Variation Of Interfacial Tension Research Articles

Analytical Study of Effects of Flow Rate, Capillarity, and Gravity on CO2/Brine Multiphase-Flow System in Horizontal Corefloods

Summary This paper presents an approximate semianalytical solution for predicting the average steady-state saturation during multiphase coreflood experiments across a wide range of capillary and gravity numbers. Recently, the influences of flow rate, gravity, and subcore heterogeneity on brine displacement efficiency have been studied with the 3D simulator TOUGH2 (Kuo et al. 2010). These studies have demonstrated that the average saturation depends on the capillary and gravity numbers in a predictable way. The purpose of this paper is to provide a simple and approximate semianalytical solution for predicting the average saturation (during two-phase coreflood experiments across a wide range of flow rates) for different average rock properties and fluid pairs. A 2D analysis of the governing equations for the multiphase-flow system at steady state is used to develop the approximate semianalytical solution. We have developed a new criterion to identify the viscous-dominated regime at the core scale. Variations of interfacial tension (IFT), core permeability, and length of the core and the effects of buoyancy, capillary, and viscous forces are all accounted for in the semianalytical solutions. We also have shown that three dimensionless numbers (NB, Ngv, Rl) and two critical gravity numbers (Ngv,c1, Ngv,c2) are required to properly capture the balance of viscous, gravity, and capillary forces. There is good agreement between the average saturations calculated from the 3D simulations and the analytical model. This new model can be used to design and interpret multiphase-flow coreflood experiments, gain better understanding of multiphase-flow displacement efficiency across a wide range of conditions and for different fluid pairs, and perhaps even provide a tool for studying the influence of subgrid-scale multiphase-flow phenomena on reservoir-scale simulations.

Stress relaxation behavior of co-continuous PS/PMMA blends after step shear strain

Stress relaxation probing on the immiscible blends is an attractive route to reveal the time-dependent morphology–viscoelasticity correlations under/after flow. However, a comprehensive understanding on the stress relaxation of co-continuous blends, especially after subjected to a shear strain, is still lacking. In this work, the stress relaxation behavior of co-continuous polystyrene/poly(methyl methacrylate) (50/50) blends with different annealing times, strain levels, and temperatures was examined under step shear strain and was correlated with the development of their morphologies. It was found that co-continuous blends display a fast relaxation process which corresponded to the relaxation of bulk polymer and a second slower relaxation process due to the recovery of co-continuous morphology. The stress relaxation rates of co-continuous blends tend to decrease due to the coarsening of instable co-continuous structure during annealing. Furthermore, the stress relaxation of the co-continuous blends is strongly affected by the change of viscosity and interfacial tension caused by the temperature. The contribution of morphological coarsening, viscosity, and interfacial tension variation on the stress relaxation behavior of co-continuous blends was discussed based on the Lee–Park model and time–temperature superposition principle, respectively.

Simultaneous influence of uni-univalent salt aqueous solutions and sodium dodecyl sulfate surfactant on interfacial tension of toluene-water

The simultaneous influence of NaCl, KCl and KI salts and well known sodium dodecyl sulfate (SDS) surfactant on the interfacial tension (IFT) of conventionally used chemical system of toluene-water was studied. The concentration range of salts was within (0.010 to 0.075) mol/dm3 and of surfactant within (1.7 to 26.0)×10−5 mol/dm3. SDS adsorption on interface is highly intensified in the presence of salts and IFT can reach to 67.1% of its initial value. Accordingly, the role of ions was investigated and the order of salts effectiveness was revealed as KI≫KCl>NaCl. The obtained data, with both effects, were nicely reproduced using an equation of state, based on Gibbs adsorption equation and the Langmuir isotherm. Two relevant important adsorption parameters exhibited reasonable variations. Furthermore, the general revealed linear variation of IFT with a previously defined “effective concentration” indicates the strong influence of the surfactant counterions.

Interfacial Tension of Methylbenzene–Water in the Presence of Hydrophilic and Hydrophobic Alumina Nanoparticles at Different Temperatures

The effect of almost low concentrations of alumina hydrophilic (bare surface) and hydrophobic (modified surface with hexadecanoic acid) nanoparticles on interfacial tension of methylbenzene (toluene)–water was investigated based on experimental results from drop weight tensiometry. Nanoparticles were suspended in either aqueous or organic phases to provide a stable nanofluid and then were contacted with another phase to measure the interfacial tension. A nanoparticle mass fraction range of 1·10–5 to 5·10–4 (± 5·10–6) and a temperature range of [293.2 to 323.2 (± 0.1)] K were used. Interesting trends of interfacial tension variation were revealed with nanoparticles concentration, showing a sharp increase up to 55.7 mN·m–1 (± 0.1 mN·m–1) at 293.2 K, and a decrease to about 14.0 mN·m–1 at 323.2 K with hydrophilic and hydrophobic forms, respectively. The effect of increasing temperature was found to reduce interfacial tension within the used ranges and significantly higher with hydrophilic nanoparticles.

