Showing papers on "Surface tension published in 2013"

3D Printing of Free Standing Liquid Metal Microstructures

Abstract: This paper describes a method to direct-write 3D liquid metal microcomponents at room temperature. The thin oxide layer on the surface of the metal allows the formation of mechanically stable structures strong enough to stand against gravity and the large surface tension of the liquid. The method is capable of printing wires, arrays of spheres, arches, and interconnects.

Adsorption and the Gibbs Surface Excess

Abstract: 1: Introduction.- 1.1. Adsorption from Solution.- 1.2. Nature of the Interface.- 1.3. Nature of the Adsorbate.- 1.4. Nature of the Bulk Phase.- 1.5. Thermodynamics of the Bulk Phase.- 1.6. Partial Molal Quantities.- 1.7. Gas or Vapor Phase.- 1.8. Binary Solution of a Liquid.- 1.9. Activity Coefficient of an Electrolyte.- 1.10. Standard Free Energy Change of a Chemical Reaction.- 1.11. Solute Distribution between Two Insoluble Liquid Phases.- 1.12. The Surface Energy.- 1.13. Surface Tension and Mechanical Equilibrium.- 1.14. Surface Free Energy.- 2: Experimental Methods and Procedures.- 2.1. Introduction.- 2.2. Measurement of Boundary Tension.- 2.3. Surface Pressure of Insoluble Film.- 2.4. Equilibrium Spreading Pressure.- 2.5. Measurement of Contact Angle.- 2.6. Adsorption by Powdered Solid from Binary Solution.- 2.7. Direct Analysis of Adsorption at the Liquid Interface.- 2.8. Water Vapor Adsorption by Biopolymers.- 2.9. Detergent-Biopolymer Binding from Equilibrium Dialysis.- 3: Adsorption at Liquid Interfaces and the Gibbs Equation.- 3.1. Introduction.- 3.2. Adsorption at Liquid Interfaces.- 3.3. The Interfacial Phase.- 3.4. Physical Model for the Surface Phase.- 3.5. The Bulk Phases.- 3.6. The Gibbs Adsorption Equation.- 3.7. Relative Surfaces Excesses.- 3.8. Total Concentration and Surface Excess.- 3.9. Adsorption and Surface Excess.- 3.10. Absolute Composition of the Interfacial Phase.- 3.11. Binary Mixture of Liquids.- 3.12. Monolayer Model.- 3.13. Boundary Tension of Solutions of Inorganic Electrolytes.- 3.14. Negative Adsorption of an Electrolyte.- 3.15. Discussion on the Derivation of the Gibbs Equation.- 3.16. Alternative Treatment for the Adsorption Equation.- 3.17. Surface Activity Coefficients.- 3.18. Summary and Comments.- 4: Adsorption at the Liquid Interface from the Multicomponent Solution.- 4.1. Introduction.- 4.2. Surface Excess for Multicomponent Solutions.- 4.3. Gibbs Equation for the Mixture of Nonelectrolytes.- 4.4. Solution of Organic Electrolytes and the Electrical Double Layer.- 4.5. Electroneutrality in the Interfacial Phase.- 4.6. Gibbs Equation for Electrolyte Adsorption.- 4.7. The Helmholtz Double Layer.- 4.8. Helmholtz Model and the Gibbs Adsorption Equation.- 4.9. Gouy-Chapman Double Layer.- 4.10. Gouy Model and the Gibbs Adsorption Equation.- 4.11. Debye-Huckel Theory and the Gibbs Adsorption Equation.- 4.12. Experimental Values of the Coefficient m.- 4.13. Stern Model of the Double Layer.- 4.14. Gibbs Equations for More Than Two Electrolyte Components.- 4.15. Gibbs Equations for Miscellaneous Types of Experimental Procedures.- 4.16. Surface Excesses for Small Cations and Anions.- 4.17. Coadsorption of Organic Ions.- 4.18. Summary and Comments.- 5: Adsorbed Monolayers and Energies of Adsorption.- 5.1. Introduction.- 5.2. Adsorbed and Spread Monolayers.- 5.3. Ideal Equation of State.- 5.4. Neutral Monolayers at the Oil-Water Interface.- 5.5. Surface Pressure and Osmotic Pressure.- 5.6. Binary Solution at the Interfacial Phase.- 5.7. Ionized Monolayers at the Oil-Water Interface.- 5.8. The Electrical Pressure and the Gouy Model.- 5.9. The Discrete-Ion Effect.- 5.10. Counterion Binding.- 5.11. Discussion on the Computation of ?e.- 5.12. Electrical Double Layer and Electrical Free Energy.- 5.13. Equation of State at the Air-Water Interface.- 5.14. Free Energies of Adsorption at the Liquid Interface.- 5.15. Generalized Form of the Surface Equation of State.- 5.16. Summary and Comments.- 6: Spread Monolayer.- 6.1. Introduction.- 6.2. States of Monomolecular Films.- 6.3. Equation of State for Monomolecular Films.- 6.4. Thermodynamics of Spread Monolayers.- 6.5. Surface Activity Coefficient.- 6.6. Protein and Polymer Films.- 6.7. Rigorous Equations of State for Polymer Films.