman; Rybtke, Morten Theil; Cámara, Miguel; Givskov, Michael; Diggle, Stephen P.; Williams, Paul

    2012-01-01

    The flow cell biofilm system is an important and widely used tool for the in vitro cultivation and evaluation of bacterial biofilms under hydrodynamic conditions of flow. This paper provides an introduction to the background and use of such systems, accompanied by a detailed guide to the assembly of the apparatus including the description of new modifications which enhance its performance. As such, this is an essential guide for the novice biofilm researcher as well as providing valuable trouble-shooting techniques for even the most experienced laboratories. The adoption of a common and reliable methodology amongst researchers would enable findings to be shared and replicated amongst the biofilm research community, with the overall aim of advancing understanding and management of these complex and widespread bacterial communities. PMID:22877233

  7. Effects of Flow Velocity and Particle Size on Transport of Ultrafine Bubbles in Porous Media

    NASA Astrophysics Data System (ADS)

    Hamamoto, S.; Nihei, N.; Ueda, Y.; Nishimura, T.

    2015-12-01

    Potential applications of ultrafine bubbles (UFBs) have drawn more attention, especially in environmental engineering fields such as soil/groundwater remediation. Understanding a transport mechanism of UFBs in soils is essential to optimize remediation techniques using UFBs. In this study, column transport experiments using glass beads with different size fraction were conducted, where UFBs created by either air or oxygen were injected to the column with different flow conditions. Effects of particle size and flow velocities on transport characteristics of UFBs were investigated based on the column experiments. The results showed that attachments of UFBs were enhanced under lower water velocity condition, exhibiting more than 50% of UFBs injected were attached inside the column. The mobility of O2-UFBs which have lower zeta potential was higher than that of Air-UFBs. A convection-dispersion model including bubble attachment and detachment terms was applied to the obtained breakthrough curves for each experiment, showing good fitness against the measured data.

  8. PDMS free-flow electrophoresis chips with integrated partitioning bars for bubble segregation.

    PubMed

    Köhler, Stefan; Weilbeer, Claudia; Howitz, Steffen; Becker, Holger; Beushausen, Volker; Belder, Detlev

    2011-01-21

    In this work, a microfluidic free-flow electrophoresis device with a novel approach for preventing gas bubbles from entering the separation area is presented. This is achieved by integrating partitioning bars to reduce the channel depth between electrode channels and separation chamber in order to obtain electrical contact and simultaneously prevent bubbles from entering the separation area. The three-layer sandwich chip features a reusable carrier plate with integrated ports for fluidic connection combined with a softlithographically cast microfluidic PDMS layer and a sealing glass slide. This design allows for a straightforward and rapid chip prototyping process. The performance of the device is demonstrated by free-flow zone electrophoretic separations of fluorescent dye mixtures as well as by the separation of labeled amines and amino acids with separation voltages up to 297 V.

  9. Bubble Drag Reduction Requires Large Bubbles

    NASA Astrophysics Data System (ADS)

    Verschoof, Ruben A.; van der Veen, Roeland C. A.; Sun, Chao; Lohse, Detlef

    2016-09-01

    In the maritime industry, the injection of air bubbles into the turbulent boundary layer under the ship hull is seen as one of the most promising techniques to reduce the overall fuel consumption. However, the exact mechanism behind bubble drag reduction is unknown. Here we show that bubble drag reduction in turbulent flow dramatically depends on the bubble size. By adding minute concentrations (6 ppm) of the surfactant Triton X-100 into otherwise completely unchanged strongly turbulent Taylor-Couette flow containing bubbles, we dramatically reduce the drag reduction from more than 40% to about 4%, corresponding to the trivial effect of the bubbles on the density and viscosity of the liquid. The reason for this striking behavior is that the addition of surfactants prevents bubble coalescence, leading to much smaller bubbles. Our result demonstrates that bubble deformability is crucial for bubble drag reduction in turbulent flow and opens the door for an optimization of the process.

  10. Large-eddy simulation of bubble-driven plume in stably stratified flow.

    NASA Astrophysics Data System (ADS)

    Yang, Di; Chen, Bicheng; Socolofsky, Scott; Chamecki, Marcelo; Meneveau, Charles

    2015-11-01

    The interaction between a bubble-driven plume and stratified water column plays a vital role in many environmental and engineering applications. As the bubbles are released from a localized source, they induce a positive buoyancy flux that generates an upward plume. As the plume rises, it entrains ambient water, and when the plume rises to a higher elevation where the stratification-induced negative buoyancy is sufficient, a considerable fraction of the entrained fluid detrains, or peels, to form a downward outer plume and a lateral intrusion layer. In the case of multiphase plumes, the intrusion layer may also trap weakly buoyant particles (e.g., oil droplets in the case of a subsea accidental blowout). In this study, the complex plume dynamics is studied using large-eddy simulation (LES), with the flow field simulated by hybrid pseudospectral/finite-difference scheme, and the bubble and dye concentration fields simulated by finite-volume scheme. The spatial and temporal characteristics of the buoyant plume are studied, with a focus on the effects of different bubble buoyancy levels. The LES data provide useful mean plume statistics for evaluating the accuracy of 1-D engineering models for entrainment and peeling fluxes. Based on the insights learned from the LES, a new continuous peeling model is developed and tested. Study supported by the Gulf of Mexico Research Initiative (GoMRI).

  11. Modeling of wall-induced force for wall-bounded bubbly flow

    NASA Astrophysics Data System (ADS)

    Kim, Dongjoo; Kim, Jungwoo; Park, Hyungmin; Lee, Jun Ho

    2014-11-01

    The two-fluid model based on Eulerian-Eulerian approach has been widely used for simulating two-phase flow in industrial applications due to much less CPU time compared with interface tracking methods. However, the two-fluid approach requires accurate modeling of mass and momentum transfers between phases. The interfacial momentum exchange terms include drag, shear-induced lift, and wall-induced force. The last one is particularly important in order to correctly predict ``wall peaking'' and ``core peaking'' phenomena observed in bubbly pipe flows. However, the wall-induced force is not fully understood yet and the wall force coefficient used in previous studies has a wide range of values, probably tuned to match experiment. Therefore, we propose a new wall-induced force model in the present study. To verify the accuracy of present model, numerical simulations are performed for several laminar bubbly flows available in the literature. The spatial distributions of void fraction, liquid velocity, and bubble velocity are compared with those with previous models as well as experimental results. Supported by the NRF Programs (NRF-2012M2A8A4055647) of Korean government.

  12. A jet-driven dynamo (JEDD) from jets-inflated bubbles in cooling flows

    NASA Astrophysics Data System (ADS)

    Soker, Noam

    2017-01-01

    I suggest that the main process that amplifies magnetic fields in cooling flows in clusters and group of galaxies is a jet-driven dynamo (JEDD). The main processes that are behind the JEDD is the turbulence that is formed by the many vortices formed in the inflation processes of bubbles, and the large scale shear formed by the propagating jet. It is sufficient that a strong turbulence exits in the vicinity of the jets and bubbles, just where the shear is large. The typical amplification time of magnetic fields by the JEDD near the jets and bubbles is approximately hundred million years. The amplification time in the entire cooling flow region is somewhat longer. The vortices that create the turbulence are those that also transfer energy from the jets to the intra-cluster medium, by mixing shocked jet gas with the intra-cluster medium gas, and by exciting sound waves. The JEDD model adds magnetic fields to the cyclical behavior of energy and mass in the jet-feedback mechanism (JFM) in cooling flows.

  13. Simultaneous 3D location and size measurement of bubbles and sand particles in a flow using interferometric particle imaging.

    PubMed

    Ouldarbi, L; Pérret, G; Lemaitre, P; Porcheron, E; Coëtmellec, S; Gréhan, G; Lebrun, D; Brunel, M

    2015-09-01

    We present a system to characterize a triphasic flow in a 3D volume (air bubbles and solid irregular particles in water) using only one CCD sensor. A cylindrical interferometric out-of-focus imaging setup is used to determine simultaneously the 3D position and the size of bubbles and irregular sand particles in a flow. The 3D position of the particles is deduced from the ellipticity of their out-of-focus image. The size of bubbles is deduced from analysis of interference fringes. The characteristics of irregular sand particles are obtained from analysis of their speckle-like pattern. Experiments are confirmed by simulations.

  14. Experimental investigation of a bubbly flow by means of an image analysis technique

    SciTech Connect

    Schmidl, W.D.; Hassan, Y.A.; Ortiz-Villafuerte, J.

    1996-12-31

    Particle Image Velocimetry (PIV) is a non-intrusive measurement technique, which can be used to study the structure of various fluid flows. PIV is used to measure the time varying full field velocity data of a particle-seeded flow field within either a two-dimensional plane or three-dimensional volume. PIV is a very efficient measurement technique since it can obtain both qualitative and quantitative spatial information about the flow field being studied. This information can be further processed into information such as vorticity and pathlines. Other flow measurement techniques (Laser Doppler Velocimetry, Hot Wire Anemometry, etc...) only provide quantitative information at a single point. PIV can be used to study turbulence structures if a sufficient amount of data can be acquired and analyzed, and it can also be extended to study two-phase flows if both phases can be distinguished. In this study, the flow structure around a bubble rising in a pipe filled with water was studied in three-dimensions. The velocity of the rising bubble and the velocity field of the surrounding water was measured. Then the turbulence intensities and Reynolds stresses were calculated from the experimental data.

  15. Population Balance Modeling of Polydispersed Bubbly Flow in Continuous-Casting Using Multiple-Size-Group Approach

    NASA Astrophysics Data System (ADS)

    Liu, Zhongqiu; Li, Linmin; Qi, Fengsheng; Li, Baokuan; Jiang, Maofa; Tsukihashi, Fumitaka

    2015-02-01

    A population balance model based on the multiple-size-group (MUSIG) approach has been developed to investigate the polydispersed bubbly flow inside the slab continuous-casting mold and bubble behavior including volume fraction, breakup, coalescence, and size distribution. The Eulerian-Eulerian approach is used to describe the equations of motion of the two-phase flow. All the non-drag forces (lift force, virtual mass force, wall lubrication force, and turbulent dispersion force) and drag force are incorporated in this model. Sato and Sekiguchi model is used to account for the bubble-induced turbulence. Luo and Svendsen model and Prince and Blanch model are used to describe the bubbles breakup and coalescence behavior, respectively. A 1/4th water model of the slab continuous-casting mold was applied to investigate the distribution and size of bubbles by injecting air through a circumferential inlet chamber which was made of the specially-coated samples of mullite porous brick, which is used for the actual upper nozzle. Against experimental data, numerical results showed good agreement for the gas volume fraction and local bubble Sauter mean diameter. The bubble Sauter mean diameter in the upper recirculation zone decreases with increasing water flow rate and increases with increasing gas flow rate. The distribution of bubble Sauter mean diameter along the width direction of the upper mold increases first, and then gradually decreases from the SEN to the narrow wall. Close agreements between the predictions and measurements demonstrate the capability of the MUSIG model in modeling bubbly flow inside the continuous-casting mold.

  16. Transient Asymmetric Flow and Bubble Transport Inside a Slab Continuous-Casting Mold

    NASA Astrophysics Data System (ADS)

    Liu, Zhongqiu; Li, Baokuan; Jiang, Maofa

    2014-04-01

    A one third scale water model experiment was conducted to observe the asymmetric flow and vortexing flow inside a slab continuous-casting mold. Dye-injection experiment was used to show the evolution of the transient flow pattern in the liquid pool without and with gas injection. The spread of the dye was not symmetric about the central plane. The flow pattern inside the mold was not stationary. The black sesames were injected into water to visualize the vortexing flow pattern on the top surface. The changes of shape and location of single vortex and two vortices with time had been observed during experiments. Plant ultrasonic testing (UT) of slabs was used to analyze the slab defects distribution, which indicated that the defects are intermittent and asymmetric. A mathematical model has been developed to analyze the time-dependent flow using the realistic geometries, which includes the submerged entry nozzle (SEN), actual mold, and part of the secondary cooling zone. The transient turbulent flow of molten steel inside the mold has been simulated using the large eddy simulation computational approach. Simulation results agree acceptably well with the water model experimentally observed and plant UT results. The oscillating motions of jet and the turbulence naturally promote the asymmetric flow even without the effects of slide gate nozzle or the existence of clogs inside the SEN. The periodic behavior of transient fluid flow in the mold is identified and characterized. The vortexing flow is resulted from asymmetric flow in the liquid pool. The vortices are located at the low-velocity side adjacent to the SEN, and the positions and sizes are different. Finally, the model is applied to investigate the influence of bubble size and casting speed on the time-dependent bubble distribution and removal fraction from the top surface inside the mold.

  17. Choked-Flow Inlet Orifice Bubbler for Creating Small Bubbles in Mercury

    SciTech Connect

    Wendel, Mark W; Abdou, Ashraf A; Riemer, Bernie

    2013-01-01

    Pressure waves created in liquid mercury pulsed spallation targets like the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory, induce cavitation damage on the target container. The cavitation damage is thought to limit the lifetime of the target for power levels at and above 1 MW. One way to mitigate the damage would be to absorb the pressure pulse energy into a dispersed population of small bubbles, however, creating a bubble size distribution that is sufficiently large and disperse in mercury is challenging due to the high surface tension. Also, measuring the population is complicated by the opacity and the high level of turbulent mixing. Recent advances in bubble diagnostics by batch sampling the mercury made it possible to compare bubble populations for different techniques in a SNS-1/20th scale test loop. More than 10 bubblers were tested and the most productive bubblers were taken for in-beam testing at the Los Alamos Neutron Science Center (LANSCE) WNR user facility. One bubbler design, referred to as the inlet-orifice bubbler, that showed moderate success in creating populations also has an added advantage that it could easily be included in the existing SNS full-scale mercury target configuration. Improvements to the bubbler were planned including a reduction of the nozzle size to choke the gas injection, thus steadying the injected mass flow and allowing multiple nozzles to work off of a common plenum. For the first time, reliable bubble population data are available in the prototypical target geometry and can be compared with populations that mitigated cavitation damage. This paper presents those experimental results.

  18. The magnitude of lift forces acting on drops and bubbles in liquids flowing inside microchannels.

    PubMed

    Stan, Claudiu A; Ellerbee, Audrey K; Guglielmini, Laura; Stone, Howard A; Whitesides, George M

    2013-02-07

    Hydrodynamic lift forces offer a convenient way to manipulate particles in microfluidic applications, but there is little quantitative information on how non-inertial lift mechanisms act and compete with each other in the confined space of microfluidic channels. This paper reports measurements of lift forces on nearly spherical drops and bubbles, with diameters from one quarter to one half of the width of the channel, flowing in microfluidic channels, under flow conditions characterized by particle capillary numbers Ca(P) = 0.0003-0.3 and particle Reynolds numbers Re(P) = 0.0001-0.1. For Ca(P) < 0.01 and Re(P) < 0.01 the measured lift forces were much larger than predictions of deformation-induced and inertial lift forces found in the literature, probably due to physicochemical hydrodynamic effects at the interface of drops and bubbles, such as the presence of surfactants. The measured forces could be fit with good accuracy using an empirical formula given herein. The empirical formula describes the power-law dependence of the lift force on hydrodynamic parameters (velocity and viscosity of the carrier phase; sizes of channel and drop or bubble), and includes a numerical lift coefficient that depends on the fluids used. The empirical formula using an average lift coefficient of ~500 predicted, within one order of magnitude, all lift force measurements in channels with cross-sectional dimensions below 1 mm.

  19. Discrete-vortex simulation of pulsating flow on a turbulent leading-edge separation bubble

    NASA Technical Reports Server (NTRS)

    Sung, Hyung Jin; Rhim, Jae Wook; Kiya, Masaru

    1992-01-01

    Studies are made of the turbulent separation bubble in a two-dimensional semi-infinite blunt plate aligned to a uniform free stream with a pulsating component. The discrete-vortex method is applied to simulate this flow situation because this approach is effective for representing the unsteady motions of the turbulent shear layer and the effect of viscosity near the solid surface. The numerical simulation provides reasonable predictions when compared with the experimental results. A particular frequency with a minimum reattachment is related to the drag reduction. The most effective frequency is dependent on the amplified shedding frequency. The turbulent flow structure is scrutinized. This includes the time-mean and fluctuations of the velocity and the surface pressure, together with correlations between the fluctuating components. A comparison between the pulsating flow and the non-pulsating flow at the particular frequency of the minimum reattachment length of the separation bubble suggests that the large-scale vortical structure is associated with the shedding frequency and the flow instabilities.

  20. Micro vapor bubble jet flow for safe and high-rate fluorescence-activated cell sorting.

    PubMed

    de Wijs, Koen; Liu, Chengxun; Dusa, Alexandra; Vercruysse, Dries; Majeed, Bivragh; Tezcan, Deniz Sabuncuoglu; Blaszkiewicz, Kamil; Loo, Josine; Lagae, Liesbet

    2017-03-29

    Safe, high-rate and cost-effective cell sorting is important for clinical cell isolation. However, commercial fluorescence-activated cell sorters (FACS) are expensive and prone to aerosol-induced sample contamination. Here we report a microfluidic cell sorter allowing high rate and fully enclosed cell sorting. The sorter chip consists of an array of micro heating hotspots. Pulsed resistive heating in the hotspots produces numerous micro vapor bubbles with short duration, which gives rise to a rapid jet flow for cell sorting. With this method, we demonstrated high sorting rate comparable to commercial FACS and the significant enrichment of rare cancer cells. This vapor bubble based cell sorting method can be a powerful tool for contamination-free and affordable clinical cell sorting such as circulating tumor cell isolation and cancer cell therapy.

  1. Fermi bubbles inflated by winds launched from the hot accretion flow in Sgr A*

    SciTech Connect

    Mou, Guobin; Yuan, Feng; Bu, Defu; Sun, Mouyuan; Su, Meng E-mail: fyuan@shao.ac.cn

    2014-08-01

    A pair of giant gamma-ray Bubbles has been revealed by Fermi-LAT. In this paper we investigate their formation mechanism. Observations have indicated that the activity of the supermassive black hole located at the Galactic center, Sgr A*, was much stronger than at the present time. Specifically, one possibility is that while Sgr A* was also in the hot accretion regime, the accretion rate should be 10{sup 3}-10{sup 4} times higher during the past ∼10{sup 7} yr. On the other hand, recent magnetohydrodynamic numerical simulations of hot accretion flows have unambiguously shown the existence and obtained the properties of strong winds. Based on this knowledge, by performing three-dimensional hydrodynamical simulations, we show in this paper that the Fermi Bubbles could be inflated by winds launched from the 'past' hot accretion flow in Sgr A*. In our model, the active phase of Sgr A* is required to last for about 10 million years and it was quenched no more than 0.2 million years ago. The central molecular zone (CMZ) is included and it collimates the wind orientation toward the Galactic poles. Viscosity suppresses the Rayleigh-Taylor and Kelvin-Helmholtz instabilities and results in the smoothness of the Bubbles edge. The main observational features of the Bubbles can be well explained. Specifically, the ROSAT X-ray features are interpreted by the shocked interstellar medium and the interaction region between the wind and CMZ gas. The thermal pressure and temperature obtained in our model are consistent with recent Suzaku observations.

  2. Multiple Size Group Modeling of Polydispersed Bubbly Flow in the Mold: An Analysis of Turbulence and Interfacial Force Models

    NASA Astrophysics Data System (ADS)

    Liu, Zhongqiu; Qi, Fengsheng; Li, Baokuan; Jiang, Maofa

    2015-04-01

    An inhomogeneous Multiple Size Group (MUSIG) model based on the Eulerian-Eulerian approach has been developed to describe the polydispersed bubbly flow inside the continuous-casting mold. A laboratory scale mold has been simulated using four different turbulence closure models (modified k - ɛ, RNG k - ɛ, k - ω, and SST) with the purpose of critically comparing their predictions of bubble Sauter mean diameter distribution with previous experimental data. Furthermore, the influences of all the interfacial momentum transfer terms including drag force, lift force, virtual mass force, wall lubrication force, and turbulent dispersion force are investigated. The breakup and coalescence effects of the bubbles are modeled according to the bubble breakup by the impact of turbulent eddies while for bubble coalescence by the random collisions driven by turbulence and wake entrainment. It has been found that the modified k - ɛ model shows better agreement than other models in predicting the bubble Sauter mean diameter profiles. Further, simulations have also been performed to understand the sensitivity of different interfacial forces. The appropriate drag force coefficient, lift force coefficient, virtual mass force coefficient, and turbulent dispersion force coefficient are chosen in accordance with measurements of water model experiments. However, the wall lubrication force does not have much effect on the current polydispersed bubbly flow system. Finally, the MUSIG model is then used to estimate the argon bubble diameter in the molten steel of the mold. The argon bubble Sauter mean diameter generated in molten steel is predicted to be larger than air bubbles in water for the similar conditions.

  3. Bubble reconstruction method for wire-mesh sensors measurements

    NASA Astrophysics Data System (ADS)

    Mukin, Roman V.

    2016-08-01

    A new algorithm is presented for post-processing of void fraction measurements with wire-mesh sensors, particularly for identifying and reconstructing bubble surfaces in a two-phase flow. This method is a combination of the bubble recognition algorithm presented in Prasser (Nuclear Eng Des 237(15):1608, 2007) and Poisson surface reconstruction algorithm developed in Kazhdan et al. (Poisson surface reconstruction. In: Proceedings of the fourth eurographics symposium on geometry processing 7, 2006). To verify the proposed technique, a comparison was done of the reconstructed individual bubble shapes with those obtained numerically in Sato and Ničeno (Int J Numer Methods Fluids 70(4):441, 2012). Using the difference between reconstructed and referenced bubble shapes, the accuracy of the proposed algorithm was estimated. At the next step, the algorithm was applied to void fraction measurements performed in Ylönen (High-resolution flow structure measurements in a rod bundle (Diss., Eidgenössische Technische Hochschule ETH Zürich, Nr. 20961, 2013) by means of wire-mesh sensors in a rod bundle geometry. The reconstructed bubble shape yields bubble surface area and volume, hence its Sauter diameter d_{32} as well. Sauter diameter is proved to be more suitable for bubbles size characterization compared to volumetric diameter d_{30}, proved capable to capture the bi-disperse bubble size distribution in the flow. The effect of a spacer grid was studied as well: For the given spacer grid and considered flow rates, bubble size frequency distribution is obtained almost at the same position for all cases, approximately at d_{32} = 3.5 mm. This finding can be related to the specific geometry of the spacer grid or the air injection device applied in the experiments, or even to more fundamental properties of the bubble breakup and coagulation processes. In addition, an application of the new algorithm for reconstruction of a large air-water interface in a tube bundle is

  4. Evaluation of flow patterns and elongated bubble characteristics during the flow boiling of halocarbon refrigerants in a micro-scale channel

    SciTech Connect

    Arcanjo, Alexandre Alves; Tibirica, Cristiano Bigonha; Ribatski, Gherhardt

    2010-09-15

    In the present study, quasi-diabatic two-phase flow pattern visualizations and measurements of elongated bubble velocity, frequency and length were performed. The tests were run for R134a and R245fa evaporating in a stainless steel tube with diameter of 2.32 mm, mass velocities ranging from 50 to 600 kg/m{sup 2} s and saturation temperatures of 22 C, 31 C and 41 C. The tube was heated by applying a direct DC current to its surface. Images from a high-speed video-camera (8000 frames/s) obtained through a transparent tube just downstream the heated sections were used to identify the following flow patterns: bubbly, elongated bubbles, churn and annular flows. The visualized flow patterns were compared against the predictions provided by Barnea et al. (1983), Felcar et al. (2007), Revellin and Thome (2007) and Ong and Thome (2009). From this comparison, it was found that the methods proposed by Felcar et al. (2007) and Ong and Thome (2009) predicted relatively well the present database. Additionally, elongated bubble velocities, frequencies and lengths were determined based on the analysis of high-speed videos. Results suggested that the elongated bubble velocity depends on mass velocity, vapor quality and saturation temperature. The bubble velocity increases with increasing mass velocity and vapor quality and decreases with increasing saturation temperature. Additionally, bubble velocity was correlated as linear functions of the two-phase superficial velocity. (author)

  5. Directed weighted network structure analysis of complex impedance measurements for characterizing oil-in-water bubbly flow

    NASA Astrophysics Data System (ADS)

    Gao, Zhong-Ke; Dang, Wei-Dong; Xue, Le; Zhang, Shan-Shan

    2017-03-01

    Characterizing the flow structure underlying the evolution of oil-in-water bubbly flow remains a contemporary challenge of great interests and complexity. In particular, the oil droplets dispersing in a water continuum with diverse size make the study of oil-in-water bubbly flow really difficult. To study this issue, we first design a novel complex impedance sensor and systematically conduct vertical oil-water flow experiments. Based on the multivariate complex impedance measurements, we define modalities associated with the spatial transient flow structures and construct modality transition-based network for each flow condition to study the evolution of flow structures. In order to reveal the unique flow structures underlying the oil-in-water bubbly flow, we filter the inferred modality transition-based network by removing the edges with small weight and resulting isolated nodes. Then, the weighted clustering coefficient entropy and weighted average path length are employed for quantitatively assessing the original network and filtered network. The differences in network measures enable to efficiently characterize the evolution of the oil-in-water bubbly flow structures.

  6. Numerical investigation on boiling flow of liquid nitrogen in a vertical tube using bubble number density approach

    NASA Astrophysics Data System (ADS)

    Shao, Xuefeng; Li, Xiangdong; Wang, Rongshun

    2016-04-01

    An average bubble number density (ABND) model was formulated and numerically resolved for the subcooled flow boiling of liquid nitrogen. The effects of bubble coalescence and breakup were taken into account. Some new closure correlations describing bubble nucleation and departure on the heating surface were selected as well. For the purpose of comparison, flow boiling of liquid nitrogen was also numerically simulated using a modified two-fluid model. The results show that the simulations performed by using the ABND model achieve encouraging improvement in accuracy in predicting heat flux and wall temperature of a vertical tube. Moreover, the influence of the bubble coalescence and breakup is shown to be great on predicting overall pressure beyond the transition point.

  7. Singular effective slip length for longitudinal flow over a dense bubble mattress

    NASA Astrophysics Data System (ADS)

    Schnitzer, Ory

    2016-11-01

    We derive accurate asymptotic expansions in the small-solid-fraction limit ɛ << 1 for the effective slip length characterising unidirectional liquid flow over a 'bubble mattress' - a periodically grooved surface, with trapped bubbles protruding between solid ridges. The slip length diverges in this limit: inversely with √{ ɛ} for contact angles θ near π / 2 , and logarithmically for 0 <= θ < π / 2 . The analysis of the velocity field entails matching 'inner' expansions valid close to the solid segments with 'outer' expansions valid on the scale of the periodicity, where the protruding bubbles appear to touch. For θ close to π / 2 , the inner-region geometry is narrow and the analysis there resembles lubrication theory; for smaller contact angles the inner region is resolved using a Schwarz-Christoffel mapping. In both cases the outer problem is solved using a mapping from a degenerate curvilinear triangle to an auxiliary half plane. The asymptotic analysis explicitly illustrates the logarithmic-to-algebraic transition, and yields a uniformly valid approximation for the slip length for arbitrary contact angles 0 <= θ <= π / 2 . We demonstrate good agreement with a numerical solution (courtesy of Ms Elena Luca).

  8. Dynamics of a bubble bouncing at a compound interface

    NASA Astrophysics Data System (ADS)

    Feng, Jie; Muradoglu, Metin; Stone, Howard A.

    2014-11-01

    Bubbly flow is extensively involved in a wide range of technological applications, which generate a great demand for understanding of bubble physics. The collision, bouncing and coalescence of moving bubbles with liquid/gas and liquid/solid interfaces, as the first stage for the formation of foams and flotation aggregates, have been the subject of many studies, but there are still unanswered questions related to how the properties of the interface influence the dynamics. For example, Zawala et al. 2013 have tried to investigate how the kinetic energy of the bubble affects the liquid film drainage during the collision with an air-water interface. Inspired by Feng et al. 2014, we study the dynamics of an air bubble bouncing at a liquid/liquid/gas interface, in which a thin layer of oil is put on top of the water. The presence of the oil layer changes the interfacial properties and thus the entire process. Combined with direct numerical simulations, extensive experiments were carried out to investigate the effects of the oil layer thickness, oil viscosity, bubble size and initial impact velocity on the bouncing of the bubble at the compound interface. In addition, a mass-spring model is proposed to describe the bubble dynamics and interactions with the oil layer.

  9. Flow patterns in a slurry-bubble-column reactor under reaction conditions

    SciTech Connect

    Toselane, B.A.; Brown, D.M.; Zou, B.S.; Dudukovic, M.P.

    1995-12-31

    The gas and liquid radioactive tracer response curves obtained in an industrial bubble column reactor of height to diameter ratio of 10 are analyzed and the suitability of the axial dispersion model for interpretation of the results is discussed. The relationship between the tracer concentration distribution and measured detector response of the soluble gas tracer (Ar-41) is possibly dominated by the dissolved gas. The one dimensional axial dispersion model cannot match all the experimental observations well and the flow pattern of the undissolved gas cannot be determined with certainty.

  10. Turbulent Bubbly Flow in a Vertical Pipe Computed By an Eddy-Resolving Reynolds Stress Model

    DTIC Science & Technology

    2014-09-19

    induced turbulence of the underlying flow and the modification of the turbulent quantities by the dispersed bubbles. Due to the lack of realisable data...is modelled with the coefficient CVM taking the standard value of 0.5. Other forces which mainly act in the lateral direc- tion, like the lift, wall... values were used for αG = 0.033 and the mean gas velocity, in accordance with the case 4 from Hosokawa and Tomiyama (2009). The domain was 160D long in

  11. Air-bubbling, hollow-fiber reactor with cell bleeding and cross-flow filtration.

    PubMed

    Nishii, K; Sode, K; Karube, I

    1990-05-01

    Continuous asymmetric reduction of dyhydrooxoisophorone (DOIP) to 4-hydroxy-2,2,6-trimethylcyclo-hexanone (4-HTMCH) was achieved by a thermophilic bacterium Bacillus stearothermophilus NK86-0151. Three reactors were used: an air-bubbling hollow-fiber reactor with cell bleeding and cross-flow filtration, an air-lift reactor, and a CSTR with PAA immobilized cells. The maximum cell concentration of 11.1 g dry wt L(-1) was obtained in an air-bubbling hollow-fiber reactor, while in the other reactors the cell densities were between 3.5 and 4.1 g dry wt L(-1) The optimum bleed ratio was 0.1 at the dilution rate 0.3 h(-1) in the hollow-fiber reactor. The highest viable cell concentration was maintained in the dilution range of 0.4-0.7 h(-1) by a combination of proper cell bleeding and cross-flow filtration. The maximum volumetric productivity of 4-HTMCH reached 826 mg L(-1) h(-1) at the dilution rate 0.54 h(-1). This value was 4 and 2 times higher than those in the air-lift reactor and CSTR, respectively. The increasing viable cell concentration increased the volumetric productivity of 4-HTMCH. A cell free product solution was continuously obtained by cross-flow filtration.

  12. Air/water subchannel measurements of the equilibrium quality and mass-flux distribution in a rod bundle. [BWR

    SciTech Connect

    Sterner, R.W.; Lahey, R.T. Jr.

    1983-07-01

    Subchannel measurements were performed in order to determine the equilibrium quality and mass flux distribution in a four rod bundle, using air/water flow. An isokinetic technique was used to sample the flow in the center, side and corner subchannels of this test section. Flow rates of the air and water in each sampled subchannel were measured. Experiments were performed for two test-section-average mass fluxes (0.333x10/sup 6/ and 0.666x10/sup 6/ lb/sub m//h-ft/sup 2/), and the test-section-average quality was varied from 0% to 0.54% for each mass flux. Single-phase liquid, bubbly, slug and churn-turbulent two-phase flow regimes were achieved. The observed data trends agreed with previous diabatic measurements in which the center subchannel had the highest quality and mass flux, while the corner subchannel had the lowest.

  13. Boundary effects on streaming flow around a bubble located at the velocity antinode of a standing wave

    NASA Astrophysics Data System (ADS)

    Alhamli, Mohammad

    2016-11-01

    A stable bubble trapped in a standing sound wave with frequency less than the resonance frequency of the bubble will be located at the velocity antinode. Steady streaming flow will develop around the bubble and is directly dependent on the bubble's boundary. Four boundary conditions are possible: 1) nonpulsating; no slip, 2) nonpulsating; free shear, 3) pulsating; no slip, and 4) pulsating; free shear. To solve for these conditions, we expanded the equations of motion with the dimensionless lateral oscillation amplitude, ɛ, using the singular perturbation method. The lateral oscillation amplitude is much smaller than the bubble radius ɛ < < a . Additionally, for the third and fourth cases, the dimensionless radial oscillation amplitude was assumed to be small, ɛ' < < 1 . We also assumed a moderate value for the frequency parameter, | M | , which is the ratio of the bubble radius to the viscous length. For the nonpulsating cases the streaming flow patterns were quadrupole and symmetric across the quadrants and the intensity increases as we increase the frequency parameter. When we introduced the pulsation, we noticed that the streaming was symmetric across the polar plane and asymmetric below the equatorial plane for midrange values of the frequency parameter.

  14. A more general Force Balance Model to predict Bubble Departure and Lift-off Diameters in flow boiling

    NASA Astrophysics Data System (ADS)

    Kommajosyula, Ravikishore; Mazzocco, Thomas; Ambrosini, Walter; Baglietto, Emilio

    2016-11-01

    Accurate prediction of Bubble Departure and Lift-off Diameters is key for development of closures in two-phase Eulerian CFD simulation of Flow Boiling, owing to its sensitivity in the Heat Flux partitioning approach. Several models ranging from simple correlations to solving complex force balance models have been proposed in literature; however, they rely on data-fitting for specific databases, and have shown to be inapplicable for general flow applications. The aim of this study is to extend the approach by proposing a more consistent and general formulation that accounts for relevant forces acting on the Bubble at the point of Departure and Lift-off. Among the key features of the model, the Bubble Inclination angle is treated as an unknown to be inferred along with the Departure Diameter, and the relative velocity of the bubble sliding on the surface, is modeled to determine the Lift-off Diameter. A novel expression is developed for the bubble growth force in terms of flow quantities, based on extensive data analysis. The model has been validated using 6 different experimental databases with varying flow conditions and 3 fluids. Results show high accuracy of predictions over a broad range, outperforming existing models both in terms of accuracy and generality. CASL - The Consortium for Advanced Simulation of LWRs.

  15. Bubble Formation on a Wall in Cross-Flowing Liquid and Surrounding Fluid Motion,With and Without Heating

    NASA Technical Reports Server (NTRS)

    Bhunia, Avijit; Kamotani, Yasuhiro; Nahra, Henry K.

    2000-01-01

    Application of gas-liquid two-phase flow systems for space-based thermal management and for the HEDS program demands a precise control of bubble size distribution in liquid. The necessity of bulk liquid motion for controlling bubble size and frequency in the space environment has been suggested by recent studies on pool, forced convection boiling and bubble formation in flowing liquid. The present work, consisting of two parts, explores bubble generation at wall in a cross-flowing liquid, i.e., in a forced convection boiling configuration. A schematic is shown. The first part looks into the bubble formation process under isothermal conditions in a reduced gravity environment, by injecting gas through a hole in the wall of a flowing liquid channel. In the latter part with channel wall heating, flow and temperature fields near a single bubble are studied under normal (1-g) and micro-gravity (mu-g) conditions. The objective of the isothermal experiments is to experimentally investigate the effects of liquid cross-flow velocity, gas flow rate, and orifice diameter on bubble formation. Data were taken mainly under reduced gravity conditions but some data were taken in normal gravity for comparison. The reduced gravity experiment was conducted aboard the NASA DC-9 Reduced Gravity Aircraft. The results show that the process of bubble formation and detachment depends on gravity, the orifice diameter (D(sub N)), the gas flow rate (Q(sub g)), and the liquid cross-flow velocity (U(sub L)). The reduced gravity data are shown. The data are analyzed based on a force balance, and two different detachment mechanisms are identified. When the gas momentum is large, the bubble detaches from the injection orifice as the gas momentum overcomes the attaching effects of liquid drag and inertia. The surface tension force is much reduced because a large part of the bubble pinning edge at the orifice is lost as the bubble axis is tilted by the liquid flow. When the gas momentum is small

  16. Interfacial Bubble Deformations

    NASA Astrophysics Data System (ADS)

    Seymour, Brian; Shabane, Parvis; Cypull, Olivia; Cheng, Shengfeng; Feitosa, Klebert

    Soap bubbles floating at an air-water experience deformations as a result of surface tension and hydrostatic forces. In this experiment, we investigate the nature of such deformations by taking cross-sectional images of bubbles of different volumes. The results show that as their volume increases, bubbles transition from spherical to hemispherical shape. The deformation of the interface also changes with bubble volume with the capillary rise converging to the capillary length as volume increases. The profile of the top and bottom of the bubble and the capillary rise are completely determined by the volume and pressure differences. James Madison University Department of Physics and Astronomy, 4VA Consortium, Research Corporation for Advancement of Science.

  17. Two-phase flow characteristic of inverted bubbly, slug and annular flow in post-critical heat flux region

    SciTech Connect

    Ishii, M.; Denten, J.P.

    1988-01-01

    Inverted annular flow can be visualized as a liquid jet-like core surrounded by a vapor annulus. While many analytical and experimental studies of heat transfer in this regime have been performed, there is very little understanding of the basic hydrodynamics of the post-CHF flow field. However, a recent experimental study was done that was able to successfully investigate the effects of various steady-state inlet flow parameters on the post-CHF hydrodynamics of the film boiling of a single phase liquid jet. This study was carried out by means of a visual photographic analysis of an idealized single phase core inverted annular flow initial geometry (single phase liquid jet core surrounded by a coaxial annulus of gas). In order to extend this study, a subsequent flow visualization of an idealized two-phase core inverted annular flow geometry (two-phase central jet core, surrounded by a coaxial annulus of gas) was carried out. The objective of this second experimental study was to investigate the effect of steady-state inlet, pre-CHF two-phase jet core parameters on the hydrodynamics of the post-CHF flow field. In actual film boiling situations, two-phase flows with net positive qualities at the CHF point are encountered. Thus, the focus of the present experimental study was on the inverted bubbly, slug, and annular flow fields in the post dryout film boiling region. Observed post dryout hydrodynamic behavior is reported. A correlation for the axial extent of the transition flow pattern between inverted annular and dispersed droplet flow (the agitated regime) is developed. It is shown to depend strongly on inlet jet core parameters and jet void fraction at the dryout point. 45 refs., 9 figs., 4 tabs.

  18. On the effects of centrifugal forces in air-water two-phase flow regime transitions in an adiabatic helical geometry

    NASA Astrophysics Data System (ADS)

    Young, Eric Paul

    Two-phase flow in helical conduits is important in many industries where reaction between components, heat transfer, and mass transport are utilized as processes. The helical design is chosen for the effects of secondary flow patterns that reduce axial dispersion, increased heat transfer, and also their compact design. The first is a result of the secondary flow, which continually transports fluid from the near wall region to the bulk of the flow. In single-phase chemical reactor design this secondary flow increases radial mixing and reduces axial dispersion. In heat exchanger design it increases laminar heat transfer while extending the Reynolds number range of laminar flow. A literature review of the work on helical pipe flow shows that the vast majority of the work is on toroidal single-phase flow, and analyses of two-phase flow are sparse. This dissertation addresses this void by presenting an analytical model of the stratified and annular flow regime transitions in helical conduits, by consideration of the governing equations and mechanisms for transition in the toroidal geometry including the major impact of pitch. Studies have taken a similar approach for straight inclined horizontal and vertical geometries, but none have been found which resolve two-phase flow in the curved geometry of a helix. The main issue in resolving the flow in this geometry is that of determining appropriate inter-phase momentum transfer, and the appropriate friction correlations for wall interaction. These issues are resolved to yield a novel attempt at modeling helical two-phase flow. Pitch is considered negligible in introduction of torsion, while the dominating influence of the centrifugal force is retained. The formulation of the governing equations are taken from a general vector form that is readily extended to a true helix that includes torsion. The predictive capability of the current model is compared to the data and observations of the two-phase helical flow studies

  19. The multiphase flow system used in exploiting depleted reservoirs: water-based Micro-bubble drilling fluid

    NASA Astrophysics Data System (ADS)

    Li-hui, Zheng; Xiao-qing, He; Li-xia, Fu; Xiang-chun, Wang

    2009-02-01

    Water-based micro-bubble drilling fluid, which is used to exploit depleted reservoirs, is a complicated multiphase flow system that is composed of gas, water, oil, polymer, surfactants and solids. The gas phase is separate from bulk water by two layers and three membranes. They are "surface tension reducing membrane", "high viscosity layer", "high viscosity fixing membrane", "compatibility enhancing membrane" and "concentration transition layer of liner high polymer (LHP) & surfactants" from every gas phase centre to the bulk water. "Surface tension reducing membrane", "high viscosity layer" and "high viscosity fixing membrane" bond closely to pack air forming "air-bag", "compatibility enhancing membrane" and "concentration transition layer of LHP & surfactants" absorb outside "air-bag" to form "incompact zone". From another point of view, "air-bag" and "incompact zone" compose micro-bubble. Dynamic changes of "incompact zone" enable micro-bubble to exist lonely or aggregate together, and lead the whole fluid, which can wet both hydrophilic and hydrophobic surface, to possess very high viscosity at an extremely low shear rate but to possess good fluidity at a higher shear rate. When the water-based micro-bubble drilling fluid encounters leakage zones, it will automatically regulate the sizes and shapes of the bubbles according to the slot width of fracture, the height of cavern as well as the aperture of openings, or seal them by making use of high viscosity of the system at a very low shear rate. Measurements of the rheological parameters indicate that water-based micro-bubble drilling fluid has very high plastic viscosity, yield point, initial gel, final gel and high ratio of yield point and plastic viscosity. All of these properties make the multiphase flow system meet the requirements of petroleum drilling industry. Research on interface between gas and bulk water of this multiphase flow system can provide us with information of synthesizing effective agents to

  20. Turbulence and wave breaking effects on air-water gas exchange

    PubMed

    Boettcher; Fineberg; Lathrop

    2000-08-28

    We present an experimental characterization of the effects of turbulence and breaking gravity waves on air-water gas exchange in standing waves. We identify two regimes that govern aeration rates: turbulent transport when no wave breaking occurs and bubble dominated transport when wave breaking occurs. In both regimes, we correlate the qualitative changes in the aeration rate with corresponding changes in the wave dynamics. In the latter regime, the strongly enhanced aeration rate is correlated with measured acoustic emissions, indicating that bubble creation and dynamics dominate air-water exchange.