Discussion of the Drop Rest Phenomenon at Millimeter Scale and Coalescence of Droplets at Micrometer Scale

Adsorption of surfactants at water-oil interfaces is of great importance in the coalescence of drops and stability of emulsions. In this work, we have studied the adsorption of nonionic surfactants Span 80 at water-oil interfaces and its influence on the drop rest phenomenon and W/O emulsion stability in a pulsed DC electrical field. The variation of interfacial tension with the concentration of surfactant was studied and the data were fitted using a surface equation of state derived from the Langmuir adsorption isotherm. A stochastic model for coalescence was used to fit the coalescence time distributions. The significance of the model parameters was discussed. The stability of the emulsion was evaluated by conductivity methods. The researches in this article indicated that both of the rest time distribution of the drops at the interface and stability of the emulsion in the electrical field was significantly affected by surfactant concentration.

Normal Stresses and Interface Displacement: Influence of Viscoelasticity on Enhanced Oil Recovery Efficiency

One of chemical Enhanced Oil Recovery (EOR) methods consists in injecting aqueous solutions of polymers into the reservoir in order to improve mobility ratio between the injected fluid and the remaining oil. This “polymer flooding” process is usually only characterized with the low shear viscosity of the injected fluid, even if these aqueous solutions are strongly shear thinning and may show high elastic properties evidenced by normal stresses appearance. In order to study the mechanisms at the interface level, we develop simple model experimentations with the goal of quantifying the influence of viscoelastic properties on fluid displacement in a simple geometry. For this purpose, we propose and characterize a model fluid formulation, for which elastic and viscous effects can be tuned systematically. We study then the displacement of a viscous oil by a Newtonian non elastic, a viscoelastic or a purely shear thinning fluid in a two dimensional flow cell. Observing the shape of the interface between aqueous fluids and displaced oil permits to appreciate viscoelasticity effects on the displacement. Using model geometries and controlled rheology fluids, we show that viscoelastic fluids tend to better displace immiscible liquids than Newtonian fluids and that those effects are closely related to the apparitions of normal stresses independently of shear thinning property or variation of interfacial tension as soon as viscous effects govern the flow.

Study on the variation of dynamic interfacial tension in the process of alkaline flooding for heavy oil

Experimental investigations have been conducted to elucidate the variation of the dynamic interfacial tension (DIFT) in the process of alkaline flooding for heavy oil. The Binnan heavy oil with high TAN (Total Acid Number) and the Zhuangxi heavy oil with low TAN were pre-equilibrated by long-term contacting with NaOH and Na2CO3 solutions. The results show that the heavy oil pre-equilibrated by NaOH solutions almost loses the interfacial activity, and the IFT increases a lot. Although there is still interfacial activity in the heavy oil which is pre-equilibrated by Na2CO3 solutions, and the dynamic interfacial tension minimum (DIFTmin) changes a little, yet the dynamic interfacial tension equilibrium value (DIFTeq) increases a lot. The effect of interfacial reaction on the interfacial property of oil with low TAN is more severe than that with high TAN. When the alkaline concentration is larger than a certain value, the IFT between the fresh oil with high TAN and the equilibrated alkaline solutions can decrease to ultralow after interfacial reaction, and the Na2CO3 system is superior to the NaOH system. However, the IFT between the fresh oil with low TAN and the equilibrated alkaline solutions increases after interfacial reaction. The above results can be used as guidance in the formulation design and mechanisms studies of alkaline flooding for improved heavy oil recovery.

A New Device for Simultaneous Measurements of Dynamic Interfacial Tension and Electrical Potential Difference

Abstract A new device for simultaneous time-resolved measurements of electromotive force (EMF) and interfacial tension (IT) at liquid–liquid interfaces is described. Two examples of applications are presented: 1) measurement of the variations in IT during simulated EMF measurements in model membrane-based ion-selective electrodes, and 2) measurements of transient changes in EMF in a system displaying IT oscillations without any chemical reaction.

