Interfacial Tension Coefficient Research Articles

ACOUSTIC RADIATION OF CHARGED DROPLETS OSCILLATING IN THE SUPERPOSITION OF GRAVITATIONAL AND ELECTROSTATIC FIELDS

The intensity of acoustic radiation and the characteristic widths (depending on the radii and charges of the drops) of the frequency ranges in which the radiation falls have been calculated for charged droplets of convective clouds and near-ground fogs, which are immobile in the superposition of gravitational and electric fields. The calculations have been carried out using the methods of classical mathematical physics taking into account two small parameters: the dimensionless oscillation amplitude and the equilibrium spheroidal deformation of a charged droplet in an external electrostatic field. All calculations have been performed using the model of an ideal incompressible electroconducting liquid. It has turned out that the acoustic radiation from clouds and fogs occurs in the ultrasonic frequency range, while the acoustic radiation of large rain-drops is in the acoustic range audible to the human ear. The boundary between the ultrasonic and sonic radiations is determined by droplet sizes, electric field strengths (in a small vicinity of the droplets), and the values of interfacial tension coefficient.

Open-source finite volume solvers for multiphase (n-phase) flows involving either Newtonian or non-Newtonian complex fluids

Two new control volume solvers multiFluidInterFoam and rheoMultiFluidInterFoam are presented for the simulation of Newtonian and non-Newtonian n-phase flows (n≥2), respectively, fully accounting for interfacial tension and contact-angle effects for each phase. The multiFluidInterFoam solver modifies certain crucial aspects of the regular multiphaseInterFoam solver provided by OpenFOAM for Newtonian flows, improving its efficiency and robustness, but most importantly improving considerably its accuracy for surface tension driven flows. The new solver uses the volume-of-fluid (VOF) method based on the MULES method and artificial interface compression for the interface capturing, in combination with a suitable continuum surface force model; i.e. the interfacial tension coefficient decomposition method is employed to treat pairings of interfacial tension between the phases. VOF smoothing is also implemented by applying a Laplacian filter on the distribution of volume fractions, and the SIMPLEC algorithm is employed for the velocity–pressure coupling. The above algorithm has also been extended with the development of the rheoMultiFluidInterFoam solver which is capable of fully taking into account complex non-Newtonian effects (e.g. yield stress, viscoelasticity, etc.) of the involved liquids. To this end, the developed solver incorporates the RheoTool toolbox (Pimenta and Alves, 2017), utilizing a wealth of constitutive equations suitable for modeling different types of fluids with complex rheology. Our solvers are tested for both the implementation of the surface tension and of the constitutive equations in a wide range of different flow setups, considering typical benchmark two-phase and three-phase flows, such as the cases of dam break with an obstacle, spreading of a floating lens, a levitating drop, and a bubble rising in an ambient fluid; flows involving Newtonian, viscoplastic and viscoelastic liquids have been considered. Comparisons against analytical solutions or previously published numerical data are performed clearly demonstrating the capability of the new solvers to efficiently and accurately simulate interfacial tension dominated three-phase flows (and n-phase flows in general) for both simple and complex liquids.

Experimental study of liquids interface oscillatory dynamics in rotating slot gap

The shape of the interface between two liquids in a non-uniformly rotating slotted gap with a circular boundary is experimentally investigated. The liquids have different densities and a high viscosity contrast. We have found that the axisymmetric interface becomes unstable with an increase in the amplitude of the modulation of the rotation rate, a quasi-stationary azimuthally periodic relief excites in a threshold manner. The shape of the interface is studied by photoregistration as a function of the rotation rate, amplitude and frequency of the rotation rate modulation. The relative volume of a viscous liquid and the properties of liquids (viscosity contrast, relative density, coefficient of interfacial tension) vary. We found that the relief develops at the interface regardless of where the more viscous liquid is located, outside or inside.

Numerical Analysis of the Deformation of Aqueous Drop Under Uniform Electric Field

This article presents a numerical analysis of the deformation of an aqueous drop in an oil phase under electric field. The configuration of analysis is a sessile aqueous drop located on an electrode. We use the charge simulation method (CSM) to calculate the electric field in the configuration. The drop profile is determined by solving the augmented Young–Laplace equation. The solution is obtained by iteratively adjusting the drop contour and the fictitious charge for the CSM. Experiments were carried out to observe the behavior of an aqueous sessile drop in a parallel electrode system. The comparison between the experimental and numerical results shows a good agreement of the drop profiles for a wide range of the applied electric field. The calculated critical electric field of drop instability is lower than the value from the experiments by 4%. We employ the numerical analysis to clarify the effects of drop size, interfacial tension coefficient, and mass density of the oil phase on the deformation and the critical electric field of the aqueous drop.