  1. Modelling flow pattern transitions for steady upward gas-liquid flow in vertical tubes. [Bubble, slug, churn and dispersed-annular; also existence regions and transitions

    SciTech Connect

    Taitel, Y.; Bornea, D.; Dukler, A.E.

    1980-05-01

    Models for predicting flow patterns in steady upward gas-liquid flow in vertical tubes (such as production-well tubing) delineate the transition boundaries between each of the four basic flow patterns for gas-liquid flow in vertical tubes: bubble, slug, churn, and dispersed-annular. Model results suggest that churn flow is the development region for the slug pattern and that bubble flow can exist in small pipes only at high liquid rates, where turbulent dispersion forces are high. Each transition depends on the flow-rate pair, fluid properties, and pipe size, but the nature of the dependence is different for each transition because of differing control mechanisms. The theoretical predictions are in reasonably good agreement with a variety of published flow maps based on experimental data.

  2. Ring Bubbles of Dolphins

    NASA Technical Reports Server (NTRS)

    Shariff, Karim; Marten, Ken; Psarakos, Suchi; White, Don J.; Merriam, Marshal (Technical Monitor)

    1996-01-01

    centrifugal force has to be balanced by a lift-like force. She then re-traces her path and injects air into the vortex from her blowhole. She can even make a ring reconnect from the helix. In the second technique, demonstrated a few times, she again swims in a curved path, releases a cloud or group of bubbles from her blowhole and turns sharply away (Which presumably strengthens the vortex). As the bubbles encounter the vortex, they travel to the center of the vortex, merge and, in a flash, elongate along the core of the vortex. In all the three types, the air-water interface is shiny smooth and stable because the pressure gradient in the vortex flow around the bubble stabilizes it. A lot of the interesting physics still remains to be explored.

  3. Modeling studies of electrolyte flow and bubble behavior in advanced Hall cells

    NASA Astrophysics Data System (ADS)

    Shekhar, R.; Evans, J. W.

    Much research was performed in recent years by corporations and university/government labs on materials for use in advanced Hall-Heroult cells. Attention has focussed on materials for use as wettable cathodes and inert anodes and much was achieved in terms of material development. Comparatively less attention was devoted to how these materials might be incorporated in new or existing cells, i.e., to how the cells should be designed and redesigned, to take full advantage of these materials. The effort, supported by the U.S. Department of Energy, to address this issue, is described. The primary objectives are cell design where electrolyte flow can be managed to promote both the removal of the anode gas bubbles and the convection of dissolved alumina in the inter-electrode region, under conditions where the anode-cathode distance is small. The principal experimental tool was a water model consisting of a large tank in which simulated anodes can be suspended in either the horizontal or vertical configurations. Gas generation was by forcing compressed air through porous graphite and the fine bubbles characteristic of inert anodes were produced by adding butanol to the water. Velocities were measured using a laser Doppler velocimeter. Velocity measurements with two different anode designs (one that is flat and the other that has grooves) are presented. The results show that the electrode configuration has a significant effect on the fluid flow pattern in the inter-electrode region. Furthermore, it is shown that rapid fluid flow is obtained when the cell is operated with a submerged anode.

  4. The structure of the axisymmetric high-Reynolds number flow around an ellipsoidal bubble of fixed shape

    NASA Astrophysics Data System (ADS)

    Blanco, Armando; Magnaudet, Jacques

    1995-06-01

    The structure of the flow around an oblate ellipsoidal bubble of fixed shape is studied by means of direct numerical simulation for Reynolds numbers Re up to 103. In agreement with a previous study by Dandy and Leal [Phys. Fluids 29, 1360 (1986)] the computations demonstrate that if the bubble aspect ratio χ is high enough a standing eddy can exist at the rear of the bubble in an intermediate range of Re. This eddy disappears beyond a certain Reynolds number and it is shown that its existence is governed by the competition between accumulation and evacuation of the vorticity in the flow. The range of Re where the eddy exists increases very rapidly with χ meaning that this structure is certainly present in many experimental situations. The evolution of the drag coefficient with Re reveals that the oblateness has a dramatic influence on the minimum value of Re beyond which Moore's theory [J. Fluid Mech. 23, 749 (1965)] can be used to predict the rise velocity of a bubble of fixed shape. In contrast, owing to the shape of the vorticity distribution at the surface of the bubble, no noticeable influence of the standing eddy on the drag is found. A quantitative comparison between the present results and those of previous authors shows that the computational description of the boundary layer around curved free surfaces is not a trivial matter since a strong influence of the numerical method is observed.

  5. A unifying framework for mass transfer dynamics in the Taylor flow of a dissolving train of bubbles

    NASA Astrophysics Data System (ADS)

    Nirmal, Ghata; Ramchandran, Arun

    2016-11-01

    Operation in the Taylor flow regime in microfluidics for estimation of mass transfer coefficients in multiphase flows has gained popularity due to the presence of high interfacial areas and well-characterized flow profiles. Although there are multiple models available for data interpretation, these are accompanied by two major limitations. First, mass transfer from the lubricating liquid film to the bulk liquid segment between bubbles has been incorrectly estimated. Second, the liquid segment is assumed to be well mixed. Both assumptions fail in the normal operating limits for Taylor flow experiments of dissolving bubbles. In this work, we rectify the two limitations described above and present a unifying framework to comprehend experimental results in a dissolving train of bubbles in microchannels. Based on a scaling analysis, the experiments can be operated in four regimes controlled by LB / R, LL/ R, Peclet number and capillary number where LB, LL and R are the bubble length, the liquid segment length and the tube radius, respectively. Finally, we present the differences in the results due to a rectangular cross-sectional shape instead of a circular one, and in particular, on the additional leakage flux through the lubricating film around the corners of the cross-section.

  6. Large Eddy Simulation of Bubbly Flow and Slag Layer Behavior in Ladle with Discrete Phase Model (DPM)-Volume of Fluid (VOF) Coupled Model

    NASA Astrophysics Data System (ADS)

    Li, Linmin; Liu, Zhongqiu; Cao, Maoxue; Li, Baokuan

    2015-07-01

    In the ladle metallurgy process, the bubble movement and slag layer behavior is very important to the refining process and steel quality. For the bubble-liquid flow, bubble movement plays a significant role in the phase structure and causes the unsteady complex turbulent flow pattern. This is one of the most crucial shortcomings of the current two-fluid models. In the current work, a one-third scale water model is established to investigate the bubble movement and the slag open-eye formation. A new mathematical model using the large eddy simulation (LES) is developed for the bubble-liquid-slag-air four-phase flow in the ladle. The Eulerian volume of fluid (VOF) model is used for tracking the liquid-slag-air free surfaces and the Lagrangian discrete phase model (DPM) is used for describing the bubble movement. The turbulent liquid flow is induced by bubble-liquid interactions and is solved by LES. The procedure of bubble coming out of the liquid and getting into the air is modeled using a user-defined function. The results show that the present LES-DPM-VOF coupled model is good at predicting the unsteady bubble movement, slag eye formation, interface fluctuation, and slag entrainment.

  7. Turbulent bubbly flow: A new method for robust local phase detection

    NASA Astrophysics Data System (ADS)

    Luther, Stefan

    2002-11-01

    Hot--film anemometry is one of the standard techniques for measurements in turbulent two phase flows. The time series contains valuable information about the local properties of the fluid as well as the gaseous phase. However, the disentanglement of the fluid and gaseous part of the signal is intricate due to its multiscale nature. Hitherto methods require an a priori knowledge of probability distribution of the signal or its derivatives. At low Reynolds number this distribution is assumed to be bi--modal and therefore an optimal (Bayesian) classifier can be derived. At high Reynolds number turbulent flow, this assumption is in general not valid. This leads to faulty classification due to intermittency or strong velocity fluctuations. We propose a novel algorithm which reformulates the problem of local phase detection as an general pattern recognition task. The algorithm consists of an optimal signal decomposition using wavelet packet dictionaries and local basis discrimination. The classification is done by learning vector quantization. The performance of the algorithm is validated for turbulent bubbly flows at various Reynolds numbers and void fractions. In particular, we discuss the feasibility of the algorithm for the evaluation of structure functions and velocity spectra, focusing on the scaling properties.

  8. An approach to mineral particle-air bubble interaction in turbulent flow of flotation cell

    SciTech Connect

    Lu, S.; Song, S.; Gou, J.; Pan, Y.

    1995-12-31

    The calculated potential energies of interaction between hydrophobic particle of three minerals (rhodochrosite, quartz and talc) and air bubble show that the energy of hydrophobic interaction is the dominant factor for their attachment. An attachment rate equation, integrating particle-bubble collision and adhesion by introducing a capture efficiency, has been put forward. It was found that the hydrophobic particle-bubble aggregates can not be disconnected in the bulk zone of flotation cell, whereas in the impeller zone the breakup may occur, particularly for the coarser particles captured by bubble. Finally, the flotation rate constant was estimated theoretically and verified by experiments.

  9. Bubble drag reduction requires large bubbles

    NASA Astrophysics Data System (ADS)

    Verschoof, Ruben; van der Veen, Roeland; Sun, Chao; Lohse, Detlef

    2016-11-01

    In the maritime industry, the injection of air bubbles into the turbulent boundary layer under the ship hull is seen as one of the most promising techniques to reduce the overall fuel consumption. A few volume percent (<= 4 %) of bubbles can reduce the overall drag up to 40% and beyond. However, the exact mechanism is unknown, thus hindering further progress and optimization. Here we show that bubble drag reduction in turbulent flow dramatically depends on the bubble size. By adding minute concentrations (6 ppm) of the surfactant Triton X-100 into otherwise completely unchanged strongly turbulent Taylor-Couette flow containing bubbles, we dramatically reduce the drag reduction from more than 40% to about 4%, corresponding to the trivial effect of the bubbles on the density and viscosity of the liquid . The reason for this striking behavior is that the addition of surfactants prevents bubble coalescence, leading to much smaller bubbles. Our result demonstrates that bubble deformability is crucial for bubble drag reduction in turbulent flow. We acknowledge support from STW and FOM.

  10. CVB: the Constrained Vapor Bubble Capillary Experiment on the International Space Station MARANGONI FLOW REGION

    NASA Technical Reports Server (NTRS)

    Wayner, Peter C., Jr.; Kundan, Akshay; Plawsky, Joel

    2014-01-01

    The Constrained Vapor Bubble (CVB) is a wickless, grooved heat pipe and we report on a full- scale fluids experiment flown on the International Space Station (ISS). The CVB system consists of a relatively simple setup a quartz cuvette with sharp corners partially filled with either pentane or an ideal mixture of pentane and isohexane as the working fluids. Along with temperature and pressure measurements, the two-dimensional thickness profile of the menisci formed at the corners of the quartz cuvette was determined using the Light Microscopy Module (LMM). Even with the large, millimeter dimensions of the CVB, interfacial forces dominate in these exceedingly small Bond Number systems. The experiments were carried out at various power inputs. Although conceptually simple, the transport processes were found to be very complex with many different regions. At the heated end of the CVB, due to a high temperature gradient, we observed Marangoni flow at some power inputs. This region from the heated end to the central drop region is defined as a Marangoni dominated region. We present a simple analysis based on interfacial phenomena using only measurements from the ISS experiments that lead to a predictive equation for the thickness of the film near the heated end of the CVB. The average pressure gradient for flow in the film is assumed due to the measured capillary pressure at the two ends of the liquid film and that the pressure stress gradient due to cohesion self adjusts to a constant value over a distance L. The boundary conditions are the no slip condition at the wall interface and an interfacial shear stress at the liquid- vapor interface due to the Marangoni stress, which is due to the high temperature gradient. Although the heated end is extremely complex, since it includes three- dimensional variations in radiation, conduction, evaporation, condensation, fluid flow and interfacial forces, we find that using the above simplifying assumptions, a simple successful

  11. Size-differentiated lateral migration of bubbles in Couette flow of two-dimensional foam

    NASA Astrophysics Data System (ADS)

    Mohammadigoushki, Hadi; Feng, James J.

    2012-11-01

    In this Talk, we report experiments on lateral migration of bubbles in a two-dimensional foam sheared in a narrow-gap Couette device. A larger bubble in an otherwise monodisperse bubble raft migrates toward the center of the gap as long as the bubble size ratio and the shear rate are each above a threshold. The migration speed is roughly two orders of magnitude higher than that of a single bubble, and increases with the shear rate and the size ratio. The bubble also deforms much more than an isolated one at the same shear rate. Modifying the Chan-Leal solution for the migration of a single submerged bubble or drop, we derive a formula that successfully predicts all the migration trajectories recorded in the experiment. The threshold for migration corresponds to the wall repulsion force overcoming the capillary force in the 2D foam. The size-differentiated bubble migration provides an explanation for previously observed size segregation in sheared 3D polydisperse foams.

  12. Size-Differentiated Lateral Migration of Bubbles in Couette Flow of Two-Dimensional Foam

    NASA Astrophysics Data System (ADS)

    Mohammadigoushki, Hadi; Feng, James J.

    2012-08-01

    We report experiments on lateral migration of bubbles in a two-dimensional foam sheared in a narrow-gap Couette device. A larger bubble in an otherwise monodisperse bubble raft migrates toward the center of the gap as long as the bubble size ratio and the shear rate are each above a threshold. The migration speed is roughly two orders of magnitude higher than that of a single bubble, and increases with the shear rate and the size ratio. The bubble also deforms much more than an isolated one at the same shear rate. Modifying the Chan-Leal solution for the migration of a single submerged bubble or drop, we derive a formula that successfully predicts all the migration trajectories recorded in the experiment. The threshold for migration corresponds to the wall repulsion force overcoming the capillary force in the two-dimensional foam. The size-differentiated bubble migration provides an explanation for previously observed size segregation in sheared three-dimensional polydisperse foams.

  13. Two-dimensional fluid dynamics in a sharply bent channel: Laminar flow, separation bubble, and vortex dynamics

    NASA Astrophysics Data System (ADS)

    Matsumoto, Daichi; Fukudome, Koji; Wada, Hirofumi

    2016-10-01

    Understanding the hydrodynamic properties of fluid flow in a curving pipe and channel is important for controlling the flow behavior in technologies and biomechanics. The nature of the resulting flow in a bent pipe is extremely complicated because of the presence of a cross-stream secondary flow. In an attempt to disentangle this complexity, we investigate the fluid dynamics in a bent channel via the direct numerical simulation of the Navier-Stokes equation in two spatial dimensions. We exploit the absence of secondary flow from our model and systematically investigate the flow structure along the channel as a function of both the bend angle and Reynolds number of the laminar-to-turbulent regime. We numerically suggest a scaling relation between the shape of the separation bubble and the flow conductance, and construct an integrated phase diagram.

  14. Capillary Channel Flow (CCF) EU2-02 on the International Space Station (ISS): An Experimental Investigation of Passive Bubble Separations in an Open Capillary Channel

    NASA Technical Reports Server (NTRS)

    Weislogel, Mark M.; Wollman, Andrew P.; Jenson, Ryan M.; Geile, John T.; Tucker, John F.; Wiles, Brentley M.; Trattner, Andy L.; DeVoe, Claire; Sharp, Lauren M.; Canfield, Peter J.; Klatte, Joerg; Dreyer, Michael E.

    2015-01-01

    It would be signicantly easier to design fluid systems for spacecraft if the fluid phases behaved similarly to those on earth. In this research an open 15:8 degree wedge-sectioned channel is employed to separate bubbles from a two-phase flow in a microgravity environment. The bubbles appear to rise in the channel and coalesce with the free surface in much the same way as would bubbles in a terrestrial environment, only the combined effects of surface tension, wetting, and conduit geometry replace the role of buoyancy. The host liquid is drawn along the channel by a pump and noncondensible gas bubbles are injected into it near the channel vertex at the channel inlet. Control parameters include bubble volume, bubble frequency, liquid volumetric flow rate, and channel length. The asymmetrically confined bubbles are driven in the cross-flow direction by capillary forces until they at least become inscribed within the section or until they come in contact with the free surface, whereupon they usually coalesce and leave the flow. The merging of bubbles enhances, but does not guarantee, the latter. The experiments are performed aboard the International Space Station as a subset of the Capillary Channel Flow experiments. The flight hardware is commanded remotely and continuously from ground stations during the tests and an extensive array of experiments is conducted identifying numerous bubble flow regimes and regime transitions depending on the ratio and magnitude of the gas and liquid volumetric flow rates. The breadth of the publicly available experiments is conveyed herein primarily by narrative and by regime maps, where transitions are approximated by simple expressions immediately useful for the purposes of design and deeper analysis.

  15. Exploiting zone trapping to avoid liberation of air bubbles in flow-based analytical procedures requiring heating.

    PubMed

    Vida, Ana C F; Zagatto, Elias A G

    2014-01-01

    In flow-based analytical procedures requiring heating, liberation of air bubbles is avoided by trapping a sample selected portion into a heated hermetic environment. The flow-through cuvette is maintained into a temperature-controlled aluminium block, thus acting as the trapping element and allowing real-time monitoring. The feasibility of the innovation was demonstrated in the spectrophotometric catalytic determination of vanadium in mineral waters. Air bubbles were not released even for temperatures as high as 95°C. The proposed system handles about 25 samples per hour, requires only 3 mg p-anisidine per determination and yields precise results (r.s.d. = 2.1%), in agreement with ICP-MS. Detection limit was evaluated (3.3 σ criterion) as 0.1 μg L(-1) V.

  16. Influence of a gas bubble on the dynamical parameters of the slug flow using particle image velocimetry

    NASA Astrophysics Data System (ADS)

    Siddiqui, M. I.; Heikal, M. R.; Munir, S.; Dass, S. C.; Aziz, A. Rashid A.

    2014-10-01

    Inlet conditions strongly affect the dynamical parameters of a two-phase slug flow. A series of experiments were carried out, in a 6m long Plexiglas pipe having internal diameter 74 mm, to investigate the influence of gas bubble on the flow dynamics inside the slugy body of a unit slug. The pipe was kept inclined at an elevation of 1.160 to consider the terrain slugging mechanism. An optical diagnostic technique, Particle Image Velocimetry (PIV) was employed at a point 3.5m from the inlet to measure the instantaneous velocity fields of the flow for each case. Single-phase liquid pipe flow and the slugy body of the two-phase slug flow are the targeted sections for study and comparison. Velocity components, turbulence intensity and average volume flux are measured and compared. The effect of gas bubble on the liquid Reynolds number is also considered. It is noticed that by increasing the gas flow rate velocity, average flux and average kinetic energy increases dramatically in a slugy body of a slug flow regime. The results are also compared with the single phase liquid flow having same liquid flow rate. Moreover it is noticed that the increase in average volume flux in a slugy body for lower liquid flow rates are more significant as compared to the higher liquid flow rates by increasing gas rate. This shows that slug can be helpful in oil transportation in terrain oil fields for lower liquid flow rates as it creates more fluctuations and vibrational forces for higher liquid flow.

  17. A new method for measuring concentration of a fluorescent tracer in bubbly gas-liquid flows

    NASA Astrophysics Data System (ADS)

    Moghaddas, J. S.; Trägårdh, C.; Kovacs, T.; Östergren, K.

    2002-06-01

    A new experimental model, the two-tracer method (TTM), based on the planar laser-induced fluorescence technique (PLIF), is presented for the measurement of the local concentration of a fluorescent tracer in the liquid phase of a bubbly two-phase system. Light scattering and shading effects due to the bubbles were compensated for using the new model. The TTM results were found to give more accurate predictions of the local concentration than the normal PLIF method in a bubbly two-phase system.

  18. Gas holdup and flow regime transition in spider-sparger bubble column: effect of liquid phase properties

    NASA Astrophysics Data System (ADS)

    Besagni, G.; Inzoli, F.; De Guido, G.; Pellegrini, L. A.

    2017-01-01

    This paper discusses the effects of the liquid velocity and the liquid phase properties on the gas holdup and the flow regime transition in a large-diameter and large-scale counter-current two-phase bubble column. In particular, we compared and analysed the experimental data obtained in our previous experimental studies. The bubble column is 5.3 m in height, has an inner diameter of 0.24 m, it was operated with gas superficial velocities in the range of 0.004–0.20 m/s and, in the counter-current mode, the liquid was recirculated up to a superficial velocity of -0.09 m/s. Air was used as the dispersed phase and various fluids (tap water, aqueous solutions of sodium chloride, ethanol and monoethylene glycol) were employed as liquid phases. The experimental dataset consist in gas holdup measurements and was used to investigate the global fluid dynamics and the flow regime transition between the homogeneous flow regime and the transition flow regime. We found that the liquid velocity and the liquid phase properties significantly affect the gas holdup and the flow regime transition. In this respect, a possible relationship (based on the lift force) between the flow regime transition and the gas holdup was proposed.

  19. Study on bubbly flow behavior in natural circulation reactor by thermal-hydraulic simulation tests with SF6-Gas and ethanol liquid

    NASA Astrophysics Data System (ADS)

    Kondo, Yoshiyuki; Suga, Keishi; Hibi, Koki; Okazaki, Toshihiko; Komeno, Toshihiro; Kunugi, Tomoaki; Serizawa, Akimi; Yoneda, Kimitoshi; Arai, Takahiro

    2009-02-01

    An advanced experimental technique has been developed to simulate two-phase flow behavior in a light water reactor (LWR). The technique applies three kinds of methods; (1) use of sulfur-hexafluoride (SF6) gas and ethanol (C2H5OH) liquid at atmospheric temperature and a pressure less than 1.0MPa, where the fluid properties are similar to steam-water ones in the LWR, (2) generation of bubble with a sintering tube, which simulates bubble generation on heated surface in the LWR, (3) measurement of detailed bubble distribution data with a bi-optical probe (BOP), (4) and measurement of liquid velocities with the tracer liquid. This experimental technique provides easy visualization of flows by using a large scale experimental apparatus, which gives three-dimensional flows, and measurement of detailed spatial distributions of two-phase flow. With this technique, we have carried out experiments simulating two-phase flow behavior in a single-channel geometry, a multi-rod-bundle one, and a horizontal-tube-bundle one on a typical natural circulation reactor system. Those experiments have clarified a) a flow regime map in a rod bundle on the transient region between bubbly and churn flow, b) three-dimensional flow behaviour in rod-bundles where inter-subassembly cross-flow occurs, c) bubble-separation behavior with consideration of reactor internal structures. The data have given analysis models for the natural circulation reactor design with good extrapolation.

  20. Marangoni Effects on the Bubble Dynamics in a Pressure Driven Flow

    NASA Technical Reports Server (NTRS)

    Park, Chang-Won; Maruvada, S. R. K.

    1996-01-01

    The motion of air bubbles and water drops in a Hele-Shaw cell filled with a silicone oil has been studied experimentally and theoretically. By adding a predetermined amount of a surfactant to the water drops we attempted to investigate the surfactant influence systematically. While the motion of air bubbles was in reasonable agreement with the predictions of Taylor and Saffman, water drops behaved quite differently in that the translational velocities were smaller by an order of magnitude and their shapes were very unusual as observed previously by Kopf-Sill and Homsy. Assuming that the surrounding fluid wets the solid wall and the bubble (or the drop) surface is rigid due to the surfactant influence, we have estimated the translational velocity of an elliptic bubble. The calculated velocities were in good agreement with the observations indicating that the surfactant influence could retard the bubble motion significantly. The present study also indicates that the unusual bubble shapes are also due to the surfactant influence.

  1. A novel technique to control the bubble formation process in a co-flow configuration with planar geometry

    NASA Astrophysics Data System (ADS)

    Ruiz-Rus, Javier; Bolaños-Jiménez, Rocío; Gutiérrez-Montes, Cándido; Martínez-Bazán, Carlos; Sevilla, Alejandro

    2015-11-01

    We present a novel technique to properly control the bubble formation frequency and size by forcing the water stream in a co-flow configuration with planar geometry through the modulation of the water velocity at the nozzle exit. The main goal of this work is to experimentally explore whether the bubbling regime, which is naturally established for certain values of the water-to-air velocity ratio, Λ =uw /ua , and the Weber number, We =ρwuw2Ho / σ , can be controlled by the imposed disturbances. A detailed experimental characterization of the forcing effect has been performed by measuring the pressure fluctuations in both the water and the air streams. In addition, the velocity amplitude, which characterizes the process, is obtained. The results show that a minimum disturbance amplitude is needed for an effective control of the bubbling process. Moreover, the process is governed by kinematic non-linear effects, and the position of the maximum deformation is shown to be described through a one-dimensional flow model for the water sheet, based on the exact solution of the Euler equation. Supported by the Spanish MINECO, Junta de Andalucía and EU Funds under projects DPI2014-59292-C3-3-P, P11-TEP7495 and UJA2013/08/05.

  2. Gas-Liquid flow characterization in bubble columns with various gas-liquid using electrical resistance tomography

    NASA Astrophysics Data System (ADS)

    Jin, Haibo; Yuhuan, Han; Suohe, Yang

    2009-02-01

    Electrical resistance tomography (ERT) is an advanced and new detecting technique that can measure and monitor the parameters of two-phase flow on line, such as gas-liquid bubble column. It is fit for the industrial process where the conductible medium serves as the disperse phase to present the key bubble flow characteristics in multi-phase medium. Radial variation of the gas holdup and mean holdups are investigated in a 0.160 m i. d. bubble column using ERT with two axial locations (Plane 1 and Plane 2). In all the experiments, air was used as the gas phase, tap water as liquid phase, and a series of experiments were done by adding KCl, ethanol, oil sodium, and glycerol to change liquid conductivity, liquid surface tension and viscosity. The superficial gas velocity was varied from 0.02 to 0.2 m/s. The effect of conductivity, surface tension, viscosity on the mean holdups and radial gas holdup distribution is discussed. The results showed that the gas holdup decrease with the increase of surface tension and increase with the increase of viscosity. Meanwhile, the settings of initial liquid conductivity slightly influence the gas holdup values, and the experimental data increases with the increase of the initial setting values in the same conditions.

  3. Femtosecond-laser-induced shockwaves in water generated at an air-water interface.

    PubMed

    Strycker, B D; Springer, M M; Traverso, A J; Kolomenskii, A A; Kattawar, G W; Sokolov, A V

    2013-10-07

    We report generation of femtosecond-laser-induced shockwaves at an air-water interface by millijoule femtosecond laser pulses. We document and discuss the main processes accompanying this phenomenon, including light emission, development of the ablation plume in the air, formation of an ablation cavity, and, subsequently, a bubble developing in water. We also discuss the possibility of remotely controlling the characteristics of laser-induced sound waves in water through linear acoustic superposition of sound waves that results from millijoule femtosecond laser-pulse interaction with an air-water interface, thus opening up the possibility of remote acoustic applications in oceanic and riverine environments.

  4. DEVELOPMENT OF A COMPUTATIONAL MULTIPHASE FLOW MODEL FOR FISCHER TROPSCH SYNTHESIS IN A SLURRY BUBBLE COLUMN REACTOR

    SciTech Connect

    Donna Post Guillen; Tami Grimmett; Anastasia M. Gribik; Steven P. Antal

    2010-09-01

    The Hybrid Energy Systems Testing (HYTEST) Laboratory is being established at the Idaho National Laboratory to develop and test hybrid energy systems with the principal objective to safeguard U.S. Energy Security by reducing dependence on foreign petroleum. A central component of the HYTEST is the slurry bubble column reactor (SBCR) in which the gas-to-liquid reactions will be performed to synthesize transportation fuels using the Fischer Tropsch (FT) process. SBCRs are cylindrical vessels in which gaseous reactants (for example, synthesis gas or syngas) is sparged into a slurry of liquid reaction products and finely dispersed catalyst particles. The catalyst particles are suspended in the slurry by the rising gas bubbles and serve to promote the chemical reaction that converts syngas to a spectrum of longer chain hydrocarbon products, which can be upgraded to gasoline, diesel or jet fuel. These SBCRs operate in the churn-turbulent flow regime which is characterized by complex hydrodynamics, coupled with reacting flow chemistry and heat transfer, that effect reactor performance. The purpose of this work is to develop a computational multiphase fluid dynamic (CMFD) model to aid in understanding the physico-chemical processes occurring in the SBCR. Our team is developing a robust methodology to couple reaction kinetics and mass transfer into a four-field model (consisting of the bulk liquid, small bubbles, large bubbles and solid catalyst particles) that includes twelve species: (1) CO reactant, (2) H2 reactant, (3) hydrocarbon product, and (4) H2O product in small bubbles, large bubbles, and the bulk fluid. Properties of the hydrocarbon product were specified by vapor liquid equilibrium calculations. The absorption and kinetic models, specifically changes in species concentrations, have been incorporated into the mass continuity equation. The reaction rate is determined based on the macrokinetic model for a cobalt catalyst developed by Yates and Satterfield [1]. The

  5. Two-phase lattice Boltzmann modelling of streaming potentials : influence of the air-water interface on the electrokinetic coupling

    NASA Astrophysics Data System (ADS)

    Fiorentino, Eve-Agnès; Toussaint, Renaud; Jouniaux, Laurence

    2016-11-01

    The streaming potential phenomenon is an electrokinetic effect that occurs in porous media. It is characterized by an electrokinetic (EK) coefficient. The aim of this paper is to simulate the EK coefficient in unsaturated conditions using the Lattice Boltzmann method in a 2-D capillary channel. The multiphase flow is simulated with the model of Shan & Chen (1993). The Poisson-Boltzmann equation is solved by implementing the model of Chai & Shi (2008). The streaming potential response shows a non-monotonous behaviour due to the combination of the increase of charge density and decrease of flow velocity with decreasing water saturation. Using a ζ potential of -20 mV at the air-water interface, an enhancement of a factor 5 to 30 of the EK coefficient, compared to the saturated state, can be observed due to the positive charge excess at this interface which is magnified by the fluid velocity away from the rock surface. This enhancement is correlated to the fractioning of the bubbles, and to the dynamic state of these bubbles, moving or entrapped in the crevices of the channel.

  6. Two-phase Lattice Boltzmann modelling of streaming potentials: influence of the air-water interface on the electrokinetic coupling

    NASA Astrophysics Data System (ADS)

    Fiorentino, Eve-Agnès; Toussaint, Renaud; Jouniaux, Laurence

    2017-02-01

    The streaming potential phenomenon is an electrokinetic effect that occurs in porous media. It is characterized by an electrokinetic (EK) coefficient. The aim of this paper is to simulate the EK coefficient in unsaturated conditions using the Lattice Boltzmann method in a 2-D capillary channel. The multiphase flow is simulated with the model of Shan & Chen. The Poisson-Boltzmann equation is solved by implementing the model of Chai & Shi. The streaming potential response shows a non-monotonous behaviour due to the combination of the increase of charge density and decrease of flow velocity with decreasing water saturation. Using a ζ potential of -20 mV at the air-water interface, an enhancement of a factor 5-30 of the EK coefficient, compared to the saturated state, can be observed due to the positive charge excess at this interface which is magnified by the fluid velocity away from the rock surface. This enhancement is correlated to the fractioning of the bubbles, and to the dynamic state of these bubbles, moving or entrapped in the crevices of the channel.

  7. CAPITAL FLOWS, CONSUMPTION BOOMS AND ASSET BUBBLES: A BEHAVIOURAL ALTERNATIVE TO THE SAVINGS GLUT HYPOTHESIS

    PubMed Central

    Laibson, David; Mollerstrom, Johanna

    2012-01-01

    Bernanke (2005) hypothesized that a “global savings glut” was causing large trade imbalances. However, we show that the global savings rates did not show a robust upward trend during the relevant period. Moreover, if there had been a global savings glut there should have been a large investment boom in the countries that imported capital. Instead, those countries experienced consumption booms. National asset bubbles explain the international imbalances. The bubbles raised consumption, resulting in large trade deficits. In a sample of 18 OECD countries plus China, movements in home prices alone explain half of the variation in trade deficits. PMID:23750045

  8. Enhanced mycobacterial diagnostics in liquid medium by microaerobic bubble flow in Portable Microbe Enrichment Unit.

    PubMed

    Hakalehto, Elias

    2013-06-01

    Portable Microbe Enrichment Unit (PMEU) method with microaerobic bubbling speeded up the growth of otherwise slowly starting and propagating Mycobacterium sp. Mycobacterium fortuitum growth was detected after 10-11h and Mycobacterium marinum produced clear growth in 4 days. A mycobacterial environmental isolate was verified in 2 days in the PMEU Spectrion(®) equipped with infrared sensors. In parallel static (without gas bubbling) cultures hardly any growth occurred. In conclusion, PMEU technology provided thus a rapid detection of environmental and clinical mycobacterial isolates. It would also help in the field diagnosis of antibiotic resistant Mycobacterium tuberculosis.

  9. Bubble Size Control to Improve Oxygen-Based Bleaching: Characterization of Flow Regimes in Pulp-Water-Gas Three-Phase Flows

    SciTech Connect

    S.M. Ghiaasiaan and Seppo Karrila

    2006-03-20

    Flow characteristics of fibrous paper pulp-water-air slurries were investigated in a vertical circular column 1.8 m long, with 5.08 cm diameter. Flow structures, gas holdup (void fraction), and the geometric and population characteristics of gas bubbles were experimentally investigated, using visual observation, Gamma-ray densitometry, and flash X-ray photography. Five distinct flow regimes could be visually identified: dispersed bubbly, layered bubbly, plug, churn-turbulent, and slug. Flow regime maps were constructed, and the regime transition lines were found to be sensitive to consistency. The feasibility of using artificial neural networks (ANNs) for the identification of the flow regimes, using the statistical characteristics of pressure fluctuations measured by a single pressure sensor, was demonstrated. Local pressure fluctuations at a station were recorded with a minimally-intrusive transducer. Three-layer, feed-forward ANNs were designed that could identify the four major flow patterns (bubbly, plug, churn, and slug) well. The feasibility of a transportable artificial neural network (ANN) - based technique for the classification of flow regimes was also examined. Local pressures were recorded at three different locations using three independent but similar transducers. An ANN was designed, trained and successfully tested for the classification of the flow regimes using one of the normalized pressure signals (from Sensor 1). The ANN trained and tested for Sensor 1 predicted the flow regimes reasonably well when applied directly to the other two sensors, indicating a good deal of transportability. An ANN-based method was also developed, whereby the power spectrum density characteristics of other sensors were adjusted before they were used as input to the ANN that was based on Sensor 1 alone. The method improved the predictions. The gas-liquid interfacial surface area concentration was also measured in the study. The gas absorption technique was applied

  10. Critical air/water blow-down in safety valves at low qualities.

    PubMed

    Moncalvo, D; Friedel, L

    2011-02-28

    Critical air/water blow-downs in safety valves for qualities from 0.01 to 0.113 and mass flow rates from 1.5 up to 4.3 kg/s have been observed in our test facility. These critical blow-downs are characterized by a large void fraction and by an intense mixing of the phases both in the valve body and in the outlet pipe. A qualitative estimation of the flow pattern in the outlet pipe using the map of Taitel and Dukler suggests that these air/water flows are intermittent flows--presumably slug flows--evolving to annular flows for qualities above 0.1. Intermittent flows are also predicted for critical air/water and air/glycerine flows taken from the literature for the same safety valve at slightly larger relieving pressures.

  11. Pulsatile flow decreases gaseous micro-bubble filtering properties of oxygenators without integrated arterial filters during cardiopulmonary bypass

    PubMed Central

    Milano, Aldo D.; Dodonov, Mikhail; Onorati, Francesco; Menon, Tiziano; Gottin, Leonardo; Malerba, Giovanni; Mazzucco, Alessandro; Faggian, Giuseppe

    2013-01-01

    OBJECTIVES Cardiopulmonary bypass (CPB) has a risk of embolic injury with an important role of gaseous micro-bubbles (GMBs), coming from CPB-circuit. Pulsatile perfusion (PP) can provide specific conditions for supplementary GMB-activity with respect to non-pulsatile (NP). We aimed to test GMB-filtering properties of three modern oxygenators under pulsatile and non-pulsatile conditions. METHODS Seventy-eight patients undergoing on-pump myocardial revascularization were randomized prospectively into three equal groups according to the oxygenator model used during CPB. Terumo Capiox-FX25, Sorin Synthesis or Maquet Quadrox-i-Adult membrane oxygenators were tested. Each group was divided equally to undergo PP or NP. GMBs were counted by means of a GAMPT-BCC200 bubble-counter with two probes placed at preoxygenator and arterial post-filter positions. Results were evaluated in terms of GMB-volume, GMB-number, amount of large over-ranged GMBs, a series of filtering indices and major neurological outcomes. RESULTS PP decreased GMB-filtering properties of the tested oxygenators. Those with integrated filters (CAPIOX-FX25 and SYNTHESIS) did not show significant differences between perfusion groups, while QUADROX-i oxygenator with external arterial filter showed significantly higher GMB-volume (P < 0.001), GMB-number (P < 0.001) and amount of over-ranged bubbles (P < 0.001) detected in arterial line during PP. Despite the differences in filtering capacity of all circuits with both types of perfusion, no important differences in clinical outcomes and major neurological events were observed. CONCLUSIONS Pulsatile flow decreases gaseous micro-bubble filtering properties of oxygenators without integrated arterial filters during CPB. PP requires specially designed circuit components to avoid the risk of additional GMB delivery. PMID:23842758

  12. The Effect of Small Bubbles on Resistance Reduction of Water Flow in Co-axial Cylinders with an Inner Rotating Cylinder

    NASA Astrophysics Data System (ADS)

    Maryami, R.; Farahat, S.; Poor, M. J.

    2015-04-01

    Drawing on effective experiments and measurement technology, the present study seeks to discuss the interaction between liquid turbulent boundary layer and a crowded group of small bubbles. Experiments are carried out using a circulating water Couette-Taylor system especially designed for small bubble experiments. Couette-Taylor system has a detailed test section, which allows measuring the effect of persistent head resistance reduction caused by small bubbles in the streamwise direction. Pressure difference is measured using sensors which are mounted at the bottom and top of the system to calculate head resistance. Pressure difference and bubble behavior are measured as a function of rotational Reynolds number up to 67.8 × 103. Small bubbles are injected constantly into annulus gap using two injectors installed at the bottom of the system and they are lifted through an array of vertical cells. Water is used to avoid uncertain interfacial property of bubbles and to produce relatively mono-sized bubble distributions. The bubble sizes range approximately from 0.9 to 1.4 mm, which are identified by the image processing method. The results suggest that head resistance is decreased after the injection of small bubble in all rotational Reynolds number under study, changing from 7,000 to 67.8 × 103. Moreover, void fraction is increased from 0 to 10.33 %. A head resistance reduction greater than 75 % was achieved in this study after the maximum measured volume of air fraction was injected into fluid flow while bubbles were distinct without making any gas layer.

  13. Sparger Effects on Gas Volume Fraction Distributions in Vertical Bubble-Column Flows as Measured by Gamma-Densitometry Tomography

    SciTech Connect

    GEORGE,DARIN L.; SHOLLENBERGER,KIM ANN; TORCZYNSKI,JOHN R.

    2000-01-18

    Gamma-densitometry tomography is applied to study the effect of sparger hole geometry, gas flow rate, column pressure, and phase properties on gas volume fraction profiles in bubble columns. Tests are conducted in a column 0.48 m in diameter, using air and mineral oil, superficial gas velocities ranging from 5 to 30 cm s{sup -1}, and absolute column pressures from 103 to 517 kPa. Reconstructed gas volume fraction profiles from two sparger geometries are presented. The development length of the gas volume fraction profile is found to increase with gas flow rate and column pressure. Increases in gas flow rate increase the local gas volume fraction preferentially on the column axis, whereas increases in column pressure produce a uniform rise in gas volume fraction across the column. A comparison of results from the two spargers indicates a significant change in development length with the number and size of sparger holes.

  14. Evaluation of flow hydrodynamics in a pilot-scale dissolved air flotation tank: a comparison between CFD and experimental measurements.

    PubMed

    Lakghomi, B; Lawryshyn, Y; Hofmann, R

    2015-01-01

    Computational fluid dynamics (CFD) models of dissolved air flotation (DAF) have shown formation of stratified flow (back and forth horizontal flow layers at the top of the separation zone) and its impact on improved DAF efficiency. However, there has been a lack of experimental validation of CFD predictions, especially in the presence of solid particles. In this work, for the first time, both two-phase (air-water) and three-phase (air-water-solid particles) CFD models were evaluated at pilot scale using measurements of residence time distribution, bubble layer position and bubble-particle contact efficiency. The pilot-scale results confirmed the accuracy of the CFD model for both two-phase and three-phase flows, but showed that the accuracy of the three-phase CFD model would partly depend on the estimation of bubble-particle attachment efficiency.

  15. Gas bubble detector

    NASA Technical Reports Server (NTRS)

    Mount, Bruce E. (Inventor); Burchfield, David E. (Inventor); Hagey, John M. (Inventor)

    1995-01-01

    A gas bubble detector having a modulated IR source focused through a bandpass filter onto a venturi, formed in a sample tube, to illuminate the venturi with modulated filtered IR to detect the presence of gas bubbles as small as 0.01 cm or about 0.004 in diameter in liquid flowing through the venturi. Means are provided to determine the size of any detected bubble and to provide an alarm in the absence of liquid in the sample tube.