- 6.8. Virial Equation of State for Two-Dimensional Polymer Films.- 6.9. Charged Monolayers of Amphiphiles and Biopolymers.- 6.10. Helmholtz Free Energy for Protein Monolayers.- 6.11. Analysis of Protein Unfolding at Interfaces.- 6.12. Monolayers of Synthetic Polyamino Acids.- 6.13. Monolayers at the Oil-Water Interface.- 6.14. Phase Rule for Two-Dimensional Films.- 6.15. Lipid Phase Transition in Monolayers.- 6.16. Mixed Monolayers.- 6.17. Miscibility in Mixed Monolayers.- 6.18. Lipid-Protein Monolayers (A Membrane Model System).- 6.19. The Insoluble Monolayer and the Gibbs Surface Excess.- 6.20. Summary and Comments.- 7: Wettability and Contact Angles.- 7.1. Introduction.- 7.2. Surface Tension of a Solid and the Contact Angle.- 7.3. Molecular Interpretation of Interfacial Tension.- 7.4. Liquid-Liquid Interfacial Tension.- 7.5. Solid-Liquid Contact Angle.- 7.6. Estimation of the Polar Forces at Solid-Liquid Interfaces.- 7.7. Liquid1-Solid-Liquid2 System.- 7.8. Contact Angle Hysteresis.- 7.9. Contact Angles and Heats of Immersion.- 7.10. Role of Polar Solid Surface Tension and Cell Adhesion.- 7.11. Summary and Comments.- 8: Adsorption at Solid-Liquid Interfaces.- 8.1. Introduction.- 8.2. Positive and Negative Excesses.- 8.3. Adsorption from a Binary Liquid Mixture by a Rigid Solid.- 8.4. Apparent Excess and the Gibbs Excess.- 8.5. Adsorption Azeotrope and Monolayer Adsorption.- 8.6. Adsorption and Adsorption Isotherm.- 8.7. Surface Activity Coefficient at the Solid-Liquid Interface.- 8.8. Adsorption from Dilute Solution.- 8.9. Langmuir Adsorption Isotherm.- 8.10. Adsorption of Inorganic Ions and Organic Dyes.- 8.11. Adsorption of Ionic Detergents.- 8.12. Adsorption of Nonionic Polymers.- 8.13. Adsorption of Biopolymers at the Solid-Liquid Interface.- 8.14. Standard Free Energy of Adsorption.- 8.15. Surface Heterogeneities.- 8.16. Summary and Comments.- 9: Adsorption of Water Vapor by Biopolymers.- 9.1. Introduction.- 9.2. Interaction of Protein with Water Molecules at Low Relative Humidity.- 9.3. Water-Protein Interaction at High Relative Humidity.- 9.4. Water Activity and Protein Hydration.- 9.5. Water-Protein Interaction and Free Energy Change.- 9.6. Interfacial Energy of Biocolloid-Water Interface.- 9.7. One-Phase Model for Protein Gel.- 9.8. Enthalpy Change for Protein Hydration.- 9.9. Water-Protein Interactions in the Presence of Electrolyte and Neutral Solute.- 9.10. Excess Binding.- 9.11. Osmotic Corrections.- 9.12. Free Energy of Excess Binding (Two-Phase Model).- 9.13. Free Energy of Excess Hydration (One-Phase Model).- 9.14. Stability of Protein in Contact with Water.- 9.15. Stability of Protein in Salt Solution.- 9.16. Thermodynamic Aspects of DNA Hydration.- 9.17. Binding of Water and Solute to DNA.- 9.18. Summary and Comments.- 10: Binding Interactions in Biological Systems.- 10.1. Introduction.- 10.2. Gibbs-Duhem Equation and Excess Binding.- 10.3. Free Energy Change due to Excess Binding Interaction.- 10.4. The Scatchard Equation.- 10.5. Entropy and Enthalpy Changes due to Excess Binding.- 10.6. DNA-Solute Binding Interaction.- 10.7. Hydrophobic Effect in DNA-Amine Binding Interaction.- 10.8. Histone-DNA Binding Interaction.- 10.9. Protein-Ligand Binding Interaction.- 10.10. Standard Free Energy Change for Protein-Ligand Binding Interaction.- 10.11. Binding of Ligand to Protein-Protein and Fat-Protein Mixtures.- 10.12. Negative Binding of Inorganic Electrolytes to a Protein.- 10.13. Free Energy of Excess Hydration.- 10.14. Evaluation of ?G, ?n1 and ?n2.- 10.15. Standard Free Energy Change for Excess Hydration.- 10.16. Free Energy of Cooperative Binding and Transduction.- 10.17. Protein-Detergent Complexes.- 10.18. Hydrophobic Character of Protein-Detergent Complexes.- 10.19. Summary and Comments.- 11: Miscellaneous Systems.- 11.1. Introduction.- 11.2. Colloidal Micelles.- 11.3. Excess Hydration of Powdered Detergents.- 11.4. Adsorption of Inorganic Electrolytes at Solid-Water Interfaces.- 11.5. Gas Adsorption at Solid and Liquid Interfaces.- 11.6. Statistical Models and the Surface Tension.- 11.7. The Electrocapillary System.- 11.8. Size and Stability of Microemulsion.- 11.9. Adsorption and Nonequilibrium States.- 11.10. Protein-Water Interfacial Tension.- 11.11. Pressure Coefficient of Surface Tension.- 11.12. Concluding Remarks.- References.- Author Index.

