Science.gov

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. 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.

  3. 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.

  4. Buoyancy effects in steeply inclined air-water bubbly shear flow in a rectangular channel

    NASA Astrophysics Data System (ADS)

    Sanaullah, K.; Arshad, M.; Khan, A.; Chughtai, I. R.

    2015-07-01

    We report measurements of two-dimensional ( B/ D = 5) fully turbulent and developed duct flows (overall length/depth, L/ D = 60; D-based Reynolds number Re > 104) for inclinations to 30° from vertical at low voidages (< 5 % sectional average) representative of disperse regime using tap water bubbles (4-6 mm) and smaller bubbles (2 mm) stabilised in ionic solution. Pitot and static probe instrumentation, primitive but validated, provided adequate (10 % local value) discrimination of main aspects of the mean velocity and voidage profiles at representative streamwise station i.e L/ D = 40. Our results can be divided into three categories of behaviour. For vertical flow (0°) the evidence is inconclusive as to whether bubbles are preferentially trapped within the wall-layer as found in some, may be most earlier experimental works. Thus, the 4-mm bubbles showed indication of voidage retention but the 2-mm bubbles did not. For nearly vertical flow (5°) there was pronounced profiling of voidage especially with 4-mm bubbles but the transverse transport was not suppressed sufficiently to induce any obvious layering. In this context, we also refer to similarities with previous work on one-phase vertical and nearly vertical mixed convection flows displaying buoyancy inhibited mean shear turbulence. However, with inclined flow (10+ degrees) a distinctively layered pattern was invariably manifested in which voidage confinement increased with increasing inclination. In this paper we address flow behavior at near vertical conditions. Eulerian, mixed and VOF models were used to compute voidage and mean velocity profiles.

  5. 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)

  6. Experimental verification of the four-sensor probe model for flow diagnosis in air water flow in vertical pipe

    NASA Astrophysics Data System (ADS)

    Pradhan, S.; Mishra, R.

    2012-05-01

    Measuring the volumetric flow rate of each of the flowing components is required to be monitored in production logging applications. Hence it is necessary to measure the flow rates of gas, oil and water in vertical and inclined oil wells. An increasing level of interest has been shown by the researchers in developing system for the flow rate measurement in multiphase flows. This paper describes the experimental methodology using a miniature, local four-sensor probe for the measurement of dispersed flow parameters in bubbly two-phase flow for spherical bubbles. To establish interdependent among different parameters corresponding to dispersed flow, the available model has been used to experimentally obtain different parameters such as volume fraction, velocity and bubble shape of the dispersed phase in the bubbly air-water flow.

  7. Interfacial area measurement and transport modeling in air-water two-phase flow

    NASA Astrophysics Data System (ADS)

    Fu, Xinyu

    In two-fluid model, the interfacial area concentration (IAC) is an important parameter that characterizes the interaction of two-phases at the interface. The accuracy of IAC modeling and local measurements largely affects the efficiency of designing and assessing two-phase flow systems. The prediction of the dynamical evolution of IAC is one of the most challenging tasks in research and application. This thesis is focused on developing advanced local measurement techniques to obtain reliable two-phase parameters and implementing efficient theoretical models for IAC source and sink terms in a two-group interfacial area transport equation based on experiments. In this study, an advanced local measurement technique using a four-sensor conductivity probe has been presented for obtaining IAC in air-water flows. It extends the existing conductivity probe method to slug and churn-turbulent flows with a unified probe design and comprehensive signal processing system. Sophisticated algorithm and software have been implemented that is robust in handling most practical conditions with high reliability. Systematic analyses on the issues of probe applications and benchmarks have been performed. The improved four-sensor method has also been applied to flow conditions with significant local recirculation, which was considered the most challenging situation for local measurement in two-phase flow. Using the well-established instrumentation, solid databases for a two-inch air-water loop have been built with sufficient information on the axial development and the radial distribution of the local parameters. Mechanistic models of major fluid particle interaction phenomena involving two bubble groups have been proposed, including the shearing-off of small bubbles from slug/cap bubbles, the wake entrainment of group-1 bubble into group-2 bubble, the wake acceleration and coalescence between group-2 bubbles, and the breakup of group-2 bubbles due to surface instability. Prediction of

  8. Turbulent bubbly flow

    NASA Astrophysics Data System (ADS)

    van den Berg, Thomas H.; Luther, Stefan; Mazzitelli, Irene M.; Rensen, Judith M.; Toschi, Federico; Lohse, Detlef

    The effect of bubbles on fully developed turbulent flow is investigated numerically and experimentally, summarizing the results of our previous papers (Mazzitelli et al., 2003, Physics of Fluids15, L5. and Journal of Fluid Mechanics488, 283; Rensen, J. et al. 2005, Journal of Fluid Mechanics538, 153). On the numerical side, we simulate Navier Stokes turbulence with a Taylor Reynolds number of Re?˜60, a large large-scale forcing, and periodic boundary conditions. The point-like bubbles follow their Lagrangian paths and act as point forces on the flow. As a consequence, the spectral slope is less steep as compared to the Kolmogorov case. The slope decrease is identified as a lift force effect. On the experimental side, we do hot-film anemometry in a turbulent water channel with Re? ˜ 200 in which we have injected small bubbles up to a volume percentage of 3%. Here the challenge is to disentangle the bubble spikes from the hot-film velocity signal. To achieve this goal, we have developed a pattern recognition scheme. Furthermore, we injected microbubbles up to a volume percentage of 0.3%. Both in the counter flowing situation with small bubbles and in the co-flow situation with microbubbles, we obtain a less spectral slope, in agreement with the numerical result.

  9. Trapping of Sodium Dodecyl Sulfate at the Air-Water Interface of Oscillating Bubbles.

    PubMed

    Corti, Mario; Pannuzzo, Martina; Raudino, Antonio

    2015-06-16

    We report that at very low initial bulk concentrations, a couple of hundred times below the critical micellar concentration (CMC), anionic surfactant sodium dodecyl sulfate (SDS) adsorbed at the air-water interface of a gas bubble cannot be removed, on the time scale of the experiment (hours), when the surrounding solution is gently replaced by pure water. Extremely sensitive interferometric measurements of the resonance frequency of the bubble-forced oscillations give precise access to the concentration of the surfactant monolayer. The bulk-interface dynamic exchange of SDS molecules is shown to be inhibited below a concentration which we believe refers to a kind of gas-liquid phase transition of the surface monolayer. Above this threshold we recover the expected concentration-dependent desorption. The experimental observations are interpreted within simple energetic considerations supported by molecular dynamics (MD) calculations. PMID:26039913

  10. Time-resolved Fast Neutron Radiography of Air-water Two-phase Flows

    NASA Astrophysics Data System (ADS)

    Zboray, Robert; Dangendorf, Volker; Mor, Ilan; Tittelmeier, Kai; Bromberger, Benjamin; Prasser, Horst-Michael

    Neutron imaging, in general, is a useful technique for visualizing low-Z materials (such as water or plastics) obscured by high-Z materials. However, when significant amounts of both materials are present and full-bodied samples have to be examined, cold and thermal neutrons rapidly reach their applicability limit as the samples become opaque. In such cases one can benefit from the high penetrating power of fast neutrons. In this work we demonstrate the feasibility of time-resolved, fast neutron radiography of generic air-water two-phase flows in a 1.5 cm thick flow channel with Aluminum walls and rectangular cross section. The experiments have been carried out at the high-intensity, white-beam facility of the Physikalisch-Technische Bundesanstalt, Germany. Exposure times down to 3.33 ms have been achieved at reasonable image quality and acceptable motion artifacts. 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 bubble velocities have been measured.

  11. DNS studies of bubbly flows

    NASA Astrophysics Data System (ADS)

    Tryggvason, Gretar; Esmaeeli, Asghar; Biswas, Souvik

    2004-11-01

    Recent stuies of bubbly flows, using direct numerical simulations, are discussed. The goal of this study is to examine the collective behavior of many bubbles as the rise Reynolds number is increased and and a single bubble rises unsteadily, as well as to examine the motion of bubbles in channels. A front-tracking/finite volume method is used to fully resolve all flow scales, including the bubbles and the flow around them. Two cases are simulated, for one the bubbles remain nearly spherical and for the other case the bubbles are deformable and wobble. The wobbly bubbles remains relatively uniformly distributed and are not susceptible to the streaming instability found by Bunner and Tryggvason (2003) for deformable bubbles at lower rise Reynolds numbers. The more spherical bubbles, on the other hand, form transients ``rafts'' somewhat similar to those seen in potential flow simulation of many bubbles. For channel flow we compare results from direct numerical simulations of bubbly flow with prediction of the steady-state two-fluid model of Antal, Lahey, and Flaherty (1991). The simulations are done assuming a two-dimensional system and the model coefficients are adjusted slightly to match the data for upflow. The results generally agree reasonably well, even though the simulated void fraction is considerably higher than the one assumed in the derivation of the model. Research supported by DOE.

  12. 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.

  13. Interfacial area transport across vertical elbows in air-water two-phase flow

    NASA Astrophysics Data System (ADS)

    Yadav, Mohan Singh

    The accurate prediction of two-phase flow using the two-fluid model requires closure relations for the interfacial area concentration ( ai), which can be provided by the interfacial area transport equation (IATE). Models have been developed for the IATE in straight pipe geometries. However, to analyze practical systems, it is important that the IATE accounts for flows in pipes with varying orientation that are interconnected via different flow restrictions. In view of this, the current study performs experiments to investigate the geometric effects of 90- degree vertical elbows in air-water two-phase flows and develops a one-group IATE applicable to vertical-upward-to-horizontal two-phase flows. The experimental facility consists of both vertical and horizontal sections constructed from 50.8 mm inner diameter acrylic pipes that are interconnected via 90-degree glass elbows. The elbows have a radius of curvature of Rc/D = 3 and are installed at L/D = 63 and 244.7 from the inlet. Experiments are performed to characterize the elbow-effect on both global and local two-phase flow parameters. A four-sensor conductivity probe is used to acquire detailed measurements of local two-phase flow parameters at thirteen axial locations along the test section in eight flow conditions that are within the bubbly flow regime at inlet. The measurements show that in bubbly flow conditions, the vertical-upward elbow causes a characteristic bimodal-type bubble distribution and the change in this distribution farther downstream of the elbow corresponds to the dissipation of the elbow-effects. In view of developing the IATE for vertical-upward to horizontal two-phase flows, predictive models for the dissipation length of the elbow-effect and closure relations for advection of gas-phase, pressure loss, and covariance of bubble interactions are developed. The new models are evaluated against the current experimental database. Overall, the model predictions agree with the data within +/-7

  14. Image processing analysis on the air-water slug two-phase flow in a horizontal pipe

    NASA Astrophysics Data System (ADS)

    Dinaryanto, Okto; Widyatama, Arif; Majid, Akmal Irfan; Deendarlianto, Indarto

    2016-06-01

    Slug flow is a part of intermittent flow which is avoided in industrial application because of its irregularity and high pressure fluctuation. Those characteristics cause some problems such as internal corrosion and the damage of the pipeline construction. In order to understand the slug characteristics, some of the measurement techniques can be applied such as wire-mesh sensors, CECM, and high speed camera. The present study was aimed to determine slug characteristics by using image processing techniques. Experiment has been carried out in 26 mm i.d. acrylic horizontal pipe with 9 m long. Air-water flow was recorded 5 m from the air-water mixer using high speed video camera. Each of image sequence was processed using MATLAB. There are some steps including image complement, background subtraction, and image filtering that used in this algorithm to produce binary images. Special treatments also were applied to reduce the disturbance effect of dispersed bubble around the bubble. Furthermore, binary images were used to describe bubble contour and calculate slug parameter such as gas slug length, gas slug velocity, and slug frequency. As a result the effect of superficial gas velocity and superficial liquid velocity on the fundamental parameters can be understood. After comparing the results to the previous experimental results, the image processing techniques is a useful and potential technique to explain the slug characteristics.

  15. 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.

  16. 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. PMID:12080141

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Numerical study of bubble generation in a turbulent two-phase Couette flow

    NASA Astrophysics Data System (ADS)

    Ovsyannikov, Andrey; Mani, Ali; Moin, Parviz; Kim, Dokyun

    2014-11-01

    The objective of this work is to develop an understanding bubble generation mechanism due to interactions between free surfaces and turbulent boundary layers as commonly seen near ship walls. To this end, we have focused on a canonical problem that involves Couette flow between two vertical parallel walls with an air-water interface in between. We have considered flow at Reynolds number of 8000 and Froude number of 3.6, both based on half domain dimension and water properties. Our calculations resolve both Kolmogorov lengths and the Hinze scale. Additionally, a conservative VOF method coupled to a subgrid Lagrangian breakup model is used to represent the ligament breakup phenomena and their resulting bubbles and drops. We will present results from these calculations revealing bubble formation rates, bubble size distribution, and effects of bubbles on modulation of turbulence Supported by ONR.

  3. 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%.

  4. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    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.

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

    PubMed

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

    2015-07-01

    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. PMID:26233413

  7. 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

  8. 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

  9. 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

  10. 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.

    2016-04-01

    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.

  11. Flow Regimes of Air-Water Counterflow Through Cross Corrugated Parallel Plates

    SciTech Connect

    de Almeida, V.F.

    2000-06-07

    Heretofore unknown flow regimes of air-water counterflow through a pair of transparent vertical parallel cross corrugated plates were observed via high-speed video. Air flows upward driven by pressure gradient and water, downward driven by gravity. The crimp geometry of the corrugations was drawn from typical corrugated sheets used as filling material in modern structured packed towers. Four regimes were featured, namely, rivulet, bicontinuous, flooding fronts, and flooding waves. It is conceivable that the regimes observed might constitute the basis for understanding how gas and liquid phases contend for available space in the interstices of structured packings in packed towers. Flow regime transitions were expressed in terms of liquid load (liquid superficial velocity) and gas flow factor parameters commonly used in pressure drop and capacity curves. We have carefully examined the range of parameters equivalent to the ill-understood high-liquid-flow operation in packed towers. More importantly, our findings should prove valuable in validating improved first-principles modeling of gas-liquid flows in these industrially important devices.

  12. 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

  13. 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

  14. 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

  15. 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

  16. Bubble Avalanches in a Slowly Flowing Foam

    NASA Astrophysics Data System (ADS)

    Durian, D. J.

    1996-03-01

    Foams consist of a dense random packing of gas bubbles in a smaller volume of liquid. As a form of matter, foams exhibit remarkable mechanical properties that arise from the bubble- packing structure in ways that are not well understood. For example they can support small static shear like a solid, but can also flow and deform arbitrarily like a liquid. Whereas the solid-like properties can be understood in terms of linear response, the liquid-like properties, as discussed here, cannot. Using novel diffusing-light spectroscopies, we have shown that large scale deformations, though macroscopically homogeneous, are accomplished by a series of microscopically inhomogeneous bubble-switching rearrangements from one tightly packed configuration to another(A.D. Gopal and D.J. Durian, Phys. Rev. Lett. 75, 2610 (1995).). Such stick-slip dynamics is reminiscent of the propagation of earthquake faults or the flow of sand, but by contrast can be studied noninvasively at the microscopic scale. We compare our observations with MD simulations predicting that bubble rearrangements exhibit self-organized criticality(T. Okuzono and K. Kawasaki, Phys. Rev. E 51, 1246 (1995).), as well as with results from a simpler model(D. Durian, Phys. Rev. Lett. 75 (1995).)^,(S.A. Langer, A.J. Liu, and D.J. Durian, unpublished.).

  17. On the prediction of the phase distribution of bubbly flow in a horizontal pipe.

    PubMed

    Yeoh, G H; Cheung, Sherman C P; Tu, J Y

    2012-01-01

    Horizontal bubbly flow is widely encountered in various industrial systems because of its ability to provide large interfacial areas for heat and mass transfer. Nonetheless, this particular flow orientation has received less attention when compared to vertical bubbly flow. Owing to the strong influence due to buoyancy, the migration of dispersed bubbles towards the top wall of the horizontal pipe generally causes a highly asymmetrical internal phase distributions, which are not experienced in vertical bubbly flow. In this study, the internal phase distribution of air-water bubbly flow in a long horizontal pipe with an inner diameter of 50.3 mm has been predicted using the population balance model based on direct quadrature method of moments (DQMOM) and multiple-size group (MUSIG) model. The predicted local radial distributions of gas void fraction, liquid velocity and interfacial area concentration have been validated against the experimental data of Kocamustafaogullari and Huang (1994). In general, satisfactory agreements between predicted and measured results were achieved. The numerical results indicated that the gas void fraction and interfacial area concentration have a unique internal structure with a prevailing maximum peak near the top wall of the pipe due to buoyancy effect. PMID:24415823

  18. On the prediction of the phase distribution of bubbly flow in a horizontal pipe

    PubMed Central

    Yeoh, G.H.; Cheung, Sherman C.P.; Tu, J.Y.

    2012-01-01

    Horizontal bubbly flow is widely encountered in various industrial systems because of its ability to provide large interfacial areas for heat and mass transfer. Nonetheless, this particular flow orientation has received less attention when compared to vertical bubbly flow. Owing to the strong influence due to buoyancy, the migration of dispersed bubbles towards the top wall of the horizontal pipe generally causes a highly asymmetrical internal phase distributions, which are not experienced in vertical bubbly flow. In this study, the internal phase distribution of air-water bubbly flow in a long horizontal pipe with an inner diameter of 50.3 mm has been predicted using the population balance model based on direct quadrature method of moments (DQMOM) and multiple-size group (MUSIG) model. The predicted local radial distributions of gas void fraction, liquid velocity and interfacial area concentration have been validated against the experimental data of Kocamustafaogullari and Huang (1994). In general, satisfactory agreements between predicted and measured results were achieved. The numerical results indicated that the gas void fraction and interfacial area concentration have a unique internal structure with a prevailing maximum peak near the top wall of the pipe due to buoyancy effect. PMID:24415823

  19. 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)

  20. 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.

  1. Experimental investigation on liquid film asymmetry in air-water horizontal annular flow

    NASA Astrophysics Data System (ADS)

    Setyawan, Andriyanto; Deendarlianto, Indarto, Neo, Fredrick

    2016-06-01

    The asymmetry of circumferential liquid film thickness distribution in an air-water horizontal annular flow has been experimentally investigated using superficial gas and liquid velocity of 10 - 40 m/s and 0.025 to 0.4 m/s, respectively. In general, the film at the bottom of the pipe will be thicker than that of the side and the top. The asymmetry parameter could be expressed in the ratio of average film thickness to the bottom film thickness or the ratio of the top-to-bottom film thickness. Measurement using compact multiple probe instrument shows that the circumferential film thickness distribution is strongly affected by superficial gas velocity. The higher gas velocity results in the more uniform liquid film circumferential distribution. In comparison to the existing correlations, the asymmetry parameter resulted from the experiment shows a good agreement. It is also shown from the experiment that a less symmetry of film thickness distribution is resulted when the gravity force is dominant. A more symmetry distribution is resulted when the inertial force takes control.

  2. 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.

  3. Modelling isothermal bubbly-cap flows using two-group averaged bubble number density approach

    NASA Astrophysics Data System (ADS)

    Cheung, S. C. P.; Yeoh, G. H.; Tu, J. Y.

    2012-09-01

    Gas-liquid flows with wide range of bubble sizes are commonly encountered in many nuclear gas-liquid flow systems. In tracking the changes of gas volume fraction and bubble size distribution under complex flow conditions, numerical studies have been performed to predict the temporal and spatial evolution of two-phase geometrical structure caused by the effects of bubble interactions in gas-liquid flows. Within literatures, the development of most coalescence and break-up mechanisms were primarily focused on the interaction of spherical bubbles. Nevertheless, cap bubbles which are precursors to the formation of slug units in the slug flow regime with increasing volume fraction become ever more prevalent at high gas velocity conditions. It has been shown through many experiments that interaction behaviors between non-spherical bubbles in a liquid flow are remarkably different when compared to those of spherical bubbles. Based on the computational fluid dynamics (CFD) framework, a three-fluid model was solved, one set of conservation equations for the liquid phase while two sets of conservation equations for the gas phase with one being Group 1 spherical bubbles and the other depicting Group 2 cap bubbles. In this initial assessment, the bubble mechanistic models proposed by Hibiki and Ishii [1] have been adopted to describe the intra-group and inter-group interactions. The numerical predictions were evaluated against the experiment data of the TOPFLOW facility for vertical, upwards, airwater flows in a large pipe diameter [2].

  4. 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.

  5. 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.

  6. 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.

  7. Transitional Bubble in Periodic Flow Phase Shift

    NASA Technical Reports Server (NTRS)

    Talan, M.; Hourmouziadis, Jean

    2004-01-01

    One particular characteristic observed in unsteady shear layers is the phase shift relative to the main flow. In attached boundary layers this will have an effect both on the instantaneous skin friction and heat transfer. In separation bubbles the contribution to the drag is dominated by the pressure distribution. However, the most significant effect appears to be the phase shift on the transition process. Unsteady transition behaviour may determine the bursting of the bubble resulting in an un-recoverable full separation. An early analysis of the phase shift was performed by Stokes for the incompressible boundary layer of an oscillating wall and an oscillating main flow. An amplitude overshoot within the shear layer as well as a phase shift were observed that can be attributed to the relatively slow diffusion of viscous stresses compared to the fast change of pressure. Experiments in a low speed facility with the boundary layer of a flat plate were evaluated in respect to phase shift. A pressure distribution similar to that on the suction surface of a turbomachinery aerofoil was superimposed generating a typical transitional separation bubble. A periodically unsteady main flow in the suction type wind tunnel was introduced via a rotating flap downstream of the test section. The experiments covered a range of the three similarity parameters of momentum-loss-thickness Reynolds-number of 92 to 226 and Strouhal-number (reduced frequency) of 0.0001 to 0.0004 at the separation point, and an amplitude range up to 19 %. The free stream turbulence level was less than 1% .Upstream of the separation point the phase shift in the laminar boundary layer does not appear to be affected significantly bay either of the three parameters. The trend perpendicular to the wall is similar to the Stokes analysis. The problem scales well with the wave velocity introduced by Stokes, however, the lag of the main flow near the wall is less than indicated analytically. The separation point

  8. 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. PMID:22326115

  9. Heat transfer coefficients in bubbly and slug flows under microgravity conditions

    SciTech Connect

    Rezkallah, K.S.; Rite, R.W.

    1996-12-31

    Experimental local heat transfer data were collected onboard NASA`s KC-135 reduced gravity aircraft for two-phase, air-water flow in vertical, upward, co-current flow through a 9.53 mm circular tube. It was found that in the bubbly and slug flow regimes (surface tension dominated regimes), reduced gravity has a tendency to lower the heat transfer coefficient by up to 50% at the lowest gas qualities. As the gas quality is increased (transition to annular flow), the difference between the 1-g and {micro}-g heat transfer coefficients is much less significant. Empirical correlations were developed in terms of the pertinent dimensionless groups; namely the superficial liquid Reynolds number, the Froude number, the Graetz number and the Morton number. The correlations predicted the experimental data within 10--25%, depending on the flow regime and the superficial gas Weber number.

  10. Magnetic susceptibility based magnetic resonance estimation of micro-bubble size for the vertically upward bubbly flow.

    PubMed

    Arbabi, A; Mastikhin, I V

    2012-12-01

    The approach originally developed for the Nuclear Magnetic Resonance analysis of stable micro-bubbles is applied to studies of vertical bubbly flows. A very fast dispersion (diffusion) of water in bubbly flows extends the fast diffusion limit down to short (2-10 ms) measurement times, permitting the use of the simplified analytical expression to extract the micro-bubble size information both in bulk and spatially resolved. The observed strong bubble-induced reduction in T(2)(*) necessitates the use of very short encoding times and pure phase encoding methods to accurately measure the void fraction. There was an expected underestimation of bubble sizes at faster flow rates due to the limitations of the theory derived for small bubble sizes and non-interacting spherical bubbles (low void fractions and slow flow rates). This approach lends itself to studies of bubbly flows and cavitating media characterized by small bubble sizes and low void fractions. PMID:23117260

  11. 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.

  12. Adsorption of egg phosphatidylcholine 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

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

    2010-03-11

    Phospholipid monolayers play a critical role in the structure and stabilization of biological interfaces, including all membranes, the alveoli of the lungs, 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 (gamma) was measured using a drop tensiometer. We observed that EPC binds irreversibly to both interfaces and at equilibrium exerts approximately 12 and 15 mN/m of pressure (Pi) 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 Pi/area relationship. To determine the surface concentration (Gamma), 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, Gamma on the bubble can be determined by overlaying the two isotherms. Both TO and EPC are 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 Pi increases, the TO is progressively ejected. To understand the Pi/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, Gamma can be estimated. This allows determination of Gamma of EPC on a TO bubble as a function of Pi. PMID:20151713

  13. 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.

  14. 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.

  15. Frictional drag reduction in bubbly Couette-Taylor flow

    NASA Astrophysics Data System (ADS)

    Murai, Yuichi; Oiwa, Hiroshi; Takeda, Yasushi

    2008-03-01

    Frictional drag reduction due to the presence of small bubbles is investigated experimentally using a Couette-Taylor flow system; i.e., shear flow between concentric cylinders. Torque and bubble behavior are measured as a function of Reynolds number up to Re =5000 while air bubbles are injected constantly and rise through an array of vortical cells. Silicone oil is used to avoid the uncertain interfacial property of bubbles and to produce nearly monosized bubble distributions. The effect of drag reduction on sensitivity and power gain are assessed. The sensitivity exceeds unity at Re <2000, proving that the effect of the reduction in drag is greater than that of the reduction in mixture density. This is due to the accumulation of bubbles toward the rotating inner cylinder, which is little affected by turbulence. The power gain, which is defined by the power saving from the drag reduction per the pumping power of bubble injection, has a maximum value of O(10) at higher Re numbers around 2500. An image processing measurement shows this is because of the disappearance of azimuthal waves when the organized bubble distribution transforms from toroidal to spiral modes. Moreover, the axial spacing of bubble clouds expands during the transition, which results in an effective reduction in the momentum exchange.

  16. 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

  17. Bubble and liquid flow characteristics in a cylindrical bath during swirl motion of bubbling jet

    NASA Astrophysics Data System (ADS)

    Iguchi, Manabu; Kondoh, Tsuneo; Uemura, Tomomasa; Yamamoto, Fujio; Morita, Zen-Ichiro

    1994-02-01

    Gas injection into a cylindrical bath through a centric bottom nozzle causes a swirl motion like rotary sloshing. Conditions indicating the initiation and cessation of the swirl motion have been made clear by many researchers. So far, the effect of the swirl motion on transport phenomena in the bath is not clear yet. The present study was made to clarify the bubble characteristics (void fraction, bubble frequency) and liquid flow characteristics (mean velocity, turbulence intensity, Reynolds shear stress) during swirl motion of bubbling jet. These two characteristics were investigated using an electro-resistivity probe and a two-dimensional LDV, respectively.

  18. 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

  19. Numerical and physical modelling of bubbly flow phenomena

    NASA Astrophysics Data System (ADS)

    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.

  20. On the paradox of thermocapillary flow about a stationary bubble

    NASA Astrophysics Data System (ADS)

    Yariv, Ehud; Shusser, Michael

    2006-07-01

    When a stationary bubble is exposed to an external temperature gradient, Marangoni stresses at the bubble surface result in fluid motion. A straightforward attempt to calculate the influence of this thermocapillary flow upon the temperature distribution fails to provide a well-behaved solution [Balasubramaniam and Subramanian, Phys. Fluids 16, 3131 (2004)]. This problem is revisited here using a regularization procedure which exploits the qualitative disparity in the long-range flow fields generated by a stationary bubble and a moving one. The regularization parameter is an (exponentially small) artificial bubble velocity, which reflects the inability of any asymptotic expansion to satisfy the condition of exact bubble equilibrium. The solution is obtained using asymptotic matching of two separate Reynolds-number expansions: an inner expansion, valid at the bubble neighborhood, and a remote outer expansion, valid far beyond the familiar Oseen region. This procedure provides a well-behaved solution, which is subsequently used to evaluate the convection-induced correction to the hydrodynamic force exerted on the bubble. The independence of that correction upon the artificial velocity confirms the adequacy of the regularization procedure to describe the stationary-bubble case. The ratio of the calculated force to that pertaining to the classical pure-conduction limit [Young, Goldstein, and Block, J. Fluid Mech. 6, 350 (1959)] is given by 1-Ma/8+o(Ma), where Ma is a radius-based Marangoni number.

  1. On the paradox of thermocapillary flow about a stationary bubble

    NASA Astrophysics Data System (ADS)

    Yariv, Ehud; Shusser, Michael

    2006-11-01

    When a stationary bubble is exposed to an external temperature gradient, Marangoni stresses at the bubble surface result in fluid motion. A straight-forward attempt to calculate the influence of this thermocapillary flow upon the temperature distribution fails to provide well-behaved solution [Balasubramaniam & Subramanian, Phys. Fluids 16, 3131 (2004)]. This paradox is resolved here using regularization procedure which exploits the qualitative disparity in the long-range flow fields generated by stationary bubble and moving one. The regularization parameter is an (exponentially small) artificial bubble velocity U, which reflects the inability of any asymptotic expansion to satisfy the condition of exact bubble equilibrium. The solution is obtained using asymptotic matching of two separate Reynolds-number expansions: an inner expansion, valid at the bubble neighborhood, and remote outer expansion, valid far beyond the familiar Oseen region. This procedure provides well-behaved solution, which is subsequently used to evaluate the convection-induced correction to the hydrodynamic force exerted on the bubble. The independence of that correction upon U confirms the adequacy of the regularization procdure to descibe the stationary-bubble case. The ratio of the calculated force to that pertaining to the classical pure-conduction limit [Young, Goldstein Block, J. Fluid Mech. 6, 350 (1959)] is given by 1 - Ma/8+ o(Ma), where Ma is radius-based Marangoni number.

  2. 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

  3. Bubble size prediction in co-flowing streams

    NASA Astrophysics Data System (ADS)

    van Hoeve, W.; Dollet, B.; Gordillo, J. M.; Versluis, M.; van Wijngaarden, L.; Lohse, D.

    2011-06-01

    In this paper, the size of bubbles formed through the breakup of a gaseous jet in a co-axial microfluidic device is derived. The gaseous jet surrounded by a co-flowing liquid stream breaks up into monodisperse microbubbles and the size of the bubbles is determined by the radius of the inner gas jet and the bubble formation frequency. We obtain the radius of the gas jet by solving the Navier-Stokes equations for low-Reynolds-number flows and by conservation of momentum. The prediction of the bubble size is based on the system's control parameters only, i.e. the inner gas flow rate Qi, the outer liquid flow rate Qo, and the tube radius R. For a very low gas-to-liquid flow rate ratio (Qi/Qo→0) the bubble radius scales as r_{b}/R \\propto \\sqrt{Q_{i}/Q_{o}} , independently of the inner-to-outer viscosity ratio ηi/ηo and of the type of the velocity profile in the gas, which can be either flat or parabolic, depending on whether high-molecular-weight surfactants cover the gas-liquid interface or not. However, in the case in which the gas velocity profiles are parabolic and the viscosity ratio is sufficiently low, i.e. ηi/ηoLt1, the bubble diameter scales as rb~(Qi/Qo)β, with β smaller than 1/2.

  4. Preferential accumulation of bubbles in Couette-Taylor flow patterns

    NASA Astrophysics Data System (ADS)

    Climent, Eric; Simonnet, Marie; Magnaudet, Jacques

    2007-08-01

    We investigate the migration of bubbles in several flow patterns occurring within the gap between a rotating inner cylinder and a concentric fixed outer cylinder. The time-dependent evolution of the two-phase flow is predicted through three-dimensional Euler-Lagrange simulations. Lagrangian tracking of spherical bubbles is coupled with direct numerical simulation of the Navier-Stokes equations. We assume that bubbles do not influence the background flow (one-way coupling simulations). The force balance on each bubble takes into account buoyancy, added-mass, viscous drag, and shear-induced lift forces. For increasing velocities of the rotating inner cylinder, the flow in the fluid gap evolves from the purely azimuthal steady Couette flow to Taylor toroidal vortices and eventually a wavy vortex flow. The migration of bubbles is highly dependent on the balance between buoyancy and centripetal forces (mostly due to the centripetal pressure gradient) directed toward the inner cylinder and the vortex cores. Depending on the rotation rate of the inner cylinder, bubbles tend to accumulate alternatively along the inner wall, inside the core of Taylor vortices or at particular locations within the wavy vortices. A stability analysis of the fixed points associated with bubble trajectories provides a clear understanding of their migration and preferential accumulation. The location of the accumulation points is parameterized by two dimensionless parameters expressing the balance of buoyancy, centripetal attraction toward the inner rotating cylinder, and entrapment in Taylor vortices. A complete phase diagram summarizing the various regimes of bubble migration is built. Several experimental conditions considered by Djéridi, Gabillet, and Billard [Phys. Fluids 16, 128 (2004)] are reproduced; the numerical results reveal a very good agreement with the experiments. When the rotation rate is increased further, the numerical results indicate the formation of oscillating bubble

  5. Experimental investigation on the interfacial characteristics of stratified air-water two-phase flow in a horizontal pipe

    NASA Astrophysics Data System (ADS)

    Hudaya, Akhmad Zidni; Kuntoro, Hadiyan Yusuf; Dinaryanto, Okto; Deendarlianto, Indarto

    2016-06-01

    The interfacial wave characteristics of stratified air-water two-phase flow in a horizontal pipe were experimentally investigated by using the flush-mounted constant electric current method (CECM) sensors. The experiments were conducted in a horizontal two-phase flow loop 9.5 m long (L) consisting of transparent acrylic pipe of 26 mm i.d. (D). To obtain the stratified flow pattern, the superficial gas and liquid velocities were set to 1.02 - 3.77 m/s and 0.016 - 0.92 m/s, respectively. Several interfacial wave patterns as described by several investigators were identified. The common parameters such as liquid hold-up, probability distribution function, wave velocity and wave frequency were investigated as the function of the liquid and gas flow rates. The interfacial curvature was calculated on the basis of the liquid hold-up data from the CECM sensors and the liquid film thickness data from the image processing technique in the previous work. As a result, it was found that the mean liquid hold-up decreases with the increase of the superficial gas velocity. In the same sub flow pattern, the wave velocity increases as the superficial gas velocity increases. On the other hand, in the two-dimensional wave region, the dominant frequency decreases with the increase of the superficial liquid velocity.

  6. 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.

  7. 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.

  8. Contactless Inductive Bubble Detection in a Liquid Metal Flow.

    PubMed

    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

  9. 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

  10. 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.