  16. Cleaning verification by air/water impingement

    NASA Technical Reports Server (NTRS)

    Jones, Lisa L.; Littlefield, Maria D.; Melton, Gregory S.; Caimi, Raoul E. B.; Thaxton, Eric A.

    1995-01-01

    This paper will discuss how the Kennedy Space Center intends to perform precision cleaning verification by Air/Water Impingement in lieu of chlorofluorocarbon-113 gravimetric nonvolatile residue analysis (NVR). Test results will be given that demonstrate the effectiveness of the Air/Water system. A brief discussion of the Total Carbon method via the use of a high temperature combustion analyzer will also be given. The necessary equipment for impingement will be shown along with other possible applications of this technology.

  17. Visualization of airflow growing soap bubbles

    NASA Astrophysics Data System (ADS)

    Al Rahbi, Hamood; Bock, Matthew; Ryu, Sangjin

    2016-11-01

    Visualizing airflow inside growing soap bubbles can answer questions regarding the fluid dynamics of soap bubble blowing, which is a model system for flows with a gas-liquid-gas interface. Also, understanding the soap bubble blowing process is practical because it can contribute to controlling industrial processes similar to soap bubble blowing. In this study, we visualized airflow which grows soap bubbles using the smoke wire technique to understand how airflow blows soap bubbles. The soap bubble blower setup was built to mimic the human blowing process of soap bubbles, which consists of a blower, a nozzle and a bubble ring. The smoke wire was placed between the nozzle and the bubble ring, and smoke-visualized airflow was captured using a high speed camera. Our visualization shows how air jet flows into the growing soap bubble on the ring and how the airflow interacts with the soap film of growing bubble.

  18. A flow visualization study of the leading edge separation bubble on a NACA 0012 airfoil with simulated glaze ice. Final Report M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Khodadoust, Abdollah

    1988-01-01

    As a part of the ongoing research in aircraft icing, the leading edge separation bubble on the NACA 0012 model with a 5-min simulated glaze ice was investigated. The flow visualization methods used oil, tuft, splitter plate, smoke, and liquid crystals to get reattachment line data for the leading edge separation bubble on both surfaces of the airfoil. On the upper surface, the bubble was found to grow larger with increasing negative angles of attack and reduce in size with increasing angles of attack. The separated flow fails to reattach beyond 6 deg for the upper surface and -5 deg for the lower surface. The results of this study compared well with those of other experiments and computational results.

  19. Flow pattern, pressure drop and void fraction of two-phase gas-liquid flow in an inclined narrow annular channel

    SciTech Connect

    Wongwises, Somchai; Pipathattakul, Manop

    2006-03-01

    Two-phase flow pattern, pressure drop and void fraction in horizontal and inclined upward air-water two-phase flow in a mini-gap annular channel are experimentally studied. A concentric annular test section at the length of 880mm with an outer diameter of 12.5mm and inner diameter of 8mm is used in the experiments. The flow phenomena, which are plug flow, slug flow, annular flow, annular/slug flow, bubbly/plug flow, bubbly/slug-plug flow, churn flow, dispersed bubbly flow and slug/bubbly flow, are observed and recorded by high-speed camera. A slug flow pattern is found only in the horizontal channel while slug/bubbly flow patterns are observed only in inclined channels. When the inclination angle is increased, the onset of transition from the plug flow region to the slug flow region (for the horizontal channel) and from the plug flow region to slug/bubbly flow region (for inclined channels) shift to a lower value of superficial air velocity. Small shifts are found for the transition line between the dispersed bubbly flow and the bubbly/plug flow, the bubbly/plug flow and the bubbly/slug-plug flow, and the bubbly/plug flow and the plug flow. The rest of the transition lines shift to a higher value of superficial air velocity. Considering the effect of flow pattern on the pressure drop in the horizontal tube at low liquid velocity, the occurrence of slug flow stops the rise of pressure drop for a short while, before rising again after the air velocity has increased. However, the pressure does not rise abruptly in the tubes with {theta}=30{sup o} and 60{sup o} when the slug/bubbly flow occurs. At low gas and liquid velocity, the pressure drop increases, when the inclination angles changes from horizontal to 30{sup o} and 60{sup o}. Void fraction increases with increasing gas velocity and decreases with increasing liquid velocity. After increasing the inclination angle from horizontal to {theta}=30{sup o} and 60{sup o}, the void fraction appears to be similar, with a

  20. Fluid Dynamics of Bubbly Liquids

    NASA Technical Reports Server (NTRS)

    Tsang, Y. H.; Koch, D. L.; Zenit, R.; Sangani, A.; Kushch, V. I.; Spelt, P. D. M.; Hoffman, M.; Nahra, H.; Fritz, C.; Dolesh, R.

    2002-01-01

    Experiments have been performed to study the average flow properties of inertially dominated bubbly liquids which may be described by a novel analysis. Bubbles with high Reynolds number and low Weber number may produce a fluid velocity disturbance that can be approximated by a potential flow. We studied the behavior of suspensions of bubbles of about 1.5 mm diameter in vertical and inclined channels. The suspension was produced using a bank of 900 glass capillaries with inner diameter of about 100 microns in a quasi-steady fashion. In addition, salt was added to the suspension to prevent bubble-bubble coalescence. As a result, a nearly monodisperse suspension of bubble was produced. By increasing the inclination angle, we were able to explore an increasing amount of shear to buoyancy motion. A pipe flow experiment with the liquid being recirculated is under construction. This will provide an even larger range of shear to buoyancy motion. We are planning a microgravity experiment in which a bubble suspension is subjected to shearing in a couette cell in the absence of a buoyancy-driven relative motion of the two phases. By employing a single-wire, hot film anemometer, we were able to obtain the liquid velocity fluctuations. The shear stress at the wall was measured using a hot film probe flush mounted on the wall. The gas volume fraction, bubble velocity, and bubble velocity fluctuations were measured using a homemade, dual impedance probe. In addition, we also employed a high-speed camera to obtain the bubble size distribution and bubble shape in a dilute suspension. A rapid decrease in bubble velocity for a dilute bubble suspension is attributed to the effects of bubble-wall collisions. The more gradual decrease of bubble velocity as gas volume fraction increases, due to subsequent hindering of bubble motion, is in qualitative agreement with the predictions of Spelt and Sangani for the effects of potential-flow bubble-bubble interactions on the mean velocity. The

  1. Does colloid shape affect detachment of colloids by a moving air-water interface?

    PubMed

    Aramrak, Surachet; Flury, Markus; Harsh, James B; Zollars, Richard L; Davis, Howard P

    2013-05-14

    Air-water interfaces interact strongly with colloidal particles by capillary forces. The magnitude of the interaction force depends on, among other things, the particle shape. Here, we investigate the effects of particle shape on colloid detachment by a moving air-water interface. We used hydrophilic polystyrene colloids with four different shapes (spheres, barrels, rods, and oblong disks), but otherwise identical surface properties. The nonspherical shapes were created by stretching spherical microspheres on a film of polyvinyl alcohol (PVA). The colloids were then deposited onto the inner surface of a glass channel. An air bubble was introduced into the channel and passed through, thereby generating a receding followed by an advancing air-water interface. The detachment of colloids by the air-water interfaces was visualized with a confocal microscope, quantified by image analysis, and analyzed statistically to determine significant differences. For all colloid shapes, the advancing air-water interface caused pronounced colloid detachment (>63%), whereas the receding interface was ineffective in colloid detachment (<1.5%). Among the different colloid shapes, the barrels were most readily removed (94%) by the advancing interface, followed by the spheres and oblong disks (80%) and the rods (63%). Colloid detachment was significantly affected by colloid shape. The presence of an edge, as it occurs in a barrel-shaped colloid, promoted colloid detachment because the air-water interface is being pinned at the edge of the colloid. This suggests that the magnitude of colloid mobilization and transport in porous media is underestimated for edged particles and overestimated for rodlike particles when a sphere is used as a model colloid.

  2. Clustering in Bubble Suspensions

    NASA Astrophysics Data System (ADS)

    Zenit, Roberto

    2000-11-01

    A monidisperse bubble suspension is studied experimentally for the limit in which the Weber number is small and the Reynolds number is large. For this regime the suspension can be modeled using potential flow theory to describe the dynamics of the interstitial fluid. Complete theoretical descriptions have been composed (Spelt and Sangani, 1998) to model the behavior of these suspensions. Bubble clustering is a natural instability that arises from the potential flow considerations, in which bubbles tend to align in horizontal rafts as they move upwards. The appearance of bubble clusters was recently corroborated experimentally by Zenit et al. (2000), who found that although clusters did appear, their strength was not as strong as the predictions. Experiments involving gravity driven shear flows are used to explain the nature of the clustering observed in these type of flows. Balances of the bubble phase pressure (in terms of a calculated diffusion coefficient) and the Maxwell pressure (from the potential flow description) are presented to predict the stability of the bubble suspension. The predictions are compared with experimental results.

  3. The pulsatile motion of a semi-infinite bubble in a channel: flow fields, and transport of an inactive surface-associated contaminant

    NASA Astrophysics Data System (ADS)

    Zimmer, Maximillian E.; Williams, Harvey A. R.; Gaver, Donald P.

    2005-08-01

    We investigate a theoretical model of the pulsatile motion of a contaminant-doped semi-infinite bubble in a rectangular channel. We examine the fluid mechanical behaviour of the pulsatile bubble, and its influence on the transport of a surface-inactive contaminant (termed surfinactant). This investigation is used to develop a preliminary understanding of surfactant responses during unsteady pulmonary airway reopening. Reopening is modelled as the pulsatile motion of a semi-infinite gas bubble in a horizontal channel of width 2a filled with a Newtonian liquid of viscosity mu and constant surface tension gamma. A modified Langmuir sorption model is assumed, which allows for the creation and respreading of a surface multilayer. The bubble is forced via a time-dependent volume flux Q(t) with mean and oscillatory components (Q_{M} and Q_{omega }, respectively) at frequency omega . The flow behaviour is governed by the dimensionless parameters: Ca_{M} {=} mu Q_{M}/(2agamma ), a steady-state capillary number, which represents the ratio of viscous to surface tension forces; Ca_{Omega } {=} mu Q_{omega }/(2agamma ), an oscillatory forcing magnitude; Omega {=} omega mu a/gamma , a dimensionless frequency that represents the ratio of viscous relaxation to oscillatory-forcing timescales; and A {=} 2Ca_{Omega }/Omega , a dimensionless oscillation amplitude. Our simulations indicate that contaminant deposition and retention in the bubble cap region occurs at moderate frequencies if retrograde bubble motion develops during the oscillation cycle. However, if oscillations are too rapid the ensuing large forward tip velocities cause a net loss of contaminant from the bubble tip. Determination of an optimal oscillation range may be important in reducing ventilator-induced lung injury associated with infant and adult respiratory distress syndromes by increasing surfactant transport to regions of collapsed airways.

  4. Non-thermal insights on mass and energy flows through the Galactic Centre and into the Fermi bubbles

    NASA Astrophysics Data System (ADS)

    Crocker, R. M.

    2012-07-01

    We construct a simple model of the star-formation- (and resultant supernova-) driven mass and energy flows through the inner ˜200 pc (in diameter) of the Galaxy. Our modelling is constrained, in particular, by the non-thermal radio continuum and γ-ray signals detected from the region. The modelling points to a current star formation rate of 0.04-0.12 M⊙ yr-1 at 2σ confidence within the region with best-fitting value in the range 0.08-0.12 M⊙ yr-1 which - if sustained over 10 Gyr - would fill out the ˜109 M⊙ stellar population of the nuclear bulge. Mass is being accreted on to the Galactic Centre (GC) region at a rate ? yr-1. The region's star formation activity drives an outflow of plasma, cosmic rays and entrained, cooler gas. Neither the plasma nor the entrained gas reaches the gravitational escape speed, however, and all this material fountains back on to the inner Galaxy. The system we model can naturally account for the recently observed ≳106 M⊙'halo' of molecular gas surrounding the Central Molecular Zone out to 100-200 pc heights. The injection of cooler, high-metallicity material into the Galactic halo above the GC may catalyze the subsequent cooling and condensation of hot plasma out of this region and explain the presence of relatively pristine, nuclear-unprocessed gas in the GC. This process may also be an important ingredient in understanding the long-term stability of the GC star formation rate. The plasma outflow from the GC reaches a height of a few kpc and is compellingly related to the recently discovered Fermi bubbles by a number of pieces of evidence. These include that the outflow advects precisely (i) the power in cosmic rays required to sustain the bubbles'γ-ray luminosity in saturation; (ii) the hot gas required to compensate for gas cooling and drop-out from the bubbles and (iii) the magnetic field required to stabilize the walls of these structures. Our modelling demonstrates that ˜109 M⊙ of hot gas is processed through

  5. Visualization of Bubble Behavior in a Packed Bed of Spheres Using Neutron Radiography

    NASA Astrophysics Data System (ADS)

    Ito, Daisuke; Saito, Yasushi

    The present paper describes gas-liquid two-phase flow measurements in a packed bed of spheres using neutron radiography. Porous debris formed during a severe accident of a nuclear reactor should be cooled by a coolant and the cooling characteristics are dominated by two-phase flow behavior in the debris bed at the initial stage of the accident. Therefore, experimental database of the two-phase flow in the porous media has been required for safety analysis of the reactor. However, it is difficult to observe the flow structure, for example, void fraction distribution in such complex flow channel. In this study, the local void fraction in a packed bed which simulates the debris bed was measured by high frame-rate neutron radiography. Experiments were performed in air-water two-phase flow in a vertical pipe. Alumina spheres with 5 mm in diameter were packed randomly in the pipe. The bubble behavior between the spheres was investigated by using the void fraction distributions estimated from the neutron radiographs. Although it was difficult to track the small bubbles in the packed bed, the move of the large bubble could be found roughly from the distribution. In addition, the fluctuation of the void fraction was compared with that of the pressure drop in the test section. From these results, the possibility of the gas velocity estimation was shown.

  6. Quantifying the evolution of flow boiling bubbles by statistical testing and image analysis: toward a general model

    PubMed Central

    Xiao, Qingtai; Xu, Jianxin; Wang, Hua

    2016-01-01

    A new index, the estimate of the error variance, which can be used to quantify the evolution of the flow patterns when multiphase components or tracers are difficultly distinguishable, was proposed. The homogeneity degree of the luminance space distribution behind the viewing windows in the direct contact boiling heat transfer process was explored. With image analysis and a linear statistical model, the F-test of the statistical analysis was used to test whether the light was uniform, and a non-linear method was used to determine the direction and position of a fixed source light. The experimental results showed that the inflection point of the new index was approximately equal to the mixing time. The new index has been popularized and applied to a multiphase macro mixing process by top blowing in a stirred tank. Moreover, a general quantifying model was introduced for demonstrating the relationship between the flow patterns of the bubble swarms and heat transfer. The results can be applied to investigate other mixing processes that are very difficult to recognize the target. PMID:27527065

  7. Quantifying the evolution of flow boiling bubbles by statistical testing and image analysis: toward a general model

    NASA Astrophysics Data System (ADS)

    Xiao, Qingtai; Xu, Jianxin; Wang, Hua

    2016-08-01

    A new index, the estimate of the error variance, which can be used to quantify the evolution of the flow patterns when multiphase components or tracers are difficultly distinguishable, was proposed. The homogeneity degree of the luminance space distribution behind the viewing windows in the direct contact boiling heat transfer process was explored. With image analysis and a linear statistical model, the F-test of the statistical analysis was used to test whether the light was uniform, and a non-linear method was used to determine the direction and position of a fixed source light. The experimental results showed that the inflection point of the new index was approximately equal to the mixing time. The new index has been popularized and applied to a multiphase macro mixing process by top blowing in a stirred tank. Moreover, a general quantifying model was introduced for demonstrating the relationship between the flow patterns of the bubble swarms and heat transfer. The results can be applied to investigate other mixing processes that are very difficult to recognize the target.

  8. Quantifying the evolution of flow boiling bubbles by statistical testing and image analysis: toward a general model.

    PubMed

    Xiao, Qingtai; Xu, Jianxin; Wang, Hua

    2016-08-16

    A new index, the estimate of the error variance, which can be used to quantify the evolution of the flow patterns when multiphase components or tracers are difficultly distinguishable, was proposed. The homogeneity degree of the luminance space distribution behind the viewing windows in the direct contact boiling heat transfer process was explored. With image analysis and a linear statistical model, the F-test of the statistical analysis was used to test whether the light was uniform, and a non-linear method was used to determine the direction and position of a fixed source light. The experimental results showed that the inflection point of the new index was approximately equal to the mixing time. The new index has been popularized and applied to a multiphase macro mixing process by top blowing in a stirred tank. Moreover, a general quantifying model was introduced for demonstrating the relationship between the flow patterns of the bubble swarms and heat transfer. The results can be applied to investigate other mixing processes that are very difficult to recognize the target.

  9. Interactions Forces and the Flow-Induced Coalescence of Drops and Bubbles

    NASA Technical Reports Server (NTRS)

    Leal, L. Gary; Israelachvili, J.

    2004-01-01

    In order to accomplish the proposed macroscale experimental goals, we designed and built a pair of miniaturized computer-controlled four-roll mills, similar but much smaller than the 4-roll mill that had been develop earlier in Prof. Leal's group for studies of drop deformation and breakup. This unique experimental facility allows for controlled experiments on the breakup and coalescence of very small drops in the size range of 20-200 micrometers in diameter for a wide variety of flows and under a wide range of flow conditions including time-dependent flows, etc. The small size of this device is necessary for coalescence studies, since coalescence occurs in viscous fluids at capillary numbers that are large enough to be experimentally accessible only for drops that are smaller than approximately 100_m in diameter. Using these miniaturized 4-roll mills, we have obtained the first quantitative data (so far as we are aware) on the flow-induced coalescence process.

  10. Flow pattern and pressure drop of vertical upward gas-liquid flow in sinusoidal wavy channels

    SciTech Connect

    Nilpueng, Kitti; Wongwises, Somchai

    2006-06-15

    Flow patterns and pressure drop of upward liquid single-phase flow and air-water two-phase flow in sinusoidal wavy channels are experimentally studied. The test section is formed by a sinusoidal wavy wall of 1.00 m length with a wave length of 67.20mm, an amplitude of 5.76mm. Different phase shifts between the side walls of the wavy channel of 0{sup o}, 90{sup o} and 180{sup o} are investigated. The flow phenomena, which are bubbly flow, slug flow, churn flow, and dispersed bubbly flow are observed and recorded by high-speed camera. When the phase shifts are increased, the onset of the transition from the bubbly flow to the churn flow shifts to a higher value of superficial air velocity, and the regions of the slug flow and the churn flow are smaller. In other words, the regions of the bubbly flow and the dispersed bubbly flow are larger as the phase shift increases. The slug flow pattern is only found in the test sections with phase shifts of 0{sup o} and 90{sup o}. Recirculating gas bubbles are always found in the troughs of the corrugations. The recirculating is higher when the phase shifts are larger. The relationship between the two-phase multipliers calculated from the measured pressure drops, and the Martinelli parameter is compared with the Lockhart-Martinelli correlation. The correlation in the case of turbulent-turbulent condition is shown to fit the data very well for the phase shift of 0{sup o} but shows greater deviation when the phase shifts are higher. (author)

  11. The hydrodynamics of bubble rise and impact with solid surfaces.

    PubMed

    Manica, Rogerio; Klaseboer, Evert; Chan, Derek Y C

    2016-09-01

    A bubble smaller than 1mm in radius rises along a straight path in water and attains a constant speed due to the balance between buoyancy and drag force. Depending on the purity of the system, within the two extreme limits of tangentially immobile or mobile boundary conditions at the air-water interface considerably different terminal speeds are possible. When such a bubble impacts on a horizontal solid surface and bounces, interesting physics can be observed. We study this physical phenomenon in terms of forces, which can be of colloidal, inertial, elastic, surface tension and viscous origins. Recent advances in high-speed photography allow for the observation of phenomena on the millisecond scale. Simultaneous use of such cameras to visualize both rise/deformation and the dynamics of the thin film drainage through interferometry are now possible. These experiments confirm that the drainage process obeys lubrication theory for the spectrum of micrometre to millimetre-sized bubbles that are covered in this review. We aim to bridge the colloidal perspective at low Reynolds numbers where surface forces are important to high Reynolds number fluid dynamics where the effect of the surrounding flow becomes important. A model that combines a force balance with lubrication theory allows for the quantitative comparison with experimental data under different conditions without any fitting parameter.

  12. Bubble Dynamics, Two-Phase Flow, and Boiling Heat Transfer in Microgravity

    NASA Technical Reports Server (NTRS)

    Chung, Jacob N.

    1998-01-01

    This report contains two independent sections. Part one is titled "Terrestrial and Microgravity Pool Boiling Heat Transfer and Critical heat flux phenomenon in an acoustic standing wave." Terrestrial and microgravity pool boiling heat transfer experiments were performed in the presence of a standing acoustic wave from a platinum wire resistance heater using degassed FC-72 Fluorinert liquid. The sound wave was created by driving a half wavelength resonator at a frequency of 10.15 kHz. Microgravity conditions were created using the 2.1 second drop tower on the campus of Washington State University. Burnout of the heater wire, often encountered with heat flux controlled systems, was avoided by using a constant temperature controller to regulate the heater wire temperature. The amplitude of the acoustic standing wave was increased from 28 kPa to over 70 kPa and these pressure measurements were made using a hydrophone fabricated with a small piezoelectric ceramic. Cavitation incurred during experiments at higher acoustic amplitudes contributed to the vapor bubble dynamics and heat transfer. The heater wire was positioned at three different locations within the acoustic field: the acoustic node, antinode, and halfway between these locations. Complete boiling curves are presented to show how the applied acoustic field enhanced boiling heat transfer and increased critical heat flux in microgravity and terrestrial environments. Video images provide information on the interaction between the vapor bubbles and the acoustic field. Part two is titled, "Design and qualification of a microscale heater array for use in boiling heat transfer." This part is summarized herein. Boiling heat transfer is an efficient means of heat transfer because a large amount of heat can be removed from a surface using a relatively small temperature difference between the surface and the bulk liquid. However, the mechanisms that govern boiling heat transfer are not well understood. Measurements of

  13. Parallelizable flood fill algorithm and corrective interface tracking approach applied to the simulation of multiple finite size bubbles merging with a free surface

    NASA Astrophysics Data System (ADS)

    Lafferty, Nathan; Badreddine, Hassan; Niceno, Bojan; Prasser, Horst-Michael

    2015-11-01

    A parallelizable flood fill algorithm is developed for identifying and tracking closed regions of fluids, dispersed phases, in CFD simulations of multiphase flows. It is used in conjunction with a newly developed method, corrective interface tracking, for simulating finite size dispersed bubbly flows in which the bubbles are too small relative to the grid to be simulated accurately with interface tracking techniques and too large relative to the grid for Lagrangian particle tracking techniques. The latter situation arising if local bubble induced turbulence is resolved, or modeled with LES. With corrective interface tracking the governing equations are solved on a static Eulerian grid. A correcting force, derived from empirical correlation based hydrodynamic forces, is applied to the bubble which is then advected using interface tracking techniques. This method results in accurate fluid-gas two-way coupling, bubble shapes, and terminal rise velocities. The flood fill algorithm and corrective interface tracking technique are applied to an air/water simulation of multiple bubbles rising and merging with a free surface. They are then validated against the same simulation performed using only interface tracking with a much finer grid.

  14. Modification of flow perturbations in a laminar separation bubble by heat transfer

    NASA Astrophysics Data System (ADS)

    Boiko, A. V.; Dovgal, A. V.; Sorokin, A. M.

    2017-02-01

    Laminar boundary layer separation in conditions of localized heat transfer is investigated at low subsonic velocity through wind-tunnel measurements and linear stability analysis. A backward-facing step flow is subjected to a stationary temperature variation generated by Peltier elements installed on the test model directly downstream of the separation line. The experimental and theoretical data clarify the response of velocity disturbances in the separation region to the temperature variation, the latter appearing primarily as a modifier of the initial wave spectrum of the amplifying separated layer oscillations.

  15. Numerical and Physical Modelling of Bubbly Flow Phenomena - Final Report to the Department of Energy

    SciTech Connect

    Andrea Prosperetti

    2004-12-21

    This report describes the main features of the results obtained in the course of this project. A new approach to the systematic development of closure relations for the averaged equations of disperse multiphase flow is outlined. The focus of the project is on spatially non-uniform systems and several aspects in which such systems differ from uniform ones are described. Then, the procedure used in deriving the closure relations is given and some explicit results shown. The report also contains a list of publications supported by this grant and a list of the persons involved in the work.

  16. Blowing magnetic skyrmion bubbles

    NASA Astrophysics Data System (ADS)

    Jiang, Wanjun; Upadhyaya, Pramey; Zhang, Wei; Yu, Guoqiang; Jungfleisch, M. Benjamin; Fradin, Frank Y.; Pearson, John E.; Tserkovnyak, Yaroslav; Wang, Kang L.; Heinonen, Olle; te Velthuis, Suzanne G. E.; Hoffmann, Axel

    2015-07-01

    The formation of soap bubbles from thin films is accompanied by topological transitions. Here we show how a magnetic topological structure, a skyrmion bubble, can be generated in a solid-state system in a similar manner. Using an inhomogeneous in-plane current in a system with broken inversion symmetry, we experimentally “blow” magnetic skyrmion bubbles from a geometrical constriction. The presence of a spatially divergent spin-orbit torque gives rise to instabilities of the magnetic domain structures that are reminiscent of Rayleigh-Plateau instabilities in fluid flows. We determine a phase diagram for skyrmion formation and reveal the efficient manipulation of these dynamically created skyrmions, including depinning and motion. The demonstrated current-driven transformation from stripe domains to magnetic skyrmion bubbles could lead to progress in skyrmion-based spintronics.

  17. An experimental and analytical investigation into the performance of centrifugal pumps operating with air-water mixtures

    NASA Astrophysics Data System (ADS)

    Sterrett, John Douglas

    1994-01-01

    An investigation was made into the performance of centrifugal pumps when two-phase non-condensable mixtures of gas and liquid are flowing. This problem is encountered during loss-of-coolant accidents in nuclear reactor systems and in the pumping of oil where natural gas may be present in the mixture. Analytical and experimental techniques were used to address the issues of scaling between a model and a prototype pump and the validity of the single-phase pump affinity laws when two-phase flows are present. The results from this effort have also provided insight into the physical phenomena which cause the degradation in pump performance. An analytical model for the motion of a single bubble through a pump impeller is provided. The results from this fundamental problem show that the Coriolis and buoyancy forces are important in describing the kinematics of a gas phase. These results show that dynamic similitude is not preserved between a model and prototype impeller when the standard single-phase pump scaling relationships are used. The motion of a single bubble is also shown to be influenced by the magnitude of the pump suction pressure. The results from an extensive series of air-water two phase pump tests are provided. A 1/4 scale pump, modeled after the Savannah River Site K-reactor pumps, was tested over a wide range of pump speeds, flow rates, and suction pressures. These results indicate that the single-phase pump affinity laws are not applicable to two-phase pump flows and that the magnitude of the pump suction pressure is an important quantity in determining the pump performance. A second analytical model is developed for two-phase flow through a pump impeller. The results from this one-dimensional, two-fluid, non-homogeneous streamline model show good agreement with the experimental data. The model results support the experimental data in showing that the single-phase pump affinity relationships are not valid for two-phase pump flows and that dynamic

  18. Bubble Combustion

    NASA Technical Reports Server (NTRS)

    Corrigan, Jackie

    2004-01-01

    A method of energy production that is capable of low pollutant emissions is fundamental to one of the four pillars of NASA s Aeronautics Blueprint: Revolutionary Vehicles. Bubble combustion, a new engine technology currently being developed at Glenn Research Center promises to provide low emissions combustion in support of NASA s vision under the Emissions Element because it generates power, while minimizing the production of carbon dioxide (CO2) and nitrous oxides (NOx), both known to be Greenhouse gases. and allows the use of alternative fuels such as corn oil, low-grade fuels, and even used motor oil. Bubble combustion is analogous to the inverse of spray combustion: the difference between bubble and spray combustion is that spray combustion is spraying a liquid in to a gas to form droplets, whereas bubble combustion involves injecting a gas into a liquid to form gaseous bubbles. In bubble combustion, the process for the ignition of the bubbles takes place on a time scale of less than a nanosecond and begins with acoustic waves perturbing each bubble. This perturbation causes the local pressure to drop below the vapor pressure of the liquid thus producing cavitation in which the bubble diameter grows, and upon reversal of the oscillating pressure field, the bubble then collapses rapidly with the aid of the high surface tension forces acting on the wall of the bubble. The rapid and violent collapse causes the temperatures inside the bubbles to soar as a result of adiabatic heating. As the temperatures rise, the gaseous contents of the bubble ignite with the bubble itself serving as its own combustion chamber. After ignition, this is the time in the bubble s life cycle where power is generated, and CO2, and NOx among other species, are produced. However, the pollutants CO2 and NOx are absorbed into the surrounding liquid. The importance of bubble combustion is that it generates power using a simple and compact device. We conducted a parametric study using CAVCHEM

  19. Gas-bubble snap-off under pressure driven flow in constricted noncircular capillaries

    SciTech Connect

    Kovscek, A.R.; Radke, C.J.

    1996-04-01

    A model for snap-off of a gas thread in a constricted cornered pore is developed. The time for wetting liquid to accumulate at a pore throat into an unstable collar is examined, as for the resulting pore-spanning lens to be displaced from the pore so that snap-off is the time may repeat. A comer-flow hydrodynamic analysis for the accumulation rate of wetting liquid due to both gradients in interfacial curvature and in applied liquid-phase pressure reveals that wetting-phase pressure gradients significantly increase the frequency of liquid accumulation for snap-off as compared to liquid rearrangement driven only by differences in pore-wall curvature. For moderate and large pressure gradients, the frequency of accumulation increases linearly with pressure gradient because of the increased rate of wetting liquid flow along pore comers. Pore topology is important to the theory, for pores with relatively small throats connected to large bodies demonstrate excellent ability to snapoff gas threads even when the initial capillary pressure is high or equivalently when the liquid saturation is low. A macroscopic momentum balance across the lens resulting from snap-off reveals that lens displacement rates are not linear with the imposed pressure drop. Instead, the frequency of lens displacement scales with powers between 0.5 and 0.6 for pores with dimensionless constriction radii between 0.15 and 0.40. Statistical percolation arguments are employed to form a generation rate expression and connect pore-level foam generation events to macroscopic pressure gradients in porous media. The rate of foam generation by capillary snap-off increases linearly with the liquid-phase pressure gradient and according to a power-law relationship with respect to the imposed gas-phase pressure gradient.

  20. Improving microalgal growth with reduced diameters of aeration bubbles and enhanced mass transfer of solution in an oscillating flow field.

    PubMed

    Yang, Zongbo; Cheng, Jun; Lin, Richen; Zhou, Junhu; Cen, Kefa

    2016-07-01

    A novel oscillating gas aerator combined with an oscillating baffle was proposed to generate smaller aeration bubbles and enhance solution mass transfer, which can improve microalgal growth in a raceway pond. A high-speed photography system (HSP) was used to measure bubble diameter and generation time, and online precise dissolved oxygen probes and pH probes were used to measure mass-transfer coefficient and mixing time. Bubble diameter and generation time decreased with decreased aeration gas rate, decreased orifice diameter, and increased water velocity in the oscillating gas aerator. The optimized oscillating gas aerator decreased bubble diameter and generation time by 25% and 58%, respectively, compared with a horizontal tubular gas aerator. Using an oscillating gas aerator and an oscillating baffle in a raceway pond increased the solution mass-transfer coefficient by 15% and decreased mixing time by 32%; consequently, microalgal biomass yield increased by 19%.

  1. Frictional drag reduction by bubble injection

    NASA Astrophysics Data System (ADS)

    Murai, Yuichi

    2014-07-01

    The injection of gas bubbles into a turbulent boundary layer of a liquid phase has multiple different impacts on the original flow structure. Frictional drag reduction is a phenomenon resulting from their combined effects. This explains why a number of different void-drag reduction relationships have been reported to date, while early works pursued a simple universal mechanism. In the last 15 years, a series of precisely designed experimentations has led to the conclusion that the frictional drag reduction by bubble injection has multiple manifestations dependent on bubble size and flow speed. The phenomena are classified into several regimes of two-phase interaction mechanisms. Each regime has inherent physics of bubbly liquid, highlighted by keywords such as bubbly mixture rheology, the spectral response of bubbles in turbulence, buoyancy-dominated bubble behavior, and gas cavity breakup. Among the regimes, bubbles in some selected situations lose the drag reduction effect owing to extra momentum transfer promoted by their active motions. This separates engineers into two communities: those studying small bubbles for high-speed flow applications and those studying large bubbles for low-speed flow applications. This article reviews the roles of bubbles in drag reduction, which have been revealed from fundamental studies of simplified flow geometries and from development of measurement techniques that resolve the inner layer structure of bubble-mixed turbulent boundary layers.

  2. ENGINEERING DEVELOPMENT OF SLURRY BUBBLE COLUMN REACTOR (SBCR) TECHNOLOGY

    SciTech Connect

    Bernard A. Toseland

    2000-12-31

    The major technical objectives of this program are threefold: (1) to develop the design tools and a fundamental understanding of the fluid dynamics of a slurry bubble column reactor to maximize reactor productivity, (2) to develop the mathematical reactor design models and gain an understanding of the hydrodynamic fundamentals under industrially relevant process conditions, and (3) to develop an understanding of the hydrodynamics and their interaction with the chemistries occurring in the bubble column reactor. Successful completion of these objectives will permit more efficient usage of the reactor column and tighter design criteria, increase overall reactor efficiency, and ensure a design that leads to stable reactor behavior when scaling up to large-diameter reactors. Washington University's work during the reporting period involved the implementation of the automated calibration device, which will provide an advanced method of determining liquid and slurry velocities at high pressures. This new calibration device is intended to replace the original calibration setup, which depended on fishing lines and hooks to position the radioactive particle. The report submitted by Washington University contains a complete description of the new calibration device and its operation. Improvements to the calibration program are also discussed. Iowa State University utilized air-water bubble column simulations in an effort to determine the domain size needed to represent all of the flow scales in a gas-liquid column at a high superficial velocity. Ohio State's report summarizes conclusions drawn from the completion of gas injection phenomena studies, specifically with respect to the characteristics of bubbling-jetting at submerged single orifices in liquid-solid suspensions.

  3. The budget of turbulent kinetic energy in bubble plumes by acoustic Doppler velocimetry

    NASA Astrophysics Data System (ADS)

    Lai, Chris; Socolofsky, Scott

    2016-11-01

    We present an experimental investigation on the TKE budget of a two-phase air-water bubble plume in an otherwise quiescent ambient. The required three-dimensional turbulent velocity field was measured by a profiling acoustic Doppler velocimeter. Experiments were carried out in a square water tank of 1m3 and covered both adjustment phase (z/D < 5) and asymptotic regime (z/D >= 5) of the plume in which the latter is characterized by a constant local Frp . The dynamic length scale D has previously been derived from a two-fluid approach and delineates the two regimes. Data on the mean flow establish the existence of an asymptotic regime when z / D > 8 with an entrainment coefficient of 0.095 and a Frp of 1.63. The data also corroborate well with previous measurements of large-scale bubble plumes. A budget of TKE was performed using curve-fits derived from the radial profiles of second- and third-order moments of turbulent velocities. From the budget, TKE production by bubbles was found to be larger than that by fluid shear. Approximately 55-60% of the total work done by bubbles is used to create fluid turbulence. This research was made possible by a Grant from The Gulf of Mexico Research Initiative to the Gulf Integrated Spill Research (GISR) Consortium.

  4. Air entrainment and bubble statistics in three-dimensional breaking waves

    NASA Astrophysics Data System (ADS)

    Deike, Luc; Melville, W. K.; Popinet, Stephane

    2015-11-01

    Wave breaking in the ocean is of fundamental importance in order to quantify wave dissipation and air-sea interaction, including gas and momentum exchange, and to improve parametrizationsfor weather and climate models. Here, we investigate air entrainment and bubble statistics in three-dimensional breaking waves through direct numerical simulations of the two-phase air-water flow using the Open Source solver Gerris. As in previous 2D simulations, the dissipation due to breaking is found to be in good agreement with previous experimental observations and inertial-scaling arguments. For radii larger than the Hinze scale, the bubble size distribution, is found to follow a power law of the radius, r-3and to scale linearly with the time dependent turbulent dissipation rate during the active breaking stages. The time-averaged bubble size distribution is found to follow the same power law of the radius and to scale linearly with the wave dissipation rate per unit length of breaking crest. We propose a phenomenological turbulent bubble break-up model that describes the numerical results and existing experimental results.

  5. Steady State Vapor Bubble in Pool Boiling

    PubMed Central

    Zou, An; Chanana, Ashish; Agrawal, Amit; Wayner, Peter C.; Maroo, Shalabh C.

    2016-01-01

    Boiling, a dynamic and multiscale process, has been studied for several decades; however, a comprehensive understanding of the process is still lacking. The bubble ebullition cycle, which occurs over millisecond time-span, makes it extremely challenging to study near-surface interfacial characteristics of a single bubble. Here, we create a steady-state vapor bubble that can remain stable for hours in a pool of sub-cooled water using a femtosecond laser source. The stability of the bubble allows us to measure the contact-angle and perform in-situ imaging of the contact-line region and the microlayer, on hydrophilic and hydrophobic surfaces and in both degassed and regular (with dissolved air) water. The early growth stage of vapor bubble in degassed water shows a completely wetted bubble base with the microlayer, and the bubble does not depart from the surface due to reduced liquid pressure in the microlayer. Using experimental data and numerical simulations, we obtain permissible range of maximum heat transfer coefficient possible in nucleate boiling and the width of the evaporating layer in the contact-line region. This technique of creating and measuring fundamental characteristics of a stable vapor bubble will facilitate rational design of nanostructures for boiling enhancement and advance thermal management in electronics. PMID:26837464

  6. Steady State Vapor Bubble in Pool Boiling.

    PubMed

    Zou, An; Chanana, Ashish; Agrawal, Amit; Wayner, Peter C; Maroo, Shalabh C

    2016-02-03

    Boiling, a dynamic and multiscale process, has been studied for several decades; however, a comprehensive understanding of the process is still lacking. The bubble ebullition cycle, which occurs over millisecond time-span, makes it extremely challenging to study near-surface interfacial characteristics of a single bubble. Here, we create a steady-state vapor bubble that can remain stable for hours in a pool of sub-cooled water using a femtosecond laser source. The stability of the bubble allows us to measure the contact-angle and perform in-situ imaging of the contact-line region and the microlayer, on hydrophilic and hydrophobic surfaces and in both degassed and regular (with dissolved air) water. The early growth stage of vapor bubble in degassed water shows a completely wetted bubble base with the microlayer, and the bubble does not depart from the surface due to reduced liquid pressure in the microlayer. Using experimental data and numerical simulations, we obtain permissible range of maximum heat transfer coefficient possible in nucleate boiling and the width of the evaporating layer in the contact-line region. This technique of creating and measuring fundamental characteristics of a stable vapor bubble will facilitate rational design of nanostructures for boiling enhancement and advance thermal management in electronics.

  7. Observation of Mass Transport Stability and Faraday Instability: Why Stable Single Bubble Sonoluminescence is Possible

    NASA Technical Reports Server (NTRS)

    Holt, R. G.; Gaitan, D. F.

    1996-01-01

    Teh region of parameter space (acoustic pressure P(sub a), bubble radius R(sub 0)) in which stable single bubble sonoluminescence (SBSL) occurs in an air-water system is a small fraction of that which is accesible. This is due ot the existence of an island of dissolution at high P(sub a) and small R(sub 0).

  8. Sinking Bubbles

    NASA Astrophysics Data System (ADS)

    Koch, Jeremy; Ewoldt, Randy

    2016-11-01

    Intuition tells us that bubbles will rise and steel objects will sink in liquids, though here we describe the opposite. With experimental demonstration and theoretical rationale, we describe how the motion of containers of liquid with immersed solid objects and air bubbles can cause curious behaviors: sinking bubbles and rising high-density particles. Bubbles and solid spheres of diameter on the order of a few millimeters are introduced into fluids with different rheological constitutive behaviors. Imposed motion of the rigid container allows for control of the trajectories of the immersed particles - without the container imparting direct shearing motion on the fluid. Results demonstrate the necessary conditions to prevent or produce net motion of the bubbles and heavy particles, both with and against gravitational expectations.

  9. Bubble contraction in free-boundary Hele-Shaw flow with surface tension and kinetic undercooling regularisation

    NASA Astrophysics Data System (ADS)

    Dallaston, Michael; McCue, Scott

    2012-11-01

    When an inviscid bubble expands into a viscous fluid in a Hele-Shaw cell, the bubble boundary is unstable, in general forming long fingers (the Saffman-Taylor instability). In order to make the problem well-posed, a regularising boundary effect must be included. The most widely studied of these are surface tension, which penalises high curvatures, and kinetic undercooling, which penalises high velocities. Both these effects act as a stabilising influence on the free boundary. Less attention has been paid to the case of contracting bubbles, which shrink to a single point (or points) in finite time. In this case, the two effects are in competition, as surface tension stabilises the boundary, while kinetic undercooling destabilises it. This leads to bifurcation behaviour in the asymptotic (near-extinction) shape of the bubble as the relative strengths of the two effects are varied. In particular, there is a critical range of parameter values for which both circular and slit-type bubbles are stable, with a third (unstable) oval-type shape also present. We discuss some numerical and analytic techniques for solving the full free boundary problem and for exploring this interesting extinction behaviour.