Effect of Capillary Pressure on Phase Behavior in Tight Rocks and Shales

Abstract: Phase behavior is important in the calculation of hydrocarbons in place and in the flow of phases through the rocks. Pore sizes can be on the order of nanometers for shale and tight-rock formations. Such small pores can affect the phase behavior of in-situ oil and gas because of increased capillary pressure. Not accounting for increased capillary pressure in small pores can lead to inaccurate estimates of ultimate recovery, and of saturation pressures. In this paper, capillary pressure is coupled with phase equilibrium equations, and the resulting system of nonlinear fugacity equations is solved to present a comprehensive examination of the effect of small pores on saturation pressures and fluid densities. Binary mixtures of methane with heavier hydrocarbons and a real reservoir fluid from the Bakken shale are considered. The results show that accounting for the impact of small pore throats on pressure/volume/temperature (PVT) properties explains the inconsistent gas/oil-ratio (GOR) behavior, high flowing bottomhole pressures, and low gas-flow rate observed in the tight Bakken formation. The small pores decrease bubble-point pressures and either decrease or increase dew-point pressures, depending on which part of the two-phase envelope is examined. Large capillary pressure also decreases the oil density in situ, which affects the oil formation volume factor and ultimate reserves calculations. A good history match for wells in the middle Bakken formation is obtained only after considering a suppressed bubblepoint pressure. The results show that the change in saturation pressures, fluid densities, and viscosities is highly dependent on the values of interfacial tension (IFT) (capillary pressure) used in the calculations.

Surface tension and contact with soft elastic solids

Abstract: Solid contacts on a microscopic level are widely described by a classical contact mechanics theory. Here Style et al. show that this theory breaks down when a small particle adheres to a soft surface where a fluid-like behaviour is observed because of the predominant role played by surface tension.

