Tesi: "Surface tension"

1

Laverty, Rory. "Surface tension /". Electronic version (PDF), 2007. http://dl.uncw.edu/etd/2007-1/r1/lavertyr/rorylaverty.pdf.

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2

Thompson, Alice B. "Surface-tension-driven coalescence". Thesis, University of Nottingham, 2012. http://eprints.nottingham.ac.uk/12522/.

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When fluid droplets coalesce, the flow is initially controlled by a balance between surface tension and viscosity. For low viscosity fluids such as water, the viscous lengthscale is quickly reached, yielding a new balance between surface tension and inertia. Numerical and asymptotic calculations have shown that there is no simply connected solution for the coalescence of inviscid fluid drops surrounded by a void, as large amplitude capillary waves cause the free surface to pinch off. We analyse in detail a linearised version of this free boundary problem. For zero density surrounding fluid, we find asymptotic solutions to the leading order linear problem for small and large contact point displacement. In both cases, this requires the solution of a mixed type boundary value problem via complex variable methods. For the large displacement solution, we match this to a WKB analysis for capillary waves away from the contact point. The composite solution shows that the interface position becomes self intersecting for sufficiently large contact point displacement. We identify a distinguished density ratio for which flows in the coalescing drops and surrounding fluid are equally important in determining the interface shape. We find a large displacement solution to the leading order two-fluid problem with a multiple-scales analysis, using a spectral method to solve the leading order periodic oscillator problem for capillary waves. This is matched to a single-parameter inner problem, which we solve numerically to obtain the correct boundary conditions for the secularity equations. We find that the composite solution for the two-fluid problem is simply connected for arbitrarily large contact-point displacement, and so zero density surrounding fluid is a singular limit.

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3

Fröba, Andreas P., Cristina Botero, Heiko Kremer e Alfred Leipertz. "Liquid viscosity and surface tension by surface light scattering". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-196257.

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4

Fröba, Andreas P., Cristina Botero, Heiko Kremer e Alfred Leipertz. "Liquid viscosity and surface tension by surface light scattering". Diffusion fundamentals 2 (2005) 69, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14402.

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5

Matthews, Thomas Robert. "Surface Properties of Poly(ethylene terephthalate)". University of Toledo / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1177515548.

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6

Clewett, James. "Emergent surface tension in boiling granular media". Thesis, University of Nottingham, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604898.

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In this thesis we present findings from an experimental and numerical study of loosely confined, dry granular gases subject to vertical vibration. We found that the system phase separates into a high-density, liquid-like phase and a low-density gas-like phase. The phase separation was shown to occur at a critical driving amplitude but is independent of frequency. To introduce our work, we give an overview of phase separation in driven granular gases. Ofpatiicular interest are: a solid-liquid-like phase separation in tightly confined, dry granular mono layers and a liquid-gas-like phase separation in loosely confined, wet granular gases. Our system differs from the above examples in two significant ways: our cell is deeper than that used to tightly confine the granular mono layers, so that we avoid the formation of a solid-like phase; our patiicles are dry and as such there are no cohesive forces between the particles. The liquid-gas phase separation is a useful system in which to study far-from-equilibrium phenomena because the particles are easily homogenised and then quenched into the phase-separating state. The system also allows us to smoothly approach the phase-transition boundaries. The phase separation was shown to be spinodal driven, with a region of negative compressibility due to an excess in the granular temperature of the particles in the dilute phase. The origin of the excess temperature was traced to the coherent motion of particles above a critical driving amplitude. By switching to a frequency modulated driving signal the phase separation was suppressed, demonstrating the requirement for coherent motion. The experiment shows the importance of using realistic driving motion in simulations. The phase-separation coarsening dynamics were shown to be similar to that of thermodynamic systems evolving under curvature driven diffusion (model B). Using the Cahn-Hilliard equation we accurately predict the dominant length scale in the early-time dynamics. In thelIDodynamics the Cahn-Hilliard equation desclibes the minimisation of an excess interfacial energy. This suggests that we might define an effective free energy for our granular system, however, as yet it is not clear what is meant by free energy in the context of a far-fi·om-equilibrium system. Finally, by studying the surface tension of quasi-2D liquid-like droplets in the steady state, we found behaviour consistent with Laplace's equation, demonstrating that the surface tension is real. Detailed measurements of the pressure in the interfacial region show that the surface tension results predominantly from an unexpected anisotropy in the kinetic energy part of the pressure tensor, in contrast to thelIDodynamic systems where surface tension arises from either the attractive interaction between pmticles or entropit considerations. The general nature of our argument for the Oligin of the surface tension means that it should apply to other granular phase separations and segregations in granular rnixhlres. As such this might be a new general mechanism in far-from-equiliblium thermodynamics. Throughout the thesis we use numerical simulations, configured with a geometry matching that of the experimental cell. To simulate the two million particles required we created a bespoke molecular dynamics code to execute using GPGPU hardware. The peliormance of our simulations was comparable to the state of the art in the literature, approximately twenty times faster than simulations on modern CPU processors.

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7

Green, James Alexander. "Mixing in surface tension driven microchannel flows". Thesis, University of Hertfordshire, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440160.

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8

Cho, Han-Jae Jeremy. "Surface tension and electroporation of lipid bilayers". Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67612.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 78-79).
Electroporation of lipid bilayers is widely used in DNA transfection, gene therapy, and targeted drug delivery and has potential applications in water desalination and filtration. A better, more thorough molecular understanding is needed, however, before such devices can be effectively used and developed. From aqueous pore formation theory, electroporation behavior is known to be largely dictated by surface energy. We hypothesize that this surface energy can be described by separate head and tail components of the lipid molecules, which can be obtained experimentally. In this thesis, we demonstrated a basic ability to electroporate lipid bilayers as well as verify its electrical behavior. We formed lipid monolayer and bilayer films and studied their wetting properties using water, formamide, and diiodomethane. We determined that the strong interaction between polar liquids (water and formamide) and hydrophilic substrates (mica and glass) can affect the wetting behavior and quality of films. In addition, we verified that the resulting surface energy of lipid tails is mostly nonpolar. The insights of this work offer a first step towards characterizing the surface energies of different lipids and how they relate to the electroporation behavior.
by Han-Jae Jeremy Cho.
S.M.