  10. Bubble, Bubble, Toil and Trouble.

    ERIC Educational Resources Information Center

    Journal of Chemical Education, 2001

    2001-01-01

    Bubbles are a fun way to introduce the concepts of surface tension, intermolecular forces, and the use of surfactants. Presents two activities in which students add chemicals to liquid dishwashing detergent with water in order to create longer lasting bubbles. (ASK)

  11. High-frame rate imaging of two-phase flow in a thin rectangular channel using fast neutrons.

    PubMed

    Zboray, R; Mor, I; Dangendorf, V; Stark, M; Tittelmeier, K; Cortesi, M; Adams, R

    2014-08-01

    We have demonstrated the feasibility of performing high-frame-rate, fast neutron radiography of air-water two-phase flows in a thin channel with rectangular cross section. The experiments have been carried out at the accelerator facility of the Physikalisch-Technische Bundesanstalt. A polychromatic, high-intensity fast neutron beam with average energy of 6 MeV was produced by 11.5 MeV deuterons hitting a thick Be target. Image sequences down to 10 ms exposure times were obtained using a fast-neutron imaging detector developed in the context of fast-neutron resonance imaging. Different two-phase flow regimes such as bubbly slug and churn flows have been examined. Two phase flow parameters like the volumetric gas fraction, bubble size and mean bubble velocities have been measured. The first results are promising, improvements for future experiments are also discussed.

  12. Tuning bubbly structures in microchannels

    PubMed Central

    Vuong, Sharon M.; Anna, Shelley L.

    2012-01-01

    Foams have many useful applications that arise from the structure and size distribution of the bubbles within them. Microfluidics allows for the rapid formation of uniform bubbles, where bubble size and volume fraction are functions of the input gas pressure, liquid flow rate, and device geometry. After formation, the microchannel confines the bubbles and determines the resulting foam structure. Bubbly structures can vary from a single row (“dripping”), to multiple rows (“alternating”), to densely packed bubbles (“bamboo” and dry foams). We show that each configuration arises in a distinct region of the operating space defined by bubble volume and volume fraction. We describe the boundaries between these regions using geometric arguments and show that the boundaries are functions of the channel aspect ratio. We compare these geometric arguments with foam structures observed in experiments using flow-focusing, T-junction, and co-flow designs to generate stable nitrogen bubbles in aqueous surfactant solution and stable droplets in oil containing dissolved surfactant. The outcome of this work is a set of design parameters that can be used to achieve desired foam structures as a function of device geometry and experimental control parameters. PMID:22655008

  13. Two Phase Flow Mapping and Transition Under Microgravity Conditions

    NASA Technical Reports Server (NTRS)

    Parang, Masood; Chao, David F.

    1998-01-01

    In this paper, recent microgravity two-phase flow data for air-water, air-water-glycerin, and air- water-Zonyl FSP mixtures are analyzed for transition from bubbly to slug and from slug to annular flow. It is found that Weber number-based maps are inadequate to predict flow-pattern transition, especially over a wide range of liquid flow rates. It is further shown that slug to annular flow transition is dependent on liquid phase Reynolds number at high liquid flow rate. This effect may be attributed to growing importance of liquid phase inertia in the dynamics of the phase flow and distribution. As a result a new form of scaling is introduced to present data using liquid Weber number based on vapor and liquid superficial velocities and Reynolds number based on liquid superficial velocity. This new combination of the dimensionless parameters seem to be more appropriate for the presentation of the microgravity data and provides a better flow pattern prediction and should be considered for evaluation with data obtained in the future. Similarly, the analysis of bubble to slug flow transition indicates a strong dependence on both liquid inertia and turbulence fluctuations which seem to play a significant role on this transition at high values of liquid velocity. A revised mapping of data using a new group of dimensionless parameters show a better and more consistent description of flow transition over a wide range of liquid flow rates. Further evaluation of the proposed flow transition mapping will have to be made after a wider range of microgravity data become available.

  14. Application of Micropore Filter Technology: Exploring the Blood Flow Path in Arterial-Line Filters and Its Effect on Bubble Trapping Functions.

    PubMed

    Herbst, Daniel P

    2017-03-01

    Conventional arterial-line filters commonly use a large volume circular shaped housing, a wetted micropore screen, and a purge port to trap, separate, and remove gas bubbles from extracorporeal blood flow. Focusing on the bubble trapping function, this work attempts to explore how the filter housing shape and its resulting blood flow path affect the clinical application of arterial-line filters in terms of gross air handling. A video camera was used in a wet-lab setting to record observations made during gross air-bolus injections in three different radially designed filters using a 30-70% glycerol-saline mixture flowing at 4.5 L/min. Two of the filters both had inlet ports attached near the filter-housing top with bottom oriented outlet ports at the bottom, whereas the third filter had its inlet and outlet ports both located at the bottom of the filter housing. The two filters with top-in bottom-out fluid paths were shown to direct the incoming flow downward as it passed through the filter, placing the forces of buoyancy and viscous drag in opposition to each other. This contrasted with the third filter's bottom-in bottom-out fluid path, which was shown to direct the incoming flow upward so that the forces of buoyancy and viscous drag work together. The direction of the blood flow path through a filter may be important to the application of arterial-line filter technology as it helps determine how the forces of buoyancy and flow are aligned with one another.

  15. Influence of bubble size on effervescent atomization. Part 1: bubble characterization and mean spray features

    NASA Astrophysics Data System (ADS)

    Lewis, Taylor; Shepard, Thomas; Forliti, David

    2016-11-01

    In the effervescent atomization process a gas-liquid bubbly mixture is ejected from a nozzle with the goal of enhancing liquid break-up. In this work, high speed images are taken of the bubbly flow inside of an effervescent atomizer as well as downstream of the atomizer exit. The use of varying porous plate media grades and channel inserts at the air injection site of the atomizer permitted independent control of mean bubble size. Digital image analyses were used for bubble characterization and measuring mean spray features. The roles of air injection geometry on bubble population parameters inside of the effervescent atomizer are detailed. The effect of bubble size is examined at multiple gas to liquid flow rate ratios for which the bubbly flow regime was maintained. Results are presented demonstrating the influence of bubble size on the average jet width, jet dark core length, and liquid break-up.

  16. Gamma densitometry tomography of gas holdup spatial distribution in industrial scale bubble columns

    SciTech Connect

    Shollenberger, K.A.; Torczynski, J.R.; Adkins, D.R.; O`Hern, T.J.; Jackson, N.B.

    1995-12-31

    Gamma-densitometry tomography (GDT) experiments have been performed to measure gas holdup spatial variations in two bubble columns: a 0.19 m inside diameter Lucite column and a 0.48 m inside diameter stainless steel vessel. Air and water were used for the measurements. Horizontal scans at one vertical position in each column were made for several air flow rates. An axi-symmetric tomographic reconstruction algorithm based on the Abel transform has been used to calculate the time averaged gas holdup radial variation. Integration of these profiles over the column cross section has yielded area-averaged gas holdup results, which have been compared with volume-averaged gas holdups determined from differential pressure measurements and from the rise in the air/water interface during gas flow. The results agree reasonably well.

  17. Bubble diagnostics

    DOEpatents

    Visuri, Steven R.; Mammini, Beth M.; Da Silva, Luiz B.; Celliers, Peter M.

    2003-01-01

    The present invention is intended as a means of diagnosing the presence of a gas bubble and incorporating the information into a feedback system for opto-acoustic thrombolysis. In opto-acoustic thrombolysis, pulsed laser radiation at ultrasonic frequencies is delivered intraluminally down an optical fiber and directed toward a thrombus or otherwise occluded vessel. Dissolution of the occlusion is therefore mediated through ultrasonic action of propagating pressure or shock waves. A vapor bubble in the fluid surrounding the occlusion may form as a result of laser irradiation. This vapor bubble may be used to directly disrupt the occlusion or as a means of producing a pressure wave. It is desirable to detect the formation and follow the lifetime of the vapor bubble. Knowledge of the bubble formation and lifetime yields critical information as to the maximum size of the bubble, density of the absorbed radiation, and properties of the absorbing material. This information can then be used in a feedback system to alter the irradiation conditions.

  18. Bubble Transport through Micropillar Arrays

    NASA Astrophysics Data System (ADS)

    Lee, Kenneth; Savas, Omer

    2012-11-01

    In current energy research, artificial photosynthetic devices are being designed to split water and harvest hydrogen gas using energy from the sun. In one such design, hydrogen gas bubbles evolve on the catalytic surfaces of arrayed micropillars. If these bubbles are not promptly removed from the surface, they can adversely affect gas evolution rates, water flow rates, sunlight capture, and heat management of the system. Therefore, an efficient method of collecting the evolved gas bubbles is crucial. Preliminary flow visualization has been conducted of bubbles advecting through dense arrays of pillars. Bubbles moving through square and hexagonal arrays are tracked, and the results are qualitatively described. Initial attempts to correlate bubble motion with relevant lengthscales and forces are also presented. These observations suggest how bubble transport within such pillar arrays can be managed, as well as guide subsequent experiments that investigate bubble evolution and collection. This material is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993.

  19. Methylglyoxal at the Air-Water Interface

    NASA Astrophysics Data System (ADS)

    Wren, S. N.; Gordon, B. P.; McWilliams, L.; Valley, N. A.; Richmond, G.

    2014-12-01

    Recently, it has been suggested that aqueous-phase processing of atmospheric α-dicarbonyl compounds such as methylglyoxal (MG) could constitute an important source of secondary organic aerosol (SOA). The uptake of MG to aqueous particles is higher than expected due to the fact that its carbonyl moieties can hydrate to form diols, as well as the fact that MG can undergo aldol condensation reactions to form larger oligomers in solution. MG is known to be surface active but an improved description of its surface behaviour is crucial to understanding MG-SOA formation, in addition to understanding its gas-to-particle partitioning and cloud forming potential. Here, we employ a combined experimental and theoretical approach involving vibrational sum frequency generation spectroscopy (VSFS), surface tensiometry, molecular dynamics simulations, and density functional theory calculations to study MG's surface adsorption, in both the presence and absence of salts. We are particularly interested in determining MG's hydration state at the surface. Our experimental results indicate that MG slowly adsorbs to the air-water interface and strongly perturbs the water structure there. This perturbation is enhanced in the presence of NaCl. Together our experimental and theoretical results suggest that singly-hydrated MG is the dominant form of MG at the surface.

  20. Hydrodynamic boundary conditions and dynamic forces between bubbles and surfaces.

    PubMed

    Manor, Ofer; Vakarelski, Ivan U; Tang, Xiaosong; O'Shea, Sean J; Stevens, Geoffrey W; Grieser, Franz; Dagastine, Raymond R; Chan, Derek Y C

    2008-07-11

    Dynamic forces between a 50 microm radius bubble driven towards and from a mica plate using an atomic force microscope in electrolyte and in surfactant exhibit different hydrodynamic boundary conditions at the bubble surface. In added surfactant, the forces are consistent with the no-slip boundary condition at the mica and bubble surfaces. With no surfactant, a new boundary condition that accounts for the transport of trace surface impurities explains variations of dynamic forces at different speeds and provides a direct connection between dynamic forces and surface transport effects at the air-water interface.

  1. Hydrodynamic Boundary Conditions and Dynamic Forces between Bubbles and Surfaces

    NASA Astrophysics Data System (ADS)

    Manor, Ofer; Vakarelski, Ivan U.; Tang, Xiaosong; O'Shea, Sean J.; Stevens, Geoffrey W.; Grieser, Franz; Dagastine, Raymond R.; Chan, Derek Y. C.

    2008-07-01

    Dynamic forces between a 50μm radius bubble driven towards and from a mica plate using an atomic force microscope in electrolyte and in surfactant exhibit different hydrodynamic boundary conditions at the bubble surface. In added surfactant, the forces are consistent with the no-slip boundary condition at the mica and bubble surfaces. With no surfactant, a new boundary condition that accounts for the transport of trace surface impurities explains variations of dynamic forces at different speeds and provides a direct connection between dynamic forces and surface transport effects at the air-water interface.

  2. Behavior of Rapidly Sheared Bubble Suspensions

    NASA Technical Reports Server (NTRS)

    Sangani, A. S.; Kushch, V. I.; Hoffmann, M.; Nahra, H.; Koch, D. L.; Tsang, Y.

    2002-01-01

    An experiment to be carried out aboard the International Space Station is described. A suspension consisting of millimeter-sized bubbles in water containing some dissolved salt, which prevents bubbles from coalescing, will be sheared in a Couette cylindrical cell. Rotation of the outer cylinder will produce centrifugal force which will tend to accumulate the bubbles near the inner wall. The shearing will enhance collisions among bubbles creating thereby bubble phase pressure that will resist the tendency of the bubbles to accumulate near the inner wall. The bubble volume fraction and velocity profiles will be measured and compared with the theoretical predictions. Ground-based research on measurement of bubble phase properties and flow in vertical channel are described.

  3. Bubble Size Distribution in a Vibrating Bubble Column

    NASA Astrophysics Data System (ADS)

    Mohagheghian, Shahrouz; Wilson, Trevor; Valenzuela, Bret; Hinds, Tyler; Moseni, Kevin; Elbing, Brian

    2016-11-01

    While vibrating bubble columns have increased the mass transfer between phases, a universal scaling law remains elusive. Attempts to predict mass transfer rates in large industrial scale applications by extrapolating laboratory scale models have failed. In a stationary bubble column, mass transfer is a function of phase interfacial area (PIA), while PIA is determined based on the bubble size distribution (BSD). On the other hand, BSD is influenced by the injection characteristics and liquid phase dynamics and properties. Vibration modifies the BSD by impacting the gas and gas-liquid dynamics. This work uses a vibrating cylindrical bubble column to investigate the effect of gas injection and vibration characteristics on the BSD. The bubble column has a 10 cm diameter and was filled with water to a depth of 90 cm above the tip of the orifice tube injector. BSD was measured using high-speed imaging to determine the projected area of individual bubbles, which the nominal bubble diameter was then calculated assuming spherical bubbles. The BSD dependence on the distance from the injector, injector design (1.6 and 0.8 mm ID), air flow rates (0.5 to 5 lit/min), and vibration conditions (stationary and vibration conditions varying amplitude and frequency) will be presented. In addition to mean data, higher order statistics will also be provided.

  4. A time splitting projection scheme for compressible two-phase flows. Application to the interaction of bubbles with ultrasound waves

    NASA Astrophysics Data System (ADS)

    Huber, Grégory; Tanguy, Sébastien; Béra, Jean-Christophe; Gilles, Bruno

    2015-12-01

    This paper is focused on the numerical simulation of the interaction of an ultrasound wave with a bubble. Our interest is to develop a fully compressible solver in the two phases and to account for surface tension effects. As the volume oscillation of the bubble occurs in a low Mach number regime, a specific care must be paid to the effectiveness of the numerical method which is chosen to solve the compressible Euler equations. Three different numerical solvers, an explicit HLLC (Harten-Lax-van Leer-Contact) solver [48], a preconditioning explicit HLLC solver [14] and the compressible projection method [21,53,55], are described and assessed with a one dimensional spherical benchmark. From this preliminary test, we can conclude that the compressible projection method outclasses the other two, whether the spatial accuracy or the time step stability are considered. Multidimensional numerical simulations are next performed. As a basic implementation of the surface tension leads to strong spurious currents and numerical instabilities, a specific velocity/pressure time splitting is proposed to overcome this issue. Numerical evidences of the efficiency of this new numerical scheme are provided, since both the accuracy and the stability of the overall algorithm are enhanced if this new time splitting is used. Finally, the numerical simulation of the interaction of a moving and deformable bubble with a plane wave is presented in order to bring out the ability of the new method in a more complex situation.

  5. Asymmetric interface temperature during vapor bubble growth

    NASA Astrophysics Data System (ADS)

    Diana, A.; Castillo, M.; Steinberg, T.; Brutin, D.

    2013-07-01

    We investigate the nucleation, growth, and detachment of single vapor bubbles at the interface microscale. Shear flow is used to investigate pool and convective boiling situations using visible and infrared visualizations. We determine a threshold Reynolds number for the onset of asymmetric interfacial temperatures. Below this threshold, bubble growth is geometrically and thermally symmetric, while above, bubbles no longer grow thermally symmetrically. This is explained by the dominance of convective heat transfer removal over viscous effects at the bubble interface. We experimentally demonstrate asymmetric interfacial temperature profiles that should be taken into account for future bubble growth modeling.

  6. Air-water interfacial areas in unsaturated soils: Evaluation of interfacial domains

    NASA Astrophysics Data System (ADS)

    Costanza-Robinson, Molly S.; Brusseau, Mark L.

    2002-10-01

    A gas-phase miscible-displacement method, using decane as an interfacial tracer, was used to measure air-water interfacial areas for a sand with water contents ranging from ˜2% to 20%. The expected trend of decreasing interfacial areas with increasing water contents was observed. The maximum estimated interfacial area of 19,500 cm-1 appears reasonable given it is smaller than the measured surface area of the porous medium (60,888 cm-1). Comparison of the experimental data presented herein with literature data provided further insight into the characterization of the air-water interface in unsaturated porous media. Specifically, comparison of interfacial areas measured using gas-phase versus aqueous-phase methods indicates that the gas-phase method generally yields larger interfacial areas than the aqueous-phase methods, even when accounting for differences in water content and physical properties of the porous media. The observations are consistent with proposed differences in interfacial accessibility of the aqueous- and gas-phase tracers. Evaluation of the data in light of functional interfacial domains, described herein, yields the hypothesis that aqueous interfacial tracers measure primarily air-water interfaces formed by "capillary water," while gas-phase tracers measure air-water interfaces formed by both capillary and surface-adsorbed (film) water. The gas- and aqueous-phase methods may each provide interfacial area information that is more relevant to specific problems of interest. For example, gas-phase interfacial area measurements may be most relevant to contaminant transport in unsaturated systems, where retention at the air-water interface may be significant. Conversely, the aqueous-phase methods may yield information with direct bearing on multiphase flow processes that are dominated by capillary-phase behavior.

  7. Primordial Bubbles within Primordial Bubbles

    NASA Astrophysics Data System (ADS)

    Occhionero, Franco; Amendola, Luca; Corasaniti, Pier Stefano

    The nucleation of primordial bubbles during an inflationary phase transition has been suggested to promote the formation of structure either above or below the horizon, depending on whether the nucleation occurs more or less than 60 e-folds before the end of inflation. Here we propose a mechanism which has both features and produces subhorizon cavities up to hundreds of h-1 Mpc -- where excess power is observed -- inside superhorizon bubbles, i.e. in open universes. For this purpose we build a new inflationary two-field model with two vacuum channels in the potential surface: by modulating the energy difference between these channels, episodes of back and forth transition occur in sequence during inflation. Thus, one physical process may i) reconcile inflation with openness and ii) seed a distribution of observable voids. Bubble spectra are given in terms of phenomenological parameters which in turn are functions of microscopic physical parameters. In principle large scale structure constrains fundamental physics: for example, to account for power at scales of hundreds of h-1 Mpc the singularity in the Euclidean action -- which separates the first from the second phase transition -- must be mild enough. The smoking gun of the process might be the imprint of non-Gaussian, ring-like signals on the microwave background at l > 1000 by the subhorizon bubbles. On the other end of the spectrum, the contribution to l =1,2 from the off-centerness of the observer in the open bubble, is being evaluated.

  8. The effects of bubble-bubble interactions on pressures and temperatures produced by bubbles collapsing near a rigid surface

    NASA Astrophysics Data System (ADS)

    Alahyari Beig, Shahaboddin; Johnsen, Eric

    2016-11-01

    Cavitation occurs in a wide range of hydraulic applications, and one of its most important consequences is structural damage to neighboring surfaces following repeated bubble collapse. A number of studies have been conducted to predict the pressures produced by the collapse of a single bubble. However, the collapse of multiple bubbles is known to lead to enhanced collapse pressures. In this study, we quantify the effects of bubble-bubble interactions on the bubble dynamics and pressures/temperatures produced by the collapse of a pair of bubbles near a rigid surface. For this purpose, we use an in-house, high-order accurate shock- and interface-capturing method to solve the 3D compressible Navier-Stokes equations for gas/liquid flows. The non-spherical bubble dynamics are investigated and the subsequent pressure and temperature fields are characterized based on the relevant parameters entering the problem: stand-off distance, geometrical configuation, collapse strength. We demonstrate that bubble-bubble interactions amplify/reduce pressures and temperatures produced at the collapse, and increase the non-sphericity of the bubbles and the collapse time, depending on the flow parameters.

  9. The Minnaert bubble: an acoustic approach

    NASA Astrophysics Data System (ADS)

    Devaud, Martin; Hocquet, Thierry; Bacri, Jean-Claude; Leroy, Valentin

    2008-11-01

    We propose an ab initio introduction to the well-known Minnaert pulsating bubble at graduate level. After a brief recall of the standard stuff, we begin with a detailed discussion of the radial movements of an air bubble in water. This discussion is managed from an acoustic point of view, and using the Lagrangian rather than the Eulerian variables. In unbounded water, the air-water system has a continuum of eigenmodes, some of them correspond to regular Fabry-Pérot resonances. A singular resonance, the lowest one, is shown to coincide with that of Minnaert. In bounded water, the eigenmodes spectrum is discrete, with a finite fundamental frequency. A spectacular quasi-locking of the latter occurs if it happens to exceed the Minnaert frequency, which provides an unforeseen one-bubble alternative version of the famous 'hot chocolate effect'. In the (low) frequency domain in which sound propagation inside the bubble reduces to a simple 'breathing' (i.e. inflation/deflation), the light air bubble can be 'dressed' by the outer water pressure forces, and is turned into the heavy Minnaert bubble. Thanks to this unexpected renormalization process, we demonstrate that the Minnaert bubble definitely behaves like a true harmonic oscillator of the spring-bob type, but with a damping term and a forcing term in apparent disagreement with those commonly admitted in the literature. Finally, we underline the double role played by the water. In order to tell the water motion associated with water compressibility (i.e. the sound) from the simple incompressible accompaniment of the bubble breathing, we introduce a new picture analogous to the electromagnetic radiative picture in Coulomb gauge, which naturally leads us to split the water displacement in an instantaneous and a retarded part. The Minnaert renormalized mass of the dressed bubble is then automatically recovered.

  10. Leverage bubble

    NASA Astrophysics Data System (ADS)

    Yan, Wanfeng; Woodard, Ryan; Sornette, Didier

    2012-01-01

    Leverage is strongly related to liquidity in a market and lack of liquidity is considered a cause and/or consequence of the recent financial crisis. A repurchase agreement is a financial instrument where a security is sold simultaneously with an agreement to buy it back at a later date. Repurchase agreement (repo) market size is a very important element in calculating the overall leverage in a financial market. Therefore, studying the behavior of repo market size can help to understand a process that can contribute to the birth of a financial crisis. We hypothesize that herding behavior among large investors led to massive over-leveraging through the use of repos, resulting in a bubble (built up over the previous years) and subsequent crash in this market in early 2008. We use the Johansen-Ledoit-Sornette (JLS) model of rational expectation bubbles and behavioral finance to study the dynamics of the repo market that led to the crash. The JLS model qualifies a bubble by the presence of characteristic patterns in the price dynamics, called log-periodic power law (LPPL) behavior. We show that there was significant LPPL behavior in the market before that crash and that the predicted range of times predicted by the model for the end of the bubble is consistent with the observations.

  11. Tiny Bubbles.

    ERIC Educational Resources Information Center

    Kim, Hy

    1985-01-01

    A simple oxygen-collecting device (easily constructed from glass jars and a lid) can show bubbles released by water plants during photosynthesis. Suggestions are given for: (1) testing the collected gas; (2) using various carbon dioxide sources; and (3) measuring respiration. (DH)

  12. Bubble dynamics in drinks

    NASA Astrophysics Data System (ADS)

    Broučková, Zuzana; Trávníček, Zdeněk; Šafařík, Pavel

    2014-03-01

    This study introduces two physical effects known from beverages: the effect of sinking bubbles and the hot chocolate sound effect. The paper presents two simple "kitchen" experiments. The first and second effects are indicated by means of a flow visualization and microphone measurement, respectively. To quantify the second (acoustic) effect, sound records are analyzed using time-frequency signal processing, and the obtained power spectra and spectrograms are discussed.

  13. pH effects on the molecular structure of β-lactoglobulin modified air-water interfaces and its impact on foam rheology.

    PubMed

    Engelhardt, Kathrin; Lexis, Meike; Gochev, Georgi; Konnerth, Christoph; Miller, Reinhard; Willenbacher, Norbert; Peukert, Wolfgang; Braunschweig, Björn

    2013-09-17

    Macroscopic properties of aqueous β-lactoglobulin (BLG) foams and the molecular properties of BLG modified air-water interfaces as their major structural element were investigated with a unique combination of foam rheology measurements and interfacial sensitive methods such as sum-frequency generation and interfacial dilatational rheology. The molecular structure and protein-protein interactions at the air-water interface can be changed substantially with the solution pH and result in major changes in interfacial dilational and foam rheology. At a pH near the interfacial isoelectric point BLG molecules carry zero net charge and disordered multilayers with the highest interfacial dilatational elasticity are formed at the air-water interface. Increasing or decreasing the pH with respect to the isoelectric point leads to the formation of a BLG monolayer with repulsive electrostatic interactions among the adsorbed molecules which decrease the interfacial dilational elasticity. The latter molecular information does explain the behavior of BLG foams in our rheological studies, where in fact the highest apparent yield stresses and storage moduli are established with foams from electrolyte solutions with a pH close to the isoelectric point of BLG. At this pH the gas bubbles of the foam are stabilized by BLG multilayers with attractive intermolecular interactions at the ubiquitous air-water interfaces, while BLG layers with repulsive interactions decrease the apparent yield stress and storage moduli as stabilization of gas bubbles with a monolayer of BLG is less effective.

  14. A hierarchy of two-fluid models with specific numerical methods for the simulation of bubbly flows/acoustic interactions

    NASA Astrophysics Data System (ADS)

    Drui, Florence; Larat, Adam; Le Chenadec, Vincent; Kokh, Samuel; Massot, Marc

    2014-11-01

    Simulating the injection, evaporation, and combustion of fuel in energy conversion applications represents a major challenge. The formulation of closed sets of equations able to accurately predict these complex systems by relying solely on averaged information has been a longstanding problem. As a consequence, no simple model is currently available that describes the complete injection process, known to range from the separated phase regime in the early stages of atomization to the dispersed regime that occurs further downstream. The benefits of such a unified formulation would be significant, both in terms of computational cost and algorithmic complexity. In order to identify the challenges in formulating one such approach, a one-pressure, one-velocity isothermal two-fluid model for bubble-acoustic wave interaction is studied and incrementally improved by introducing additional variables that characterize the micro-structure of bubbles. The elastic and dissipative structures of the models are investigated in depth, and their performances compared to reference solutions (Drew & Passman, 1999). Numerical strategies are devised which can accurately handle the whole hierarchy and related stiffness, and rely on Suliciu's relaxation method as well as an asymptotic-preserving treatmen

  15. Hydrodynamics of a fixed camphor boat at the air-water interface

    NASA Astrophysics Data System (ADS)

    Singh, Dhiraj; Akella, Sathish; Singh, Ravi; Mandre, Shreyas; Bandi, Mahesh

    2015-11-01

    A camphor tablet, when introduced at the air-water interface undergoes sublimation and the camphor vapour spreads radially outwards across the surface. This radial spreading of camphor is due to Marangoni forces setup by the camphor concentration gradient. We report experiments on the hydrodynamics of this process for a camphor tablet held fixed at the air-water interface. During the initial transient, the time-dependent spread radius R (t) of camphor scales algebraically with time t (R (t) ~t 1 / 2) in agreement with empirical scalings reported for spreading of volatile oils on water surface. But unlike surfactants, the camphor stops spreading when the influx of camphor from the tablet onto the air-water interface is balanced by the outflux of camphor due to evaporation, and a steady-state condition is reached. The spreading camphor however, shears the underlying fluid and sets up bulk convective flow. We explain the coupled steady-state dynamics between the interfacial camphor spreading and bulk convective flow with a boundary layer approximation, supported by experimental evidence. This work was supported by the Collective Interactions Unit, OIST Graduate University.

  16. Generation of Bubbly Suspensions in Low Gravity

    NASA Technical Reports Server (NTRS)

    Nahra, Henry K.; Hoffmann, Monica I.; Hussey, Sam; Bell, Kimberly R.

    2000-01-01

    Generation of a uniform monodisperse bubbly suspension in low gravity is a rather difficult task because bubbles do not detach as easily as on Earth. Under microgravity, the buoyancy force is not present to detach the bubbles as they are formed from the nozzles. One way to detach the bubbles is to establish a detaching force that helps their detachment from the orifice. The drag force, established by flowing a liquid in a cross or co-flow configuration with respect to the nozzle direction, provides this additional force and helps detach the bubbles as they are being formed. This paper is concerned with studying the generation of a bubbly suspension in low gravity in support of a flight definition experiment titled "Behavior of Rapidly Sheared Bubbly Suspension." Generation of a bubbly suspension, composed of 2 and 3 mm diameter bubbles with a standard deviation <10% of the bubble diameter, was identified as one of the most important engineering/science issues associated with the flight definition experiment. This paper summarizes the low gravity experiments that were conducted to explore various ways of making the suspension. Two approaches were investigated. The first was to generate the suspension via a chemical reaction between the continuous and dispersed phases using effervescent material, whereas the second considered the direct injection of air into the continuous phase. The results showed that the reaction method did not produce the desired bubble size distribution compared to the direct injection of bubbles. However, direct injection of air into the continuous phase (aqueous salt solution) resulted in uniform bubble-diameter distribution with acceptable bubble-diameter standard deviation.

  17. Full-Volume, Three-Dimensional, Transient Measurements of Bubbly Flows Using Particle Tracking Velocimetry and Shadow Image Velocimetry Coupled with Pattern Recognition Techniques

    SciTech Connect

    Yassin Hassan

    2001-11-30

    Develop a state-of-the-art non-intrusive diagnostic tool to perform simultaneous measurements of both the temporal and three-dimensional spatial velocity of the two phases of a bubbly flow. These measurements are required to provide a foundation for studying the constitutive closure relations needed in computational fluid dynamics and best-estimate thermal hydraulic codes employed in nuclear reactor safety analysis and severe accident simulation. Such kinds of full-field measurements are not achievable through the commonly used point-measurement techniques, such as hot wire, conductance probe, laser Doppler anemometry, etc. The results can also be used in several other applications, such as the dynamic transport of pollutants in water or studies of the dispersion of hazardous waste.

  18. Bernoulli Suction Effect on Soap Bubble Blowing?

    NASA Astrophysics Data System (ADS)

    Davidson, John; Ryu, Sangjin

    2015-11-01

    As a model system for thin-film bubble with two gas-liquid interfaces, we experimentally investigated the pinch-off of soap bubble blowing. Using the lab-built bubble blower and high-speed videography, we have found that the scaling law exponent of soap bubble pinch-off is 2/3, which is similar to that of soap film bridge. Because air flowed through the decreasing neck of soap film tube, we studied possible Bernoulli suction effect on soap bubble pinch-off by evaluating the Reynolds number of airflow. Image processing was utilized to calculate approximate volume of growing soap film tube and the volume flow rate of the airflow, and the Reynolds number was estimated to be 800-3200. This result suggests that soap bubbling may involve the Bernoulli suction effect.

  19. Boundary Integral Technique for Explosion Bubble Collapse Analysis

    DTIC Science & Technology

    1993-08-01

    34 Applied Scientific Research, vol. 38, pp. 145-164, 1982a. 37 1p Prosperetti, A. "A Generalization of the Rayleigh Plesset Equation of Bubble Dynamics...Dispersed Two - Phase Flow." Journal of Multiphase Flow, vol. 10, no. 4, pp. 425-444, 1984. Prosperetti, A., and A. Lezzi. "Bubble Dynamics in a Compressible...oscillating system. This process is termed bubble pulsation. During the contraction phase of the bubble pulsation, variations in the surrounding fluid pressure

  20. Detailed flow and force measurements in a rotated triangular tube bundle subjected to two-phase cross-flow

    NASA Astrophysics Data System (ADS)

    Pettigrew, M. J.; Zhang, C.; Mureithi, N. W.; Pamfil, D.

    2005-05-01

    Two-phase cross-flow exists in many shell-and-tube heat exchangers. A detailed knowledge of the characteristics of two-phase cross-flow in tube bundles is required to understand and formulate flow-induced vibration parameters such as damping, fluidelastic instability, and random excitation due to turbulence. An experimental program was undertaken with a rotated-triangular array of cylinders subjected to air/water flow to simulate two-phase mixtures. The array is made of relatively large diameter cylinders (38 mm) to allow for detailed two-phase flow measurements between cylinders. Fiber-optic probes were developed to measure local void fraction. Local flow velocities and bubble diameters or characteristic lengths of the two-phase mixture are obtained by using double probes. Both the dynamic lift and drag forces were measured with a strain gauge instrumented cylinder.

  1. Rheology and microrheology of materials at the air-water interface

    NASA Astrophysics Data System (ADS)

    Walder, Robert Benjamin

    2008-10-01

    The study of materials at the air-water interface is an important area of research in soft condensed matter physics. Films at the air-water interface have been a system of interest to physics, chemistry and biology for the last 20 years. The unique properties of these surface films provide ideal models for 2-d films, surface chemistry and provide a platform for creating 2 dimensional analogue materials to cellular membranes. Measurements of the surface rheology of cross-linked F-actin networks associated with a lipid monolayer at the air-water interface of a Langmuir monolayer have been performed. The rheological measurements are made using a Couette cell. These data demonstrate that the network has a finite elastic modulus that grows as a function of the cross-linking concentration. We also note that under steady-state flow the system behaves as a power law fluid in which the effective viscosity decreases with imposed shear. A Langmuir monolayer trough that is equipped for simultaneous microrheology and standard rheology measurements has been constructed. The central elements are the trough itself with a full range of optical tools accessing the air-water interface from below the trough and a portable knife-edge torsion pendulum that can access the interface from above. The ability to simultaneously measure the mechanical response of Langmuir monolayers on very different length scales is an important step for our understanding of the mechanical response of two-dimensional viscoelastic networks. The optical tweezer microrheometer is used to study the micromechanical properties of Langmuir monolayers. Microrheology measurements are made a variety of surface pressures that correspond to different ordered phases of the monolayer. The complex shear modulus shows an order of magnitude increase for the liquid condensed phase of DPPC compared to the liquid expanded phase.

  2. Bubbling orientifolds

    NASA Astrophysics Data System (ADS)

    Mukhi, Sunil; Smedbäck, Mikael

    2005-08-01

    We investigate a class of 1/2-BPS bubbling geometries associated to orientifolds of type-IIB string theory and thereby to excited states of the SO(N)/Sp(N) Script N = 4 supersymmetric Yang-Mills theory. The geometries are in correspondence with free fermions moving in a harmonic oscillator potential on the half-line. Branes wrapped on torsion cycles of these geometries are identified in the fermi fluid description. Besides being of intrinsic interest, these solutions may also occur as local geometries in flux compactifications where orientifold planes are present to ensure global charge cancellation. We comment on the extension of this procedure to M-theory orientifolds.

  3. Bubble Growth in Lunar Basalts

    NASA Astrophysics Data System (ADS)

    Zhang, Y.

    2009-05-01

    Although Moon is usually said to be volatile-"free", lunar basalts are often vesicular with mm-size bubbles. The vesicular nature of the lunar basalts suggests that they contained some initial gas concentration. A recent publication estimated volatile concentrations in lunar basalts (Saal et al. 2008). This report investigates bubble growth on Moon and compares with that on Earth. Under conditions relevant to lunar basalts, bubble growth in a finite melt shell (i.e., growth of multiple regularly-spaced bubbles) is calculated following Proussevitch and Sahagian (1998) and Liu and Zhang (2000). Initial H2O content of 700 ppm (Saal et al. 2008) or lower is used and the effect of other volatiles (such as carbon dioxide, halogens, and sulfur) is ignored. H2O solubility at low pressures (Liu et al. 2005), concentration-dependent diffusivity in basalt (Zhang and Stolper 1991), and lunar basalt viscosity (Murase and McBirney 1970) are used. Because lunar atmospheric pressure is essentially zero, the confining pressure on bubbles is completely supplied by the overlying magma. Due to low H2O content in lunar basaltic melt (700 ppm H2O corresponds to a saturation pressure of 75 kPa), H2O bubbles only grow in the upper 16 m of a basalt flow or lake. A depth of 20 mm corresponds to a confining pressure of 100 Pa. Hence, vesicular lunar rocks come from very shallow depth. Some findings from the modeling are as follows. (a) Due to low confining pressure as well as low viscosity, even though volatile concentration is very low, bubble growth rate is extremely high, much higher than typical bubble growth rates in terrestrial melts. Hence, mm-size bubbles in lunar basalts are not strange. (b) Because the pertinent pressures are so low, bubble pressure due to surface tension plays a main role in lunar bubble growth, contrary to terrestrial cases. (c) Time scale to reach equilibrium bubble size increases as the confining pressure increases. References: (1) Liu Y, Zhang YX (2000) Earth

  4. Acoustic trapping in bubble-bounded micro-cavities

    NASA Astrophysics Data System (ADS)

    O'Mahoney, P.; McDougall, C.; Glynne-Jones, P.; MacDonald, M. P.

    2016-12-01

    We present a method for controllably producing longitudinal acoustic trapping sites inside microfluidic channels. Air bubbles are injected into a micro-capillary to create bubble-bounded `micro-cavities'. A cavity mode is formed that shows controlled longitudinal acoustic trapping between the two air/water interfaces along with the levitation to the centre of the channel that one would expect from a lower order lateral mode. 7 μm and 10 μm microspheres are trapped at the discrete acoustic trapping sites in these micro-cavities.We show this for several lengths of micro-cavity.

  5. Measurement of the Surface Dilatational Viscosity of an Insoluble Surfactant Monolayer at the Air/Water Interface Using a Pendant Drop Apparatus

    NASA Technical Reports Server (NTRS)

    Lorenzo, Jose; Couzis, Alex; Maldarelli, Charles; Singh, Bhim S. (Technical Monitor)

    2000-01-01

    When a fluid interface with surfactants is at rest, the interfacial stress is isotropic (as given by the equilibrium interfacial tension), and is described by the equation of state which relates the surface tension to the surfactant surface concentration. When surfactants are subjected to shear and dilatational flows, flow induced interaction of the surfactants; can create interfacial stresses apart from the equilibrium surface tension. The simplest relationship between surface strain rate and surface stress is the Boussinesq-Scriven constitutive equation completely characterized by three coefficients: equilibrium interfacial tension, surface shear viscosity, and surface dilatational viscosity Equilibrium interfacial tension and surface shear viscosity measurements are very well established. On the other hand, surface dilatational viscosity measurements are difficult because a flow which change the surface area also changes the surfactant surface concentration creating changes in the equilibrium interfacial tension that must be also taken into account. Surface dilatational viscosity measurements of existing techniques differ by five orders of magnitude and use spatially damped surface waves and rapidly expanding bubbles. In this presentation we introduce a new technique for measuring the surface dilatational viscosity by contracting an aqueous pendant drop attached to a needle tip and having and insoluble surfactant monolayer at the air-water interface. The isotropic total tension on the surface consists of the equilibrium surface tension and the tension due to the dilation. Compression rates are undertaken slow enough so that bulk hydrodynamic stresses are small compared to the surface tension force. Under these conditions we show that the total tension is uniform along the surface and that the Young-Laplace equation governs the drop shape with the equilibrium surface tension replaced by the constant surface isotropic stress. We illustrate this technique using

  6. Shear turbulence, Langmuir circulation and scalar transfer at an air-water interface

    NASA Astrophysics Data System (ADS)

    Hafsi, Amine; Tejada-Martinez, Andres; Veron, Fabrice

    2016-11-01

    DNS of an initially quiescent coupled air-water interface driven by an air-flow with free stream speed of 5 m/s generates gravity-capillary waves and small-scale (centimeter-scale) Langmuir circulation (LC) beneath the interface. In addition to LC, the waterside turbulence is characterized by shear turbulence with structures similar to classical "wall streaks" in wall-bounded flow. These streaks, denoted here as "shear streaks", consist of downwind-elongated vortices alternating in sign in the crosswind direction. The presence of interfacial waves causes interaction between these vortices giving rise to bigger vortices, namely LC. LES with momentum equation augmented with the Craik-Leibovich (C-L) vortex force is used to understand the roles of the shear streaks (i.e. the shear turbulence) and the LC in determining scalar flux from the airside to the waterside and vertical scalar transport beneath. The C-L force consists of the cross product between the Stokes drift velocity (induced by the interface waves) and the flow vorticity. It is observed that Stokes drift shear intensifies the shear streaks (with respect to flow without wave effects) leading to enhanced scalar flux at the air-water interface. LC leads to increased vertical scalar transport at depths below the interface.

  7. Armoring confined bubbles in concentrated colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Yu, Yingxian; Khodaparast, Sepideh; Stone, Howard

    2016-11-01

    Encapsulation of a bubble with microparticles is known to significantly improve the stability of the bubble. This phenomenon has recently gained increasing attention due to its application in a variety of technologies such as foam stabilization, drug encapsulation and colloidosomes. Nevertheless, the production of such colloidal armored bubble with controlled size and particle coverage ratio is still a great challenge industrially. We study the coating process of a long air bubble by microparticles in a circular tube filled with a concentrated microparticles colloidal suspension. As the bubble proceeds in the suspension of particles, a monolayer of micro-particles forms on the interface of the bubble, which eventually results in a fully armored bubble. We investigate the phenomenon that triggers and controls the evolution of the particle accumulation on the bubble interface. Moreover, we examine the effects of the mean flow velocity, the size of the colloids and concentration of the suspension on the dynamics of the armored bubble. The results of this study can potentially be applied to production of particle-encapsulated bubbles, surface-cleaning techniques, and gas-assisted injection molding.

