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A discontinuous Galerkin front tracking method for two-phase flows with surface tension

Description: A Discontinuous Galerkin method for solving hyperbolic systems of conservation laws involving interfaces is presented. The interfaces are represented by a collection of element boundaries and their position is updated using an arbitrary Lagrangian-Eulerian method. The motion of the interfaces and the numerical fluxes are obtained by solving a Riemann problem. As the interface is propagated, a simple and effective remeshing technique based on distance functions regenerates the grid to preserve its quality. Compared to other interface capturing techniques, the proposed approach avoids smearing of the jumps across the interface which leads to an improvement in accuracy. Numerical results are presented for several typical two-dimensional interface problems, including flows with surface tension.
Date: December 28, 2008
Creator: Nguyen, V.-T.; Peraire, J.; Cheong, K.B. & Persson, P.-O.
Partner: UNT Libraries Government Documents Department

Estimating the Maximum Splat Diameter of a Solidifying Droplet

Description: We present a simple analytical model for the estimation of the maximum splat diameter of an impacting droplet on a subcooled target. This work is an extension of the isothermal model of Pasandideh-Fard et al. (1996). The model uses an energy conservation argument, applied between the initial and final drop configurations, to approximately capture the dynamics of spreading. The effects of viscous dissipation, surface tension, and contact angle are taken into account. Tests against limited experimental data at high Reynolds and Weber numbers indicate that an accuracy of the order of 5% is achieved with no adjustable parameters required. Agreement with experimental data in the limit We {yields} {infinity} is also very good. We additionally propose a simple model for the estimation of the thickness of the freezing layer developed at the droplet-substrate contact during droplet spreading. This model accounts for the effect of thermal contact resistance and its predictions compare favorably with experimental data.
Date: March 31, 1999
Creator: Hadjiconstantinou, N.G.
Partner: UNT Libraries Government Documents Department

Surface Tension Estimates for Droplet Formation in Slurries with Low Concentrations of Hydrophobic Particles, Polymer Flocculants or Surface-Active Contaminants

Description: In support of the K-Basin project, Pacific Northwest National Laboratory (PNNL) was requested to evaluate the appropriate surface tension value to use in models predicting the formation of droplets from spray leaks of K-Basin slurries. The specific issue was whether it was more appropriate to use the surface tension of pure water in model predictions for all plausible spray leaks or to use a lower value. The surface tension of K-Basin slurries is potentially affected not only by particles but by low concentrations of nonionic polyacrylamide flocculant and perhaps by contaminants with surfactant properties, which could decrease the surface tension below that of water. A lower surface tension value typically results in smaller droplets being formed with a larger fraction of droplets in the respirable size range, so using the higher surface tension value of pure water is not conservative and thus needs a strong technical basis.
Date: June 10, 2011
Creator: Gauglitz, Phillip A.; Mahoney, Lenna A.; Blanchard, Jeremy & Bamberger, Judith A.
Partner: UNT Libraries Government Documents Department

Dynamical modeling of surface tension

Description: In a recent review it is said that free-surface flows ``represent some of the difficult remaining challenges in computational fluid dynamics``. There has been progress with the development of new approaches to treating interfaces, such as the level-set method and the improvement of older methods such as the VOF method. A common theme of many of the new developments has been the regularization of discontinuities at the interface. One example of this approach is the continuum surface force (CSF) formulation for surface tension, which replaces the surface stress given by Laplace`s equation by an equivalent volume force. Here, we describe how CSF might be made more useful. Specifically, we consider a derivation of the CSF equations from a minimization of surface energy as outlined by Jacqmin. This reformulation suggests that if one eliminates the computation of curvature in terms of a unit normal vector, parasitic currents may be eliminated For this reformulation to work, it is necessary that transition region thickness be controlled. Various means for this, in addition to the one discussed by Jacqmin are discussed.
Date: August 1, 1996
Creator: Brackbill, J.U. & Kothe, D.B.
Partner: UNT Libraries Government Documents Department

A new method for measuring the dynamic surface tension of complex-mixture liquid drops