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9

Zhao, Yajing S. M. Massachusetts Institute of Technology. "Dropwise condensation of water and low surface tension fluids on structured surfaces". Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118679.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 55-57).
Condensation is a ubiquitous process often observed in nature and our daily lives. The large amount of latent heat released during the condensation process has been harnessed in many industrial processes such as power generation, building heating and cooling, desalination, dew harvesting, thermal management, and refrigeration. Condensation has two modes: dropwise mode and filmwise mode. Although it has been known for decades that dropwise condensation outperforms filmwise condensation in heat transfer owing to the droplet shedding effects which can efficiently reduce thermal resistance, filmwise condensation still dominates industrial applications currently due to the high costs, low robustness and technical challenges of manufacturing dropwise coatings. During water condensation, dropwise mode can be readily promoted with thin hydrophobic coatings. Superhydrophobic surfaces made out of hydrophobic coatings on micro-or-nano-engineered surfaces have shown further heat transfer enhancement in dropwise condensation of water; however, the applications of these micro- or nanoscale structured surface designs have been restricted by the high manufacturing expenses and short range of subcooling limit. Recent studies have shown that the combination of millimeter sized geometric features and plain hydrophobic coatings can effectively manipulate droplet distribution of water condensate, which provides opportunities to locally facilitate dropwise condensation at relatively low manufacturing expenses as compared to those delicate micro- and nano-structured hydrophobic surfaces. Low surface tension fluids such as hydrocarbons pose a unique challenge to achieving dropwise condensation, because common hydrophobic coatings are not capable of repelling low surface tension fluids. Recent development in lubricant infused surfaces (LIS) offers promising solutions to achieving dropwise condensation of low surface tension fluids by replacing the solid-condensate interface in conventional hydrophobic coatings with a smooth lubricant-condensate interface. However, only a few experimental studies have applied LIS to promoting dropwise condensation of low surface tension fluids (y as low as 15 mN/m). In this work, we investigated dropwise condensation of both water (y ~ 72 mN/m) and a low surface tension fluid, namely butane (y - 13 mN/m) on structured surfaces. For water condensation, we studied the effects of millimeter sized geometric structures on dropwise condensation heat transfer under two different environments: pure vapor and an air-vapor mixture. Our experimental results show that, although convex structures enable faster droplet growth in an air-vapor mixture, the same structures impose the opposite effect during pure vapor condensation, hindering droplet growth. We developed a numerical model for each case to predict the heat flux distribution along the structured surface, and the model shows good agreement with experimental results. This work demonstrates that the effects of geometric features on dropwise condensation are not invariable but rather dependent on the scenario of resistances to heat and mass transfer in the system. For butane condensation, based on a design guideline we recently developed for lubricant infused surfaces, we successfully designed an energy-favorable combination of lubricant and structured solid substrate, which was further demonstrated to promote dropwise condensation of butane. The fundamental understanding of dropwise condensation of water and low surface tension fluids on structured surfaces developed in this study provides useful guidelines for condensation applications including power generation, desalination, dew harvesting, and thermal management.
by Yajing Zhao.
S.M.

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10

Saksono, Prihambodo Hendro. "On finite element modelling of surface tension phenomena". Thesis, Swansea University, 2002. https://cronfa.swan.ac.uk/Record/cronfa42392.

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The objective of this work is to develop a computational framework for modelling the motion of liquid phase between moving particles associated with the processing of complex multiphase materials. The liquid phase may be present at various levels of saturation and necessarily includes numerous and irregular free surfaces. In this kind of situation the surface tension is dominant and governs the interparticle motion that plays a fundamental role during material processing. This work focuses on surface tension modelling using the finite element method. Two issues related to the modelling of surface tension are addressed in this thesis, the first one is the development of a finite element procedure capable of modelling accurately the motion of the free surface boundaries between the gas and liquid phases. The second issue is finite element modelling of surface tension at such boundaries. The finite element formulation is based on the use of the incremental flow formulation of the Lagrangian form of the initial boundary value problem governing the free surface flow. The incompressibility constraint associated with the Newtonian fluid employed in this work is imposed using the penalty method. With regard to the surface tension model, the constitutive model commonly known as the Laplace-Young equation is employed. In the Lagrangian framework the surface tension formulation emerges naturally through the weak form of the Laplace-Young equation and the use of the surface divergence theorem reduces the continuity requirement across the element boundary from to C[1] to C[0]. The performance of the finite element model of surface tension is validated by means of numerical examples for both equilibrium and dynamic cases. The finite element results are compared against both analytical solutions and experimental results.

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11

Tooley, Scott. "The effects of surface tension on free surface flows intersecting rigid walls". Thesis, University of East Anglia, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251709.

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12

Adler, Jeanette. "Film Formation and Surface Tension Studies of Powder Coatings". Thesis, KTH, Fibre and Polymer Technology, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3935.

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In industrial use of paint systems a swift processing is crucial. Another very important issue is to improve the quality of the final coating. This report investigates the film formation process of powder coatings, specially the spreading of individual powder particles. The obtained results can be used to understand and control the film formation process. In this way the desired levelling can be achieved and thus the desired gloss or other surface characteristics that may be required. This means that the method could be used when evaluating different polymer and additive combinations that could be used to change film formation behaviour or curing time for powder coating systems to suit various substrates. It makes it possible to avoid and minimize different surface defects as orange peel or cratering in the powder coated film.

We used a reflection optical microscope to better understand the film formation process and especially the spreading of a powder melt on surfaces with various surface energies. The obtained data were: the particle diameter, the area, area ratio and the contact angle of the powder particle as a function of time and temperature. This information can be used to derive the surface tension of any powder melt.

In this report we evaluate the dependencies of temperature, heat rate and surface energy for powder coatings on different substrates. The method provides information that can be used to optimize the film formation of a specific powder coating/substrate combination. This method can be used to evaluate the powder spreading and levelling on different substrates from a surface tension point of view.

We found, as expected, that the powder flows out on a hydrophilic surface and is inhibited by a hydrophobic. The increase of the area ratio on a hydrophilic surface was about five times as the initial area coverage and on a hydrophobic surface only two times the initial area coverage. The contact angle between the melted powder particle on the different surface types could be calculated. The melt surface tension could be calculated since three substrates surfaces with various surface energies were used. The melt surface tension was found to be about 18.5 mN/m.

Sammanfattning

Vid industriell användning av ett färgsystem är det viktigt med en snabb och smidig målningsprocess. En viktig del är att förbättra kvaliteten på den färdiga ytan. Denna rapport undersöker filmbildningsprocessen för pulverfärg, närmare bestämt spridningen av individuella pulverpartiklar. Resultaten från utvärderingen av denna metod kan användas för att bättre förstå och få kontroll över filmbildningsprocessen. Med denna undersökningsmetod kan den önskade utslätningen uppnås och därmed den önskade glansen eller annan yteffekt som kan vara önskvärd.

Metoden kan användas för att utvärdera olika polymer- och additivkombinationer som kan användas för att ändra filmbildningens uppförande eller bestämma härdningstiden för en pulverfärg att passa ett visst substrat. Metoden gör det möjligt att förhindra och minska olika ytdefekter såsom apelsinskals- eller kratereffekter i pulverfärgens yta.

Ett optiskt reflectionsmikroskop användes för att bättre kunna förstå filmbildningsprocessen och särskilt spridningen av smält pulver på substrat med olika ytenergier. De mätdata vi fick var partikeldiameter, area, areaförändring och kontaktvinkeln för pulverpartiklar som funktion av tid och temperatur. Ur denna information kunde pulversmältans ytenergier härledas.

I denna rapport utvärderas pulvrets beroende av temperatur, uppvärmning och ytenergi på olika substrat. Denna metod ger information som kan användas för att optimera filmbildningen av en specifik kombination av pulverfärg och substrat. Denna metod kan också användas för att utvärdera pulverspridning och utjämning av färgfilmen på olika substrat med avseende på ytenergierna.

Som förväntat flyter pulvret ut på hydrofila ytor och utflytningen ändras på en hydrofob yta. På en hydrofil yta sprider sig partikeln till fem gånger den ursprungliga arean över substratet och motsvarande två gånger för en hydrofob yta. Kontaktvinkeln mellan en smält pulverpartikel på olika sorters substrat från utförda mätningar beräknas utifrån utförda mätningar. Kontaktvinklar mellan pulver och olika substrat kan användas för att beräkna smältans ytspänning. Smältans ytspänning kan beräknas då experiment gjorts på tre sorters ytor med olika kända ytenergier. Smältans ytspänning var 18,5 mN/m.

Slutsatsen är att det går att observera och utvärdera resultaten av utsmältningsförloppet för pulverfärg med denna metod.

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13

Erla, Adamsdóttir Lilý. "Tension Attention! : Dancing Embroidery". Thesis, Högskolan i Borås, Akademin för textil, teknik och ekonomi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:hb:diva-12400.