Effect of uni-univalent salts on the mass transfer of isobutyric acid between cumene and water

Effect of NaCl and KCl salts on single drop hydrodynamic and mass transfer of isobutyric acid from aqueous to cumene phases was studied. Drop size, extraction fraction and mass transfer coefficient were decreased as a consequence of isobutyrate ion adsorption which is quite obvious from interfacial tension variations. Both the used salts caused similar trends in variations; however, KCl was to some extent more efficient. These were while solute equilibrium distribution coefficient was shifted toward higher values. Using the combined mass transfer model, accompanied with a derived empirical correlation exhibited a nice agreement, with relative deviation values mostly within ±13.6%.

Equilibrium interfacial tension and the influence of extreme dilutions of uni-univalent salts: An expression of the “Jones–Ray effect”

There are inevitable low levels of salt content in qualified waters which can alter accurate estimations of water interfacial tension with organic immiscible liquids. In this study, the equilibrium interfacial tension variation of extremely diluted (0.001mmol·dm−3 to 0.050mmol·dm−3) aqueous solutions of NaCl, KCl and KI, and toluene at different temperatures of (20.0 to 50.0)°C was studied. Measurements were performed by the drop-weight method. Interfacial tension becomes reduced by (0.41 to 0.86)mN·m−1 at the highest salt concentrations used and different temperatures. A linear decrease in this parameter was also observed with increasing temperature. The order of this salt effect on the interfacial tension follows: KI>KCl≈NaCl at all temperatures except 50.0°C where KCl has a stronger effect than NaCl. Assuming that inorganic ions do not penetrate the non-polar organic phase, the Petersen–Saykally model for surface tension which predicts the descending trend of variations and is based on the well-known “Jones–Ray effect” was used for modelling the data provided. Good agreement was found with three adjustable parameters for each salt and temperature.

Influence on droplet formation in the presence of nanoparticles in a microfluidic T-junction

The droplet formation in the presence of nanoparticles was studied in a T-shaped microfluidic device numerically. Nanoparticles in continuous phase did not influence droplet formation dynamics obviously. Contrarily, the presence of nanoparticles in dispersed phase will influence evidently droplet formation dynamics, the possible reason is that the accumulation of nanoparticles at the liquid-liquid interface would cause the variation of interfacial tension and the anisotropy of nanoparticles? movement at interface. Discussions on microscopic mechanism of droplet formation in the presence of nanoparticles were carried out.

Ethanol effects on binary and ternary supported lipid bilayers with gel/fluid domains and lipid rafts

Ethanol–lipid bilayer interactions have been a recurrent theme in membrane biophysics, due to their contribution to the understanding of membrane structure and dynamics. The main purpose of this study was to assess the interplay between membrane lateral heterogeneity and ethanol effects. This was achieved by in situ atomic force microscopy, following the changes induced by sequential ethanol additions on supported lipid bilayers formed in the absence of alcohol. Binary phospholipid mixtures with a single gel phase, dipalmitoylphosphatidylcholine (DPPC)/cholesterol, gel/fluid phase coexistence DPPC/dioleoylphosphatidylcholine (DOPC), and ternary lipid mixtures containing cholesterol, mimicking lipid rafts (DOPC/DPPC/cholesterol and DOPC/sphingomyelin/cholesterol), i.e., with liquid ordered/liquid disordered (ld/lo) phase separation, were investigated. For all compositions studied, and in two different solid supports, mica and silicon, domain formation or rearrangement accompanied by lipid bilayer thinning and expansion was observed. In the case of gel/fluid coexistence, low ethanol concentrations lead to a marked thinning of the fluid but not of the gel domains. In the case of ld/lo all the bilayer thins simultaneously by a similar extent. In both cases, only the more disordered phase expanded significantly, indicating that ethanol increases the proportion of disordered domains. Water/bilayer interfacial tension variation and freezing point depression, inducing acyl chain disordering (including opening and looping), tilting, and interdigitation, are probably the main cause for the observed changes. The results presented herein demonstrate that ethanol influences the bilayer properties according to membrane lateral organization.