  11. A monolithic mass tracking formulation for bubbles in incompressible flow

    SciTech Connect

    Aanjaneya, Mridul Patkar, Saket Fedkiw, Ronald

    2013-08-15

    We devise a novel method for treating bubbles in incompressible flow that relies on the conservative advection of bubble mass and an associated equation of state in order to determine pressure boundary conditions inside each bubble. We show that executing this algorithm in a traditional manner leads to stability issues similar to those seen for partitioned methods for solid–fluid coupling. Therefore, we reformulate the problem monolithically. This is accomplished by first proposing a new fully monolithic approach to coupling incompressible flow to fully nonlinear compressible flow including the effects of shocks and rarefactions, and then subsequently making a number of simplifying assumptions on the air flow removing not only the nonlinearities but also the spatial variations of both the density and the pressure. The resulting algorithm is quite robust, has been shown to converge to known solutions for test problems, and has been shown to be quite effective on more realistic problems including those with multiple bubbles, merging and pinching, etc. Notably, this approach departs from a standard two-phase incompressible flow model where the air flow preserves its volume despite potentially large forces and pressure differentials in the surrounding incompressible fluid that should change its volume. Our bubbles readily change volume according to an isothermal equation of state.

  12. 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.

  13. DNS and modeling of bubbly flows in vertical channels

    NASA Astrophysics Data System (ADS)

    Ma, Ming; Lu, Jiacai; Tryggvason, Gretar

    2014-11-01

    The transient motion of bubbly flow, in a vertical channel is studied, using direct numerical simulations (DNS) where every continuum length and time scale is resolved. Nearly spherical bubbles of the same size, injected into laminar upflow, are quickly pushed to the walls due to lift. The velocity then slows down, eventually resulting in some of the bubbles returning to the core forming a mixture where the weight matches the imposed pressure gradient and the void fraction is easily predicted. Unlike the statistically steady state, where the flow structure is relatively simple and in some cases depends only on the sign of the lift coefficient, the transient evolution is more sensitive to the governing parameters. The DNS results are used to provide values for the unresolved closure terms in a simple average model for the flow, found by mining the data, using various techniques such as regression and neural networks. Results for a large number of bubbles of several different sizes in turbulent upflow are also presented and the prospects of using a similar approach for LES-like simulations of more complex flows are discussed, including the simplification of the interface structure resulting from filtering. Research supported by DOE (CASL) and NSF Grant CBET 1335913.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  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. A Study on Bubble Departure and Bubble Lift-Off in Sub-Cooled Nucleate Boiling Flows

    SciTech Connect

    Wu, Wen; Chen, Peipei; Jones, Barclay G.; Newell, Ty A.

    2006-07-01

    This research examines bubble departure and bubble lift-off phenomena under subcooled nucleate boiling condition, using a high fidelity digital imaging apparatus. Refrigerant R- 134a is chosen as a simulant fluid due to its merits of having smaller surface tension, reduced latent heat, and lower boiling temperature than water. Images at frame rates up to 4000 frames/s were obtained with varying experimental parameters e.g. pressure, inlet sub-cooled level, and flow rate, etc., showing characteristics of bubble behavior under different conditions. Bubble size and position information was calculated via Canny's algorithm for edge detection and Fitzgibbon's algorithm for ellipse fitting. Bubble departure and lift-off radiuses were obtained and compared with existing bubble forces and detachment models proposed by Thorncroft et al., with good agreement observed. (authors)

  20. 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.

  1. 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

  2. Mixing of spherical bubbles with time-dependent radius in incompressible flows

    NASA Astrophysics Data System (ADS)

    Pérez-Muñuzuri, Vicente; Garaboa-Paz, Daniel

    2016-02-01

    The motion of contracting and expanding bubbles in an incompressible chaotic flow is analyzed in terms of the finite-time Lyapunov exponents. The viscous forces acting on the bubble surface depend not only on the relative acceleration but also on the time dependence of the bubble volume, which is modeled by the Rayleigh-Plesset equation. The effect of bubble coalescence on the coherent structures that develop in the flow is studied using a simplified bubble merger model. Contraction and expansion of the bubbles is favored in the vicinity of the coherent structures. Time evolution of coalescence bubbles follows a Lévy distribution with an exponent that depends on the initial distance between bubbles. Mixing patterns were found to depend heavily on merging and on the time-dependent volume of the bubbles.

  3. 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.

  4. Bubble pinch-off in a rotating flow.

    PubMed

    Bergmann, Raymond; Andersen, Anders; van der Meer, Devaraj; Bohr, Tomas

    2009-05-22

    We create air bubbles at the tip of a "bathtub vortex" which reaches to a finite depth. The bathtub vortex is formed by letting water drain through a small hole at the bottom of a rotating cylindrical container. The tip of the needlelike surface dip is unstable at high rotation rates and releases bubbles which are carried down by the flow. Using high-speed imaging we find that the minimal neck radius of the unstable tip decreases in time as a power law with an exponent close to 1/3. This exponent was found by Gordillo et al. [Phys. Rev. Lett. 95, 194501 (2005)10.1103/PhysRevLett.95.194501] to govern gas flow driven pinch-off, and indeed we find that the volume oscillations of the tip creates a considerable air flow through the neck. We argue that the Bernoulli pressure reduction caused by this air flow can become sufficient to overcome the centrifugal forces and cause the final pinch-off. PMID:19519033

  5. Experimental investigation of flow instabilities in a laminar separation bubble

    NASA Astrophysics Data System (ADS)

    Simoni, D.; Ubaldi, M.; Zunino, P.

    2014-06-01

    The present paper reports the results of a detailed experimental study aimed at investigating the dynamics of a laminar separation bubble, from the origin of separation up to the breakdown to turbulence of the large scale coherent structures generated as a consequence of the Kelvin-Helmholtz instability process. Measurements have been performed along a flat plate installed within a double contoured test section, designed to produce an adverse pressure gradient typical of Ultra-High-Lift turbine blade profiles, which induces the formation of a laminar separation bubble at low Reynolds number condition. Measurements have been carried out by means of complementary techniques: hot-wire (HW) anemometry, Laser Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV). The high accuracy 2-dimensional LDV results allow investigating reverse flow magnitude and both Reynolds normal and shear stress distributions along the separated flow region, while the high frequency response of the HW anemometer allows analyzing the amplification process of flow oscillations induced by instability mechanisms. PIV results complement the flow field analysis providing information on the generation and evolution of the large scale coherent structures shed as a consequence of the separated shear layer roll-up, through instantaneous velocity vector maps. The simultaneous analysis of the data obtained by means of the different measuring techniques allows an in depth view of the instability mechanisms involved in the transition/reattachment processes of the separated shear layer.

  6. 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.

  7. A new flooding correlation development and its critical heat flux predictions under low air-water flow conditions in Savannah River Site assembly channels

    SciTech Connect

    Lee, S.Y. )

    1993-10-01

    The upper limit to countercurrent flow, namely, flooding, is important to analyze the reactor coolability during an emergency cooling system (ECS) phase as a result of a large-break loss-of-coolant accident (LOCA) such as a double-ended guillotine break in the Savannah River Site (SRS) reactor system. During normal operation, the reactor coolant system utilizes downward flow through concentric heated tubes with ribs, which subdivided each annular channel into four subchannels. In this paper, a new flooding correlation has been developed based on the analytical models and literature data for adiabatic, steady-state, one-dimensional, air-water flow to predict flooding phenomenon in the SRS reactor assembly channel, which may have a counter-current air-water flow pattern during the ECS phase. In addition, the correlation was benchmarked against the experimental data conducted under the Oak Ridge National Laboratory multislit channel, which is close to the SRS assembly geometry. Furthermore, the correlation has also been used as a constitutive relationship in a new two-component two-phase thermal-hydraulics code FLOWTRAN-TF, which has been developed for a detailed analysis of SRS reactor assembly behavior during LOCA scenarios. Finally, the flooding correlation was applied to the predictions of critical heat flux, and the results were compared with the data taken by the SRS heat transfer laboratory under a single annular channel with ribs and a multiannular prototypic test rig.

  8. BEM-based numerical study of three-dimensional compressible bubble dynamics in stokes flow

    NASA Astrophysics Data System (ADS)

    Abramova, O. A.; Akhatov, I. Sh.; Gumerov, N. A.; Itkulova, Yu. A.

    2014-09-01

    The dynamics of compressible gas bubbles in a viscous shear flow and an acoustic field at low Reynolds numbers is studied. The numerical approach is based on the boundary element method (BEM), which is effective as applied to the three-dimensional simulation of bubble deformation. However, the application of the conventional BEM to compressible bubble dynamics faces difficulties caused by the degeneration of the resulting algebraic system. Additional relations based on the Lorentz reciprocity principle are used to cope with this problem. Test computations of the dynamics of a single bubble and bubble clusters in acoustic fields and shear flows are presented.

  9. A Lagrangian Model to Predict the Modification of Near-Surface Scalar Mixing Ratios and Air-Water Exchange Fluxes in Offshore Flow

    NASA Astrophysics Data System (ADS)

    Rowe, Mark D.; Perlinger, Judith A.; Fairall, Christopher W.

    2011-07-01

    A model was developed to predict the modification with fetch in offshore flow of mixing ratio, air-water exchange flux, and near-surface vertical gradients in mixing ratio of a scalar due to air-water exchange. The model was developed for planning and interpretation of air-water exchange flux measurements in the coastal zone. The Lagrangian model applies a mass balance over the internal boundary layer (IBL) using the integral depth scale approach, previously applied to development of the nocturnal boundary layer overland. Surface fluxes and vertical profiles in the surface layer were calculated using the NOAA COARE bulk algorithm and gas transfer model (e.g., Blomquist et al. 2006, Geophys Res Lett 33:1-4). IBL height was assumed proportional to the square root of fetch, and estimates of the IBL growth rate coefficient, α, were obtained by three methods: (1) calibration of the model to a large dataset of air temperature and humidity modification over Lake Ontario in 1973, (2) atmospheric soundings from the 2004 New England Air Quality Study and (3) solution of a simplified diffusion equation and an estimate of eddy diffusivity from Monin-Obukhov similarity theory (MOST). Reasonable agreement was obtained between the calibrated and MOST values of α for stable, neutral, and unstable conditions, and estimates of α agreed with previously published parametrizations that were valid for the stable IBL only. The parametrization of α provides estimates of IBL height, and the model estimates modification of scalar mixing ratio, fluxes, and near-surface gradients, under conditions of coastal offshore flow (0-50 km) over a wide range in stability.

  10. 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.

  11. Characterization of acoustic droplet vaporization for control of bubble generation under flow conditions.

    PubMed

    Kang, Shih-Tsung; Huang, Yi-Luan; Yeh, Chih-Kuang

    2014-03-01

    This study investigated the manipulation of bubbles generated by acoustic droplet vaporization (ADV) under clinically relevant flow conditions. Optical microscopy and high-frequency ultrasound imaging were used to observe bubbles generated by 2-MHz ultrasound pulses at different time points after the onset of ADV. The dependence of the bubble population on droplet concentration, flow velocity, fluid viscosity and acoustic parameters, including acoustic pressure, pulse duration and pulse repetition frequency, was investigated. The results indicated that post-ADV bubble growth spontaneously driven by air permeation markedly affected the bubble population after insonation. The bubbles can grow to a stable equilibrium diameter as great as twice the original diameter in 0.5-1 s, as predicted by the theoretical calculation. The growth trend is independent of flow velocity, but dependent on fluid viscosity and droplet concentration, which directly influence the rate of gas uptake by bubbles and the rate of gas exchange across the wall of the semipermeable tube containing the bubbles and, hence, the gas content of the host medium. Varying the acoustic pressure does not markedly change the formation of bubbles as long as the ADV thresholds of most droplets are reached. Varying pulse duration and pulse repetition frequency markedly reduces the number of bubbles. Lengthening pulse duration favors the production of large bubbles, but reduces the total number of bubbles. Increasing the PRF interestingly provides superior performance in bubble disruption. These results also suggest that an ADV bubble population cannot be assessed simply on the basis of initial droplet size or enhancement of imaging contrast by the bubbles. Determining the optimal acoustic parameters requires careful consideration of their impact on the bubble population produced for different application scenarios. PMID:24433748

  12. 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.

  13. Evolution of Bubbles through Gas Injection from a Micro-Tube into Liquid Cross-Flow

    NASA Astrophysics Data System (ADS)

    Ghaemi, Sina; Rahimi, Payam; Nobes, David

    2008-11-01

    Generation of small-size bubbles is of importance in many processes such as chemical, medical and food industries. The most common method of bubble generation is injection of gas from an orifice into the liquid phase. In spite of simplicity of this method, appropriate conditions should exist to avoid bubble growth and obtain required small-size bubbles. Thorough understanding of the bubble formation and growth can reveal the required conditions and ensure detachment of the bubbles from the orifice with desired timing to control their size. In this work, evolution of bubbles from a micro-size gas injection tube into liquid cross-flow is investigated. Special attention has been devoted to optimize the conditions to generate micro-size bubbles. Specifically, the influence of gas injection tube size and location, gas and liquid Reynolds numbers and the geometry of the mixing chamber on the bubbles evolution is studied. High-speed shadowgraphy technique is applied to investigate bubbles size and shape. A Particle Tracking Velocimetry algorithm is also applied to calculate bubbles velocity. The velocity field of the liquid flow surrounding the bubbles is also characterized using a Mirco-Stereo-Particle Image Velocimetry technique.

  14. Introductory Applicaton of Defocusing DPIV to the Study of Bubbly Shear Flows

    NASA Astrophysics Data System (ADS)

    Pereira, Francisco; Gharib, Morteza; Dabiri, Dana; Modarress, Darius

    1999-11-01

    A study of a three-dimensional bubbly flow is presented to demonstrate the applicability of the newly developed defocusing digital particle image velocimetry technique. The DDPIV instrument provides bubble size and location information within a one cubic foot volume. A three-dimensional two-phase flow measurement is performed to obtain a full-field quantitative description of the global dynamics of air bubbles in a vortical shear flow generated by a model boat propeller. Clouds of sub-millimeter air bubbles are injected upstream the propeller. The velocity field is calculated from volumetric cross-correlation of consecutive three-dimensional sets of bubble locations, whereas the bubble size information is estimated from the blurred image of bubbles. Flow analysis is presented in terms of vorticity and bubble trajectory. The bubble size distribution upstream and downstream the propeller is discussed. Growth and collapse of bubbles are detected and related to the respective velocity field in the suction and high-pressure regions of the propeller.

  15. Expansion of bubbles under a pulsatile flow regime in decompressed ovine blood vessels.

    PubMed

    Arieli, Ran; Marmur, Abraham

    2016-02-01

    After decompression of ovine large blood vessels, bubbles nucleate and expand at active hydrophobic spots on their luminal aspect. These bubbles will be in the path of the blood flow within the vessel, which might replenish the supply of gas-supersaturated plasma in their vicinity and thus, in contrast with our previous estimations, enhance their growth. We used the data from our previous study on the effect of pulsatile flow in ovine blood vessels stretched on microscope slides and photographed after decompression from hyperbaric exposure. We measured the diameter of 46 bubbles in 4 samples taken from 3 blood vessels (pulmonary artery, pulmonary vein, and aorta) in which both a "multi-bubble active spot" (MBAS)--which produces several bubbles at a time, and at least one "single-bubble active spot" (SBAS)--which produces a single bubble at a time, were seen together. The linear expansion rate for diameter in SBAS ranged from 0.077 to 0.498 mm/min and in MBAS from 0.001 to 0.332 mm/min. There was a trend toward a reduced expansion rate for bubbles in MBAS compared with SBAS. The expansion rate for bubbles in an MBAS when it was surrounded by others was very low. Bubble growth is related to gas tension, and under a flow regime, bubbles expand from a diameter of 0.1 to 1mm in 2-24 min at a gas supersaturation of 620 kPa and lower. There are two phases of bubble development. The slow and disperse initiation of active spots (from nanobubbles to gas micronuclei) continues for more than 1h, whereas the fast increase in size (2-24 min) is governed by diffusion. Bubble-based decompression models should not artificially reduce diffusion constants, but rather take both phases of bubble development into consideration. PMID:26592146

  16. Voronoï analysis of bubbly flows via ultrafast X-ray tomographic imaging

    NASA Astrophysics Data System (ADS)

    Lau, Yuk Man; Müller, Karolin; Azizi, Salar; Schubert, Markus

    2016-03-01

    Although clustering of bubbles plays a significant role in bubble column reactors regarding the heat and mass transfer due to bubble-bubble and flow field interactions, it has yet to be fully understood. Contrary to flows in bubble columns, most literature studies on clustering report numerical and experimental results on dilute or micro-bubbly flows. In this paper, clustering of bubbles in a cylindrical bubble column of 100 mm diameter is experimentally investigated. Ultrafast X-ray tomographic imaging is used to obtain the bubble positions within a hybrid Eulerian framework. By means of Voronoï analysis, the clustering behavior of bubbles is investigated. Experiments are performed with different superficial gas velocities, where Voronoï diagrams are constructed at several column heights. From the PDFs of the Voronoï diagrams, it is shown that the bubble structuring in terms of Voronoï cell volumes develops slower than the bubble size distribution. The latter reaches a steady state earlier with increasing column height. The measured PDFs are compared with the PDF of randomly distributed points, which showed that the amount of bubbles as part of clusters (Voronoï cells < V/overline{V}_{cluster}) as well as bubbles as part of voids (Voronoï cells > V/overline{V}_{void}) increases with the superficial gas velocity. It is found that all experiments have an approximate cluster limit V/overline{V}_{cluster} of 0.63, while the void limit V/overline{V}_{void} varies between 1.5 and 3.0.

  17. Implications of surfactant-induced flow for miscible-displacement estimation of air-water interfacial areas in unsaturated porous media.

    PubMed

    Costanza-Robinson, Molly S; Zheng, Zheng; Henry, Eric J; Estabrook, Benjamin D; Littlefield, Malcolm H

    2012-10-16

    Surfactant miscible-displacement experiments represent a conventional means of estimating air-water interfacial area (A(I)) in unsaturated porous media. However, changes in surface tension during the experiment can potentially induce unsaturated flow, thereby altering interfacial areas and violating several fundamental method assumptions, including that of steady-state flow. In this work, the magnitude of surfactant-induced flow was quantified by monitoring moisture content and perturbations to effluent flow rate during miscible-displacement experiments conducted using a range of surfactant concentrations. For systems initially at 83% moisture saturation (S(W)), decreases of 18-43% S(W) occurred following surfactant introduction, with the magnitude and rate of drainage inversely related to the surface tension of the surfactant solution. Drainage induced by 0.1 mM sodium dodecyl benzene sulfonate, commonly used for A(I) estimation, resulted in effluent flow rate increases of up to 27% above steady-state conditions and is estimated to more than double the interfacial area over the course of the experiment. Depending on the surfactant concentration and the moisture content used to describe the system, A(I) estimates varied more than 3-fold. The magnitude of surfactant-induced flow is considerably larger than previously recognized and casts doubt on the reliability of A(I) estimation by surfactant miscible-displacement. PMID:23033988

  18. Optical measurements of gas bubbles in oil behind a cavitating micro-orifice flow

    NASA Astrophysics Data System (ADS)

    Iben, Uwe; Wolf, Fabian; Freudigmann, Hans-Arndt; Fröhlich, Jochen; Heller, Winfried

    2015-06-01

    In hydraulic systems, it is common for air release to occur behind valves or throttles in the form of bubbles. These air bubbles can affect the behavior and the performance of these systems to a substantial extent. In the paper, gas release in a liquid flow behind an orifice is analyzed by optical methods for various operation points. The bubbles are observed with a digital camera, and a detection algorithm based on the Hough transformation is used to determine their number and size. The appearance of gas bubbles is very sensitive to the inlet and outlet pressure of the orifice. Gas bubbles are only observed if choking cavitation occurs. An empirical relationship between an adjusted cavitation number and the appearance of gas release is presented. It is assumed that the observed bubbles contain mostly air. With the applied pressure differences, up to 30 % of the dissolved air was degassed in the form of bubbles.

  19. 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.

  20. Bubble shape and breakage events in a vertical pipe at the boiler flow line

    NASA Astrophysics Data System (ADS)

    Fsadni, Andrew; Ge, Yunting

    2014-03-01

    The theoretical and experimental aspects concerning the typical bubble shape at the flow line of a standard domestic central heating system are investigated. This is done in support of the on-going research on two-phase flows in domestic central heating systems. Bubble nucleation and detachment at the primary heat exchanger wall of a domestic central heating boiler results in a bubbly two-phase flow in the system pipe work. Bubbly flow results in undesired cold spots at higher points in the system, consequently diminishing system performance. An experimental analysis was done on the bubble shape at the exit of the boiler through the application of photographic techniques. The results are presented in terms of the measured bubble aspect ratios at some principal system operating conditions. The dimensionless Eotvos and bubble Reynolds number were calculated and tabulated with the measured mean diameters. The data was subsequently correlated to the bubble shape regime diagram. Results suggest that most bubbles are quasi-spherical in shape with a noticeable elongation at lower bulk fluid Reynolds numbers.

  1. The terminal velocity of a bubble in an oscillating flow.

    SciTech Connect

    Torczynski, John Robert; Kraynik, Andrew Michael; Romero, Louis Anthony

    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 {alpha} = R{sup 2} {phi}/R{sup 2} {phi} {nu}.-{nu}, where R is the bubble radius, {phi} is the driving frequency, and {nu} is the liquid kinematic viscosity. If {alpha} is large, this term is unimportant, but if {alpha} is small, this term is the dominant factor in determining the terminal velocity.

  2. Phase-field simulation of gas bubble growth and flow in a Hele-Shaw cell

    NASA Astrophysics Data System (ADS)

    Sun, Ying

    2005-11-01

    A diffuse interface model has been developed for gas bubble growth and dynamics in a supersaturated liquid. The liquid becomes supersaturated in the gas species because of a drop in the pressure or temperature. The bubbles grow by gas diffusion in the liquid towards the bubble interfaces. During bubble growth, flows are induced by the large density contrast between the phases. The bubbles coarsen due to surface tension effects. The process widely exists in biological systems, materials processing, oil recovery, and other applications. The flows in the gas and liquid phases are solved using a diffuse interface model for two-phase flows with surface tension, phase change, and density and viscosity differences between the phases. This diffuse-interface model for flow is coupled with a phase-field equation for calculating the interface motion, and a species conservation equation for the gas transport. The model is validated for a single bubble growing inside a semi-infinite liquid, and convergence of the results with respect to the interface width is demonstrated. Large-scale numerical simulations for multiple bubbles inside a Hele-Shaw cell reveal the presence of complex interface dynamics and flows. The bubble dynamics, including coarsening and coalescence, are investigated as a function of the initial gas concentration, surface tension, and the density and viscosity contrasts between the phases.

  3. Internal Flow in a Free Drop (IFFD) Bubble Surface Tension Experiment

    NASA Technical Reports Server (NTRS)

    1999-01-01

    This digital QuickTime movie is of the Internal Flow in a Free Drop (IFFD) Bubble Surface Tension Experiment taking place in the Microgravity laboratory at NASA's Marshall Space Flight Center (MSFC) in Huntsville, Alabama. The Bubble provides scientists with information about fluid surface tensions in a low-gravity environment.

  4. Determining Flow Type and Shear Rate in Magmas From Bubble Shapes and Orientations

    NASA Astrophysics Data System (ADS)

    Rust, A. C.; Manga, M.; Cashman, K. V.

    2001-12-01

    To compare bubble geometries in obsidian to bubbles deformed under known conditions, we measure the deformation of air bubbles in corn syrup in simple shear. We use these experimental data and results of theoretical, numerical and experimental studies to interpret the shear environments that formed the textures preserved in obsidian samples. In particular, we use the shapes and orientations of bubbles in obsidian to estimate shear rates and assess flow type (simple vs. pure shear). This technique can be used to determine shear rates in volcanic conduits, the origin of pyroclastic obsidian, and the emplacement history and dynamics of obsidian flows. The deformation of a bubble is governed by the competing stresses from shearing that deforms, and surface tension that rerounds. The ratio of these stresses is the capillary number, Ca. An initially spherical bubble placed in a low Reynolds number, steady flow field deforms with a time-dependent shape and orientation until it reaches a steady geometry or breaks into smaller bubbles. A useful measure of the magnitude of flow-induced bubble deformation is the dimensionless parameter, D=(l-b)/(l+b) where l and b are the semi-major and semi-minor axes of the sheared bubble. For small deformations (Ca<< 1), low Reynolds number flow and bubble viscosity << suspending fluid viscosity, D ~ 2 Ca in pure shear and D ~ Ca in simple shear. In pure shear flow, bubble elongations are parallel to the shear direction regardless of the magnitude of bubble deformation. However, in simple shear flow, the angle between the bubble elongation and the flow varies with Ca, which is proportional to bubble radius and shear rate. Because the relationships between Ca and bubble orientation and shape for pure and simple shear differ, we can distinguish between these flow types using bubble geometries preserved in obsidian. Furthermore, because Ca is a function of shear rate, we can use relationships between Ca and D to calculate shear rates when

  5. Bubble production using a Non-Newtonian fluid in microfluidic flow focusing device

    NASA Astrophysics Data System (ADS)

    Wang, Yi-Lin; Ward, Thomas; Grant, Christine

    2012-02-01

    We experimentally study the production of micrometer-sized bubbles using microfluidic technology and a flow-focusing geometry. Bubbles are produced by using a mixture containing aqueous polyacrylamide of concentrations ranging from 0.01-0.10% by weight and several solution also containing a sodium-lauryl-sulfate (SLS) surfactant at concentrations ranging 0.01-0.1% by weight. The fluids are driven by controlling the static pressure above a hydrostatic head of the liquid while the disperse phase fluid static pressure is held constant (air). In the absence of surfactant the bubble production is discontinuous. The addition of surfactant stabilizes the bubble production. In each type of experiment, the bubble length l, velocity U and production frequency φ are measured and compared as a function of the inlet pressure ratio. The bubbles exhibit a contraction in their downstream length as a function of the polymer concentration which is investigated.

  6. 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.

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

    PubMed Central

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

    2012-01-01

    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. PMID:23049158

  8. Experimental study of the liquid flow near a single sonoluminescent bubble

    PubMed

    Verraes; Lepoint-Mullie; Lepoint; Longuet-Higgins

    2000-07-01

    Tracers (sulphur particles produced in situ by a bubble itself, fuchsin spots and dust) were used to probe the liquid flows in the neighborhood of single sonoluminescent bubbles maintained in levitation in a resonant acoustic setup. The flows caused by the bubble were distinguished clearly from the streamings (mean Lagrangian velocity: approximately 20 microm/s) associated with resonant cells in the absence of a bubble. The liquid flow due to the presence of the bubble formed around it over a few mm. The radial component of the Lagrangian velocities (maximum value measured: approximately 260 microm/s) of this flow evolved as r(-1) , with r as the distance from the bubble, while the tangential component remained approximately constant (approximately 20 microm/s). In the Appendix by M. S. Longuet-Higgins, a simplified model of microstreaming involving a spherical bubble in translational and radial oscillation gives a qualitative description of the experiments. A fairly good agreement was observed between the experiments and the modeling, which involved a dipole flow enclosed in a Stokeslet. PMID:10923877

  9. 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.

  10. MR relaxometry of micro-bubbles in the vertical bubbly flow at a low magnetic field (0.2T).

    PubMed

    Arbabi, A; Hall, J; Richard, P; Wilkins, S; Mastikhin, I V

    2014-10-17

    Measurements of the vertical bubbly flow were performed at a low magnetic field of 0.2T. The void fraction data were acquired. The susceptibility-induced changes in T2 relaxation time were analyzed using the previously introduced approaches by Sukstanskii et al. and Ziener et al., originally developed for the Magnetic Resonance analysis of randomly distributed and isolated spherical inclusions, and a simple model of a spherical particle, respectively. The CPMG signal decay due to the presence of spherical inclusions was approximated as linear vs. CPMG inter-echo times to extract the average inclusion's size information. Two equations were derived for a simplified analysis of gas-liquid systems with basic T2 measurements, and without prior knowledge on the gas-liquid susceptibility or a need for the magnetic gradient setup. They can provide estimates for the void fraction and the average inclusion size, provided the CPMG inter-echo time requirements are met. For the control samples, there was a good agreement with the theory. For the bubbly flows, a good agreement was observed between the Magnetic Resonance and optics-based estimates for the slowest airflow rate. The deviation, however, increased for higher airflow rates. The introduced approach lends itself to the characterization of multi-phase systems such as cavitating media and well-separated bubbly flows. PMID:25462942

  11. MR relaxometry of micro-bubbles in the vertical bubbly flow at a low magnetic field (0.2 T)

    NASA Astrophysics Data System (ADS)

    Arbabi, A.; Hall, J.; Richard, P.; Wilkins, S.; Mastikhin, I. V.

    2014-12-01

    Measurements of the vertical bubbly flow were performed at a low magnetic field of 0.2 T. The void fraction data were acquired. The susceptibility-induced changes in T2 relaxation time were analyzed using the previously introduced approaches by Sukstanskii et al. and Ziener et al., originally developed for the Magnetic Resonance analysis of randomly distributed and isolated spherical inclusions, and a simple model of a spherical particle, respectively. The CPMG signal decay due to the presence of spherical inclusions was approximated as linear vs. CPMG inter-echo times to extract the average inclusion's size information. Two equations were derived for a simplified analysis of gas-liquid systems with basic T2 measurements, and without prior knowledge on the gas-liquid susceptibility or a need for the magnetic gradient setup. They can provide estimates for the void fraction and the average inclusion size, provided the CPMG inter-echo time requirements are met. For the control samples, there was a good agreement with the theory. For the bubbly flows, a good agreement was observed between the Magnetic Resonance and optics-based estimates for the slowest airflow rate. The deviation, however, increased for higher airflow rates. The introduced approach lends itself to the characterization of multi-phase systems such as cavitating media and well-separated bubbly flows.

  12. Tangential stress beneath wind-driven air water interfaces

    NASA Astrophysics Data System (ADS)

    Banner, Michael L.; Peirson, William L.

    1998-06-01

    The detailed structure of the aqueous surface sublayer flow immediately adjacent to the wind-driven air water interface is investigated in a laboratory wind-wave flume using particle image velocimetry (PIV) techniques. The goal is to investigate quantitatively the character of the flow in this crucial, very thin region which is often disrupted by microscale breaking events. In this study, we also examine critically the conclusions of Okuda, Kawai & Toba (1977), who argued that for very short, strongly forced wind-wave conditions, shear stress is the dominant mechanism for transmitting the atmospheric wind stress into the water motion waves and surface drift currents. In strong contrast, other authors have more recently observed very substantial normal stress contributions on the air side. The availability of PIV and associated image technology now permits a timely re-examination of the results of Okuda et al., which have been influential in shaping present perceptions of the physics of this dynamically important region. The PIV technique used in the present study overcomes many of the inherent shortcomings of the hydrogen bubble measurements, and allows reliable determination of the fluid velocity and shear within 200 [mu]m of the instantaneous wind-driven air water interface.

  13. Bubble motion through a generalized power-law fluid flowing in a vertical tube.

    PubMed

    Mukundakrishnan, Karthik; Eckmann, David M; Ayyaswamy, P S

    2009-04-01

    Intravascular gas embolism may occur with decompression in space flight, as well as during cardiac and vascular surgery. Intravascular bubbles may be deposited into any end organ, such as the heart or the brain. Surface interactions between the bubble and the endothelial cells lining the vasculature result in serious impairment of blood flow and can lead to heart attack, stroke, or even death. To develop effective therapeutic strategies, there is a need for understanding the dynamics of bubble motion through blood and its interaction with the vessel wall through which it moves. Toward this goal, we numerically investigate the axisymmetric motion of a bubble moving through a vertical circular tube in a shear-thinning generalized power-law fluid, using a front-tracking method. The formulation is characterized by the inlet Reynolds number, capillary number, Weber number, and Froude number. The flow dynamics and the associated wall shear stresses are documented for a combination of two different inlet flow conditions (inlet Reynolds numbers) and three different effective bubble radii (ratio of the undeformed bubble radii to the tube radii). The results of the non-Newtonian model are then compared with that of the model assuming a Newtonian blood viscosity. Specifically, for an almost occluding bubble (effective bubble radius = 0.9), the wall shear stress and the bubble residence time are compared for both Newtonian and non-Newtonian cases. Results show that at low shear rates, for a given pressure gradient the residence time for a non-Newtonian flow is higher than that for a Newtonian flow. PMID:19426324

  14. 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.

  15. Characterization of flow turbulence in large-scale bubble-plume experiments

    NASA Astrophysics Data System (ADS)

    García, Carlos M.; García, Marcelo H.

    2006-07-01

    Flow turbulence generated by a bubble plume in a large tank is characterized. Two different turbulence mechanisms contributing to the mixing and transport process are identified on velocity signals recorded outside of the bubble-plume core: a macro-scale process governed by the wandering motion of the bubble-plume; and an intermediate- and micro-scale process represented by the Kolmogorov power spectrum. A methodology is presented to characterize the different processes and their contributions to the turbulence parameters. The results help to understand the bubble-plume phenomenon and provide a basis to validate numerical models of bubble-plumes used in the design of combined-sewer-overflow reservoirs.

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. Influence of sonication conditions on the efficiency of ultrasonic cleaning with flowing micrometer-sized air bubbles.

    PubMed

    Tuziuti, Toru

    2016-03-01

    This paper describes the sizes of cleaned areas under different sonication conditions with the addition of flowing micrometer-sized air bubbles. The differences in the cleaned area of a glass plate pasted with silicon grease as a dirty material under different sonication conditions were investigated after tiny bubbles were blown on the dirty plate placed in an underwater sound field. The ultrasound was applied perpendicular to the bubble flow direction. The shape of the cleaned areas was nearly elliptical, so the lengths of the minor and major axes were measured. The length of the minor axis under sweep conditions (amplitude modulation), for which the average power was lower than that for continuous wave (CW) irradiation, was comparable to that for CW irradiation and was slightly larger than under bubble flow only. Not only the relatively high power for CW irradiation, but also the larger angular change of the bubble flow direction under sweep conditions contributed to the enlargement of the cleaned area in the direction of the minor axis. The combination of bubble flow and sonication under sweep or CW conditions produced a larger cleaned area compared with bubble flow only, although the increase was not higher than 20%. A rapid change from an air to water interface caused by the bubble flow and water jets caused by the collapse of bubbles due to violent pulsation is the main cleaning mechanism under a combination of ultrasound and bubble flow. PMID:26422770

  2. Pressure effects on bubble-column flow characteristics

    SciTech Connect

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

    1996-03-01

    Bubble-column reactors are used in the chemical processing industry for two-phase and three-phase chemical reactions. Hydrodynamic effects must be considered when attempting to scale these reactors to sizes of industrial interest, and diagnostics are needed to acquire data for the validation of multiphase scaling predictions. This paper discusses the use of differential pressure (DP) and gamma- densitometry tomography (GDT) measurements to ascertain the gas distribution in a two-phase bubble column reactor. Tests were performed on an industrial scale reactor (3-m tall, 0.48-m inside diameter) using a 5-Curie cesium-137 source with a sodium-iodide scintillation detector. GDT results provide information on the time- averaged cross-sectional distribution of gas in the liquid, and DP measurements provide information on the time and volume averaged axial distribution of gas. Close agreement was observed between the two methods of measuring the gas distribution in the bubble column. The results clearly show that, for a fixed volumetric flowrate through the reactor, increasing the system pressure leads to an increase in the gas volume fraction or ``gas holdup`` in the liquid. It is also shown from this work that GDT can provide useful diagnostic information on industrial scale bubble-column reactors.

  3. 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.