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This Master’s degree project explores the design possibilities of thread tension, to create a transformation in an interactive, 3D embroidered, wooden surface. The aim is to create a playful visual expression on a surface triggered by interaction. The surface is manipulated by embroidery and the embroidery is manipulated by the tension in the thread. Together all parts create a simple mechanism that allows the viewer to sink into a playful loop of a rising and collapsing structure. Dancing embroidery. The work explores the potential of the thread as a key factor together with interaction to make a transformation of a surface possible. The thread is used both in the function of the surface and at the same time it creates a strong visual expression as it stands out to show its strength and power.

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14

Whittaker, Kipp 1980. "A finite element surface tension model with forces based on surface energy minimization". Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/89934.

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15

Lin, Yixin. "A Local Surface Reconstruction Algorithm for Surface Tension Simulation in Smoothed Particle Hydrodynamics". University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1613752656589083.

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16

Gao, Guangyue. "Some Controllability and Stabilization Problems of Surface Waves on Water with Surface tension". Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/64377.

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The thesis consists of two parts. The first part discusses the initial value problem of a fifth-order Korteweg-de Vries type of equation w_t + w_xxx - w_xxxxx - ⁿ∑_j=1 a_jw^jw_x = 0, w(x, 0) = w₀(x) posed on a periodic domain x ∈ [0, 2π] with boundary conditions w_ix(0, t) = w_ix(2π, t), i = 0, 2, 3, 4 and an L²-stabilizing feedback control law w_x(2π, t) = αw_x(0, t) + (1 - α)w_xxx(0; t) where n is a fixed positive integer, a_j, j = 1, 2, ... n, α are real constants, and |α| < 1. It is shown that for w₀(x) ∈ H¹_α(0, 2π) with the boundary conditions described above, the problem is locally well-posed for w ∈ C([0, T]; H¹_α(0, 2π)) with a conserved volume of w, [w] = ∫^2π₀ w(x, t)dx. Moreover, the solution with small initial condition exists globally and approaches to [w₀(x)]/(2π) as t → + ∞. The second part concerns wave motions on water in a rectangular basin with a wave generator mounted on a side wall. The linear governing equations are used and it is assumed that the surface tension on the free surface is not zero. Two types of generators are considered, flexible and rigid. For the flexible case, it is shown that the system is exactly controllable. For the rigid case, the system is not exactly controllable in a finite-time interval. However, it is approximately controllable. The stability problem of the system with the rigid generator controlled by a static feedback is also studied and it is proved that the system is strongly stable for this case.
Ph. D.

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17

Lervåg, Karl Yngve. "Simulation of two-phase flow with varying surface tension". Thesis, Norwegian University of Science and Technology, Department of Mathematical Sciences, 2008. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9738.

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This thesis is a study on the effects of varying surface tension along an interface separating two fluids. Varying surface tension leads to tangential forces along the interface. This is often called the Marangoni effect. These forces are discussed in detail, and two test cases are considered to analyse the Marangoni effect, and to verify the present implementation. The first test studies steady-state two-phase flow where the fluids are separated with plane interfaces and the flow is driven by a linear surface-tension gradient. The second case is an analysis of the initial forces on a two-dimensional droplet due to a linear surface-tension gradient. The tests indicate that the present implementation is capable of simulating two-phase flow with a given surface-tension gradient. The underlying model is a two-phase flow model for Newtonian fluids with constant viscosity and density. The two-phase model is based on the Navier-Stokes equations coupled with a singular surface force, which together with the difference in fluid properties induces discontinuities across the interface. The Navier-Stokes equations are solved using a projection method, and a combination of the level-set method for capturing the interface and the ghost-fluid method (GFM) for handling the interface discontinuities. The thesis also discusses the effect of surfactants on an interface. The presence of surfactants reduces the local surface tension, and a non-uniform surfactant distribution results in varying surface tension and the Marangoni effect. A surfactant model is reviewed, where an equation of state couples the surface tension to the surfactant concentration and a transport equation is used to solve the surfactant mass-conservation.

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18

Wheeler, David. "Computational modelling of surface tension phenomena in metals processing". Thesis, University of Greenwich, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399303.

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19

Guzmán, Ramírez Roberto Antonio. "Surface tension driven flow on a thin reaction front". Master's thesis, Pontificia Universidad Católica del Perú, 2017. http://tesis.pucp.edu.pe/repositorio/handle/123456789/8503.

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Surface tension driven convection affects the propagation of chemical reaction fronts in liquids. The changes in surface tension across the front generate this type of convection. The resulting fluid motion increases the speed and changes the shape of fronts as observed in the iodate-arsenous acid reaction. We calculate these effects using a thin front approximation, where the reaction front is modeled by an abrupt discontinuity between reacted and unreacted substances. We analyze the propagation of reaction fronts of small curvature. In this case the front propagation equation becomes the deterministic Kardar-Parisi-Zhang (KPZ) equation with the addition of fluid flow. These results are compared to calculations based on a set of reaction-diffusion-convection equations.
Tesis

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20

Nayar, Kishor Govind. "An experimental investigation of the surface tension of seawater". Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92181.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 89-93).
Surface tension of seawater was measured for absolute salinities S = (20.01, 35.18, 40.49, 79.39, 121.54) g/kg across a temperature range of T = (0 - 90)°C at atmospheric pressure using the Wilhelmy plate method. The uncertainty within measurements varied between 0.04 - 0.33 mN/m with the average uncertainty being 0.12 mN/m. The experimental procedures were validated with tests conducted on ACS reagent grade water and aqueous sodium chloride solutions. A best fit correlation was developed expressing surface tension of seawater as a function of temperature and salinity. The average absolute deviation between measurements and the correlation was 0.19% while the maximum deviation was 0.60%. The surface tension of seawater was found to be comparable to within 1.37% of the surface tension of aqueous sodium chloride. The surface tension of 0.2 [mu]m microfiltered and ultraviolet radiation treated natural seawater was found to be similar to that of laboratory prepared seawater.
by Kishor Govind Nayar.
S.M.

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21

Albernaz, Daniel. "Phase change, surface tension and turbulence in real fluids". Doctoral thesis, KTH, Fysiokemisk strömningsmekanik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-183487.

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Sprays are extensively used in industry, especially for fuels in internal combustion and gas turbine engines. An optimal fuel/air mixture prior to combustion is desired for these applications, leading to greater efficiency and minimal levels of emissions. The optimization depends on details regarding the different breakups, evaporation and mixing processes. Besides, one should take into consideration that these different steps depend on physical properties of the gas and fuel, such as density, viscosity, heat conductivity and surface tension. In this thesis the phase change and surface tension of a droplet for different flow conditions are studied by means of numerical simulations.This work is part of a larger effort aiming to developing models for sprays in turbulent flows. We are especially interested in the atomization regime, where the liquid breakup causes the formation of droplet sizes much smaller than the jet diameter. The behavior of these small droplets is important to shed more light on how to achieve the homogeneity of the gas-fuel mixture as well as that it directly contributes to the development of large-eddy simulation (LES) models. The numerical approach is a challenging process as one must take into account the transport of heat, mass and momentum for a multiphase flow. We choose a lattice Boltzmann method (LBM) due to its convenient mesoscopic natureto simulate interfacial flows. A non-ideal equation of state is used to control the phase change according to local thermodynamic properties. We analyze the droplet and surrounding vapor for a hydrocarbon fuel close to the critical point. Under forced convection, the droplet evaporation rate is seen to depend on the vapor temperatureand Reynolds number, where oscillatory flows can be observed. Marangoni forces are also present and drivethe droplet internal circulation once the temperature difference at the droplet surface becomes significant.In isotropic turbulence, the vapor phase shows increasing fluctuations of the thermodynamic variables oncethe fluid approaches the critical point. The droplet dynamics is also investigated under turbulent conditions, where the presence of coherent structures with strong shear layers affects the mass transfer between the liquid-vapor flow, showing also a correlation with the droplet deformation. Here, the surface tension and droplet size play a major role and are analyzed in detail.