  8. Slowing down bubbles with sound

    NASA Astrophysics Data System (ADS)

    Poulain, Cedric; Dangla, Remie; Guinard, Marion

    2009-11-01

    We present experimental evidence that a bubble moving in a fluid in which a well-chosen acoustic noise is superimposed can be significantly slowed down even for moderate acoustic pressure. Through mean velocity measurements, we show that a condition for this effect to occur is for the acoustic noise spectrum to match or overlap the bubble's fundamental resonant mode. We render the bubble's oscillations and translational movements using high speed video. We show that radial oscillations (Rayleigh-Plesset type) have no effect on the mean velocity, while above a critical pressure, a parametric type instability (Faraday waves) is triggered and gives rise to nonlinear surface oscillations. We evidence that these surface waves are subharmonic and responsible for the bubble's drag increase. When the acoustic intensity is increased, Faraday modes interact and the strongly nonlinear oscillations behave randomly, leading to a random behavior of the bubble's trajectory and consequently to a higher slow down. Our observations may suggest new strategies for bubbly flow control, or two-phase microfluidic devices. It might also be applicable to other elastic objects, such as globules, cells or vesicles, for medical applications such as elasticity-based sorting.

  9. Temperature measurements in cavitation bubbles

    NASA Astrophysics Data System (ADS)

    Coutier-Delgosha, Olivier

    2016-11-01

    Cavitation is usually a nearly isothermal process in the liquid phase, but in some specific flow conditions like hot water or cryogenic fluids, significant temperature variations are detected. In addition, a large temperature increase happens inside the cavitation bubbles at the very end of their collapse, due to the fast compression of the gas at the bubble core, which is almost adiabatic. This process is of primary interest in various biomedical and pharmaceutical applications, where the mechanisms of bubble collapse plays a major role. To investigate the amplitude and the spatial distribution of these temperature variations inside and outside the cavitation bubbles, a system based on cold wires has been developed. They have been tested in a configuration of a single bubble obtained by submitting a small air bubble to a large amplitude pressure wave. Some promising results have been obtained after the initial validation tests. This work is funded by the Office of Naval Research Global under Grant N62909-16-1-2116, Dr. Salahuddin Ahmed & Ki-Han Kim program managers.

  10. Bubble baths: just splashing around?

    NASA Astrophysics Data System (ADS)

    Robinson, Wesley; Speirs, Nathan; Sharker, Saberul Islam; Hurd, Randy; Williams, Bj; Truscott, Tadd

    2016-11-01

    Soap Bubbles on the water surface would seem to be an intuitive means for splash suppression, but their presence appears to be a double edged sword. We present on the water entry of hydrophilic spheres where the liquid surface is augmented by the presence of a bubble layer, similar to a bubble bath. While the presence of a bubble layer can diminish splashing upon impact at low Weber numbers, it also induces cavity formation at speeds below the critical velocity. The formation of a cavity generally results in larger Worthington jets and thus, larger amounts of ejected liquid. Bubble layers induce cavity formation by wetting the sphere prior to liquid impact, causing them to form cavities similar to those created by hydrophobic spheres. Droplets present on a pre-wetted sphere disrupt the flow of the advancing liquid during entry, pushing it away from the impacting body to form an entrained air cavity. This phenomena was noted by Worthington with pre-wetted stone marbles, and suggests that the application of a bubble layer is generally ineffective as a means of splash suppression.

  11. Electrolytic Bubble Growth on Pillared Arrays

    NASA Astrophysics Data System (ADS)

    Lee, Kenneth; Savas, Omer

    2013-11-01

    In current energy research, artificial photosynthetic (AP) devices are being designed to split water and harvest hydrogen gas using sunlight. In one such design, hydrogen gas bubbles evolve on catalytic surfaces of arrayed micropillars. If these bubbles are not promptly removed from the surface, they can adversely affect gas evolution rates, water flow rates, sunlight capture, and heat management of the system - all of which deteriorate device performance. Therefore, understanding how to remove evolved gas bubbles from the pillar surfaces is crucial. Flow visualization of electrolytic bubble nucleation and detachment from the catalytic pillar surfaces has been conducted. The bubble departure diameter and lift-off frequency are extracted and compared with known correlations from boiling heat transfer. Bubble tracking indicates that bubble detachment is enhanced by local interactions with neighboring bubbles. These observations suggest how hydrogen gas bubbles can be effectively removed from pillared surfaces to prolong AP device longevity. Joint Center for Artificial Photosynthesis, a U.S. Department of Energy (DOE) Energy Innovations Hub.

  12. Single Bubble Sonoluminescence

    NASA Astrophysics Data System (ADS)

    Farley, Jennifer; Hough, Shane

    2003-05-01

    Single Bubble Sonoluminescence is the emission of light from a single bubble suspended in a liquid caused by a continuum of repeated implosions due to pressure waves generated from a maintained ultrasonic sinusoidal wave source. H. Frenzel and H. Schultz first studied it in 1934 at the University of Cologne. It was not until 1988 with D.F. Gaitan that actual research began with single bubble sonoluminescence. Currently many theories exist attempting to explain the observed bubble phenomenon. Many of these theories require spherical behavior of the bubble. Observation of the bubble has shown that the bubble does not behave spherically in most cases. One explanation for this is known as jet theory. A spectrum of the bubble will give us the mean physical properties of the bubble such as temperature and pressure inside the bubble. Eventually, with the aide of fluorocene dye a full spectrum of the bubble will be obtained.

  13. External exposure to radionuclides in air, water, and soil

    SciTech Connect

    Eckerman, K.F.; Ryman, J.C.

    1996-05-01

    Federal Guidance Report No. 12 tabulates dose coefficients for external exposure to photons and electrons emitted by radionuclides distributed in air, water, and soil. The dose coefficients are intended for use by Federal Agencies in calculating the dose equivalent to organs and tissues of the body.

  14. Drainage of the air-water-quartz film: experiments and theory.

    PubMed

    Manica, Rogerio; Chan, Derek Y C

    2011-01-28

    Experimental results of the kinetics of drainage of the trapped water film between an approaching air bubble and a quartz plate have been analysed using recent theoretical advances in formulating and solving the flow problem in deformable films. Excellent agreement is obtained between experimental data and a model that assumes the bubble-water interface is tangentially immobile in its hydrodynamic response. The coupling between hydrodynamic pressure, disjoining pressure and film deformation is critical in determining the dynamic behaviour of the drainage process. The Reynolds parallel film model that omits the effects of film deformation predicts results that are qualitatively incorrect.

  15. Interfacial Charge Effects on Sticky Bubble Morphology in a Microchannel

    NASA Astrophysics Data System (ADS)

    Hui, Jonathan; Huang, Peter

    2015-11-01

    Many multiphase fluidic processes in small conduits, such as petroleum extraction and biochemical analysis, can encounter disastrous flow blockages due to the lodging of immiscible bubbles or droplets. The complete drainage of a thin-film lubrication layer surrounding an adhered bubble demands a significantly higher threshold pressure gradient in order to reinitiate bulk flows. In this work, we investigate bubble morphology due to the lubrication layer drainage process that results in bubble adhesion and study how an electrostatically charged bubble interface and charged channel wall may affect bubble morphology in preventing bubble adhesion. We report on our multiphysics computational analysis of an oversized gas bubble in a water-filled microchannel under the influence of surface tension and interfacial electrostatic forces. Acknowledgment is made to the Donors of the American Chemical Society Petroleum Research Fund for support of this research.

  16. Two-phase gas-liquid flow characteristics inside a plate heat exchanger

    SciTech Connect

    Nilpueng, Kitti; Wongwises, Somchai

    2010-11-15

    In the present study, the air-water two-phase flow characteristics including flow pattern and pressure drop inside a plate heat exchanger are experimentally investigated. A plate heat exchanger with single pass under the condition of counter flow is operated for the experiment. Three stainless steel commercial plates with a corrugated sinusoidal shape of unsymmetrical chevron angles of 55 and 10 are utilized for the pressure drop measurement. A transparent plate having the same configuration as the stainless steel plates is cast and used as a cover plate in order to observe the flow pattern inside the plate heat exchanger. The air-water mixture flow which is used as a cold stream is tested in vertical downward and upward flow. The results from the present experiment show that the annular-liquid bridge flow pattern appeared in both upward and downward flows. However, the bubbly flow pattern and the slug flow pattern are only found in upward flow and downward flow, respectively. The variation of the water and air velocity has a significant effect on the two-phase pressure drop. Based on the present data, a two-phase multiplier correlation is proposed for practical application. (author)

  17. Bubble Growth and Detachment from a Needle

    NASA Astrophysics Data System (ADS)

    Shusser, Michael; Rambod, Edmond; Gharib, Morteza

    1999-11-01

    The release of bubbles from an underwater nozzle or orifice occurs in large number of applications, such as perforated plate columns, blood oxygenators and various methods of water treatment. It is also a widely used method in laboratory research on multiphase flow and acoustics for generating small bubbles in a controlled fashion. We studied experimentally the growth and pinch-off of air bubbles released from a submerged needle into a quiescent liquid or a liquid flowing parallel to the needle. Micron-sized bubbles were generated by an air-liquid dispenser. High-speed imaging was performed to study the formation and detachment of bubbles from the tip of the needle. The impact of the needle diameter was investigated and the size and number of produced bubbles were assessed for different flow rates of air and for different velocities of the imposed upward liquid flow. The results were compared with available theoretical models and numerical computations. The existence of a critical gas flow rate and two regimes of bubble growth were verified.

  18. Bubble-driven inertial micropump

    NASA Astrophysics Data System (ADS)

    Torniainen, Erik D.; Govyadinov, Alexander N.; Markel, David P.; Kornilovitch, Pavel E.

    2012-12-01

    The fundamental action of the bubble-driven inertial micropump is investigated. The pump has no moving parts and consists of a thermal resistor placed asymmetrically within a straight channel connecting two reservoirs. Using numerical simulations, the net flow is studied as a function of channel geometry, resistor location, vapor bubble strength, fluid viscosity, and surface tension. Two major regimes of behavior are identified: axial and non-axial. In the axial regime, the drive bubble either remains inside the channel, or continues to grow axially when it reaches the reservoir. In the non-axial regime, the bubble grows out of the channel and in all three dimensions while inside the reservoir. The net flow in the axial regime is parabolic with respect to the hydraulic diameter of the channel cross-section, but in the non-axial regime it is not. From numerical modeling, it is determined that the net flow is maximal when the axial regime crosses over to the non-axial regime. To elucidate the basic physical principles of the pump, a phenomenological one-dimensional model is developed and solved. A linear array of micropumps has been built using silicon-SU8 fabrication technology that is used to manufacture thermal inkjet printheads. Semi-continuous pumping across a 2 mm-wide channel has been demonstrated experimentally. Measured net flow with respect to viscosity variation is in excellent agreement with simulation results.

  19. Two-phase flow interfacial structures in a rod bundle geometry

    NASA Astrophysics Data System (ADS)

    Paranjape, Sidharth S.

    Interfacial structure of air-water two-phase flow in a scaled nuclear reactor rod bundle geometry was studied in this research. Global and local flow regimes were obtained for the rod bundle geometry. Local two-phase flow parameters were measured at various axial locations in order to understand the transport of interfacial structures. A one-dimensional two-group interfacial area transport model was evaluated using the local parameter database. Air-water two-phase flow experiments were performed in an 8 X 8 rod bundle test section to obtain flow regime maps at various axial locations. Area averaged void fraction was measured using parallel plate type impedance void meters. The cumulative probability distribution functions of the signals from the impedance void meters were used along with a self organizing neural network to identify flow regimes. Local flow regime maps revealed the cross-sectional distribution of flow regimes in the bundle. Local parameters that characterize interfacial structure, that is, void fraction alpha, interfacial area concentration, ai, bubble Sauter mean diameter, DSm and bubble velocity, vg were measured using four sensor conductivity probe technique. The local data revealed the distribution of the interfacial structure in the radial direction, as well as its development in the axial direction. In addition to this, the effect of spacer grid on the flow structure at different gas and liquid velocities was revealed by local parameter measurements across the spacer grids. A two-group interfacial area transport equation (IATE) specific to rod bundle geometry was derived. The derivation of two-group IATE required certain assumption on the bubble shapes in the subchannels and the bubbles spanning more than a subchannel. It was found that the geometrical relationship between the volume and the area of a cap bubble distorted by rods was similar to the one derived for a confined channel under a specific geometrical transformation. The one

  20. Shapes of Bubbles and Drops in Motion.

    ERIC Educational Resources Information Center

    O'Connell, James

    2000-01-01

    Explains the shape distortions that take place in fluid packets (bubbles or drops) with steady flow motion by using the laws of Archimedes, Pascal, and Bernoulli rather than advanced vector calculus. (WRM)

  1. Acoustic bubble removal method

    NASA Technical Reports Server (NTRS)

    Trinh, E. H.; Elleman, D. D.; Wang, T. G. (Inventor)

    1983-01-01

    A method is described for removing bubbles from a liquid bath such as a bath of molten glass to be used for optical elements. Larger bubbles are first removed by applying acoustic energy resonant to a bath dimension to drive the larger bubbles toward a pressure well where the bubbles can coalesce and then be more easily removed. Thereafter, submillimeter bubbles are removed by applying acoustic energy of frequencies resonant to the small bubbles to oscillate them and thereby stir liquid immediately about the bubbles to facilitate their breakup and absorption into the liquid.

  2. Period-adding bifurcations and chaos in a bubble column.

    PubMed

    Piassi, Viviane S M; Tufaile, Alberto; Sartorelli, Jose Carlos

    2004-06-01

    We obtained period-adding bifurcations in a bubble formation experiment. Using the air flow rate as the control parameter in this experiment, the bubble emission from the nozzle in a viscous fluid undergoes from single bubbling to a sequence of periodic bifurcations of k to k+1 periods, occasionally interspersed with some chaotic regions. Our main assumption is that this period-adding bifurcation in bubble formation depends on flow rate variations in the chamber under the nozzle. This assumption was experimentally tested by placing a tube between the air reservoir and the chamber under the nozzle in the bubble column experiment. By increasing the tube length, more period-adding bifurcations were observed. We associated two main types of bubble growth to the flow rate fluctuations inside the chamber for different bubbling regimes. We also studied the properties of piecewise nonlinear maps obtained from the experimental reconstructed attractors, and we concluded that this experiment is a spatially extended system.

  3. Liquid jet pumped by rising gas bubbles

    NASA Technical Reports Server (NTRS)

    Hussain, N. A.; Siegel, R.

    1975-01-01

    A two-phase mathematical model is proposed for calculating the induced turbulent vertical liquid flow. Bubbles provide a large buoyancy force and the associated drag on the liquid moves the liquid upward. The liquid pumped upward consists of the bubble wakes and the liquid brought into the jet region by turbulent entrainment. The expansion of the gas bubbles as they rise through the liquid is taken into account. The continuity and momentum equations are solved numerically for an axisymmetric air jet submerged in water. Water pumping rates are obtained as a function of air flow rate and depth of submergence. Comparisons are made with limited experimental information in the literature.

  4. Phase-detection measurements in free-surface turbulent shear flows

    NASA Astrophysics Data System (ADS)

    Chanson, Hubert

    2016-04-01

    High-velocity self-aerated flows are described as ‘white waters’ because of the entrained air bubbles. The air entrainment induces a drastic change in the multiphase flow structure of the water column and this leads to significant bubble-turbulence interactions, turbulence modulation and associated mixing processes impacting on the bulk flow properties. In these high-velocity free-surface turbulent flows, the phase-detection needle probe is a most reliable instrumentation. The signal processing of a phase-detection probe is re-visited herein. It is shown that the processing may be performed on the raw probe signal as well as the thresholded data. The latter yields the time-averaged void fraction, the bubble count rate, the particle chord time distributions and the particle clustering properties within the particulate flow regions. The raw probe signal analysis gives further the auto-correlation time scale and the power spectrum density function. Finally dimensional considerations are developed with a focus on the physical modelling of free-surface flows in hydraulic structures. It is argued that the notion of scale effects must be defined in terms of some specific set of air-water flow properties within well-defined testing conditions, while a number of free-surface flow characteristics are more prone to scale effects than others, even in large-size physical facilities.

  5. The acoustic emissions of cavitation bubbles in stretched vortices.

    PubMed

    Chang, Natasha A; Ceccio, Steven L

    2011-11-01

    Pairs of unequal strength, counter-rotating vortices were produced in order to examine the inception, dynamics, and acoustic emission of cavitation bubbles in rapidly stretching vortices. The acoustic signatures of these cavitation bubbles were characterized during their inception, growth, and collapse. Growing and collapsing bubbles often produced a sharp, broadband, pop sound. The spectrum of these bubbles, and the peak resonant frequency can generally be related to quiescent flow bubble dynamics and corresponding resonant frequencies. However, some elongated cavitation bubbles produced a short tonal burst, or chirp, with frequencies on the order of a few kilohertz. Theses frequencies are too low to be related to resonant frequencies of a bubble in a quiescent flow. Instead, the frequency content of the acoustic signal during bubble inception and growth is related to the volumetric oscillations of the bubble while it interacted with vortical flow that surrounds the bubble (i.e., the resonant frequency of the vortex-bubble system). A relationship was determined between the observed peak frequency of the oscillations, the highly stretched vortex properties, and the water nuclei content. It was found that different cavitation spectra could relate to different flow and fluid properties and therefore would not scale in the same manner.

  6. Interfacial area, velocity and void fraction in two-phase slug flow

    SciTech Connect

    Kojasoy, G.; Riznic, J.R.

    1997-12-31

    The internal flow structure of air-water plug/slug flow in a 50.3 mm dia transparent pipeline has been experimentally investigated by using a four-sensor resistivity probe. Liquid and gas volumetric superficial velocities ranged from 0.55 to 2.20 m/s and 0.27 to 2.20 m/s, respectively, and area-averaged void fractions ranged from about 10 to 70%. The local distributions of void fractions, interfacial area concentration and interface velocity were measured. Contributions from small spherical bubbles and large elongated slug bubbles toward the total void fraction and interfacial area concentration were differentiated. It was observed that the small bubble void contribution to the overall void fraction was small indicating that the large slug bubble void fraction was a dominant factor in determining the total void fraction. However, the small bubble interfacial area contribution was significant in the lower and upper portions of the pipe cross sections.

  7. Forced convection heat transfer to air/water vapor mixtures

    NASA Technical Reports Server (NTRS)

    Richards, D. R.; Florschuetz, L. W.

    1986-01-01

    Heat transfer coefficients were measured using both dry air and air/water vapor mixtures in the same forced convection cooling test rig (jet array impingement configurations) with mass ratios of water vapor to air up to 0.23. The primary objective was to verify by direct experiment that selected existing methods for evaluation of viscosity and thermal conductivity of air/water vapor mixtures could be used with confidence to predict heat transfer coefficients for such mixtures using as a basis heat transfer data for dry air only. The property evaluation methods deemed most appropriate require as a basis a measured property value at one mixture composition in addition to the property values for the pure components.

  8. Thermodynamic and transport properties of air/water mixtures

    NASA Technical Reports Server (NTRS)

    Fessler, T. E.

    1981-01-01

    Subroutine WETAIR calculates properties at nearly 1,500 K and 4,500 atmospheres. Necessary inputs are assigned values of combinations of density, pressure, temperature, and entropy. Interpolation of property tables obtains dry air and water (steam) properties, and simple mixing laws calculate properties of air/water mixture. WETAIR is used to test gas turbine engines and components operating in relatively humid air. Program is written in SFTRAN and FORTRAN.

  9. 14 CFR 1274.926 - Clean Air-Water Pollution Control Acts.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 5 2011-01-01 2010-01-01 true Clean Air-Water Pollution Control Acts. 1274... AGREEMENTS WITH COMMERCIAL FIRMS Other Provisions and Special Conditions § 1274.926 Clean Air-Water Pollution Control Acts. Clean Air-Water Pollution Control Acts July 2002 If this cooperative agreement or...

  10. Spherical bubble motion in a turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Felton, Keith; Loth, Eric

    2001-09-01

    Monodisperse dilute suspensions of spherical air bubbles in a tap-water turbulent vertical boundary layer were experimentally studied to note their motion and distribution. Bubbles with diameters of 0.37-1.2 mm were injected at various transverse wall-positions for free-stream velocities between 0.4 and 0.9 m/s. The bubbles were released from a single injector at very low frequencies such that two-way coupling and bubble-bubble interaction were negligible. The experimental diagnostics included ensemble-averaged planar laser intensity profiles for bubble concentration distribution, as well as Cinematic Particle Image Velocimetry with bubble tracking for bubble hydrodynamic forces. A variety of void distributions within the boundary layer were found. For example, there was a tendency for bubbles to collect along the wall for higher Stokes number conditions, while the lower Stokes number conditions produced Gaussian-type profiles throughout the boundary layer. In addition, three types of bubble trajectories were observed—sliding bubbles, bouncing bubbles, and free-dispersion bubbles. Instantaneous liquid forces acting on individual bubbles in the turbulent flow were also obtained to provide the drag and lift coefficients (with notable experimental uncertainty). These results indicate that drag coefficient decreases with increasing Reynolds number as is conventionally expected but variations were observed. In general, the instantaneous drag coefficient (for constant bubble Reynolds number) tended to be reduced as the turbulence intensity increased. The averaged lift coefficient is higher than that given by inviscid theory (and sometimes even that of creeping flow theory) and tends to decrease with increasing bubble Reynolds number.

  11. Effective rheology of bubbles moving in a capillary tube.

    PubMed

    Sinha, Santanu; Hansen, Alex; Bedeaux, Dick; Kjelstrup, Signe

    2013-02-01

    We calculate the average volumetric flux versus pressure drop of bubbles moving in a single capillary tube with varying diameter, finding a square-root relation from mapping the flow equations onto that of a driven overdamped pendulum. The calculation is based on a derivation of the equation of motion of a bubble train, considering the capillary forces and the entropy production associated with the viscous flow. We also calculate the configurational probability of the positions of the bubbles.

  12. NOVEL METHODS FOR MEASURING AIR-WATER INTERFACIAL AREA IN UNSATURATED POROUS MEDIA

    PubMed Central

    Brusseau, Mark L.; Ouni, Asma El; Araujo, Juliana B.; Zhong, Hua

    2015-01-01

    Interfacial partitioning tracer tests (IPTT) are used to measure air-water interfacial area for unsaturated porous media. The standard IPTT method involves conducting tests wherein an aqueous surfactant solution is introduced into a packed column under unsaturated flow conditions. Surfactant-induced drainage has been observed to occur for this method in some cases, which can complicate data analysis and impart uncertainty to the measured values. Two novel alternative approaches for conducting IPTTs are presented herein that are designed in part to prevent surfactant-induced drainage. The two methods are termed the dual-surfactant IPTT (IPTT-DS) and the residual-air IPTT (IPTT-RA). The two methods were used to measure air-water interfacial areas for two natural porous media. System monitoring during the tests revealed no measurable surfactant-induced drainage. The measured interfacial areas compared well to those obtained with the standard IPTT method conducted in such a manner that surfactant-induced drainage was prevented. PMID:25732632

  13. Liquid jet pumped by rising gas bubbles

    NASA Technical Reports Server (NTRS)

    Hussain, N. A.; Siegel, R.

    1975-01-01

    From observations of a stream of gas bubbles rising through a liquid, a two-phase mathematical model is proposed for calculating the induced turbulent vertical liquid flow. The bubbles provide a large buoyancy force and the associated drag on the liquid moves the liquid upward. The liquid pumped upward consists of the bubble wakes and the liquid brought into the jet region by turbulent entrainment. The expansion of the gas bubbles as they arise through the liquid is taken into account. The continuity and momentum equations are solved numerically for an axisymmetric air jet submerged in water. Water pumping rates are obtained as a function of air flow rate and depth of submergence. Comparisons are made with limited experimental information in the literature.

  14. The Isolated Bubble Regime in Pool Nucleate Boiling

    NASA Technical Reports Server (NTRS)

    Buyevich, Y. A.; Webbon, Bruce W.; Callaway, Robert (Technical Monitor)

    1995-01-01

    We consider an isolated bubble boiling regime in which vapour bubbles are intermittently produced at a prearranged set of nucleation site on an upward facing overheated wall plane. In this boiling regime, the bubbles depart from the wall and move as separate entities. Except in the matter of rise velocity, the bubbles do not interfere and are independent of one another. However, the rise velocity is dependent on bubble volume concentration in the bulk. Heat transfer properties specific to this regime cannot be described without bubble detachment size, and we apply our previously developed dynamic theory of vapour bubble growth and detachment to determine this size. Bubble growth is presumed to be thermally controlled. Two limiting cases of bubble evolution are considered: the one in which buoyancy prevails in promoting bubble detachment and the one in which surface tension prevails. We prove termination of the isolated regime of pool nucleate boiling to result from one of the four possible causes, depending on relevant parameters values. The first cause consists in the fact that the upward flow of rising bubbles hampers the downward liquid flow, and under certain conditions, prevents the liquid from coming to the wall in an amount that would be sufficient to compensate for vapour removal from the wall. The second cause is due to the lateral coalescence of growing bubbles that are attached to their corresponding nucleation sites, with ensuing generation of larger bubbles and extended vapour patches near the wall. The other two causes involve longitudinal coalescence either 1) immediately in the wall vicinity, accompanied by the establishment of the multiple bubble boiling regime, or 2) in the bulk, with the formation of vapour columns. The longitudinal coalescence in the bulk is shown to be the most important cause. The critical wall temperature and the heat flux density associated with isolated bubble regime termination are found to be functions of the physical and

  15. How are soap bubbles blown? Fluid dynamics of soap bubble blowing

    NASA Astrophysics Data System (ADS)

    Davidson, John; Lambert, Lori; Sherman, Erica; Wei, Timothy; Ryu, Sangjin

    2013-11-01

    Soap bubbles are a common interfacial fluid dynamics phenomenon having a long history of delighting not only children and artists but also scientists. In contrast to the dynamics of liquid droplets in gas and gas bubbles in liquid, the dynamics of soap bubbles has not been well documented. This is possibly because studying soap bubbles is more challenging due to there existing two gas-liquid interfaces. Having the thin-film interface seems to alter the characteristics of the bubble/drop creation process since the interface has limiting factors such as thickness. Thus, the main objective of this study is to determine how the thin-film interface differentiates soap bubbles from gas bubbles and liquid drops. To investigate the creation process of soap bubbles, we constructed an experimental model consisting of air jet flow and a soap film, which consistently replicates the conditions that a human produces when blowing soap bubbles, and examined the interaction between the jet and the soap film using the high-speed videography and the particle image velocimetry.

  16. Experimental study on wake structure of single rising clean bubble

    NASA Astrophysics Data System (ADS)

    Sato, Ayaka; Takedomi, Yuta; Shirota, Minori; Sanada, Toshiyuki; Watanabe, Masao

    2007-11-01

    Wake structure of clean bubble rising in quiescent silicone oil solution of photochromic dye is experimentally studied. A single bubble is generated, immediately after UV sheet light illuminates the part of the liquid just above the bubble generation nozzle in order to activate photochromic dye. Once the bubble passes across the colored part of the liquid, the bubble is accompanied by some portion of activated dye tracers; hence the flow structure in the rear of the single rising bubble is visualized. We capture stereo images of both wake structure and bubble motion. We study how wake structure changes with the increase in bubble size. We observe the stable axisymmetric wake structure, which is called `standing eddy' when bubble size is relatively small, and then wake structure becomes unstable and starts to oscillate with the increase in bubble size. With further increase in bubble size, a pair of streamwise vortices, which is called `double thread', is observed. We discuss in detail this transition from the steady wake to unsteady wake structure, especially double thread wake development and hairpin vortices shedding, in relation to the transition from rectilinear to spiral or zigzag bubble motions.

  17. Sonoporation from Jetting Cavitation Bubbles

    PubMed Central

    Ohl, Claus-Dieter; Arora, Manish; Ikink, Roy; de Jong, Nico; Versluis, Michel; Delius, Michael; Lohse, Detlef

    2006-01-01

    The fluid dynamic interaction of cavitation bubbles with adherent cells on a substrate is experimentally investigated. We find that the nonspherical collapse of bubbles near to the boundary is responsible for cell detachment. High-speed photography reveals that a wall bounded flow leads to the detachment of cells. Cells at the edge of the circular area of detachment are found to be permanently porated, whereas cells at some distance from the detachment area undergo viable cell membrane poration (sonoporation). The wall flow field leading to cell detachment is modeled with a self-similar solution for a wall jet, together with a kinetic ansatz of adhesive bond rupture. The self-similar solution for the δ-type wall jet compares very well with the full solution of the Navier-Stokes equation for a jet of finite thickness. Apart from annular sites of sonoporation we also find more homogenous patterns of molecule delivery with no cell detachment. PMID:16950843

  18. Forces on ellipsoidal bubbles in a turbulent shear layer

    NASA Astrophysics Data System (ADS)

    Ford, Barry; Loth, Eric

    1998-01-01

    The objective of this research was to gain fundamental knowledge of the drag and lift forces on ellipsoidal air bubbles in water in a turbulent flow. This was accomplished by employing a cinematic two-phase particle image velocimetry (PIV) system to evaluate bubbly flow in a two-stream, turbulent, planar free shear layer of filtered tap water. Ellipsoidal air bubbles with nominal diameters from 1.5 to 4.5 mm were injected directly into the shear layer through a single slender tube. The cinematic PIV allowed for high resolution of the unsteady liquid velocity vector field. Triple-pulsed bubble images were obtained in a temporal sequence, such that the bubble size and bubble trajectory could be accurately determined. The bubble's oscillation characteristics, velocity, acceleration, and buoyancy force were obtained from the trajectory data. A bubble dynamic equation was then applied to allow determination of the time-evolving lift and drag forces acting upon bubbles within the shear layer. The results indicate that for a fixed bubble diameter (and fixed Bond and Morton numbers), the drag coefficient decreases for an increasing Reynolds number. This is fundamentally different than the increasing drag coefficient trend seen for ellipsoidal bubbles rising in quiescent baths for increasing diameter (and increasing Bond number), but is qualitatively consistent with the trend for spherical bubbles. A new empirical expression for the dependence of the drag coefficient on Reynolds number for air bubbles in tap water for both quiescent and turbulent flows is constructed herein. Finally, the instantaneous side forces measured in this study were dominated by the inherent deformation-induced vortex shedding of the bubble wake rather than the inviscid lift force based on the background fluid vorticity.

  19. Constrained Vapor Bubble

    NASA Technical Reports Server (NTRS)

    Huang, J.; Karthikeyan, M.; Plawsky, J.; Wayner, P. C., Jr.

    1999-01-01

    The nonisothermal Constrained Vapor Bubble, CVB, is being studied to enhance the understanding of passive systems controlled by interfacial phenomena. The study is multifaceted: 1) it is a basic scientific study in interfacial phenomena, fluid physics and thermodynamics; 2) it is a basic study in thermal transport; and 3) it is a study of a heat exchanger. The research is synergistic in that CVB research requires a microgravity environment and the space program needs thermal control systems like the CVB. Ground based studies are being done as a precursor to flight experiment. The results demonstrate that experimental techniques for the direct measurement of the fundamental operating parameters (temperature, pressure, and interfacial curvature fields) have been developed. Fluid flow and change-of-phase heat transfer are a function of the temperature field and the vapor bubble shape, which can be measured using an Image Analyzing Interferometer. The CVB for a microgravity environment, has various thin film regions that are of both basic and applied interest. Generically, a CVB is formed by underfilling an evacuated enclosure with a liquid. Classification depends on shape and Bond number. The specific CVB discussed herein was formed in a fused silica cell with inside dimensions of 3x3x40 mm and, therefore, can be viewed as a large version of a micro heat pipe. Since the dimensions are relatively large for a passive system, most of the liquid flow occurs under a small capillary pressure difference. Therefore, we can classify the discussed system as a low capillary pressure system. The studies discussed herein were done in a 1-g environment (Bond Number = 3.6) to obtain experience to design a microgravity experiment for a future NASA flight where low capillary pressure systems should prove more useful. The flight experiment is tentatively scheduled for the year 2000. The SCR was passed on September 16, 1997. The RDR is tentatively scheduled for October, 1998.

  20. Primary Particles from different bubble generation techniques

    NASA Astrophysics Data System (ADS)

    Butcher, A. C.; King, S. M.; Rosenoern, T.; Nilsson, E. D.; Bilde, M.

    2011-12-01

    Sea spray aerosols (SSA) are of major interest to global climate models due to large uncertainty in their emissions and ability to form Cloud Condensation Nuclei (CCN). In general, SSA are produced from wind breaking waves that entrain air and cause bubble bursting on the ocean surface. Preliminary results are presented for bubble generation, bubble size distribution, and CCN activity for laboratory generated SSA. In this study, the major processes of bubble formation are examined with respect to particle emissions. It has been suggested that a plunging jet closely resembles breaking wave bubble entrainment processes and subsequent bubble size distributions (Fuentes, Coe et al. 2010). Figure 1 shows the different particle size distributions obtained from the various bubble generation techniques. In general, frits produce a higher concentration of particles with a stronger bimodal particle size distribution than the various jet configurations used. The experiments consist of a stainless steel cylinder closed at both ends with fittings for aerosol sampling, flow connections for the recirculating jet, and air supply. Bubble generation included a recirculating jet with 16 mm or 4 mm nozzles, a stainless steel frit, or a ceramic frit. The chemical composition of the particles produced via bubble bursting processes has been probed using particle CCN activity. The CCN activity of sodium chloride, artificial sea salt purchased from Tropic Marin, and laboratory grade artificial sea salt (Kester, Duedall et al. 1967) has been compared. Considering the the limits of the shape factor as rough error bars for sodium chloride and bubbled sea salt, the CCN activity of artificial sea salt, Tropic Marin sea salt, and sodium chloride are not significantly different. This work has been supported by the Carlsberg Foundation.

  1. On the bubble rise velocity of a continually released bubble chain in still water and with crossflow

    NASA Astrophysics Data System (ADS)

    Wang, Binbin; Socolofsky, Scott A.

    2015-10-01

    The rise velocities of in-chain bubbles continually released from a single orifice in still water with and without crossflow are investigated in a series of laboratory experiments for wobbling ellipsoidal bubbles with moderate Reynolds number. For the limiting case in still water, that is, crossflow velocity = 0, the theoretical turbulent wake model correctly predicts the in-chain bubble rise velocity. In this case, the bubble rise velocities VB are enhanced compared to the terminal velocities of the isolated bubbles V0 due to wake drafting and are scaled with flow rate Q and bubble diameter D. Here, we also derive an updated wake model with consideration of the superposition of multiple upstream bubble wakes, which removes the nonlinear behavior of the non-distant (i.e., local) wake model. For the cases with crossflow, the enhancement of the in-chain bubble rise velocity can be significantly reduced, and imaging of the experiments shows very organized paring and grouping trajectories of rising bubbles not observed in still water under different crossflow velocities. The in-chain bubble rise velocities in crossflow are described by two models. First, an empirical model is used to correct the still-water equation for the crossflow effect. In addition, a semi-theoretical model considering the turbulent wake flow and the crossflow influence is derived and used to develop a theoretical normalization of bubble rise velocity, crossflow velocity, and the released bubble flow rate. The theoretical model suggests there are two different regimes of bubble-bubble interaction, with strong interaction occurring for the non-dimensional crossflow velocity Uc + = π Uc 3 D 3 V 0 / ( 18 g β Q 2 ) less than 0.06 and weaker interaction occurring for Uc + greater than 0.06, where Uc is the crossflow velocity, g is the acceleration of gravity, and β is the mixing length coefficient.

  2. Acoustic bubble traps

    NASA Astrophysics Data System (ADS)

    Geisler, Reinhard; Kurz, Thomas; Lauterborn, Werner

    2000-07-01

    A small, oscillating bubble in a liquid can be trapped in the antinode of an acoustic standing wave field. Bubble stability is required for the study of single bubble sonoluminescence (SBSL). The properties of the acoustic resonator are essential for the stable trapping of sonoluminescing bubbles. Resonators can be chosen according to the intended application: size and geometry can be varied in a wide range. In this work, the acoustic responses of different resonators were measured by means of holographic interferometry, hydrophones and a laser vibrometer. Also, high-speed photography was used to observe the bubble dynamics. Several single, stable sonoluminescent bubbles were trapped simultaneously within an acoustic resonator in the pressure antinodes of a higher harmonic mode (few bubble sonoluminescence, FBSL).

  3. Polydopamine Films from the Forgotten Air/Water Interface.

    PubMed

    Ponzio, Florian; Payamyar, Payam; Schneider, Anne; Winterhalter, Mathias; Bour, Jérôme; Addiego, Frédéric; Krafft, Marie-Pierre; Hemmerle, Joseph; Ball, Vincent

    2014-10-02

    The formation of polydopamine under mild oxidation conditions from dopamine solutions with mechanical agitation leads to the formation of films that can functionalize all kinds of materials. In the absence of stirring of the solution, we report the formation of polydopamine films at the air/water interface (PDA A/W) and suggest that it arises from an homogeneous nucleation process. These films grow two times faster than in solution and can be deposited on hydrophilic or hydrophobic substrates by the Langmuir-Schaeffer technique. Thanks to this new method, porous and hydrophobic materials like polytetrafluoroethylene (PTFE) membranes can be completely covered with a 35 nm thick PDA A/W film after only 3h of reaction. Finally the oxidation of a monomer followed by a polymerization in water is not exclusive to polydopamine since we also transferred polyaniline functional films from the air/water interface to solid substrates. These findings suggest that self-assembly from a solution containing hydrophilic monomers undergoing a chemical transformation (here oxidation and oligomerization) could be a general method to produce films at the liquid/air interface.

  4. Gas separation and bubble behavior at a woven screen

    NASA Astrophysics Data System (ADS)

    Conrath, Michael; Dreyer, Michael E.

    Gas-liquid two phase flows are widespread and in many applications the separation of both phases is necessary. Chemical reactors, water treatment devices or gas-free delivery of liquids like propellant are only some of them. We study the performance of a woven metal screen in respect to its phase separation behavior under static and dynamic conditions. Beside hydraulic screen resistance and static bubble point, our study also comprises the bubble detachment from the screen upon gas breakthrough. Since a woven screen is essentially an array of identical pores, analogies to bubble detachment from a needle can be established. While the bubble point poses an upper limit for pressurized gas at a wetted screen to preclude gas breakthrough, the necessary pressure for growing bubbles to detach from the screen pores a lower limit when breakthrough is already in progress. Based on that inside, the dynamic bubble point effects were constituted that relate to a trapped bubble at such a screen in liquid flow. A trapped is caused to break through the screen by the flow-induced pressure drop across it. Our model includes axially symmetric bubble shapes, degree of coverage of the screen and bubble pressurization due to hydraulic losses in the rest of the circuit. We have built an experiment that consists of a Dutch Twilled woven screen made of stainless steel in a vertical acrylic glass tube. The liquid is silicon oil SF0.65. The screen is suspended perpendicular to the liquid flow which is forced through it at variable flow rate. Controlled injection of air from a needle allows us to examine the ability of the screen to separate gas and liquid along the former mentioned effects. We present experimental data on static bubble point and detachment pressure for breakthrough at different gas supply rates that suggest a useful criterion for reliable static bubble point measurements. Results for the dynamic bubble point are presented that include i) screen pressure drop for different

  5. Dynamics of two interacting bubbles in a nonspherical ultrasound field.

    PubMed

    Liang, Jinfu; Wang, Xun; Yang, Jing; Gong, Lunxun

    2017-03-01

    In this paper, we present and analyze a model of the oscillations of a pair of gas bubbles driven by nonspherical ultrasound. We derived our model based on the perturbation and potential flow theories and use it to study three cases of oscillation of two bubbles under driving ultrasound with different initial phases, different separation distances between the bubbles and different sound pressure amplitudes. For the driving ultrasound with different initial phases, we obtain the in-phase and anti-phase radial pulsations of the bubbles in incompressible liquid. We also study the effect of the secondary Bjerknes force on the oscillation of bubbles separated by different relative distances. Lastly, we analyze the ratio of a nonspherical to a spherical partial quantity, and the results show that the bubbles survive longer with decreases in both the pressure amplitude of nonspherical ultrasound and the initial bubbles radii.

  6. Heat transfer and bubble dynamics in slurry bubble columns for Fischer-Tropsch clean alternative energy

    NASA Astrophysics Data System (ADS)

    Wu, Chengtian

    With the increasing demand for alternative energy resources, the Fischer-Tropsch (FT) process that converts synthesis gas into clean liquid fuels has attracted more interest from the industry. Slurry bubble columns are the most promising reactors for FT synthesis due to their advantages over other reactors. Successful operation, design, and scale-up of such reactors require detailed knowledge of hydrodynamics, bubble dynamics, and transport characteristics. However, most previous studies have been conducted at ambient pressure or covered only low superficial gas velocities. The objectives of this study were to experimentally investigate the heat transfer coefficient and bubble dynamics in slurry bubble columns at conditions that can mimic FT conditions. The air-C9C 11-FT catalysts/glass beads systems were selected to mimic the physical properties of the gas, liquid, and solid phases at commercial FT operating conditions. A heat transfer coefficient measurement technique was developed, and for the first time, this technique was applied in a pilot scale (6-inch diameter) high pressure slurry bubble column. The effects of superficial gas velocity, pressure, solids loading, and liquid properties on the heat transfer coefficients were investigated. Since the heat transfer coefficient can be affected by the bubble properties (Kumar et al., 1992), in this work bubble dynamics (local gas holdup, bubble chord length, apparent bubble frequency, specific interfacial area, and bubble velocity) were studied using the improved four-point optical probe technique (Xue et al., 2003; Xue, 2004). Because the four-point optical technique had only been successfully applied in a churn turbulent flow bubble column (Xue, 2004), this technique was first assessed in a small scale slurry bubble column in this study. Then the bubble dynamics were studied at the same conditions as the heat transfer coefficient investigation in the same pilot scale column. The results from four-point probe

  7. Denaturation resistance of beta-lactoglobulin in monomolecular films at the air-water interface.

    PubMed

    Lin, Jhih-Min; White, John W

    2009-10-29

    Using X-ray reflectometry we report strong differences in the denaturation response of beta-lactoglobulin adsorbed as a monomolecular film at the air-water interface from that observed in mixed denaturant/beta-lactoglobulin bulk solutions. Using the "flow trough" technique an isolated monomolecular film of the protein showed little change in structure when subjected to a 4.0 M guanidinium hydrochloride substrate. Unlike the bulk solution where a new protein layer structure appears, small changes in the protein packing and the roughness of the film are the only evidence of change. These parameters have been studied as a function of denaturant concentration and film quality. The strength of the response depends on the degree of perfection of the originally formed film; quickly formed films are more easily denatured. As the response is so subtle, possible interfering effects such as denaturant release of protein adsorbed on the trough have been quantified.