  4. Modeling and simulation of multiple bubble entrainment and interactions with two dimensional vortical flows

    NASA Astrophysics Data System (ADS)

    Finn, Justin; Shams, Ehsan; Apte, Sourabh V.

    2011-02-01

    Simulations of bubble entrainment and interactions with two dimensional vortical flows are preformed using a discrete element model. In this Eulerian-Lagrangian approach, solution to the carrier phase is obtained using direct numerical simulation whereas motion of subgrid bubbles is modeled using Lagrangian tracking. The volumetric displacement of the fluid by the finite size of the bubbles is modeled along with interphase momentum-exchange for a realistic coupling of the bubbles to the carrier phase. In order to assess the importance of this volumetric coupling effect, even at low overall volume loading, simulations of a small number of microbubbles entrained in a traveling vortex tube are studied in detail. The test case resembles the experiments conducted by Sridhar and Katz [JFM, 1999] on bubble entrainment in vortex rings. It is shown that under some conditions, the entrainment of eight small bubbles, 1100 μm or less in diameter, result in significant levels of vortex distortion when modeled using the volumetric coupling effect. Neglecting these effects, however, does not result in any vortex distortion due to entrained bubbles. The nondimensionalized vortex strength versus bubble settling locations are compared with experimental data to show collapse of the data along the trends observed in experiments only when the volumetric effects are modeled. Qualitative and quantitative assessments of this distortion observed with volumetric coupling are made using three methods; bubble induced vortex asymmetry, relative change in the decay of angular momentum, and relative change in the peak vorticity. It is found that in all cases the volumetric effects result in a relative increase of the vortex decay rate. The concept of a relative reaction force, defined as the ratio of net bubble to fluid reaction to the local driving force of the vortex, is introduced to analyze this effect. It is shown that the global increases in vortex decay rate are directly proportional to

  5. The effects of bubbles on the structure of upward gas-liquid flow

    NASA Astrophysics Data System (ADS)

    Gubaidulin, D. A.; Snigerev, B. A.

    2016-01-01

    The paper presents the results of study of the local structure of turbulent gas-liquid flow in vertical pipe. A mathematical model based on the use of Eulerian description for both phases taking into account the action of different forces of interfacial interaction. Special attention is paid to the development of approaches for the simulation of polydispersed bubbly flows taking into account processes of coagulation and fragmentation. Comparison of simulation results with experimental data showed that the developed approach allows to obtain detailed information about the structures of turbulent gas-liquid flows, the distribution of bubbles by size.

  6. Helium bubble flow visualization of the spanwise separation on a NACA 0012 with simulated glaze ice

    NASA Technical Reports Server (NTRS)

    Kerho, M.; Bragg, M.; Shin, J.

    1992-01-01

    Research was performed to experimentally visualize and document the flow separation due to simulated glaze ice accretion on a NACA 0012 semispan with 30 deg sweep using helium bubbles as flow tracers. Results are compared to Navier-Stokes computational simulations for different angles of attack. Prior to acquiring data for the semispan model, a two dimensional experiment was conducted to determine the accuracy of using the helium bubbles as flow tracers. Results from the three dimensional experiment compare well to the computational simulations.

  7. Helium bubble flow visualization of the spanwise separation on a NACA 0012 with simulated glaze ice

    NASA Technical Reports Server (NTRS)

    Kerho, M.; Bragg, M.; Shin, J.

    1992-01-01

    Research has been performed to experimentally visualize and document the flow separation due to simulated glaze ice accretion on a NACA 0012 semispan with 30-deg sweep using helium bubbles as flow tracers. Results are compared to Navier-Stokes computational simulations for different angles of attack. Prior to acquiring data for the semispan model, a two-dimensional experiment was conducted to determine the accuracy of using the helium bubbles as flow tracers. Results from the 3D experiment compare well to the computational simulations.

  8. 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.

  9. 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. PMID:26178406

  10. 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.

  11. A Generalized Eulerian-Lagrangian Analysis, with Application to Liquid Flows with Vapor Bubbles

    NASA Technical Reports Server (NTRS)

    Dejong, Frederik J.; Meyyappan, Meyya

    1993-01-01

    Under a NASA MSFC SBIR Phase 2 effort an analysis has been developed for liquid flows with vapor bubbles such as those in liquid rocket engine components. The analysis is based on a combined Eulerian-Lagrangian technique, in which Eulerian conservation equations are solved for the liquid phase, while Lagrangian equations of motion are integrated in computational coordinates for the vapor phase. The novel aspect of the Lagrangian analysis developed under this effort is that it combines features of the so-called particle distribution approach with those of the so-called particle trajectory approach and can, in fact, be considered as a generalization of both of those traditional methods. The result of this generalization is a reduction in CPU time and memory requirements. Particle time step (stability) limitations have been eliminated by semi-implicit integration of the particle equations of motion (and, for certain applications, the particle temperature equation), although practical limitations remain in effect for reasons of accuracy. The analysis has been applied to the simulation of cavitating flow through a single-bladed section of a labyrinth seal. Models for the simulation of bubble formation and growth have been included, as well as models for bubble drag and heat transfer. The results indicate that bubble formation is more or less 'explosive'. for a given flow field, the number density of bubble nucleation sites is very sensitive to the vapor properties and the surface tension. The bubble motion, on the other hand, is much less sensitive to the properties, but is affected strongly by the local pressure gradients in the flow field. In situations where either the material properties or the flow field are not known with sufficient accuracy, parametric studies can be carried out rapidly to assess the effect of the important variables. Future work will include application of the analysis to cavitation in inducer flow fields.

  12. A generalized Eulerian-Lagrangian analysis, with application to liquid flows with vapor bubbles

    NASA Astrophysics Data System (ADS)

    Dejong, Frederik J.; Meyyappan, Meyya

    1993-07-01

    Under a NASA MSFC SBIR Phase 2 effort an analysis has been developed for liquid flows with vapor bubbles such as those in liquid rocket engine components. The analysis is based on a combined Eulerian-Lagrangian technique, in which Eulerian conservation equations are solved for the liquid phase, while Lagrangian equations of motion are integrated in computational coordinates for the vapor phase. The novel aspect of the Lagrangian analysis developed under this effort is that it combines features of the so-called particle distribution approach with those of the so-called particle trajectory approach and can, in fact, be considered as a generalization of both of those traditional methods. The result of this generalization is a reduction in CPU time and memory requirements. Particle time step (stability) limitations have been eliminated by semi-implicit integration of the particle equations of motion (and, for certain applications, the particle temperature equation), although practical limitations remain in effect for reasons of accuracy. The analysis has been applied to the simulation of cavitating flow through a single-bladed section of a labyrinth seal. Models for the simulation of bubble formation and growth have been included, as well as models for bubble drag and heat transfer. The results indicate that bubble formation is more or less 'explosive'. for a given flow field, the number density of bubble nucleation sites is very sensitive to the vapor properties and the surface tension. The bubble motion, on the other hand, is much less sensitive to the properties, but is affected strongly by the local pressure gradients in the flow field. In situations where either the material properties or the flow field are not known with sufficient accuracy, parametric studies can be carried out rapidly to assess the effect of the important variables. Future work will include application of the analysis to cavitation in inducer flow fields.

  13. 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.

  14. 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.

  15. 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.

  16. An experimental study on the effect of air bubble injection on the flow induced rotational hub

    SciTech Connect

    Nouri, N.M.; Sarreshtehdari, A.

    2009-01-15

    Modification of shear stress due to air bubbles injection in a rotary device was investigated experimentally. Air bubbles inject to the water flow crosses the neighbor of the hub which can rotate just by water flow shear stresses, in this device. Increasing air void fraction leads to decrease of shear stresses exerted on the hub surface until in high void fractions, the hub motion stopped as observed. Amount of skin friction decrease has been estimated by counting central hub rotations. Wall shear stress was decreased by bubble injection in all range of tested Reynolds number, changing from 50,378 to 71,238, and also by increasing air void fraction from zero to 3.06%. Skin friction reduction more than 85% was achieved in this study as maximum measured volume of air fraction injected to fluid flow while bubbles are distinct and they do not make a gas layer. Significant skin friction reduction obtained in this special case indicate that using small amount of bubble injection causes large amount of skin friction reduction in some rotary parts in the liquid phases like as water. (author)

  17. 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)

  18. Creating Small Gas Bubbles in Flowing Mercury Using Turbulence at an Orifice

    SciTech Connect

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

    2010-01-01

    Pressure waves created in liquid mercury pulsed spallation targets have been shown to create cavitation damage to 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, creating such a population in mercury is difficult due to the high surface tension and particularly the non-wetting behavior of mercury on gas-injection hardware. If the larger injected gas bubbles can be broken down into small bubbles after they are introduced to the flow, then the material interface problem is avoided. Research at the Oak Ridge National Labarotory is underway to develop a technique that has shown potential to provide an adequate population of small-enough bubbles to a flowing spallation target. This technique involves gas injection at an orifice of a geometry that is optimized to the turbulence intensity and pressure distribution of the flow, while avoiding coalescence of gas at injection sites. The most successful geometry thus far can be described as a square-toothed orifice having a 2.5 bar pressure drop in the nominal flow of 12 L/s for one of the target inlet legs. High-speed video and high-resolution photography have been used to quantify the bubble population on the surface of the mercury downstream of the gas injection sight. Also, computational fluid dynamics has been used to optimize the dimensions of the toothed orifice based on a RANS computed mean flow including turbulent energies such that the turbulent dissipation and pressure field are best suited for turbulent break-up of the gas bubbles.

  19. Acoustic monitoring of gas emissions from the seafloor. Part I: quantifying the volumetric flow of bubbles

    NASA Astrophysics Data System (ADS)

    Leblond, Isabelle; Scalabrin, Carla; Berger, Laurent

    2014-09-01

    Three decades of continuous ocean exploration have led us to identify subsurface fluid related processes as a key phenomenon in marine earth science research. The number of seep areas located on the seafloor has been constantly increasing with the use of multi-scale imagery techniques. Due to recent advances in transducer technology and computer processing, multibeam echosounders are now commonly used to detect submarine gas seeps escaping from the seafloor into the water column. A growing number of en- route surveys shows that sites of gas emissions escaping from the seafloor are much more numerous than previously thought. Estimating the temporal variability of the gas flow rate and volumes escaping from the seafloor has thus become a challenge of relevant interest which could be addressed by sea-floor continuous acoustic monitoring. Here, we investigate the feasibility of estimating the volumetric flow rates of gas emissions from horizontal backscattered acoustic signals. Different models based on the acoustic backscattering theory of bubbles are presented. The forward volume backscattering strength and the inversion volumetric flow rate solutions were validated with acoustic measurements from artificial gas flow rates generated in controlled sea-water tank experiments. A sensitivity analysis was carried out to investigate the behavior of the 120-kHz forward solution with respect to model input parameters (horizontal distance between transducer and bubble stream, bubble size distribution and ascent rate). The most sensitive parameter was found to be the distance of the bubble stream which can affect the volume backscattering strength by 20 dB within the horizontal range of 0-200 m. Results were used to derive the detection probability of a bubble stream for a given volume backscattering strength threshold according to different bubble flow rates and horizontal distance.

  20. 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.

  1. On the relevance of bubbles and potential flows for stellar convection

    NASA Astrophysics Data System (ADS)

    Miller Bertolami, M. M.; Viallet, M.; Prat, V.; Barsukow, W.; Weiss, A.

    2016-04-01

    Recently Pasetto et al. have proposed a new method to derive a convection theory appropriate for the implementation in stellar evolution codes. Their approach is based on the simple physical picture of spherical bubbles moving within a potential flow in dynamically unstable regions, and a detailed computation of the bubble dynamics. Based on this approach, the authors derive a new theory of convection which is claimed to be parameter-free, non-local and time-dependent. This is a very strong claim, as such a theory is the holy grail of stellar physics. Unfortunately, we have identified several distinct problems in the derivation which ultimately render their theory inapplicable to any physical regime. In addition, we show that the framework of spherical bubbles in potential flows is unable to capture the essence of stellar convection, even when equations are derived correctly.

  2. Bubble-size distributions produced by wall injection of air into flowing freshwater, saltwater and surfactant solutions

    NASA Astrophysics Data System (ADS)

    Winkel, Eric S.; Ceccio, Steven L.; Dowling, David R.; Perlin, Marc

    2004-12-01

    As air is injected into a flowing liquid, the resultant bubble characteristics depend on the properties of the injector, near-wall flow, and flowing liquid. Previous research has shown that near-wall bubbles can significantly reduce skin-friction drag. Air was injected into the turbulent boundary layer on a test section wall of a water tunnel containing various concentrations of salt and surfactant (Triton-X-100, Union Carbide). Photographic records show that the mean bubble diameter decreased monotonically with increasing salt and surfactant concentrations. Here, 33 ppt saltwater bubbles had one quarter, and 20 ppm Triton-X-100 bubbles had one half of the mean diameter of freshwater bubbles.

  3. 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.

  4. 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).

  5. 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.

  6. 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.

  7. Foam flows in 2D porous media: intermittency and bubble fragmentation

    NASA Astrophysics Data System (ADS)

    Meheust, Y.; Géraud, B.; Jones, S. A.; Dollet, B.; Cantat, I.

    2014-12-01

    Flowing foams are used in many engineering and technical applications. A well-known application is oil recovery. Another one is the remediation of polluted soils: the foam is injected into the ground in order to mobilize chemical species present in the medium. Apart from potential interesting physico-chemical and biochemical properties, foams have peculiar flow properties that applications might benefit of. In particular, viscous dissipation arises mostly from the contact zones between the soap films and the walls, which results in peculiar friction laws allowing the foam to invade narrow pores more efficiently than Newtonian fluids would. In most experimental studies no local information of the foam structure is possible, and only global quantities such as the effective viscosity can be measured. Using two-dimensional transparent flow cells, we have previously shown that foam structural [1] and elastic [2] effects significantly impact the flow of foams in porous media. We now present an investigation of foam flow through a two-dimensional (2D) porous medium consisting of circular obstacles positioned randomly in a Hele-Shaw cell (see figure). The foam structure is recorded in time by a video camera and subsequently analyzed by image processing, which provides us with the velocity field and spatial distribution of bubble sizes. The flow exhibits a rich phenomenology, including flow irreversibility, preferential flow paths, local flow intermittency/non-stationarity (despite the imposed permanent global flow rate). Moreover, the medium impacts the nature of the flowing fluid by selecting the bubble size through bubble fragmentation. We investigate how preferential flow paths and intermittency depend on the imposed global flow rate and foam quality (the water content), and show that the spatial distribution of bubble sizes is to some extent correlated with the velocity field. We furthermore measure the evolution, along the flow direction, of the probability density

  8. 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.

  9. 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

  10. Recalcitrant bubbles

    PubMed Central

    Shanahan, Martin E. R.; Sefiane, Khellil

    2014-01-01

    We demonstrate that thermocapillary forces may drive bubbles against liquid flow in ‘anomalous' mixtures. Unlike ‘ordinary' liquids, in which bubbles migrate towards higher temperatures, we have observed vapour bubbles migrating towards lower temperatures, therefore against the flow. This unusual behaviour may be explained by the temperature dependence of surface tension of these binary mixtures. Bubbles migrating towards their equilibrium position follow an exponential trend. They finally settle in a stationary position just ‘downstream' of the minimum in surface tension. The exponential trend for bubbles in ‘anomalous' mixtures and the linear trend in pure liquids can be explained by a simple model. For larger bubbles, oscillations were observed. These oscillations can be reasonably explained by including an inertial term in the equation of motion (neglected for smaller bubbles). PMID:24740256

  11. 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.

  12. Friction Drag Reduction of External Flows with Bubble and Gas Injection

    NASA Astrophysics Data System (ADS)

    Ceccio, Steven L.

    2010-01-01

    The lubrication of external liquid flow with a bubbly mixture or gas layer has been the goal of engineers for many years, and this article presents the underlying principles and recent advances of this technology. It reviews the use of partial and supercavities for drag reduction of axisymmetric objects moving within a liquid. Partial cavity flows can also be used to reduce the friction drag on the nominally two-dimensional portions of a horizontal surface, and the basic flow features of two-dimensional cavities are presented. Injection of gas can lead to the creation of a bubbly mixture near the flow surface that can significantly modify the flow within the turbulent boundary layer, and there have been significant advances in the understanding of the underlying physical process of drag reduction. Moreover, with sufficient gas flux, the bubbles flowing beneath a solid surface can coalesce to form a thin drag-reducing air layer. The current applications of these techniques to underwater vehicles and surface ships are discussed.

  13. Quantitative measurement by artificial vision of small bubbles in flowing mercury

    NASA Astrophysics Data System (ADS)

    Paquit, Vincent C.; Wendel, Mark W.; Felde, David K.; Riemer, Bernie W.

    2011-03-01

    At the Spallation Neutron Source (SNS), an accelerator-based neutron source located at the Oak Ridge National Laboratory (Tennessee, USA), the production of neutrons is obtained by accelerating protons against a mercury target. This self-cooling target, however, suffers rapid heat deposition by the beam pulse leading to large pressure changes and thus to cavitations that may be damaging to the container. In order to locally compensate for pressure increases, a small-bubble population is added to the mercury flow using gas bubblers. The geometry of the bubblers being unknown, we are testing several bubblers' configurations and are using machine vision techniques to characterize their efficiency by quantitative measurement of the created bubble population. In this paper we thoroughly detail the experimental setup and the image processing techniques used to quantitatively assess the bubble population. To support this approach we are comparing our preliminary results for different bubblers and operating modes, and discuss potential improvements.

  14. Quantitative measurement by artificial vision of small bubbles in flowing mercury

    SciTech Connect

    Paquit, Vincent C; Wendel, Mark W; Felde, David K; Riemer, Bernie

    2011-01-01

    At the Spallation Neutron Source (SNS), an accelerator-based neutron source located at the Oak Ridge National Laboratory (Tennessee, USA), the production of neutrons is obtained by accelerating protons against a mercury target. This self-cooling target, however, suffers rapid heat deposition by the beam pulse leading to large pressure changes and thus to cavitations that may be damaging to the container. In order to locally compensate for pressure increases, a small-bubble population is added to the mercury flow using gas bubblers. The geometry of the bubblers being unknown, we are testing several bubblers configurations and are using machine vision techniques to characterize their efficiency by quantitative measurement of the created bubble population. In this paper we thoroughly detail the experimental setup and the image processing techniques used to quantitatively assess the bubble population. To support this approach we are comparing our preliminary results for different bubblers and operating modes, and discuss potential improvements.

  15. 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.

  16. Size-selective sorting in bubble streaming flows: Particle migration on fast time scales

    NASA Astrophysics Data System (ADS)

    Thameem, Raqeeb; Rallabandi, Bhargav; Hilgenfeldt, Sascha

    2015-11-01

    Steady streaming from ultrasonically driven microbubbles is an increasingly popular technique in microfluidics because such devices are easily manufactured and generate powerful and highly controllable flows. Combining streaming and Poiseuille transport flows allows for passive size-sensitive sorting at particle sizes and selectivities much smaller than the bubble radius. The crucial particle deflection and separation takes place over very small times (milliseconds) and length scales (20-30 microns) and can be rationalized using a simplified geometric mechanism. A quantitative theoretical description is achieved through the application of recent results on three-dimensional streaming flow field contributions. To develop a more fundamental understanding of the particle dynamics, we use high-speed photography of trajectories in polydisperse particle suspensions, recording the particle motion on the time scale of the bubble oscillation. Our data reveal the dependence of particle displacement on driving phase, particle size, oscillatory flow speed, and streaming speed. With this information, the effective repulsive force exerted by the bubble on the particle can be quantified, showing for the first time how fast, selective particle migration is effected in a streaming flow. We acknowledge support by the National Science Foundation under grant number CBET-1236141.

  17. Investigation of liquid phase axial dispersion in Taylor bubble flow by radiotracer residence time distribution analysis

    NASA Astrophysics Data System (ADS)

    Chughtai, I. R.; Iqbal, W.; Din, G. U.; Mehdi, S.; Khan, I. H.; Inayat, M. H.; Jin, J. H.

    2013-05-01

    A gas-liquid Taylor bubble flow occurs in small diameter channels in which gas bubbles are separated by slugs of pure liquid. This type of flow regime is well suited for solid catalyzed gas-liquid reactors in which the reaction efficiency is a strong function of axial dispersion in the regions of pure liquid. This paper presents an experimental study of liquid phase axial dispersion in a Taylor bubble flow developed in a horizontal tube using high speed photography and radiotracer residence time distribution (RTD) analysis. A parametric dependence of axial dispersion on average volume fraction of gas phase was also investigated by varying the relative volumetric flow rates of the two phases. 137mBa produced from a 137Cs/137mBa radionuclide generator was used as radiotracer and measurements were made using the NaI(Tl) scintillation detectors. Validation of 137mBa in the form of barium chloride as aqueous phase radiotracer was also carried out. Axial Dispersion Model (ADM) was used to simulate the hydrodynamics of the system and the results of the experiment are presented. It was observed that the system is characterized by very high values of Peclet Number (Pe˜102) which reveals an approaching plug type flow. The experimental and model estimated values of mean residence times were observed in agreement with each other.

  18. 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.

  19. 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.

  20. 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.

  1. Pool boiling enhancement through bubble induced convective liquid flow in feeder microchannels

    NASA Astrophysics Data System (ADS)

    Jaikumar, A.; Kandlikar, S. G.

    2016-01-01

    Bubbles departing from the nucleation sites induce a liquid flow from the bulk to the heated surface during pool boiling. Alternating the nucleating regions with non-nucleating regions facilitates separate liquid-vapor pathways for departing vapor bubbles and returning liquid. We explored an additional enhancement through liquid feeder channels on the heater surface directing the returning liquid towards the nucleating region. The nucleating bubbles were confined to the nucleating region as the returning liquid flow induced strong convective currents over the non-nucleating regions. In the best performing configuration, the nucleating regions were 0.5 mm wide, separated by non-nucleating regions of width 2.125 mm, which corresponded to the bubble departure diameter. The non-nucleating regions contained 0.5 mm wide feeder channels directing liquid towards the nucleating region. High speed images indicated distinct vapor columns over the nucleating regions with liquid channeled through the feeder channels. At higher heat fluxes, the strong liquid currents established over the feeder channels suppressed any undesirable nucleation in them keeping the separated vapor-liquid pathways functional. This enhancement technique resulted in a critical heat flux of 394 W/cm2 at a wall superheat of 5.5 °C which translated to a heat transfer coefficient of 713 kW/m2 °C. The additional surface area and high heat transfer coefficient due to microchannel flow in feeder channels, and the unobstructed surface available for the bubbles to expand over the prime heat transfer surface area before departing were seen to be responsible for their superior performance.

  2. Bubble-free on-chip continuous-flow polymerase chain reaction: concept and application.

    PubMed

    Wu, Wenming; Kang, Kyung-Tae; Lee, Nae Yoon

    2011-06-01

    Bubble formation inside a microscale channel is a significant problem in general microfluidic experiments. The problem becomes especially crucial when performing a polymerase chain reaction (PCR) on a chip which is subject to repetitive temperature changes. In this paper, we propose a bubble-free sample injection scheme applicable for continuous-flow PCR inside a glass/PDMS hybrid microfluidic chip, and attempt to provide a theoretical basis concerning bubble formation and elimination. Highly viscous paraffin oil plugs are employed in both the anterior and posterior ends of a sample plug, completely encapsulating the sample and eliminating possible nucleation sites for bubbles. In this way, internal channel pressure is increased, and vaporization of the sample is prevented, suppressing bubble formation. Use of an oil plug in the posterior end of the sample plug aids in maintaining a stable flow of a sample at a constant rate inside a heated microchannel throughout the entire reaction, as compared to using an air plug. By adopting the proposed sample injection scheme, we demonstrate various practical applications. On-chip continuous-flow PCR is performed employing genomic DNA extracted from a clinical single hair root sample, and its D1S80 locus is successfully amplified. Also, chip reusability is assessed using a plasmid vector. A single chip is used up to 10 times repeatedly without being destroyed, maintaining almost equal intensities of the resulting amplicons after each run, ensuring the reliability and reproducibility of the proposed sample injection scheme. In addition, the use of a commercially-available and highly cost-effective hot plate as a potential candidate for the heating source is investigated. PMID:21461443

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

    PubMed

    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

  4. A comparative study of two-phase flow models relevant to bubble column dynamics

    NASA Astrophysics Data System (ADS)

    Minev, P. D.; Lange, U.; Nandakumar, K.

    1999-09-01

    Multiphase flow modelling is still a major challenge in fluid dynamics and, although many different models have been derived, there is no clear evidence of their relevance to certain flow situations. That is particularly valid for bubbly flows, because most of the studies have considered the case of fluidized beds. In the present study we give a general formulation to five existing models and study their relevance to bubbly flows. The results of the linear analysis of those models clearly show that only two of them are applicable to that case. They both show a very similar qualitative linear stability behaviour. In the subsequent asymptotic analysis we derive an equation hierarchy which describes the weakly nonlinear stability of the models. Their qualitative behaviour up to first order with respect to the small parameter is again identical. A permanent-wave solution of the first two equations of the hierarchy is found. It is shown, however, that the permanent-wave (soliton) solution is very unlikely to occur for the most common case of gas bubbles in water. The reason is that the weakly nonlinear equations are unstable due to the low magnitude of the bulk modulus of elasticity. Physically relevant stabilization can eventually be achieved using some available experimental data. Finally, a necessary condition for existence of a fully nonlinear soliton is derived.

  5. 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.

  6. Effect of added mass on the interaction of bubbles in a low-Reynolds-number shear flow.

    PubMed

    Lavrenteva, Olga; Prakash, Jai; Nir, Avinoam

    2016-02-01

    Equal size air bubbles that are entrapped by a Taylor vortex of the secondary flow in a Couette device, thereby defying buoyancy, slowly form a stable ordered ring with equal separation distances between all neighbors. We present two models of the process dynamics based on force balance on a bubble in the presence of other bubbles positioned on the same streamline in a simple shear flow. The forces taken into account are the viscous resistance, the added mass force, and the inertia-induced repulsing force between two bubbles in a low-Reynolds-number shear flow obtained in Prakash et al. [J. Prakash et al., Phys. Rev. E 87, 043002 (2013)]. The first model of the process assumes that each bubble interacts solely with its nearest neighbors. The second model takes into account pairwise interactions among all the bubbles in the ring. The performed dynamic simulations were compared to the experimental results reported in Prakash et al. [J. Prakash et al., Phys. Rev. E 87, 043002 (2013)] and to the results of quasistationary models (ignoring the added mass effect) suggested in that paper. It is demonstrated that taking into account the effect of added mass, the models describe the major effect of the bubbles' ordering, provide good estimation of the relaxation time, and also predict nonmonotonic behavior of the separation distance between the bubbles, which exhibit over- and undershooting of equilibrium separations. The latter effects were observed in experiments, but are not predicted by the quasistationary models. PMID:26986411

  7. Influence of electrolyte concentration on holdup, flow regime transition and local flow properties in a large scale bubble column

    NASA Astrophysics Data System (ADS)

    Besagni, Giorgio; Inzoli, Fabio

    2015-11-01

    We experimentally investigate the influence of the electrolyte concentration on holdup, flow regime transition and local flow properties in a large scale bubble column, with air and water as working fluids. The column is 0.24 m inner diameter, 5.3 m height and the air is introduced by a spider sparger up to a superficial gas velocity of 0.2 m/s. The influence of five NaCl concentrations are investigated by using gas holdup and optical probe measurements. The gas holdup measurements are used for analysing the flow regime transition between the homogeneous and the transition regime and the optical probe is used for studying the local flow characteristics at different radial positions. The presence of NaCl - up to a critical concentration - increases the gas holdup. The increase in the gas holdup is due to the inhibition of the coalescence between the bubbles and, thus, the extension of the homogeneous regime. The results are in agreement with the previous literature on smaller bubble columns.

  8. 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).

  9. 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.

  10. Experimental Study of the Morphology and Dynamics of Gas-Laden Layers Under the Anodes in an Air-Water Model of Aluminum Reduction Cells

    NASA Astrophysics Data System (ADS)

    Vékony, Klára; Kiss, László I.

    2012-10-01

    The bubble layer formed under an anode and the bubble-induced flow play a significant role in the aluminum electrolysis process. The bubbles covering the anode bottom reduce the efficient surface that can carry current. In our experiments, we filmed and studied the bubble layer under the anode in a real-size air-water electrolysis cell model. Three different flow regimes were found depending on the gas generation rate. The covering factor was found to be proportional to the gas generation rate and inversely proportional to the angle of inclination. A correlation between the average height of the entire bubble layer and the position under the anode was determined. From this correlation and the measured contact sizes, the volume of the accumulated gas was calculated. The sweeping effect of large bubbles was observed. Moreover, the small bubbles under the inner edge of the anode were observed to move backward as a result of the escape of huge gas pockets, which means large momentum transport occurs in the bath.

  11. 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.

  12. 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

    2014-09-01

    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.

  13. 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.

  14. 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.

  15. Investigation on Two-phase Flow Dynamics with Discrete Bubble Model

    NASA Astrophysics Data System (ADS)

    Ami, Takeyuki; Umekawa, Hisashi; Ozawa, Mamoru; Shoji, Masahiro

    Conventional modeling including drift-flux model and two-fluid model is based on “continuous flow hypothesis”, being constructed by time-averaging, and thus both phases are defined in every spatio-temporal space. This makes it possible to apply to a variety of two-phase flow dynamics, while the intrinsic void fraction fluctuations, typically observed in slug and churn flows, are hardly simulated. In order to break through such a problem caused by time-averaging, discrete bubble model based on one-dimensional mass conservation equation, i.e. void propagation equation, has been developed. This model takes into account, as momentum effects, the wake effect induced by preceding bubbles, the local pressure fluctuation and the compressibility of gas phase together with the phase re-distribution due to geometrical constrains. Thus obtained spatio-temporal fluctuation characteristics of void fraction well simulated inherent two-phase behavior not only in a steady flow but also in an oscillatory flow.

  16. Perturbed breakup of gas bubbles in water: memory, gas flow, and coalescence.

    PubMed

    Keim, Nathan C

    2011-05-01

    The pinch-off of an air bubble from an underwater nozzle ends in a singularity with a remarkable sensitivity to a variety of perturbations. I report on experiments that break both the axial (i.e., vertical) and azimuthal symmetry of the singularity formation. The density of the inner gas influences the axial asymmetry of the neck near pinch-off. For denser gases, flow through the neck late in collapse changes the pinch-off dynamics. Gas density is also implicated in the formation of satellite bubbles. The azimuthal shape oscillations described by Schmidt et al. can be initiated by anisotropic boundary conditions in the liquid as well as with an asymmetric nozzle shape. I measure the n=3 oscillatory mode and observe the nonlinear, highly three-dimensional outcomes of pinch-off with large azimuthal perturbations. These are consistent with prior theory. PMID:21728665

  17. 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.

  18. 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.

  19. Combining liquid inertia with pressure recovery from bubble expansion for enhanced flow boiling

    NASA Astrophysics Data System (ADS)

    Kalani, A.; Kandlikar, S. G.

    2015-11-01

    In this paper, we demonstrate using liquid inertia force in a taper gap microchannel geometry to provide a high level of heat dissipation capacity accompanied by a high heat transfer coefficient and low pressure drop during flow boiling. The high mass flux increases liquid inertia force and promotes vapor removal from the manifold, thereby increasing critical heat flux (CHF) and heat transfer coefficient. The tapered gap above the microchannels provides an increasing cross-sectional area in the flow direction. This gap allows bubbles to emerge from microchannels and expand within the gap along the flow direction. The bubble evaporation and expansion in tapered gap causes pressure recovery and reduces the total pressure drop. The pressure recovery increases with the increased evaporation rate at higher heat fluxes. Using a 6% taper and a moderately high inlet liquid flow Reynolds number of 1095, we have reached a CHF of 1.07 kW/cm2 with a heat transfer coefficient of 295 kW/m2 °C and a pressure drop of 30 kPa.

  20. 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)

  1. A Nonlinear Shallow-Water Model Combined with Gas Bubble Effect for Melt Flows and Interface Instability in Aluminum Reduction Cells

    NASA Astrophysics Data System (ADS)

    Xu, Yujie; Zhang, Hongliang; Li, Jie; Lai, Yanqing

    2013-11-01

    A nonlinear shallow-water model combined with the effect of anode gas bubbles was derived for the melt flows and interface instability in aluminum reduction cells. Both the electromagnetic forces and the drag forces between the bath and gas bubbles, as the main driven forces for the melt flows, were taken into account in this model. A comparative numerical study was carried out using both the model considering the bubble and the model without considering the bubble. The results show the effect of the bubble cannot be neglected in a fluid dynamics analysis for the aluminum reduction cell. The bath flow, induced by the motion of bubbles, presents a series of small eddies rather than large eddies as the metal flow pattern shows. The horizontal drag forces between the bath and the bubbles in the bath layer enlarge the deformation of the metal-bath interface, to some extent, but have a positive influence on stabilizing the metal-bath interface perturbations.

  2. Mass Transfer from Gas Bubbles to Impinging Flow of Biological Fluids with Chemical Reaction

    PubMed Central

    Yang, Wen-Jei; Echigo, R.; Wotton, D. R.; Ou, J. W.; Hwang, J. B.

    1972-01-01

    The rates of mass transfer from a gas bubble to an impinging flow of a biological fluid such as whole blood and plasma are investigated analytically and experimentally. Gases commonly found dissolved in body fluids are included. Consideration is given to the effects of the chemical reaction between the dissolved gas and the liquid on the rate of mass transfer. Through the application of boundary layer theory the over-all transfer is found to be Sh/(Re)1/2 = 0.845 Sc1/3 in the absence of chemical reaction, and Sh/(Re) 1/2 = F′ (0) in the presence of chemical reaction, where Sh, Re, and Sc are the Sherwood, Reynolds, and Schmidt numbers, respectively, and F′ (0) is a function of Sc and the dimensionless reaction rate constant. Analytical results are also obtained for the bubble lifetime and the bubble radius-time history. These results, which are not incompatible with experimental results, can be applied to predict the dissolution of the entrapped gas emboli in the circulatory system of the human body. PMID:4642218

  3. 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.

  4. Unscrambling the Omlette: a New Bubble and Crystal Clustering Mechanism in Chaotically Mixed Magma Flows

    NASA Astrophysics Data System (ADS)

    Robertson, J.; Metcalfe, G.; Wang, S.; Barnes, S. J.

    2014-12-01

    The concentration of bubbles, crystals or droplets into small volumes of magma is a key trigger for many interesting magmatic processes. For example, gas slugs driving Strombolian eruptions form from the coalesence of exsolved bubbles within a volcanic conduit, while Ni-Cu-PGE magmatic sulfide deposits require a concentration of dense sulfide droplets from a large volume of magma to form a massive ore body. However the physical mechanism for this clustering remains unresolved - especially since small particles in active magma flows are expected to mostly track flow streamlines rather than clustering. We have uncovered a previously unreported clustering mechanism which is applicable to magmatic flows. This mechanism involves the interaction of particles with two kinds of chaotic flow structure: (a) high-strain regions within the well-mixed chaotic zones of the flow, and (b) unmixed islands of stability within the chaotic flow, known as Kolmogorov-Arnold-Moser (KAM) regions. The first figure shows the difference between chaotic and KAM regions in a chaotic laminar pipe flow. Trapping occurs when particles are scattered from high-strain regions in the chaotic zones and become trapped in the KAM regions, leading to a rapid concentration of particles relative to their original distribution (shown in the second series of figures). Using a combination of these analogue experiments and theoretical analysis we outline the conditions under which this clustering process can occur. We examine the onset of secondary density-related instabilities and the effects of increased particle-particle interaction within the clustered particles, and highlight the impact of particle clustering on the dynamics of magma ascent and emplacement.