QC 20160314

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22

Haywood, Kieran. "The dynamic surface properties and foam stability of protein solutions". Thesis, University of Reading, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252241.

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23

Lee, Chee-kwan. "Modelling of flexible surfaces using a point mass system /". [Hong Kong : University of Hong Kong], 1992. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13204889.

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24

El, Kosseifi Nadine. "Simulation numérique de l'ébullition pour les procédés de trempe industrielle". Phd thesis, Ecole Nationale Supérieure des Mines de Paris, 2012. http://pastel.archives-ouvertes.fr/pastel-00734601.

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Cette thèse porte sur la modélisation de l'ébullition qui joue un rôle important dans les vitessesde refroidissement des pièces, elle possède un volet numérique et un volet expérimental. Lessimulations et les expériences envisagées se situent à deux échelles. A l'échelle d'une ou quelquesbulles de vapeur, il s'agit de faire des simulations multiphasiques très précises en prenant encompte, la tension de surface, les calculs directs d'écoulement à grand nombre de Reynolds, etrendant compte du détachement et de la coalescences des bulles. Des observations expérimentalessont réalisées à la même échelle en contrôlant en surface la nucléation d'une bulle de vapeur àl'aide d'une caméra rapide. Des mesures de champs de vitesse par PIV et de température par twocolor LIF thermometry sont réalisées dans les mêmes conditions. Ceci a permit de confronter lacroissance, la dynamique et les formes des bulles observées et calculés. Les techniques numériquesles plus avancées sont utilisées : Eléments finis stabilisé VMS, level set, adaptation anisotropeet calcul intensif. Les modéles numériques proposés dans cette thèse permettent de passer àl'échelle macroscopique des pièces industrielles en considérant un film de vapeur (ou une phasede mélange liquide vapeur). L'enjeu supplémentaire étant de modéliser la turbulence induite parl'ébullition dans une approche de type CFD.

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25

Baker, John Alex. "Quasi Steady Capillary Corner Flow". PDXScholar, 2010. https://pdxscholar.library.pdx.edu/open_access_etds/139.

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It is possible to drain slender containers filled with wetting liquids via capillary flows along the interior corners of the container. Usually the well established equations governing such flows demand numerical techniques. In the case of container draining unique boundary conditions resulting from local section geometry allow for a quasi-steady assumption and in turn permit analytical solutions. The quasi-steady assumption may also be employed for certain problems in which the corner flows cause passive capillary migration of the fluid within the container. The analytic solutions are useful because of the ease in which geometric effects may be observed. Container draining and capillary migration by means of corner flows are studied in a variety of container geometries. It is shown that careful selection of cross sectional shape can be used to maximize drain rates and minimize capillary migration times. Three-dimensional effects for these flows are investigated in tapering containers. Some simple micro-scale experiments are reported that provide confidence in the assumptions and application of the important boundary conditions that enable the solutions.

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26

Braun, Frank Nicholas. "Surface phase transitions in liquid crystals". Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242564.

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27

Staggemeier, Bethany Ann. "Dynamic surface tension detection : novel applications to continuous flow analysis and interfacial analysis /". Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/11584.

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28

Lambert, Pierre. "Les effets de tension de surface en microtechnique et microrobotique". Habilitation à diriger des recherches, Université de Franche-Comté, 2007. http://tel.archives-ouvertes.fr/tel-00536852.

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Le travail présenté dans ce manuscript tire son origine de la descente d'échelle présente en passant de l'assemblage conventionnel vers le micro-assemblage. On se rendra rapidement compte que ce changement d'échelle nécessitera la maîtrise en profondeur de nombreux phénomènes physiques gouvernant les petites échelles, dont notamment les effets de la tension de surface et l'adhésion, concepts le plus souvent inconnus des ingénieurs mécaniciens. Ce document se décline en trois parties principales, visant à étudier les effets de la tension de surface dans les Microsystèmes. La première partie positionne nos contributions par rapport à l'état de l'art, présentant principalement l'étude des forces de capillarité (forces axiales et radiales, études statiques et dynamiques, aux échelles allant du millimètre au nanomètre). La deuxième partie du travail décrit le développement de bancs d'essai qui ont servi à valider notre travail théorique : cela consiste essentiellement en la mise au point de dispositifs de mesure de forces, du nanonewton au newton. La troisième partier assemble les cas d'études qui ont été traits: assemblage de produits horlogers, préhenseurs, dispositifs d'alimentation, assemblage hybride, mécanique des sols, électrosprays... Le but était de développer des modèles utiles aux communautés de la mécanique de précision et de la microrobotique. Nous espérons ainsi avoir proposé des modèles de forces de capillarité qui pourront être appliqués à de nombreux domaines applicatifs : assemblage et packaging, microrobotique, mécanique des sols, microfluidique...

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29

Lookingbill, Scott David, e Scott David Lookingbill. "Effects of concentration-dependent surface tension on vadose zone instrumentation". Thesis, The University of Arizona, 1997. http://hdl.handle.net/10150/626774.

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Many of the organic compounds of environmental interest which are commonly found at contaminated sites have the effect of lowering the surface tension of water in proportion to their aqueous concentration. Laboratory studies were conducted to investigate the effects of reduced surface tension on instruments commonly used to measure pressure head in the vadose zone. Gypsum block electrical resistance sensors and heat dissipation probes were calibrated in tap water and in butanol solutions. A scaling relationship was used to correct pressure head measurements taken in liquids of reduced surface tension. The results indicate that the these measurements would be in error in that they would underestimate pressure head for solutions of lower surface tension to the same factor by which surface tension was reduced. This would result in pressure head gradient and flux being underestimated as well. Therefore, surface tension effects on these instruments should be considered when measuring pressure head in soils contaminated with organic compounds.

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30

Zhou, YunZhen. "Design of a digital vision system for measuring surface tension". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0021/MQ57746.pdf.

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31

Kunka, Mark David. "Nonlinear evolution of small peclet number dendrites with surface tension /". The Ohio State University, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487868114110492.

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32

Zhou, Yun Zhen Larry Carleton University Dissertation Engineering Mechanical and Aerospace. "Design of a digital vision system for measuring surface tension". Ottawa, 2000.

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33

Hataya, Yasushi. "Decaying solution of a Navier-Stokes flow without surface tension". 京都大学 (Kyoto University), 2004. http://hdl.handle.net/2433/147884.

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34

Nguyen, Tri Nguyen. "Numerical Methods for Compressible Multi-phase flows with Surface Tension". Doctoral thesis, Università degli studi di Trento, 2017. https://hdl.handle.net/11572/368017.