Wettability of Supercritical Carbon Dioxide/Water/Quartz Systems: Simultaneous Measurement of Contact Angle and Interfacial Tension at Reservoir Conditions

Abstract: Injection of carbon dioxide in deep saline aquifers is considered as a method of carbon sequestration. The efficiency of this process is dependent on the fluid-fluid and rock-fluid interactions inside the porous media. For instance, the final storage capacity and total amount of capillary-trapped CO2 inside an aquifer are affected by the interfacial tension between the fluids and the contact angle between the fluids and the rock mineral surface. A thorough study of these parameters and their variations with temperature and pressure will provide a better understanding of the carbon sequestration process and thus improve predictions of the sequestration efficiency. In this study, the controversial concept of wettability alteration of quartz surfaces in the presence of supercritical carbon dioxide (sc-CO2) was investigated. A novel apparatus for measuring interfacial tension and contact angle at high temperatures and pressures based on Axisymmetric Drop Shape Analysis with no-Apex (ADSA-NA) method was developed and validated with a simple system. Densities, interfacial tensions, and dynamic contact angles of CO2/water/quartz systems were determined for a wide range of pressures and temperatures relevant to geological sequestration of CO2 in the subcritical and supercritical states. Image analysis was performed with ADSA-NA method that allows the determination of both interfacial tensions and contact angles with high accuracy. The results show that supercritical CO2 alters the wettability of quartz surface toward less water-wet conditions compared to subcritical CO2. Also we observed an increase in the water advancing contact angles with increasing temperature indicating less water-wet quartz surfaces at higher temperatures.

Interfacial rheology of asphaltenes at oil-water interfaces and interpretation of the equation of state.

Abstract: In an earlier study,(1) oil–water interfacial tension was measured by the pendant drop technique for a range of oil-phase asphaltene concentrations and viscosities. The interfacial tension was found to be related to the relative surface coverage during droplet expansion. The relationship was independent of aging time and bulk asphaltenes concentration, suggesting that cross-linking did not occur at the interface and that only asphaltene monomers were adsorbed. The present study extends this work to measurements of interfacial rheology with the same fluids. Dilatation moduli have been measured using the pulsating droplet technique at different frequencies, different concentrations (below and above CNAC), and different aging times. Care was taken to apply the technique in conditions where viscous and inertial effects are small. The elastic modulus increases with frequency and then plateaus to an asymptotic value. The asymptotic or instantaneous elasticity has been plotted against the interfacial tension, in...

Recovery of nonwetting characteristics by surface modification of gallium-based liquid metal droplets using hydrochloric acid vapor.

Abstract: The applicability of gallium-based liquid metal alloy has been limited by the oxidation problem. In this paper, we report a simple method to remove the oxide layer on the surface of such alloy to recover its nonwetting characteristics, using hydrochloric acid (HCl) vapor. Through the HCl vapor treatment, we successfully restored the nonwetting characteristics of the alloy and suppressed its viscoelasticity. We analyzed the change of surface chemistry before and after the HCl vapor treatment using X-ray photoelectron spectroscopy (XPS) and low-energy ion-scattering spectroscopy (LEIS). Results showed that the oxidized surface of the commercial gallium-based alloy Galinstan (Ga2O3 and Ga2O) was replaced with InCl3 and GaCl3 after the treatment. Surface tension and static contact angle on a Teflon-coated glass of the HCl-vapor-treated Galinstan were measured to be 523.8 mN/m and 152.5°. A droplet bouncing test was successfully carried out to demonstrate the nonwetting characteristics of the HCl-vapor-treated...

A coherent picture of water at extreme negative pressure

Abstract: Liquid water at atmospheric pressure can be supercooled to 41 C (ref. 1) and superheated to C302 C (ref. 2). Experiments involving fluid inclusions of water in quartz suggest that water is capable of sustaining pressures as low as 140 MPa before it breaks by cavitation3. Other techniques, for which cavitation occurs consistently at around 30MPa (ref. 4), produce results that cast doubt on this claim. Here we reproduce the fluid-inclusion experiment, performing repeated measurements on a single sample--a method used in meteorology5, bioprotection6 and protein crystallization7, but not yet in liquid water under large mechanical tension. The resulting cavitation statistics are characteristic of a thermally activated process, and both the free energy and the volume of the critical bubble are well described by classical nucleation theory when the surface tension is reduced by less than 10%, consistent with homogeneous cavitation. The line of density maxima of water at negative pressure is found to reach 922:8 kgm3 at around 300 K, which further constrains its contested phase diagram.