  5. 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

  6. 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.

  7. Experimental study of oscillatory motion of particles and bubbles with applications to Coriolis flow meters

    NASA Astrophysics Data System (ADS)

    Weinstein, J. A.; Kassoy, D. R.; Bell, M. J.

    2008-10-01

    The present experimental study is designed to measure the motion of a spherical particle in a noninertial reference frame when the environment oscillates horizontally at a prescribed frequency and amplitude. Measurements are compared with theoretical equations of motion, for example, Basset [A Treatise on Hydrodynamics (Deighton Hall, London, 1888), Vol. 2], over wide ranges of density ratio (ρf/ρp), inverse Stokes number (δ), and amplitude ratio (Ap/Af), the three most critical nondimensional parameters. The experimental configuration consists of a bubble or solid sphere rising or falling in a bubble column while vibration occurs in the horizontal direction. Motion is measured with a high speed video camera and contemporary image and signal processing techniques are used to evaluate the data. The setup closely resembles multiphase flow in a Coriolis flow meter, a device which measures mass flow rate and density by oscillating two tubes at resonance. Accurate predictions of the motion of the sphere may lead to estimates of measurement errors due to entrained gas or solid particles. Excellent agreement for amplitude and phase shift is found between theory and experiment over the full range of testing, which is defined by small oscillatory Reynolds numbers (Re<2.5), finite Strouhal numbers (5

  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. Cell membrane deformation and bioeffects produced by tandem bubble-induced jetting flow

    PubMed Central

    Yuan, Fang; Yang, Chen; Zhong, Pei

    2015-01-01

    Cavitation with bubble–bubble interaction is a fundamental feature in therapeutic ultrasound. However, the causal relationships between bubble dynamics, associated flow motion, cell deformation, and resultant bioeffects are not well elucidated. Here, we report an experimental system for tandem bubble (TB; maximum diameter = 50 ± 2 μm) generation, jet formation, and subsequent interaction with single HeLa cells patterned on fibronectin-coated islands (32 × 32 μm) in a microfluidic chip. We have demonstrated that pinpoint membrane poration can be produced at the leading edge of the HeLa cell in standoff distance Sd ≤ 30 μm, driven by the transient shear stress associated with TB-induced jetting flow. The cell membrane deformation associated with a maximum strain rate on the order of 104 s−1 was heterogeneous. The maximum area strain (εA,M) decreased exponentially with Sd (also influenced by adhesion pattern), a feature that allows us to create distinctly different treatment outcome (i.e., necrosis, repairable poration, or nonporation) in individual cells. More importantly, our results suggest that membrane poration and cell survival are better correlated with area strain integral (∫​εA2dt) instead of εA,M, which is characteristic of the response of materials under high strain-rate loadings. For 50% cell survival the corresponding area strain integral was found to vary in the range of 56 ∼ 123 μs with εA,M in the range of 57 ∼ 87%. Finally, significant variations in individual cell’s response were observed at the same Sd, indicating the potential for using this method to probe mechanotransduction at the single cell level. PMID:26663913

  10. On the Influence of Heating Surface Structure on Bubble Detachment in Sub-Cooled Nucleate Boiling Flows

    SciTech Connect

    Wen Wu; Peipei Chen; Jones, Barclay G.; Newell, Ty A.

    2006-07-01

    This research examines the influence of heating surface structure on bubble detachment, which includes bubble departure and bubble lift-off, under sub-cooled nucleate boiling condition, in order to obtain better understanding to the bubble dynamics on horizontal flat heat exchangers. Refrigerant R-134a is chosen as a simulant fluid due to its merits of having smaller surface tension, reduced latent heat, and lower boiling temperature than water. Experiments were run with varying experimental parameters e.g. pressure, inlet sub-cooled level, and flow rate, etc. High speed digital images at frame rates up to 4000 frames/s were obtained, showing characteristics of bubble movement. Bubble radius and center coordinates were calculated via Canny's algorithm for edge detection and Fitzgibbon's algorithm for ellipse fitting. Results were compared against the model proposed by Klausner et al. for prediction of bubble detachment sizes. Good overall agreement was shown, with several minor modifications and suggestions made to the assumptions of the model. (authors)

  11. A Subgrid Model for Predicting Air Entrainment Rates in Bubbly Flows

    NASA Astrophysics Data System (ADS)

    Ma, Jingsen; Oberai, Assad A.; Drew, Donald E.; Lahey, Richard T., Jr.; Moraga, Francisco J.

    2008-11-01

    In this talk we present a fairly simple subgrid air entrainment model that accurately predicts the rate of air entrainment, which is critical in simulating multiphase (air/water) flows. The derivation of this model begins by assuming that a thin sheet of air is carried into the water by the inertia of the liquid at the free surface. A momentum balance on the entrained gas layer results in an expression for the entrained volumetric gas flow rate, in terms of the local liquid velocity, gas viscosity etc., which are readily available from a multiphase RANS-type simulation. This model has been validated against extensive experimental data on both plunging jets and hydraulic jumps over a wide range of liquid velocities. It was implemented in a two-fluid computational fluid dynamics code (CFDShipM) to be used to predict the void fraction distribution underneath a plunging liquid jet at different depths and jet velocities. The results were found to match the experimental observations very well. The application of this model to more challenging problems, including hydraulic jumps and full-scale ship simulations, is currently underway.

  12. a Comprehensive Model for Capillary Pressure Difference across a Drop/bubble Flowing Through a Constricted Capillary

    NASA Astrophysics Data System (ADS)

    Liang, Mingchao; Wei, Junhong; Han, Hongmei; Fu, Chengguo; Liu, Jianjun

    2015-09-01

    The capillary pressure is one of the crucial parameters in many science and engineering applications such as composite materials, interface science, chemical engineering, oil exploration, etc. The drop/bubble formation and its mechanisms that affect the permeability of porous media have steadily attracted much attention in the past. When a drop/bubble moves from a larger capillary to a smaller one, it is often obstructed by an additional pressure difference caused by the capillary force. In this paper, a comprehensive model is derived for the capillary pressure difference when a drop/bubble flows through a constricted capillary, i.e. a geometrically constricted passage with an abrupt change in radius. The proposed model is expressed as a function of the smaller capillary radius, pore-throat ratio, contact angle, surface tension and length of the drop/bubble in the smaller capillary. The model predictions are compared with the available experimental data, and good agreement is found between them.

  13. Role of bubble growth dynamics on microscale heat transfer events in microchannel flow boiling process

    NASA Astrophysics Data System (ADS)

    Bigham, Sajjad; Moghaddam, Saeed

    2015-12-01

    For nearly two decades, the microchannel flow boiling heat transfer process has been the subject of numerous studies. A plethora of experimental studies have been conducted to decipher the underlying physics of the process, and different hypotheses have been presented to describe its microscopic details. Despite these efforts, the underlying assumptions of the existing hypothesis have remained largely unexamined. Here, using data at the microscopic level provided by a unique measurement approach, we deconstruct the boiling heat transfer process into a set of basic mechanisms and explain their role in the overall surface heat transfer. We then show how this knowledge allows to relate the bubble growth and flow dynamics to the surface heat flux.

  14. Analysis and Measurement of Bubble Dynamics and Associated Flow Field in Subcooled Nucleate Boiling Flows

    SciTech Connect

    Barclay G. Jones

    2008-10-01

    In recent years, subooled nucleate boiling (SNB) has attrcted expanding research interest owing to the emergence of axial offset anomaly (AOA) or crud-induced power shigt (CIPS) in many operating US PWRs, which is an unexpected deviation in the core axial power distribution from the predicted power curves. Research indicates that the formation of the crud, which directly leads to AOA phenomena, results from the presence of the subcooled nucleate boiling, and is especially realted to bubble motion occurring in the core region.

  15. Discrete Bubble Modeling for Cavitation Bubbles

    NASA Astrophysics Data System (ADS)

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

    2007-03-01

    Dynaflow, Inc. has conducted extensive studies on non-spherical bubble dynamics and interactions with solid and free boundaries, vortical flow structures, and other bubbles. From these studies, emerged a simplified Surface Averaged Pressure (SAP) spherical bubble dynamics model and a Lagrangian bubble tracking scheme. In this SAP scheme, the pressure and velocity of the surrounding flow field are averaged on the bubble surface, and then used for the bubble motion and volume dynamics calculations. This model is implemented using the Fluent User Defined Function (UDF) as Discrete Bubble Model (DBM). The Bubble dynamics portion can be solved using an incompressible liquid modified Rayleigh-Plesset equation or a compressible liquid modified Gilmore equation. The Discrete Bubble Model is a very suitable tool for the studies on cavitation inception of foils and turbo machinery, bubble nuclei effects, noise from the bubbles, and can be used in many practical problems in industrial and naval applications associated with flows in pipes, jets, pumps, propellers, ships, and the ocean. Applications to propeller cavitation, wake signatures of waterjet propelled ships, bubble-wake interactions, modeling of cavitating jets, and bubble entrainments around a ship will be presented.

  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. 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.

  18. A TOUGH2 equation-of-state module for the simulation of two-phase flow of air, water, and a miscible gelling liquid

    SciTech Connect

    Finsterle, S.; Moridis, G.J.; Pruess, K.

    1994-05-01

    The injection of grout into the subsurface can be used to encapsulate contaminated regions of an aquifer, or to form underground barriers for the isolation of contaminant sources and to prevent the spreading of existing plumes. This requires identifying grouts, or barrier fluids, which when injected into the subsurface exhibit a large increase in viscosity and eventually solidify, sealing the permeable zones in the aquifer. Simulation and modeling analysis are indispensable tools for designing the injection and predicting the performance of the barrier. In order to model flow and transport in such systems, the thermophysical properties of the fluid mixtures have to be provided, and the governing mass- and energy-balance equations for multiphase flow in porous media have to be solved numerically. The equation-of-state module EOS11 described herein is an extension of the EOS7 module of the TOUGH2 code for flow of saline water and air. In the modeling approach, the chemical grout is treated as a miscible fluid the viscosity of which is a function of time and concentration of the gelling agent in the pore water. If a certain high viscosity is reached and the movement of the grout plume ceases, the gel is assumed to solidify, leading to a new porous medium with changed soil characteristics, i.e. reduced porosity and permeability, increased capillary strength for a given water content, and changed initial saturation distribution.

  19. Vertical Mobilization of a Residual Oil Phase in a Bead Pack Due to Flow of Discrete Gas Bubbles

    NASA Astrophysics Data System (ADS)

    Pakkala, Konark; Udell, Kent

    2007-11-01

    Mobilization of trapped oil ganglia is of interest in soil and groundwater clean-up and enhanced oil recovery applications. In this work, experiments with glass beads and various oil phase compositions were performed to determine the volumetric fraction of the non-aqueous phase liquid that may be mobilized with rising discrete gas bubbles. Experiments were performed using 6 mm and 2 mm beads. The oil phase liquids included dodecane, perchloroethene, and trichloroethene representing both spreading and non-spreading oil phases. It was found that bubbles were quite effective in mobilizing all three oils including those with densities greater than that of the suspending water. The effectiveness of the mobilization was greater in bead packs with larger beads than in packs comprised of small beads. Volumetric fractional flows of the oil phase were up to 10% of the bubble-droplet volumes, with volumetric fractions decreasing with decreasing oil phase saturations and bead size. The geometry of the oil ganglia/gas bubble combinatory body was also a function of the bead size with smaller beads producing larger, flatter gas bubbles, and the large beads producing bubbles and ganglia of similar size and geometries as the beads themselves.

  20. 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.

  1. Gas bubble dimensions in Archean lava flows indicate low air pressure at 2.7 Ga

    NASA Astrophysics Data System (ADS)

    Som, S. M.; Buick, R.; Hagadorn, J.; Blake, T.; Perreault, J.; Harnmeijer, J.; Catling, D. C.

    2014-12-01

    Air pressure constrains atmospheric composition, which, in turn, is linked to the Earth system through biogeochemical cycles and fluxes of volatiles from and to the Earth's interior. Previous studies have only placed maximum levels on surface air pressure for the early Earth [1]. Here, we calculate an absolute value for Archean barometric pressure using gas bubble size (vesicle) distributions in uninflated basaltic lava flows that solidified at sea level 2.7 billion years ago in the Pilbara Craton, Western Australia. These vesicles have been filled in by secondary minerals deposited during metasomatism and so are now amydules, but thin sections show that infilling did not change vesicle dimensions. Amygdule dimensions are measured using high-resolution X-ray tomography from core samples obtained from the top and bottom of the lava flows. The modal size expressed at the top and at the bottom of an uninflated flow can be linked to atmospheric pressure using the ideal gas law. Such a technique has been verified as a paleoaltimeter using Hawaiian Quaternary lava flows [2]. We use statistical methods to estimate the mean and standard deviation of the volumetric size of the amygdules by applying 'bootstrap'resampling and the Central Limit Theorem. Our data indicate a surprisingly low atmospheric pressure. Greater nitrogen burial under anaerobic conditions likely explains lower pressure. Refs: [1] Som et al. (2012) Nature 484, 359-262. D. L. Sahagian et al. (2002) J. Geol., 110, 671-685.

  2. CFD analysis of the two-phase bubbly flow characteristics in helically coiled rectangular and circular tube heat exchangers

    NASA Astrophysics Data System (ADS)

    Hussain, Alamin; Fsadni, Andrew M.

    2016-03-01

    Due to their ease of manufacture, high heat transfer efficiency and compact design, helically coiled heat exchangers are increasingly being adopted in a number of industries. The higher heat transfer efficiency over straight pipes is due to the secondary flow that develops as a result of the centrifugal force. In spite of the widespread use of helically coiled heat exchangers, and the presence of bubbly two-phase flow in a number of systems, very few studies have investigated the resultant flow characteristics. This paper will therefore present the results of CFD simulations for the two-phase bubbly flow in helically coiled heat exchangers as a function of the volumetric void fraction and the tube cross-section design. The CFD results are compared to the scarce flow visualisation experimental results available in the open literature.

  3. Effective slip lengths for longitudinal shear flow over partial-slip circular bubble mattresses

    NASA Astrophysics Data System (ADS)

    Crowdy, Darren

    2015-12-01

    The problem of longitudinal shear flow over a circular bubble mattress with partial slip and protrusion angle 90o is solved in a quasi-analytical fashion by a novel transform scheme recently devised by the author. The general approach can be readily adapted to other mixed boundary value problems. From the analysis explicit approximations for the effective slip lengths are found as a function of the Navier-slip parameter and the area fraction of the surface covered by protrusions. These new approximation formulas for the slip lengths both unify and extend those based on empirical polynomial fits to numerical data given recently by Ng and Wang (2011 Fluid Dyn. Res. 43 065504).

  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. 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

    2011-12-01

    The Hybrid Energy Systems Testing (HYTEST) Laboratory at the Idaho National Laboratory was established to develop and test hybrid energy systems with the principal objective of reducing dependence on imported fossil fuels. A central component of the HYTEST is the slurry bubble column reactor (SBCR) in which the gas-to-liquid reactions are performed to synthesize transportation fuels using the Fischer Tropsch (FT) process. These SBCRs operate in the churn-turbulent flow regime, which is characterized by complex hydrodynamics, coupled with reacting flow chemistry and heat transfer. Our team is developing a research tool to aid in understanding the physicochemical processes occurring in the SBCR. 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) consisting of thirteen species, which are CO reactant, H2 reactant, hydrocarbon product, and H2O product in small bubbles, large bubbles, and the bulk fluid plus catalyst is outlined. Mechanistic submodels for interfacial momentum transfer in the churn-turbulent flow regime are incorporated, along with bubble breakup/coalescence and two-phase turbulence submodels. The absorption and kinetic models, specifically changes in species concentrations, have been incorporated into the mass continuity equation. The reaction rate is based on the macrokinetic model for a cobalt catalyst developed by Yates and Satterfield. The model includes heat generation produced by the exothermic chemical reaction, as well as heat removal from a constant temperature heat exchanger. A property method approach is employed to incorporate vapor-liquid equilibrium (VLE) in a robust manner. Physical and thermodynamic properties as functions of changes in both pressure and temperature are obtained from VLE calculations performed external to the CMFD solver. The novelty of this approach is in its simplicity, as well as its

  6. Experimental Study of Oscillatory Motion of Particles and Bubbles with Applications to Coriolis Flow Meters

    NASA Astrophysics Data System (ADS)

    Kassoy, David R.; Weinstein, Joel A.; Bell, Mark J.

    2008-11-01

    The experimental study is designed to measure the motion of a spherical particle in a non-inertial reference frame when the environment oscillates horizontally at a prescribed frequency and amplitude. Measurements are compared with equations of motion over a wide range of fluid to particle density ratios and amplitude ratios as well as inverse Stokes numbers, the three most critical non-dimensional parameters. The experimental configuration consists of a bubble or solid sphere rising or falling in a vertical column while vibration occurs in the horizontal direction. Motion is measured with a high speed video camera and contemporary image and signal processing techniques are used to evaluate the data. Excellent agreement for amplitude and phase shift is found between theory and experiment over the full range of testing, which is defined by small oscillatory Reynolds numbers, finite Strouhal numbers, widely varying density ratios, inverse Stokes numbers, and amplitude ratios. The setup closely resembles multiphase flow in a Coriolis flow meter, a device which measures mass flow rate and density by oscillating two tubes at resonance. Accurate predictions of the motion of the sphere may lead to estimates of measurement errors due to entrained gas or solid particles.

  7. 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.

  8. A Lagrangian-Eulerian Mapping Solver for Direct Numerical Simulation of Bubble-Laden Turbulent Shear Flows Using the Two-Fluid Formulation

    NASA Astrophysics Data System (ADS)

    Druzhinin, O. A.; Elghobashi, S. E.

    1999-09-01

    In a recent study we showed that the two-fluid (TF) formulation can be used in the direct numerical simulation (DNS) of bubble- (or particle-) laden decaying isotropic turbulence with considerable saving in CPU-time and memory as compared to the trajectory approach employed by many researchers. In the present paper, we develop a Lagrangian-Eulerian mapping (LEM) solver for DNS of bubble-laden turbulent shear flows using TF. The purpose of LEM is to resolve the large gradients of bubble velocity and concentration which result from the absence of the diffusion terms in the equations of bubble-phase motion and the preferential accumulation of bubbles. A standard finite-difference scheme (FDS) fails to resolve these gradients. We examine the performance of the new method in DNS of a bubble-laden Taylor-Green vortex, spatially developing plane mixing layer, and homogeneous shear turbulent flow.

  9. STABILITY OF AQUEOUS FILMS BETWEEN BUBBLES

    PubMed Central

    Ohnishi, Satomi; Vogler, Erwin A.; Horn, Roger G.

    2010-01-01

    Film thinning experiments have been conducted with aqueous films between two air phases in a thin film pressure balance. The films are free of added surfactant but simple NaCl electrolyte is added in some experiments. Initially the experiments begin with a comparatively large volume of water in a cylindrical capillary tube a few mm in diameter, and by withdrawing water from the center of the tube the two bounding menisci are drawn together at a prescribed rate. This models two air bubbles approaching at a controlled speed. In pure water the results show three regimes of behavior depending on the approach speed: at slow speed (<1 µm/s) it is possible to form a flat film of pure water, ~100 nm thick, that is stabilised indefinitely by disjoining pressure due to repulsive double-layer interactions between naturally-charged air/water interfaces. The data are consistent with a surface potential of −57 mV on the bubble surfaces. At intermediate approach speed (~1 – 150 µm/s) the films are transiently stable due to hydrodynamic drainage effects, and bubble coalescence is delayed by ~10 – 100 s. At approach speeds greater than ~150 µm/s the hydrodynamic resistance appears to become negligible, and the bubbles coalesce without any measurable delay. Explanations for these observations are presented that take into account DLVO and Marangoni effects entering through disjoining pressure, surface mobility and hydrodynamic flow regimes in thin film drainage. In particular, it is argued that the dramatic reduction in hydrodynamic resistance is a transition from viscosity-controlled drainage to inertia-controlled drainage associated with a change from immobile to mobile air/water interfaces on increasing the speed of approach of two bubbles. A simple model is developed that accounts for the boundaries between different film stability or coalescence regimes. Predictions of the model are consistent with the data, and the effects of adding electrolyte can be explained. In

  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. Analysis of Bubble Flow in the Deep-Penetration Molten Pool of Vacuum Electron Beam Welding

    NASA Astrophysics Data System (ADS)

    Luo, Yi; Wan, Rui; Zhu, Yang; Xie, Xiaojian

    2015-03-01

    Based on the vacuum electron beam welding with deep-penetration process, the convection phenomenon of the bubble flow in partially penetrated and fully penetrated molten pool of AZ91D magnesium alloy was simulated under the unsteady-state conditions. At the same time, the distributions of the cavity-type defects in deep-penetration weld were studied. The results showed that the cavity-type defects are more prone to distribute at the bottom of the weld and accumulate along the axis of the weld for the partially penetrated weld seam; there is a high incidence of cavity-type defects in the middle of the weld for the fully penetrated weld seam. As a smooth escape channel for the gas phase is formed in the fully penetrated molten pool, the possibility of gas escaping is much higher than that in the partially penetrated molten pool. A high liquid convection velocity is more conducive to the escape of the gas in molten pool. The liquid convection velocity in the fully penetrated molten pool is higher than that in the partially penetrated molten pool. So, the final gas fraction in the fully penetrated molten pool is low. Therefore, the appearance of cavity-type defects in the fully penetrated weld seam is less than that in the partially penetrated weld seam.

  12. Experimental study on exciting force by two-phase cross flow

    SciTech Connect

    Nakamura, T.; Fujita, K.; Shiraki, K.; Kanazawa, H.; Sakata, K.

    1982-01-01

    Buffeting forces acting on tube arrays and induced by air-water two-phase cross flow, in the range of bubble flow and slug flow (or froth flow), are experimentally examined. Experimental results are treated by statistical modal analysis for use in design calculation. Based on these results, a hypothesis, especially applicable in the region of slug flow, is proposed to explain the experimental results. 9 refs.

  13. 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. PMID:25109646

  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. The derivation of thermal relaxation time between two-phase bubbly flow

    NASA Astrophysics Data System (ADS)

    Mohammadein, S. A.

    2006-03-01

    Thermal relaxation time constant is derived analytically for the relaxed model with unequal phase-temperatures of a vapour bubble at saturation temperature and a non-steady temperature field around the growing vapour bubble. The energy and state equation are solved between two finite boundary conditions. Thermal relaxation time perform a good agreement with Mohammadein (in Doctoral thesis, PAN, Gdansk, 1994) and Moby Dick experiment in terms of non-equilibrium homogeneous model (Bilicki et al. in Proc R Soc Lond A428:379-397, 1990) for lower values of initial void fraction. Thermal relaxation is affected by Jacob number, superheating, initial bubble radius and thermal diffusivity.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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. PMID:21227579

  2. 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

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. The motion of bubbles and particles in oscillating liquids with applications to multiphase flow in Coriolis meters

    NASA Astrophysics Data System (ADS)

    Weinstein, Joel Aaron

    Coriolis flow meters measure mass flow and density of liquids and gases to very high accuracies. However, when two or more phases are present simultaneously in a pipeline, measurement accuracy can be severely reduced. Coriolis meters have an inherent advantage over volumetric meters in measuring pure liquid quantities in applications involving liquids with entrained gas because the mass flow rate of an aerated mixture is close to that of the liquid flow rate. However, Coriolis meters use two oscillating flow tubes to make measurements, with the assumption that the fluid moves directly with the tubes in the oscillatory direction. When multiple phases or components of different density are present, this assumption is not valid and errors result. The current research involves analytic and experimental efforts to understand, model, and reduce errors due to multiphase flow in a Coriolis meter. The main error mechanism studied is phase decoupling, or the relative motion of the dispersed phase with respect to the continuous phase. Dilute mixtures involving solid particles in liquids are considered in addition to bubbly fluids. Equations of motion for spherical particles and bubbles in non-inertial oscillating reference frames are non-dimensionalized and solved with a variety of boundary conditions. Theoretical results for amplitude ratio and phase angle between sphere and fluid are verified with high speed video camera experiments. Phase decoupling is found to depend on meter and fluid parameters such as frequency, oscillation amplitude, and viscosity. Practical recommendations based on experimental and model results are made to improve measurement accuracy. Reducing bubble size by turbulent mixing and using a Coriolis meter with a minimum tube oscillation frequency and maximum amplitude are found to be the most practical ways to reduce errors due to relative phase motion. Power dissipation, density error, and other parameters of interest in the design and operation of a

  8. Bubble Velocities in Slowly Sheared Bubble Rafts

    NASA Astrophysics Data System (ADS)

    Dennin, Michael

    2004-03-01

    Many complex fluids, such as foams, emulsions, colloids, and granular matter, exhibit interesting flow behavior when subjected to slow, steady rates of strain. The flow is characterized by irregular fluctuations in the stress with corresponding nonlinear rearrangements of the individual particles. We focus on the flow behavior of a model two-dimensional system: bubble rafts. Bubble rafts consist of a single layer of soap bubbles floating on the surface of a liquid subphase, usually a soap-water solution. The bubbles are sheared using a Couette geometry, i.e. concentric cylinders. We rotate the outer cylinder at a constant rate and measure the motions of individual bubbles and the stress on the inner cylinder. We will report on the velocity profiles of the bubbles averaged over long-times and averaged over individual stress events. The long-time average velocities are well described by continuum models for fluids with the one surprising feature that there exists a critical radius at which the shear-rate is discontinuous. The individual profiles are highly nonlinear and strongly correlated with the stress fluctuations. We will discuss a number of interesting questions. Can the average profiles be understood in a simple way given the individual velocities? Is there a clear "classification" for the individual profiles, or are they purely random? What sets the critical radius for a given set of flow conditions?

  9. The influence of polymeric membrane gas spargers on hydrodynamics and mass transfer in bubble column bioreactors.

    PubMed

    Tirunehe, Gossaye; Norddahl, B

    2016-04-01

    Gas sparging performances of a flat sheet and tubular polymeric membranes were investigated in 3.1 m bubble column bioreactor operated in a semi batch mode. Air-water and air-CMC (Carboxymethyl cellulose) solutions of 0.5, 0.75 and 1.0 % w/w were used as interacting gas-liquid mediums. CMC solutions were employed in the study to simulate rheological properties of bioreactor broth. Gas holdup, bubble size distribution, interfacial area and gas-liquid mass transfer were studied in the homogeneous bubbly flow hydrodynamic regime with superficial gas velocity (U G) range of 0.0004-0.0025 m/s. The study indicated that the tubular membrane sparger produced the highest gas holdup and densely populated fine bubbles with narrow size distribution. An increase in liquid viscosity promoted a shift in bubble size distribution to large stable bubbles and smaller specific interfacial area. The tubular membrane sparger achieved greater interfacial area and an enhanced overall mass transfer coefficient (K La) by a factor of 1.2-1.9 compared to the flat sheet membrane. PMID:26857370

  10. Clustering in bubbly liquids

    NASA Astrophysics Data System (ADS)

    Figueroa, Bernardo; Zenit, Roberto

    2004-11-01

    We are conducting experiments to determine the amount of clustering that occurs when small gas bubbles ascend in clean water. In particular, we are interested in flows for which the liquid motion around the bubbles can be described, with a certain degree of accuracy, using potential flow theory. This model is applicable for the case of bubbly liquids in which the Reynolds number is large and the Weber number is small. To clearly observe the formation of bubble clusters we propose the use of a Hele-Shaw-type channel. In this thin channel the bubbles cannot overlap in the depth direction, therefore the identification of bubble clusters cannot be misinterpreted. Direct video image analysis is performed to calculate the velocity and size of the bubbles, as well as the formation of clusters. Although the walls do affect the motion of the bubbles, the clustering phenomena does occur and has the same qualitative behavior as in fully three-dimensional flows. A series of preliminary measurements are presented. A brief discussion of our plans to perform PIV measurements to obtain the liquid velocity fields is also presented.

  11. Multipoint observations of the structure and evolution of foreshock bubbles and their relation to hot flow anomalies

    NASA Astrophysics Data System (ADS)

    Liu, Terry Z.; Turner, Drew L.; Angelopoulos, Vassilis; Omidi, Nick

    2016-06-01

    When backstreaming foreshock ions pass through approaching solar wind discontinuities, they may get concentrated upstream of the discontinuities and form foreshock bubbles (FBs). Because FBs result in very intense global pressure variations upstream of and inside Earth's magnetosphere, they are important for solar wind-magnetosphere coupling. Information about these recently discovered phenomena is limited, however. To elucidate FB spatial structure, evolution, expansion, and formation conditions, we use multipoint Time History of Events and Macroscale Interactions during Substorms observations in which three or more spacecraft observed the same events. From single-case studies of two foreshock bubbles and one hot flow anomaly (HFA), we demonstrate how we determine FB spatial structure, evolution, and expansion and propose a model to explain these properties. We discuss the different conditions leading to formation of FBs and HFAs. Multiple case studies of six FBs, five HFAs, and one spontaneous HFA show that FBs typically expand faster than HFAs and their expansion speed is likely determined by the solar wind speed.

  12. On the use of area-averaged void fraction and local bubble chord length entropies as two-phase flow regime indicators

    NASA Astrophysics Data System (ADS)

    Hernández, Leonor; Juliá, J. Enrique; Paranjape, Sidharth; Hibiki, Takashi; Ishii, Mamoru

    2010-11-01

    In this work, the use of the area-averaged void fraction and bubble chord length entropies is introduced as flow regime indicators in two-phase flow systems. The entropy provides quantitative information about the disorder in the area-averaged void fraction or bubble chord length distributions. The CPDF (cumulative probability distribution function) of void fractions and bubble chord lengths obtained by means of impedance meters and conductivity probes are used to calculate both entropies. Entropy values for 242 flow conditions in upward two-phase flows in 25.4 and 50.8-mm pipes have been calculated. The measured conditions cover ranges from 0.13 to 5 m/s in the superficial liquid velocity j f and ranges from 0.01 to 25 m/s in the superficial gas velocity j g. The physical meaning of both entropies has been interpreted using the visual flow regime map information. The area-averaged void fraction and bubble chord length entropies capability as flow regime indicators have been checked with other statistical parameters and also with different input signals durations. The area-averaged void fraction and the bubble chord length entropies provide better or at least similar results than those obtained with other indicators that include more than one parameter. The entropy is capable to reduce the relevant information of the flow regimes in only one significant and useful parameter. In addition, the entropy computation time is shorter than the majority of the other indicators. The use of one parameter as input also represents faster predictions.

  13. Bubble stimulation efficiency of dinoflagellate bioluminescence.

    PubMed

    Deane, Grant B; Stokes, M Dale; Latz, Michael I

    2016-02-01

    Dinoflagellate bioluminescence, a common source of bioluminescence in coastal waters, is stimulated by flow agitation. Although bubbles are anecdotally known to be stimulatory, the process has never been experimentally investigated. This study quantified the flash response of the bioluminescent dinoflagellate Lingulodinium polyedrum to stimulation by bubbles rising through still seawater. Cells were stimulated by isolated bubbles of 0.3-3 mm radii rising at their terminal velocity, and also by bubble clouds containing bubbles of 0.06-10 mm radii for different air flow rates. Stimulation efficiency, the proportion of cells producing a flash within the volume of water swept out by a rising bubble, decreased with decreasing bubble radius for radii less than approximately 1 mm. Bubbles smaller than a critical radius in the range 0.275-0.325 mm did not stimulate a flash response. The fraction of cells stimulated by bubble clouds was proportional to the volume of air in the bubble cloud, with lower stimulation levels observed for clouds with smaller bubbles. An empirical model for bubble cloud stimulation based on the isolated bubble observations successfully reproduced the observed stimulation by bubble clouds for low air flow rates. High air flow rates stimulated more light emission than expected, presumably because of additional fluid shear stress associated with collective buoyancy effects generated by the high air fraction bubble cloud. These results are relevant to bioluminescence stimulation by bubbles in two-phase flows, such as in ship wakes, breaking waves, and sparged bioreactors. PMID:26061152

  14. Two-phase flow bubbly mixing for liquid metal magnetohydrodynamic energy conversion

    NASA Astrophysics Data System (ADS)

    Fabris, G.; Kwack, E.; Harstad, K.; Back, L. H.

    Experiments aimed at improving mixer design and investigating the effects of surfactants on the two-phase mixture in two-phase liquid metal MHD (LMMHD) energy conversion systems are described. In addition to conventional photography, flash X-ray imaging was used as a diagnostic tool. It was demonstrated that a high void fraction (0.8) and low velocity slip ratio (1.2) two-phase homogeneous bubbly mixture can be created. It is expected that such a two-phase mixture can be further expanded in a LMMHD generator while maintaining low velocity slip. In such a way, high generator and overall system efficiency would be achieved, making LMMHD systems competitive for a number of commercial applications.

  15. Two-phase flow bubbly mixing for liquid metal magnetohydrodynamic energy conversion

    NASA Technical Reports Server (NTRS)

    Fabris, G.; Kwack, E.; Harstad, K.; Back, L. H.

    1990-01-01

    Experiments aimed at improving mixer design and investigating the effects of surfactants on the two-phase mixture in two-phase liquid metal MHD (LMMHD) energy conversion systems are described. In addition to conventional photography, flash X-ray imaging was used as a diagnostic tool. It was demonstrated that a high void fraction (0.8) and low velocity slip ratio (1.2) two-phase homogeneous bubbly mixture can be created. It is expected that such a two-phase mixture can be further expanded in a LMMHD generator while maintaining low velocity slip. In such a way, high generator and overall system efficiency would be achieved, making LMMHD systems competitive for a number of commercial applications.

  16. 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

  17. Variation of Local Surface Properties of an Air Bubble in Water Caused by Its Interaction with Another Surface.

    PubMed

    Del Castillo, Lorena A; Ohnishi, Satomi; Carnie, Steven L; Horn, Roger G

    2016-08-01

    Surface and hydrodynamic forces acting between an air bubble and a flat mica surface in surfactant-free water and in 1 mM KCl solution have been investigated by observing film drainage using a modified surface force apparatus (SFA). The bubble shapes observed with the SFA are compared to theoretical profiles computed from a model that considers hydrodynamic interactions, surface curvature, and disjoining pressure arising from electrical double layer and van der Waals interactions. It is shown that the bubble experiences double-layer forces, and a final equilibrium wetting film between the bubble and mica surfaces is formed by van der Waals repulsion. However, comparison with the theoretical model reveals that the double-layer forces are not simply a function of surface separation. Rather, they appear to be changed by one of more of the following: the bubble's dynamic deformation, its proximity to another surface, and/or hydrodynamic flow in the aqueous film that separate them. The same comments apply to the hydrodynamic mobility or immobility of the air-water interface. Together the results show that the bubble's surface is "soft" in two senses: in addition to its well-known deformability, its local properties are affected by weak external forces, in this case the electrical double-layer interactions with a nearby surface and hydrodynamic flow in the neighboring aqueous phase. PMID:27391417

  18. 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.