Deformation of a hydrophobic ferrofluid droplet suspended in a viscous medium under uniform magnetic fields

The effect of applied magnetic fields on the deformation of a biocompatible hydrophobic ferrofluid drop suspended in a viscous medium is investigated numerically and compared with experimental data. A numerical formulation for the time-dependent simulation of magnetohydrodynamics of two immiscible non-conducting fluids is used with a volume-of-fluid scheme for fully deformable interfaces. Analytical formulae for ellipsoidal drops and near-spheroidal drops are reviewed and developed for code validation. At low magnetic fields, both the experimental and numerical results follow the asymptotic small deformation theory. The value of interfacial tension is deduced from an optimal fit of a numerically simulated shape with the experimentally obtained drop shape, and appears to be a constant for low applied magnetic fields. At high magnetic fields, on the other hand, experimental measurements deviate from numerical results if a constant interfacial tension is implemented. The difference can be represented as a dependence of apparent interfacial tension on the magnetic field. This idea is investigated computationally by varying the interfacial tension as a function of the applied magnetic field and by comparing the drop shapes with experimental data until a perfect match is found. This estimation method provides a consistent correlation for the variation in interfacial tension at high magnetic fields. A conclusion section provides a discussion of physical effects which may influence the microstructure and contribute to the reported observations.

Interfacial rheology as a tool to study the potential of cyclodextrin polymers to stabilize oil–water interfaces

The aim of this work is to characterize rheologically the interfacial properties of oil/water interfaces stabilized with β-cyclodextrin (CD)-based inclusion complexes. Interfacial experiments were conducted using two different hydrophobic oils: Parsol MCX and Squalene. Dilatational interfacial rheology was performed with a dynamic drop tensiometer, allowing the determination of the interfacial tension from the drop profile, and the calculation of rheological values (phase angle, elastic and viscous moduli) from the correlation between the drop area and the interfacial tension sinusoidal variations. Practically, an oil drop was formed in the aqueous phase containing the CD-derivative. With Parsol MCX, no correlation was observed, indicating that surfactants were not adsorbed at the interface. With Squalene, two β-CD-derivatives were used: monomers and polymers. With monomers, a solid membrane was created, impeding any rheological measurements. This is consistent with the crystallization of the system and the impossibility to formulate an emulsion with monomers. With polymers, an effective correlation of the drop area with the interfacial tension variation demonstrated the adsorption of the CD-complex at the interface. Rheological values clearly indicated the formation of an elastic interface, preventing droplets coalescence: an emulsion formulated with β-CD polymers results in a better stabilization.

Effect of aqueous phase pH on liquid–liquid extraction with impinging-jets contacting technique

The influence of aqueous phase pH on the rate of liquid–liquid extraction was investigated using a two impinging-jets contacting device with a high velocity of jet flows. The recommended chemical system of toluene–acetone–water was employed. Applying pH values from its natural value of 5.6–8, a range in which most industrial waters are lain, for the jets colliding force within 70.3–214.6 mN, leads a reduction in extraction efficiency and overall volumetric mass transfer coefficient up to about 18.9% and 35.2% respectively. A significant high variation is observed when the aqueous phase pH exceeds the water neutral value toward alkali conditions. These variations can be attributed to the adsorption of hydroxyl ions and lowering interfacial tension. A comparison between the results in this work and those for drop dispersion extraction indicates a high sensitivity in the impinging technique. As expected, increasing jets force improves the performance of the contacting device; however, simultaneously, the retarding effect of pH would be intensified. The variation of interfacial tension with pH was obtained and with the aid of dimensionless numbers, an empirical correlation was developed for the prediction of overall volumetric mass transfer coefficient.

Salting-out effect of NaCl on the rate of mass transfer of liquid–liquid extraction in a two impinging-jets contacting device

The effect of very low NaCl addition in the recommended liquid–liquid extraction chemical system of toluene–acetone–water was investigated using a two impinging-jets contacting device with a high velocity of jet flows. By Adding salt within the concentration range of 10 −6–10 −4 mol/L, while the pH was constant and with the jets colliding force within 70.34–214.6 mN, the extraction efficiency and overall volumetric mass transfer coefficient found enhancements to about 22.7% and 35.6% respectively. A high trend of variation is observed for the salt concentrations till only about 10 −5 mol/L. This phenomenon can be attributed to the hydration of ions which favours acetone to be transferred easier. Increasing jets force in the impingement of the streams provides a higher efficiency in the extraction process within the range used. In this regard, the variation of interfacial tension with salt concentration was investigated and using the dimensionless Weber and Eotvos numbers in accord with the conditions, an empirical correlation was developed for the prediction of extraction efficiency in the impinging-jets contacting device.