Description: A simple and accurate technique has been developed for measuring dynamic surface tension. The new technique is based on growing a drop at the end of a fine capillary into another immiscible fluid and can follow the changes in tension at a freshly formed interface during its entire period of evolution. When the relative importance of the surface tension force is large compared to gravitational and viscous forces, shapes of growing drops are sections of spheres and the difference in pressure between the interior and the exterior of the drop {triangle}p is related to the surface tension {sigma} and the radius of curvature R by the static Young-Laplace formula {triangle}p = 2{sigma}/R. In contrast to related work, the new technique can determine the surface tension of an interface with a surface age of a few to tens of milliseconds by measuring transient drop shapes and pressures in 1/6 to 1 millisecond. The capabilities of the new method are demonstrated by performing tension measurements on liquid systems that do not exhibit dynamic surface tension as well as ones that exhibit significant dynamic tension effects. Tension measurements made with surfactant-laden solutions show that variation of surface tension is nonmonotonic in time. In such systems, the dynamic behavior of surface tension is shown to depend upon both the rate of interfacial dilatation and that of surfactant transport. A maximum in the surface tension is attained when the lowering of the surfactant concentration on the drop interface due to its dilatation is balanced by the addition of fresh surfactant to the interface by convection and diffusion.
Date: June 29, 1994
Creator: Zhang, X.; Harris, M.T. & Basaran, O.A.
Partner: UNT Libraries Government Documents Department

Towards Chip Scale Liquid Chromatography and High Throughput Immunosensing

Description: This work describes several research projects aimed towards developing new instruments and novel methods for high throughput chemical and biological analysis. Approaches are taken in two directions. The first direction takes advantage of well-established semiconductor fabrication techniques and applies them to miniaturize instruments that are workhorses in analytical laboratories. Specifically, the first part of this work focused on the development of micropumps and microvalves for controlled fluid delivery. The mechanism of these micropumps and microvalves relies on the electrochemically-induced surface tension change at a mercury/electrolyte interface. A miniaturized flow injection analysis device was integrated and flow injection analyses were demonstrated. In the second part of this work, microfluidic chips were also designed, fabricated, and tested. Separations of two fluorescent dyes were demonstrated in microfabricated channels, based on an open-tubular liquid chromatography (OT LC) or an electrochemically-modulated liquid chromatography (EMLC) format. A reduction in instrument size can potentially increase analysis speed, and allow exceedingly small amounts of sample to be analyzed under diverse separation conditions. The second direction explores the surface enhanced Raman spectroscopy (SERS) as a signal transduction method for immunoassay analysis. It takes advantage of the improved detection sensitivity as a result of surface enhancement on colloidal gold, the narrow width of Raman band, and the stability of Raman scattering signals to distinguish several different species simultaneously without exploiting spatially-separated addresses on a biochip. By labeling gold nanoparticles with different Raman reporters in conjunction with different detection antibodies, a simultaneous detection of a dual-analyte immunoassay was demonstrated. Using this scheme for quantitative analysis was also studied and preliminary dose-response curves from an immunoassay of a mo del antigen were obtained. Simultaneous detection of several analytes at the same address can potentially increase the analysis speed, and can further expand the analysis capability of a microarray chip.
Date: September 21, 2000
Creator: Ni, J.
Partner: UNT Libraries Government Documents Department

Flow of a two-dimensional liquid metal jet in a strong magnetic field.

Description: A combined effect of surface tension, gravity, inertia and a transverse nonuniform magnetic field on the steady, two-dimensional jet (or curtain) flow is studied with reference to liquid metal divertors of tokamaks [1] and coating flows [2]. Here main fundamental aspects of the flow are presented. More details on the assumptions, analysis and results are given in [3].
Date: August 1, 2002
Creator: Reed, C. B. & Molokov, S.
Partner: UNT Libraries Government Documents Department