  19. 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.

  20. 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

  1. Bubble dielectrophoresis

    NASA Technical Reports Server (NTRS)

    Jones, T. B.; Bliss, G. W.

    1977-01-01

    The theoretical principles related to bubble dielectrophoresis are examined, taking into account the polarization force, aspects of bubble deformation, the electrostatic bubble levitation theorem, and the equation of motion. The measurement of the dielectrophoretic force on static and dynamic bubbles represents a convenient experimental method for the study of the general problem of dielectrophoresis. The experiments reported include static-force measurements, static-levitation experiments, and dynamic-force measurements.

  2. 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

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

    PubMed

    Xiao, Qingtai; Xu, Jianxin; Wang, Hua

    2016-01-01

    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

  4. 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.

  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. 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

  7. 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. PMID:27378067

  8. Separation-bubble flow solution using Euler/Navier-Stokes zonal approach with downstream compatibility conditions

    NASA Technical Reports Server (NTRS)

    Liu, C. H.; Wong, T. C.; Kandil, O. A.

    1988-01-01

    The two-dimensional flow over a blunt leading-edge plate is simulated on the basis of an Euler/Navier-Stokes zonal scheme. The scheme uses an implicit upwind finite-volume scheme, which is based on the van Leer flux-vector splitting. It is shown that the Euler/Navier-Stokes zonal scheme with downstream boundary-layer compatibility conditions is accurate and efficient.

  9. 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

  10. Rheology of dense bubble suspensions

    NASA Astrophysics Data System (ADS)

    Kang, Sang-Yoon; Sangani, Ashok S.; Tsao, Heng-Kwong; Koch, Donald L.

    1997-06-01

    The rheological behavior of rapidly sheared bubble suspensions is examined through numerical simulations and kinetic theory. The limiting case of spherical bubbles at large Reynolds number Re and small Weber number We is examined in detail. Here, Re=ργa2/μ and We=ργ2a3/s, a being the bubble radius, γ the imposed shear, s the interfacial tension, and μ and ρ, respectively, the viscosity and density of the liquid. The bubbles are assumed to undergo elastic bounces when they come into contact; coalescence can be prevented in practice by addition of salt or surface-active impurities. The numerical simulations account for the interactions among bubbles which are assumed to be dominated by the potential flow of the liquid caused by the motion of the bubbles and the shear-induced collision of the bubbles. A kinetic theory based on Grad's moment method is used to predict the distribution function for the bubble velocities and the stress in the suspension. The hydrodynamic interactions are incorporated in this theory only through their influence on the virtual mass and viscous dissipation in the suspension. It is shown that this theory provides reasonable predictions for the bubble-phase pressure and viscosity determined from simulations including the detailed potential flow interactions. A striking result of this study is that the variance of the bubble velocity can become large compared with (γa)2 in the limit of large Reynolds number. This implies that the disperse-phase pressure and viscosity associated with the fluctuating motion of the bubbles is quite significant. To determine whether this prediction is reasonable even in the presence of nonlinear drag forces induced by bubble deformation, we perform simulations in which the bubbles are subject to an empirical drag law and show that the bubble velocity variance can be as large as 15γ2a2.

  11. 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.

  12. On the stability of the production of bubbles in yield-stress fluid using flow-focusing and T-junction devices

    NASA Astrophysics Data System (ADS)

    Laborie, B.; Rouyer, F.; Angelescu, D. E.; Lorenceau, E.

    2016-06-01

    We investigate experimentally the stability of bubble production in yield-stress fluids (YSF) and highly viscous silicone oil, using flow-focusing and T-junction devices. When the exit channel is initially pre-filled with the fluid and the gas is pressure-driven, the production is highly unstable, despite a regular frequency of bubble production in the junction. As observed for pressure-driven bubble trains in Newtonian fluids, we report that two mechanisms can explain these observations: (i) drastic reduction of the hydrodynamic pressure drop along the channel during the transient bubble production, which induces a rapid increase of the gas flow rate and (ii) thin film deposition resulting in a cascade of plug break-up and bubble coalescence. While the drastic reduction of the pressure drop is inevitable in such two-phase flows, we show that modifying the surfaces of the channel can help to stabilize the system when the continuous phase is a YSF. To do so, we measure the thickness of the film deposited on the channel wall for rough and smooth channels. Our results are rationalized by introducing the inverse of the Bingham number Bi-1 comparing the viscous stress to the yield stress. For Bi-1 ≥ 1, a fast fluidization process associated to efficient deposition of YSF on the channel wall leads to a rapid destabilization of bubble production. However, for Bi-1 < 1, the deposition driven by capillarity can be hindered by the wall-slip induced by the existence of the yield stress: the thickness of the deposited film is very thin and corresponds to the equivalent roughness of the channels. It is typically 40 μm thick for rough surfaces and below the limit of resolution of our set-up for smooth surfaces. In this regime of Bi-1 and for smooth surfaces, the length of the plugs barely vanishes, thus the start-up flow is less prone to destabilization. These results therefore potentially open routes to steady production of aerated YSF on smooth channels in the regime 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. Unsteady 2-phase flow instrumentation and measurement

    NASA Astrophysics Data System (ADS)

    Bernier, R. J.

    The performance of a transverse field electromagnetic flowmeter in a steady two phase flow was investigated analytically for a disperse and an annular flow regime. The flowmeter output voltage was found to be proportional to the mean velocity of the liquid phase. Experiments in a steady air water mixture showed good agreement with the analysis. An impedance void fraction meter was designed and built to conduct measurements of unsteady void fractions. Short electrodes excited by voltages of opposite polarity were used in combination with a highly sensitive signal processor. The steady state calibration indicated that the meter was somewhat sensitive to the void fraction distribution for the bubbly flow regime. However, the transition to a churn turbulent regime greatly affected the meer steady state response. The dynamic capability of the void fraction meter was estimated by comparison of the statistical properties of the voltage fluctuations in a nominally steady bubbly flow with those of a shot noise process.

  15. 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.

  16. 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.

  17. Physical modeling studies of electrolyte flow due to gas evolution and some aspects of bubble behavior in advanced hall cells: Part I. Flow in cells with a flat anode

    NASA Astrophysics Data System (ADS)

    Shekhar, R.; Evans, J. W.

    1994-06-01

    The need for energy reduction in the electrolytic production of aluminum led to the concept of advanced Hall cells that can be operated at lower interelectrode gaps compared to existing cells. However, gas bubbles generated by the anodic reaction increase the resistivity of electrolyte and cancel out part of the reduction in interelectrode resistance expected from bringing the electrodes closer together. Therefore, the primary objective of this work was to determine a cell design in which flow can be managed to promote the removal of anode gas bubbles from the interelectrode gap. In particular, this article focuses on advanced Hall cells equipped with “flat” anodes, similar to those used in existing cells. The principal experimental tool has been a “water” model consisting of a large tank in which simulated anodes can be suspended in either the horizontal or near-horizontal configurations. Gas was generated by forcing compressed air through porous graphite, and the fine bubbles characteristic of inert anodes used in advanced Hall cells were produced by adding butanol to water. Velocities were measured using a laser-Doppler velocimeter (LDV). This study indicates that the existing cell configuration might not be the optimum configuration for advanced Hall cells. The results also show that operation of an advanced Hall cell with a fully submerged anode should give rise to higher electrolyte velocities and thus rapid removal of bubbles. The bubble effect should be further lowered in a near-horizontal configuration; however, the flow pattern could have an adverse effect on current efficiency and alumina distribution in the cell. It has also been shown that the bubble size, and, therefore, the physical properties of the electrolyte, can have a significant effect on the electrolyte flow pattern in the interelectrode gap.

  18. Numerical simulation of subcooled flow boiling

    NASA Astrophysics Data System (ADS)

    Park, Won Cheol

    Sub-cooled flow boiling in a U-bend has been examined using numerical methods. An Eulerian/Eulerian mathematical description was used with a multiphase computational algorithm to predict several types of flows and to examine sub-cooled flow boiling. As a prelude to the study of sub-cooled boiling and two-phase flows, single-phase laminar and turbulent flows in a U-bend were investigated. Air-water bubbly up flow in a vertical straight duct followed by a U-bend with heat transfer was analyzed. In such a flow, as the flow develops through the U-bend the bubbles move from center and outer wall toward inner wall. After half way through the U-bend, the fluids do not have sufficient time for complete reorganization in the presence of centrifugal forces and the pressure gradients. After the U-bend, the bubbles finally reach the original distribution in about forty diameters. The heat transfer in the U-bend was also calculated and as expected heat transfer rate on the outer wall is higher than on the inner wall. For air-water bubbly two-phase flow, Nusselt numbers in the U-bend can be as high as 400 percent of the value in the straight duct on one of the walls. The method of partitioned wall heat flux was used to study sub-cooled flow boiling. For sub-cooled flow boiling in a U-bend, axial and lateral velocity distributions as well as quality and void fraction variations were analyzed. Computed axial and lateral variations of void fraction compare favorably with existing experimental data. As expected, the pressure drop for bubbly flow through the U-bend is larger than for single-phase flow by as much as fifty percent. Computed pressure drop for flow with phase change falls between the predictions of two different correlations in the literature, and thus seems reasonable. Predictions of heat transfer and void fraction under sub-cooled flow boiling using two-fluid models need better quantitative knowledge related to the mechanisms associated with bubble growth and

  19. 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

  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%. PMID:27035474

  1. Morphology of Two-Phase Layers with Large Bubbles

    NASA Astrophysics Data System (ADS)

    Vékony, Klára; Kiss, László I.

    2010-10-01

    The understanding of formation and movement of bubbles nucleated during aluminum reduction is essential for a good control of the electrolysis process. In our experiments, we filmed and studied the formation of a bubble layer under the anode in a real-size air-water electrolysis cell model. The maximum height of the bubbles was found to be up to 2 cm because of the presence of the so-called Fortin bubbles. Also, the mean height of the bubble layer was found to be much higher than published previously. The Fortin bubbles were investigated more closely, and their shape was found to be induced by a gravity wave formed at the gas-liquid interface. In addition, large bubbles were always observed to break up into smaller parts right before escaping from under the anode. This breakup and escape led to a large momentum transfer in the bath.

  2. 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.

  3. 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.

  4. Fuel system bubble dissipation device

    SciTech Connect

    Iseman, W.J.

    1987-11-03

    This patent describes a bubble dissipation device for a fuel system wherein fuel is delivered through a fuel line from a fuel tank to a fuel control with the pressure of the fuel being progressively increased by components including at least one pump stage and an ejector in advance of the pump state. The ejector an ejector casing with a wall defining an elongate tubular flow passage which forms a portion of the fuel line to have all of the fuel flow through the tubular flow passage in flowing from the fuel tank to the fuel control, a nozzle positioned entirely within the tubular flow passage and spaced from the wall to permit fuel flow. The nozzle has an inlet and an outlet with the inlet connected to the pump stage to receive fuel under pressure continuously from the pump stage, a bubble accumulation chamber adjoining and at a level above the ejector casing and operatively connected to the fuel line in advance of the ejector casing. The bubble accumulation chamber is of a size to function as a fuel reservoir and hold an air bubble containing vapor above the level of fuel therein and having an outlet adjacent the bottom thereof operatively connected to the tubular flow passage in the ejector casing at an inlet end, a bubble accumulation chamber inlet above the level of the bubble accumulation chamber outlet whereby fuel can flow through the bubble accumulation chamber from the inlet to the outlet thereof with a bubble in the fuel rising above the fuel level in the bubble accumulation chamber.

  5. Steady State Vapor Bubble in Pool Boiling

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    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.

  6. Steady State Vapor Bubble in Pool Boiling.

    PubMed

    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

  7. 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

  8. 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)

  9. Noninvasive evaluation of flow changes and gas bubbles in the circulation by combined use of color-flow-imaging and computer postprocessing.

    PubMed

    Brubakk, A O; Torp, H; Angelsen, B A

    1991-01-01

    Significant circulatory changes occur in microgravity and gas bubbles may be present in the circulation as a result of decompression during EVA. A system for the non-invasive evaluation of circulatory changes and gas bubbles in the circulation is described. This system is based on an ultrasonic scanning and Doppler system (CFM 700(750), Vingmed Sound, Horten Norway) together with programs to transmit the data to a Macintosh [correction of Mackintosh] II computer. A method for measuring pulsatile blood pressure non-invasively is also included. On the computer, programs for the calculation of cardiovascular parameters and the analysis of ultrasonic images containing gas bubbles have been developed. PMID:11537142

  10. 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. PMID:24709611

  11. 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.

  12. Effect of bubble size on micro-bubble drag reduction

    NASA Astrophysics Data System (ADS)

    Shen, Xiaochun

    2005-11-01

    The effect of bubble size on micro-bubble drag reduction was investigated experimentally in a high-speed turbulent channel flow of water. A variety of near-wall injection techniques were used to create a bubbly turbulent boundary layer. The resulting wall friction force was measured directly by a floating element force balance. The bubble size was determined from photographic imaging. Using compressed nitrogen to force flow through a slot injector located in the plate beneath the boundary layer of the tunnel test section, a surfactant solution (Triton X-100, 19ppm) and salt water solution (35ppt) generated bubbles of average size between ˜500 microns and ˜200 microns and ˜100 microns, respectively (40 < d^+ < 200). In addition hollow spherical glass beads (˜75 microns (d^+ = 30) and specific gravity 0.18) and previously prepared lipid stabilized gas bubbles of ˜ 30 micron (d^+ =12) were injected. The results indicate that the drag reduction is related strongly to the injected gas volume flux and the static pressure in the boundary layer. Changing bubble size had essentially no influence on the measured friction drag, suggesting that friction drag is not a strong function of bubble size. [Sponsored by the Office of Naval Research.

  13. Exploring Bubbles

    NASA Astrophysics Data System (ADS)

    O'Geary, Melissa A.

    Bubbles provide an enjoyable and festive medium through which to teach many concepts within the science topics of light, color, chemistry, force, air pressure, electricity, buoyancy, floating, density, among many others. In order to determine the nature of children's engagement within a museum setting and the learning opportunities of playing with bubbles, I went to a children's interactive museum located in a metropolitan city in the Northeastern part of the United States.

  14. Comparing Different Models for Fast Earthward Flows in the Magnetotail: Moving Flux Ropes, Unsteady Reconnection, Pressure-Depleted Plasma Bubbles, and Atypical Currents Sheets

    NASA Astrophysics Data System (ADS)

    Sitnov, M. I.; Runov, A. V.; Ohtani, S.

    2007-12-01

    The physics of fast earthward flows or BBFs, a major mechanism of bursty transfer of the plasma and magnetic flux in the terrestrial magnetotail, remains uncertain and controversial. A part of observations can be explained as signatures of earthward moving flux ropes or secondary plasmoids dragged by the earthward part a larger-scale reconnection region [Slavin et al., 2003]. The statistics of variations of the z-component of the magnetospheric magnetic field in the central plasma sheet [Ohtani et al., 2004] suggest no changes of the magnetic field topology for another group of BBFs. These observations can be explained as signatures of either unsteady reconnection, which remains located tailward of the spacecraft, or other phenomena that are connected but not identical to reconnection in its active phase. These are the plasma bubbles, flux tubes with the reduced specific entropy that may move earthward faster than the neighboring flux tubes due to the buoyancy force. However, the original model of bubbles arising from local reductions of the plasma pressure [Pontius and Wolf, 1990] also explains only a part of observations. Another part [Angelopoulos et al., 1992] reveals no reduction of the plasma pressure in BBFs. One more model, which explains both missing magnetic topology changes and no reduction of the plasma pressure [Sitnov et al., 2005] describes the bubble as a seam in the body of the tail plasma, which appears after the formation and tailward retreat of a small plasmoid, and which is composed of atypical, embedded and bifurcated thin current sheets. Signatures of such atypical current sheets have been convincingly demonstrated recently in CLUSTER observations [Runov et al., 2003]. In this presentation we elaborate the BBF models and compare them with 2001 and 2002 tail CLUSTER observations in the central plasma sheet. These include full-particle simulations of the secondary plasmoid formation in tail-like systems, two- and three- dimensional features and

  15. Heated Gas Bubbles

    NASA Technical Reports Server (NTRS)

    2004-01-01

    Fluid Physics is study of the motion of fluids and the effects of such motion. When a liquid is heated from the bottom to the boiling point in Earth's microgravity, small bubbles of heated gas form near the bottom of the container and are carried to the top of the liquid by gravity-driven convective flows. In the same setup in microgravity, the lack of convection and buoyancy allows the heated gas bubbles to grow larger and remain attached to the container's bottom for a significantly longer period.

  16. 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.

  17. Observation of Microhollows Produced by Bubble Cloud Cavitation

    NASA Astrophysics Data System (ADS)

    Yamakoshi, Yoshiki; Miwa, Takashi

    2012-07-01

    When an ultrasonic wave with sound pressure less than the threshold level of bubble destruction irradiates microbubbles, the microbubbles aggregate by an acoustic radiation force and form bubble clouds. The cavitation of bubble clouds produces a large number of microhollows (microdips) on the flow channel wall. In this study, microhollow production by bubble cloud cavitation is evaluated using a blood vessel phantom made of N-isopropylacrylamide (NIPA) gel. Microbubble dynamics in bubble cloud cavitation is observed by a microscope with a short pulse light emitted diode (LED) light source. Microhollows produced on the flow channel wall are evaluated by a confocal laser microscope with a water immersion objective. It is observed that a mass of low-density bubbles (bubble mist) is formed by bubble cloud cavitation. The spatial correlation between the bubble mist and the microhollows shows the importance of the bubble mist in microhollow production by bubble cloud cavitation.

  18. Influence of bubble size on micro-bubble drag reduction

    NASA Astrophysics Data System (ADS)

    Shen, Xiaochun; Ceccio, Steven L.; Perlin, Marc

    2006-09-01

    Micro-bubble drag reduction experiments were conducted in a turbulent water channel flow. Compressed nitrogen was used to force flow through a slot injector located in the plate beneath the boundary layer of the tunnel test section. Gas and bubbly mixtures were injected into a turbulent boundary layer (TBL), and the resulting friction drag was measured downstream of the injector. Injection into tap water, a surfactant solution (Triton X-100, 20 ppm), and a salt-water solution (35 ppt) yielded bubbles of average diameter 476, 322 and 254 μm, respectively. In addition, lipid stabilized gas bubbles (44 μm) were injected into the boundary layer. Thus, bubbles with d + values of 200 to 18 were injected. The results indicate that the measured drag reduction by micro-bubbles in a TBL is related strongly to the injected gas volumetric flow rate and the static pressure in the boundary layer, but is essentially independent of the size of the micro-bubbles over the size range tested.

  19. 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.

  20. Electrolysis Bubbles Make Waterflow Visible

    NASA Technical Reports Server (NTRS)

    Schultz, Donald F.

    1990-01-01

    Technique for visualization of three-dimensional flow uses tiny tracer bubbles of hydrogen and oxygen made by electrolysis of water. Strobe-light photography used to capture flow patterns, yielding permanent record that is measured to obtain velocities of particles. Used to measure simulated mixing turbulence in proposed gas-turbine combustor and also used in other water-table flow tests.

  1. 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.

  2. Flowing Foam: T1 events and solid-liquid transitions.

    NASA Astrophysics Data System (ADS)

    Dennin, Michael

    2005-11-01

    Flowing aqueous foam is found in many applications ranging from oil recovery, to fire fighting, to spreading shaving cream. Aqueous foam consists of gas bubbles with liquid walls. One of the striking features of foam is that despite being composed entirely of fluids, its mechanical properties are either those of a solid (elastic response) or fluid (viscous flow), depending on the nature of the applied stress and strains. We study the transition between these two regimes using a model foam system: bubble rafts. Bubble rafts are a single layer of bubbles floating on the air-water surface. This allows us to track the motion of all the bubbles during flow. In this talk, we will present two main results. First, we will discuss the observation of the coexistence between a solid-like and fluid-like state during flow. Second, we will discuss the role played by nonlinear, topological rearrangements, known as T1 events, in determining the mechanical response of the system.

  3. Formation, disruption and mechanical properties of a rigid hydrophobin film at an air-water interface

    NASA Astrophysics Data System (ADS)

    Walker, Lynn; Kirby, Stephanie; Anna, Shelley; CMU Team

    Hydrophobins are small, globular proteins with distinct hydrophilic and hydrophobic regions that make them extremely surface active. The behavior of hydrophobins at surfaces has raised interest in their potential industrial applications, including use in surface coatings, food foams and emulsions, and as dispersants. Practical use of hydrophobins requires an improved understanding of the interfacial behavior of these proteins, both individually and in the presence of surfactants. Cerato-ulmin (CU) is a hydrophobin that has been shown to strongly stabilize air bubbles and oil droplets through the formation of a persistent protein film at the interface. In this work, we characterize the adsorption behavior of CU at air/water interfaces by measuring the surface tension and interfacial rheology as a function of adsorption time. CU is found to strongly, irreversibly adsorb at air/water interfaces; the magnitude of the dilatational modulus increases with adsorption time and surface pressure, until the CU eventually forms a rigid film. The persistence of this film is tested through the addition of SDS, a strong surfactant, to the bulk. SDS is found to co-adsorb to interfaces pre-coated with a CU film. At high concentrations, the addition of SDS significantly decreases the dilatational modulus, indicating disruption and displacement of CU. These results lend insight into the complex interfacial interactions between hydrophobins and surfactants. Funding from GoMRI.

  4. Effect of humidity on the adsorption kinetics of lung surfactant at air-water interfaces.

    PubMed

    Zuo, Yi Y; Gitiafroz, Roya; Acosta, Edgar; Policova, Zdenka; Cox, Peter N; Hair, Michael L; Neumann, A Wilhelm

    2005-11-01

    The in vitro adsorption kinetics of lung surfactant at air-water interfaces is affected by both the composition of the surfactant preparations and the conditions under which the assessment is conducted. Relevant experimental conditions are surfactant concentration, temperature, subphase pH, electrolyte concentration, humidity, and gas composition of the atmosphere exposed to the interface. The effect of humidity on the adsorption kinetics of a therapeutic lung surfactant preparation, bovine lipid extract surfactant (BLES), was studied by measuring the dynamic surface tension (DST). Axisymmetric drop shape analysis (ADSA) was used in conjunction with three different experimental methodologies, i.e., captive bubble (CB), pendant drop (PD), and constrained sessile drop (CSD), to measure the DST. The experimental results obtained from these three methodologies show that for 100% relative humidity (RH) at 37 degrees C the rate of adsorption of BLES at an air-water interface is substantially slower than for low humidity. It is also found that there is a difference in the rate of surface tension decrease measured from the PD and CB/CSD methods. These experimental results agree well with an adsorption model that considers the combined effects of entropic force, electrostatic interaction, and gravity. These findings have implications for the development and evaluation of new formulations for surfactant replacement therapy. PMID:16262325

  5. 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.

  6. 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. PMID:23961700

  7. 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)

  8. 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.

  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. Can bubbles sink ships?

    NASA Astrophysics Data System (ADS)

    Hueschen, Michael A.

    2010-02-01

    I investigate the interplay between the buoyancy force and the upwelling (or drag) force which act on a floating object when bubbles are rising through a body of water. Bubbles reduce the buoyant force by reducing the density of the water, but if they entrain an upwelling flow of water as they rise, they can produce a large upward drag force on the floating object. In an upwelling flow, our model ship (density=0.94 g/cm3) floats in a foam whose density is only 0.75 g/cm3. Comparing results with and without upwelling currents is an interesting demonstration and has real-world applications to ships in the ocean.

  11. 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.

  12. Noninvasive evaluation of flow changes and gas bubbles in the circulation by combined use of color-flow-imaging and computer postprocessing

    NASA Astrophysics Data System (ADS)

    Brubakk, A. O.; Torp, H.; Angelsen, B. A. J.

    A system for obtaining cardiovascular data by using an ultrasonic scanner combined with a noninvasive method for measuring pulsatile pressure and computer-based postprocessing capabilities has been developed. The system is based on an ultrasonic scanning and Doppler system together with programs to transmit the data to a Macintosh II computer. A system for detecting and counting air bubbles in the circulation system through analysis of ultrasonic images containing gas bubbles has also been developed. The basic instrumentation incorporated in these systems is described and the postprocessing of ultrasound data is discussed in detail. The ability to perform postprocessing of data directly on the spacecraft, thereby making it possible to change experimental setup based on results is cited as one of the primary advantages of this system.

  13. 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.

  14. 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.

  15. 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.

  16. Microfluidics with compound ``bubble-drops''

    NASA Astrophysics Data System (ADS)

    Khan, Saif A.; Duraiswamy, Suhanya

    2008-11-01

    ``Bubble-drops'' are compound fluid particles comprising a gas bubble and liquid drop that flow as a single fluid object through another immiscible liquid in a microchannel network. These fluid particles represent discrete multiphase `quanta', and expand the sphere of application of droplet microfluidics to inter-phase phenomena. We present here a simple method to generate monodisperse bubble-drop trains in microfabricated channel networks. The difference in drag force exerted on flowing bubbles and drops by the immiscible carrier liquid implies different translational speeds, thus providing the driving force for bubble-drop formation. We outline the criteria for stable generation and analyze factors influencing bubble-drop dynamics. We will also highlight several applications in chemical and biological synthesis and screening.

  17. 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.

  18. A new bubble dynamics model to study bubble growth, deformation, and coalescence

    NASA Astrophysics Data System (ADS)

    Huber, C.; Su, Y.; Nguyen, C. T.; Parmigiani, A.; Gonnermann, H. M.; Dufek, J.

    2014-01-01

    We propose a new bubble dynamics model to study the evolution of a suspension of bubbles over a wide range of vesicularity, and that accounts for hydrodynamical interactions between bubbles while they grow, deform under shear flow conditions, and exchange mass by diffusion coarsening. The model is based on a lattice Boltzmann method for free surface flows. As such, it assumes an infinite viscosity contrast between the exsolved volatiles and the melt. Our model allows for coalescence when two bubbles approach each other because of growth or deformation. The parameter (disjoining pressure) that controls the coalescence efficiency, i.e., drainage time for the fluid film between the bubbles, can be set arbitrarily in our calculations. We calibrated this parameter by matching the measured time for the drainage of the melt film across a range of Bond numbers (ratio of buoyancy to surface tension stresses) with laboratory experiments of a bubble rising to a free surface. The model is then used successfully to model Ostwald ripening and bubble deformation under simple shear flow conditions. The results we obtain for the deformation of a single bubble are in excellent agreement with previous experimental and theoretical studies. For a suspension, we observe that the collective effect of bubbles is different depending on the relative magnitude of viscous and interfacial stresses (capillary number). At low capillary number, we find that bubbles deform more readily in a suspension than for the case of a single bubble, whereas the opposite is observed at high capillary number.

  19. 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.

  20. Pulling bubbles from a bath

    NASA Astrophysics Data System (ADS)

    Kao, Justin C. T.; Blakemore, Andrea L.; Hosoi, A. E.

    2010-06-01

    Deposition of bubbles on a wall withdrawn from a liquid bath is a phenomenon observed in many everyday situations—the foam lacing left behind in an emptied glass of beer, for instance. It is also of importance to the many industrial processes where uniformity of coating is desirable. We report work on an idealized version of this situation, the drag-out of a single bubble in Landau-Levich-Derjaguin flow. We find that a well-defined critical wall speed exists, separating the two regimes of bubble persistence at the meniscus and bubble deposition on the moving wall. Experiments show that this transition occurs at Ca∗˜Bo0.73. A similar result is obtained theoretically by balancing viscous stresses and gravity.

  1. 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

  2. Mechanisms of single bubble cleaning.

    PubMed

    Reuter, Fabian; Mettin, Robert

    2016-03-01

    The dynamics of collapsing bubbles close to a flat solid is investigated with respect to its potential for removal of surface attached particles. Individual bubbles are created by nanosecond Nd:YAG laser pulses focused into water close to glass plates contaminated with melamine resin micro-particles. The bubble dynamics is analysed by means of synchronous high-speed recordings. Due to the close solid boundary, the bubble collapses with the well-known liquid jet phenomenon. Subsequent microscopic inspection of the substrates reveals circular areas clean of particles after a single bubble generation and collapse event. The detailed bubble dynamics, as well as the cleaned area size, is characterised by the non-dimensional bubble stand-off γ=d/Rmax, with d: laser focus distance to the solid boundary, and Rmax: maximum bubble radius before collapse. We observe a maximum of clean area at γ≈0.7, a roughly linear decay of the cleaned circle radius for increasing γ, and no cleaning for γ>3.5. As the main mechanism for particle removal, rapid flows at the boundary are identified. Three different cleaning regimes are discussed in relation to γ: (I) For large stand-off, 1.8<γ<3.5, bubble collapse induced vortex flows touch down onto the substrate and remove particles without significant contact of the gas phase. (II) For small distances, γ<1.1, the bubble is in direct contact with the solid. Fast liquid flows at the substrate are driven by the jet impact with its subsequent radial spreading, and by the liquid following the motion of the collapsing and rebounding bubble wall. Both flows remove particles. Their relative timing, which depends sensitively on the exact γ, appears to determine the extension of the area with forces large enough to cause particle detachment. (III) At intermediate stand-off, 1.1<γ<1.8, only the second bubble collapse touches the substrate, but acts with cleaning mechanisms similar to an effective small γ collapse: particles are removed by

  3. Experimental Investigation and Simulation of Ferrous Biooxidation and Flow Hydrodynamics in a Bubble Column Bioreactor Using CFD Approach

    NASA Astrophysics Data System (ADS)

    Mousavi, S. M.; Jafari, A.; Yaghmaei, S.; Vossoughi, M.; Turunen, I.

    2008-05-01

    In the present attempt a set of experiments and a 3D simulation using a commercially available computational fluid dynamics package (FLUENT) were adopted to investigate complex behavior involving hydrodynamics and ferrous biological oxidation in a gas-liquid bubble column reactor. By combining the hydrodynamics and chemical species transport equations, the velocity field, air volume fraction and ferrous biooxidation rate in the column were simulated. The kinetic model proposed by Nemati and Webb (1998) was used to simulate the biooxidation rate in the column. Gas-liquid interactions were modeled using an Eulerian model in three dimensions. The effects of inlet air velocity and initial substrate (Fe+2) concentration on the velocity field, air volume fraction and biooxidation rate of ferrous iron in the column were investigated. To validate the model, simulation was compared with the experimental data in the presence of Acidithiobacillus ferrooxidans in an aerated column where the superficial gas velocity was adjusted between 0 and 0.5 m/s. It was found that the initial ferrous concentration and the inlet air velocity had a pronounced effect on the ferrous biooxidation rate. The results indicated that the maximum biooxidation rate can be obtained at superficial air velocity of 0.1 m/s and initial ferrous concentration of 6.7 g/L.

  4. Bubble bath soap poisoning

    MedlinePlus

    ... medlineplus.gov/ency/article/002762.htm Bubble bath soap poisoning To use the sharing features on this page, please enable JavaScript. Bubble bath soap poisoning occurs when someone swallows bubble bath soap. ...

  5. 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

  6. Determining the gas permeability coefficient of a porous medium by means of the bubble-counting flow meter

    NASA Astrophysics Data System (ADS)

    Skoczylas, Norbert

    2015-08-01

    In this paper the conception of a low-cost device to determine the coefficient of permeability was presented. In the apparatus a non-typical source of gas and gas flow meter has been used. A used flow meter allows us to measure very low gas flow rates. The upper measurement range limit of the constructed device was about 20 cm3 min-1, whereas the lower measurement range limit was estimated to be approximately 0.01 cm3 min-1.

  7. Numerical study of the effect of an embedded surface-heat source on the separation bubble of supersonic flow

    NASA Technical Reports Server (NTRS)

    Degani, D.

    1983-01-01

    A numerical study of the conjugated problem of a separated supersonic flow field and a conductive solid wall with an embedded heat source is presented. Implicit finite-difference schemes were used to solve the two-dimensional time-dependent compressible Navier-Stokes equations and the time-dependent heat-conduction equation for the solid in both general coordinate systems. A detailed comparison between the thin-layer and Navier-Stokes models was made for steady and unsteady supersonic flow and showed insignificant differences. Steady-state and transient cases were computed and the results show that a temperature pulse at the solid-fluid interface can be used to detect the flow direction near the wall in the vicinity of separation without significant distortion of the flow field.

  8. MOBI: Microgravity Observations of Bubble Interactions

    NASA Technical Reports Server (NTRS)

    Koch, Donald L.; Sangani, Ashok

    2004-01-01

    One of the greatest uncertainties affecting the design of multiphase flow technologies for space exploration is the spatial distribution of phases that will arise in microgravity or reduced gravity. On Earth, buoyancy-driven motion predominates whereas the shearing of the bubble suspension controls its behavior in microgravity. We are conducting a series of ground-based experiments and a flight experiment spanning the full range of ratios of buoyancy to shear. These include: (1) bubbles rising in a quiescent liquid in a vertical channel; (2) weak shear flow induced by slightly inclining the channel; (3) moderate shear flow in a terrestrial vertical pipe flow; and (4) shearing of a bubble suspension in a cylindrical Couette cell in microgravity. We consider nearly monodisperse suspensions of 1 to 1.8 mm diameter bubbles in aqueous electrolyte solutions. The liquid velocity disturbance produced by bubbles in this size range can often be described using an inviscid analysis. Electrolytic solutions lead to hydrophilic repulsion forces that stabilize the bubble suspension without causing Marangoni stresses. We will discuss the mechanisms that control the flow behavior and phase distribution in the ground-based experiments and speculate on the factors that may influence the suspension flow and bubble volume fraction distribution in the flight experiment.

  9. Energy spectra in bubbly turbulence

    NASA Astrophysics Data System (ADS)

    Luther, Stefan; van den Berg, Thomas H.; Rensen, Judith; Lohse, Detlef

    2004-11-01

    The energy spectrum of single phase turbulent flow - apart from intermittency corrections - has been known since Kolomogorov 1941, E(k) ∝ k-5/3. How do bubbles modify this spectrum? To answer this question, we inject micro bubbles (radius 100 μm) in fully turbulent flow (Re_λ=200) up to volume concentrations of 0.3 %. Energy spectra and velocity structure functions are measured with hot-film anemometry. Under our experimental conditions, we find an enhancement of energy on small scales confirming numerical predictions by Mazzitelli, Lohse, and Toschi [Phys. Fluids 15, L5 (2003)]. They propose a mechanism in which bubbles are clustering most likely in downflow regions. This clustering is a lift force effect suppressing large vortical structures, while enhancing energy input on small scales.

  10. 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.

  11. 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.

  12. Bubble migration during hydrate formation

    NASA Astrophysics Data System (ADS)

    Shagapov, V. Sh.; Chiglintseva, A. S.; Rusinov, A. A.