Effect of Initial Water Saturation on Oil Displacement Efficiency by Nanosuspensions

This article deals with the study of the initial water saturation effect of a porous medium on the oil recovery factor using a water-based nanosuspension. The initial water saturation of the porous medium in the computations varied within the range from 0 to 90%. The nanoparticle SiO2 concentration varied from 0 to 1 wt%. The particle sizes were equal to 5, 18, 22, and 50 nm. Experimentally measured wetting angles and the interfacial tension coefficient depending on the concentration and size of nanoparticles were used in computations. A mathematical model was developed, describing the transfer and diffusion of nanoparticles within the aqueous phase during immiscible displacement of oil by nanosuspension from a porous medium. Using the developed model, a systematic computational study of the effect of the initial water saturation of the core micromodel on the oil recovery factor using nanosuspension was carried out. It was revealed that with an increase in the initial water saturation, the oil recovery factor monotonically decreased in the case of displacement both by water and nanosuspension. It was shown that with an increase in the concentration of nanoparticles and a decrease in their size, the oil recovery factor increased. At that, the relative increase in the recovery factor had a maximum at an initial water saturation equal to 60%.

Investigation of the interfacial tension at the interface between water and asphaltene solution in toluene

The dynamics of the interfacial tension coefficient at the interface between water and model solutions of asphaltenes of different concentrations in toluene has been studied. It has been shown that, over time, the interfacial tension decreases due to the adsorption of asphaltene molecules at the interface. With an increase in the concentration of asphaltenes in the solution, the decrease in interfacial tension occurs more intensively. The results of a study of the elongation of a water drop in a solution under the influence of an electric field are presented. It is shown that after the formation of an adsorption film, a higher electric field must be applied to stretch the droplet, and the relative elongation depends nonlinearly on the applied voltage. Keywords: interfacial tension coefficient, asphaltenes, adsorption film, drop elongation.

Исследование межфазного натяжения на границе воды и раствора асфальтенов в толуоле

The dynamics of the interfacial tension coefficient at the interface between water and model solutions of asphaltenes of different concentrations in toluene has been studied. It has been shown that, over time, the interfacial tension decreases due to the adsorption of asphaltene molecules at the interface. With an increase in the concentration of asphaltenes in the solution, the decrease in interfacial tension occurs more intensively. The results of a study of the elongation of a water drop in a solution under the influence of an electric field are presented. It is shown that after the formation of an adsorption film, a higher stress must be applied to stretch the droplet, and the relative elongation depends nonlinearly on the applied stress. The studies were carried out using the suspended drop method.

The effect of surfactant on the drag and wall correction factor of a drop in a bounded medium

Abstract In the present article, the analytical solution for creeping motion of a drop/bubble characterized by insoluble surfactant is examined at the instant it passes the center of a spherical container filled with Newtonian fluid at low Reynolds number. The presence of surfactant characterizes the interfacial region by an axisymmetric interfacial tension gradient and coefficient of surface dilatational viscosity. Under the assumption of the small capillary number, the deformation of spherical phase interface is not taken into account. The computations not only yield information on drag force and wall correction factor, but also on interfacial velocity and flow field for different values of surface tension gradient and surface dilatational viscosity. In the limiting cases, the analytical solutions describing the drag force and wall correction factor for a drop in a bounded medium reduces to expressions previously stated by other authors in literature. The results reveal the strong influence of the surface dilatational viscosity and surface tension gradient on the motion of drop/bubble. Increasing the surface tension gradient and surface dilatational viscosity, results in linear variation of drag force. When the surface tension gradient increases, the drag force for unbounded medium increases more as compared to the bounded medium hence wall correction factor decreases with increase in surface tension gradient whereas it increases with increase in surface dilatational viscosity.

Determination of Interfacial Tension of Nanomaterials and the Effect of Particle Size on Interfacial Tension.

