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NUMERICAL SIMULATION OF VORTEX BREAKDOWN

Description: Vortex breakdown is simulated by a three dimensional Lagrangian method using vortex filaments. The filaments are approximated by vortex elements and their velocity is computed by a Biot-Savart type law of interaction. The numerical calculations show the development of an axisymmetric bubble with a recirculation zone and resemble in many respects the results obtained in the physical experiments on vortex breakdown.
Date: October 1, 1978
Creator: Prete, Vincenza Del
Partner: UNT Libraries Government Documents Department

Implications for the Cryogenic Fielding of Leaking Beryllium Capsules

Description: In this paper we show that the ambient temperature measured leakage time constant, {tau}{sub RT}, is related to the leakage at cryogenic temperature, R{sub C}, by R{sub C}= 0.23{rho}{sub DT}V{sub sh}/ {tau}{sub RT} where {rho}{sub DT} is the density of cryogenic DT vapor, and V{sub sh} is the internal volume of the shell. We then calculate the size of voids that may result from leakage at the Be/DT interface, depending upon the number of leakage sites and {tau}{sub RT}. Even for the slowest leakers the potential void growth is excessive. Reasons that voids have not been seen in DT layering experiments to date include the lack of a technique to see isolated micronish bubbles, however possible mechanisms preventing void formation are also discussed.
Date: February 20, 2007
Creator: Cook, R
Partner: UNT Libraries Government Documents Department

Mechanisms of gas precipitation in plasma-exposed tungsten

Description: Precipitation in subsurface bubbles is a key process that governs how hydrogen isotopes migrate through and become trapped within plasma-exposed tungsten. We describe a continuum-scale model of hydrogen diffusion in plasma-exposed materials that includes the effects of precipitation. The model can account for bubble expansion via dislocation loop punching, using an accurate equation of state to determine the internal pressure. This information is used to predict amount of hydrogen trapped by bubbles, as well as the conditions where the bubbles become saturated. In an effort to validate the underlying assumptions, we compare our results with published positron annihilation and thermal desorption spectroscopy data, as well as our own measurements using the tritium plasma experiment (TPE).
Date: May 1, 2012
Creator: Kolasinski, R. D.; Cowgill, D. F.; Donovan, D. C. & Shimada, M.
Partner: UNT Libraries Government Documents Department

{open_quotes}Bubble fusion{close_quotes}: Preliminary estimates of spherical micro-implosions in cavitating liquids

Description: Liquids irradiated with intense ultrasonic waves can generate small cavities or bubbles. Upon nonlinear expansion to a state of disequilibrium, wherein the externally imposed hydrostatic pressure far exceeds that of entrapped non-condensable gas, these bubbles undergo a rapid and violent collapse. This collapse, if symmetric, can generate high pressures and temperatures through a number of possible mechanisms. The simplest and oldest explanation suggests a focusing of the kinetic energy of all the surrounding liquid onto the collapsing bubble and the subsequent heating of entrapped gases under either adiabatic or isothermal conditions. Although induced by externally imposed millisecond pressure oscillations, these collapses can occur on sub-microsecond timescales and are accompanied by picosecond light emissions; this combination of sound and light is called sonoluminescence. Recent explanations of observed high temperatures and picosecond radiation pulses accompanying such collapses are based on the interaction of multiple shock waves that are launched off the inward cavity wall. Other potential explanations invoke dipole emissions induced by intermolecular collisions or the release of Casimir energy when a dielectric hole is filled. Conjectures have been made that the processes responsible for sonoluminescence may be extended to generated conditions where thermonuclear fusion might occur. Such an achievement would extend scientific interest in sonoluminescence out of a purely chemical context to include the study of matter subjected to more extreme conditions. The main goal of this {open_quotes}scoping{close_quotes} study is to understand better conditions where deuterium-tritium fusion might be observed in conjunction with micro-implosions in cavitating liquids; prognoses of fusion application at this point are unintended.
Date: February 1, 1995
Creator: Krakowski, R.A.
Partner: UNT Libraries Government Documents Department