On the transition between two-phase and single-phase interface dynamics in multicomponent fluids at supercritical pressures

Abstract: A theory that explains the operating pressures where liquid injection processes transition from exhibiting classical two-phase spray atomization phenomena to single-phase diffusion-dominated mixing is presented. Imaging from a variety of experiments have long shown that under certain conditions, typically when the pressure of the working fluid exceeds the thermodynamic critical pressure of the liquid phase, the presence of discrete two-phase flow processes become diminished. Instead, the classical gas-liquid interface is replaced by diffusion-dominated mixing. When and how this transition occurs, however, is not well understood. Modern theory still lacks a physically based model to quantify this transition and the precise mechanisms that lead to it. In this paper, we derive a new model that explains how the transition occurs in multicomponent fluids and present a detailed analysis to quantify it. The model applies a detailed property evaluation scheme based on a modified 32-term Benedict-Webb-Rubin equation of state that accounts for the relevant real-fluid thermodynamic and transport properties of the multicomponent system. This framework is combined with Linear Gradient Theory, which describes the detailed molecular structure of the vapor-liquid interface region. Our analysis reveals that the two-phase interface breaks down not necessarily due to vanishing surface tension forces, but due to thickened interfaces at high subcritical temperatures coupled with an inherent reduction of the mean free molecular path. At a certain point, the combination of reduced surface tension, the thicker interface, and reduced mean free molecular path enter the continuum length scale regime. When this occurs, inter-molecular forces approach that of the multicomponent continuum where transport processes dominate across the interfacial region. This leads to a continuous phase transition from compressed liquid to supercritical mixture states. Based on this theory, a regime diagram for liquid injection is developed that quantifies the conditions under which classical sprays transition to dense-fluid jets. It is shown that the chamber pressure required to support diffusion-dominated mixing dynamics depends on the composition and temperature of the injected liquid and ambient gas. To illustrate the method and analysis, we use conditions typical of diesel engine injection. We also present a companion set of high-speed images to provide experimental validation of the presented theory. The basic theory is quite general and applies to a wide range of modern propulsion and power systems such as liquid rockets, gas turbines, and reciprocating engines. Interestingly, the regime diagram associated with diesel engine injection suggests that classical spray phenomena at typical injection conditions do not occur.

Versatile surface tension and adhesion for SPH fluids

Abstract: Realistic handling of fluid-air and fluid-solid interfaces in SPH is a challenging problem. The main reason is that some important physical phenomena such as surface tension and adhesion emerge as a result of inter-molecular forces in a microscopic scale. This is different from scalar fields such as fluid pressure, which can be plausibly evaluated on a macroscopic scale using particles. Although there exist techniques to address this problem for some specific simulation scenarios, there does not yet exist a general approach to reproduce the variety of effects that emerge in reality from fluid-air and fluid-solid interactions. In order to address this problem, we present a new surface tension force and a new adhesion force. Different from the existing work, our surface tension force can handle large surface tensions in a realistic way. This property lets our approach handle challenging real scenarios, such as water crown formation, various types of fluid-solid interactions, and even droplet simulations. Furthermore, it prevents particle clustering at the free surface where inter-particle pressure forces are incorrect. Our adhesion force allows plausible two-way attraction of fluids and solids and can be used to model different wetting conditions. By using our forces, modeling surface tension and adhesion effects do not require involved techniques such as generating a ghost air phase or surface tracking. The forces are applied to the neighboring fluid-fluid and fluid-boundary particle pairs in a symmetric way, which satisfies momentum conservation. We demonstrate that combining both forces allows simulating a variety of interesting effects in a plausible way.