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In this thesis we present a new and accurate series of computation methods for compressible multi-phase flows with capillary effects based upon the full seven-equation Baer-Nunziato model. For that reason, there are some numerical methods to obtain high accuracy solutions, which will be shown here. First, a high resolution shock capturing Total Variation Diminishing (TVD) finite volume scheme is used on both Cartesian and unstructured triangular grids. Regarding the TVD finite volume scheme on the unstructured grid, time-accurate local time stepping (LTS) is applied to compute the solutions of the governing PDE system, in which the results are also compared with time-accurate global time stepping. Second, we propose a novel high order accurate numerical method for the solution of the seven equation Baer-Nunziato model based on ADER discontinuous Galerkin (DG) finite element schemes combined with a posteriori subcell finite volume limiting and adaptive mesh refinement (AMR). In multi-phase flows, the difficulty is to design accurate numerical methods for resolving the phase interface, as well as the simulation of the phenomena occurring at the interface, such as surface tension effects, heat transfer and friction. This is because of the interactions of the fluids at the phase interface and its complex geometry. So the accurate simulation of compressible multi-phase flows with surface tension effects is currently still one of the most challenging problems in computational fluid dynamics (CFD). In this work, we present a novel path-conservative finite volume discretization of the continuum surface force method (CSF) of Brackbill et al. to account for the surface tension effect due to curvature of the phase interface. This is achieved in the context of a diffuse interface approach, based on the seven equation Baer-Nunziato model of compressible multi-phase flows. Such diffuse interface methods for compressible multi-phase flows including capillary effects have first been proposed by Perigaud and Saurel. Regarding the high order accuracy of a diffuse interface approach, the interface is captured and allowed to travel across one single possibly refined cell, and is computed in the context of multi-dimensional high accurate space/time DG schemes with AMR and a posteriori sub-cell stabilization. The surface tension terms of the CSF approach are considered as a part of the non-conservative hyperbolic system. We propose to integrate the CSF source term as a non-conservative product and not simply as a source term, following the ideas on path conservative finite volume schemes put forward by Castro and ParÃ©s. For the validation of the current numerical methods, we compare our numerical results with those published previously in the literature.

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35

Nguyen, Tri Nguyen. "Numerical Methods for Compressible Multi-phase flows with Surface Tension". Doctoral thesis, University of Trento, 2017. http://eprints-phd.biblio.unitn.it/2023/1/Nguyen_Tri_Nguyen_PhD_Thesis.pdf.

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Abstract (sommario):

In this thesis we present a new and accurate series of computation methods for compressible multi-phase flows with capillary effects based upon the full seven-equation Baer-Nunziato model. For that reason, there are some numerical methods to obtain high accuracy solutions, which will be shown here. First, a high resolution shock capturing Total Variation Diminishing (TVD) finite volume scheme is used on both Cartesian and unstructured triangular grids. Regarding the TVD finite volume scheme on the unstructured grid, time-accurate local time stepping (LTS) is applied to compute the solutions of the governing PDE system, in which the results are also compared with time-accurate global time stepping. Second, we propose a novel high order accurate numerical method for the solution of the seven equation Baer-Nunziato model based on ADER discontinuous Galerkin (DG) finite element schemes combined with a posteriori subcell finite volume limiting and adaptive mesh refinement (AMR). In multi-phase flows, the difficulty is to design accurate numerical methods for resolving the phase interface, as well as the simulation of the phenomena occurring at the interface, such as surface tension effects, heat transfer and friction. This is because of the interactions of the fluids at the phase interface and its complex geometry. So the accurate simulation of compressible multi-phase flows with surface tension effects is currently still one of the most challenging problems in computational fluid dynamics (CFD). In this work, we present a novel path-conservative finite volume discretization of the continuum surface force method (CSF) of Brackbill et al. to account for the surface tension effect due to curvature of the phase interface. This is achieved in the context of a diffuse interface approach, based on the seven equation Baer-Nunziato model of compressible multi-phase flows. Such diffuse interface methods for compressible multi-phase flows including capillary effects have first been proposed by Perigaud and Saurel. Regarding the high order accuracy of a diffuse interface approach, the interface is captured and allowed to travel across one single possibly refined cell, and is computed in the context of multi-dimensional high accurate space/time DG schemes with AMR and a posteriori sub-cell stabilization. The surface tension terms of the CSF approach are considered as a part of the non-conservative hyperbolic system. We propose to integrate the CSF source term as a non-conservative product and not simply as a source term, following the ideas on path conservative finite volume schemes put forward by Castro and Parés. For the validation of the current numerical methods, we compare our numerical results with those published previously in the literature.

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36

Colinet, Pierre. "Amplitude equations and nonlinear dynamics of surface-tension and buoyancy-driven convective instabilities". Doctoral thesis, Universite Libre de Bruxelles, 1997. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/212204.

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This work is a theoretical contribution to the study of thermo-hydrodynamic instabilities in fluids submitted to surface-tension (Marangoni) and buoyancy (Rayleigh) effects in layered (Benard) configurations. The driving constraint consists in a thermal (or a concentrational) gradient orthogonal to the plane of the layer(s).

Linear, weakly nonlinear as well as strongly nonlinear analyses are carried out, with emphasis on high Prandtl (or Schmidt) number fluids, although some results are also given for low-Prandtl number liquid metals. Attention is mostly devoted to the mechanisms responsible for the onset of complex spatio-temporal behaviours in these systems, as well as to the theoretical explanation of some existing experimental results.

As far as linear stability analyses (of the diffusive reference state) are concerned, a number of different effects are studied, such as Benard convection in two layers coupled at an interface (for which a general classification of instability modes is proposed), surface deformation effects and phase-change effects (non-equilibrium evaporation). Moreover, a number of different monotonous and oscillatory instability modes (leading respectively to patterns and waves in the nonlinear regime) are identified. In the case of oscillatory modes in a liquid layer with deformable interface heated from above, our analysis generalises and clarifies earlier works on the subject. A new Rayleigh-Marangoni oscillatory mode is also described for a liquid layer with an undeformable interface heated from above (coupling between internal and surface waves).

Weakly nonlinear analyses are then presented, first for monotonous modes in a 3D system. Emphasis is placed on the derivation of amplitude (Ginzburg-Landau) equations, with universal structure determined by the general symmetry properties of the physical system considered. These equations are thus valid outside the context of hydrodynamic instabilities, although they generally depend on a certain number of numerical coefficients which are calculated for the specific convective systems studied. The nonlinear competitions of patterns such as convective rolls, hexagons and squares is studied, showing the preference for hexagons with upflow at the centre in the surface-tension-driven case (and moderate Prandtl number), and of rolls in the buoyancy-induced case.

A transition to square patterns recently observed in experiments is also explained by amplitude equation analysis. The role of several fluid properties and of heat transfer conditions at the free interface is examined, for one-layer and two-layer systems. We also analyse modulation effects (spatial variation of the envelope of the patterns) in hexagonal patterns, leading to the description of secondary instabilities of supercritical hexagons (Busse balloon) in terms of phase diffusion equations, and of pentagon-heptagon defects in the hexagonal structures. In the frame of a general non-variational system of amplitude equations, we show that the pentagon-heptagon defects are generally not motionless, and may even lead to complex spatio-temporal dynamics (via a process of multiplication of defects in hexagonal structures).

The onset of waves is also studied in weakly nonlinear 2D situations. The competition between travelling and standing waves is first analysed in a two-layer Rayleigh-Benard system (competition between thermal and mechanical coupling of the layers), in the vicinity of special values of the parameters for which a multiple (Takens-Bogdanov) bifurcation occurs. The behaviours in the vicinity of this point are numerically explored. Then, the interaction between waves and steady patterns with different wavenumbers is analysed. Spatially quasiperiodic (mixed) states are found to be stable in some range when the interaction between waves and patterns is non-resonant, while several transitions to chaotic dynamics (among which an infinite sequence of homoclinic bifurcations) occur when it is resonant. Some of these results have quite general validity, because they are shown to be entirely determined by quadratic interactions in amplitude equations.

Finally, models of strongly nonlinear surface-tension-driven convection are derived and analysed, which are thought to be representative of the transitions to thermal turbulence occurring at very high driving gradient. The role of the fastest growing modes (intrinsic length scale) is discussed, as well as scalings of steady regimes and their secondary instabilities (due to instability of the thermal boundary layer), leading to chaotic spatio-temporal dynamics whose preliminary analysis (energy spectrum) reveals features characteristic of hydrodynamic turbulence. Some of the (2D and 3D) results presented are in qualitative agreement with experiments (interfacial turbulence).