  8. Near-surface physics during convection affecting air-water gas transfer

    NASA Astrophysics Data System (ADS)

    Fredriksson, S. T.; Arneborg, L.; Nilsson, H.; Handler, R. A.

    2016-05-01

    The gas flux at the water surface is affected by physical processes including turbulence from wind shear, microscale wave breaking, large-scale breaking, and convection due to heat loss at the surface. The main route in the parameterizations of the gas flux has been to use the wind speed as a proxy for the gas flux velocity, indirectly taking into account the dependency of the wind shear and the wave processes. The interest in the contributions from convection processes has increased as the gas flux from inland waters (with typically lower wind and sheltered conditions) now is believed to play a substantial role in the air-water gas flux budget. The gas flux is enhanced by convection through the mixing of the mixed layer as well as by decreasing the diffusive boundary layer thickness. The direct numerical simulations performed in this study are shown to be a valuable tool to enhance the understanding of this flow configuration often present in nature.

  9. Numerical solution of axisymmetric, unsteady free-boundary problems at finite Reynolds number. I - Finite-difference scheme and its application to the deformation of a bubble in a uniaxial straining flow

    NASA Astrophysics Data System (ADS)

    Kang, I. S.; Leal, L. G.

    1987-07-01

    A numerical technique for solving axisymmetric, unsteady free-boundary problems in fluid mechanics is presented. This finite-difference method is a generalization of the steady algorithm reported by Ryskin and Leal (1984). In this scheme, all boundary surfaces of the solution domain at any time coincide exactly with a coordinate line of a numerically generated orthogonal coordinate system. Thus, unreasonable grid deformation during calculation is not a problem. A transient algorithm for applying the orthogonal mapping technique to unsteady free-boundary problems is developed. The unsteady deformation of a bubble in a uniaxial extensional flow for Reynolds numbers between 0.1 and 100 is considered as an example.

  10. Interaction of lithotripter shockwaves with single inertial cavitation bubbles.

    PubMed

    Klaseboer, Evert; Fong, Siew Wan; Turangan, Cary K; Khoo, Boo Cheong; Szeri, Andrew J; Calvisi, Michael L; Sankin, Georgy N; Zhong, Pei

    2007-01-01

    The dynamic interaction of a shockwave (modelled as a pressure pulse) with an initially spherically oscillating bubble is investigated. Upon the shockwave impact, the bubble deforms non-spherically and the flow field surrounding the bubble is determined with potential flow theory using the boundary-element method (BEM). The primary advantage of this method is its computational efficiency. The simulation process is repeated until the two opposite sides of the bubble surface collide with each other (i.e. the formation of a jet along the shockwave propagation direction). The collapse time of the bubble, its shape and the velocity of the jet are calculated. Moreover, the impact pressure is estimated based on water-hammer pressure theory. The Kelvin impulse, kinetic energy and bubble displacement (all at the moment of jet impact) are also determined. Overall, the simulated results compare favourably with experimental observations of lithotripter shockwave interaction with single bubbles (using laser-induced bubbles at various oscillation stages). The simulations confirm the experimental observation that the most intense collapse, with the highest jet velocity and impact pressure, occurs for bubbles with intermediate size during the contraction phase when the collapse time of the bubble is approximately equal to the compressive pulse duration of the shock wave. Under this condition, the maximum amount of energy of the incident shockwave is transferred to the collapsing bubble. Further, the effect of the bubble contents (ideal gas with different initial pressures) and the initial conditions of the bubble (initially oscillating vs. non-oscillating) on the dynamics of the shockwave-bubble interaction are discussed.

  11. Interaction of lithotripter shockwaves with single inertial cavitation bubbles

    PubMed Central

    Klaseboer, Evert; Fong, Siew Wan; Turangan, Cary K.; Khoo, Boo Cheong; Szeri, Andrew J.; Calvisi, Michael L.; Sankin, Georgy N.; Zhong, Pei

    2008-01-01

    The dynamic interaction of a shockwave (modelled as a pressure pulse) with an initially spherically oscillating bubble is investigated. Upon the shockwave impact, the bubble deforms non-spherically and the flow field surrounding the bubble is determined with potential flow theory using the boundary-element method (BEM). The primary advantage of this method is its computational efficiency. The simulation process is repeated until the two opposite sides of the bubble surface collide with each other (i.e. the formation of a jet along the shockwave propagation direction). The collapse time of the bubble, its shape and the velocity of the jet are calculated. Moreover, the impact pressure is estimated based on water-hammer pressure theory. The Kelvin impulse, kinetic energy and bubble displacement (all at the moment of jet impact) are also determined. Overall, the simulated results compare favourably with experimental observations of lithotripter shockwave interaction with single bubbles (using laser-induced bubbles at various oscillation stages). The simulations confirm the experimental observation that the most intense collapse, with the highest jet velocity and impact pressure, occurs for bubbles with intermediate size during the contraction phase when the collapse time of the bubble is approximately equal to the compressive pulse duration of the shock wave. Under this condition, the maximum amount of energy of the incident shockwave is transferred to the collapsing bubble. Further, the effect of the bubble contents (ideal gas with different initial pressures) and the initial conditions of the bubble (initially oscillating vs. non-oscillating) on the dynamics of the shockwave–bubble interaction are discussed. PMID:19018296

  12. Bubble formation in a quiescent pool of gold nanoparticle suspension.

    PubMed

    Vafaei, Saeid; Wen, Dongsheng

    2010-08-11

    This paper begins with an extensive review of the formation of gas bubbles, with a particular focus on the dynamics of triple lines, in a pure liquid and progresses into an experimental study of bubble formation on a micrometer-sized nozzle immersed in a quiescent pool of aqueous gold nanofluid. Unlike previous studies of triple line dynamics in a nanofluid under evaporation or boiling conditions, which are mainly caused by the solid surface modification due to particle sedimentation, this work focuses on the roles of nanoparticles suspended in the liquid phase. The experiments are conducted under a wide range of flow rates and nanoparticle concentrations, and many interesting phenomena are revealed. It is observed that nanofluids prevent the spreading of the triple line during bubble formation, i.e. the triple line is pinned somewhere around the middle of the tube wall during the rapid bubble formation stage whereas it spreads to the outer edge of the tube for pure water. A unique 'stick-slip' movement of the triple line is also observed for bubbles forming in nanofluids. At a given bubble volume, the radius of the contact line is found to be smaller for higher particle concentrations, but a reverse trend is found for the dynamic bubble contact angle. With the increase of particle concentration, the bubble frequency is raised and the bubble departure volume is decreased. The bubble shape is found to be in a good agreement with the prediction from Young-Laplace equation for given flow rates. The influence of nanoparticles on other detailed characteristics related to bubble growth inside, including the variation of bubble volume expansion rate, the radius of the curvature at the apex, the bubble height and bubble volume, is revealed. It is suggested that the variation of surface tensions and the resultant force balance at the triple line might be responsible for the modified dynamics of the triple line.

  13. Oscillating plasma bubbles. I. Basic properties and instabilities

    SciTech Connect

    Stenzel, R. L.; Urrutia, J. M.

    2012-08-15

    Plasma bubbles are created in an ambient discharge plasma. A bubble is a plasma volume of typically spherical shape, which is separated from the ambient plasma by a negatively biased grid of high transparency. Ions and electrons from the ambient plasma flow into the bubble volume. In steady state the flow of particles and currents is divergence-free, which is established by the plasma potential inside the bubble. The grid has two sheaths, one facing the ambient plasma, the other the bubble plasma. The inner sheath is observed to become unstable, causing the plasma potential in the bubble to oscillate. The instability arises from an excess of ions and a deficiency of electrons. Its frequency is in the range of the ion plasma frequency but depends on all parameters which influence the charge density in the sheath. When the grid voltage is very negative, electrons cannot enter the outer sheath, and the inner sheath becomes a virtual anode which reflects ions such that the bubble interior is empty. When an electron source is placed into the bubble it can neutralize the ions and the bubble refills. Without plasma sources or sinks the bubble plasma is extremely sensitive to perturbations by probes. Modified current-voltage characteristics of Langmuir and emissive probes are demonstrated. A sequence of papers first describes the basic steady-state properties, then the time evolution of bubbles, the effects of electron sources in bubbles, and the role of the grid and bubble geometry. The physics of plasma bubbles is important to several fields of basic plasma physics such as sheaths, sheath instabilities, diagnostic probes, electrostatic confinement, and current and space charge neutralization of beams.

  14. Acoustic Bubble Removal from Boiling Surfaces

    NASA Technical Reports Server (NTRS)

    Prosperetti, Andrea

    2002-01-01

    The object of the study was the investigation of the forces generated by standing acoustic waves on vapor bubbles, both far and near boundaries. In order to accomplish this objective, in view of the scarcity of publications on the topic, it has been necessary to build an edifice of knowledge about vapor bubbles in sound and flow fields from the ground up, as it were. We have addressed problems of gradually greater difficulty as follows: 1. In the first place, the physics of an stationary isolated bubble subject to a sound field in an unbounded liquid was addressed; 2. The case of bubbles translating in a stationary pressure field was then considered; 3. This was followed by a study of the combined effects of sound and translation, 4. And of a neighboring boundary 5. Finally, a new method to deal with nonspherical bubbles was developed- In addition to the work on vapor bubbles, some studies on gas bubbles were conducted in view of NASA's interest in the phenomenon of sonoluminescence.

  15. Production of Gas Bubbles in Reduced Gravity Environments

    NASA Technical Reports Server (NTRS)

    Oguz, Hasan N.; Takagi, Shu; Misawa, Masaki

    1996-01-01

    In a wide variety of applications such as waste water treatment, biological reactors, gas-liquid reactors, blood oxygenation, purification of liquids, etc., it is necessary to produce small bubbles in liquids. Since gravity plays an essential role in currently available techniques, the adaptation of these applications to space requires the development of new tools. Under normal gravity, bubbles are typically generated by forcing gas through an orifice in a liquid. When a growing bubble becomes large enough, the buoyancy dominates the surface tension force causing it to detach from the orifice. In space, the process is quite different and the bubble may remain attached to the orifice indefinitely. The most practical approach to simulating gravity seems to be imposing an ambient flow to force bubbles out of the orifice. In this paper, we are interested in the effect of an imposed flow in 0 and 1 g. Specifically, we investigate the process of bubble formation subject to a parallel and a cross flow. In the case of parallel flow, we have a hypodermic needle in a tube from which bubbles can be produced. On the other hand, the cross flow condition is established by forcing bubbles through an orifice on a wall in a shear flow. The first series of experiments have been performed under normal gravity conditions and the working fluid was water. A high quality microgravity facility has been used for the second type and silicone oil is used as the host liquid.

  16. Interfacial area and two-phase flow structure development measured by a double-sensor probe

    SciTech Connect

    Leung, Waihung; Revankar, S.T.; Ishii, Yoshihiko; Ishii, Mamoru.

    1992-06-01

    In this report, we studied the local phasic characters of dispersed flow regime both at the entrance and at the fully developed regions. Since the dispersed phase is distributed randomly in the medium and enclosed in relatively small interfaces, the phasic measurement becomes difficult to obtain. Local probe must be made with a miniaturized sensor in order to reduce the interface distortion. The double-sensor resistivity probe has been widely used in local void fraction and interface velocity measurements because the are small in comparison with the interfaces. It has been tested and proved to be an accurate local phasic measurement tool. In these experiments, a double-sensor probe was employed to measure the local void fraction and interface velocity in an air-water system. The test section was flow regime can be determined by visualization. Furthermore, local phasic measurements can be verified by photographic studies. We concentrated our study on the bubbly flow regime only. The local measurements were conducted at two axial locations, L/D = 8 and 60, in which the first measurement represents the entrance region where the flow develops, and the second measurement represents the fully developed flow region where the radial profile does not change as the flow moves along the axial direction. Four liquid flow rates were chosen in combination with four different gas injection rates. The superficial liquid velocities were j{sub t} = 1.0, 0.6,0.4, and 0.1 m/s and superficial gas velocities were j{sub g} = 0.0965, 0.0696, 0.0384, and 0.0192 m/s. These combinations put the two-phase flow well in the bubbly flow regime. In this sequence of phenomenological studies, the local void fraction, interface area concentration, sauter mean diameter, bubble velocity and bubble frequency were measured.

  17. Force Balance Model for Bubble Rise, Impact, and Bounce from Solid Surfaces.

    PubMed

    Manica, Rogerio; Klaseboer, Evert; Chan, Derek Y C

    2015-06-23

    A force balance model for the rise and impact of air bubbles in a liquid against rigid horizontal surfaces that takes into account effects of buoyancy and hydrodynamic drag forces, bubble deformation, inertia of the fluid via an added mass force, and a film force between the bubble and the rigid surface is proposed. Numerical solution of the governing equations for the position and velocity of the center of mass of the bubbles is compared against experimental data taken with ultraclean water. The boundary condition at the air-water interface is taken to be stress free, which is consistent for bubbles in clean water systems. Features that are compared include bubble terminal velocity, bubbles accelerating from rest to terminal speed, and bubbles impacting and bouncing off different solid surfaces for bubbles that have already or are yet to attain terminal speed. Excellent agreement between theory and experiments indicates that the forces included in the model constitute the main physical ingredients to describe the bouncing phenomenon.

  18. Exploring the mechanisms of rising bubbles in marine biofouling prevention

    NASA Astrophysics Data System (ADS)

    Menesses, Mark; Belden, Jesse; Dickenson, Natasha; Bird, James

    2015-11-01

    Fluid motion, such as flow past a ship, is known to inhibit the growth of marine biofouling. Bubbles rising along a submerged structure also exhibit this behavior, which is typically attributed to buoyancy induced flow. However, the bubble interface may also have a direct influence on inhibiting growth that is independent of the surrounding flow. Here we aim to decouple these two mechanisms through a combination of field and laboratory experiments. In this study, a wall jet and a stream of bubbles are used to create two flows near a submerged solid surface where biofouling occurs. The flow structure characteristics were recorded using PIV. This experimental analysis allows for us to compare the efficacy of each flow relative to its flow parameters. Exploration of the mechanisms at play in the prevention of biofouling by use of rising bubbles provides a foundation to predict and optimize this antifouling technique under various conditions.

  19. Shear characteristics, miscibility, and topography of sodium caseinate-monoglyceride mixed films at the air-water interface.

    PubMed

    Rodríguez Patino, Juan M; Carrera Sánchez, Cecilio

    2004-01-01

    In this contribution, we are concerned with the study of structure, topography, and surface rheological characteristics (under shear conditions) of mixed sodium caseinate and monoglycerides (monopalmitin and monoolein) at the air/water interface. Combined surface chemistry (surface film balance and surface shear rheometry) and microscopy (Brewster angle microscopy, BAM) techniques have been applied in this study to mixtures of insoluble lipids and sodium caseinate spread at the air-water interface. At a macroscopic level, sodium caseinate and monoglycerides form an heterogeneous and practically immiscible monolayer at the air-water interface. The images from BAM show segregated protein and monoglyceride domains that have different topography. At surface pressures higher than that for the sodium caseinate collapse, this protein is displaced from the interface by monoglycerides. These results and those derived from interfacial shear rheology (at a macroscopic level) appear to support the idea that immiscibility and heterogeneity of these emulsifiers at the interface have important repercussions on the shear characteristics of the mixed films, with the alternating flow of segregated monoglyceride domains (of low surface shear viscosity, etas) and protein domains (of high etas) across the canal.

  20. Motion of a bubble ring in a viscous fluid

    NASA Astrophysics Data System (ADS)

    Cheng, M.; Lou, J.; Lim, T. T.

    2013-06-01

    In this paper, lattice Boltzmann method was undertaken to study the dynamics of a vortex ring bubble (or bubble ring) in a viscous incompressible fluid. The study is motivated partly by our desire to assess whether a bubble ring keeps increasing its radius and decreasing its rise velocity as it rises through fluid as was predicted by Turner ["Buoyant vortex rings," Proc. R. Soc. London, Ser. A 239, 61 (1957)], 10.1098/rspa.1957.0022 and Pedley ["The toroidal bubble," J. Fluid Mech. 32, 97 (1968)], 10.1017/S0022112068000601, or does the ring like a rising bubble, eventually reaches a steady state where its radius and velocity remain constant as was predicted by Joseph et al. [Potential Flows of Viscous and Viscoelastic Fluids (Cambridge University Press, 2008)]. The parameters investigated included ring circulation, Reynolds number, density ratio and Bond number. Our numerical results show that a rising bubble ring increases its radius and decreases its velocity, but the process is interrupted by ring instability that eventually causes it to break up into smaller bubbles. This finding is consistent with the stability analysis by Pedley, who predicted that a bubble ring has a finite lifespan and is ultimately destroyed by surface tension instability. Furthermore, it is found that increasing initial circulation has a stabilizing effect on a bubble ring while increasing Reynolds number or Bond number hastens ring instability, resulting in an earlier break up into smaller bubbles; the number of bubbles depends on the wavenumber of the perturbation.

  1. Viscosity of bubble- and crystal- bearing magmas: Analogue results

    NASA Astrophysics Data System (ADS)

    Namiki, A.; Manga, M.

    2006-12-01

    Natural magmas often include both phenocrysts and bubbles. Such magmas can be regarded as suspensions including particles and bubbles and should have a viscosity different from the particle- and bubble- free melt. Viscosity is one of the key physical properties that affects eruption dynamics and magma flow. To understand the relation between the viscosity and the volume fraction of bubbles and particles, we directly measure the viscosity of suspensions with both particles and bubbles. Measurements are performed with the 4 degree cone-and-plate type rheometer (Thermo HAAKE Rheoscope 1), which allows us to observe the samples in situ during the measurement. The suspending fluid is corn syrup whose viscosity is 1.7 Pa·s at 23 °C. Particles are Techpolymer (polymethylmethacrylate) 40 μm diameter spheres. Bubbles are made by dissolving baking soda and citric acid; reaction between them generates carbon dioxide. No surfactant is added. The Peclet number is sufficiently large that Brownian motion does not influence our results. The measured viscosity for the suspensions with particles, and with both particles and bubbles, show strong shear thinning. The measured viscosities during increasing and decreasing shear rate differ from each other, indicating that the microstructure is modified by flow. When the deformation of bubbles is not significant, the measured viscosity with bubbles is higher than that without bubbles, and vice versa.

  2. Instability of a water-spout flow

    NASA Astrophysics Data System (ADS)

    Carrión, Luis; Herrada, Miguel A.; Shtern, Vladimir N.

    2016-03-01

    The paper studies the linear stability of a steady axisymmetric air-water motion in a vertical sealed cylinder, driven by the rotating top disk, motivated by possible applications in aerial bioreactors. As the flow strength Re increases, a vortex breakdown bubble (VBB) emerges near the bottom center and expands toward the interface. Regions of clockwise meridional circulation of air and water become separated by a thin anticlockwise circulation layer (TCL) adjacent to the interface in water. This study reveals that instability develops for larger Re than those at which VBB and TCL emerge. The instability focuses in the air region being typically of shear-layer type. The instability is centrifugal if the air volume fraction is small.

  3. Reynolds and froude number effect on the flow past an interface-piercing circular cylinder

    NASA Astrophysics Data System (ADS)

    Koo, Bonguk; Yang, Jianming; Yeon, Seong Mo; Stern, Frederick

    2014-09-01

    The two-phase turbulent flow past an interface-piercing circular cylinder is studied using a high-fidelity orthogonal curvilinear grid solver with a Lagrangian dynamic subgrid-scale model for large-eddy simulation and a coupled level set and volume of fluid method for air-water interface tracking. The simulations cover the sub-critical and critical and post critical regimes of the Reynolds and sub and super-critical Froude numbers in order to investigate the effect of both dimensionless parameters on the flow. Significant changes in flow features near the air-water interface were observed as the Reynolds number was increased from the sub-critical to the critical regime. The interface makes the separation point near the interface much delayed for all Reynolds numbers. The separation region at intermediate depths is remarkably reduced for the critical Reynolds number regime. The deep flow resembles the single-phase turbulent flow past a circular cylinder, but includes the effect of the free-surface and the limited span length for sub-critical Reynolds numbers. At different Froude numbers, the air-water interface exhibits significantly changed structures, including breaking bow waves with splashes and bubbles at high Froude numbers. Instantaneous and mean flow features such as interface structures, vortex shedding, Reynolds stresses, and vorticity transport are also analyzed. The results are compared with reference experimental data available in the literature. The deep flow is also compared with the single-phase turbulent flow past a circular cylinder in the similar ranges of Reynolds numbers. Discussion is provided concerning the limitations of the current simulations and available experimental data along with future research

  4. Powder wettability at a static air-water interface.

    PubMed

    Dupas, Julien; Forny, Laurent; Ramaioli, Marco

    2015-06-15

    The reconstitution of a beverage from a dehydrated powder involves several physical mechanisms that determine the practical difficulty to obtain a homogeneous drink in a convenient way and within an acceptable time for the preparation of a beverage. When pouring powder onto static water, the first hurdle to overcome is the air-water interface. We propose a model to predict the percentage of powder crossing the interface in 45 s, namely the duration relevant for this application. We highlight theoretically the determinant role of the contact angle and of the particle size distribution. We validate experimentally the model for single spheres and use it to predict the wettability performance of commercial food powders for different contact angles and particles sizes. A good agreement is obtained when comparing the predictions and the wettability of the tested powders.

  5. Reacting chemistry at the air-water interface

    NASA Astrophysics Data System (ADS)

    Murakami, Tomoyuki; Morgan, Thomas; Huwel, Lutz; Graham, William

    2016-09-01

    Plasma interaction with gas-liquid interfaces is becoming increasingly important in biological applications, chemical analysis and medicine. It introduces electrons, new ionic species and reactive species and contributes to chemical and electrical self-organization at the interface. To provide insight into the associated physics and chemistry at work in the evolution of the plasma in the air-water interface (AWI), a time-dependent one-dimensional modelling has been developed. The numerical simulation is used to solve the kinetic equations and help identify the important reaction mechanisms and describe the phenomena associated with hundreds of reacting pathways in gas-phase and liquid-phase AWI chemistry. This work was partly supported by JSPS KAKENHI Grant Number 16K04998.

  6. Unsteady thermocapillary migration of bubbles

    NASA Technical Reports Server (NTRS)

    Dill, Loren H.; Balasubramaniam, R.

    1988-01-01

    Upon the introduction of a gas bubble into a liquid possessing a uniform thermal gradient, an unsteady thermo-capillary flow begins. Ultimately, the bubble attains a constant velocity. This theoretical analysis focuses upon the transient period for a bubble in a microgravity environment and is restricted to situations wherein the flow is sufficiently slow such that inertial terms in the Navier-Stokes equation and convective terms in the energy equation may be safely neglected (i.e., both Reynolds and Marangoni numbers are small). The resulting linear equations were solved analytically in the Laplace domain with the Prandtl number of the liquid as a parameter; inversion was accomplished numerically using a standard IMSL routine. In the asymptotic long-time limit, the theory agrees with the steady-state theory of Young, Goldstein, and Block. The theory predicts that more than 90 percent of the terminal steady velocity is achieved when the smallest dimensionless time, i.e., the one based upon the largest time scale-viscous or thermal-equals unity.

  7. Tightrope walking bubbles

    NASA Astrophysics Data System (ADS)

    de Maleprade, Helene; Clanet, Christophe; Quere, David

    2016-11-01

    A fiber can hold a certain amount of liquid, which allows us to capture flying drops and control their motion. Immersed in water, a fiber can efficiently capture air bubbles only if it is hydrophobic. Using a superhydrophobic coating on an inclined wire, we experimentally control the rising velocity of air bubbles walking along the tightrope. We discuss the nature of the friction around the walker, and the resulting speed of bubbles.

  8. ISSUES IN SIMULATING ELEMENTAL MERCURY AIR/WATER EXCHANGE AND AQUEOUS MONOMETHYLMERCURY SPECIATION

    EPA Science Inventory

    This presentation focuses on two areas relevant to assessing the global fate and bioavailability of mercury: elemental mercury air/water exchange and aqueous environmental monomethylmercury speciation.

  9. [Virus adsorption from batch experiments as influenced by air-water interface].

    PubMed

    Zhang, Hui; Zhao, Bing-zi; Zhang, Jia-bao; Zhang, Cong-zhi; Wang, Qiu-ying; Chen, Ji

    2007-12-01

    The presence of air-water interface in batch sorption experiments may result in inaccurate estimation of virus adsorption onto various soils. A batch sorption experiment was conducted to compare the adsorption results of MS2 in different soils under presence/absence of air-water interface. Soils with sterilization/nonterilization treatment were used. Virus recovery efficiency in a blank experiment (no soil) was also evaluated as affected by different amount of air-water interface. The presence of air-water interface altered the results of virus adsorption in different soils with different extent, with Sandy fluvo-aquic soil being the most considerably affected, followed by Red loam soil, and the least being Red clay soil, probably because of different soil properties associated with virus adsorption/inactivation. Soil sterilization resulted in more significant difference of virus adsorption onto the Sandy fluvo-aquic soil between the presence and absence of air-water interface, while a reduced difference was observed in the Red loam soil. The presence of air-water interface significantly decreased virus recovery efficiency, with the values being decreased with increase in the amount of air-water interface. Soil particles likely prohibit viruses from reaching the air-water interface or alter the forces at the solid-water-air interface so that the results from the blank experiment did not truly represent results from control blank, which probably resulted in adsorption difference between presence and absence of the air-water interface.

  10. Analysis of the three-dimensional structure of a bubble wake using PIV and Galilean decomposition

    SciTech Connect

    Hassan, Y.A.; Schmidl, W.D.; Ortiz-Villafuerte, J.; Scharf, J.R.

    1999-07-01

    Bubbly flow plays a key role in a variety of natural and industrial processes. An accurate and complete description of the phase interactions in two-phase bubbly flow is not available at this time. These phase interactions are, in general, always three-dimensional and unsteady. Therefore, measurement techniques utilized to obtain qualitative and quantitative data from two-phase flow should be able to acquire transient and three-dimensional data, in order to provide information to test theoretical models and numerical simulations. Even for dilute bubble flows, in which bubble interaction is at a minimum, the turbulent motion of the liquid generated by the bubble is yet to be completely understood. For many years, the design of systems with bubbly flows was based primarily on empiricism. Dilute bubbly flows are an extension of single bubble dynamics, and therefore improvements in the description and modeling of single bubble motion, the flow field around the bubble, and the dynamical interactions between the bubble and the flow will consequently improve bubbly flow modeling. The improved understanding of the physical phenomena will have far-reaching benefits in upgrading the operation and efficiency of current processes and in supporting the development of new and innovative approaches. A stereoscopic particle image velocimetry measurement of the flow generated by the passage of a single air-bubble rising in stagnant water, in a circular pipe is presented. Three-dimensional velocity fields within the measurement zone were obtained. Ensemble-averaged instantaneous velocities for a specific bubble path were calculated and interpolated to obtain mean three-dimensional velocity fields. A Galilean velocity decomposition is used to study the vorticity generated in the flow.

  11. Bacterial Inactivation by a Singlet Oxygen Bubbler: Identifying Factors Controlling the Toxicity of 1O2 Bubbles

    PubMed Central

    Bartusik, Dorota; Aebisher, David; Lyons, Alan

    2013-01-01

    A microphotoreactor device was developed to generate bubbles (sized: 1.4 mm diameter, 90 μL) containing singlet oxygen at levels toxic to bacteria and fungus. As singlet oxygen decays rapidly to triplet oxygen, the bubbles leave behind no waste or by-products other than O2. From a comparative study in deaerated, air saturated, and oxygenated solutions, it was reasoned that the singlet oxygen bubbles inactivate Escherichia coli and Aspergillus fumigatus, mainly by an oxygen gradient inside and outside of the bubble such that singlet oxygen is solvated and diffuses through the aqueous solution until it reacts with the target organism. Thus, singlet oxygen bubble toxicity was inversely proportional to the amount of dissolved oxygen in solution. In a second mechanism, singlet oxygen interacts directly with E. coli that accumulate at the gas-liquid interface although this mechanism operates at a rate approximately 10 times slower. Due to encapsulation in the gaseous core of the bubble and a 0.98 ms lifetime, the bubbles can traverse relatively long 0.39 mm distances carrying 1O2 far into the solution; by comparison the diffusion distance of 1O2 fully solvated in H2O is much shorter (~150 nm). Bubbles that reached the outer air/water interface contained no 1O2. The mechanism by which 1O2 deactivated organisms was explored through the addition of detergent molecules and Ca2+ ions. Results indicate that the preferential accumulation of E. coli at the air-water interface of the bubble leads to enhanced toxicity of bubbles containing 1O2. The singlet oxygen device offers intriguing possibilities for creating new types of disinfection strategies based on photodynamic (1O2) bubble carriers. PMID:23075418

  12. Air-water CO2 exchange in five hypereutrophic lakes in Bangalore, India

    NASA Astrophysics Data System (ADS)

    Singh, G.; Ghosh, P.; Bala, G.; Bastviken, D.

    2014-12-01

    Inland water bodies play a significant role in terrestrial carbon cycling, rather than being just conduits for the transport of terrestrial carbon to the oceans. Recent syntheses estimate that freshwaters emit substantial amounts of CO2 (1.4 Pg C yr-1) (Tranvik et al. 2009) and CH4 (0.65 Pg C yr-1) (Bastviken et al. 2011), which are similar in magnitude to the global terrestrial carbon sink (2.5 ± 1.7 Pg C yr-1) (IPCC 2013). However, eutrophic waters, which constitute the majority of the global freshwater supply (ILEC/UNEP 1994, Liu et al. 2012, Carpenter et al. 1998), are vastly underrepresented in these estimates. These waters, due to high primary productivity leading to CO2 undersaturation, can act as sinks rather than sources of CO2, thus reversing the role of lakes in the carbon cycle (Balmer and Downing 2011, Pacheco et al. 2013). We are investigating the air-water CO2 exchange of five hypereutrophic lakes in urban Bangalore using a novel Non-Dispersive Infrared (NDIR)-based CO2 sensor installed in flux chambers that can be used to measure CO2 exchange in lakes in situ. This work is a part of a larger study called Bangalore Carbon Mapping Study that aims to track the spatial flows of carbon in an urban area of a developing country. Preliminary observations reveal that these lakes absorb CO2 during the photosynthetic hours, at an average rate of 3.4 mg C m-2 h-1. The ongoing study will characterize the complete diurnal cycle of CO2 exchange, its variation over different seasons, and its relationships with various limnological and catchment characteristics. The flux estimates thus produced will also be compared with those predicted by the current models for air-water gas exchange based on wind speed.

  13. Prospects for bubble fusion

    SciTech Connect

    Nigmatulin, R.I.; Lahey, R.T. Jr.

    1995-09-01

    In this paper a new method for the realization of fusion energy is presented. This method is based on the superhigh compression of a gas bubble (deuterium or deuterium/thritium) in heavy water or another liquid. The superhigh compression of a gas bubble in a liquid is achieved through forced non-linear, non-periodic resonance oscillations using moderate amplitudes of forcing pressure. The key feature of this new method is a coordination of the forced liquid pressure change with the change of bubble volume. The corresponding regime of the bubble oscillation has been called {open_quotes}basketball dribbling (BD) regime{close_quotes}. The analytical solution describing this process for spherically symmetric bubble oscillations, neglecting dissipation and compressibility of the liquid, has been obtained. This solution shown no limitation on the supercompression of the bubble and the corresponding maximum temperature. The various dissipation mechanisms, including viscous, conductive and radiation heat losses have been considered. It is shown that in spite of these losses it is possible to achieve very high gas bubble temperatures. This because the time duration of the gas bubble supercompression becomes very short when increasing the intensity of compression, thus limiting the energy losses. Significantly, the calculated maximum gas temperatures have shown that nuclear fusion may be possible. First estimations of the affect of liquid compressibility have been made to determine possible limitations on gas bubble compression. The next step will be to investigate the role of interfacial instability and breaking down of the bubble, shock wave phenomena around and in the bubble and mutual diffusion of the gas and the liquid.

  14. Acoustical bubble trapper applied to hemodialysis.

    PubMed

    Palanchon, P; Birmelé, B; Tranquart, F

    2008-04-01

    Gaseous microemboli can arise in extracorporeal lines and devices such as dialysis machines. They are associated with severe pulmonary side effects in patients undergoing chronic hemodialysis sessions. The goal of this study was to develop a gaseous emboli trapper using ultrasound waves to remove any air bubble from the tubing system before they reach the patient. A homemade bubble trapper, developed in the laboratory, consists of a Perspex block containing a main channel connected to the tubing of a hemodialysis machine and a second subchannel positioned perpendicularly to the main one, used to trap the air microemboli. The microemboli flowing in the main channel were insonified through an acoustic window with an ultrasound wave, at a frequency of 500 kHz and with a maximal acoustic pressure of 500 kPa, generated by a single-element transducer positioned 3 cm away from the main flow. The radiation force induced by the ultrasound beam acts directly on the flowing air emboli, by pushing them into the subchannel. Two Doppler probes operating both at 2 MHz, connected to a DWL Doppler machine were placed before and after the bubble trapper to count sequentially the number of embolic events. The flow of the machine was varied between 200 mL/min and 500 mL/min. Depending on the flow velocity, the number of microembolic signals (MES) detected by the Doppler probes before and after the trapping system was identical and ranged from 5 to 150 MES/min in absence of the ultrasound irradiation. When the air bubble trapper was activated, a reduction of the number of MES, up to 70%, was achieved. Doppler recordings suggest that the circulating bubbles were either fragmented into smaller bubble fragments or directly got pushed into the second subchannel where they were collected. This simple approach using an ultrasound-based trapping system was shown to operate adequately with the current settings and can be used to filter air microemboli.

  15. Proceedings of the Second International Colloquium on Drops and Bubbles

    NASA Technical Reports Server (NTRS)

    Lecroissette, D. H. (Editor)

    1982-01-01

    Applications of bubble and drop technologies are discussed and include: low gravity manufacturing, containerless melts, microballoon fabrication, ink printers, laser fusion targets, generation of organic glass and metal shells, and space processing. The fluid dynamics of bubbles and drops were examined. Thermomigration, capillary flow, and interfacial tension are discussed. Techniques for drop control are presented and include drop size control and drop shape control.

  16. Axisymmetric bubble pinch-off at high Reynolds numbers.

    PubMed

    Gordillo, J M; Sevilla, A; Rodríguez-Rodríguez, J; Martínez-Bazán, C

    2005-11-04

    Analytical considerations and potential-flow numerical simulations of the pinch-off of bubbles at high Reynolds numbers reveal that the bubble minimum radius, rn, decreases as tau proportional to r2n sqrt[1lnr2n], where tau is the time to break up, when the local shape of the bubble near the singularity is symmetric. However, if the gas convective terms in the momentum equation become of the order of those of the liquid, the bubble shape is no longer symmetric and the evolution of the neck changes to a rn proportional to tau1/3 power law. These findings are verified experimentally.

  17. An active bubble trap and debubbler for microfluidic systems.

    PubMed

    Skelley, Alison M; Voldman, Joel

    2008-10-01

    We present a novel, fully integrated microfluidic bubble trap and debubbler. The 2-layer structure, based on a PDMS valve design, utilizes a featured membrane to stop bubble progression through the device. A pneumatic chamber directly above the trap is evacuated, and the bubble is pulled out through the gas-permeable PDMS membrane. Normal device operation, including continuous flow at atmospheric pressure, is maintained during the entire trapping and debubbling process. We present a range of trap sizes, from 2 to 10 mm diameter, and can trap and remove bubbles up to 25 microL in under 3 h.

  18. Effects of Gravity on Bubble Formation at a Plate Orifice

    NASA Technical Reports Server (NTRS)

    Webbon, Bruce W.; Buyevich, Yu A.

    1995-01-01

    A model of the dynamic regime of gas injection through a submerged plate orifice into an ideally wetting liquid is developed in the circumstance when successively detached bubbles may be regarded as independent objects. Two major factors favor bubble detachment: the buoyancy force and a force due to the momentum inflow into the bubble with injected gas. In normal and moderately reduced gravity, the first factor dominates. At relatively low flow rates, a growing bubble is modeled as a spherical segment touching the orifice perimeter during the whole period of its evolution till detachment. If the flow rate exceeds a critical value, another stage of bubble evolution occurs in which an almost spherical gas envelope is connected with the orifice by a nearly cylindrical gaseous stem that lengthens as the bubble rises above the plate. The bubble continues to grow until the gas supply through the stem is completely cut off, after which back flow of gas into the stem from the bubble becomes possible. In microgravity, the second factor prevails, and the latter stage is always present irrespective of the flow rate. However, the gas envelope rises and the stem lengthens very slowly. This difference in the underlying physical mechanisms provides for key properties of bubble growth and detachment being drastically different in appreciable and sufficiently reduced gravity. The frequency of bubble formation slightly decreases with and the detachment volume is almost proportional to the gas flow rate in the first case, in accordance with familiar relations. In the second case, the first variable is proportional to the flow rate whereas the second one is independent of it. Effects of other parameters, such as the orifice radius, gas and liquid densities, and surface tension are discussed.

  19. Acoustical emission from bubbles

    NASA Astrophysics Data System (ADS)

    Longuet-Higgins, Michael S.

    1991-12-01

    The scientific objectives of this report are to investigate the dynamics of bubbles formed from a free surface (particularly the upper surface of the ocean) by breaking waves, and the resulting emission of underwater sound. The chief natural source of underwater sound in the ocean at frequencies from 0.5 to 50 kHz is known to be the acoustical emission from newly-formed bubbles and bubble clouds, particularly those created by breaking waves and rain. Attention has been drawn to the occurrence of high-speed jets directed into the bubble just after bubble closure. They have been observed both in rain-drop impacts and in the release of bubbles from an underwater nozzle. Qualitatively they are similar to the inward jets seen in the collapse of a cavitation bubble. There is also a similarity to the highly-accelerated upward jets in standing water waves (accelerations greater than 20g) or in bubbles bursting at a free surface. We have adopted a theoretical approach based on the dynamics of incompressible fluids with a free surface.

  20. Evaporation, Boiling and Bubbles

    ERIC Educational Resources Information Center

    Goodwin, Alan

    2012-01-01

    Evaporation and boiling are both terms applied to the change of a liquid to the vapour/gaseous state. This article argues that it is the formation of bubbles of vapour within the liquid that most clearly differentiates boiling from evaporation although only a minority of chemistry textbooks seems to mention bubble formation in this context. The…

  1. Let Them Blow Bubbles.

    ERIC Educational Resources Information Center

    Korenic, Eileen

    1988-01-01

    Describes a series of activities and demonstrations involving the science of soap bubbles. Starts with a recipe for bubble solution and gives instructions for several activities on topics such as density, interference colors, optics, static electricity, and galaxy formation. Contains some background information to help explain some of the effects.…

  2. Simulating Surfzone Bubbles

    DTIC Science & Technology

    2012-09-30

    D (Ripple) and 3-D ( Truchas ) Navier- Stokes solvers. In the continuation of this work, our objectives are to: 1) Implement a physics-based...a bubble phase with multiple bubble size (or, more accurately, mass) bins. The existing 3-D model Truchas has been extended to include Carrica et al

  3. Nozzle-Free Liquid Microjetting via Homogeneous Bubble Nucleation

    NASA Astrophysics Data System (ADS)

    Lee, Taehwa; Baac, Hyoung Won; Ok, Jong G.; Youn, Hong Seok; Guo, L. Jay

    2015-04-01

    We propose and demonstrate a physical mechanism for producing liquid microjets by taking an optoacoustic approach that can convert light to sound through a carbon-nanotube-coated lens, where light from a pulsed laser is converted to high momentum sound wave. The carbon-nanotube lens can focus high-amplitude sound waves to a microspot of <1 00 μ m near the air-water interface from the water side, leading to microbubbles in water and subsequent microjets into the air. Laser-flash shadowgraphy visualizes two consecutive jets closely correlated with bubble dynamics. Because of the acoustic scattering from the interface, negative pressure amplitudes are significantly increased up to 80 MPa, even allowing homogeneous bubble nucleation. As a demonstration, this nozzle-free approach is applied to inject colored liquid into a tissue-mimicking gel as well as print a material on a glass substrate.

  4. A bubble detection system for propellant filling pipeline

    SciTech Connect

    Wen, Wen; Zong, Guanghua; Bi, Shusheng

    2014-06-15

    This paper proposes a bubble detection system based on the ultrasound transmission method, mainly for probing high-speed bubbles in the satellite propellant filling pipeline. First, three common ultrasonic detection methods are compared and the ultrasound transmission method is used in this paper. Then, the ultrasound beam in a vertical pipe is investigated, suggesting that the width of the beam used for detection is usually smaller than the internal diameter of the pipe, which means that when bubbles move close to the pipe wall, they may escape from being detected. A special device is designed to solve this problem. It can generate the spiral flow to force all the bubbles to ascend along the central line of the pipe. In the end, experiments are implemented to evaluate the performance of this system. Bubbles of five different sizes are generated and detected. Experiment results show that the sizes and quantity of bubbles can be estimated by this system. Also, the bubbles of different radii can be distinguished from each other. The numerical relationship between the ultrasound attenuation and the bubble radius is acquired and it can be utilized for estimating the unknown bubble size and measuring the total bubble volume.