    2015-03-01

    A model of the process of migration of methane bubbles in water under thermobaric conditions of hydrate formation is proposed. The peculiarities of the temperature field evolution, migration rate, and changes in the radius and volume fraction of gas hydrate bubbles are studied. It is shown that, with a constant mass flow of gas from the reservoir bottom, for all parameters of the surfacing gas hydrate disperse system, there is a quasistationary pattern in the form of a "step"-like wave. Depending on the relationship of the initial gas bubble density with the average gas density in the hydrate composition determined by the depth from which bubbles rise to the surface, the final radius of hydrate particles may be larger or smaller than the initial gas bubble radii. It is established that the speed at which gas hydrate inclusions rise to the surface decreases by several times due to an increase in their weight during hydrate formation. The influence of the depth of the water reservoir whose bottom is a gas flow source on the dynamics of hydrate formation is studied.

  13. Capillarity-Driven Bubble Separations

    NASA Astrophysics Data System (ADS)

    Wollman, Andrew; Weislogel, Mark; Dreyer, Michael

    2013-11-01

    Techniques for phase separation in the absence of gravity continue to be sought after 5 decades of space flight. This work focuses on the fundamental problem of gas bubble separation in bubbly flows through open wedge-shaped channel in a microgravity environment. The bubbles appear to rise in the channel and coalesce with the free surface. Forces acting on the bubble are the combined effects of surface tension, wetting conditions, and geometry; not buoyancy. A single dimensionless group is identified that characterizes the bubble behavior and supportive experiments are conducted in a terrestrial laboratory, in a 2.1 second drop tower, and aboard the International Space Station as part of the Capillary Channel Flow (CCF) experiments. The data is organized into regime maps that provide insight on passive phase separations for applications ranging from liquid management aboard spacecraft to lab-on-chip technologies. NASA NNX09AP66A, NASA Oregon Space Grant NNX10AK68H, NASA NNX12AO47A, DLR 50WM0535/0845/1145

  14. 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.

  15. 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)

  16. 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.

  17. 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)

  18. 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

  19. 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...

  20. Oscillating plasma bubbles. II. Pulsed experiments

    SciTech Connect

    Stenzel, R. L.; Urrutia, J. M.

    2012-08-15

    Time-dependent phenomena have been investigated in plasma bubbles which are created by inserting spherical grids into an ambient plasma and letting electrons and ions form a plasma of different parameters than the ambient one. There are no plasma sources inside the bubble. The grid bias controls the particle flux. There are sheaths on both sides of the grid, each of which passes particle flows in both directions. The inner sheath or plasma potential develops self consistently to establish charge neutrality and divergence free charge and mass flows. When the electron supply is restricted, the inner sheath exhibits oscillations near the ion plasma frequency. When all electrons are excluded, a virtual anode forms on the inside sheath, reflects all ions such that the bubble is empty. By pulsing the ambient plasma, the lifetime of the bubble plasma has been measured. In an afterglow, plasma electrons are trapped inside the bubble and the bubble decays as slow as the ambient plasma. Pulsing the grid voltage yields the time scale for filling and emptying the bubble. Probes have been shown to modify the plasma potential. Using pulsed probes, transient ringing on the time scale of ion transit times through the bubble has been observed. The start of sheath oscillations has been investigated. The instability mechanism has been qualitatively explained. The dependence of the oscillation frequency on electrons in the sheath has been clarified.

  1. Rising motion of a bubble layer near a vertical wall

    NASA Astrophysics Data System (ADS)

    Dabiri, Sadegh; Bhuvankar, Pramod

    2015-11-01

    Bubbly flows in vertical pipes and channels form a wall-peak distribution of bubbles under certain conditions. The dynamics of the bubbles near the wall is different than in an unbounded liquid. Here we report the rising motion of bubbles in a liquid near a vertical wall. In a simulation of a bubbly flow in a periodic domain with a vertical wall on one side, an average pressure gradient is 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 a shear flow which is in turn generated by rising motion of bubbles. The rise velocity of the bubbles on the wall and the average rise velocity of the liquid depend on three dimensionless parameters, Archimedes number, Eotvos number, and the average volume fraction of bubbles near 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.

  2. Novel methods for measuring air-water interfacial area in unsaturated porous media.

    PubMed

    Brusseau, Mark L; El Ouni, Asma; Araujo, Juliana B; Zhong, Hua

    2015-05-01

    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

  3. 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

  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. 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.

  6. Formation of a Rigid Hydrophobin Film and Disruption by an Anionic Surfactant at an Air/Water Interface.

    PubMed

    Kirby, Stephanie M; Zhang, Xujun; Russo, Paul S; Anna, Shelley L; Walker, Lynn M

    2016-06-01

    Hydrophobins are amphiphilic proteins produced by fungi. Cerato-ulmin (CU) is a hydrophobin that has been associated with Dutch elm disease. Like other hydrophobins, CU stabilizes air bubbles and oil droplets through the formation of a persistent protein film at the interface. The behavior of hydrophobins at surfaces has raised interest in their potential applications, including use in surface coatings, food foams, and emulsions and as dispersants. The practical use of hydrophobins requires an improved understanding of the interfacial behavior of these proteins, alone and in the presence of added surfactants. In this study, the adsorption behavior of CU at air/water interfaces is characterized by measuring the surface tension and interfacial rheology as a function of adsorption time. CU is found to adsorb irreversibly at air/water interfaces. The magnitude of the dilatational modulus increases with adsorption time and surface pressure until CU eventually forms a rigid film. The persistence of this film is tested through the sequential addition of strong surfactant sodium dodecyl sulfate (SDS) to the bulk liquid adjacent to the interface. SDS is found to coadsorb to interfaces precoated with a CU film. At high concentrations, the addition of SDS significantly decreases the dilatational modulus, indicating disruption and displacement of CU by SDS. Sequential adsorption results in mixed layers with properties not observed in interfaces generated from complexes formed in the bulk. These results lend insight to the complex interfacial interactions between hydrophobins and surfactants. PMID:27164189

  7. Why do bubbles in Guinness sink?

    NASA Astrophysics Data System (ADS)

    Benilov, E. S.; Cummins, C. P.; Lee, W. T.

    2013-02-01

    Stout beers show the counter-intuitive phenomena of sinking bubbles, while the beer is settling. Previous research suggests that this phenomenon is due to the small size of the bubbles in these beers and the presence of a circulatory current, directed downwards near the side of the wall and upwards in the interior of the glass. The mechanism by which such a circulation is established and the conditions under which it will occur has not been clarified. In this paper, we use simulations and experiments to demonstrate that the flow in a glass of stout beer depends on the shape of the glass. If it narrows downwards (as the traditional stout glass, the pint, does), the flow is directed downwards near the wall and upwards in the interior and sinking bubbles will be observed. If the container widens downwards, the flow is opposite to that described above and only rising bubbles will be seen.

  8. Multi-Phase Flow and Heat Transfer Symposium-Workshop, 3rd, Miami Beach, FL, April 18-20, 1983, Proceedings of Condensed Papers

    NASA Astrophysics Data System (ADS)

    Veziroglu, T. N.

    Attempts at analytical predictions of stable operating regimes for multi-phase flows are reported, together with experimental results. The fundamentals and regimes of multi-phase flows are explored, including the behavior of bubbles in liquid flows. Attention is given to incidences of flow pressure drop and heat transfer properties in air-water dispersed flow, during blowdown, and in MHD flows. Mass transfer and phase changes conditions are investigated in turbulent flows, in the cockpit environment, and in the formation of alloys. Consideration is given to boiling and condensation phenomena on surfaces, in pools, and in tubes and fins, and to instabilities and turbulence. Reactor safety is discussed, as are numerical models for multi-phase flow, steam generation and distribution with solar and geothermal heat sources, and characteristics of transients and wave propagation. Fluidized bed flows are examined, together with measurement techniques and the characteristics of suspensions. No individual items are abstracted in this volume

  9. Air/water oxydesulfurization of coal: laboratory investigation

    SciTech Connect

    Warzinski, R. P.; Friedman, S.; Ruether, J. A.; LaCount, R. B.

    1980-08-01

    Air/water oxidative desulfurization has been demonstrated in autoclave experiments at the Pittsburgh Energy Technology Center for various coals representative of the major US coal basins. This experimentation has shown that the reaction proceeds effectively for pulverized coals at temperatures of 150 to 200/sup 0/C with air at a total system pressure of 500 to 1500 psig. Above 200/sup 0/C, the loss of coal and product heating value increases due to oxidative consumption of carbon and hydrogen. The pyritic sulfur solubilization reactions are typically complete (95 percent removal) within 15 to 40 minutes at temperature; however, significant apparent organic sulfur removal requires residence times of up to 60 minutes at the higher temperatures. The principal products of the reaction are sulfuric acid, which can be neutralized with limestone, and iron oxide. Under certain conditions, especially for high pyritic sulfur coals, the precipitation of sulfur-containing compounds from the products of the pyrite reaction may cause anomalous variations in the sulfur form data. The influence of various parameters on the efficiency of sulfur removal from coal by air/water oxydesulfurization has been studied.

  10. Modelling of Air Bubble Rising in Water and Polymeric Solution

    NASA Astrophysics Data System (ADS)

    Hassan, N. M. S.; Khan, M. M. K.; Rasul, M. G.; Subaschandar, N.

    2010-06-01

    This study investigates a Computational Fluid Dynamics (CFD) model for a single air bubble rising in water and xanthan gum solution. The bubble rise characteristics through the stagnant water and 0.05% xanthan gum solution in a vertical cylindrical column is modelled using the CFD code Fluent. Single air bubble rise dispersed into the continuous liquid phase has been considered and modelled for two different bubble sizes. Bubble velocity and vorticity magnitudes were captured through a surface-tracking technique i.e. Volume of Fluid (VOF) method by solving a single set of momentum equations and tracking the volume fraction of each fluid throughout the domain. The simulated results of the bubble flow contours at two different heights of the cylindrical column were validated by the experimental results and literature data. The model developed is capable of predicting the entire flow characteristics of different sizes of bubble inside the liquid column.

  11. 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.

  12. Bubble behavior during solidification in low gravity

    NASA Technical Reports Server (NTRS)

    Papazian, J. M.; Wilcox, W. R.; Gutowski, R.

    1979-01-01

    The trapping and behavior of gas bubbles were studied during low-gravity solidification of carbon tetrabromide, a transparent metal-model material. The experiment was performed during a NASA-sponsored sounding rocket flight and involved gradient freeze solidification of a gas-saturated melt. Gas bubbles were evolved at the solid-liquid interface during the low-gravity interval. No large-scale thermal migration of bubbles, bubble pushing by the solid-liquid interface, or bubble detachment from the interface were observed during the low-gravity experiment. A unique bubble motion-fluid flow event occurred in one specimen: a large bubble moved downward and caused some circulation of the melt. The gas bubbles that were trapped by the solid in commercial-purity material formed voids that had a cylindrical shape, in contrast to the spherical shape that had been observed in a prior low-gravity experiment. These shapes were not influenced by the gravity level (0.0001 g-0 vs g-0), but were dependent upon the initial temperature gradient. In higher purity material, however, the shape of the voids changed from cylindrical in 1g to spherical in low gravity.

  13. Estuary Turbulence and Air-Water Carbon Dioxide Exchange

    NASA Astrophysics Data System (ADS)

    Orton, Philip Mark

    The mixing of constituents between estuarine bottom and surface waters or between estuarine surface waters and the atmosphere are two topics of growing interest, in part due to the potentially important role of estuaries in global carbon budgets. These two types of mixing are typically driven by turbulence, and a research project was developed to improve the scientific understanding of atmospheric and tidal controls on estuary turbulence and airwater exchange processes. Highlights of method development and field research on the Hudson River estuary include several deployments of bottom mounted current profilers to quantify the turbulent kinetic energy (TKE) budget, and construction and deployment of an instrumented catamaran that makes autonomous measurements of air-water CO2 exchange (FCO2), water TKE dissipation at 50 cm depth (epsilon50), and other physical properties just above and below the air-water interface. On the Hudson, wind correlates strongly with epsilon50, but surface water speed and airwater heat flux also have moderate correlations with epsilon50. In partially mixed estuaries such as the Hudson, as well as salt wedge estuaries, baroclinic pressure forcing typically causes spring ebb tides to have much stronger upper water column shear than flood tides. The Hudson data are used to show that this shear leads to local shear instability and stronger near-surface turbulence on spring ebbs. Also, buoyancy budget terms are compared to demonstrate how water-to-air heat fluxes can influence stratification and indirectly influence epsilon50. Looking more closely at the role of wind forcing, it is demonstrated that inland propagation of the sea breeze on warm sunny days leads to arrival in phase with peak solar forcing at seaward stations, but several hours later at up-estuary stations. Passage of the sea breeze front raises the air-water CO2 flux by 1-2 orders of magnitude, and drives epsilon50 comparable to spring tide levels in the upper meter of the water

  14. Preheating in bubble collisions

    SciTech Connect

    Zhang Jun; Piao Yunsong

    2010-08-15

    In a landscape with metastable minima, the bubbles will inevitably nucleate. We show that when the bubbles collide, due to the dramatic oscillation of the field at the collision region, the energy deposited in the bubble walls can be efficiently released by the explosive production of the particles. In this sense, the collision of bubbles is actually highly inelastic. The cosmological implications of this result are discussed.

  15. Linear and nonlinear microrheology of lysozyme layers forming at the air-water interface.

    PubMed

    Allan, Daniel B; Firester, Daniel M; Allard, Victor P; Reich, Daniel H; Stebe, Kathleen J; Leheny, Robert L

    2014-09-28

    We report experiments studying the mechanical evolution of layers of the protein lysozyme adsorbing at the air-water interface using passive and active microrheology techniques to investigate the linear and nonlinear rheological response, respectively. Following formation of a new interface, the linear shear rheology, which we interrogate through the Brownian motion of spherical colloids at the interface, becomes viscoelastic with a complex modulus that has approximately power-law frequency dependence. The power-law exponent characterizing this frequency dependence decreases steadily with increasing layer age. Meanwhile, the nonlinear microrheology, probed via the rotational motion of magnetic nanowires at the interface, reveals a layer response characteristic of a shear-thinning power-law fluid with a flow index that decreases with age. We discuss two possible frameworks for understanding this mechanical evolution: gelation and the formation of a soft glass phase. PMID:24969505

  16. 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.

  17. Measuring Air-Water Interfacial Area via the Interfacial Partitioning Tracer Test Method

    NASA Astrophysics Data System (ADS)

    El Ouni, A.; Zhong, H.; Mainhagu, J.; Araujo, J. B.; Brusseau, M. L.

    2012-12-01

    Interfacial partitioning tracer tests (IPTT) are one method available for measuring air-water interfacial area (Aa-w). Two variations of the aqueous IPTT method are compared. One involves the standard approach comprising tracer injection under steady unsaturated-flow conditions with a uniform water-saturation distribution within the column. The other involves tracer injection under steady saturated-flowconditions in the presence of trapped residual air. Sodium dodecylbezenesulfonate (SDBS) and pentafluorobenzoic acid (PFBA) were used as the partitioning andnonreactive tracers, respectively. A sandy soil with a median grain diameter of 0.234 mm was used as the porous medium. Initial water saturation, Sw,was approximately 80%. Water saturation was monitored gravimetrically during the experiments. The results of the experiments will be assessed and compared to those of prior studies.

  18. Near-surface turbulence for evaporative convection at an air/water interface

    NASA Astrophysics Data System (ADS)

    Flack, K. A.; Saylor, J. R.; Smith, G. B.

    2001-11-01

    Turbulence measurements are reported for the flow beneath an air/water interface undergoing evaporative convection. Measurements were obtained using a two component laser Doppler velocimeter system. Two hydrodynamic boundary conditions were considered for the free surface: a shear free surface, which is the case when surfactants are absent, and a constant elasticity surface, created by depositing a monolayer of oleyl alcohol. The shear free boundary condition case results in significantly higher levels of near surface turbulence than the constant elasticity case. This difference between the two cases decreases with distance from the free surface. Profiles of the turbulent fluctuations were obtained for the horizontal and vertical velocity components and are compared with the somewhat analogous case of a heated solid wall.

  19. Microscopic dynamics of nanoparticle monolayers at air-water interface.

    PubMed

    Bhattacharya, R; Basu, J K

    2013-04-15

    We present results of surface mechanical and particle tracking measurements of nanoparticles trapped at the air-water interface as a function of their areal density. We monitor both the surface pressure (Π) and isothermal compression modulus (ϵ) as well as the dynamics of nanoparticle clusters, using fluorescence confocal microscopy while they are compressed to very high density near the two dimensional close packing density Φ∼0.82. We observe non-monotonic variation in both ϵ and the dynamic heterogeneity, characterized by the dynamical susceptibility χ4 with Φ, in such high density monolayers. We provide insight into the underlying nature of such transitions in close packed high density nanoparticle monolayers in terms of the morphology and flexibility of these soft colloidal particles. We discuss the significance our results in the context of related studies on two dimensional granular or colloidal systems. PMID:23411354

  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. Microrheology Using Optical Tweezers at the Air-Water Interface

    NASA Astrophysics Data System (ADS)

    Boatwright, Thomas; Levine, Alex; Dennin, Michael

    2010-11-01

    Microrheological techniques have been used successfully to determine mechanical properties of materials important in cellular structure. Also critical to cellular mechanical functions are biological membranes. Many aspects of biological membranes can be modeled using Langmuir monolayers, which are single layers surfactants at the air-water interface. The macroscopic mechanical properties of Langmuir monolayers have been extensively characterized. In contrast to macroscopic measurements, we report on experimental methods for studying the rheological properties of Langmuir monolayers on the micron scale. A water immersion optical tweezers system is used to trap ˜1 micron diameter beads in a monolayer. The passive motion of the trapped beads is recorded at high frequency and the complex shear modulus is calculated. Preliminary microrheological data of a fatty acid monolayer showing dependence on surface pressure will be presented. Experimental obstacles will also be discussed.

  2. The role of bubbles during air-sea gas exchange

    NASA Astrophysics Data System (ADS)

    Emerson, Steven; Bushinsky, Seth

    2016-06-01

    The potential for using the air-sea exchange rate of oxygen as a tracer for net community biological production in the ocean is greatly enhanced by recent accuracy improvements for in situ measurements of oxygen on unmanned platforms. A limiting factor for determining the exchange process is evaluating the air-sea flux contributed by bubble processes produced by breaking waves, particularly during winter months under high winds. Highly accurate measurements of noble gases (Ne, Ar & Kr) and nitrogen, N2, in seawater are tracers of the importance of bubble process in the surface mixed layer. We use measured distributions of these gases in the ventilated thermocline of the North Pacific and an annual time series of N2 in the surface ocean of the NE Subarctic Pacific to evaluate four different air-water exchange models chosen to represent the range of model interpretation of bubble processes. We find that models must have an explicit bubble mechanism to reproduce concentrations of insoluble atmospheric gases, but there are periods when they all depart from observations. The recent model of Liang et al. (2013) stems from a highly resolved model of bubble plumes and categorizes bubble mechanisms into those that are small enough to collapse and larger ones that exchange gases before they resurface, both of which are necessary to explain the data.

  3. Cavitation bubble dynamics in microfluidic gaps of variable height.

    PubMed

    Quinto-Su, Pedro A; Lim, Kang Y; Ohl, Claus-Dieter

    2009-10-01

    We study experimentally the dynamics of laser-induced cavitation bubbles created inside a narrow gap. The gap height, h , is varied from 15 to 400 microm and the resulting bubble dynamics is compared to a semiunbounded fluid. The cavitation bubbles are created with pulsed laser light at constant laser energy and are imaged with a high-speed camera. The bubble lifetime increases with decreasing gap height by up to 50% whereas the maximum projected bubble radius remains constant. Comparing the radial dynamics to potential flow models, we find that with smaller gaps, the bubble-induced flow becomes essentially planar, thus slower flows with reduced shear. These findings might have important consequences for microfluidic applications where it is desirable to tune the strength and range of the interactions such as in the case of cell lysis and cell membrane poration. PMID:19905487

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. [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. PMID:18290440

  11. 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.

  12. 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.

  13. Bubble Manipulation by Self Organization of Bubbles inside Ultrasonic Wave

    NASA Astrophysics Data System (ADS)

    Yamakoshi, Yoshiki; Koganezawa, Masato

    2005-06-01

    Microbubble manipulation using ultrasonic waves is a promising technology in the fields of future medicine and biotechnology. For example, it is considered that bubble trapping using ultrasonic waves may play an important role in drug or gene delivery systems in order to trap the drugs or genes in the diseased tissue. Usually, when bubbles are designed so that they carry payloads, such as drug or gene, they tend to be harder than free bubbles. These hard bubbles receive a small acoustic radiation force, which is not sufficient for bubble manipulation. In this paper, a novel method of microbubble manipulation using ultrasonic waves is proposed. This method uses seed bubbles in order to manipulate target bubbles. When the seed bubbles are introduced into the ultrasonic wave field, they start to oscillate to produce a bubble aggregation of a certain size. Then the target bubbles are introduced, the target bubbles attach around the seed bubbles producing a bubble mass with bilayers (inner layer: seed bubbles, outer layer: target bubbles). The target bubbles are manipulated as a bilayered bubble mass. Basic experiments are carried out using polyvinyl chloride (PVC) shell bubbles. No target bubbles are trapped when only the target bubbles are introduced. However, they are trapped if the seed bubbles are introduced in advance.

  14. Wind driven vertical transport in a vegetated, wetland water column with air-water gas exchange

    NASA Astrophysics Data System (ADS)

    Poindexter, C.; Variano, E. A.

    2010-12-01

    Flow around arrays of cylinders at low and intermediate Reynolds numbers has been studied numerically, analytically and experimentally. Early results demonstrated that at flow around randomly oriented cylinders exhibits reduced turbulent length scales and reduced diffusivity when compared to similarly forced, unimpeded flows (Nepf 1999). While horizontal dispersion in flows through cylinder arrays has received considerable research attention, the case of vertical dispersion of reactive constituents has not. This case is relevant to the vertical transfer of dissolved gases in wetlands with emergent vegetation. We present results showing that the presence of vegetation can significantly enhance vertical transport, including gas transfer across the air-water interface. Specifically, we study a wind-sheared air-water interface in which randomly arrayed cylinders represent emergent vegetation. Wind is one of several processes that may govern physical dispersion of dissolved gases in wetlands. Wind represents the dominant force for gas transfer across the air-water interface in the ocean. Empirical relationships between wind and the gas transfer coefficient, k, have been used to estimate spatial variability of CO2 exchange across the worlds’ oceans. Because wetlands with emergent vegetation are different from oceans, different model of wind effects is needed. We investigated the vertical transport of dissolved oxygen in a scaled wetland model built inside a laboratory tank equipped with an open-ended wind tunnel. Plastic tubing immersed in water to a depth of approximately 40 cm represented emergent vegetation of cylindrical form such as hard-stem bulrush (Schoenoplectus acutus). After partially removing the oxygen from the tank water via reaction with sodium sulfite, we used an optical probe to measure dissolved oxygen at mid-depth as the tank water re-equilibrated with the air above. We used dissolved oxygen time-series for a range of mean wind speeds to estimate the

  15. 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

  16. 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.

  17. 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.

  18. Numerical modeling of bubble dynamics in magmas

    NASA Astrophysics Data System (ADS)

    Huber, Christian; Su, Yanqing; Parmigiani, Andrea

    2014-05-01

    Understanding the complex non-linear physics that governs volcanic eruptions is contingent on our ability to characterize the dynamics of bubbles and its effect on the ascending magma. The exsolution and migration of bubbles has also a great impact on the heat and mass transport in and out of magma bodies stored at shallow depths in the crust. Multiphase systems like magmas are by definition heterogeneous at small scales. Although mixture theory or homogenization methods are convenient to represent multiphase systems as a homogeneous equivalent media, these approaches do not inform us on possible feedbacks at the pore-scale and can be significantly misleading. In this presentation, we discuss the development and application of bubble-scale multiphase flow modeling to address the following questions : How do bubbles impact heat and mass transport in magma chambers ? How efficient are chemical exchanges between the melt and bubbles during magma decompression? What is the role of hydrodynamic interactions on the deformation of bubbles while the magma is sheared? Addressing these questions requires powerful numerical methods that accurately model the balance between viscous, capillary and pressure stresses. We discuss how these bubble-scale models can provide important constraints on the dynamics of magmas stored at shallow depth or ascending to the surface during an eruption.

  19. 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

  20. Modeling of surface cleaning by cavitation bubble dynamics and collapse.

    PubMed

    Chahine, Georges L; Kapahi, Anil; Choi, Jin-Keun; Hsiao, Chao-Tsung

    2016-03-01

    Surface cleaning using cavitation bubble dynamics is investigated numerically through modeling of bubble dynamics, dirt particle motion, and fluid material interaction. Three fluid dynamics models; a potential flow model, a viscous model, and a compressible model, are used to describe the flow field generated by the bubble all showing the strong effects bubble explosive growth and collapse have on a dirt particle and on a layer of material to remove. Bubble deformation and reentrant jet formation are seen to be responsible for generating concentrated pressures, shear, and lift forces on the dirt particle and high impulsive loads on a layer of material to remove. Bubble explosive growth is also an important mechanism for removal of dirt particles, since strong suction forces in addition to shear are generated around the explosively growing bubble and can exert strong forces lifting the particles from the surface to clean and sucking them toward the bubble. To model material failure and removal, a finite element structure code is used and enables simulation of full fluid-structure interaction and investigation of the effects of various parameters. High impulsive pressures are generated during bubble collapse due to the impact of the bubble reentrant jet on the material surface and the subsequent collapse of the resulting toroidal bubble. Pits and material removal develop on the material surface when the impulsive pressure is large enough to result in high equivalent stresses exceeding the material yield stress or its ultimate strain. Cleaning depends on parameters such as the relative size between the bubble at its maximum volume and the particle size, the bubble standoff distance from the particle and from the material wall, and the excitation pressure field driving the bubble dynamics. These effects are discussed in this contribution. PMID:25982895

  1. 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. PMID:19018296

  2. 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.

  3. 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.

  4. Impact of Gas-liquid Two-phase Flow on Fluid Borne Noise

    NASA Astrophysics Data System (ADS)

    Taniwaki, Mitsuhiro; Shimomura, Nobuo

    In pipe lines such as those found in refrigeration cycle, a gas-liquid two-phase flow may occur because of a pressure change in the pipe. This flow causes noise. A vapor phase ratio in a fluid and the behavior of bubbles are related to the outbreak of noise. This experimental study investigated the fluid borne noise caused by gas-liquid two-phase flow passing through a contracted section in horizontal pipe. In the experiment, sound pressure was measured for two purposes: to see the influence of the air-water ratio on sound pressure and to see the change in sound pressure when a single bubble passed through a contracted section in horizontal pipe. The experiment showed that the fluid borne noise of gas-liquid two-phase flow grew louder than that of a liquid single-phase flow. As for the frequency distribution of the fluid borne noise, the sound pressure level was higher in the high frequency band. Furthermore, the fluid borne noise grew louder with increasing bubble diameter.

  5. 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.

  6. 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

  7. 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. PMID:26035016

  8. Electrowetting of soap bubbles

    NASA Astrophysics Data System (ADS)

    Arscott, Steve

    2013-07-01

    A proof-of-concept demonstration of the electrowetting-on-dielectric of a sessile soap bubble is reported here. The bubbles are generated using a commercial soap bubble mixture—the surfaces are composed of highly doped, commercial silicon wafers covered with nanometer thick films of Teflon®. Voltages less than 40 V are sufficient to observe the modification of the bubble shape and the apparent bubble contact angle. Such observations open the way to inter alia the possibility of bubble-transport, as opposed to droplet-transport, in fluidic microsystems (e.g., laboratory-on-a-chip)—the potential gains in terms of volume, speed, and surface/volume ratio are non-negligible.

  9. 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.

  10. 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.

  11. Recognition of highly overlapping ellipse-like bubble images

    NASA Astrophysics Data System (ADS)

    Honkanen, Markus; Saarenrinne, Pentti; Stoor, Tuomas; Niinimäki, Jouko

    2005-09-01

    This study describes a robust bubble image recognition algorithm that detects the in-focus, ellipse-like bubble images from experimental images with heavily overlapping bubbles. The principle of the overlapping object recognition (OOR) algorithm is that it calculates the overall perimeter of a segment, finds the points at the perimeter that represent the connecting points of overlapping objects, clusters the perimeter arcs that belong to the same object and fits ellipses on the clustered arcs of the perimeter. The accuracy of the algorithm is studied with simulated images of overlapping ellipses, providing an RMS error of 0.9 pixels in size measurement. The algorithm is utilized in measurements of bubble size distributions with a direct imaging (DI) technique in which a digital camera and a pulsed back light are used to detect bubble outlines. The measurement system is calibrated with stagnant bubbles in a gel in order to define the bubble size dependent effective thickness of the measurement volume and the grey scale gradient threshold as a focus criterion. The described concept with a novel bubble recognition algorithm enables DI measurements in denser bubbly flows with increased reliability and accuracy of the measurement results. The measurement technique is applied to the study of the turbulent bubbly flow in a papermaking machine, in the outlet pipe of a centrifugal pump.

  12. 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.

  13. Two-phase flow in smooth and rough fractures: Measurement and correlation by porous-medium and pipe flow models

    SciTech Connect

    Fourar, M.; Bories, S. ); Lenormand, R. ); Persoff, P. )

    1993-11-01

    Two-phase (air-water) flow experiments were conducted in horizontal artificial fractures. The fractures were between glass plates that were either smooth or artificially roughened by gluing a layer of glass beads to them. One smooth fracture with an aperture of 1 mm and three rough fractures, one with the two surfaces in contact and two without contact, were studied. For both types of fractures, the flow structures are similar to those observed in two-phase flow in a pipe, with structures (bubbles, fingering bubbles, films, and drops) depending on the gas and liquid flow rates. The pressure gradients measured for different liquid and gas velocities were interpreted by three models. First, using Darcy's law leads to relative permeability curves similar to conventional ones for porous media. However, these curves depend not only on saturation but also on flow rats. This effect is caused by inertial forces which are not included in this approach. Second, the standard approach for two-phase flow in pipes (Lockhart and Martinelli's equation) agrees with experimental results, at least for small pressure gradients. Finally, the best fit was obtained by treating the two phases as one homogeneous phase. All the properties are averaged, and the pressure drop is deduced from an empirical correlation between the two-phase Reynolds number and the friction factor. 22 refs., 11 figs.

  14. 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... Violating Facilities” published pursuant to 40 CFR 15.20. By acceptance of a cooperative agreement in...

  15. 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... Violating Facilities” published pursuant to 40 CFR 15.20. By acceptance of a cooperative agreement in...

  16. 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... Violating Facilities” published pursuant to 40 CFR 15.20. By acceptance of a cooperative agreement in...

  17. 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. 1274.926 Section 1274.926 Aeronautics and Space NATIONAL AERONAUTICS AND SPACE ADMINISTRATION COOPERATIVE AGREEMENTS WITH COMMERCIAL FIRMS Other Provisions and Special Conditions § 1274.926 Clean Air-Water Pollution Control Acts. Clean...

  18. Measurement of velocities in gas-liquid two-phase flow using Laser Doppler Velocimetry

    SciTech Connect

    Vassallo, P.F.; Trabold, T.A.; Moore, W.E.; Kirouac, G.J.

    1992-09-01

    Measurements of bubble and liquid velocities in two-phase flow have been made using a new forward/backward scattering Laser Doppler Velocimetry (LDV) technique. This work was performed in a 6.4 by 11.1 mm vertical duct using known air/water mixtures. A standard LDV fiber optic probe was used to measure the bubble velocity, using direct backscattered light. A novel retro-reflector and lens assembly permitted the same probe to measure the liquid velocity with direct forward-scattered light. The bubble velocity was confirmed by independent measurements with a high-speed video system. The liquid velocity was confirmed by demonstrating the dominance of the liquid seed data rate in the forward-scatter measurement. Experimental data are presented to demonstrate the accuracy of the technique for a wide range of flow conditions, from bubbles as small as 0.75-mm-diam to slugs as large as 10-mm wide by 30-mm long. In the slug regime, the LDV technique performed velocity measurements for both phases, for void fractions up to 50%, which was the upper limit of our experimental investigation.

  19. 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.

  20. 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

  1. Sonochemistry and bubble dynamics.

    PubMed

    Mettin, Robert; Cairós, Carlos; Troia, Adriano

    2015-07-01

    The details of bubble behaviour in chemically active cavitation are still not sufficiently well understood. Here we report on experimental high-speed observations of acoustically driven single-bubble and few-bubble systems with the aim of clarification of the connection of their dynamics with chemical activity. Our experiment realises the sonochemical isomerization reaction of maleic acid to fumaric acid, mediated by bromine radicals, in a bubble trap set-up. The main result is that the reaction product can only be observed in a parameter regime where a small bubble cluster occurs, while a single trapped bubble stays passive. Evaluations of individual bubble dynamics for both cases are given in form of radius-time data and numerical fits to a bubble model. A conclusion is that a sufficiently strong collapse has to be accompanied by non-spherical bubble dynamics for the reaction to occur, and that the reason appears to be an efficient mixing of liquid and gas phase. This finding corroborates previous observations and literature reports on high liquid phase sonochemical activity under distinct parameter conditions than strong sonoluminescence emissions. PMID:25194210

  2. Structure and dynamics of the wake of bubbles and its relevance for bubble interaction

    NASA Astrophysics Data System (ADS)

    Brücker, Christoph

    1999-07-01

    The flow in the wake of single and two interacting air bubbles freely rising in water is studied experimentally using digital-particle-image-velocimetry in combination with high-speed recording. The experiments focus on ellipsoidal bubbles of diameter of about 0.4-0.8 cm which show spiraling, zigzagging, and rocking motion during their rise in water, which was seeded with small tracer particles for flow visualization. Under counterflow conditions in the vertical channel, the bubbles are retained in the center of the observation region, which allows the wake oscillations and bubble interaction to be observed over several successive periods. By simultaneous diffuse illumination in addition to the light sheet, we were able to record both the path and shape oscillations of the bubble, as well as the wake structure in a horizontal and vertical cross section. The results show that the zigzagging motion is coupled to a regular generation and discharge of alternate oppositely oriented hairpin-like vortex structures. Associated with the wake oscillation, the bubble experiences a strong asymmetric deformation in the equatorial plane at the inversion points of the zigzag path. The zigzag motion is superimposed on a small lateral drift of the bubble, which implies the existence of a net lift force. This is explained by the observed different strength of the hairpin vortices in the zig and zag path; a seemingly familiar phenomenon was found in recent numerical results of the sphere wake flow. For spiraling bubbles the wake is approximately steady to an observer moving with the bubble. It consists of a twisted pair of streamwise vortex filaments which are wound in a helical path and are attached to the bubble base at an asymmetrical position. The minor axis of the bubble is tilted in the tangential plane as well as in the radial plane toward the spiral center. Due to the pressure field induced by the asymmetrically attached wake two components of the lift force exist, one that

  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. Steady bubble rise and deformation in Newtonian and viscoplastic fluids and conditions for bubble entrapment

    NASA Astrophysics Data System (ADS)

    Tsamopoulos, J.; Dimakopoulos, Y.; Chatzidai, N.; Karapetsas, G.; Pavlidis, M.