Superphobicity/philicity Janus Fabrics with Switchable, Spontaneous, Directional Transport Ability to Water and Oil Fluids

Abstract: Herein we demonstrate that switchable, spontaneous, directional-transport ability to both water and oil fluids can be created on fabric materials through wet-chemistry coating and successive UV irradiation treatment. When the fabric showed directional transport to a liquid, it prevented liquids of higher surface tension from penetration, but allowed liquids of lower surface tension to permeate, from either side. The directional transport ability can be switched from one fluid to another simply by heating the fabric at an elevated temperature and then re-irradiating the fabric with UV light for required period of time. By attaching liquid drops vertically upwards to a horizontally-laid fabric, we further demonstrated that this novel directional fluid transport was an automatic process driven by surface property alone, irrespective of gravity's effect. This novel fabric may be useful for development of “smart” textiles and functional membranes for various applications.

Mechanically robust superamphiphobic aluminum surface with nanopore-embedded microtexture.

Abstract: A simple fabrication technique was developed for preparing a mechanically robust superamphiphobic surface on an aluminum (Al) plate. Dual geometric architectures with micro- and nanoscale structures were formed on the surface of the Al plate by a combination of simple chemical etching and anodization. This proposed methodology involves (1) fabrication of irregular microscale plateaus on the surface of the Al plate, (2) formation of nanopores, and (3) fluorination. Wettability measurements indicated that the fabricated Al surface became super-repellent toward a broad range of liquids with surface tension in the range 27.5–72 mN/m. By varying the anodization time, we measured and compared the effects of morphological change on the wettability. The adhesion property and mechanical durability of the fabricated superamphiphobic Al surface were evaluated by the Scotch tape and hardness tests, respectively. The results showed that the fabricated Al surface retained mechanical robustness because the down-directed...

Tensile testing of ultra-thin films on water surface

Abstract: The surface of water provides an excellent environment for gliding movement, in both nature and modern technology, from surface living animals such as the water strider, to Langmuir–Blodgett films. The high surface tension of water keeps the contacting objects afloat, and its low viscosity enables almost frictionless sliding on the surface. Here we utilize the water surface as a nearly ideal underlying support for free-standing ultra-thin films and develop a novel tensile testing method for the precise measurement of mechanical properties of the films. In this method, namely, the pseudo free-standing tensile test, all specimen preparation and testing procedures are performed on the water surface, resulting in easy handling and almost frictionless sliding without specimen damage or substrate effects. We further utilize van der Waals adhesion for the damage-free gripping of an ultra-thin film specimen. Our approach can potentially be used to explore the mechanical properties of emerging two-dimensional materials. The mechanical testing of thin films is non-trivial, due to their very fine dimensions. Kim et al. use the inherent surface tension of water as a platform for the frictionless tensile testing of gold films, with a thickness as fine as 55 nm.

Almost Exponential Decay of Periodic Viscous Surface Waves without Surface Tension

Abstract: We consider a viscous fluid of finite depth below the air, occupying a three-dimensional domain bounded below by a fixed solid boundary and above by a free moving boundary. The fluid dynamics are governed by the gravity-driven incompressible Navier–Stokes equations, and the effect of surface tension is neglected on the free surface. The long time behavior of solutions near equilibrium has been an intriguing question since the work of Beale (Commun Pure Appl Math 34(3):359–392, 1981). This paper is the third in a series of three (Guo in Local well-posedness of the viscous surface wave problem without surface tension, Anal PDE 2012, to appear; in Decay of viscous surface waves without surface tension in horizontally infinite domains, Preprint, 2011) that answers this question. Here we consider the case in which the free interface is horizontally periodic; we prove that the problem is globally well-posed and that solutions decay to equilibrium at an almost exponential rate. In particular, the free interface decays to a flat surface. Our framework contains several novel techniques, which include: (1) a priori estimates that utilize a “geometric” reformulation of the equations; (2) a two-tier energy method that couples the boundedness of high-order energy to the decay of low-order energy, the latter of which is necessary to balance out the growth of the highest derivatives of the free interface; (3) a localization procedure that is compatible with the energy method and allows for curved lower surface geometry. Our decay estimates lead to the construction of global-in-time solutions to the surface wave problem.

Robust superamphiphobic film from electrospun TiO2 nanostructures.

