Negative Spreading Coefficient Research Articles

Analytical solutions of critical oil film thickness of negative spreading coefficient in a capillary corner

In this paper, by combining applications of minimum surface free energy with capillary force balance equations, and considering that the total free energy change is zero at thermodynamic equilibrium, an analytical equation of the oil film critical thickness to spread over a water film in a three-dimensional capillary corner is derived. The derivation is based on the analysis proposed by Dong et al. [Journal of Colloid and Interface Science 172 (1995) 21–36]. This analytical solution allows the critical oil film thickness in three-phase systems to be calculated conveniently without lengthy calculation and be readily applied in simulation of three-phase systems in porous media using predictive models. The equation was examined by comparing the analytical solutions with the numerical results by Dong et al. Using the analytical solution, the reason why the oil phase spreads between the gas and water phases in three-phase systems in porous media was analyzed. The spreading of oil phase is controlled by the free energy change, and the spreading of oil phase only occurs in the system when the free energy change during the oil spreading process is negative. Also, there is a critical oil film thickness controlling this process that is a function of interfacial tension, contact angles, and corner angles. This analytical solution of critical oil film thickness can also be utilized to find the correlation of three-phase capillary pressure when the system is in thermodynamic equilibrium for water-wet porous media. This correlation should be useful in pore-scale simulation of three-phase flow of spreading oil.

Statics and dynamics of drops spreading on a liquid-liquid interface

Lattice Boltzmann simulations along with a diffuse interface model are used to simulate the capillary driven, symmetric spreading of a fluid drop on another fluid-fluid interface. While the equilibrium shapes of the drops with negative spreading coefficient are comprehensively represented on a phase diagram, the dynamics leading to equilibrium shapes are shown to be universal with power-law behaviors exhibited only in the limit of the small spreading coefficient.

Residual liquids saturation development during two and three phase flow under gravity in square capillaries at different temperatures

An experimental study on heavy oil with air (two phase flow) and water and air (three phase flow) at different temperatures was carried out in square capillaries under gravity drainage conditions. Fluid retention characteristics (in the corners of capillaries) were determined and evaluated using the trapping number (NT). In air–heavy oil systems, when NT<2.7E−2, the residual oil saturation (Sor) was constant and equal at 55 and 85°C. The Sor was controlled by capillary forces regardless of viscous and gravity forces, including free fall gravity drainage (FFGD). For higher NT, the Sor was a function of competition between gravity, viscous and capillary forces. The Sor was always higher at 85°C compared to 55°C for the same gas injection rate and the difference increased as the NT augmented. FFGD experiments demonstrated that heavy oil retention depended on the Bond number and increased linearly as the Bond number increased.In the three phase systems (air–heavy oil–water) the oil retention did not diminish with the presence of water, which was also constant for the entire interval of NT at 55 and 85°C. High viscous forces originated from heavy oil were responsible for no change in the Sor. However, due to the water-wet nature of the capillary tubes, water was not completely swept. More Sor and residual water saturation were observed in air–water–heavy oil configuration, especially at 85°C, due to the unfavorable viscosity ratio oil/water and the negative spreading coefficient of water in oil in the presence of air. Finally, the change of wettability from water wet to oil wet did not modify the Sor but the water saturation decreased slightly for air–heavy oil–water systems.

Measurement of maximum stable drop size in aerated dilute liquid–liquid dispersions in stirred tanks

Turbulence intensity, or hydromechanical stress, is a controlling parameter in many industrially relevant processes. Especially fermentation processes are often characterized by intense aeration and agitation, operating conditions for which the measurement of turbulence intensity is extremely difficult. Since the maximum stable drop diameter in a break-up controlled dispersion is directly correlated with turbulence intensity, the measurement of drop sizes can enable an indirect access to the intensity of turbulence under such operating conditions. This work presents the constraints and the development of a method for the measurement of maximum stable drop size in aerated liquid–liquid dispersions in stirred tanks for the purpose of characterizing turbulence intensity. Continuous and dispersed phase properties were selected to achieve a break-up controlled dispersion with negligible coalescence. This was accomplished mainly by applying a dilute dispersion, a low ionic strength and by incorporating a dispersed phase, paraffin oil, with a negative spreading coefficient. The negative spreading coefficient prevents coalescence due to drop–bubble interactions for aerated operating conditions. It was demonstrated that the off-line measured drop size distributions are representative for the conditions in the bioreactor and are not altered by sample handling. The sampling and measurement procedure was found to be highly reproducible with a standard deviation for the maximum stable drop size for independent experiments of approximately 10%. Relevant constraints for the application of the method in large-scale experiments were discussed and accounted for during method development to allow a later application in production scale equipment.

Spreading of Multi-component Oils on Water

The spreading of multi-component oils on water has been investigated by direct observations and predicted from measurements of the interfacial tensions and surface tensions of decane, toluene, heptane, and their mixtures. Pure decane does not naturally spread at ambient conditions, as indicated by its negative spreading coefficient. However, when decane is mixed with toluene and heptane, the mixture spreads on water over a wide range of compositions. The spreading coefficients are highly nonlinear with respect to concentration and feature a maximum. The spreading is ascribed to preferential accumulation of toluene at the oil/water interface and heptane at the oil/vapor interface. Molecular dynamics simulations corroborate the hypothesis of preferential accumulation. The accumulation of lighter alkanes at the oil/vapor interface reduces the surface tension, and the accumulation of aromatics at the oil/water interface decreases the interfacial tension. As a consequence, the oil mixture spreads over water.