    We examine the buoyancy-driven rise of a bubble in a Newtonian or a viscoplastic fluid assuming axial symmetry and steady flow. Bubble pressure and rise velocity are determined, respectively, by requiring that its volume remains constant and its centre of mass remains fixed at the centre of the coordinate system. The continuous constitutive model suggested by Papanastasiou is used to describe the viscoplastic behaviour of the material. The flow equations are solved numerically using the mixed finite-element/Galerkin method. The nodal points of the computational mesh are determined by solving a set of elliptic differential equations to follow the often large deformations of the bubble surface. The accuracy of solutions is ascertained by mesh refinement and predictions are in very good agreement with previous experimental and theoretical results for Newtonian fluids. We determine the bubble shape and velocity and the shape of the yield surfaces for a wide range of material properties, expressed in terms of the Bingham Bn=tau_y(*}/rho({*}g^{*)) R_b(*) Bond Bo =rho(*}g({*)) R_b({*) 2}/gamma(*) and Archimedes Ar=rho(*2}g({*)) R_b(*3}/mu_o({*2)) numbers, where *o the viscosity, *y the yield stress of the material, g* the gravitational acceleration and R*b the radius of a spherical bubble of the same volume. If the fluid is viscoplastic, the material will not be deforming outside a finite region around the bubble and, under certain conditions, it will not be deforming either behind it or around its equatorial plane in contact with the bubble. As Bn increases, the yield surfaces at the bubble equatorial plane and away from the bubble merge and the bubble becomes entrapped. When Bo is small and the bubble cannot deform from the spherical shape the critical Bn is 0.143, i.e. it is a factor of 3/2 higher than the critical Bn for the entrapment of a solid sphere in a Bingham fluid, in direct correspondence with the 3/2 higher terminal velocity of a bubble over that of a sphere

  5. 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.

  6. Trapping and release of bubbles from a linear pore

    NASA Astrophysics Data System (ADS)

    Juel, Anne; Dawson, Geoffrey; Lee, Sungyon

    2012-11-01

    Multiphase flows of practical interest are characterized by complex vessel geometries ranging from natural porous media to man-made lab-on-a-chip devices. Models based on the over-simplification of the pore geometry often suppress fundamental physical behavior. We study the effect on bubble motion of a sudden streamwise expansion of a square tube. The extent to which a bubble driven by constant flux flow broadens to partially fill the expansion depends on the balance between viscous and surface tension stresses, measured by the capillary number Ca . This broadening is accompanied by the slowing and momentary arrest of the bubble as Ca is reduced towards its critical value for trapping. For Ca < Cac the pressure drag forces on the quasi-arrested bubble are insufficient to force the bubble out of the expansion so it remains trapped. We examine the conditions for trapping by varying bubble volume, flow rate of the carrier fluid, and length of expanded region, and find that Cac depends non-monotonically on the size of the bubble. We verify with experiments and a capillary static model that a bubble is released if the work of the pressure forces over the length of the expansion exceeds the surface energy required for the trapped bubble to reenter the constricted square tube.

  7. 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.

  8. 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.

  9. 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.

  10. Bubble plumes generated during recharge of basaltic magma reservoirs

    NASA Astrophysics Data System (ADS)

    Phillips, Jeremy C.; Woods, Andrew W.

    2001-03-01

    CO 2 is relatively insoluble in basaltic magma at low crustal pressures. It therefore exists as a gas phase in the form of bubbles in shallow crustal reservoirs. Over time these bubbles may separate gravitationally from the magma in the chamber. As a result, any new magma which recharges the chamber from deeper in the crust may be more bubble-rich and hence of lower density than the magma in the chamber. Using scaling arguments, we show that for typical recharge fluxes, such a source of low-viscosity, bubble-rich basalt may generate a turbulent bubble plume within the chamber. We also show that the bubbles are typically sufficiently small to have a low Reynolds number and to remain in the flow. We then present a series of analogue laboratory experiments which identify that the motion of such a turbulent bubble-driven line plume is well described by the classical theory of buoyant plumes. Using the classical plume theory we then examine the effect of the return flow associated with such bubble plumes on the mixing and redistribution of bubbles within the chamber. Using this model, we show that a relatively deep bubbly layer of magma may form below a thin foam layer at the roof. If, as an eruption proceeds, there is a continuing influx at the base of the chamber, then our model suggests that the bubble content of the bubbly layer may gradually increase. This may lead to a transition from lava flow activity to more explosive fire-fountaining activity. The foam layer at the top of the chamber may provide a flux for the continual outgassing from the flanks of the volcano [Ryan, Am. Geophys. Union Geophys. Monogr. 91 (1990)] and if it deepens sufficiently it may contribute to the eruptive activity [Vergniolle and Jaupart, J. Geophys. Res. 95 (1990) 2793-3001].

  11. Gases in Tektite Bubbles.

    PubMed

    O'keefe, J A; Lowman, P D; Dunning, K L

    1962-07-20

    Spectroscopic analysis of light produced by electrodeless discharge in a tektite bubble showed the main gases in the bubble to be neon, helium, and oxygen. The neon and helium have probably diffused in from the atmosphere, while the oxygen may be atmospheric gas incorporated in the tektite during its formation. PMID:17801113

  12. 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…

  13. Cost versus Enrollment Bubbles

    ERIC Educational Resources Information Center

    Vedder, Richard K.; Gillen, Andrew

    2011-01-01

    The defining characteristic of a bubble is unsustainable growth that eventually reverses. Bubbles typically arise when uncertainty leads to unsustainable trends, and the authors argue that there are two areas in which higher education has experienced what appear to be unsustainable trends, namely, college costs (the costs to students, parents, and…

  14. 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.…

  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

    2005-11-01

    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. PMID:16383983

  17. A modelling and experimental study of the bubble trajectory in a non-Newtonian crystal suspension

    NASA Astrophysics Data System (ADS)

    Hassan, N. M. S.; Khan, M. M. K.; Rasul, M. G.

    2010-12-01

    This paper presents an experimental and computational study of air bubbles rising in a massecuite-equivalent non-Newtonian crystal suspension. The bubble trajectory inside the stagnant liquid of a 0.05% xanthan gum crystal suspension was investigated and modelled using the computational fluid dynamics (CFD) model to gain an insight into the bubble flow characteristics. The CFD code FLUENT was used for numerical simulation, and the bubble trajectory calculations were performed through a volume of fluid (VOF) model. The influences of the Reynolds number (Re), the Weber number (We) and the bubble aspect ratio (E) on the bubble trajectory are discussed. The conditions for the bubbles' path oscillations are identified. The experimental results showed that the path instability for the crystal suspension was less rapid than in water. The trajectory analysis indicated that 5.76 mm diameter bubbles followed a zigzag motion in the crystal suspension. Conversely, the smaller bubbles (5.76 mm) followed a path of least horizontal movement and larger bubbles (21.21 mm) produced more spiral motion within the crystal suspension. Path instability occurred for bubbles of 15.63 and 21.21 mm diameter, and they induced both zigzag and spiral trajectories within the crystal suspension. At low Re and We, smaller bubbles (5.76 mm) produced a zigzag trajectory, whereas larger bubbles (15.63 and 21.21 mm) showed both zigzag and spiral trajectories at intermediate and moderately high Re and We in the crystal suspension. The simulation results illustrated that a repeating pattern of swirling vortices was created for smaller bubbles due to the unstable wake and unsteady flow of these bubbles. This is the cause of the smaller bubbles moving in a zigzag way. Larger bubbles showed two counter-rotating trailing vortices at the back of the bubble. These vortices induced a velocity component to the gas-liquid interface and caused a deformation. Hence, the larger bubbles produced a path transition.

  18. The Bubbling Galactic Disk

    NASA Astrophysics Data System (ADS)

    Churchwell, E.; Povich, M. S.; Allen, D.; Taylor, M. G.; Meade, M. R.; Babler, B. L.; Indebetouw, R.; Watson, C.; Whitney, B. A.; Wolfire, M. G.; Bania, T. M.; Benjamin, R. A.; Clemens, D. P.; Cohen, M.; Cyganowski, C. J.; Jackson, J. M.; Kobulnicky, H. A.; Mathis, J. S.; Mercer, E. P.; Stolovy, S. R.; Uzpen, B.; Watson, D. F.; Wolff, M. J.

    2006-10-01

    A visual examination of the images from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) has revealed 322 partial and closed rings that we propose represent partially or fully enclosed three-dimensional bubbles. We argue that the bubbles are primarily formed by hot young stars in massive star formation regions. We have found an average of about 1.5 bubbles per square degree. About 25% of the bubbles coincide with known radio H II regions, and about 13% enclose known star clusters. It appears that B4-B9 stars (too cool to produce detectable radio H II regions) probably produce about three-quarters of the bubbles in our sample, and the remainder are produced by young O-B3 stars that produce detectable radio H II regions. Some of the bubbles may be the outer edges of H II regions where PAH spectral features are excited and may not be dynamically formed by stellar winds. Only three of the bubbles are identified as known SNRs. No bubbles coincide with known planetary nebulae or W-R stars in the GLIMPSE survey area. The bubbles are small. The distribution of angular diameters peaks between 1' and 3' with over 98% having angular diameters less than 10' and 88% less than 4'. Almost 90% have shell thicknesses between 0.2 and 0.4 of their outer radii. Bubble shell thickness increases approximately linearly with shell radius. The eccentricities are rather large, peaking between 0.6 and 0.7; about 65% have eccentricities between 0.55 and 0.85.

  19. 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.

  20. 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.

  1. Wall slip of bubbles in foams

    NASA Astrophysics Data System (ADS)

    Saugey, A.; Drenckhan, W.; Weaire, D.

    2006-05-01

    We present a computational analysis of the flow of liquid foam along a smooth wall, as encountered in the transport of foams in vessels and pipes. We concentrate on the slip of the bubbles at the wall and present some novel finite element calculations of this motion for the case of fully mobile gas/liquid interfaces. Our two-dimensional simulations provide for the first time the bubble shapes and entire flow field, giving detailed insight into the distribution of stresses and dissipation in the system. In particular, we investigate the relationship between the drag force and the slip velocity of the bubble, which for small slip velocities obeys power laws, as predicted by previous semianalytical treatments.

  2. A bubble detection system for propellant filling pipeline

    NASA Astrophysics Data System (ADS)

    Wen, Wen; Zong, Guanghua; Bi, Shusheng

    2014-06-01

    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.

  3. A bubble detection system for propellant filling pipeline.

    PubMed

    Wen, Wen; Zong, Guanghua; Bi, Shusheng

    2014-06-01

    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. PMID:24985851

  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. Bubble-raft collapse and the nonequilibrium dynamics of two-state elastica

    NASA Astrophysics Data System (ADS)

    Kuo, Chin-Chang; Kachan, Devin; Levine, Alex J.; Dennin, Michael

    2016-03-01

    We report on the collapse of bubble rafts under compression in a closed rectangular geometry. A bubble raft is a single layer of bubbles at the air-water interface. A collapse event occurs when bubbles submerge beneath the neighboring bubbles under compression, causing the structure of the bubble raft to go from single-layer to multilayer. We studied the collapse dynamics as a function of compression velocity. At higher compression velocity we observe a more uniform distribution of collapse events, whereas at lower compression velocities the collapse events accumulate at the system boundaries. We propose that this system can be understood in terms of a linear elastic sheet coupled to a local internal (Ising) degree of freedom. The two internal states, which represent one bubble layer versus two, couple to the elasticity of the sheet by locally changing the reference state of the material. By exploring the collapse dynamics of the bubble raft, one may address the basic nonlinear mechanics of a number of complex systems in which elastic stress is coupled to local internal variables.

  6. 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.

  7. Bubbling behaviors induced by gas-liquid mixture permeating through a porous medium

    NASA Astrophysics Data System (ADS)

    Hu, Liang; Li, Mingbo; Chen, Wenyu; Xie, Haibo; Fu, Xin

    2016-08-01

    This paper investigates the bubbling behaviors induced by gas-liquid mixture permeating through porous medium (PM), which was observed in developing immersion lithography system and was found having great differences with traditional bubbling behaviors injected with only gas phase through the PM. An experimental setup was built up to investigate the bubbling characteristics affected by the mixed liquid phase. Both the flow regimes of gas-liquid mixture in micro-channel (upstream of the PM) and the bubbling flow regimes in water tank (downstream of the PM) were recorded synchronously by high-speed camera. The transitions between the flow regimes are governed by gas and liquid Weber numbers. Based on the image analysis, the characteristic parameters of bubbling region, including the diameter of bubbling area on PM surface, gas-phase volume flux, and dispersion angle of bubbles in suspending liquid, were studied under different proportions of gas and liquid flow rate. Corresponding empirical correlations were developed to describe and predict these parameters. Then, the pertinent bubble characteristics in different bubbling flow regimes were systematically investigated. Specifically, the bubble size distribution and the Sauter mean diameter affected by increasing liquid flow rate were studied, and the corresponding analysis was given based on the hydrodynamics of bubble-bubble and bubble-liquid interactions. According to dimensionless analysis, the general prediction equation of Sauter mean diameter under different operating conditions was proposed and confirmed by experimental data. The study of this paper is helpful to improve the collection performance of immersion lithography and aims to reveal the differences between the bubbling behaviors on PM caused by only gas flow and gas-liquid mixture flow, respectively, for the researches of fluid flow.

  8. 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

  9. 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. PMID:25849088

  10. Bubbles, Bubbles: Integrated Investigations with Floating Spheres

    ERIC Educational Resources Information Center

    Reeder, Stacy

    2007-01-01

    In this article, the author describes integrated science and mathematics activities developed for fourth-grade students to explore and investigate three-dimensional geometric shapes, Bernoulli's principle, estimation, and art with and through bubbles. Students were engaged in thinking and reflection on the questions their teachers asked and were…

  11. Effects of gravity level on bubble formation and rise in low-viscosity liquids

    NASA Astrophysics Data System (ADS)

    Suñol, Francesc; González-Cinca, Ricard

    2015-05-01

    We present an experimental analysis of the effects of gravity level on the formation and rise dynamics of bubbles. Experiments were carried out with millimeter-diameter bubbles in the hypergravity environment provided by the large-diameter centrifuge of the European Space Agency. Bubble detachment from a nozzle is determined by buoyancy and surface tension forces regardless of the gravity level. Immediately after detachment, bubble trajectory is deviated by the Coriolis force. Subsequent bubble rise is dominated by inertial forces and follows a zig-zag trajectory with amplitude and frequency dependent on the gravity level. Vorticity production is enhanced as gravity increases, which destabilizes the flow and therefore the bubble path.

  12. 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.

  13. 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

  14. 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.

  15. Turbulent shear control with oscillatory bubble injection

    NASA Astrophysics Data System (ADS)

    Park, Hyun Jin; Oishi, Yoshihiko; Tasaka, Yuji; Murai, Yuichi; Takeda, Yasushi

    2009-02-01

    It is known that injecting bubbles into shear flow can reduce the frictional drag. This method has advantages in comparison to others in simplicity of installation and also in environment. The amount of drag reduction by bubbles depends on the void fraction provided in the boundary layer. It means, however, that certain power must be consumed to generate bubbles in water, worsening the total power-saving performance. We propose oscillatory bubble injection technique to improve the performance in this study. In order to prove this idea of new type of drag reduction, velocity vector field and shear stress profile in a horizontal channel flow are measured by ultrasonic velocity profiler (UVP) and shear stress transducer, respectively. We measure the gas-liquid interface from the UVP signal, as well. This compound measurement with different principles leads to deeper understanding of bubble-originated drag reduction phenomena, in particular for unsteady process of boundary layer alternation. At these experiments, the results have demonstrated that the intermittency promotes the drag reduction more than normal continuous injection for the same void fraction supplied.

  16. Sheathless hydrodynamic positioning of buoyant drops and bubbles inside microchannels

    NASA Astrophysics Data System (ADS)

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

    2011-09-01

    Particles, bubbles, and drops carried by a fluid in a confined environment such as a pipe can be subjected to hydrodynamic lift forces, i.e., forces that are perpendicular to the direction of the flow. We investigated the positioning effect of lift forces acting on buoyant drops and bubbles suspended in a carrier fluid and flowing in a horizontal microchannel. We report experiments on drops of water in fluorocarbon liquid, and on bubbles of nitrogen in hydrocarbon liquid and silicone oil, inside microchannels with widths on the order of 0.1-1 mm. Despite their buoyancy, drops and bubbles could travel without contacting with the walls of channels; the most important parameters for reaching this flow regime in our experiments were the viscosity and the velocity of the carrier fluid, and the sizes of drops and bubbles. The dependencies of the transverse position of drops and bubbles on these parameters were investigated. At steady state, the trajectories of drops and bubbles approached the center of the channel for drops and bubbles almost as large as the channel, carried by rapidly flowing viscous liquids; among our experiments, these flow conditions were characterized by larger capillary numbers and smaller Reynolds numbers. Analytical models of lift forces developed for the flow of drops much smaller than the width of the channel failed to predict their transverse position, while computational fluid dynamic simulations of the experiments agreed better with the experimental measurements. The degrees of success of these predictions indicate the importance of confinement on generating strong hydrodynamic lift forces. We conclude that, inside microfluidic channels, it is possible to support and position buoyant drops and bubbles simply by flowing a single-stream (i.e., “sheathless”) carrier liquid that has appropriate velocity and hydrodynamic properties.

  17. 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.

  18. Significance of viscoelastic effects on the rising of a bubble and bubble-to-bubble interaction

    NASA Astrophysics Data System (ADS)

    Fernandez, Arturo

    2011-11-01

    Numerical results for the rising of a bubble and the interaction between two bubbles in non-Newtonian fluids will be discussed. The computations are carried out using a multiscale method combining front-tracking with Brownian dynamics simulations. The evaluation of the material properties for the non-Newtonian fluid will be discussed firstly. The results from the computations of a single bubble show how elastic effects modify the deformation and rising of the bubble by pulling the tail of it. The relationship between the strength of the elastic forces and the discontinuity in the bubble terminal velocity, when plotted versus bubble volume, is also observed in the computations. The bubble-to-bubble interaction is dominated not only by elastic effects but also by the shear-thinning caused by the leading bubble, which leads the trailing bubble to accelerate faster and coalesce with the leading bubble.

  19. 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.

  20. 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.

  1. 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...

  2. Monolayers at air-water interfaces: from origins-of-life to nanotechnology.

    PubMed

    Ariga, Katsuhiko; Hill, Jonathan P

    2011-08-01

    The air-water interface presents several interesting features, namely a) a molecularly flat environment, b) a boundary region between two phases with different dielectric constants, c) permits or promotes dynamic interactions within the interface region, and d) a point of interaction between hydrophobic compounds and aqueous molecules. Accordingly, Langmuir monolayers at the air-water interface have several unique characteristics and properties, which require investigation. In this review-type personal account, typical examples of molecular recognition and molecular patterning at air-water interfaces are first introduced, followed by descriptions of specific and unusual properties of monolayers on water. In addition, two examples of our own results concerning Langmuir monolayers are explained. We have selected examples from two apparently unrelated research areas, these being the origin of life and future nanotechnology, in order to emphasize the diverse scientific contribution of research on monolayers at the air-water interface. PMID:21739568

  3. Aerator Combined With Bubble Remover

    NASA Technical Reports Server (NTRS)

    Dreschel, Thomas W.

    1993-01-01

    System produces bubble-free oxygen-saturated water. Bubble remover consists of outer solid-walled tube and inner hydrophobic, porous tube. Air bubbles pass from water in outer tube into inner tube, where sucked away. Developed for long-term aquaculture projects in space. Also applicable to terrestrial equipment in which entrained bubbles dry membranes or give rise to cavitation in pumps.

  4. Dense bubble traffic in microfluidic loops: Selection rules and clogging.

    PubMed

    Hourtane, Virginie; Bodiguel, Hugues; Colin, Annie

    2016-03-01

    We study the repartition of monodisperse bubbles at the inlet node of an asymmetric microfluidic loop for low to high bubble densities. In large loops, we evidence a new regime. Contrary to the classical belief, we point out that bubbles are directed not towards the arm having the higher total flow rate but towards the arm with the higher water flow rate at low and moderate relative gas flow rates. At higher rates, they enter the longer arm when they reach close packing in the shorter arm. In small loops, we evidence a clogging regime at high relative gas flow rates. Collisions between bubbles coming from the two arms at the outlet clog the longer arm. We propose a comprehensive analysis allowing us to explain these results. PMID:27078414

  5. Dense bubble traffic in microfluidic loops: Selection rules and clogging

    NASA Astrophysics Data System (ADS)

    Hourtane, Virginie; Bodiguel, Hugues; Colin, Annie

    2016-03-01

    We study the repartition of monodisperse bubbles at the inlet node of an asymmetric microfluidic loop for low to high bubble densities. In large loops, we evidence a new regime. Contrary to the classical belief, we point out that bubbles are directed not towards the arm having the higher total flow rate but towards the arm with the higher water flow rate at low and moderate relative gas flow rates. At higher rates, they enter the longer arm when they reach close packing in the shorter arm. In small loops, we evidence a clogging regime at high relative gas flow rates. Collisions between bubbles coming from the two arms at the outlet clog the longer arm. We propose a comprehensive analysis allowing us to explain these results.

  6. 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)

  7. 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)

  8. 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.

  9. Bubble Dynamics on a Heated Surface

    NASA Technical Reports Server (NTRS)

    Kassemi, M.; Rashidnia, N.

    1999-01-01

    In this work, we study steady and oscillatory thermocapillary and natural convective flows 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. A combined numerical-experimental approach is adopted here. The temperature field is visualized using Mach-Zehnder and/or Wollaston Prism Interferometry and the flow field is observed by a laser sheet flow visualization technique. A finite element numerical model is developed which solves the transient two-dimensional continuity, momentum, and energy equations and includes the effects of temperature-dependent surface tension and bubble surface deformation. Below the critical Marangoni number, the steady state low-g and 1-g temperature and velocity fields predicted by the finite element model are in excellent agreement with both the visualization experiments in our laboratory and recently published experimental results in the literature. Above the critical Marangoni number, the model predicts an oscillatory flow which is also closely confirmed by experiments. It is shown that the dynamics of the oscillatory flow are directly controlled by the thermal and hydrodynamic interactions brought about by combined natural and thermocapillary convection. Therefore, as numerical simulations show, there are considerable differences between the 1-g and low-g temperature and flow fields at both low and high Marangoni numbers. This has serious implications for both materials processing and fluid management in space.

  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. Air-water analogy and the study of hydraulic models

    NASA Technical Reports Server (NTRS)

    Supino, Giulio

    1953-01-01

    The author first sets forth some observations about the theory of models. Then he established certain general criteria for the construction of dynamically similar models in water and in air, through reference to the perfect fluid equations and to the ones pertaining to viscous flow. It is, in addition, pointed out that there are more cases in which the analogy is possible than is commonly supposed.

  13. 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.

  14. 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.

  15. The influence of bubble plumes on air-seawater gas transfer velocities

    NASA Astrophysics Data System (ADS)

    Asher, W. E.; Karle, L. M.; Higgins, B. J.; Farley, P. J.; Monahan, E. C.; Leifer, I. S.

    1996-05-01

    Laboratory results have demonstrated that bubble plumes are a very efficient air-water gas transfer mechanism. Because breaking waves generate bubble plumes, it could be possible to correlate the air-sea gas transport velocity kL with whitecap coverage. This correlation would then allow kL to be predicted from measurements of apparent microwave brightness temperature through the increase in sea surface microwave emissivity associated with breaking waves. In order to develop this remote-sensing-based method for predicting air-sea gas fluxes, a whitecap simulation tank was used to measure evasive and invasive kL values for air-seawater transfer of carbon dioxide, oxygen, helium, sulfur hexafluoride, and dimethyl sulfide at cleaned and surfactant-influenced water surfaces. An empirical model has been developed that can predict kL from bubble plume coverage, diffusivity, and solubility. The observed dependence of kL on molecular diffusivity and aqueous-phase solubility agrees with the predictions of modeling studies of bubble-driven air-water gas transfer. It has also been shown that soluble surfactants can decrease kL even in the presence of breaking waves.

  16. 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. PMID:26840001

  17. 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.

  18. 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

  19. Plasma in sonoluminescing bubble.

    PubMed

    An, Yu

    2006-12-22

    With the new accommodation coefficient of water vapor evaluated by molecular dynamics model, the maximum temperature of a sonoluminescing bubble calculated with the full partial differential equations easily reaches few tens of thousands degrees. Though at this temperature the gas is weakly ionized (10% or less), the gas density inside a sonoluminescing bubble at the moment of the bubble's flashing is so high that there still forms a dense plasma. The light emission of the bubble is calculated by the plasma model which is compared with that by the bremsstrahlung (electron-ion, electron-neutral atom) and recombination model. The calculation by the two models shows that for the relatively low maximum temperature (< 30,000 K) of the bubble, the pulse width is independent of the wavelength and the spectrum deviates the black body radiation type; while for the relatively high maximum temperature (approximately 60,000 K), the pulse width is dependent of the wavelength and the spectrum is an almost perfect black body radiation spectrum. The maximum temperature calculated by the gas dynamics equations is much higher than the temperature fitted by the black body radiation formula. PMID:16797657

  20. 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.

  1. BLOWING COSMIC BUBBLES

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This NASA Hubble Space Telescope image reveals an expanding shell of glowing gas surrounding a hot, massive star in our Milky Way Galaxy. This shell is being shaped by strong stellar winds of material and radiation produced by the bright star at the left, which is 10 to 20 times more massive than our Sun. These fierce winds are sculpting the surrounding material - composed of gas and dust - into the curve-shaped bubble. Astronomers have dubbed it the Bubble Nebula (NGC 7635). The nebula is 10 light-years across, more than twice the distance from Earth to the nearest star. Only part of the bubble is visible in this image. The glowing gas in the lower right-hand corner is a dense region of material that is getting blasted by radiation from the Bubble Nebula's massive star. The radiation is eating into the gas, creating finger-like features. This interaction also heats up the gas, causing it to glow. Scientists study the Bubble Nebula to understand how hot stars interact with the surrounding material. Credit: Hubble Heritage Team (AURA/STScI/NASA)

  2. 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.

  3. 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. PMID:25650274

  4. 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.

  5. 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.

  6. 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.

  7. 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. PMID:24584069

  8. 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.

  9. A dual-surfactant approach for the interfacial partitioning tracer test measurement of air-water interfacial area

    NASA Astrophysics Data System (ADS)

    El Ouni, A.; Brusseau, M. L.

    2013-12-01

    Interfacial partitioning tracer tests (IPTT) are one method available for measuring air-water interfacial area (A_ia). The method has been shown to provide uncertain measurements that are influenced by surfactant-enhanced drainage. The purpose of this work is to test a revised method that minimizes formation of interfacial-tension gradients in order to prevent surfactant-induced drainage. The method employs a dual-surfactant injection under steady unsaturated-flow conditions. Sodium dodecylbezene sulfonate (SDBS) and pentafluorobenzoic acid (PFBA) were used as the partitioning and nonreactive tracers, respectively. Sodium dodecyl sulfate (SDS) was used as the surfactant in the background solution. Three types of porous media were used for the study: a sandy soil, a well-sorted sand, and glass beads. Water saturation was monitored gravimetrically during the experiments. The results obtained with the revised method are compared to those obtained with the standard IPTT method.

  10. 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.

  11. 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.

  12. Size distributions of micro-bubbles generated by a pressurized dissolution method

    NASA Astrophysics Data System (ADS)

    Taya, C.; Maeda, Y.; Hosokawa, S.; Tomiyama, A.; Ito, Y.

    2012-03-01

    Size of micro-bubbles is widely distributed in the range of one to several hundreds micrometers and depends on generation methods, flow conditions and elapsed times after the bubble generation. Although a size distribution of micro-bubbles should be taken into account to improve accuracy in numerical simulations of flows with micro-bubbles, a variety of the size distribution makes it difficult to introduce the size distribution in the simulations. On the other hand, several models such as the Rosin-Rammler equation and the Nukiyama-Tanazawa equation have been proposed to represent the size distribution of particles or droplets. Applicability of these models to the size distribution of micro-bubbles has not been examined yet. In this study, we therefore measure size distribution of micro-bubbles generated by a pressurized dissolution method by using a phase Doppler anemometry (PDA), and investigate the applicability of the available models to the size distributions of micro-bubbles. Experimental apparatus consists of a pressurized tank in which air is dissolved in liquid under high pressure condition, a decompression nozzle in which micro-bubbles are generated due to pressure reduction, a rectangular duct and an upper tank. Experiments are conducted for several liquid volumetric fluxes in the decompression nozzle. Measurements are carried out at the downstream region of the decompression nozzle and in the upper tank. The experimental results indicate that (1) the Nukiyama-Tanasawa equation well represents the size distribution of micro-bubbles generated by the pressurized dissolution method, whereas the Rosin-Rammler equation fails in the representation, (2) the bubble size distribution of micro-bubbles can be evaluated by using the Nukiyama-Tanasawa equation without individual bubble diameters, when mean bubble diameter and skewness of the bubble distribution are given, and (3) an evaluation method of visibility based on the bubble size distribution and bubble

  13. 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.

  14. Effect of direct bubble-bubble interactions on linear-wave propagation in bubbly liquids

    NASA Astrophysics Data System (ADS)

    Fuster, D.; Conoir, J. M.; Colonius, T.

    2014-12-01

    We study the influence of bubble-bubble interactions on the propagation of linear acoustic waves in bubbly liquids. Using the full model proposed by Fuster and Colonius [J. Fluid Mech. 688, 253 (2011), 10.1017/jfm.2011.380], numerical simulations reveal that direct bubble-bubble interactions have an appreciable effect for frequencies above the natural resonance frequency of the average size bubble. Based on the new results, a modification of the classical wave propagation theory is proposed. The results obtained are in good agreement with previously reported experimental data where the classical linear theory systematically overpredicts the effective attenuation and phase velocity.

  15. 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.

  16. Drag Reduction by Bubble-Covered Surfaces Found in PDMS Microchannel through Depressurization.

    PubMed

    Gao, Yang; Li, Jiang; Shum, Ho Cheung; Chen, Haosheng

    2016-05-17

    Drag reduction was found in polydimethylsiloxane (PDMS) microchannels when the flow was pulled by depressurization at the inlet, and it was attributed to the formation of the bubbles on the PDMS surface. The formed bubbles were examined by atomic force microscopy (AFM), and the resultant effective slip length was measured by microparticle image velocimetry (μPIV). The drag reduction was found to decrease as the bubbles grew and detached from the surface, causing a pulsatile flow in the microchannel. PMID:27123905

  17. Mechanics of collapsing cavitation bubbles.

    PubMed

    van Wijngaarden, Leen

    2016-03-01

    A brief survey is given of the dynamical phenomena accompanying the collapse of cavitation bubbles. The discussion includes shock waves, microjets and the various ways in which collapsing bubbles produce damage. PMID:25890856

  18. Detailed simulations of air-water interaction phenomena in ocean waves

    NASA Astrophysics Data System (ADS)

    Iafrati, A.; Durante, D.

    2012-04-01

    In the present contribution the flow induced in air by ocean waves is investigated. The air-water interaction problem is of obvious interest in the context of wind generated waves. However, the flow induced in the lower atmosphere layer by ocean waves has also important effects on the exchange processes between atmosphere and ocean and in some circumstances it influences weather conditions on large scales. The problem is studied numerically by a two-dimensional Navier-Stokes solver which models the flow in air and water as that of a single incompressible fluid with density and viscosity expressed as a smooth function of the distance from the interface. The free surface is captured as the zero level set of the distance function. The distance from the interface is reinitialized every time step, so that the thickness of the transition region remains constant in time. The method is applied to two problems characterized by quite different length scales and steepnesses. In both cases the limits associated to the numerical approach and possible effects on the results are discussed. The first application is an attempt of investigating the role played by the flow in air on the dissipation rate of swells. The interest for such problem stems from some studies according to which the flow in air has an important effect on the dissipation of the steepest swells (Ardhuin et al, 2009). Motivated by the above findings, numerical simulations are performed in order to investigate the characteristics of the flow induced in air by swell with wavelengths in a range 50 to 300 m. Results are presented in terms of vorticity field in air with quantitative analyses of the vertical flux of horizontal momentum and of the viscous dissipation in the air phase. The thickness of the air layer which is influenced by the passage of the swell is also given. The second study analyzes the flow induced in air by the evolution of modulated wave trains. In this case the fundamental wavelength is 0.6 m

  19. 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. PMID:25698045

  20. Hadron bubble evolution into the quark sea

    SciTech Connect

    Freese, K. ); Adams, F.C. )

    1990-04-15

    A solution is presented for the evolution of hadron bubbles which nucleate in the quark sea if there is a first-order quark-hadron phase transition at a temperature {ital T}{sub {ital c}} on the order of 100 MeV. We make three assumptions: (1) the dominant mechanism for transport of latent heat is radiative, e.g., neutrinos; (2) the distance between nucleation sites is greater than the neutrino mean free path; and (3) the effects of hydrodynamic flow can be neglected. Bubbles nucleate with a characteristic radius 1 fm/{Delta}, where {Delta} is a dimensionless parameter for the undercooling (we take {Delta}{ge}10{sup {minus}4}, so that the expansion of the Universe can be neglected). We argue that bubbles grow stably and remain spherical until the radius becomes as large as the neutrino mean free path, {ital l}{congruent}10 cm. The growth then becomes diffusion limited and the bubbles become unstable to formation of dendrites, or fingerlike structures, because latent heat can diffuse away more easily from long fingers than from spheres. We study the nonlinear evolution of structure with a geometrical model'' and argue that the hadron bubbles ultimately look like stringy seaweed. The percolation of seaweed-shaped bubbles can leave behind regions of quark phase that are quite small. In fact, one might expect the typical scale to be {ital L}{sub {ital Q}}={ital l}{congruent}10 cm. Protons can easily diffuse out of such small regions (and neutrons back in). Thus, these instabilities can lead to important modifications of inhomogeneous nucleosynthesis, which requires {ital L}{sub {ital Q}}{approx gt}1 m.

  1. Hadron bubble evolution into the quark sea

    NASA Astrophysics Data System (ADS)

    Freese, Katherine; Adams, Fred C.

    1990-04-01

    A solution is presented for the evolution of hadron bubbles which nucleate in the quark sea if there is a first-order quark-hadron phase transition at a temperature Tc on the order of 100 MeV. We make three assumptions: (1) the dominant mechanism for transport of latent heat is radiative, e.g., neutrinos; (2) the distance between nucleation sites is greater than the neutrino mean free path; and (3) the effects of hydrodynamic flow can be neglected. Bubbles nucleate with a characteristic radius 1 fm/Δ, where Δ is a dimensionless parameter for the undercooling (we take Δ>=10-4, so that the expansion of the Universe can be neglected). We argue that bubbles grow stably and remain spherical until the radius becomes as large as the neutrino mean free path, l~=10 cm. The growth then becomes diffusion limited and the bubbles become unstable to formation of dendrites, or fingerlike structures, because latent heat can diffuse away more easily from long fingers than from spheres. We study the nonlinear evolution of structure with a ``geometrical model'' and argue that the hadron bubbles ultimately look like stringy seaweed. The percolation of seaweed-shaped bubbles can leave behind regions of quark phase that are quite small. In fact, one might expect the typical scale to be LQ=l~=10 cm. Protons can easily diffuse out of such small regions (and neutrons back in). Thus, these instabilities can lead to important modifications of inhomogeneous nucleosynthesis, which requires LQ>~1 m.