Annular Thin-Film Flows Driven by Azimuthal Variations in Interfacial Tension

We consider a thin viscous film that lines a rigid cylindrical tube and surrounds a core of in-viscid fluid, and we model the flow that is driven by a prescribed azimuthally varying tension at the core-film interface, with dimensional form σ * m ― a * cos(nθ) (where constants n e ℕ and σ* m , a * ∈ ℝ). Neglecting axial variations, we seek steady two-dimensional solutions with the full symmetries of the evolution equation. For a * = 0 (constant interfacial tension), the fully symmetric steady solution is neutrally stable and there is a continuum of steady solutions, whereas for a* ≠ 0 and n = 2, 3, 4, ..., the fully symmetric steady solution is linearly unstable. For n = 2 and n = 3, we analyse the weakly nonlinear stability of the fully symmetric steady solution, assuming that 0 0 and n = 1, 2, 3,..., the film can evolve towards a steady solution featuring a drained region. We investigate the draining dynamics using matched asymptotic methods.

Adsorption of Methane on Water under Hydrate Formation Conditions

AbstractThe variation of interfacial tension with pressure has been determined systemically for water in equilibrium with compressed methane at temperature from 274.2 to 282.2 K in the range of pressure from 0.1 to 10.1 MPa using the pendant‐drop method. The results show that the interface tension decreased with increasing pressure when temperature was specified. Pressure has a great influence upon the interface tension at higher pressure. The surface excess concentrations of methane on water at different temperatures and pressures were calculated. The results showed that higher pressure and lower temperature corresponded to higher adsorption concentration of methane. At the same time, the surface adsorption free energies of methane were also calculated, indicating that the adsorption of methane on water under hydrate formation condition is more preferable than that at 298.2 K.

A generalized correlation for predicting gas–condensate relative permeability at near wellbore conditions

It is a well established finding, both experimentally and theoretically that relative permeability ( k r) of gas–condensate systems at low interfacial tension (IFT) depends on velocity and IFT. There are a number of correlations available both in the literature and commercial reservoir simulators that account for the coupling (i.e., the increase of k r as velocity increases and/or IFT decreases) and inertial (i.e., the reduction of k r as velocity increases) effects at near wellbore conditions. These functional forms, which with the exception of Whitson et al. (Whitson, C.H., Fevang, O., Saevareid, A., Oct. 1999. Gas condensate relative permeability for well calculations, SPE 56476. Proc. of SPE Annual Technical Conference and Exhibition Texas) are based on saturation, estimate the two effects separately and include a number of parameters, which should be determined by cumbersome and expensive k r measurements at low IFT and high velocity conditions. We have previously reported the development of a fractional flow based correlation (Jamiolahmady, M., Danesh, A., Henderson, G.D. and Tehrani, D.H., Dec. 2006. Variations of gas–condensate relative permeability with production rate at near wellbore conditions: a general correlation, SPE Reserv. Eng. Evalu. J., 9 (6), pp. 688–697), which expressed the combined effect of coupling and inertia simultaneously, but its dependency on fluid viscosity limited its use to the range of IFT values studied. In this paper we present a generalized correlation based on relative-permeability-ratio, which is closely related to a fractional flow of gas and condensate. The parameters of the new correlation are either universal, applicable to all types of rocks, or can be determined from commonly measured petrophysical data. The performance of the correlation has been evaluated over a relatively wide range of IFT and velocity variations. This has been conducted by comparing its prediction with the gas–condensate relative permeability values measured on porous media with very different characteristics. These data had not been used in developing the correlation. The results are quite satisfactory confirming the generality of the correlation in providing reliable information on gas–condensate relative permeability values for near wellbore conditions.

Determination of Dynamic Interfacial Tension and Its Effect on Droplet Formation in the T-Shaped Microdispersion Process

Interfacial tension is an important physical property affecting the droplet formation process in microfluidic devices. This work presents the variation of dynamic interfacial tension caused by slow adsorption of surfactant, as well as its influence on the liquid/liquid microdispersion process in a T-shaped microchannel. Using hexane/water-Tween 20 as the working system, it was observed that the droplet size changed with the variation of surfactant concentration when the concentration of Tween 20 was lower than 10 mmol/L, but hardly changed at higher concentrations, which was caused by the unsaturated adsorption and saturated adsorption of surfactant, respectively. The saturated interfacial tension was measured with an interfacial tension meter, and the relationship between the interfacial tension and the droplet diameter was established. Accordingly, the dynamic interfacial tension with unsaturated adsorption of surfactant was determined. The main factors affecting the dynamic interfacial tension were discussed, and a semiempirical equation was established to characterize those effects.