Abstract: Rice-shaped TiO2 nanostructures are fabricated by electrospinning for creating a robust superamphiphobic coating on glass substrates. The as-fabricated TiO2 nanostructures (sintered at 500 °C) are superhydrophilic in nature which upon silanization turn into superamphiphobic surface with surface contact angle (SCA) values achieved using water (surface tension, γ = 72.1 mN/m) and hexadecane (surface tension, γ = 27.5 mN/m) being 166° and 138.5°, respectively. The contact angle hysteresis for the droplet of water and hexadecane are measured to be 2 and 12°, respectively. Thus, we have successfully fabricated superior self-cleaning coatings that possess exceptional superamphiphobic property by employing a simple, cost-effective, and scalable technique called electrospinning. Furthermore, the coating showed good mechanical and thermal stability with strong adherence to glass surface, thus revealing the potential for real applications.

Understanding high-pressure gas-liquid interface phenomena in Diesel engines

Abstract: Injection of liquid fuel (or oxidizer in the case of liquid rockets) in systems where the working fluid exceeds the thermodynamic critical condition of the liquid phase is not well understood. Under some conditions when operating pressures exceed the liquid phase critical pressure, surface tension forces become diminished so that the classical low-pressure gas-liquid interface is replaced by a diffusion dominated mixing layer. These two extremes have been well recognized in the liquid rocket community for years. In other systems, however, the significance of surface tension forces is not clear. Here we focus on this topic in the context of Diesel engine fuel injection processes. We derive a coupled model to obtain a theoretical analysis that quantifies under what conditions the interfacial dynamics transition between the classical non-continuum “jump” conditions associated with two phase flows and a continuous gas-liquid interfacial diffusion layer. We present high-speed imaging from the Sandia non-reacting n-dodecane experiment that provides corroborating evidence that continuous gas-liquid interfacial mixing dynamics occur at high-pressure Diesel engine conditions. At constant chamber density and supercritical fuel pressures, liquid structures affected by surface tension such as ligaments and drops develop at low ambient temperatures. But at engine-relevant high-temperature conditions, a different, more diffusive mixture preparation process without measurable fuel drops is found. These two conditions are studied using our model. It applies a real-fluid model that accounts for the relevant thermodynamic non-ideal multicomponent mixture states in the system and combines this with Linear Gradient Theory, which facilitates the calculation of the detailed vapor–liquid interfacial structure. At high ambient temperature, our model shows interfaces with substantially increased thicknesses in comparison to the low temperature condition. Our analysis reveals that gas-liquid interfacial diffusion layers develop, contrary to conventional wisdom, not necessarily because of vanishing surface tension forces, but because of the combination of a reduction in mean free molecular path and broadening interfaces, which then enter the continuum length scale regime. Then, instead of inter-molecular forces, transport processes dominate.

Temperature and Composition Effect on CO2 Miscibility by Interfacial Tension Measurement

Abstract: Crude oil reservoirs have different temperatures, compositions, and pressures, therefore oil recovery performance by CO2 injection varies from one case to another. Furthermore, it is predicted that lower interfacial tension between injected CO2 and reservoir fluid results in more oil recovery. In this study, we investigate the effect of temperature on the equilibrium interfacial tension between CO2 and three different oil fluids at different pressures. Also minimum miscible pressure (MMP) is measured by the vanishing interfacial tension (VIT) technique to determine the temperature effect on the CO2 miscible gas injection. The results on different pure and mixtures of hydrocarbon fluids show that for pressures up to 5.2 MPa, the higher the temperature was, the lower was the interfacial tension (IFT) measured. However, for the cases with pressure higher than 5.2 MPa, as the temperature was increased, the IFT increased too. In addition the VIT technique is used to measure the MMP of CO2 and pure paraffin; th...

Solid surface tension measured by a liquid drop under a solid film

Abstract: We show that a drop of liquid a few hundred microns in diameter placed under a solid, elastic, thin film (∼10 μm thick) causes it to bulge by tens of microns. The deformed shape is governed by equilibrium of tensions exerted by the various interfaces and the solid film, a form of Neumann’s triangle. Unlike Young’s equation, which specifies the contact angles at the junction of two fluids and a (rigid) solid, and is fundamentally underdetermined, both tensions in the solid film can be determined here if the liquid–vapor surface tension is known independently. Tensions in the solid film have a contribution from elastic stretch and a constant residual component. The residual component, extracted by extrapolation to films of vanishing thickness and supported by analysis of the elastic deformation, is interpreted as the solid–fluid surface tension, demonstrating that compliant thin-film structures can be used to measure solid surface tensions.