The unique physical and chemical properties and performances of nanomaterials are closely related to the interfacial tension. However, there is no method to accurately measure the interfacial tension of nanomaterials. In addition, the effect of particle size on the interfacial tension of nanoparticles is unclear, and there exist conflicting conclusions about the value and sign of Tolman length. In this paper, a novel method of determining the interfacial tension (solid-liquid and solid-gas interfaces), temperature coefficient of interfacial tension, and Tolman lengths of nanomaterials by adsorption thermodynamics and kinetics was presented. The interfacial tension and its temperature coefficient of the solid-liquid interface of nano cadmium sulfide before adsorption were obtained, and further, the Tolman length was also obtained. The experimental results show that the particle size of nanoparticles has significant effects on the interfacial tension and its temperature coefficient. When the radius is larger than 10 nm, the interfacial tension and its temperature coefficient are almost constant with the decrease of the radius. When the radius is less than 10 nm, the interfacial tension decreases sharply and the temperature coefficient increases sharply with the decrease of the radius, and the temperature coefficient of the interfacial tension is negative. The Tolman length of the solid-liquid interface of nanoparticles is proved to be positive, and the particle size also has a significant effect on the Tolman length. The Tolman length decreases with the decrease of particle size. However, the effects of particle size on the Tolman length become significant only when the particle radius approach or reach the order of magnitudes of molecular (or atomic) radius. The effects of particle size on interfacial tension and Tolman length of nano cadmium sulfide obtained in this paper can provide significant references for the research and applications of interface thermodynamics of other nanomaterials.

Ternary fluid lattice Boltzmann simulation of dynamic interfacial tension induced by mixing inside microdroplets

AbstractA ternary fluid color‐gradient lattice Boltzmann model is proposed to investigate the effect of mixing‐induced dynamic interfacial tension on the diffusive mixing of two fluids inside microdroplets moving in a third continuous phase through a baffled channel. The diffusion coefficient of binary mixtures and dynamic interfacial tension in this model can be directly defined and independently adjusted. The simulation results show that the dynamic interfacial tension between miscible binary fluids at interfaces with ambient phase would lead to the motion of the interface and redistribution of solutes inside the droplet during mixing. The larger initial interfacial tension gradient would improve mixing efficiency at early stages by promoting faster solute flow. The present model can be easily applied to quantitatively characterize the mixing behavior inside droplets in the practical processes involving the dynamic interfacial tension phenomenon and inspire new designs for mixing intensification.

Effect of interface deformation on hydrodynamics of liquid–liquid two-phase flow in a confined microchannel

Effect of interface deformation on flow patterns, recirculation flow, vorticity magnitude, and liquid film thickness of liquid–liquid two-phase flow in a confined microchannel was investigated via a simulation method using the VOF-CSF model. The quantitative control over the droplet interface deformation is achieved by systematically studying the influences of diameter ratio, viscosity ratio, continuous phase flow rate as well as interfacial tension coefficient, and further, the corresponding interface deformation mechanisms are comprehensively revealed based on the force field characteristics. Especially, two typical flow field structures inside the droplet are clarified to quantitatively distinguish the liquid–liquid two-phase flow patterns, namely slug and plug flow, and the transition law of flow field structure is also investigated. The slug flow is characterized by two vortices inside the droplet and the dominant forces are the differential pressure force and shearing force. However, in plug flow, two additional secondary recirculating vortices are observed, in which the Laplace pressure force plays a significant role. Moreover, it is also found that the vorticity magnitude is positively correlated with the interface deformation coefficient. Taking multiple variables with a wide range into account, a universal correlation model for predicting the liquid film thickness with several dimensionless numbers is established. Finally, the obtained results could provide theoretical guidance for designing a liquid–liquid two-phase flow microsystem to enhance heat and mass transfer and reaction process.

Study of surface and rheological properties of clayless biopolymer drilling mud treated with M-1 surfactants

An important issue of improving the quality of the initial opening of the reservoir through the use of a system of drilling fluids treated with surfactant M-1. For high-quality disclosure, it is proposed to use clay-free biopolymer drilling mud. The main analyzed features of M-1 use as an additive to biopolymer drilling mud used in Ukrainian deposits. The formulation is substantiated and the study of clay-free biopolymer solution for primary opening of productive layers is carried out. Processed non-ionic surface active agent (surfactant) M-1 model biopolymer clayless drilling mud. With the use of oil (density 838 kg /m3) Kachanivsky oilfield conducted measuring the interfacial tension coefficient at the interface "mud filtrate – oil" stalagmometric metod by changes in the concentration range (% by weight) M-1 from 0 to 5. The influence of M-1 concentration on the interfacial tension coefficient at the interface of "oil – biopolymer drilling fluid filtrate" is shown and the critical concentration of micelle formation (CCM) of surfactant in the filtrate is found, the excess of which does not reduce the interfacial tension. It has been experimentally established that with increasing concentrations of M-1, the interfacial tension factor at the interface between the phases of "oil – filtrate of the drilling fluid" is sharply reduced, which leads to an increase in the formation fluid formation fluid. The rheological properties of drilling fluids with rotational viscometry are determined. Polynomial dependences of temperature influence on rheological properties without clay biopolymer drilling mud have been established.