  2. Thermocapillary migration of a small chain of bubbles

    NASA Technical Reports Server (NTRS)

    Wei, Huailiang; Subramanian, R. S.

    1993-01-01

    The quasistatic thermocapillary migration of a chain of two or three spherical bubbles in an unbounded fluid possessing a uniform temperature gradient is investigated in the limit of vanishing Reynolds and Peclet numbers. The line of bubble centers is permitted to be either parallel or perpendicular to the direction of the undisturbed temperature gradient. The governing equations are solved by a truncated-series, boundary-collocation technique. Results are presented which demonstrate the impact of the presence of other bubbles on a test bubble. In the three-bubble case, a simple pairwise-additive approximation is constructed from the reflections solution, and found to perform well except when the bubbles are close to each other. Also, features of the flow topology in the fluid are explored. Separated reverse flow wakes are found in the axisymmetric problem, and other interesting structures are noted for the case in which the line of centers is perpendicular to the applied temperature gradient. The observed flow structure is shown to be the result of superposition of simpler basic flows.

  3. Forced convection heat transfer to air/water vapor mixtures

    NASA Technical Reports Server (NTRS)

    Richards, D. R.; Florschuetz, L. W.

    1984-01-01

    Heat transfer coefficients were measured using both dry and humid air in the same forced convection cooling scheme and were compared using appropriate nondimensional parameters (Nusselt, Prandtl and Reynolds numbers). A forced convection scheme with a complex flow field, two dimensional arrays of circular jets with crossflow, was utilized with humidity ratios (mass ratio of water vapor to air) up to 0.23. The dynamic viscosity, thermal conductivity and specific heat of air, steam and air/steam mixtures are examined. Methods for determining gaseous mixture properties from the properties of their pure components are reviewed as well as methods for determining these properties with good confidence. The need for more experimentally determined property data for humid air is discussed. It is concluded that dimensionless forms of forced convection heat transfer data and empirical correlations based on measurements with dry air may be applied to conditions involving humid air with the same confidence as for the dry air case itself, provided that the thermophysical properties of the humid air mixtures are known with the same confidence as their dry air counterparts.

  4. Interaction of Charged Colloidal Particles at the Air-Water Interface.

    PubMed

    Girotto, Matheus; Dos Santos, Alexandre P; Levin, Yan

    2016-07-01

    We study, using Monte Carlo simulations, the interaction between charged colloidal particles confined to the air-water interface. The dependence of force on ionic strength and counterion valence is explored. For 1:1 electrolyte, we find that the electrostatic interaction at the interface is very close to the one observed in the bulk. On the other hand, for salts with multivalent counterions, an interface produces an enhanced attraction between like charged colloids. Finally, we explore the effect of induced surface charge at the air-water interface on the interaction between colloidal particles. PMID:26551757

  5. Micrometeorological measurement of hexachlorobenzene and polychlorinated biphenyl compound air-water gas exchange in Lake Superior and comparison to model predictions

    NASA Astrophysics Data System (ADS)

    Rowe, M. D.; Perlinger, J. A.

    2012-01-01

    Air-water exchange fluxes of persistent, bioaccumulative and toxic (PBT) substances are frequently estimated using the Whitman two-film (W2F) method, but micrometeorological flux measurements of these compounds over water are rarely attempted. We measured air-water exchange fluxes of hexachlorobenzene (HCB) and polychlorinated biphenyls (PCBs) on 14 July 2006 in Lake Superior using the modified Bowen ratio (MBR) method. Measured fluxes were compared to estimates using the W2F method, and to estimates from an Internal Boundary Layer Transport and Exchange (IBLTE) model that implements the NOAA COARE bulk flux algorithm and gas transfer model. We reveal an inaccuracy in the estimate of water vapor transfer velocity that is commonly used with the W2F method for PBT flux estimation, and demonstrate the effect of use of an improved estimation method. Flux measurements were conducted at three stations with increasing fetch in offshore flow (15, 30, and 60 km) in southeastern Lake Superior. This sampling strategy enabled comparison of measured and predicted flux, as well as modification in near-surface atmospheric concentration with fetch, using the IBLTE model. Fluxes estimated using the W2F model were compared to fluxes measured by MBR. In five of seven cases in which the MBR flux was significantly greater than zero, concentration increased with fetch at 1-m height, which is qualitatively consistent with the measured volatilization flux. As far as we are aware, these are the first reported micrometeorological air-water exchange flux measurements of PCBs.

  6. Cohesion of Bubbles in Foam

    ERIC Educational Resources Information Center

    Ross, Sydney

    1978-01-01

    The free-energy change, or binding energy, of an idealized bubble cluster is calculated on the basis of one mole of gas, and on the basis of a single bubble going from sphere to polyhedron. Some new relations of bubble geometry are developed in the course of the calculation. (BB)

  7. A robust and accurate approach to computing compressible multiphase flow: Stratified flow model and AUSM{sup +}-up scheme

    SciTech Connect

    Chang, Chih-Hao . E-mail: chchang@engineering.ucsb.edu; Liou, Meng-Sing . E-mail: meng-sing.liou@grc.nasa.gov

    2007-07-01

    In this paper, we propose a new approach to compute compressible multifluid equations. Firstly, a single-pressure compressible multifluid model based on the stratified flow model is proposed. The stratified flow model, which defines different fluids in separated regions, is shown to be amenable to the finite volume method. We can apply the conservation law to each subregion and obtain a set of balance equations. Secondly, the AUSM{sup +} scheme, which is originally designed for the compressible gas flow, is extended to solve compressible liquid flows. By introducing additional dissipation terms into the numerical flux, the new scheme, called AUSM{sup +}-up, can be applied to both liquid and gas flows. Thirdly, the contribution to the numerical flux due to interactions between different phases is taken into account and solved by the exact Riemann solver. We will show that the proposed approach yields an accurate and robust method for computing compressible multiphase flows involving discontinuities, such as shock waves and fluid interfaces. Several one-dimensional test problems are used to demonstrate the capability of our method, including the Ransom's water faucet problem and the air-water shock tube problem. Finally, several two dimensional problems will show the capability to capture enormous details and complicated wave patterns in flows having large disparities in the fluid density and velocities, such as interactions between water shock wave and air bubble, between air shock wave and water column(s), and underwater explosion.

  8. Onset of particle trapping and release via acoustic bubbles.

    PubMed

    Chen, Yun; Fang, Zecong; Merritt, Brett; Strack, Dillon; Xu, Jie; Lee, Sungyon

    2016-08-01

    Trapping and sorting of micro-sized objects is one important application of lab on a chip devices, with the use of acoustic bubbles emerging as an effective, non-contact method. Acoustically actuated bubbles are known to exert a secondary radiation force (FSR) on micro-particles and stabilize them on the bubble surface, when this radiation force exceeds the external hydrodynamic forces that act to keep the particles in motion. While the theoretical expression of FSR has been derived by Nyborg decades ago, no direct experimental validation of this force has been performed, and the relationship between FSR and the bubble's ability to trap particles in a given lab on a chip device remains largely empirical. In order to quantify the connection between the bubble oscillation and the resultant FSR, we experimentally measure the amplitude of bubble oscillations that give rise to FSR and observe the trapping and release of a single microsphere in the presence of the mean flow at the corresponding acoustic parameters using an acoustofluidic device. By combining well-developed theories that connect bubble oscillations to the acoustic actuation, we derive the expression for the critical input voltage that leads to particle release into the flow, in good agreement with the experiments. PMID:26805706

  9. Effect of flow rate and CO 2 content on the phase and morphology of CaCO 3 prepared by bubbling method

    NASA Astrophysics Data System (ADS)

    Han, Yong Sheng; Hadiko, Gunawan; Fuji, Masayoshi; Takahashi, Minoru

    2005-04-01

    Calcium carbonate particle attracts more and more attention because of its wide application in papermaking, rubbers, plastics and paints. In this paper, the CaCO 3 particles were prepared by passing the mixed gas (CO 2/N 2) into CaCl 2 solution. The effect of flow rate and CO 2 content on the phase and morphology of precipitated CaCO 3 was investigated with the help of SEM and XRD measurements. Both the results of SEM and XRD showed that more vaterite was formed at a high flow rate or high CO 2 content, which was attributed to the slowing down of the transformation of vaterite to calcite. The change of pH and reaction time with the flow rate was also studied and the dissolution of carbon dioxide was analyzed.

  10. Double Bubble? No Trouble!

    ERIC Educational Resources Information Center

    Shaw, Mike I.; Smith, Greg F.

    1995-01-01

    Describes a soap-solution activity involving formation of bubbles encasing the students that requires only readily available materials and can be adapted easily for use with various grade levels. Discusses student learning outcomes including qualitative and quantitative observations and the concept of surface tension. (JRH)

  11. Oscillations of soap bubbles

    NASA Astrophysics Data System (ADS)

    Kornek, U.; Müller, F.; Harth, K.; Hahn, A.; Ganesan, S.; Tobiska, L.; Stannarius, R.

    2010-07-01

    Oscillations of droplets or bubbles of a confined fluid in a fluid environment are found in various situations in everyday life, in technological processing and in natural phenomena on different length scales. Air bubbles in liquids or liquid droplets in air are well-known examples. Soap bubbles represent a particularly simple, beautiful and attractive system to study the dynamics of a closed gas volume embedded in the same or a different gas. Their dynamics is governed by the densities and viscosities of the gases and by the film tension. Dynamic equations describing their oscillations under simplifying assumptions have been well known since the beginning of the 20th century. Both analytical description and numerical modeling have made considerable progress since then, but quantitative experiments have been lacking so far. On the other hand, a soap bubble represents an easily manageable paradigm for the study of oscillations of fluid spheres. We use a technique to create axisymmetric initial non-equilibrium states, and we observe damped oscillations into equilibrium by means of a fast video camera. Symmetries of the oscillations, frequencies and damping rates of the eigenmodes as well as the coupling of modes are analyzed. They are compared to analytical models from the literature and to numerical calculations from the literature and this work.

  12. The Bubble N10

    NASA Astrophysics Data System (ADS)

    Gama, D.; Lepine, J.; Wu, Y.; Yuan, J.

    2014-10-01

    We studied the environment surrounding the infrared bubble N10 in molecular and infrared emission. There is an HII region at the center of this bubble. We investigated J=1-0 transitions of molecules ^{12}CO, ^{13}CO and C^{18}O towards N10. This object was detected by GLIMPSE, a survey carried out between 3.6 and 8.0 μ m. We also analyzed the emission at 24 μ m, corresponding to the emission of hot dust, with a contribution of small grains heated by nearby O stars. Besides, the contribution at 8 μ m is dominated by PAHs (polycyclic aromatic hydrocarbons) excited by radiation from the PDRs of bubbles. In the case of N10, it is proposed that the excess at 4.5 μ m IRAC band indicate an outflow, a signature of early stages of massive star formation. This object was the target of observations at the PMO 13.7 m radio telescope. The bubble N10 presents clumps, from which we can derive physical features through the observed parameters. We also intended to discuss the evolutionary stage of the clumps and their distribution. It can lead us to understand the triggered star formation scenario in this region.

  13. The Liberal Arts Bubble

    ERIC Educational Resources Information Center

    Agresto, John

    2011-01-01

    The author expresses his doubt that the general higher education bubble will burst anytime soon. Although tuition, student housing, and book costs have all increased substantially, he believes it is still likely that the federal government will continue to pour billions into higher education, largely because Americans have been persuaded that it…

  14. Bubbly Little Star

    NASA Technical Reports Server (NTRS)

    2007-01-01

    In this processed Spitzer Space Telescope image, baby star HH 46/47 can be seen blowing two massive 'bubbles.' The star is 1,140 light-years away from Earth.

    The infant star can be seen as a white spot toward the center of the Spitzer image. The two bubbles are shown as hollow elliptical shells of bluish-green material extending from the star. Wisps of green in the image reveal warm molecular hydrogen gas, while the bluish tints are formed by starlight scattered by surrounding dust.

    These bubbles formed when powerful jets of gas, traveling at 200 to 300 kilometers per second, or about 120 to 190 miles per second, smashed into the cosmic cloud of gas and dust that surrounds HH 46/47. The red specks at the end of each bubble show the presence of hot sulfur and iron gas where the star's narrow jets are currently crashing head-on into the cosmic cloud's gas and dust material.

    Whenever astronomers observe a star, or snap a stellar portrait, through the lens of any telescope, they know that what they are seeing is slightly blurred. To clear up the blurring in Spitzer images, astronomers at the Jet Propulsion Laboratory developed an image processing technique for Spitzer called Hi-Res deconvolution.

    This process reduces blurring and makes the image sharper and cleaner, enabling astronomers to see the emissions around forming stars in greater detail. When scientists applied this image processing technique to the Spitzer image of HH 46/47, they were able to see winds from the star and jets of gas that are carving the celestial bubbles.

    This infrared image is a three-color composite, with data at 3.6 microns represented in blue, 4.5 and 5.8 microns shown in green, and 24 microns represented as red.

  15. Bubble Formation at a Submerged Orifice for Aluminum Foams Produced by Gas Injection Method

    NASA Astrophysics Data System (ADS)

    Fan, Xueliu; Chen, Xiang; Liu, Xingnan; Zhang, Huiming; Li, Yanxiang

    2013-02-01

    The bubble formation at a submerged orifice in the process of aluminum foams produced by gas injection method is investigated. The experimental results show that the increase of the gas flow rate and the orifice diameter can lead to increasing of the bubble size. The large orifice can make the frequency of bubble formation decrease by slowing down the increase of the gas chamber pressure when the gas flow rate increases. The effect of the gas chamber volume on the bubble size can be ignored in the experiment when it expands from 1 to 125 cm3. A theoretical model of bubble formation, expansion, and detachment under constant flow conditions is established to predict the bubble size. The theoretical predictions for air-aluminum melt systems are consistent with the experimental results.

  16. Flow regimes of adiabatic gas-liquid two-phase under rolling conditions

    NASA Astrophysics Data System (ADS)

    Yan, Chaoxing; Yan, Changqi; Sun, Licheng; Xing, Dianchuan; Wang, Yang; Tian, Daogui

    2013-07-01

    Characteristics of adiabatic air/water two-phase flow regimes under vertical and rolling motion conditions were investigated experimentally. Test sections are two rectangular ducts with the gaps of 1.41 and 10 mm, respectively, and a circular tube with 25 mm diameter. Flow regimes were recorded by a high speed CCD-camera and were identified by examining the video images. The experimental results indicate that the characteristics of flow patterns in 10 mm wide rectangular duct under vertical condition are very similar to those in circular tube, but different from the 1.41 mm wide rectangular duct. Channel size has a significant influence on flow pattern transition, boundary of which in rectangular channels tends asymptotically towards that in the circular tube with increasing the width of narrow side. Flow patterns in rolling channels are similar to each other, nevertheless, the effect of rolling motion on flow pattern transition are significantly various. Due to the remarkable influences of the friction shear stress and surface tension in the narrow gap duct, detailed flow pattern maps of which under vertical and rolling conditions are indistinguishable. While for the circular tube with 25 mm diameter, the transition from bubbly to slug flow occurs at a higher superficial liquid velocity and the churn flow covers more area on the flow regime map as the rolling period decreases.

  17. It's Alive!: Students Observe Air-Water Interface Samples Rich with Organisms

    ERIC Educational Resources Information Center

    Avant, Thomas

    2002-01-01

    This article describes an experiment, designed by Cindy Henk, manager of the Socolofsky Microscopy Center at Louisiana State University (LSU), that involved collecting and viewing microorganisms in the air-water interface. The experiment was participated by Leesville High School microbiology students. The students found that the air-water…

  18. Understanding the structure of hydrophobic surfactants at the air/water interface from molecular level.

    PubMed

    Zhang, Li; Liu, Zhipei; Ren, Tao; Wu, Pan; Shen, Jia-Wei; Zhang, Wei; Wang, Xinping

    2014-11-25

    Understanding the behavior of fluorocarbon surfactants at the air/water interface is crucial for many applications, such as lubricants, paints, cosmetics, and fire-fighting foams. In this study, molecular dynamics (MD) simulations were employed to investigate the microscopic properties of non-ionic fluorocarbon surfactants at the air/water interface. Several properties, including the distribution of head groups, the distribution probability of the tilt angle between hydrophobic tails with respect to the xy plane, and the order parameter of surfactants, were computed to probe the structure of hydrophobic surfactants at the air/water interface. The effects of the monomer structure on interfacial phenomena of non-ionic surfactants were investigated as well. It is observed that the structure of fluorocarbon surfactants at the air/water interface is more ordered than that of hydrocarbons, which is dominated by the van der Waals interaction between surfactants and water molecules. However, replacing one or two CF2 with one or two CH2 group does not significantly influence the interfacial structure, suggesting that hydrocarbons may be promising alternatives to perfluorinated surfactants. PMID:25358083

  19. THE EFFECT OF SALINITY ON RATES OF ELEMENTAL MERCURY AIR/WATER EXCHANGE

    EPA Science Inventory

    The U.S. EPA laboratory in Athens, Georgia i spursuing the goal of developing a model for describing toxicant vapor phase air/water exchange under all relevant environmental conditions. To date, the two-layer exchange model (suitable for low wind speed conditions) has been modif...

  20. The behavior of NaOH at the air-water interface, a computational study

    SciTech Connect

    Wick, Collin D.; Dang, Liem X.

    2010-07-14

    Molecular dynamics simulations with a polarizable multi-state empirical valence bond model were carried out to investigate NaOH dissociation and pairing in water bulk and at the air-water interface. It was found that NaOH readily dissociates in the bulk, and the effect of the air-water interface on NaOH dissociation is fairly minor. Also, NaOH complexes were found to be strongly repelled from the air-water interface, which is consistent with surface tension measurements. At the same time, a very strong preference for the hydroxide anion to be oriented towards the air was found that persisted a few angstroms towards the liquid from the Gibbs dividing surface of the air-water interface. This was due to a preference for the hydroxide anion to have its hydrogen pointing towards the air, and the fact that the sodium ion was more likely to be found near the hydroxide oxygen than hydrogen. As a consequence, the simulation results show that surfaces of NaOH solutions should be negatively charged, in agreement with experimental observations, but also that the hydroxide has little surface affinity. This provides the possibility that the surface of water can be devoid of hydroxide anions, but still have a strong negative charge. This work was supported by the US Department of Energy Basic Energy Sciences' Chemical Sciences, Geosciences & Biosciences Division. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  1. Hydrodynamics of a self-propelled camphor boat at the air-water interface

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    A camphor tablet, when placed at the air-water interface undergoes sublimation and camphor vapour spreads radially outwards across the surface due to Marangoni forces. This steady camphor influx from tablet onto the air-water interface is balanced by the camphor outflux due to evaporation. When spontaneous fluctuations in evaporation break the axial symmetry of Marangoni force acting radially outwards, the camphor tablet is propelled like a boat along the water surface. We report experiments on the hydrodynamics of a self-propelled camphor boat at air-water interfaces. We observe three different modes of motion, namely continuous, harmonic and periodic, due to the volatile nature of camphor. We explain these modes in terms of ratio of two time-scales: the time-scale over which viscous forces are dominant over the Marangoni forces (τη) and the time-scale over which Marangoni forces are dominant over the viscous forces (τσ). The continuous, harmonic and periodic motions are observed when τη /τσ ~ 1 , τη /τσ >= 1 and τη /τσ >> 1 respectively. Experimentally, the ratio of the time scales is varied by changing the interfacial tension of the air-water interface using Sodium Dodecyl Sulfate. This work was supported by the Collective Interactions Unit, OIST Graduate University.

  2. Two-dimensional Rayleigh model of vapor bubble evolution

    SciTech Connect

    Amendt, P; Friedman, M; Glinsky, M; Gurewitz, E; London, R A; Strauss, M

    1999-01-14

    The understanding of vapor bubble generation in an aqueous tissue near a fiber tip has required advanced two dimensional (2D) hydrodynamic simulations. For 1D spherical bubble expansion a simplified and useful Rayleigh-type model can be applied. For 2D bubble evolution, such a model does not exist. The present work proposes a Rayleigh-type model for 2D bubble expansion that is faster and simpler than the 2D hydrodynamic simulations. The model is based on a flow potential representation of the hydrodynamic motion controlled by a Laplace equation and a moving boundary condition. We show that the 1D Rayleigh equation is a specific case of our model. The Laplace equation is solved for each time step by a finite element solver using a triangulation of the outside bubble region by a fast unstructured mesh generator. Two problems of vapor bubbles generated by short-pulse lasers near a fiber tip-are considered: (a) the outside region has no boundaries except the fiber, (b) the fiber and the bubble are confined in a long channel, which simulates a fiber in a vessel wall. Our simulations for problems of type (a) include features of bubble evolution as seen in experiments, including a collapse away from the fiber tip. A different behavior was obtained for problems of type (b) when the channel boundary is close to the fiber. In this case the bubble's expansion and collapse are both extremely slow in the direction normal to this boundary and distortion of the bubble is observed.

  3. Measurements of liquid-phase turbulence in gas-liquid two-phase flows using particle image velocimetry

    NASA Astrophysics Data System (ADS)

    Zhou, Xinquan; Doup, Benjamin; Sun, Xiaodong

    2013-12-01

    Liquid-phase turbulence measurements were performed in an air-water two-phase flow loop with a circular test section of 50 mm inner diameter using a particle image velocimetry (PIV) system. An optical phase separation method--planar laser-induced fluorescence (PLIF) technique—which uses fluorescent particles and an optical filtration technique, was employed to separate the signals of the fluorescent seeding particles from those due to bubbles and other noises. An image pre-processing scheme was applied to the raw PIV images to remove the noise residuals that are not removed by the PLIF technique. In addition, four-sensor conductivity probes were adopted to measure the radial distribution of the void fraction. Two benchmark tests were performed: the first was a comparison of the PIV measurement results with those of similar flow conditions using thermal anemometry from previous studies; the second quantitatively compared the superficial liquid velocities calculated from the local liquid velocity and void fraction measurements with the global liquid flow rate measurements. The differences of the superficial liquid velocity obtained from the two measurements were bounded within ±7% for single-phase flows and two-phase bubbly flows with the area-average void fraction up to 18%. Furthermore, a preliminary uncertainty analysis was conducted to investigate the accuracy of the two-phase PIV measurements. The systematic uncertainties due to the circular pipe curvature effects, bubble surface reflection effects and other potential uncertainty sources of the PIV measurements were discussed. The purpose of this work is to facilitate the development of a measurement technique (PIV-PLIF) combined with image pre-processing for the liquid-phase turbulence in gas-liquid two-phase flows of relatively high void fractions. The high-resolution data set can be used to more thoroughly understand two-phase flow behavior, develop liquid-phase turbulence models, and assess high

  4. Bubble-Turbulence Interaction in Binary Fluids

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    Multiphase flows represent a central issue in many natural, biological and industrial fields. For instance, liquid jets vaporization, petroleum refining and boiling, emulsions in pharmaceutical applications, are all characterized by a disperse phase, such as solid particles or liquid bubbles, which evolve in a Newtonian carrier fluid. Features such as the global evaporation rates of liquid fuels in air or the homogeneity of the emulsions are controlled by the finest interaction details occurring between the two phases. In this paper we study the rising motion of a bubble induced by buoyancy in a viscous fluid. Usually this issue is tackled by tracking the bubble interface by means of sharp interface methods. However this approach requires "ad hoc" techniques to describe changes in the topological features of the deforming interface and to enforce the mass preservation. Here the problem is addressed by using a different philosophy based on a diffuse interface method, that allows a straightforward analysis of complex phenomena such as bubbles coalescence and break up without any numerical expedient. The model we adopt, funded on a solid thermodynamical and physical base, relies on the Cahn-Hilliard equation for the disperse phase, see Cahn & Hilliard (1958) and Elliott & Songmu (1986).

  5. Bubbles and droplets in magnetic fluids

    NASA Astrophysics Data System (ADS)

    Yecko, Philip

    2006-11-01

    In this work, the behavior of ferrofluid droplets and of bubbles rising in a ferrofluid is studied using direct numerical simulations based on a volume of fluid (VOF) method. A ferrofluid is a suspension of small (5--15 nm) magnetic particles in a carrier liquid which may be water or a hydrocarbon oil, stabilized against settling by Brownian motion and against agglomeration by coating each particle with a layer of surfactant. Although their main application is the fluid O-ring found in computer hard disk drives, ferrofluids have been more recently recognized for their use in micro- and nano-fluidic pumping, and applications to drug delivery are under investigation. Because ferrofluids are opaque, numerical simulations offer a unique opportunity to visualize flows that cannot be easily visualized experimentally, yet little effort has been directed to numerical simulations of realistic magnetic fluids. In this work, we develop and test a multiphase simulation code, based on Surfer, which can dynamically follow the behavior of small numbers of droplets, bubbles or layers of ferrofluid and ordinary viscous fluid for so-called linear magnetic material. In the rising bubble tests, we quantify the vertical elongation of the bubble and the resulting reduction in drag and rise time. In the falling droplet experiments, we demonstrate the effect of variable magnetic properties on the shape and trajectory of the droplet, including the instability threshold where droplet fission occurs.

  6. Analysis of transitional separation bubbles on infinite swept wings

    NASA Technical Reports Server (NTRS)

    Davis, R. L.; Carter, J. E.

    1986-01-01

    A previously developed two-dimensional local inviscid-viscous interaction technique for the analysis of airfoil transitional separation bubbles, ALESEP (Airfoil Leading Edge Separation), has been extended for the calculation of transitional separation bubbles over infinite swept wings. As part of this effort, Roberts' empirical correlation, which is interpreted as a separated flow empirical extension of Mack's stability theory for attached flows, has been incorporated into the ALESEP procedure for the prediction of the transition location within the separation bubble. In addition, the viscous procedure used in the ALESEP techniques has been modified to allow for wall suction. A series of two-dimensional calculations is presented as a verification of the prediction capability of the interaction techniques with the Roberts' transition model. Numerical tests have shown that this two-dimensional natural transition correlation may also be applied to transitional separation bubbles over infinite swept wings. Results of the interaction procedure are compared with Horton's detailed experimental data for separated flow over a swept plate which demonstrates the accuracy of the present technique. Wall suction has been applied to a similar interaction calculation to demonstrate its effect on the separation bubble. The principal conclusion of this paper is that the prediction of transitional separation bubbles over two-dimensional or infinite swept geometries is now possible using the present interacting boundary layer approach.

  7. Rigorous buoyancy driven bubble mixing for centrifugal microfluidics.

    PubMed

    Burger, S; Schulz, M; von Stetten, F; Zengerle, R; Paust, N

    2016-01-21

    We present batch-mode mixing for centrifugal microfluidics operated at fixed rotational frequency. Gas is generated by the disk integrated decomposition of hydrogen peroxide (H2O2) to liquid water (H2O) and gaseous oxygen (O2) and inserted into a mixing chamber. There, bubbles are formed that ascent through the liquid in the artificial gravity field and lead to drag flow. Additionaly, strong buoyancy causes deformation and rupture of the gas bubbles and induces strong mixing flows in the liquids. Buoyancy driven bubble mixing is quantitatively compared to shake mode mixing, mixing by reciprocation and vortex mixing. To determine mixing efficiencies in a meaningful way, the different mixers are employed for mixing of a lysis reagent and human whole blood. Subsequently, DNA is extracted from the lysate and the amount of DNA recovered is taken as a measure for mixing efficiency. Relative to standard vortex mixing, DNA extraction based on buoyancy driven bubble mixing resulted in yields of 92 ± 8% (100 s mixing time) and 100 ± 8% (600 s) at 130g centrifugal acceleration. Shake mode mixing yields 96 ± 11% and is thus equal to buoyancy driven bubble mixing. An advantage of buoyancy driven bubble mixing is that it can be operated at fixed rotational frequency, however. The additional costs of implementing buoyancy driven bubble mixing are low since both the activation liquid and the catalyst are very low cost and no external means are required in the processing device. Furthermore, buoyancy driven bubble mixing can easily be integrated in a monolithic manner and is compatible to scalable manufacturing technologies such as injection moulding or thermoforming. We consider buoyancy driven bubble mixing an excellent alternative to shake mode mixing, in particular if the processing device is not capable of providing fast changes of rotational frequency or if the low average rotational frequency is challenging for the other integrated fluidic operations. PMID:26607320

  8. Micro bubble formation and bubble dissolution in domestic wet central heating systems

    NASA Astrophysics Data System (ADS)

    Fsadni, Andrew M.; Ge, Yunting

    2012-04-01

    16 % of the carbon dioxide emissions in the UK are known to originate from wet domestic central heating systems. Contemporary systems make use of very efficient boilers known as condensing boilers that could result in efficiencies in the 90-100% range. However, research and development into the phenomenon of micro bubbles in such systems has been practically non-existent. In fact, such systems normally incorporate a passive deaerator that is installed as a `default' feature with no real knowledge as to the micro bubble characteristics and their effect on such systems. High saturation ratios are known to occur due to the widespread use of untreated tap water in such systems and due to the inevitable leakage of air into the closed loop circulation system during the daily thermal cycling. The high temperatures at the boiler wall result in super saturation conditions which consequently lead to micro bubble nucleation and detachment, leading to bubbly two phase flow. Experiments have been done on a test rig incorporating a typical 19 kW domestic gas fired boiler to determine the expected saturation ratios and bubble production and dissolution rates in such systems.

  9. Liquid-Gas Relative Permeabilities in Fractures: Effects of Flow Structures, Phase Transformation and Surface Roughness

    SciTech Connect

    Chih-Ying Chen

    2005-06-30

    Two-phase flow through fractured media is important in petroleum, geothermal, and environmental applications. However, the actual physics and phenomena that occur inside fractures are poorly understood, and oversimplified relative permeability curves are commonly used in fractured reservoir simulations. In this work, an experimental apparatus equipped with a high-speed data acquisition system, real-time visualization, and automated image processing technology was constructed to study three transparent analog fractures with distinct surface roughnesses: smooth, homogeneously rough, and randomly rough. Air-water relative permeability measurements obtained in this study were compared with models suggested by earlier studies and analyzed by examining the flow structures. A method to evaluate the tortuosities induced by the blocking phase, namely the channel tortuosity, was proposed from observations of the flow structure images. The relationship between the coefficients of channel tortuosity and the relative permeabilities was studied with the aid of laboratory experiments and visualizations. Experimental data from these fractures were used to develop a broad approach for modeling two-phase flow behavior based on the flow structures. Finally, a general model deduced from these data was proposed to describe two-phase relative permeabilities in both smooth and rough fractures. For the theoretical analysis of liquid-vapor relative permeabilities, accounting for phase transformations, the inviscid bubble train models coupled with relative permeability concepts were developed. The phase transformation effects were evaluated by accounting for the molecular transport through liquid-vapor interfaces. For the steam water relative permeabilities, we conducted steam-water flow experiments in the same fractures as used for air-water experiments. We compared the flow behavior and relative permeability differences between two-phase flow with and without phase transformation effects

  10. CONTINUOUSLY SENSITIVE BUBBLE CHAMBER

    DOEpatents

    Good, R.H.

    1959-08-18

    A radiation detector of the bubble chamber class is described which is continuously sensitive and which does not require the complex pressure cycling equipment characteristic of prior forms of the chamber. The radiation sensitive element is a gas-saturated liquid and means are provided for establishing a thermal gradient across a region of the liquid. The gradient has a temperature range including both the saturation temperature of the liquid and more elevated temperatures. Thus a supersaturated zone is created in which ionizing radiations may give rise to visible gas bubbles indicative of the passage of the radiation through the liquid. Additional means are provided for replenishing the supply of gas-saturated liquid to maintaincontinuous sensitivity.

  11. Classification of gas-liquid flow patterns by the norm entropy of wavelet decomposed pressure fluctuations across a bluff body

    NASA Astrophysics Data System (ADS)

    Sun, Zhiqiang; Chen, Yanping; Gong, Hui

    2012-12-01

    Identification of gas-liquid flow patterns remains one of the paramount needs in multiphase flow metering. It is hardly possible to realize accurate measurement and control of parameters in a gas-liquid flow system without a clear understanding of its flow pattern. Here we explore the characterization of gas-liquid flow patterns using the norm entropy extracted from the wavelet decomposed pressure fluctuations across a bluff body. Experiments on air-water two-phase flow at ambient temperature and atmospheric pressure are carried out in the bubble, plug, slug and annular flow patterns. On the basis of the experimental results, two original flow-pattern maps are constructed: one is coordinated with the average norm entropy versus the total mass flow rate, and the other is the average norm entropy versus the volumetric void fraction. Verification tests demonstrate that the overall identification rates of the flow-pattern maps developed exceed 95%. This approach provides an effective and simple solution to the classification of gas-liquid flow patterns.

  12. Magnetic bubble domain memories

    NASA Technical Reports Server (NTRS)

    Ypma, J. E.

    1974-01-01

    Some attractive features of Bubble Domain Memory and its relation to existing technologies are discussed. Two promising applications are block access mass memory and tape recorder replacement. The required chip capabilities for these uses are listed, and the specifications for a block access mass memory designed to fit between core and HPT disk are presented. A feasibility model for a tape recorder replacement is introduced.

  13. Slurry bubble column hydrodynamics

    NASA Astrophysics Data System (ADS)

    Rados, Novica

    Slurry bubble column reactors are presently used for a wide range of reactions in both chemical and biochemical industry. The successful design and scale up of slurry bubble column reactors require a complete understanding of multiphase fluid dynamics, i.e. phase mixing, heat and mass transport characteristics. The primary objective of this thesis is to improve presently limited understanding of the gas-liquid-solid slurry bubble column hydrodynamics. The effect of superficial gas velocity (8 to 45 cm/s), pressure (0.1 to 1.0 MPa) and solids loading (20 and 35 wt.%) on the time-averaged solids velocity and turbulent parameter profiles has been studied using Computer Automated Radioactive Particle Tracking (CARPT). To accomplish this, CARPT technique has been significantly improved for the measurements in highly attenuating systems, such as high pressure, high solids loading stainless steel slurry bubble column. At a similar set of operational conditions time-averaged gas and solids holdup profiles have been evaluated using the developed Computed Tomography (CT)/Overall gas holdup procedure. This procedure is based on the combination of the CT scans and the overall gas holdup measurements. The procedure assumes constant solids loading in the radial direction and axially invariant cross-sectionally averaged gas holdup. The obtained experimental holdup, velocity and turbulent parameters data are correlated and compared with the existing low superficial gas velocities and atmospheric pressure CARPT/CT gas-liquid and gas-liquid-solid slurry data. The obtained solids axial velocity radial profiles are compared with the predictions of the one dimensional (1-D) liquid/slurry recirculation phenomenological model. The obtained solids loading axial profiles are compared with the predictions of the Sedimentation and Dispersion Model (SDM). The overall gas holdup values, gas holdup radial profiles, solids loading axial profiles, solids axial velocity radial profiles and solids