Achieving tunable surface tension in the pseudopotential lattice Boltzmann modeling of multiphase flows

Abstract: In this paper, we aim to address an important issue about the pseudopotential lattice Boltzmann (LB) model, which has attracted much attention as a mesoscopic model for simulating interfacial dynamics of complex fluids, but suffers from the problem that the surface tension cannot be tuned independently of the density ratio. In the literature, a multirange potential was devised to adjust the surface tension [Sbragaglia et al., Phys. Rev. E 75, 026702 (2007)]. However, it was recently found that the density ratio of the system will be changed when the multirange potential is employed to adjust the surface tension. An alternative approach is therefore proposed in the present work. The basic strategy is to add a source term to the LB equation so as to tune the surface tension of the pseudopotential LB model. The proposed approach can guarantee that the adjustment of the surface tension does not affect the mechanical stability condition of the pseudopotential LB model, and thus provides a separate control of the surface tension and the density ratio. Meanwhile, it still retains the mesoscopic feature and the computational simplicity of the pseudopotential LB model. Numerical simulations are carried out for stationary droplets, capillary waves, and droplet splashing on a thin liquid film. The numerical results demonstrate that the proposed approach is capable of achieving a tunable surface tension over a very wide range and can keep the density ratio unchanged when adjusting the surface tension.

Local well-posedness of the viscous surface wave problem without surface tension

Abstract: We consider a viscous fluid of finite depth below the air, occupying a three-dimensional domain bounded below by a fixed solid boundary and above by a free moving boundary. The domain is allowed to have a horizontal cross-section that is either periodic or infinite in extent. The fluid dynamics are governed by the gravity-driven incompressible Navier–Stokes equations, and the effect of surface tension is neglected on the free surface. This paper is the first in a series of three on the global well-posedness and decay of the viscous surface wave problem without surface tension. Here we develop a local well-posedness theory for the equations in the framework of the nonlinear energy method, which is based on the natural energy structure of the problem. Our proof involves several novel techniques, including: energy estimates in a “geometric” reformulation of the equations, a well-posedness theory of the linearized Navier–Stokes equations in moving domains, and a time-dependent functional framework, which couples to a Galerkin method with a time-dependent basis.

Dynamic properties of mixed nanoparticle/surfactant adsorption layers

Abstract: The adsorption films of silica nanoparticles modified by a cationic surfactant (cetyltrimethylammonium bromide, CTAB) at the air–water interface were investigated by the dilational surface rheology and optical methods. Special attention was paid to the slow changes of surface properties with the surface age. The surface tension and dynamic dilational surface elasticity were measured as a function of CTAB concentration. The whole surfactant concentration range can be divided into four regions characterized by different surface rheological behavior. Depending on the CTAB concentration, the surface elasticity close to the equilibrium may reach extremely high values (∼1000 mN m−1) and strongly depends on the applied surface strain. This occurs at surfactant concentrations below the region where the dispersion becomes turbid, indicating particle aggregation in the bulk. The Brewster angle microscopy and ellipsometry show that the adsorption layer becomes fragile and inhomogeneous in this region.

Surfactant Adsorption and Interfacial Tension Investigations on Cyclopentane Hydrate

Abstract: Gas hydrates represent an unconventional methane resource and a production/safety risk to traditional oil and gas flowlines. In both systems, hydrate may share interfaces with both aqueous and hydrocarbon fluids. To accurately model macroscopic properties, such as relative permeability in unconventional systems or dispersion viscosity in traditional systems, knowledge of hydrate interfacial properties is required. This work presents hydrate cohesive force results measured on a micromechanical force apparatus, and complementary water–hydrocarbon interfacial tension data. By combining a revised cohesive force model with experimental data, two interfacial properties of cyclopentane hydrate were estimated: hydrate–water and hydrate–cyclopentane interfacial tension values at 0.32 ± 0.05 mN/m and 47 ± 5 mN/m, respectively. These fundamental physiochemical properties have not been estimated or measured for cyclopentane hydrate to date. The addition of surfactants in the cyclopentane phase significantly reduced t...