Coal Cleaning by Gas Agglomeration

Description: The gas agglomeration method of coal cleaning was demonstrated with laboratory scale mixing equipment which made it possible to generate microscopic gas bubbles in aqueous suspensions of coal particles. A small amount of i-octane was introduced to enhance the hydrophobicity of the coal. Between 1.0 and 2.5 v/w% i-octane was sufficient based on coal weight. Coal agglomerates or aggregates were produced which were bound together by small gas bubbles.
Date: March 1, 1998
Creator: Shen, Meiyu; Abbott, Royce & Wheelock, T. D.
Partner: UNT Libraries Government Documents Department

Cap Bubble Drift Velocity in a Confined Test Section

Description: In the two-group interfacial area transport equation, bubbles are categorized into two groups, i.e., spherical/distorted bubbles as group 1 and cap/slug/churn-turbulent bubbles as group 2. The bubble rise velocities for both groups of bubbles may be estimated by the drift flux model by applying different distribution parameters and drift velocities for both groups. However, the drift velocity for group 2 bubbles is not always applicable (when the wall effect becomes important) as in the current test loop of interest where the flow channel is confined by two parallel flat walls, with a dimension of 200-mm in width and 10-mm in gap. The previous experiments indicated that no stable slug flow existed in this test section, which was designed to permit visualization of the flow patterns and bubble characteristics without the distortion associated with curved surfaces. In fact, distorted cap bubbly and churn-turbulent flow was observed. Therefore, it is essential to developed a correlation for cap bubble drift velocity in this confined flow channel. Since the rise velocity of a cap bubble depends on its size, a high-speed movie camera is used to capture images of cap bubbles to obtain the bubble size information. Meanwhile, the rise velocity of cap and elongated bubbles (called cap bubbles hereafter) is investigated by examining the captured images frame by frame. As a result, the conventional correlation of drift velocity for slug bubbles is modified and acceptable agreements between the measurements and correlation estimation are achieved.
Date: October 9, 2002
Creator: Sun, Xiaodong; Kim, Seungjin; Ishii, Mamoru; Lincoln, Frank W. & Beus, Stephen G.
Partner: UNT Libraries Government Documents Department

INERTIAL PRESSURE AND VOID FORMATION: GENERAL CONSIDERATIONS

Description: A wave equation for the pressure in a mixture of water and gas bubbles (such as found in the KEWB Reactor) is derived. The driving force may be either the production of additional bubbles or the growth of existent bubbles. Several illustrative solutions to the wave equation are found. (W.L.H.)
Date: May 25, 1960
Creator: Warner, C.
Partner: UNT Libraries Government Documents Department

GAS DIFFUSION INTO A BUBBLE OF FIXED RADIUS

Description: The problem of radiolytic gas diffusion into a bubble of fixed radius is solved. A constant source of radiolytic gas is assumed. The concentration of gas at the bubble surface is related to the pressure within the bubble by Henry's constant. (W. L.H.)
Date: July 15, 1960
Creator: Warner, C. III
Partner: UNT Libraries Government Documents Department

M-theory through the looking glass: Tachyon condensation in the E8 heterotic string

Description: We study the spacetime decay to nothing in string theory and M-theory. First we recall a nonsupersymmetric version of heterotic M-theory, in which bubbles of nothing -- connecting the two E_8 boundaries by a throat -- are expected to be nucleated. We argue that the fate of this system should be addressed at weak string coupling, where the nonperturbative instanton instability is expected to turn into a perturbative tachyonic one. We identify the unique string theory that could describe this process: The heterotic model with one E_8 gauge group and a singlet tachyon. We then use worldsheet methods to study the tachyon condensation in the NSR formulation of this model, and show that it induces a worldsheet super-Higgs effect. The main theme of our analysis is the possibility of making meaningful alternative gauge choices for worldsheet supersymmetry, in place of the conventional superconformal gauge. We show in a version of unitary gauge how the worldsheet gravitino assimilates the goldstino and becomes dynamical. This picture clarifies recent results of Hellerman and Swanson. We also present analogs of R_\xi gauges, and note the importance of logarithmic CFT in the context of tachyon condensation.
Date: September 20, 2007
Creator: Horava, Petr; Horava, Petr & Keeler, Cynthia A.
Partner: UNT Libraries Government Documents Department