Hydrodynamics of triple emulsion droplet generation in a flow-focusing microfluidic device

A numerical research is conducted to investigate the triple emulsion droplet generation in a three-dimensional axisymmetric flow-focusing device. The simulation predicts three flow regimes: dripping, jetting, and threading. The hydrodynamics underlying the droplet generation and effects of operation conditions on the droplet generation are clarified. An increase in flow rate of one dispersed phase results in the larger droplet enclosing this phase and smaller droplet enclosed by this phase. As the interfacial tension between any two phases increases or viscosity of any phases decrease, the flow regime transits from jetting to dripping, accompanied by a decrease in the droplet size. Increasing the interfacial tension coefficient or decreasing the viscosity under both two regimes can increase the droplet size. Additionally, regime diagrams for single, middle, and triple emulsion droplet generation are compared, and an empirical equation is proposed to predict the flow regime transition.

Computational study of enhanced oil recovery from a porous medium using nanosuspension

The paper presents the results of direct numerical simulations of the process of oil displacement by nanosuspension with SiO2 particles from two-dimensional micromodels of a porous medium with different values of permeability. In the calculations, the experimentally measured values of the interfacial tension coefficient and the contact angle of wetting were used. The calculations were performed for pure water and a suspension of silicon oxide nanoparticles with a mass concentration of 1%. The computational study was performed using the VOF method. The influence of the displacement fluid flow rate, nanoparticle concentration and core permeability on the efficiency of oil displacement by nanosuspension was studied. As a result of the work, it was shown that the use of nanosuspensions makes it possible to increase the oil recovery factor. It is shown that with an increase in the mass concentration of particles, the value of the oil recovery factor increases.

Numerical study of the indentation formation of a compound droplet in a constriction

A compound droplet deforming in a constricted tube widely appears in drug delivery and microfluidic devices. In such a constriction, an indentation can present at the trailing surface of the droplet. However, this aspect has not been fully investigated and understood so far. This study focuses on the effects of some dimensionless parameters on the negative curvature, i.e., indentation, at the trailing surface of a compound droplet moving through a constricted tube. The presence of the constriction at the middle of the tube length enhances the droplet indentation. Numerical results were obtained for the capillary number Ca (varied in range of 0.1–1.0), the inner-to-outer droplet radius ratio R21 (varied in range of 0.2–0.9), the droplet-to-tube radius ratio R10 (varied in range of 0.2–0.9), the inner-to-outer interfacial tension coefficient ratio σ21 (varied in range of 0.1–6.4), and the normalized depth of the constriction d/R (varied in range of 0.0–0.8). The results reveal that the most influencing factor is Ca, increasing its value leads to the increment of the maximum indentation at the trailing surface of the inner and outer droplets. The indentation is also increased with increasing the value of R10 and d/R. In contrast, increasing R21 results in a decrease in the indentation at the trailing surface of the outer droplet. When increasing σ21, the indentation at the trailing surface of the inner one is quickly suppressed, while the outer droplet is minorly affected. We also point out the patterns of the trailing surface of the inner and outer droplets and their transitions from one to the other patterns in the diagrams based on these parameters.

An Experimental Study of the Effect of the Addition of Silicon Oxide Nanoparticles on the Wettability Characteristics of Rocks with Respect to Oil

The results of an experimental study of the interfacial tension and surface wettability in the nanosuspension/oil/rock system are given. The effect of the concentration and size of silicon oxide nanoparticles on the coefficient of interfacial tension and the contact angle of wetting has been systematically studied for the first time. A wide range of weight concentrations of nanoparticles (from 0 to 1 wt %) and their average sizes (from 5 to 50 nm) are considered. It is established that the use of nanosuspensions makes it possible to radically change the wettability of rocks with respect to oil. In this case, this effect depends substantially on the concentration and size of nanoparticles.