Solvent problems in first PUREX cycle

Description: In March, 1988, the first PUREX cycle suffered uranium contamination of the solvent, 30% TBP in n-paraffin. Initial indication of maloperation was uranium contamination of the plutonium product stream, 1BP. Uranium in relatively large quantities, 10{sup {minus}3} to 10{sup {minus}4} g/L, was found in the solvent in Tank 14.7. This tank contains first cycle solvent that has been through the solvent washing system and is destined for return back to the cycle. Solvent, contained in Tank 14.7 under normal operating conditions, has <1 {times} 10{sup {minus}4} g U/L following the carbonate-acid-carbonate washing sequence. Work at SRL showed that the interfacial tension of the contaminated solvent, as sampled, was 2.5, indicating that substances, possibly long chain acids, were present that could affect disengaging times for the solvent. Virgin 30% TBP in n-paraffin has a interfacial tension of around 10 or better, for example. Tests conducted by Reif also showed that the contaminated solvent picked up significantly more fission products, Ru{sup 106} and Zr{sup 95}, than did virgin solvent. The contaminated solvent, following contact with alumina, had a greatly improved interfacial tension of 9.5 and exhibited much less pickup of both Ru{sup 106} and Zr{sup 95}. In a H-Area process testing, contact of process solvent with alumina produced improved interfacial tension values and reduced Zr{sup 95} pickup by the 7.5% TBP used there. From these tests, it is concluded that the contaminated solvent resulted from inefficient washing in the solvent washing system for first PUREX cycle. Nominal solvent chemistry should result if the solvent is properly washed in the carbonate-acid-carbonate process cycle. However, attention and study should be given to this solvent system because of the decline of its interfacial tension values. Such deterioration in solvent quality could be a portent of problems to come. Treatment with alumina, as was done with ...
Date: March 30, 1988
Creator: Holcomb, H. P.
Partner: UNT Libraries Government Documents Department

Equilibrium fluid interface behavior under low- and zero-gravity conditions. II

Description: We describe here recent mathematical results that form the basis of our forthcoming space experiment, developed jointly with Mark Weislogel of NASA Lewis Research Center, which is scheduled for the Glovebox on the Mir 23 / NASA 4 Mission in December 1996. The mathematical basis for the Angular Liquid Bridge is described. The anticipated liquid behavior used in the apparatus is illustrated.
Date: May 1, 1996
Creator: Concus, P. & Finn, R.
Partner: UNT Libraries Government Documents Department

Equilibrium liquid free-surface configurations: Mathematical theory and space experiments

Description: Small changes in container shape or in contact angle can give rise to large shifts of liquid in a microgravity environment. We describe some of our mathematical results that predict such behavior and that form the basis for physical experiments in space. The results include cases of discontinuous dependence on data and symmetry-breaking type of behavior. 23 refs., 9 figs.
Date: June 1, 1996
Creator: Concus, P. & Finn, R.
Partner: UNT Libraries Government Documents Department

Some free boundary problems in potential flow regime usinga based level set method

Description: Recent advances in the field of fluid mechanics with moving fronts are linked to the use of Level Set Methods, a versatile mathematical technique to follow free boundaries which undergo topological changes. A challenging class of problems in this context are those related to the solution of a partial differential equation posed on a moving domain, in which the boundary condition for the PDE solver has to be obtained from a partial differential equation defined on the front. This is the case of potential flow models with moving boundaries. Moreover the fluid front will possibly be carrying some material substance which will diffuse in the front and be advected by the front velocity, as for example the use of surfactants to lower surface tension. We present a Level Set based methodology to embed this partial differential equations defined on the front in a complete Eulerian framework, fully avoiding the tracking of fluid particles and its known limitations. To show the advantages of this approach in the field of Fluid Mechanics we present in this work one particular application: the numerical approximation of a potential flow model to simulate the evolution and breaking of a solitary wave propagating over a slopping bottom and compare the level set based algorithm with previous front tracking models.
Date: December 9, 2008
Creator: Garzon, M.; Bobillo-Ares, N. & Sethian, J.A.
Partner: UNT Libraries Government Documents Department

Two-phase viscoelastic jetting

Description: A coupled finite difference algorithm on rectangular grids is developed for viscoelastic ink ejection simulations. The ink is modeled by the Oldroyd-B viscoelastic fluid model. The coupled algorithm seamlessly incorporates several things: (1) a coupled level set-projection method for incompressible immiscible two-phase fluid flows; (2) a higher-order Godunov type algorithm for the convection terms in the momentum and level set equations; (3) a simple first-order upwind algorithm for the convection term in the viscoelastic stress equations; (4) central difference approximations for viscosity, surface tension, and upper-convected derivative terms; and (5) an equivalent circuit model to calculate the inflow pressure (or flow rate) from dynamic voltage.
Date: December 10, 2008
Creator: Yu, J.-D.; Sakai, S. & Sethian, J. A.
Partner: UNT Libraries Government Documents Department