Pressure effects on bubble-column flow characteristics

Description: 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.
Date: March 1, 1996
Creator: Adkins, D.R.; Shollenberger, K.A.; O`Hern, T.J. & Torczynski, J.R.
Partner: UNT Libraries Government Documents Department

COAL CLEANING BY GAS AGGLOMERATION

Description: The agglomeration of ultrafine-size coal particles in an aqueous suspension by means of microscopic gas bubbles was demonstrated in numerous experiments with a scale model mixing system. Coal samples from both the Pittsburgh No. 8 Seam and the Upper Freeport Seam were used for these experiments. A small amount of i-octane was added to facilitate the process. Microscopic gas bubbles were generated by saturating the water used for suspending coal particles with gas under pressure and then reducing the pressure. Microagglomerates were produced which appeared to consist of gas bubbles encapsulated in coal particles. Since dilute particle suspensions were employed, it was possible to monitor the progress of agglomeration by observing changes in turbidity. By such means it became apparent that the rate of agglomeration depends on the concentration of microscopic gas bubbles and to a lesser extent on the concentration of i-octane. Similar results were obtained with both Pittsburgh No. 8 coal and Upper Freeport coal.
Date: September 30, 1998
Creator: SHEN, MEIYU; ABBOTT, ROYCE & WHEELOCK, T.D.
Partner: UNT Libraries Government Documents Department

Growth rate exponents of Richtmyer-Meshkov mixing layers

Description: The Richtmyer-Meshkov mixing layer is initiated by the passing of a shock over an interface between fluid of differing densities. The energy deposited during the shock passage undergoes a relaxation process during which the fluctuational energy in the flow field decays and the spatial gradients of the flow field decrease in time. This late stage of Richtmyer-Meshkov mixing layers is studied from the viewpoint of self-similarity. Analogies with weakly anisotropic turbulence suggest that both the bubble-side and spike-side widths of the mixing layer should evolve as power-laws in time, with the same power-law exponents and virtual time origin for both sides. The analogy also bounds the power-law exponent between 2/7 and 2/5. It is then shown that the assumption of identical power-law exponents for bubbles and spikes yields that are in good agreement with experiment at modest density ratios.
Date: January 13, 2004
Creator: Zhou, Y & Clark, T
Partner: UNT Libraries Government Documents Department

Feasibility of measuring 3He bubble diameter populations in deuterium-tritium ice layers using Mie scattering

Description: In this report, I assess the feasibility of using Mie scattering to quantify the diameter distribution of {sup 3}He bubbles in DT ice layers. Mie scattering methods are often used for He diameter m measurements of particulates in emulsions like pigments and ink products. These measurements suggests that similar techniques could be used to measure the distribution of {sup 3}He bubbles He in DT ice layers, which is important for NIF ICF capsules. To investigate the achievable performance of bubble diameter measurements using Mie scattering, I performed numerical modeling using exact analytical expressions.
Date: January 22, 2007
Creator: Izumi, N
Partner: UNT Libraries Government Documents Department

Star in a jar

Description: A sonoluminescing bubble has been modeled as a thermally conducting, partially ionized two-component plasma. The use of accurate equations-of-state, plasma physics, and radiation physics distinguishes our model from all previous models. The model provides an explanation of many features of single bubble sonoluminescence that have not been collectively accounted for in previous models, including the origin of the picosecond pulse widths and spectra. The calculated spectra for sonoluminescing nitrogen and argon bubbles suggest that a sonoluminescing air bubble probably contains only argon, in agreement with a recent theoretical analysis.
Date: August 11, 1997
Creator: Moss, W.C.; Clarke, D.B. & Young, D.A.
Partner: UNT Libraries Government Documents Department