Doctorat en sciences appliquées
info:eu-repo/semantics/nonPublished

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37

Da, Rocha Sandro Roberto Possatti. "CO₂-water interface : interfacial tension, emulsions, microemulsions, and computer simulations /". Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004246.

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38

Swickrath, Michael J. "THE DESIGN AND FABRICATION OF AUTONOMOUS POLYMER-BASED SURFACE TENSION-CONFINED MICROFLUIDIC PLATFORMS". Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1196092156.

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39

Koran, Karen M. "Surface interactions of surface washing agents an examination of detergency, interfacial tension and contact angle /". Cincinnati, Ohio : University of Cincinnati, 2007. http://www.ohiolink.edu/etd/view.cgi?ucin1186105489.

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40

KORAN, KAREN M. "SURFACE INTERACTIONS OF SURFACE WASHING AGENTS: AN EXAMINATION OF DETERGENCY, INTERFACIAL TENSION AND CONTACT ANGLE". University of Cincinnati / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1186105489.

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41

Youssef, Nivine T. M. "Dynamic surface tension and strain rate dependent viscosity : material characterization using free surface oscillating jets /". The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488192447428292.

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42

Moreira, Roger Matsumoto. "Nonlinear interactions between water waves, free surface flows and singularities". Thesis, University of Bristol, 2001. http://hdl.handle.net/1983/48c03019-9f5d-4aae-83b5-d9ea23c2f6ec.

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43

Larson, Hans Christian. "Replacement Rates of Initially Hydrocarbon-Filled Microscopic Cavities with Water". BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/7496.

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Abstract (sommario):

Wetting behaviors influence many aspects of life and industry from consumer product goods to oil recovery to cosmetics. While the traditional solid-liquid-vapor (SLV) system has been studied for many years now, wetting transitions in the solid-liquid-liquid (SLL) system has remained relatively unexplored. The purpose of this work is to bring light to the wetting transition of the solid-liquid-liquid system and to understand the replacement rates of initially hydrocarbon-filled microscopic cavities with water and the factors affecting these rates. Factors studied were viscosity, density, diffusion related properties, and surface related properties in both hydrocarbon-saturated and hydrocarbon-non-saturated conditions. Cylindrical microscopic cavities were etched in a silicon wafer, filled with various organic solvents dyed with fluorophores, then submerged in water. Through fluorescence microscopy techniques, the transition or replacement rates of the initially hydrocarbon-filled cavities with water in both hydrocarbon-saturated and hydrocarbon-absent water conditions are observed. Among the factors we investigated, namely viscosity, density, surface chemistry, and diffusive flux (composed of solubility and diffusivity), diffuse flux dominated replacement rates in hydrocarbon-absent water conditions. By using hydrocarbon-saturated water, diffusive flux was minimized, allowing for deeper investigation of other factors. In the hydrocarbon-saturated scenario, replacement rates are largely affected by initial fluid motion, specific cavity geometry, and cavity penetration mechanisms. Image analysis reveals the geometry of the oils in the cavities and shows how the transition from hydrocarbon-fully-filled to hydrocarbon-partially-filled states occurs in the SLL system.

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44

Lenders, Cyrille. "Study of microbubbles mechanical behavior: application to the design of an actuated table for micromanipulation in liquid media". Doctoral thesis, Universite Libre de Bruxelles, 2010. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210089.

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The scope of this thesis is micromanipulation in liquid media. This scientific field aims at understanding the relevant phenomena existing during the manipulation in a liquid of microcomponents having a size between $1,micrometer$ and a few millimeters. This work focuses on the study of surface tension forces in immersed media, because they have favorable scaling effect. The main idea is to use gas bubbles as actuation mean in a liquid, and requires to study the mechanical properties of these bubbles. The originality of the approach is the combination of two effects: surface tension and gas compressibility.

The first step was the study of an efficient mean to generate a single bubble of predefined size. After a detailed review, it appeared that volume controlled bubble generation was a promising method. We have then developed a model to predict the size of a bubble, and emphasized the possible existence of a growing instability. An analytic dimensionless study allowed to define a criterion to predict the existence of this instability.

The second step aimed at the mechanical characterization in quasi static equilibrium of a gas bubble caught between two solids. The purpose is to predict the force generated by the bubble, together with its stiffness. The model implemented allowed to infer interesting properties, notably a high compliance whose value is controllable by fluidic parameters. This compliance property being very important during micromanipulation, a demonstrator making use of gas bubbles has been designed and manufactured. It consists in a compliant microtable actuated by three bubbles. This work opens the way to new actuation or sensing means, using the transduction between fluidic and mechanic energy operated by a capillary bridge.

/

Cette thèse a pour contexte la micromanipulation en milieu liquide. Cette thématique scientifique vise à comprendre les phénomènes qui interviennent lors de la manipulation dans un liquide de microcomposants, dont la taille peut varier entre $1,micrometer$ et quelques millimètres. Les travaux de cette thèse se sont focalisés sur l'étude des forces de tension de surface en milieu immergé, car elles bénéficient d'effets d'échelle favorables. L'idée poursuivie est d'utiliser des bulles de gaz comme un moyen d'actionnement dans les milieux liquides, et nécessite d'étudier les propriétés mécaniques de ces bulles. L'originalité de l'approche repose sur la combinaison de deux effets :la tension de surface et la compressibilité du gaz.

La première étape a été l'étude d'un moyen efficace pour générer une unique bulle de gaz de taille voulue. Après une analyse exhaustive, il est apparu que la génération de bulle par le contrôle en volume était une méthode prometteuse. Nous avons alors développé un modèle permettant de prédire la taille d'une bulle, et mis en évidence la possible existence d'une instabilité de la croissance de ces bulles. Une étude analytique adimensionnelle nous a permis de définir un critère pour prédire l'existence ou non de cette instabilité.

La seconde étape a porté sur la caractérisation mécanique en régime quasi statique d'une bulle de gaz en contact avec deux solides. Le but étant de prédire la force générée par une bulle de gaz sur les solides ainsi que sa raideur. Le modèle implémenté a permis de déduire des propriétés intéressantes des bulles de gaz, notamment une grande compliance dont la valeur peut être contrôlée par des paramètres fluidiques. Cette propriété de compliance étant très recherchée en micromanipulation, un démonstrateur exploitant les bulles de gaz a été conçu. Il s'agit d'une microtable compliante actionnée par trois bulles. Ces travaux ouvrent la voie vers de nouveaux modes d'actionnement ou de capteur utilisant la transduction entre une énergie fluidique et mécanique opérée par un ménisque capillaire.
Doctorat en Sciences de l'ingénieur
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45

Kippax, Paul. "Interfacial adsorption of non-ionic amphiphiles". Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243470.

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46

Suerich-Gulick, Irmgard Frances. "Axial stretching, viscosity, surface tension and turbulence in free surface vortices at low-head hydropower intakes". Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=119367.