  5. The influence of bubbles on the perception carbonation bite.

    PubMed

    Wise, Paul M; Wolf, Madeline; Thom, Stephen R; Bryant, Bruce

    2013-01-01

    Although many people naively assume that the bite of carbonation is due to tactile stimulation of the oral cavity by bubbles, it has become increasingly clear that carbonation bite comes mainly from formation of carbonic acid in the oral mucosa. In Experiment 1, we asked whether bubbles were in fact required to perceive carbonation bite. Subjects rated oral pungency from several concentrations of carbonated water both at normal atmospheric pressure (at which bubbles could form) and at 2.0 atmospheres pressure (at which bubbles did not form). Ratings of carbonation bite under the two pressure conditions were essentially identical, indicating that bubbles are not required for pungency. In Experiment 2, we created controlled streams of air bubbles around the tongue in mildly pungent CO2 solutions to determine how tactile stimulation from bubbles affects carbonation bite. Since innocuous sensations like light touch and cooling often suppress pain, we predicted that bubbles might reduce rated bite. Contrary to prediction, air bubbles flowing around the tongue significantly enhanced rated bite, without inducing perceived bite in blank (un-carbonated) solutions. Accordingly, though bubbles are clearly not required for carbonation bite, they may well modulate perceived bite. More generally, the results show that innocuous tactile stimulation can enhance chemogenic pain. Possible physiological mechanisms are discussed.

  6. Bubble collision with gravitation

    SciTech Connect

    Hwang, Dong-il; Lee, Bum-Hoon; Lee, Wonwoo; Yeom, Dong-han E-mail: bhl@sogang.ac.kr E-mail: innocent.yeom@gmail.com

    2012-07-01

    In this paper, we study vacuum bubble collisions with various potentials including gravitation, assuming spherical, planar, and hyperbolic symmetry. We use numerical calculations from double-null formalism. Spherical symmetry can mimic the formation of a black hole via multiple bubble collisions. Planar and especially hyperbolic symmetry describes two bubble collisions. We study both cases, when two true vacuum regions have the same field value or different field values, by varying tensions. For the latter case, we also test symmetric and asymmetric bubble collisions, and see details of causal structures. If the colliding energy is sufficient, then the vacuum can be destabilized, and it is also demonstrated. This double-null formalism can be a complementary approach in the context of bubble collisions.

  7. Micrometeorological Measurement of Fetch- and Atmospheric Stability-Dependent Air- Water Exchange of Legacy Semivolatile Organic Contaminants in Lake Superior

    NASA Astrophysics Data System (ADS)

    Perlinger, J. A.; Tobias, D. E.; Rowe, M. D.

    2008-12-01

    Coastal waters including the Laurentian Great Lakes are particularly susceptible to local, regional, and long- range transport and deposition of semivolatile organic contaminants (SOCs) as gases and/or associated with particles. Recently-marketed SOCs can be expected to undergo net deposition in surface waters, whereas legacy SOCs such as polychlorinated biphenyls (PCBs) are likely to be at equilibrium with respect to air-water exchange, or, if atmospheric concentrations decrease through, e.g., policy implementation, to undergo net gas emission. SOC air-water exchange flux is usually estimated using the two-film model. This model describes molecular diffusion through the air and water films adjacent to the air-water interface. Air-water exchange flux is estimated as the product of SOC fugacity, typically based on on-shore gaseous concentration measurements, and a transfer coefficient, the latter which is estimated from SOC properties and environmental conditions. The transfer coefficient formulation commonly applied neglects resistance to exchange in the internal boundary layer under atmospherically stable conditions, and the use of on-shore gaseous concentration neglects fetch-dependent equilibration, both of which will tend to cause overestimation of flux magnitude. Thus, for legacy chemicals or in any highly contaminated surface water, the rate at which the water is cleansed through gas emission tends to be over-predicted using this approach. Micrometeorological measurement of air-water exchange rates of legacy SOCs was carried out on ships during four transect experiments during off-shore flow in Lake Superior using novel multicapillary collection devices and thermal extraction technology to measure parts-per-quadrillion SOC levels. Employing sensible heat in the modified Bowen ratio, fluxes at three over-water stations along the transects were measured, along with up-wind, onshore gaseous concentration and aqueous concentration. The atmosphere was unstable for

  8. Bubble Dynamics on a Heated Surface

    NASA Technical Reports Server (NTRS)

    Kassemi, Mohammad; Rashidnia, Nasser

    1996-01-01

    In this work, we study the combined thermocapillary and natural convective flow generated by a bubble on a heated solid surface. The interaction between gas and vapor bubbles with the surrounding fluid is of interest for both space and ground-based processing. On earth, the volumetric forces are dominant, especially, in apparatuses with large volume to surface ratio. But in the reduced gravity environment of orbiting spacecraft, surface forces become more important and the effects of Marangoni convection are easily unmasked. In order to delineate the roles of the various interacting phenomena, a combined numerical-experimental approach is adopted. The temperature field is visualized using Mach-Zehnder interferometry and the flow field is observed by a laser sheet flow visualization technique. A finite element numerical model is developed which solves the two-dimensional momentum and energy equations and includes the effects of bubble surface deformation. Steady state temperature and velocity fields predicted by the finite element model are in excellent qualitative agreement with the experimental results. A parametric study of the interaction between Marangoni and natural convective flows including conditions pertinent to microgravity space experiments is presented. Numerical simulations clearly indicate that there is a considerable difference between 1-g and low-g temperature and flow fields induced by the bubble.

  9. On the deformation of gas bubbles in liquids

    NASA Astrophysics Data System (ADS)

    Legendre, Dominique; Zenit, Roberto; Velez-Cordero, J. Rodrigo

    2012-04-01

    We consider the deformation of gas bubbles rising in different liquids over a wide range of Morton numbers, from O(10-11) to O(1), and bubble diameters. We have collected data from the literature and performed new experiments for relatively large Morton numbers. A simple expression is proposed to describe the evolution of the bubble deformation, which is consistent with the analytical solution of Moore ["The rise of a gas bubble in a viscous liquid," J. Fluid Mech. 6, 113 (1959)]. It appears that deformation can be predicted correctly by considering the Morton and Weber numbers. The variation of the bubble interfacial area is also analyzed; this quantity is very important for the case of bubbly flow modeling but has not been measured directly to date.

  10. Bubble Impact with a Solid Wall

    NASA Astrophysics Data System (ADS)

    Garg, Vishrut; Thete, Sumeet; Basaran, Osman

    2016-11-01

    In diverse natural and industrial processes, and in particular in process equipment widely used in oil and gas production, bubbles and drops that are immersed in a continuous liquid phase frequently collide with solid walls. In this talk, the impact with a solid wall of a gas bubble that is surrounded by a liquid that is either a Newtonian or a non-Newtonian fluid is analyzed by numerical simulation. Special attention is paid to the thin film that forms between the approaching bubble and the solid wall. Flow regimes that arise as the film thickness decreases are scrutinized and rationalized by comparison of the computational predictions to well-known and new analytical results from lubrication theory based thin film literature. Finally, flow transitions that occur as the lubrication theory breaks down and inertia becomes significant are investigated.

  11. Scaling law for bubbles rising near vertical walls

    NASA Astrophysics Data System (ADS)

    Dabiri, Sadegh; Bhuvankar, Pramod

    2016-06-01

    This paper examines the rising motion of a layer of gas bubbles next to a vertical wall in a liquid in the presence of an upward flow parallel to the wall to help with the understanding of the fluid dynamics in a bubbly upflow in vertical channels. Only the region near the wall is simulated with an average pressure gradient applied to the domain that balances the weight of the liquid phase. The upward flow is created by the rising motion of the bubbles. The bubbles are kept near the wall by the lateral lift force acting on them as a result of rising in the shear layer near the wall. The rise velocity of the bubbles sliding on the wall and the average rise velocity of the liquid depend on three dimensionless parameters, Archimedes number, Ar, Eötvös number, Eo, and the average volume fraction of bubbles on the wall. In the limit of small Eo, bubbles are nearly spherical and the dependency on Eo becomes negligible. In this limit, the scaling of the liquid Reynolds number with Archimedes number and the void fraction is presented. A scaling argument is presented based on viscous dissipation analysis that matches the numerical findings. Viscous dissipation rates are found to be high in a thin film region between the bubble and the wall. A scaling of the viscous dissipation and steady state film thickness between the bubble and the wall with Archimedes number is presented.

  12. Bubble motion measurements during foam drainage and coarsening.

    PubMed

    Maurdev, G; Saint-Jalmes, A; Langevin, D

    2006-08-15

    We have studied bubble motion within a column of foam allowed to undergo free drainage. We have measured bubble motion upward with time and as a function of their initial positions. Depending on the gas used, which sets the coarsening and drainage rates, different bubble upward motion types have been identified (constant speed, acceleration or deceleration) and explained in relation with liquid downward flows. The proofs of the consistency between bubble upward motion and liquid downward flow are obtained both by comparing the bubble motion curves to the liquid drainage ones, and by comparing the time variations of the liquid fraction extracted from bubble motion to direct liquid fraction measurements by electrical conductimetry. The agreement between bubble position tracking and electrical conductivity shows in particular that it is possible to determine the drainage regime from such simple bubble motion measurements. This work also allowed us to demonstrate a special case of foam coarsening and expansion, occurring when the foam gas is less soluble than the outside one, caused by diffusion of this external gas into the foam. All these results allow us to build a picture of drainage and coarsening seen from the bubble point of view.

  13. 14 CFR 1274.926 - Clean Air-Water Pollution Control Acts.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 5 2012-01-01 2012-01-01 false Clean Air-Water Pollution Control Acts...-Water Pollution Control Acts. Clean Air-Water Pollution Control Acts July 2002 If this cooperative... 91-604) and section 308 of the Federal Water Pollution Control Act, as amended (33 U.S.C. 1251 et...

  14. 14 CFR 1274.926 - Clean Air-Water Pollution Control Acts.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 5 2010-01-01 2010-01-01 false Clean Air-Water Pollution Control Acts...-Water Pollution Control Acts. Clean Air-Water Pollution Control Acts July 2002 If this cooperative... 91-604) and section 308 of the Federal Water Pollution Control Act, as amended (33 U.S.C. 1251 et...

  15. 14 CFR 1274.926 - Clean Air-Water Pollution Control Acts.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 5 2013-01-01 2013-01-01 false Clean Air-Water Pollution Control Acts...-Water Pollution Control Acts. Clean Air-Water Pollution Control Acts July 2002 If this cooperative... 91-604) and section 308 of the Federal Water Pollution Control Act, as amended (33 U.S.C. 1251 et...

  16. 14 CFR § 1274.926 - Clean Air-Water Pollution Control Acts.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 5 2014-01-01 2014-01-01 false Clean Air-Water Pollution Control Acts. Â...-Water Pollution Control Acts. Clean Air-Water Pollution Control Acts July 2002 If this cooperative... 91-604) and section 308 of the Federal Water Pollution Control Act, as amended (33 U.S.C. 1251 et...

  17. On the coefficients of small eddy and surface divergence models for the air-water gas transfer velocity

    NASA Astrophysics Data System (ADS)

    Wang, Binbin; Liao, Qian; Fillingham, Joseph H.; Bootsma, Harvey A.

    2015-03-01

    Recent studies suggested that under low to moderate wind conditions without bubble entraining wave breaking, the air-water gas transfer velocity k+ can be mechanistically parameterized by the near-surface turbulence, following the small eddy model (SEM). Field measurements have supported this model in a variety of environmental forcing systems. Alternatively, surface divergence model (SDM) has also been shown to predict the gas transfer velocity across the air-water interface in laboratory settings. However, the empirically determined model coefficients (α in SEM and c1 in SDM) scattered over a wide range. Here we present the first field measurement of the near-surface turbulence with a novel floating PIV system on Lake Michigan, which allows us to evaluate the SEM and SDM in situ in the natural environment. k+ was derived from the CO2 flux that was measured simultaneously with a floating gas chamber. Measured results indicate that α and c1 are not universal constants. Regression analysis showed that α˜log>(ɛ>) while the near-surface turbulence dissipation rate ɛ is approximately greater than 10-6 m2 s-3 according to data measured for this study as well as from other published results measured in similar environments or in laboratory settings. It also showed that α scales linearly with the turbulent Reynolds number. Similarly, coefficient c1 in the SDM was found to linearly scale with the Reynolds number. These findings suggest that larger eddies are also important parameters, and the dissipation rate in the SEM or the surface divergence β' in the SDM alone may not be adequate to determine k+ completely.

  18. The Importance of Moving Air-Water Interfaces for Colloid Transport in Porous Media

    NASA Astrophysics Data System (ADS)

    Flury, M.

    2015-12-01

    In the vadose zone, or in unsaturated porous media in general, transport of colloids is usually less pronounced than in groundwater. An important retention mechanism for colloids in unsaturated porous media is attachment to air-water interfaces. However, air-water interfaces can also lead to colloid mobilization and enhanced transport if air-water interfaces are moving, such as during infiltration, imbibition, and drainage. Colloid attachment to air-water interfaces is caused by surface tension forces, and these forces usually exceed other interactions forces; therefore, surface tension forces play a dominant role for colloid transport in unsaturated porous media. In this presentation, experimental and theoretical evidence of surface tension forces acting on colloids will be presented, and the role of moving air-water interfaces will be discussed.

  19. Air-water gas exchange of toxaphene in Lake Superior.

    PubMed

    Jantunen, Liisa M; Bidleman, Terry F

    2003-06-01

    Parallel air and water samples were collected in Lake Superior during August 1996 and May 1997, to determine the levels and air-water exchange direction of toxaphene. Concentration of toxaphene in water did not vary across Lake Superior or between seasons (averaging 918 +/- 218 pg/L) but atmospheric levels were lower in May (12 +/- 4.6 pg/m3) than in August (28 +/- 10 pg/m3). Two recalcitrant congeners, Parlar 26 and 50, also were determined. These congeners were enriched in the air samples, compared to a standard of technical toxaphene, but not in the water. Water-air fugacity ratios varied from 1.4 to 2.6 in August and 1.3 to 4.7 in May, implying volatilization of toxaphene from the lake. Estimated net fluxes ranged from 5.4 to 13 and 1.8 to 6.4 nm/m2d, respectively. The temperature dependence of toxaphene partial pressure (P) in air was log P/Pa = -3.291/T(a) + 1.67, where T(a) is air temperature. By using this relationship, the atmospheric levels of toxaphene, fugacity ratios, and net fluxes were estimated for the entire year. Fugacity ratios were highest in the winter and lowest in the summer; thus toxaphene was predicted to undergo net volatilization from the lake during all months. A net removal of approximately 220 kg/year by gas exchange was estimated.

  20. Proton Transfers at the Air-Water Interface

    NASA Astrophysics Data System (ADS)

    Mishra, Himanshu

    Proton transfer reactions at the interface of water with hydrophobic media, such as air or lipids, are ubiquitous on our planet. These reactions orchestrate a host of vital phenomena in the environment including, for example, acidification of clouds, enzymatic catalysis, chemistries of aerosol and atmospheric gases, and bioenergetic transduction. Despite their importance, however, quantitative details underlying these interactions have remained unclear. Deeper insight into these interfacial reactions is also required in addressing challenges in green chemistry, improved water quality, self-assembly of materials, the next generation of micro-nanofluidics, adhesives, coatings, catalysts, and electrodes. This thesis describes experimental and theoretical investigation of proton transfer reactions at the air-water interface as a function of hydration gradients, electrochemical potential, and electrostatics. Since emerging insights hold at the lipid-water interface as well, this work is also expected to aid understanding of complex biological phenomena associated with proton migration across membranes. Based on our current understanding, it is known that the physicochemical properties of the gas-phase water are drastically different from those of bulk water. For example, the gas-phase hydronium ion, H3O +(g), can protonate most (non-alkane) organic species, whereas H 3O+(aq) can neutralize only relatively strong bases. Thus, to be able to understand and engineer water-hydrophobe interfaces, it is imperative to investigate this fluctuating region of molecular thickness wherein the 'function' of chemical species transitions from one phase to another via steep gradients in hydration, dielectric constant, and density. Aqueous interfaces are difficult to approach by current experimental techniques because designing experiments to specifically sample interfacial layers (< 1 nm thick) is an arduous task. While recent advances in surface-specific spectroscopies have provided

  1. Nonlinear Acoustics at the Air-Water Free Surface

    NASA Astrophysics Data System (ADS)

    Pree, Seth; Naranjo, Brian; Putterman, Seth

    2016-11-01

    According to linear acoustics, airborne sound incident on a water surface transmits only a tenth of a percent of its energy. This difficulty of transmitting energy across the water surface limits the feasibility of standoff ultrasound imaging. We propose to overcome this long standing problem by developing new methods of coupling into the medium at standoff. In particular, we believe that the acoustic nonlinearity of both the air and the medium may yield a range of effects in the vicinity of the surface permitting an efficient transmission of ultrasound from the air into the medium. The recent commercial availability of parametric speakers that deliver modulated 100kHz ultrasound at 135dB to nonlinearly generate music at 95dB provides an interesting platform with which to revisit the transmission of sound across acoustic impedance mismatches. We show results of experimental studies of the behavior of the air-water free surface when subjected to large amplitude acoustic pressures from the air. This work was supported by the ARO STIR program.

  2. The Effect of Rain on Air-Water Gas Exchange

    NASA Technical Reports Server (NTRS)

    Ho, David T.; Bliven, Larry F.; Wanninkhof, Rik; Schlosser, Peter

    1997-01-01

    The relationship between gas transfer velocity and rain rate was investigated at NASA's Rain-Sea Interaction Facility (RSIF) using several SF, evasion experiments. During each experiment, a water tank below the rain simulator was supersaturated with SF6, a synthetic gas, and the gas transfer velocities were calculated from the measured decrease in SF6 concentration with time. The results from experiments with IS different rain rates (7 to 10 mm/h) and 1 of 2 drop sizes (2.8 or 4.2 mm diameter) confirm a significant and systematic enhancement of air-water gas exchange by rainfall. The gas transfer velocities derived from our experiment were related to the kinetic energy flux calculated from the rain rate and drop size. The relationship obtained for mono-dropsize rain at the RSIF was extrapolated to natural rain using the kinetic energy flux of natural rain calculated from the Marshall-Palmer raindrop size distribution. Results of laboratory experiments at RSIF were compared to field observations made during a tropical rainstorm in Miami, Florida and show good agreement between laboratory and field data.

  3. Air-water interface equilibrium partitioning coefficients of aromatic hydrocarbons

    NASA Astrophysics Data System (ADS)

    Cheng, Wen-Hsi; Chu, Fu-Sui; Liou, Jia-Jiunn

    The single equilibration technique was used to determine the equilibrium partitioning coefficients ( pc) of an air-water interface for target aromatic volatile organic compounds (VOCs), including benzene, toluene and ethylbenzene. The tested liquid concentrations ( CL) of VOC ranged from 0.5 to 20 mg/l, and the temperatures ( Tw) of the solutions were 300, 305, 310 and 315 K, respectively. The pc values were calculated using the gaseous concentrations ( Cg*) of aromatic hydrocarbons in equilibrium with the aqueous phase and the formula pc=( Cg*/ CL). The heats of VOC of liquid and gaseous phase transfer (Δ Htr) in pure water, and the highly linear regression relationship (with squared correlation coefficients, R2, from 0.900 to 0.999) between ( ln C g*) and (1/ Tw) are also evaluated. Experimental results indicated that the pc values of the target VOC components increase with Tw but, in contrast, are not significantly affected by CL in pure water. However, pc of more soluble compounds, like iso-propanol and methyl ethyl ketone, have been evaluated to be significant with CL in the earlier investigation. Finally, the co-solute effect on pc is also evaluated in this work, as determining pc of the aromatic hydrocarbons by using aqueous ethanol (in a volume ration of 1-15%) as solutes.

  4. Bubble-induced cave collapse.

    PubMed

    Girihagama, Lakshika; Nof, Doron; Hancock, Cathrine

    2015-01-01

    Conventional wisdom among cave divers is that submerged caves in aquifers, such as in Florida or the Yucatan, are unstable due to their ever-growing size from limestone dissolution in water. Cave divers occasionally noted partial cave collapses occurring while they were in the cave, attributing this to their unintentional (and frowned upon) physical contact with the cave walls or the aforementioned "natural" instability of the cave. Here, we suggest that these cave collapses do not necessarily result from cave instability or contacts with walls, but rather from divers bubbles rising to the ceiling and reducing the buoyancy acting on isolated ceiling rocks. Using familiar theories for the strength of flat and arched (un-cracked) beams, we first show that the flat ceiling of a submerged limestone cave can have a horizontal expanse of 63 meters. This is much broader than that of most submerged Florida caves (~ 10 m). Similarly, we show that an arched cave roof can have a still larger expanse of 240 meters, again implying that Florida caves are structurally stable. Using familiar bubble dynamics, fluid dynamics of bubble-induced flows, and accustomed diving practices, we show that a group of 1-3 divers submerged below a loosely connected ceiling rock will quickly trigger it to fall causing a "collapse". We then present a set of qualitative laboratory experiments illustrating such a collapse in a circular laboratory cave (i.e., a cave with a circular cross section), with concave and convex ceilings. In these experiments, a metal ball represented the rock (attached to the cave ceiling with a magnet), and the bubbles were produced using a syringe located at the cave floor.

  5. Bubble-Induced Cave Collapse

    PubMed Central

    Girihagama, Lakshika; Nof, Doron; Hancock, Cathrine

    2015-01-01

    Conventional wisdom among cave divers is that submerged caves in aquifers, such as in Florida or the Yucatan, are unstable due to their ever-growing size from limestone dissolution in water. Cave divers occasionally noted partial cave collapses occurring while they were in the cave, attributing this to their unintentional (and frowned upon) physical contact with the cave walls or the aforementioned “natural” instability of the cave. Here, we suggest that these cave collapses do not necessarily result from cave instability or contacts with walls, but rather from divers bubbles rising to the ceiling and reducing the buoyancy acting on isolated ceiling rocks. Using familiar theories for the strength of flat and arched (un-cracked) beams, we first show that the flat ceiling of a submerged limestone cave can have a horizontal expanse of 63 meters. This is much broader than that of most submerged Florida caves (~ 10 m). Similarly, we show that an arched cave roof can have a still larger expanse of 240 meters, again implying that Florida caves are structurally stable. Using familiar bubble dynamics, fluid dynamics of bubble-induced flows, and accustomed diving practices, we show that a group of 1-3 divers submerged below a loosely connected ceiling rock will quickly trigger it to fall causing a “collapse”. We then present a set of qualitative laboratory experiments illustrating such a collapse in a circular laboratory cave (i.e., a cave with a circular cross section), with concave and convex ceilings. In these experiments, a metal ball represented the rock (attached to the cave ceiling with a magnet), and the bubbles were produced using a syringe located at the cave floor. PMID:25849088

  6. Experimental and modeling studies of two-phase flow in pipelines

    SciTech Connect

    Manabe, Ryo; Tochikawa, Tetsuro; Tsukuda, M.; Arihara, Norio

    1997-11-01

    The objectives of this study are to develop and evaluate a mechanistic model for gas/liquid two-phase flow in pipelines. A mechanistic model has been developed by combining currently available models and correlations. The approach of the modeling study was based on the work by Xiao et al. Modifications have been made on the annular flow model by implementing the currently developed film-thickness-distribution model. An experimental database has been developed for model evaluation. Seventy-five runs of steady-state air/water flow tests in horizontal and slightly inclined pipes were conducted using a large-scale experimental facility. The experimental program was set up in a wide range of experimental conditions to cover the intermittent, dispersed bubble, and annular flow patterns. An evaluation of the model was carried out for each flow pattern, namely, intermittent, dispersed bubble, and annular flow. The comparisons between the measured and calculated pressure drops show good agreement for each flow pattern. Also, overall evaluation revealed that the proposed model provided the best performance among the commonly used empirical correlations, such as Beggs and Brill, Mukherjee and Brill, and Dukler et al.

  7. Formation and X-ray emission from hot bubbles in planetary nebulae - I. Hot bubble formation

    NASA Astrophysics Data System (ADS)

    Toalá, J. A.; Arthur, S. J.

    2014-10-01

    We carry out high-resolution two-dimensional radiation-hydrodynamic numerical simulations to study the formation and evolution of hot bubbles inside planetary nebulae. We take into account the evolution of the stellar parameters, wind velocity and mass-loss rate from the final thermal pulses during the asymptotic giant branch (AGB) through to the post-AGB stage for a range of initial stellar masses. The instabilities that form at the interface between the hot bubble and the swept-up AGB wind shell lead to hydrodynamical interactions, photoevaporation flows and opacity variations. We explore the effects of hydrodynamical mixing combined with thermal conduction at this interface on the dynamics, photoionization, and emissivity of our models. We find that even models without thermal conduction mix significant amounts of mass into the hot bubble. When thermal conduction is not included, hot gas can leak through the gaps between clumps and filaments in the broken swept-up AGB shell and this depressurises the bubble. The inclusion of thermal conduction evaporates and heats material from the clumpy shell, which expands to seal the gaps, preventing a loss in bubble pressure. The dynamics of bubbles without conduction is dominated by the thermal pressure of the thick photoionized shell, while for bubbles with thermal conduction it is dominated by the hot, shocked wind.

  8. Liquid-bubble Interaction under Surf Zone Breaking Waves

    NASA Astrophysics Data System (ADS)

    Derakhti, M.; Kirby, J. T., Jr.

    2014-12-01

    Liquid-bubble interaction, especially in complex two-phase bubbly flow under breaking waves, is still poorly understood. Derakhti and Kirby (2014a,b) have recently studied bubble entrainment and turbulence modulation by dispersed bubbles under isolated unsteady breaking waves along with extensive model verifications and convergence tests. In this presentation, we continue this examination with attention turned to the simulation of periodic surf zone breaking waves. In addition, the relative importance of preferential accumulation of dispersed bubbles in coherent vortex cores is investigated. Heavier-than-liquid particles, i.e. sediment, tend to accumulate in regions of high strain rate and avoid regions of intense vorticity. In contrast, lighter-than-liquid particles such as bubbles tend to congregate in vortical regions. We perform a three dimensional (3D) large-eddy simulation (LES) using a Navier-Stokes solver extended to incorporate entrained bubble populations, using an Eulerian-Eulerian formulation for the polydisperse bubble phase. The volume of fluid (VOF) method is used for free surface tracking. The model accounts for momentum exchange between dispersed bubbles and liquid phase as well as bubble-induced dissipation. We investigate the formation and evolution of breaking-induced turbulent coherent structures (BTCS) under both plunging and spilling periodic breaking waves as well as BTCS's role on the intermittent 3D distributions of bubble void fraction in the surf zone. We particularly examine the correlation between bubble void fractions and Q-criterion values to quantify this interaction. Also, the vertical transport of dispersed bubbles by downburst type coherent structures in the transition region is compared to that by obliquely descending eddies. All the results are summarized at different zones from outer to inner surf zone.

  9. Effects of Gravity on Bubble Formation in an Annular Jet

    NASA Technical Reports Server (NTRS)

    Koepp, R. A.; Parthasarathy, R. N.; Gollahalli, S. R.

    2004-01-01

    The effects of gravity on the bubble formation in an annular jet were studied. The experiments were conducted in the 2.2-second drop tower at the NASA Glenn Research Center. Terrestrial gravity experiments were conducted at the Fluid Dynamics Research Laboratory at the University of Oklahoma. Stainless steel tubing with inner diameters of 1/8" (gas inner annulus) and 5/16" (liquid outer annulus) served as the injector. A rectangular test section, 6" x 6" x 14" tall, made out of half-inch thick Lexan was used. Images of the annular jet were acquired using a high-speed camera. The effects of gravity and varying liquid and gas flow rates on bubble size, wavelength, and breakup length were documented. In general, the bubble diameter was found to be larger in terrestrial gravity than in microgravity for varying Weber numbers (0.05 - 0.16 and 5 - 11) and liquid flow rates (1.5 ft/s - 3.0 ft/s). The wavelength was found to be larger in terrestrial gravity than in microgravity, but remained constant for varying Weber numbers. For low Weber numbers (0.05 - 0.16), the breakup length in microgravity was significantly higher than in terrestrial gravity. Comparison with linear stability analysis showed estimated bubble sizes within 9% of experimental bubble sizes. Bubble size compared to other terrestrial gravity experiments with same flow conditions showed distinct differences in bubble size, which displayed the importance of injector geometry on bubble formation.

  10. Cavitation erosion by single laser-produced bubbles

    NASA Astrophysics Data System (ADS)

    Philipp, A.; Lauterborn, W.

    1998-04-01

    In order to elucidate the mechanism of cavitation erosion, the dynamics of a single laser-generated cavitation bubble in water and the resulting surface damage on a flat metal specimen are investigated in detail. The characteristic effects of bubble dynamics, in particular the formation of a high-speed liquid jet and the emission of shock waves at the moment of collapse are recorded with high-speed photography with framing rates of up to one million frames/s. Damage is observed when the bubble is generated at a distance less than twice its maximum radius from a solid boundary ([gamma]=2, where [gamma]=s/Rmax, s is the distance between the boundary and the bubble centre at the moment of formation and Rmax is the maximum bubble radius). The impact of the jet contributes to the damage only at small initial distances ([gamma][less-than-or-eq, slant]0.7). In this region, the impact velocity rises to 83 m s[minus sign]1, corresponding to a water hammer pressure of about 0.1 GPa, whereas at [gamma]>1, the impact velocity is smaller than 25 m s[minus sign]1. The largest erosive force is caused by the collapse of a bubble in direct contact with the boundary, where pressures of up to several GPa act on the material surface. Therefore, it is essential for the damaging effect that bubbles are accelerated towards the boundary during the collapse phases due to Bjerknes forces. The bubble touches the boundary at the moment of second collapse when [gamma]<2 and at the moment of first collapse when [gamma]<1. Indentations on an aluminium specimen are found at the contact locations of the collapsing bubble. In the range [gamma]=1.7 to 2, where the bubble collapses mainly down to a single point, one pit below the bubble centre is observed. At [gamma][less-than-or-eq, slant]1.7, the bubble shape has become toroidal, induced by the jet flow through the bubble centre. Corresponding to the decay of this bubble torus into multiple tiny bubbles each collapsing separately along the

  11. Tribonucleation of bubbles

    PubMed Central

    Wildeman, Sander; Lhuissier, Henri; Sun, Chao; Lohse, Detlef; Prosperetti, Andrea

    2014-01-01

    We report on the nucleation of bubbles on solids that are gently rubbed against each other in a liquid. The phenomenon is found to depend strongly on the material and roughness of the solid surfaces. For a given surface, temperature, and gas content, a trail of growing bubbles is observed if the rubbing force and velocity exceed a certain threshold. Direct observation through a transparent solid shows that each bubble in the trail results from the early coalescence of several microscopic bubbles, themselves detaching from microscopic gas pockets forming between the solids. From a detailed study of the wear tracks, with atomic force and scanning electron microscopy imaging, we conclude that these microscopic gas pockets originate from a local fracturing of the surface asperities, possibly enhanced by chemical reactions at the freshly created surfaces. Our findings will be useful either for preventing undesired bubble formation or, on the contrary, for “writing with bubbles,” i.e., creating controlled patterns of microscopic bubbles. PMID:24982169

  12. Bubble core field modification by residual electrons inside the bubble

    SciTech Connect

    Wu Haicheng; Xie Baisong; Zhao Xueyan; Zhang Shan; Hong Xueren; Liu Mingping

    2010-11-15

    Bubble core field modification due to the nondepleted electrons present inside the bubble is investigated theoretically. These residual electrons induce charge and current densities that can induce the bubble core field modification as well as the bubble shape change. It is found that the electrons entering into the bubble move backward at almost light speed and would weaken the transverse bubble fields. This reduces the ratio of longitudinal to transverse radius of the bubble. For the longitudinal bubble field, two effects compensate with each other because of their competition between the enhancement by the shortening of bubble shape and the reduction by the residual electrons. Therefore the longitudinal field is hardly changeable. As a comparison we perform particle-in-cell simulations and it is found that the results from theoretical consideration are consistent with simulation results. Implication of the modification of fields on bubble electron acceleration is also discussed briefly.

  13. Soap bubbles in analytical chemistry. Conductometric determination of sub-parts per million levels of sulfur dioxide with a soap bubble.

    PubMed

    Kanyanee, Tinakorn; Borst, Walter L; Jakmunee, Jaroon; Grudpan, Kate; Li, Jianzhong; Dasgupta, Purnendu K

    2006-04-15

    Soap bubbles provide a fascinating tool that is little used analytically. With a very low liquid volume to surface area ratio, a soap bubble can potentially provide a very useful interface for preconcentration where mass transfer to an interfacial surface is important. Here we use an automated system to create bubbles of uniform size and film thickness. We utilize purified Triton-X 100, a nonionic surfactant, to make soap bubbles. We use such bubbles as a gas-sampling interface. Incorporating hydrogen peroxide into the bubble provides a system where electrical conductance increases as the bubble is exposed to low concentrations of sulfur dioxide gas. We theoretically derive the conductance of a hollow conducting spherical thin film with spherical cap electrodes. We measure the film thickness by incorporating a dye in the bubble making solution and laser transmission photometry and find that it agrees well with the geometrically computed thickness. With the conductance of the bubble-making soap solution being measured by conventional methods, we show that the measured values of the bubble conductance with known bubble and electrode dimensions closely correspond to the theoretically computed value. Finally, we demonstrate that sub-ppm levels of SO(2) can readily be detected by the conductivity change of a hydrogen peroxide-doped soap bubble, measured in situ, when the gas flows around the bubble.

  14. Viscosity Destabilizes Sonoluminescing Bubbles

    NASA Astrophysics Data System (ADS)

    Toegel, Ruediger; Luther, Stefan; Lohse, Detlef

    2006-03-01

    In single-bubble sonoluminescence (SBSL) microbubbles are trapped in a standing sound wave, typically in water or water-glycerol mixtures. However, in viscous liquids such as glycol, methylformamide, or sulphuric acid it is not possible to trap the bubble in a stable position. This is very peculiar as larger viscosity normally stabilizes the dynamics. Suslick and co-workers call this new mysterious state of SBSL “moving-SBSL.” We identify the history force (a force nonlocal in time) as the origin of this destabilization and show that the instability is parametric. A force balance model quantitatively accounts for the observed quasiperiodic bubble trajectories.

  15. Viscosity destabilizes sonoluminescing bubbles.

    PubMed

    Toegel, Ruediger; Luther, Stefan; Lohse, Detlef

    2006-03-24

    In single-bubble sonoluminescence (SBSL) microbubbles are trapped in a standing sound wave, typically in water or water-glycerol mixtures. However, in viscous liquids such as glycol, methylformamide, or sulphuric acid it is not possible to trap the bubble in a stable position. This is very peculiar as larger viscosity normally stabilizes the dynamics. Suslick and co-workers call this new mysterious state of SBSL "moving-SBSL." We identify the history force (a force nonlocal in time) as the origin of this destabilization and show that the instability is parametric. A force balance model quantitatively accounts for the observed quasiperiodic bubble trajectories.

  16. Rotating bubble membrane radiator

    DOEpatents

    Webb, Brent J.; Coomes, Edmund P.

    1988-12-06

    A heat radiator useful for expelling waste heat from a power generating system aboard a space vehicle is disclosed. Liquid to be cooled is passed to the interior of a rotating bubble membrane radiator, where it is sprayed into the interior of the bubble. Liquid impacting upon the interior surface of the bubble is cooled and the heat radiated from the outer surface of the membrane. Cooled liquid is collected by the action of centrifical force about the equator of the rotating membrane and returned to the power system. Details regarding a complete space power system employing the radiator are given.

  17. Cardiovascular bubble dynamics.

    PubMed

    Bull, Joseph L

    2005-01-01

    Gas bubbles can form in the cardiovascular system as a result of patho-physiological conditions or can be intentionally introduced for diagnostic or therapeutic reasons. The dynamic behavior of these bubbles is caused by a variety of mechanisms, such as inertia, pressure, interfacial tension, viscosity, and gravity. We review recent advances in the fundamental mechanics and applications of cardiovascular bubbles, including air embolism, ultrasound contrast agents, targeted microbubbles for drug delivery and molecular imaging, cavitation-induced tissue erosion for ultrasonic surgery, microbubble-induced angiogenesis and arteriogenesis, and gas embolotherapy.

  18. Two-frequency driven single-bubble sonoluminescence

    NASA Astrophysics Data System (ADS)

    Krefting, Dagmar; Mettin, Robert; Lauterborn, Werner

    2002-11-01

    Sonoluminescing single bubbles driven simultaneously by two harmonic frequencies were recently reported to increase the maximum light output up to a factor of 3 with respect to single mode excitation. In this paper, experimental and numerical results on single-bubble sonoluminescence (SBSL) in an air/water system using the fundamental mode of 25 kHz and the second harmonic at 50 kHz are presented. The region of light emission is mapped in the three-dimensional parameter space spanned by the two driving pressure amplitudes and their relative phase. Good agreement was seen between measured light output, maximum bubble radius, and stability boundaries and the numerical model which is based on spherical bubble oscillations regarding diffusive and shape stability. The maximum brightness was enhanced by a factor up to 2.5 with respect to single mode SBSL. However, long-term measurements reveal great variation of the emission at fundamental mode driven SBSL and of the boost factor reached with two frequencies. The overall brightness maxima of both excitation methods within a period of several hours turn out to show little difference. copyright 2002 Acoustical Society of America.

  19. Two-frequency driven single-bubble sonoluminescence.

    PubMed

    Krefting, Dagmar; Mettin, Robert; Lauterborn, Werner

    2002-11-01

    Sonoluminescing single bubbles driven simultaneously by two harmonic frequencies were recently reported to increase the maximum light output up to a factor of 3 with respect to single mode excitation. In this paper, experimental and numerical results on single-bubble sonoluminescence (SBSL) in an air/water system using the fundamental mode of 25 kHz and the second harmonic at 50 kHz are presented. The region of light emission is mapped in the three-dimensional parameter space spanned by the two driving pressure amplitudes and their relative phase. Good agreement was seen between measured light output, maximum bubble radius, and stability boundaries and the numerical model which is based on spherical bubble oscillations regarding diffusive and shape stability. The maximum brightness was enhanced by a factor up to 2.5 with respect to single mode SBSL. However, long-term measurements reveal great variation of the emission at fundamental mode driven SBSL and of the boost factor reached with two frequencies. The overall brightness maxima of both excitation methods within a period of several hours turn out to show little difference.

  20. Air-water oxygen exchange in a large whitewater river

    USGS Publications Warehouse

    Hall, Robert O.; Kennedy, Theodore A.; Rosi-Marshall, Emma J.

    2012-01-01

    Air-water gas exchange governs fluxes of gas into and out of aquatic ecosystems. Knowing this flux is necessary to calculate gas budgets (i.e., O2) to estimate whole-ecosystem metabolism and basin-scale carbon budgets. Empirical data on rates of gas exchange for streams, estuaries, and oceans are readily available. However, there are few data from large rivers and no data from whitewater rapids. We measured gas transfer velocity in the Colorado River, Grand Canyon, as decline in O2 saturation deficit, 7 times in a 28-km segment spanning 7 rapids. The O2 saturation deficit exists because of hypolimnetic discharge from Glen Canyon Dam, located 25 km upriver from Lees Ferry. Gas transfer velocity (k600) increased with slope of the immediate reach. k600 was -1 in flat reaches, while k600 for the steepest rapid ranged 3600-7700 cm h-1, an extremely high value of k600. Using the rate of gas exchange per unit length of water surface elevation (Kdrop, m-1), segment-integrated k600 varied between 74 and 101 cm h-1. Using Kdrop we scaled k600 to the remainder of the Colorado River in Grand Canyon. At the scale corresponding to the segment length where 80% of the O2 exchanged with the atmosphere (mean length = 26.1 km), k600 varied 4.5-fold between 56 and 272 cm h-1 with a mean of 113 cm h-1. Gas transfer velocity for the Colorado River was higher than those from other aquatic ecosystems because of large rapids. Our approach of scaling k600 based on Kdrop allows comparing gas transfer velocity across rivers with spatially heterogeneous morphology.

  1. Chemistry in Soap Bubbles.

    ERIC Educational Resources Information Center

    Lee, Albert W. M.; Wong, A.; Lee, H. W.; Lee, H. Y.; Zhou, Ning-Huai

    2002-01-01

    Describes a laboratory experiment in which common chemical gases are trapped inside soap bubbles. Examines the physical and chemical properties of the gases such as relative density and combustion. (Author/MM)

  2. What's in a Bubble?

    ERIC Educational Resources Information Center

    Saunderson, Megan

    2000-01-01

    Describes a unit on detergents and bubbles that establishes an interest in the properties of materials and focuses on active learning involving both hands- and minds-on learning rather than passive learning. (ASK)

  3. Micro-PIV of Bubble Splitting in a Bifurcation

    NASA Astrophysics Data System (ADS)

    Stephenson, Samantha; Li, David; Hellmeier, Forian; Pitre, John; Fowlkes, J. Brian; Bull, Joseph

    2014-11-01

    Gas embolotherapy is a proposed treatment for cancerous tumors. For this treatment, a liquid droplet solution is injected into the bloodstream and focused ultrasound is used to vaporize droplets upstream of the tumor site, resulting in bubbles that are approximately 125x larger in volume. These bubbles will then occlude the blood vessels, thereby depriving the tumor of nutrients leading to eventual tumor necrosis. However, once the bubbles are formed, they will continue to travel through the bloodstream, through bifurcations that split in to smaller daughter vessels before lodging to occlude flow. Micro-particle imaging velocimetry (PIV) was used to study the flow field surrounding the leading edge of the bubble at the bifurcation point. Consistent symmetric bubble splitting at several different flow rates was achieved. Roll angle of the bifurcation was varied to encourage uneven bubble splitting and reversal. In the absence of the bubble, Poiseuille flow was verified in the parent channel. Results were compared to a boundary elements model developed by Calderon et al. 2010. This research was funded by the NIH Grant R01EB006476.