Bubble Dynamics in a Superheated Liquid

Description: This report presents an extensive literature survey on bubble dynamics. Growth of a single spherical bubble moving in a uniformly superheated liquid is considered. Equations of motion and energy are presented in the forms that take into consideration the interaction between the motion and the growth. The fourth-order Runge-Kutta method is used to obtain a simultaneous solution of equations of motion and growth rate, and the solution is compared with available experimental results. Results for liquid sodium are presented for a range of pressures and Jakob numbers.
Date: September 1977
Creator: Sha, William T. & Shah, V. L.
Partner: UNT Libraries Government Documents Department

Engineering Development of Slurry Bubble Column Reactor (SBCR) Technology

Description: This report summarizes the procedures used and results obtained in determining radial gas holdup profiles, via gamma ray scanning, and in assessing liquid and gas mixing parameters, via radioactive liquid and gas tracers, during Fischer Tropsch synthesis. The objectives of the study were (i) to develop a procedure for detection of gas holdup radial profiles in operating reactors and (ii) to test the ability of the developed, previously described, engineering models to predict the observed liquid and gas mixing patterns. It was shown that the current scanning procedures were not precise enough to obtain an accurate estimate of the gas radial holdup profile and an improved protocol for future use was developed. The previously developed physically based model for liquid mixing was adapted to account for liquid withdrawal from the mid section of the column. The ability of our engineering mixing models for liquid and gas phase to predict both liquid and gas phase tracer response was established and illustrated.
Date: July 31, 2002
Creator: Gupta, Puneet
Partner: UNT Libraries Government Documents Department

EXPERIMENTAL BUBBLE FORMATION IN A LARGE SCALE SYSTEM FOR NEWTONIAN AND NONNEWTONIAN FLUIDS

Description: 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.
Date: June 26, 2008
Creator: Leishear, R & Michael Restivo, M
Partner: UNT Libraries Government Documents Department

MECHANISTIC STUDIES OF IMPROVED FOAM EOR PROCESSES

Description: The objective of this research is to widen the application of foam to enhanced oil recovery (EOR) by investigating fundamental mechanisms of foams in porous media. This research will lay the groundwork for more applied research on foams for improved sweep efficiency in miscible gas, steam and surfactant-based EOR. Task 1 investigates the pore-scale interactions between foam bubbles and polymer molecules. Task 2 examines the mechanisms of gas trapping, and interaction between gas trapping and foam effectiveness. Task 3 investigates mechanisms of foam generation in porous media.
Date: January 5, 2005
Creator: Rossen, William R.
Partner: UNT Libraries Government Documents Department

MECHANISTIC STUDIES OF IMPROVED FOAM EOR PROCESSES

Description: The objective of this research is to widen the application of foam to enhanced oil recovery (EOR) by investigating fundamental mechanisms of foams in porous media. This research is to lay the groundwork for more-applied research on foams for improved sweep efficiency in miscible gas, steam and surfactant-based EOR. Task 1 investigates the pore-scale interactions between foam bubbles and polymer molecules. Task 2 examines the mechanisms of gas trapping, and interaction between gas trapping and foam effectiveness. Task 3 investigates mechanisms of foam generation in porous media.
Date: March 16, 2005
Creator: Rossen, William R.
Partner: UNT Libraries Government Documents Department

Extended Rayleigh model of bubble evolution with material strength compared to detailed dynamic simulations

Description: The validity of an extended Rayleigh model for laser generated bubbles in soft tissue is examined. This model includes surface tension, viscosity, a realistic water equation of state, material strength and failure, stress wave emission, and linear growth of interface instabilities. It is compared to dynamic simulations using LATIS, which include stress wave propagation, water equation of state, material strength and failure, and viscosity. The model and the simulations are compared using 1-D spherical geometry with bubble in center and a 2-D cylindrical geometry of a laser fiber in water with a bubble formed at the end of the fiber. The model executes over 300x faster on computer than the dynamic simulations.
Date: March 4, 1997
Creator: Glinsky, M.E.; Amendt, P.A.; Bailey, D.S.; London, R.A.; Rubenchik, A.M. & Strauss, M.
Partner: UNT Libraries Government Documents Department