Experimental study of nanoparticle size and material effect on the oil wettability characteristics of various rock types

The paper presents the results of systematic experimental studies of interfacial tension (IFT) and oil wettability of three different types of rock (dolomite, metabasalt, and sandstone) in nanosuspensions. Nanoparticles of silicon and aluminum oxides were used at the concentration ranged from 0.01 to 1 wt%. It is shown that with increasing NP concentration, the contact angle of an oil droplet resting on a rock in a nanosuspension increases quite essentially (from 33 to 153°). The nanoparticle size and compositional effects on interfacial tension coefficient and contact angle (CA) within a wide range of particle concentrations were systematically studied for the first time. The contact angle oil/dolomite/nanofluid increased from 92 to 151° with decrease in the SiO2 nanoparticle size 50 nm to 5 nm. With an increase in the NP size from 5 to 50 nm, there was a decrease in interfacial tension of about 30%. The first-ever experiments were conducted to study the influence of nanoparticles in water on the oil wettability of various types of hydrophilic and hydrophobic rocks. It is shown that the wettability characteristics of various types of rocks can be controlled by adding minor amounts of nanoparticles of different sizes and compositions to influence the parameters that play a key role in the problems related to oil recovery enhancement during reservoir flooding.

Dripping, Jetting and Regime Transition of Droplet Formation in a Buoyancy-Assisted Microfluidic Device.

Buoyancy-assisted droplet formation in a quiescent continuous phase is an effective technique to produce highly monodispersed droplets, especially millimetric droplets. A comprehensive study combining visualization experiment and numerical simulation was carried out to explore the underlying physics of single droplet generation in a buoyancy-assisted microfluidic device. Typical regimes, including dripping and jetting, were examined to gain a deep insight into the hydrodynamic difference between the regimes. Particularly, the transition from dripping regime to jetting regime was investigated to give an in-depth understanding of the transitional behaviors. The effects of interfacial tension coefficient on the droplet size and formation regimes are discussed, and a regime diagram is summarized. The results show that oscillation of the interface in dripping regimes after detachment is caused by the locally accelerated fluid during the neck pinching process. Droplet formation patterns with the characteristics of both dripping regime and jetting regime are observed and recognized as the transitional regime, and the interface oscillation lasts longer than that in dripping regime, implying intensive competition between interfacial tension and inertial force. Reducing interfacial tension coefficient results in the dripping-to-jetting transition occurring at a lower flow rate of the dispersed phase. The regime diagram indicates that only the inertial force is the indispensable condition of triggering the transition from dripping to jetting.

Association of Lennard-Jones particles in nanoconfined aqueous solution: Theory and molecular dynamics simulations

We develop a new Gibbs free energy-based association model and perform series of molecular dynamics (MD) simulations to study the association behavior of Lennard-Jones (LJ) particles in nanoconfined aqueous solution. In the association model, the total Gibbs free energy is the sum of free energy cost in the nucleation of a densely packed cluster with an isotropic shape and a radius dependent interfacial tension coefficient, and the translation entropy of dispersed particles outside the cluster. Two key theoretical expressions – total Gibbs free energy formula and the thermodynamic equilibrium equation – are obtained to estimate the cluster aggregation number for a given LJ particle number and the corresponding total Gibbs free energy. Using MD simulations, we observe that the association state transforms from the stable dispersion state, through the reversible state, finally to the stable aggregation state as the LJ particle number increases. In the reversible state, the system reversibly switch in between the dispersion and aggregation states. The existence of three types of association states is also found for LJ particles with the varied well depth. According to our model, the Gibbs free energy curve shows from a single minimum, through two minima, finally to a single minimum, leading to the transformation of association states. The occurrence of reversible state transition is attributed to the free energy barrier of the order of thermal fluctuation in water between the dispersion and aggregation states. These findings deepen the understanding of nucleation/aggregation of hydrophobic gas molecules or particles in solution under nanoconfinement.

Spatial Waveform Analysis of Ultrasonically Excited Capillary Waves for Measurements of Interfacial Tension Coefficient in Microgravity

A simplified method for measurements of low interfacial tension coefficient which is applicable for binary mixtures is proposed. The technique is based on generating progressive capillary waves at a liquid interface by radiation pressure of a short ultrasound pulse in microgravity condition. The waveforms are then processed in the spatial domain. The method presents the advantage of strongly reducing data volume of necessary images for analysis and, consequently, significantly minimizing both data processing and time expenses thanks to the analysis in spatial domain instead of time domain as hitherto reported in the literature.