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Abstract (sommario):

Free surface vortices at low-head hydropower intakes can harm plant performance or cause premature failure of mechanical components by inducing unsteady or non-uniform flow or by entraining air, ice or floating debris down towards the turbines. Laboratory-scale physical modelling to assess vortex activity in proposed intakes is effective and remains the standard practice in industry, but it is costly and uncertainty remains as to how viscosity, turbulence and surface tension influence the translation of observed vortex characteristics from the laboratory model to the full-scale intake. Computational fluid dynamics (CFD) has been proposed as a potentially cheaper alternative without scale effects, but it requires further validation. This work sheds additional light on scale effects in laboratory-scale models and assesses the ability of a widely used commercial CFD package to predict vortex characteristics within the constraints of the hydraulic engineering context. A physical laboratory-scale model of a simplified intake is constructed with piers that produce vortices in their wake and that roughly resemble those that support trash racks at hydropower intakes. Instantaneous measurements of the three-dimensional velocity field inside the vortex are taken over a range of vortex intensities produced by eight operating conditions, with simultaneous recording of the free surface depression. The collected data are used to adapt Burgers's vortex model to link vortex characteristics (the characteristic radius, the bulk circulation, the depth and shape of the free surface depression, and the size of the largest floating particles entrained) to the operating conditions and intake geometry. The resulting model is then used to examine how viscosity, turbulence and surface tension influence vortex characteristics and their scaling behaviour. Finally, three operating conditions documented experimentally are numerically modelled using CFD with asimplified custom turbulence modelling strategy. The experimental results indicate that the axial profile of axial velocity in the vortex core, in combination with effective radial diffusivity due to viscosity and/or turbulence, plays a key role in determining the vortex characteristic radius. The magnitude of surface tension effects is shown to be relatively easily predicted and possibly far less important than scale effects associated with viscosity and turbulence. The CFD results further support the conclusion that modelling turbulence in interaction with the vortices remains one of the principal hurdles to overcome in predicting vortex characteristics at intakes in an industrial context.
La présence de tourbillons à l'amont de prises d'eau de centrales hydroélectriques à basse chute peut nuire à la performance de la centrale ou causer le bris prématuré de composants mécaniques, en provoquant des conditions d'écoulement non uniformes ou en entraînant de l'air, de la glace ou des débris flottants vers les turbines. Les modèles physiques à échelle réduite sont efficaces pour évaluer la présence de tourbillons à l'amont de prises d'eau proposées et ce mode d'évaluation demeure la pratique courante en industrie. C'est par contre une technique coûteuse et des incertitudes demeurent quant à l'influence de la viscosité, la turbulence et la tension superficielle sur le transfert des caractéristiques de tourbillons observés en modèle de laboratoire vers l'échelle de la centrale à grandeur nature. L'analyse numérique de dynamique des fluides (CFD) est souvent proposée comme alternative moins coûteuse et sans les effets d'échelle, mais le besoin d'une évaluation plus détaillée demeure. Le travail présenté ici apporte des nouvelles idées sur les effets d'échelle dans les modèles physiques à échelle réduite et évalue la capacité d'un logiciel commercial de CFD couramment utilisé pour prédire les caractéristiques de tourbillons dans les limites du contexte de génie hydraulique. Un modèle physique simplifié d'une prise d'eau à échelle réduite est construit avec des piliers provoquant un décollement qui génère des tourbillons. Ces piliers reproduisent approximativement ceux qui retiennent les grilles qui filtrent les gros débris dans les centrales hydroélectriques. Des mesures tridimensionnelles du champ de vitesse instantané sont collectées à l'intérieur des tourbillons de diverses intensités produits par huit conditions d'exploitation étudiées, avec enregistrement simultané de la dépression de la surface libre produite par le tourbillon. Les données ainsi collectées sont utilisées pour adapter le modèle de vortex de Burgers afin de lier les caractéristiques des tourbillons (le rayon caractéristique, la circulation totale, la profondeur et la forme de la dépression de la surface libre, et la dimension des plus grandes particules flottantes entraînées par le tourbillon) à la géométrie de la prise d'eau et aux conditions d'exploitation. Ce modèle adapté est ensuite utilisé pour examiner l'influence de la viscosité, de la turbulence et de la tension superficielle sur les caractéristiques des tourbillons et les lois de changement d'échelle. Enfin, trois conditions d'exploitation documentées expérimentalement sont simulées par CFD en utilisant une stratégie simplifiée de modélisation de turbulence adaptée pour cette étude. Les résultats expérimentaux indiquent que le profil de vitesse axiale le long de l'axe du du tourbillon en son centre, en combinaison avec la diffusivité radiale réelle due à la viscosité et/ou à la turbulence, a une influence déterminante sur la dimension du rayon caractéristique du tourbillon. L'amplitude des effets de tension superficielle peut être prédite relativement facilement et serait possiblement beaucoup moins importante que l'amplitude des effets d'échelle liés à la viscosité et à la turbulence. Les résultats des simulations par CFD renforcent la conclusion que la modélisation de la turbulence en interaction avec les tourbillons demeure un des obstacles principaux à surmonter afin de pouvoir prédire les caractéristiques de tourbillons aux prises d'eau dans un contexte industriel.

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47

Norgaard, Henrik, e Lars Nygaard. "Measurement and Calculation of Surface Tension of Oil, Gas and Glycol". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elkraftteknikk, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-26343.

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The importance of surface tension in separation design was evaluated in this report. Surface tension was found to have importance when calculating essentialdesign parameters, like droplet size, which is is fundamental in several vessel designoperations. Other impacts of surface tension in separation are the ability tosustain a liquid film and avoid droplet re-entrainment into the gas flow, both beingdiscussed in the report. Miscalculation of surface tension could lead to incorrectsizing of separation equipment, subsequently causing expensive fault in operationand decreased separation effect.The main objective of this thesis was to experimentally measure surface tensionwith the pendant drop technique. Although surface tension was the main task,density and solubility data were also collected and evaluated, as they too areimportant parameters in separator design. The measurements were carried outon MEG/water systems because of low availability of such data in the literature.The deviation of the surface tension measurements was calculated on the basis ofrecommendations from ISO, and the total average deviation for all mixtures wasstated to be 2.00%.The second objective was to evaluate models for the calculation of surface tensionin process simulation software. The simulation tools PRO/II, HYSYS, PVTSimand NeqSim were used for calculation. PRO/II and HYSYS use simple models thatare based on pure component values. PVTsim utilizes the well-known parachormethod when simulating hydrocarbon systems, while for MEG/water systems ituses a model based on the corresponding state theory. NeqSim uses the most complicatedand computational demanding model, the gradient theory, which is basedon thermodynamics. Some of the software have additional models implemented,but in this thesis the default models have been used.The MEG/water and hydrocarbon systems were simulated in the software, andthereafter compared against the experimental data.The results of the comparison regarding hydrocarbon systems showed two distincttendencies. Firstly, the performance of PRO/II and HYSYS was not adequate.They both were, with a few exceptions, overestimating the surface tension for allmixtures. Second, even though the performance of both PVTsim and NeqSimcould be termed satisfactory, NeqSim was superior to the estimations of PVTsimthroughout most of the experimental data. The only exception was for the ternarysystems, on which the base of surface tension data was rather insufficient.The results of the comparison regarding glycol systems showed that all softwareoverestimate the surface tension. NeqSim was once again the software with thebest accuracy, and the CPA equation of state was the overall preferred choice. Incontrast to hydrocarbon mixtures PVTsim now has a large discrepancy throughout.However, the accuracy improved drastically for the 50 wt% MEG/50 wt%water mixture. PRO/II and HYSYS performed better than they did on hydrocarbonmixtures, especially for the 100wt%MEG mixture. However, as water wasadded to the composition, PRO/II’s deviation increased substantially.

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48

Schwartz, Elliot M. (Elliot Marc). "Measurement of the surface tension of electromagnetically-levitated droplets in microgravity". Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/32164.