Dynamics of Bubbles Rising in Finite and Infinite Media

Description: The dynamic behavior of single bubbles rising in quiescent liquid Suva (R134a) in a duct has been examined through the use of a high speed video system. Size, shape and velocity measurements obtained with the video system reveal a wide variety of characteristics for the bubbles as they rise in both finite and infinite media. This data, coupled with previously published data for other working fluids, has been used to assess and extend a rise velocity model given by Fan and Tsuchiya. As a result of this assessment, a new rise velocity model has been developed which maintains the physically consistent characteristics of the surface tension in the distorted bubbly regime. In addition, the model is unique in that it covers the entire range of bubble sizes contained in the spherical, distorted and planar slug regimes.
Date: October 27, 2000
Creator: Maneri, C.C. & Vassallo, P.F.
Partner: UNT Libraries Government Documents Department

The Shape of a Gravity Finger

Description: A new gravity finger model was proposed in this report in the absence of interfacial tension but in the presence of gravities. This model considered differences in density and viscosity of the two fluids. Thus, it was able to represent both stable and unstable displacements, and the finger development along either the upper or the bottom walls of a channel. This solution recovers the Saffman - Taylar solution if gravity is neglected. The results of the solution are very similar to the solutions proposed by Brener et al. for the gravity number up to 10. The solution provided in this work only has one free parameter while the solution of Brener et al. has three.
Date: September 11, 2000
Creator: Zhan, Lang & Yortsos, Yanis
Partner: UNT Libraries Government Documents Department

Evaluation of high-efficiency gas-liquid contactors for natural gas processing. Semi-annual report, April--September 1995

Description: The objective of this proposed program is to ensure reliable supply of high-quality natural gas by reducing the cost of treating subquality natural gas containing H{sub 2}O, CO{sub 2}, H{sub 2}S and/or trace quantities of other gaseous impurities by applying high-efficiency rotating and structured packing gas liquid contactors. Work accomplished during this reporting period are discussed for the following tasks: Task 2, field experimental site seletion; Task 3, field experimental skid unit design and preliminary economic evaluations; and Task 6, fluid dynamic studies.
Date: November 1, 1995
Partner: UNT Libraries Government Documents Department

Foaming characteristics of refigerant/lubricant mixtures

Description: The air-conditioning and refrigeration industry has moved to HFC refrigerants which have zero ozone depletion and low global warming potential due to regulations on CFC and HCFC refrigerants and concerns for the environment. The change in refrigerants has prompted the switch from mineral oil and alkylbenzene lubricants to polyolester-based lubricants. This change has also brought about a desire for lubricant, refrigerant and compressor manufacturers to understand the foaming properties of alternative refrigerant/ lubricant mixtures, as well as the mechanisms which affect these properties. The objectives of this investigation are to experimentally determine the foaming absorption and desorption rates of HFC and blended refrigerants in polyolester lubricant and to define the characteristics of the foam formed when the refrigerant leaves the refrigerant/ lubricant mixture after being exposed to a pressure drop. The refrigerants being examined include baseline refrigerants: CFC-12 (R-12) and HCFC-22 (R-22); alternative refrigerants: HFC-32 (R-32), R-125, R-134a, and R-143a; and blended refrigerants: R-404A, R-407C, and R-410A. The baseline refrigerants are tested with ISO 32 (Witco 3GS) and ISO 68 (4GS) mineral oils while the alternative and blended refrigerants are tested with two ISO 68 polyolesters (Witco SL68 and ICI RL68H).
Date: April 1, 1997
Creator: Goswami, D.Y.; Shah, D.O.; Jotshi, C.K.; Bhagwat, S.; Leung, M. & Gregory, A.
Partner: UNT Libraries Government Documents Department