  4. Blowing DNA bubbles.

    PubMed

    Severin, N; Zhuang, W; Ecker, C; Kalachev, A A; Sokolov, I M; Rabe, J P

    2006-11-01

    We report here experimental observations which indicate that topologically or covalently formed polymer loops embedded in an ultrathin liquid film on a solid substrate can be "blown" into circular "bubbles" during scanning force microscopy (SFM) imaging. In particular, supercoiled vector DNA has been unraveled, moved, stretched, and overstretched to two times its B-form length and then torn apart. We attribute the blowing of the DNA bubbles to the interaction of the tapping SFM tip with the ultrathin liquid film.

  5. 2012 Problem 8: Bubbles

    NASA Astrophysics Data System (ADS)

    Zhu, Kejing; Xia, Qing; Wang, Sihui; Zhou, Huijun

    2015-10-01

    When a large number of bubbles exist in the water, an object may float on the surface or sink. The assumption of equivalent density is proposed in this article to explain the concrete example. According to the assumption, an object is floatable only if its density is less than the equivalent density of the water-bubble mixture. This conclusion is supported by the floating experiment and by measuring the pressure underwater to a satisfactory approximation.

  6. Bubble coalescence in magmas

    NASA Technical Reports Server (NTRS)

    Herd, Richard A.; Pinkerton, Harry

    1993-01-01

    The most important factors governing the nature of volcanic eruptions are the primary volatile contents, the ways in which volatiles exsolve, and how the resulting bubbles grow and interact. In this contribution we assess the importance of bubble coalescence. The degree of coalescence in alkali basalts has been measured using Image Analysis techniques and it is suggested to be a process of considerable importance. Binary coalescence events occur every few minutes in basaltic melts with vesicularities greater than around 35 percent.

  7. Computational Fluid Dynamics of Acoustically Driven Bubble Systems

    NASA Astrophysics Data System (ADS)

    Glosser, Connor; Lie, Jie; Dault, Daniel; Balasubramaniam, Shanker; Piermarocchi, Carlo

    2014-03-01

    The development of modalities for precise, targeted drug delivery has become increasingly important in medical care in recent years. Assemblages of microbubbles steered by acoustic pressure fields present one potential vehicle for such delivery. Modeling the collective response of multi-bubble systems to an intense, externally applied ultrasound field requires accurately capturing acoustic interactions between bubbles and the externally applied field, and their effect on the evolution of bubble kinetics. In this work, we present a methodology for multiphysics simulation based on an efficient transient boundary integral equation (TBIE) coupled with molecular dynamics (MD) to compute trajectories of multiple acoustically interacting bubbles in an ideal fluid under pulsed acoustic excitation. For arbitrary configurations of spherical bubbles, the TBIE solver self-consistently models transient surface pressure distributions at bubble-fluid interfaces due to acoustic interactions and relative potential flows induced by bubble motion. Forces derived from the resulting pressure distributions act as driving terms in the MD update at each timestep. The resulting method efficiently and accurately captures individual bubble dynamics for clouds containing up to hundreds of bubbles.

  8. An experimental study of turbulent two-phase flow in hydraulic jumps and application of a triple decomposition technique

    NASA Astrophysics Data System (ADS)

    Wang, Hang; Felder, Stefan; Chanson, Hubert

    2014-07-01

    Intense turbulence develops in the two-phase flow region of hydraulic jump, with a broad range of turbulent length and time scales. Detailed air-water flow measurements using intrusive phase-detection probes enabled turbulence characterisation of the bubbly flow, although the phenomenon is not a truly random process because of the existence of low-frequency, pseudo-periodic fluctuating motion in the jump roller. This paper presents new measurements of turbulent properties in hydraulic jumps, including turbulence intensity, longitudinal and transverse integral length and time scales. The results characterised very high turbulent levels and reflected a combination of both fast and slow turbulent components. The respective contributions of the fast and slow motions were quantified using a triple decomposition technique. The decomposition of air-water detection signal revealed "true" turbulent characteristics linked with the fast, microscopic velocity turbulence of hydraulic jumps. The high-frequency turbulence intensities were between 0.5 and 1.5 close to the jump toe, and maximum integral turbulent length scales were found next to the bottom. Both decreased in the flow direction with longitudinal turbulence dissipation. The results highlighted the considerable influence of hydrodynamic instabilities of the flow on the turbulence characterisation. The successful application of triple decomposition technique provided the means for the true turbulence properties of hydraulic jumps.

  9. A multi-functional bubble-based microfluidic system

    PubMed Central

    Khoshmanesh, Khashayar; Almansouri, Abdullah; Albloushi, Hamad; Yi, Pyshar; Soffe, Rebecca; Kalantar-zadeh, Kourosh

    2015-01-01

    Recently, the bubble-based systems have offered a new paradigm in microfluidics. Gas bubbles are highly flexible, controllable and barely mix with liquids, and thus can be used for the creation of reconfigurable microfluidic systems. In this work, a hydrodynamically actuated bubble-based microfluidic system is introduced. This system enables the precise movement of air bubbles via axillary feeder channels to alter the geometry of the main channel and consequently the flow characteristics of the system. Mixing of neighbouring streams is demonstrated by oscillating the bubble at desired displacements and frequencies. Flow control is achieved by pushing the bubble to partially or fully close the main channel. Patterning of suspended particles is also demonstrated by creating a large bubble along the sidewalls. Rigorous analytical and numerical calculations are presented to describe the operation of the system. The examples presented in this paper highlight the versatility of the developed bubble-based actuator for a variety of applications; thus providing a vision that can be expanded for future highly reconfigurable microfluidics. PMID:25906043

  10. Bubble Formation at a Submerged Orifice in Reduced Gravity

    NASA Technical Reports Server (NTRS)

    Buyevich, Yu A.; Webbon, Bruce W.

    1994-01-01

    The dynamic regime of gas injection through a circular plate orifice into an ideally wetting liquid is considered, when successively detached bubbles may be regarded as separate identities. In normal gravity and at relatively low gas flow rates, a growing bubble is modeled as a spherical segment touching the orifice perimeter during the whole time of its evolution. If the flow rate exceeds a certain threshold value, another stage of the detachment process takes place in which an almost spherical gas envelope is connected with the orifice by a nearly cylindrical stem that lengthens as the bubble rises above the plate. The bubble shape resembles then that of a mushroom and the upper envelope continues to grow until the gas supply through the stem is completely cut off. Such a stage is always present under conditions of sufficiently low gravity, irrespective of the flow rate. Two major reasons make for bubble detachment: the buoyancy force and the force due to the momentum inflow into the bubble with the injected gas. The former force dominates the process at normal gravity whereas the second one plays a key role under negligible gravity conditions. It is precisely this fundamental factor that conditions the drastic influence on bubble growth and detachment that changes in gravity are able to cause. The frequency of bubble formation is proportional to and the volume of detached bubbles is independent of the gas flow rate in sufficiently low gravity, while at normal and moderately reduced gravity conditions the first variable slightly decreases and the second one almost linearly increases as the flow rate grows. Effects of other parameters, such as the orifice radius, gas and liquid densities, and surface tension are discussed.

  11. Experimental and numerical study of viscosity effects on the dynamics of the Benjamin bubble

    NASA Astrophysics Data System (ADS)

    Mariotti, Alessandro; Andreussi, Paolo; Salvetti, Maria Vittoria

    2014-11-01

    The ``Benjamin bubble'' is a gas bubble, which, due to gravity, forms and moves in a horizontal pipe, initially filled with stagnant liquid, once one end of the pipe is opened. In water this bubble moves with a constant velocity, which can be predicted by a non-viscous model. The Benjamin bubble velocity is also the base of state-of the-art predictions of the bubble drift velocity in the slug flow regime occurring e.g. in oil transport pipelines. Thus, it is interesting to investigate the dynamics of the Benjamin bubble in highly viscous oils. The findings of experiments and numerical simulations aimed at characterizing the effects of viscosity on the dynamics of the Benjamin bubble are presented. Experiments and simulations were carried out for a large range of fluid viscosities. The results show that two different flow regimes can be defined according to the Reynolds number. For high Reynolds, the bubble velocity and shape do not change in time, as for the classical Benjamin model. Conversely, for low Reynolds (heavy oils) the bubble velocity decreases along the pipe and the height of the bubble front is progressively reduced. We also show that the two different flow regimes are due to the critical or subcritical flow conditions of the liquid phase under the bubble.

  12. Analysis of airfoil transitional separation bubbles

    NASA Technical Reports Server (NTRS)

    Davis, R. L.; Carter, J. E.

    1984-01-01

    A previously developed local inviscid-viscous interaction technique for the analysis of airfoil transitional separation bubbles, ALESEP (Airfoil Leading Edge Separation) has been modified to utilize a more accurate windward finite difference procedure in the reversed flow region, and a natural transition/turbulence model has been incorporated for the prediction of transition within the separation bubble. Numerous calculations and experimental comparisons are presented to demonstrate the effects of the windward differencing scheme and the natural transition/turbulence model. Grid sensitivity and convergence capabilities of this inviscid-viscous interaction technique are briefly addressed. A major contribution of this report is that with the use of windward differencing, a second, counter-rotating eddy has been found to exist in the wall layer of the primary separation bubble.

  13. Cationic Gemini surfactant at the air/water interface.

    PubMed

    Qibin, Chen; Xiaodong, Liang; Shaolei, Wang; Shouhong, Xu; Honglai, Liu; Ying, Hu

    2007-10-15

    The surface properties and structures of a cationic Gemini surfactant with a rigid spacer, p-xylyl-bis(dimethyloctadecylammonium bromide) ([C(18)H(37)(CH(3))(2)N(+)CH(2)C(6)H(4)CH(2)N(+)(CH(3))(2)C(18)H(37)],2Br(-), abbreviated as 18-Ar-18,2Br(-1)), at the air/water interface were investigated. It is found that the surface pressure-molecular area isotherms observed at different temperatures do not exhibit a plateau region but display an unusual "kink" before collapse. The range of the corresponding minimum compressibility and maximum compressibility modulus indicates that the monolayer is in the liquid-expanded state. The monolayers were transferred onto mica and quartz plates by the Langmuir-Blodgett (LB) technique. The structures of monolayers at various surface pressures were studied by atomic force microscopy (AFM) and UV-vis spectroscopy, respectively. AFM measurements show that at lower surface pressures, unlike the structures of complex or hybrid films formed by Gemini amphiphiles with DNA, dye, or inorganic materials or the Langmuir film formed by the nonionic Gemini surfactant, in this case network-like labyrinthine interconnected ridges are formed. The formation of the structures can be interpreted in terms of the spinodal decomposition mechanism. With the increase of the surface pressure up to 35 mN/m, surface micelles dispersed in the network-like ridges gradually appear which might be caused by both the spinodal decomposition and dewetting. The UV-vis adsorption shows that over the whole range of surface pressures, the molecules form a J-aggregate in LB films, which implies that the spacers construct a pi-pi aromatic stacking. This pi-pi interaction between spacers and the van der Waals interaction between hydrophobic chains lead to the formation of both networks and micelles. The labyrinthine interconnected ridges are formed first because of the rapid evaporation of solvent during the spreading processes; with increasing surface pressure, some of the

  14. Generalized Faxén's theorem: Evaluating first-order (hydrodynamic drag) and second-order (acoustic radiation) forces on finite-sized rigid particles, bubbles and droplets in arbitrary complex flows

    NASA Astrophysics Data System (ADS)

    Annamalai, Subramanian; Balachandar, S.

    2016-11-01

    In recent times, study of complex disperse multiphase problems involving several million particles (e.g. volcanic eruptions, spray control etc.) is garnering momentum. The objective of this work is to present an accurate model (termed generalized Faxén's theorem) to predict the hydrodynamic forces on such inclusions (particles/bubbles/droplets) without having to solve for the details of flow around them. The model is developed using acoustic theory and the force obtained as a summation of infinite series (monopole, dipole and higher sources). The first-order force is the time-dependent hydrodynamic drag force arising from the dipole component due to interaction between the gas and the inclusion at the microscale level. The second-order force however is a time-averaged differential force (contributions arise both from monopole and dipole), also known as the acoustic radiation force primarily used to levitate particles. In this work, the monopole and dipole strengths are represented in terms of particle surface and volume averages of the incoming flow properties and therefore applicable to particle sizes of the order of fluid length scale and subjected to any arbitrary flow. Moreover, this model can also be used to account for inter-particle coupling due to neighboring particles. U.S. DoE, NNSA, Advanced Simulation and Computing Program, Cooperative Agreement under PSAAP-II, Contract No. DE-NA0002378.

  15. Amyloid fibril formation at a uniformly sheared air/water interface

    NASA Astrophysics Data System (ADS)

    Posada, David; Hirsa, Amir

    2013-11-01

    Amyloid fibril formation is a process by which protein molecules in solution form nuclei and aggregate into fibrils. Amyloid fibrils have long been associated with several common diseases such as Parkinson's disease and Alzheimer's. More recently, fibril protein deposition has been implicated in uncommon disorders leading to the failure of various organs including the kidneys, heart, and liver. Fibrillization can also play a detrimental role in biotherapeutic production. Results from previous studies show that a hydrophobic interface, such air/water, can accelerate fibrillization. Studies also show that agitation accelerates fibrillization. When attempting to elucidate fundamental mechanisms of fibrillization and distinguish the effects of interfaces and flow, it can be helpful to experiment with uniformly sheared interfaces. A new Taylor-Couette device is introduced for in situ, real-time high resolution microscopy. With a sub-millimeter annular gap, surface tension acts as the channel floor, permitting a stable meniscus to be placed arbitrarily close to a microscope to study amyloid fibril formation over long periods.

  16. Heat transfer mechanisms in bubbly Rayleigh-Bénard convection.

    PubMed

    Oresta, Paolo; Verzicco, Roberto; Lohse, Detlef; Prosperetti, Andrea

    2009-08-01

    The heat transfer mechanism in Rayleigh-Bénard convection in a liquid with a mean temperature close to its boiling point is studied through numerical simulations with pointlike vapor bubbles, which are allowed to grow or shrink through evaporation and condensation and which act back on the flow both thermally and mechanically. It is shown that the effect of the bubbles is strongly dependent on the ratio of the sensible heat to the latent heat as embodied in the Jakob number Ja. For very small Ja the bubbles stabilize the flow by absorbing heat in the warmer regions and releasing it in the colder regions. With an increase in Ja, the added buoyancy due to the bubble growth destabilizes the flow with respect to single-phase convection and considerably increases the Nusselt number.

  17. Modelling of bubble trajectories in a pump impeller

    NASA Astrophysics Data System (ADS)

    Dupoiron, Marine; Linden, Paul

    2015-11-01

    A vertical rotating flow in an annulus gap with an increasing diameter is used to approximate the flow in a pump impeller. We study a spherical gas bubble released at the flow inlet, subject to turbulent drag and added mass forces. Bubbles trajectories have been computed for different geometries, rotation speeds and bubble size, showing a deviation from the liquid streamlines in the angular and radial directions. This effect is related to the pump performance in multiphase conditions: the velocity difference between the gas and the liquid phases changes the final pressure rise produced by the impeller. In some extreme cases, the centrifugal force can be large enough to prevent bubbles from exiting the impeller at all, leading to an unwanted gas accumulation and the blockage of the pump. We eventually quantify the effects of geometrical and operational parameters on the pump behaviour. Work done in collaboration with Schlumberger Gould Research, Cambridge.

  18. Experimental study of the laminar-turbulent transition of a concave wall in a parallel flow

    NASA Technical Reports Server (NTRS)

    Bippes, H.

    1978-01-01

    The instability of the laminar boundary layer flow along a concave wall was studied. Observations of these three-dimensional boundary layer phenomena were made using the hydrogen-bubble visualization technique. With the application of stereo-photogrammetric methods in the air-water system it was possible to investigate the flow processes qualitatively and quantitatively. In the case of a concave wall of sufficient curvature, a primary instability occurs first in the form of Goertler vortices with wave lengths depending upon the boundary layer thickness and the wall curvature. At the onset the amplification rate is in agreement with the linear theory. Later, during the non-linear amplification stage, periodic spanwise vorticity concentrations develop in the low velocity region between the longitudinal vortices. Then a meandering motion of the longitudinal vortex streets subsequently ensues, leading to turbulence.

  19. Theory and experiment on particle trapping and manipulation via optothermally generated bubbles.

    PubMed

    Zhao, Chenglong; Xie, Yuliang; Mao, Zhangming; Zhao, Yanhui; Rufo, Joseph; Yang, Shikuan; Guo, Feng; Mai, John D; Huang, Tony Jun

    2014-01-21

    We present a theoretical analysis and experimental demonstration of particle trapping and manipulation around optothermally generated bubbles. We show that a particle located within 500 μm of a surface bubble can be attracted towards a bubble by drag force resulting from a convective flow. Once the particle comes in contact with the bubble's surface, a balance between surface tension forces and pressure forces traps the particle on the bubble surface, allowing the particle to move with the bubble without detaching. The proposed mechanism is confirmed by computational fluid dynamics simulations, force calculations, and experiments. Based on this mechanism, we experimentally demonstrated a novel approach for manipulating microparticles via optothermally generated bubbles. Using this approach, randomly distributed microparticles were effectively collected and carried to predefined locations. Single particles were also manipulated along prescribed trajectories. This bubble-based particle trapping and manipulation technique can be useful in applications such as micro assembly, particle concentration, and high-precision particle separation.

  20. A CRITICAL ASSESSMENT OF ELEMENTAL MERCURY AIR/WATER EXCHANGE PARTNERS

    EPA Science Inventory

    Although evasion of elemental mercury from aquatic systems can significantly deplete net mercury accumulation resulting from atmospheric deposition, the current ability to model elemental mercury air/water exchange is limited by uncertainties in our understanding of all gaseous a...

  1. The dynamics of histotripsy bubbles

    NASA Astrophysics Data System (ADS)

    Kreider, Wayne; Bailey, Michael R.; Sapozhnikov, Oleg A.; Khokhlova, Vera A.; Crum, Lawrence A.

    2011-09-01

    Histotripsy describes treatments in which high-amplitude acoustic pulses are used to excite bubbles and erode tissue. Though tissue erosion can be directly attributed to bubble activity, the genesis and dynamics of bubbles remain unclear. Histotripsy lesions that show no signs of thermal coagulative damage have been generated with two different acoustic protocols: relatively long acoustic pulses that produce local boiling within milliseconds and relatively short pulses that are higher in amplitude but likely do not produce boiling. While these two approaches are often distinguished as `boiling' versus `cavitation', such labels can obscure similarities. In both cases, a bubble undergoes large changes in radius and vapor is transported into and out of the bubble as it oscillates. Moreover, observations from both approaches suggest that bubbles grow to a size at which they cease to collapse violently. In order to better understand the dynamics of histotripsy bubbles, a single-bubble model has been developed that couples acoustically excited bubble motions to the thermodynamic state of the surrounding liquid. Using this model for bubbles exposed to histotripsy sound fields, simulations suggest that two mechanisms can act separately or in concert to lead to the typically observed bubble growth. First, nonlinear acoustic propagation leads to the evolution of shocks and an asymmetry in the positive and negative pressures that drive bubble motion. This asymmetry can have a rectifying effect on bubble oscillations whereby the bubble grows on average during each acoustic cycle. Second, vapor transport to/from the bubble tends to produce larger bubbles, especially at elevated temperatures. Vapor transport by itself can lead to rectified bubble growth when the ambient temperature exceeds 100 °C (`boiling') or local heating in the vicinity of the bubble leads to a superheated boundary layer.

  2. Artificial neural network for bubbles pattern recognition on the images

    NASA Astrophysics Data System (ADS)

    Poletaev, I. E.; Pervunin, K. S.; Tokarev, M. P.

    2016-10-01

    Two-phase bubble flows have been used in many technological and energy processes as processing oil, chemical and nuclear reactors. This explains large interest to experimental and numerical studies of such flows last several decades. Exploiting of optical diagnostics for analysis of the bubble flows allows researchers obtaining of instantaneous velocity fields and gaseous phase distribution with the high spatial resolution non-intrusively. Behavior of light rays exhibits an intricate manner when they cross interphase boundaries of gaseous bubbles hence the identification of the bubbles images is a complicated problem. This work presents a method of bubbles images identification based on a modern technology of deep learning called convolutional neural networks (CNN). Neural networks are able to determine overlapping, blurred, and non-spherical bubble images. They can increase accuracy of the bubble image recognition, reduce the number of outliers, lower data processing time, and significantly decrease the number of settings for the identification in comparison with standard recognition methods developed before. In addition, usage of GPUs speeds up the learning process of CNN owning to the modern adaptive subgradient optimization techniques.

  3. Influence of mass transfer on bubble plume hydrodynamics.

    PubMed

    Lima Neto, Iran E; Parente, Priscila A B

    2016-03-01

    This paper presents an integral model to evaluate the impact of gas transfer on the hydrodynamics of bubble plumes. The model is based on the Gaussian type self-similarity and functional relationships for the entrainment coefficient and factor of momentum amplification due to turbulence. The impact of mass transfer on bubble plume hydrodynamics is investigated considering different bubble sizes, gas flow rates and water depths. The results revealed a relevant impact when fine bubbles are considered, even for moderate water depths. Additionally, model simulations indicate that for weak bubble plumes (i.e., with relatively low flow rates and large depths and slip velocities), both dissolution and turbulence can affect plume hydrodynamics, which demonstrates the importance of taking the momentum amplification factor relationship into account. For deeper water conditions, simulations of bubble dissolution/decompression using the present model and classical models available in the literature resulted in a very good agreement for both aeration and oxygenation processes. Sensitivity analysis showed that the water depth, followed by the bubble size and the flow rate are the most important parameters that affect plume hydrodynamics. Lastly, dimensionless correlations are proposed to assess the impact of mass transfer on plume hydrodynamics, including both the aeration and oxygenation modes.

  4. Particle image velocimetry studies of bubble growth and detachment by high-speed photography

    NASA Astrophysics Data System (ADS)

    Stickland, Mathew; Dempster, William; Lothian, Lee; Oldroyd, Andrew

    1997-05-01

    An understanding of bubble flows is important in the design of process equipment, particularly in the chemical and power industries. In vapor-liquid processes the mass and heat transfer between the phases is dominated by the liquid-vapor interface and is determined by the number, size, and shape of the bubbles. For bubble flows these characteristics are often controlled by the generation mechanisms and, since bubble flows are often generated at an orifice, it is important to determine the controlling parameters which dictate how bubbles grow and detach. For bubbles growing at orifices the liquid displacement is an important feature and affects the pressure distribution acting on the bubble and the heat and mass transfer that may occur at the bubble interface. Therefore, in this study, the characteristics of the liquid velocity field are studied experimentally using Particle image Velocimetry (PIV) during growth, detachment and translation of a bubble being generated at an orifice supplied with a constant mass flow rate of air. The process is transient and occurs over a period of approximately 50 msecs. In order to map the transient flow field a combination of high speed cine and cross correlation PIV image processing has been used to determine the liquid velocity vector field during the bubble growth process. The paper contains details of the PIV technique and presents several of the velocity vector maps calculated.

  5. Experimental study of the decrease in the temperature of an air/water-cooled turbine blade

    NASA Astrophysics Data System (ADS)

    Ryzhov, A. A.; Sereda, A. V.; Shaiakberov, V. F.; Iskakov, K. M.; Shatalov, Iu. S.

    Results of the full-scale testing of an air/water-cooled deflector-type turbine blade are reported. Data on the decrease in the temperature of the cooling air and of the blade are presented and compared with the calculated values. An analysis of the results indicates that the use of air/water cooling makes it possible to significantly reduce the temperature of the cooling air and of the blade with practically no increase in the engine weight and dimensions.

  6. Micropropulsion by an acoustic bubble for navigating microfluidic spaces.

    PubMed

    Feng, Jian; Yuan, Junqi; Cho, Sung Kwon

    2015-03-21

    This paper describes an underwater micropropulsion principle where a gaseous bubble trapped in a suspended microchannel and oscillated by external acoustic excitation generates a propelling force. The propelling swimmer is designed and microfabricated from parylene on the microscale (the equivalent diameter of the cylindrical bubble is around 60 μm) using microphotolithography. The propulsion mechanism is studied and verified by computational fluid dynamics (CFD) simulations as well as experiments. The acoustically excited and thus periodically oscillating bubble generates alternating flows of intake and discharge through an opening of the microchannel. As the Reynolds number of oscillating flow increases, the difference between the intake and discharge flows becomes significant enough to generate a net flow (microstreaming flow) and a propulsion force against the channel. As the size of the device is reduced, however, the Reynolds number is also reduced. To maintain the Reynolds number in a certain range and thus generate a strong propulsion force in the fabricated device, the oscillation amplitude of the bubble is maximized (resonated) and the oscillation frequency is set high (over 10 kHz). Propelling motions by a single bubble as well as an array of bubbles are achieved on the microscale. In addition, the microswimmer demonstrates payload carrying. This propulsion mechanism may be applied to microswimmers that navigate microfluidic environments and possibly narrow passages in human bodies to perform biosensing, drug delivery, imaging, and microsurgery.

  7. Colliding with a crunching bubble

    SciTech Connect

    Freivogel, Ben; Freivogel, Ben; Horowitz, Gary T.; Shenker, Stephen

    2007-03-26

    In the context of eternal inflation we discuss the fate of Lambda = 0 bubbles when they collide with Lambda< 0 crunching bubbles. When the Lambda = 0 bubble is supersymmetric, it is not completely destroyed by collisions. If the domain wall separating the bubbles has higher tension than the BPS bound, it is expelled from the Lambda = 0 bubble and does not alter its long time behavior. If the domain wall saturates the BPS bound, then it stays inside the Lambda = 0 bubble and removes a finite fraction of future infinity. In this case, the crunch singularity is hidden behind the horizon of a stable hyperbolic black hole.

  8. Signals features extraction in liquid-gas flow measurements using gamma densitometry. Part 1: time domain

    NASA Astrophysics Data System (ADS)

    Hanus, Robert; Zych, Marcin; Petryka, Leszek; Jaszczur, Marek; Hanus, Paweł

    2016-03-01

    The paper presents an application of the gamma-absorption method to study a gas-liquid two-phase flow in a horizontal pipeline. In the tests on laboratory installation two 241Am radioactive sources and scintillation probes with NaI(Tl) crystals have been used. The experimental set-up allows recording of stochastic signals, which describe instantaneous content of the stream in the particular cross-section of the flow mixture. The analyses of these signals by statistical methods allow to determine the mean velocity of the gas phase. Meanwhile, the selected features of signals provided by the absorption set, can be applied to recognition of the structure of the flow. In this work such three structures of air-water flow as: plug, bubble, and transitional plug - bubble one were considered. The recorded raw signals were analyzed in time domain and several features were extracted. It was found that following features of signals as the mean, standard deviation, root mean square (RMS), variance and 4th moment are most useful to recognize the structure of the flow.

  9. Optimization of bubble column performance for nanoparticle collection.

    PubMed

    Cadavid-Rodriguez, M C; Charvet, A; Bemer, D; Thomas, D

    2014-04-30

    Fibrous media embody the most effective and widely used method of separating ultrafine particles from a carrier fluid. The main problem associated with them is filter clogging, which induces an increasingly marked pressure drop with time and thus imposes regular media cleaning or replacement. This context has prompted the idea of investigating bubble columns, which operate at constant pressure drop, as alternatives to fibrous filters. This study examines the influence of different operating conditions, such as liquid height, air flow rate, bubble size and presence of granular beds on ultrafine particle collection. Experimental results show that bubble columns are characterised by high collection efficiency, when they feature a large liquid height and small diameter bubbling orifices, while their efficiencies remain lower than those of fibrous filters. Gas velocity does not greatly influence collection efficiency, but the inclusion of a granular bed, composed of beads, increases the bubble residence time in the column, thereby increasing the column collection efficiency.

  10. Approach to universality in axisymmetric bubble pinch-off

    NASA Astrophysics Data System (ADS)

    Gekle, Stephan; Snoeijer, Jacco H.; Lohse, Detlef; van der Meer, Devaraj

    2009-09-01

    The pinch-off of an axisymmetric air bubble surrounded by an inviscid fluid is compared in four physical realizations: (i) cavity collapse in the wake of an impacting disk, (ii) gas bubbles injected through a small orifice, (iii) bubble rupture in a straining flow, and (iv) a bubble with an initially necked shape. Our boundary-integral simulations suggest that all systems eventually follow the universal behavior characterized by slowly varying exponents predicted by J. Eggers [Phys. Rev. Lett. 98, 094502 (2007)]. However, the time scale for the onset of this final regime is found to vary by orders of magnitude depending on the system in question. While for the impacting disk it is well in the millisecond range, for the gas injection needle universal behavior sets in only a few microseconds before pinch-off. These findings reconcile the different views expressed in recent literature about the universal nature of bubble pinch-off.

  11. Measurement Of Gas Bubbles In Mercury Using Proton Radiography

    SciTech Connect

    Riemer, Bernie; Bingham, Philip R; Mariam, Fesseha G; Merrill, Frank E

    2007-01-01

    An experiment using proton radiography on a small mercury loop for testing gas bubble injection was conducted at the Los Alamos Neutron Science Center (LANSCE) in December 2006. Small gas bubble injection is one of the approaches under development to reduce cavitation damage in the U.S. Spallation Neutron Source mercury target vessel. Several hundred radiograph images were obtained as the test loop was operated over range of conditions that included two jet type bubble generators, two needle type bubble generators, various mercury flow speeds and gas injection rates, and use of helium, argon and xenon. This paper will describe the analysis of the radiograph images and present the obtained bubble measurement data.

  12. A Bubble Bursts

    NASA Technical Reports Server (NTRS)

    2005-01-01

    RCW 79 is seen in the southern Milky Way, 17,200 light-years from Earth in the constellation Centaurus. The bubble is 70-light years in diameter, and probably took about one million years to form from the radiation and winds of hot young stars.

    The balloon of gas and dust is an example of stimulated star formation. Such stars are born when the hot bubble expands into the interstellar gas and dust around it. RCW 79 has spawned at least two groups of new stars along the edge of the large bubble. Some are visible inside the small bubble in the lower left corner. Another group of baby stars appears near the opening at the top.

    NASA's Spitzer Space Telescope easily detects infrared light from the dust particles in RCW 79. The young stars within RCW 79 radiate ultraviolet light that excites molecules of dust within the bubble. This causes the dust grains to emit infrared light that is detected by Spitzer and seen here as the extended red features.

  13. The Dueling Bubble Experiment

    NASA Astrophysics Data System (ADS)

    Roy, Anshuman; Borrell, Marcos; Felts, John; Leal, Gary; Hirsa, Amir

    2007-11-01

    When two drops or bubbles are brought into close proximity to each other, the thin film of the fluid between them drains as they are squeezed together. If the film becomes thin enough that intermolecular forces of attraction overwhelm capillary forces, the drops/bubbles coalesce and the time it takes for this to happen, starting from the point of apparent contact is referred to as the drainage time. One practical version of this scenario occurs during the formation of foams, when the thin film forms between gas bubbles that are growing in volume with time. We performed an experimental study that is intended to mimic this process in which the two drops (or bubbles) in the size range of 50-100 microns diameter are created by oozing a liquid/gas out of two capillaries of diameter less than 100 microns directly facing each other and immersed in a second fluid. We present measurements of drainage times for the cases of very low viscosity ratios PDMS drops in Castor oil (less than 0.05) and bubbles of air in PDMS, and highlight the differences that arise in part due to the different boundary conditions for thin film drainage for liquid-liquid versus gas-liquid systems, and in part due to the different Hamaker constants for the two systems.

  14. Bubbles of Metamorphosis

    NASA Astrophysics Data System (ADS)

    Prakash, Manu

    2011-11-01

    Metamorphosis presents a puzzling challenge where, triggered by a signal, an organism abruptly transforms its entire shape and form. Here I describe the role of physical fluid dynamic processes during pupal metamorphosis in flies. During early stages of pupation of third instar larvae into adult flies, a physical gas bubble nucleates at a precise temporal and spatial location, as part of the normal developmental program in Diptera. Although its existence has been known for the last 100 years, the origin and control of this ``cavitation'' event has remained completely mysterious. Where does the driving negative pressure for bubble nucleation come from? How is the location of the bubble nucleation site encoded in the pupae? How do molecular processes control such a physical event? What is the role of this bubble during development? Via developing in-vivo imaging techniques, direct bio-physical measurements in live insect pupal structures and physical modeling, here I elucidate the physical mechanism for appearance and disappearance of this bubble and predict the site of nucleation and its exact timing. This new physical insight into the process of metamorphosis also allows us to understand the inherent design of pupal shell architectures in various species of insects. Milton Award, Harvard Society of Fellows; Terman Fellowship, Stanford

  15. Capillary forces between sediment particles and an air-water interface.

    PubMed

    Chatterjee, Nirmalya; Lapin, Sergey; Flury, Markus

    2012-04-17

    In the vadose zone, air-water interfaces play an important role in particle fate and transport, as particles can attach to the air-water interfaces by action of capillary forces. This attachment can either retard or enhance the movement of particles, depending on whether the air-water interfaces are stationary or mobile. Here we use three standard PTFE particles (sphere, circular cylinder, and tent) and seven natural mineral particles (basalt, granite, hematite, magnetite, mica, milky quartz, and clear quartz) to quantify the capillary forces between an air-water interface and the different particles. Capillary forces were determined experimentally using tensiometry, and theoretically assuming volume-equivalent spherical, ellipsoidal, and circular cylinder shapes. We experimentally distinguished between the maximum capillary force and the snap-off force when the air-water interface detaches from the particle. Theoretical and experimental values of capillary forces were of similar order of magnitude. The sphere gave the smallest theoretical capillary force, and the circular cylinder had the largest force due to pinning of the air-water interface. Pinning was less pronounced for natural particles when compared to the circular cylinder. Ellipsoids gave the best agreement with measured forces, suggesting that this shape can provide a reasonable estimation of capillary forces for many natural particles.

  16. EXPERIMENTAL BUBBLE FORMATION IN A LARGE SCALE SYSTEM FOR NEWTONIAN AND NONNEWTONIAN FLUIDS

    SciTech Connect

    Leishear, R; Michael Restivo, M

    2008-06-26

    The complexities of bubble formation in liquids increase as the system size increases, and a photographic study is presented here to provide some insight into the dynamics of bubble formation for large systems. Air was injected at the bottom of a 28 feet tall by 30 inch diameter column. Different fluids were subjected to different air flow rates at different fluid depths. The fluids were water and non-Newtonian, Bingham plastic fluids, which have yield stresses requiring an applied force to initiate movement, or shearing, of the fluid. Tests showed that bubble formation was significantly different in the two types of fluids. In water, a field of bubbles was formed, which consisted of numerous, distributed, 1/4 to 3/8 inch diameter bubbles. In the Bingham fluid, large bubbles of 6 to 12 inches in diameter were formed, which depended on the air flow rate. This paper provides comprehensive photographic results related to bubble formation in these fluids.

  17. Mass flow rate measurements in gas-liquid flows by means of a venturi or orifice plate coupled to a void fraction sensor

    SciTech Connect

    Oliveira, Jorge Luiz Goes; Passos, Julio Cesar

    2009-01-15

    Two-phase flow measurements were carried out using a resistive void fraction meter coupled to a venturi or orifice plate. The measurement system used to estimate the liquid and gas mass flow rates was evaluated using an air-water experimental facility. Experiments included upward vertical and horizontal flow, annular, bubbly, churn and slug patterns, void fraction ranging from 2% to 85%, water flow rate up to 4000 kg/h, air flow rate up to 50 kg/h, and quality up to almost 10%. The fractional root mean square (RMS) deviation of the two-phase mass flow rate in upward vertical flow through a venturi plate is 6.8% using the correlation of Chisholm (D. Chisholm, Pressure gradients during the flow of incompressible two-phase mixtures through pipes, venturis and orifice plates, British Chemical Engineering 12 (9) (1967) 454-457). For the orifice plate, the RMS deviation of the vertical flow is 5.5% using the correlation of Zhang et al. (H.J. Zhang, W.T. Yue, Z.Y. Huang, Investigation of oil-air two-phase mass flow rate measurement using venturi and void fraction sensor, Journal of Zhejiang University Science 6A (6) (2005) 601-606). The results show that the flow direction has no significant influence on the meters in relation to the pressure drop in the experimental operation range. Quality and slip ratio analyses were also performed. The results show a mean slip ratio lower than 1.1, when bubbly and slug flow patterns are encountered for mean void fractions lower than 70%. (author)

  18. Effects of Gravity on Sheared Turbulence Laden with Bubbles or Droplets

    NASA Technical Reports Server (NTRS)

    Elghobashi, Said; Lasheras, Juan

    1999-01-01

    The objective of this numerical/experimental study is to improve the understanding of the effects of gravity on the two-way interaction between dispersed particles (bubbles or liquid droplets) and the carrier turbulent flow. The first phase of the project considers isotropic turbulence. Turbulent homogeneous shear flows laden with droplets/bubbles will be studied in the next phase. The experiments reported here are concerned with the dispersion of liquid droplets by homogeneous turbulence under various gravitational conditions and the effect of these droplets on the evolution of the turbulence of the carrier fluid (air). Direct numerical simulations (DNS) of bubble - laden isotropic decaying turbulence are performed using the two-fluid approach (TF) instead of the Eulerian-Lagrangian approach (EL). The motivation for using the TF formulation is that EL requires considerable computational resources especially for the case of two-way coupling where the instantaneous trajectories of a large number of individual bubbles need to be computed. The TF formulation is developed by spatially averaging the instantaneous equations of the carrier flow and bubble phase over a scale of the order of the Kolmogorov length scale which, in our case, is much larger than the bubble diameter. On that scale, the bubbles are treated as a continuum (without molecular diffusivity) characterized by the bubble phase velocity field and concentration (volume fraction). The bubble concentration, C, is assumed small enough to neglect the bubble-bubble interactions.

  19. A first attempt to enhance the 2-D single-crystal growth of a protein at an air/water interface from hydrodynamics

    NASA Astrophysics Data System (ADS)

    Drazek, L.; Legrand, J.-F.; Davoust, L.

    2005-02-01

    An alternative technique to grow a 2-D crystal of protein at a functionalized air/water interface is proposed. The first part of this paper briefly reviews 2-D crystal growth at a fluid interface and deals with our first experiments on streptavidin whose 2-D (poly)crystallization ability is well known. In the experiments, the involved air/water interface is functionalized with a mixed lipidic monolayer made of DOPC and biotinylated lipids. The second part of the paper relates to an alternative strategy we propose in order to enhance the 2-D single-crystal growth of a protein at a liquid interface. The idea is to get benefit from an axisymmetric swirling flow driven in a water sub-phase confined within an annular channel. The swirl is expected to control the distribution of the proteins at the air/water interface and to promote the growth of a 2-D single crystal from the smallest to the largest radii (radial segregation). An analytical modelling based on a low Reynolds number asymptotic development demonstrates how two control parameters, the mean channel curvature and the Reynolds number of the shear flow, can be helpful in tuning the magnitude of the swirl and therefore the crystal growth.

  20. Laboratory air bubble generation of various size distributions

    SciTech Connect

    Puleo, Jack A.; Johnson, Rex V.; Kooney, Tim N.

    2004-11-01

    Air bubble size in aqueous environments is an important factor governing natural processes ranging from fluid/atmosphere gas transfer to noise production. Bubbles are also known to affect various scientific instruments. In this study we investigate the production capability of eight inexpensive bubble generators using optical imaging techniques. Specific emphasis is directed towards determining bubble size and distribution for a given device, flow conditions, and type of water used (fresh vs salt). In almost all cases tested here, bubbles produced in salt water were more numerous, and smaller than for the same bubbler and conditions in fresh water. For porous media, the finer the pore size, the smaller the bubble produced with some variation depending on thickness of material containing the pore and water type. While no single generator tested was capable of spanning all the bubble sizes observed (100 to 6000 microns), the data contained herein will enable proper choice of bubbler or combinations thereof for future studies depending on the size and distribution of bubbles required.

  1. Disproportionate emission of bubble streams with killer whale biphonic calls: perspectives on production and function.

    PubMed

    Bowles, Ann E; Grebner, Dawn M; Musser, Whitney B; Nash, Juliette S; Crance, Jessica L

    2015-02-01

    Stereotyped pulsed calls were attributed to 11 killer whales (Orcinus orca) with and without synchronous bubble streams in three datasets collected from two facilities from 1993 to 2012. Calls with and without synchronous bubble streams and divergent overlapping high frequency components ("biphonic" vs "monophonic") were compared. Subjects produced bubbles significantly more often when calls had divergent high frequency components. However, acoustic features in one biphonic call shared by five subjects provided little evidence for an acoustic effect of synchronous bubble flow. Disproportionate bubbling supported other evidence that biphonic calls form a distinct category, but suggested a function in short-range communication.

  2. Bubbles from nothing

    SciTech Connect

    Blanco-Pillado, Jose J.; Ramadhan, Handhika S.; Shlaer, Benjamin E-mail: handhika@cosmos.phy.tufts.edu

    2012-01-01

    Within the framework of flux compactifications, we construct an instanton describing the quantum creation of an open universe from nothing. The solution has many features in common with the smooth 6d bubble of nothing solutions discussed recently, where the spacetime is described by a 4d compactification of a 6d Einstein-Maxwell theory on S{sup 2} stabilized by flux. The four-dimensional description of this instanton reduces to that of Hawking and Turok. The choice of parameters uniquely determines all future evolution, which we additionally find to be stable against bubble of nothing instabilities.

  3. Multivariate bubbles and antibubbles

    NASA Astrophysics Data System (ADS)

    Fry, John

    2014-08-01

    In this paper we develop models for multivariate financial bubbles and antibubbles based on statistical physics. In particular, we extend a rich set of univariate models to highe