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Preston, Daniel J. (Daniel John). "Enhanced condensation heat transfer for water and low surface tension fluids". Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/113167.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 68-79).
Vapor condensation is routinely used as an effective means of transferring heat or separating fluids for applications ranging from personal electronic device thermal management to natural gas processing and electric power generation. Filmwise condensation, where the condensed fluid forms a liquid film, is prevalent in typical industrial-scale systems. Conversely, dropwise condensation, where the condensate forms discrete liquid droplets, results in an improvement in heat transfer performance of up to an order of magnitude compared to filmwise condensation. We explored rare earth oxides (REOs) as a potential coating to induce dropwise condensation of water; specifically, we experimentally demonstrated that the mechanism for REO hydrophobicity results from adsorption of contaminants from the atmosphere. We also used graphene, which is hydrophobic in nature, as a coating to achieve robust dropwise water condensation. With a graphene coating, we demonstrated a 4x improvement in water condensation heat transfer compared to filmwise condensation with robustness superior to state-of-the-art hydrophobic monolayer coatings. Meanwhile, low surface tension condensates pose a unique challenge since they often form a film, even on hydrophobic coatings. Lubricant infused surfaces (LIS) represent a potential solution, where a lubricant immiscible with the low surface tension condensate is infused into a rough structure on the condenser surface to repel the condensate. We developed a detailed surface-energy-based model to provide design guidelines for any arbitrary LIS system. We then characterized heat transfer coefficients during condensation of low surface tension fluids on LIS in a controlled environmental chamber for the first time, where a 5x improvement was demonstrated compared to filmwise condensation. The improved condensation heat transfer coefficients realized by LIS for low surface tension fluids and by REOs and graphene for water present opportunities for significant energy savings in device thermal management, heating and cooling, and power generation.
by Daniel John Preston.
Ph. D.

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50

Fraser, Justin. "Surface tension driven water pumping : a bio inspired passive water pump". Thesis, Stellenbosch : Stellenbosch University, 2015. http://hdl.handle.net/10019.1/97105.

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Thesis (MEng)--Stellenbosch University, 2015.
ENGLISH ABSTRACT: The purpose of this study is to construct and test a surface tension driven water pump. The surface tension driven water pump is a passive water pump which uses a similar mechanism to that of trees to pump water. This study was conducted at the Department of Mechanical and Mechatronic Engineering at the University of Stellenbosch. For the study an extensive literature survey was done encompassing aspects such as water properties, surface tension (basic principles, capillary forces, temperature and contaminant effects, wettability), bubble formation (nucleation theory and tensile strength of water) and, finally water and mineral transport in trees (plant structures and mechanisms, limiting factors, misconceptions and organic substance transport). Previous work by botanists who demonstrate the transpiration mechanism needed for water transport in trees was also considered. The study further required the development of a theoretical thermal-hydraulic model to simulate the pumping performance for the surface tension driven water pump. The developed water pump was also experimentally tested with particular focus on design improvement, pumping performance, pump behaviour, potential pumping head as well as water collection capability. The experimental data was statistically analysed by multi-linear regression. Both the experimental data and statically generated predictions were compared to the theoretical thermal-hydraulic model. The results show that a working surface tension driven pump was constructed. Evaporation rates of up to 400 mL/hr.m2 were obtained, with pumping head heights reaching up to 1.8 m and a maximum pump functional lifespan of 13 days. The results further suggest that there is a good correlation between the various statistical fits and the experimental data. The developed theoretical thermal-hydraulic model was also found to be in good agreement with the experimental results. A sensitivity analysis of the theoretical and statistical models showed that the statistical models fairs poorly under extrapolation. Additionally, the mechanistic causes of pump failure as well as the effect of heat and pumping head on water pumping performance were identified. Thereafter, the water collection efficiency was established to be 98% on average. Further testing revealed that the pumping performance of larger area or multiple grouped “leaves” are less accurately predicted with the theoretical model than a single “leaf”. In conclusion, the results provide some support that the surface tension driven pump may be used as a water transport system in an artificial photosynthesis project, if the functional lifespan of the pump can be greatly improved. It is recommended that a more rigid hydrophilic material be used in the “leaf” interface and that multiple narrower conduits be used instead of a single larger pipe. Additional future work may include the development of pit-like structures to prevent air spreading throughout the system as well as a simple mechanism for evaporative control.
AFRIKAANSE OPSOMMING: Die doel van hierdie ondersoek is om 'n oppervlakspanning-aangedrewe waterpomp te bou en te toets. Die oppervlakspanning-aangedrewe waterpomp is ‘n passiewe waterpomp wat gebruik maak van ‘n meganisme soortgelyke aan dié van bome om water te pomp. Hierdie ondersoek is by die Departement Meganiese en Megatroniese Ingenieurswese by die Universiteit van Stellenbosch uitgevoer. Vir die ondersoek is 'n uitgebreide literatuurstudie gedoen wat aspekte soos water eienskappe, oppervlakspanning (basiese beginsels, kapillêre kragte, die uitwerking van temperatuur, onsuiwerhede asook benatbaarheid), lugborrelvorming (kernvormingsteorie en die treksterkte van water) en uiteindelik water- en mineraalvervoer in bome (plantstrukture en -meganismes, beperkende faktore, wanpersepsies en die vervoer van organiese stowwe) insluit. Vorige navoring deur plantkundiges, wat die watervervoermeganismes in bome demonstreer, is ook in ag geneem. Die ondersoek het die ontwikkeling van 'n teoretiese termies-hidrouliese model ingesluit, wat gebruik is om die oppervlakspanning-aangedrewe waterpomp se werking te voorspel. Die waterpomp is ook eksperimenteel getoets met die fokus op ontwerpverbetering, pompwerkverrigting, pompwerking, potensiële pompopvoerdrukhoogte sowel as die waterversamelingsvermoë. Die eksperimentele data is statisties ontleed deur middel van meervoudige liniêre regressie. Beide die eksperimentele data en statisties-gegenereerde voorspellings is vergelyk met die teoretiese termies-hidrouliese-model. Die resultate toon dat 'n werkende oppervlakspanning-aangedrewe pomp gebou is. ‘n Verdampingstempo van tot 400 mL/hr.m2, pompopvoerdrukhoogte van tot 1.8m en 'n maksimum funksionele pompleeftyd van 13 dae is bereik. Die resultate dui verder daarop dat daar 'n goeie korrelasie tussen die verskillende statistiese lynpassings en die eksperimentele data is. Die teoretiese termies-hidrouliese-model wat ontwikkel is, toon 'n goeie ooreenkoms met die eksperimentele resultate. 'n Sensitiwiteitsanalise van die teoretiese en statistiese modelle het getoon dat die statistiese modelle swak voorspellings maak as geëkstrapoleerde data gebruik word. Verder is die meganismes wat pompweiering veroorsaak, die effek van hitte asook die effek van pompopvoerdrukhoogte op die pomp se werkverrigting geïdentifiseer. Daarna is die doeltreffendheid van waterversamelingsvermoë vir die waterpomp vasgestel op gemiddeld 98%. Verdere toetse het getoon dat die pompwerkverrigting van groter gegroepeerde "blare" minder akkuraat met die teoretiese model voorspel word as vir 'n enkele "blaar". Ten slotte: Die resultate toon dat die oppervlakspanning-aangedrewe waterpomp as 'n water vervoer stelsel gebruik kan word in 'n kunsmatige fotosinteseprojek, indien die funksionele leeftyd van die pomp verbeter kan word. Dit word aanbeveel dat 'n sterker hidrofiliese materiaal in die "blaar"-koppelvlak gebruik word en dat verskeie nouer leipype gebruik word in plaas van 'n enkele groter pyp. Bykomende toekomstige werk kan die ontwikkeling van put-agtige strukture insluit wat die verspeiding van lug deur die hele stelsel voorkom, sowel as 'n eenvoudige meganisme wat die verdampingstempo beheer.

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