Predicting the precipiation of amorphous silica from geothermal brines

Description: The voluminous gel-like deposits encountered at Cerro Prieto, Wairakei, and Niland consist of flocculated colloidal amorphous silica. The crumbly grey and white scales associated with the gel-like materials are cemented colloidal aggregates. This colloidal silica is produced by homogeneous nucleation in the liquid phase; i.e., nucleation by growth of polymers to critical nucleus size without the participation of some preexisting solid particle. With most substances heterogeneous nucleation is dominant, and homogeneous nucleation is very slow, rare in nature, and difficult to study in the laboratory. The precipitation of amorphous silica is an apparent exception to this because of the very low surface tension of the silica-water interface--between 35 and 50 ergs cm{sup -2} over the range of major practical interest. By comparison, the surface tension of the water-air interface is about 70-80 ergs cm{sup -2}. This means that enormous numbers of particles can be produced by homogeneous nucleation (on the order 10{sup 17} to 10{sup 18} per liter), and this completely swamps the effects of heterogeneous nucleation.
Date: January 1, 1978
Creator: Weres, Oleh; Yee, Andrew & Tsao, Leon
Partner: UNT Libraries Government Documents Department

Fabrication and Characterization of Suspended Carbon Nanotube Devices in Liquid

Description: Suspended carbon nanotube devices are a promising platform for future bio-electronic applications. Suspended carbon nanotube transistors have been previously fabricated in air; however all previous attempts to bring them into liquid failed. We analyze forces acting on the suspended nanotube devices during immersion into liquids and during device operation and show that surface tension forces acting on the suspended nanotubes during transfer into the liquid phase are responsible for the nanotube damage. We have developed a new strategy that circumvents these limitations by coating suspended nanotubes with a rigid inorganic shell in the gas phase. The coating reinforces the nanotubes and allows them to survive transfer through the interface. Subsequent removal of the coating in the solution phase restores pristine suspended nanotubes. We demonstrate that devices fabricated using this technique preserve their original electrical characteristics.
Date: October 30, 2006
Creator: Artyukhin, A; Stadermann, M; Stroeve, P; Bakajin, O & Noy, A
Partner: UNT Libraries Government Documents Department

Density functional theory of simple polymers in a slit pore: 3. Surface tension

Description: In a previous study of tangent site chains near a surface, the inhomogeneous density profiles were found through Density Functional theory. In the current study, the surface tensions of these systems are found from the results of the previous study through a thermodynamic integration. The calculated surface tensions are then compared to those found directly through computer simulation. Both the surface tension and surface excess for polymeric systems are shown to qualitatively differ from those of atomic systems, although certain similarities are seen at high densities.
Date: April 4, 2000
Partner: UNT Libraries Government Documents Department

Electroslag Remelting (ESR) Slags for Removal of Radioactive Oxide Contaminants from Stainless Steel, Annual Report (1998-1999)

Description: Decontamination of radioactive contaminated stainless steel using the ESR process is investigated by conducting thermophysical and thermochemical laboratory studies on the slag. The ESR base slag investigated in this research project is 60wt%CaF{sub 2}-20wt%CaO-20wt%Al{sub 2}O{sub 3}. In this report, we present the data obtained to date on relevant slag properties, capacity to incorporate the radioactive contaminant (using CeO{sub 3}) as surrogate, simulant for PUO{sub 2} and UO{sub 2}, slag-metal partition coefficient, volatilization rate and volatile species, viscosity, electrical conductivity and surface tension as a function of temperature. The impact of these properties on the ESR decontamination process is presented.
Date: August 1, 1999
Creator: PAL, UDAY B.
Partner: UNT Libraries Government Documents Department

Liquid/vapor surface tension of metals: Embedded atom method with charge gradient corrections

Description: Molecular dynamics (MD) simulations for three separately parameterized embedded atom methods (EAM) function sets are used to determine the liquid/vapor surface tension {gamma} for Al, Ni, Cu, Ag, and Au. The three EAM models differ in both the functional forms employed and the fitting procedure used. All the EAM potentials underestimate {gamma} but one of the models performs consistently better than the others. The authors show that including a correction to the local charge density associated with gradients in the density together with exploiting the invariance of the EAM bulk potential to appropriate transformations in the charge density can lead to improved values for {gamma}, as well as for solid free surface energies, within existing EAM function sets.
Date: March 21, 2000
Partner: UNT Libraries Government Documents Department