Chitosan films: crosslinking with EDTA modifies physicochemical and mechanical properties

The present study was aimed to develop chitosan-EDTA films and evaluate their physico-chemical and mechanical properties. The physical properties suggested lowest swelling, volume and volume index of films prepared by employing equal weight of chitosan (CH) and EDTA (1.5% w/v). The CH:EDTA film (1:l, on weight basis) showed minimum contact angle, work of adhesion and high negative spreading coefficient indicating lipophilic behavior of film. Further, the FTIR and DSC analysis suggested maximum crosslinking density in film prepared with equal proportion of CH and EDTA. The mechanical properties explored using texture analyzer revealed increasing the proportions of EDTA rendered the films more flexible and decreased their hardness. Furthermore, in vitro permeation of 5-FU and mesalamine with different solubilities showed minimum permeation across CH–EDTA (1:1) film, indicating high crosslinking density that decreased void space inside the film. Hence, the CH–EDTA conjugate could be considered to be possess great potential for various pharmaceutical applications such as film based delivery systems, controlled and sustained delivery systems etc.

On integrable singularities and apparent contact angles within a classical paradigm

Far from claiming any ultimate resolution of the contact line paradoxes, we draw the reader’s attention to the fact that a somewhat controversial paradigm, originally employed by de Gennes and collaborators, actually appears both to be quite reasonable at its foundations and to lead to physically consistent final results in a wide variety of situations. Curiously enough, while containing a singularity in itself, the approach nonetheless renders the classical contact-line singularities — both hydrodynamic and thermal — integrable, in particular as far as several quantities of interest are concerned. It is also readily applicable to quite a few situations: from equilibrium shapes and moving contact lines of a non-volatile liquid, to cases with evaporation into (and even condensation from, although it is not studied here) either a pure-vapor or an inert-gas atmosphere. The paradigm actually consists in an approach involving both the (positive or negative) spreading coefficient and the disjoining pressure in the form of a positive inverse cubic law, a conceptual framework that most notably describes structures with truncated precursor films on a macroscopically bare solid surface. Whether or not the remaining integrable divergences at molecular scale can truly be considered as “benign” has to be discussed on the basis of more involved mesoscopic or microscopic approaches, quite outside the scope of the present study.

Measurement of the kinetic rate constants for the adsorption of superspreading trisiloxanes to an air/aqueous interface and the relevance of these measurements to the mechanism of superspreading

Super-spreading trisiloxane surfactants are a class of amphiphiles which consist of nonpolar trisiloxane headgroups (((CH 3) 3SiO) 2Si(CH 3)(CH 2) 3) and polar parts composed of between four and eight ethylene oxides (ethoxylates, OCH 2CH 2). Millimeter-sized aqueous drops of trisiloxane solutions at concentrations well above the critical aggregate concentration spread rapidly on very hydrophobic surfaces, completely wetting out at equilibrium. The wetting out can be understood as a consequence of the ability of the trisiloxanes at the advancing perimeter of the drop to adsorb at the air/aqueous and aqueous/hydrophobic solid interfaces and to reduce considerably the tensions of these interfaces, creating a positive spreading coefficient. The rapid spreading can be due to maintaining a positive spreading coefficient at the perimeter as the drop spreads. However, the air/aqueous and solid/aqueous interfaces at the perimeter are depleted of surfactant by interfacial expansion as the drop spreads. The spreading coefficient can remain positive if the rate of surfactant adsorption onto the solid and fluid surfaces from the spreading aqueous film at the perimeter exceeds the diluting effect due to the area expansion. This task is made more difficult by the fact that the reservoir of surfactant in the film is continually depleted by adsorption to the expanding interfaces. If the adsorption cannot keep pace with the area expansion at the perimeter, and the surface concentrations become reduced at the contact line, a negative spreading coefficient which retards the drop movement can develop. In this case, however, a Marangoni mechanism can account for the rapid spreading if the surface concentrations at the drop apex are assumed to remain high compared to the perimeter so that the drop is pulled out by the higher tension at the perimeter than at the apex. To maintain a high apex concentration, surfactant adsorption must exceed the rate of interfacial dilation at the apex due to the outward flow. This is conceivable because, unlike that at the contact line, the surfactant reservoir in the liquid at the drop center is not continually depleted by adsorption onto an expanding solid surface. In an effort to understand the rapid spreading, we measure the kinetic rate constants for adsorption of unaggregated trisiloxane surfactant from the sublayer to the air/aqueous surface. The kinetic rate of adsorption, computed assuming the bulk concentration of monomer to be uniform and undepleted, represents the fastest that surfactant monomer can adsorb onto the air/aqueous surface in the absence of direct adsorption of aggregates. The kinetic constants are obtained by measuring the dynamic tension relaxation as trisiloxanes adsorb onto a clean pendant bubble interface. We find that the rate of kinetic adsorption is only of the same order as the area expansion rates observed in superspreading, and therefore the unaggregated flux cannot maintain very high surface concentrations at the air/aqueous interface, either at the apex or at the perimeter. Hence in order to maintain either a positive spreading coefficient or a Marangoni gradient, the surfactant adsorptive flux needs to be augmented, and the direct adsorption of aggregates (which in the case of the trisiloxanes are bilayers and vesicles) is suggested as one possibility.

Pattern formation in thin liquid films with insoluble surfactants

The problem of pattern formation in thin liquid films with insoluble surfactants under attractive and repulsive forces is addressed. A thin fluid film bounded by a wall is modeled by a set of two nonlinear evolution equations for the film thickness and surfactant concentration on the free interface. We perform a bifurcation analysis valid for the general case of apolar and polar forces and predict a supercritical bifurcation to new stationary and periodic structures. Numerical simulations for the particular case of a negative apolar spreading coefficient (attractive van der Waals forces) and a positive polar spreading coefficient (repulsive hydration pressure) are discussed in terms of the analytical predictions. Nonlinearities in the competition between attractive and repulsive forces can lead to formation of periodic patterns for the film thickness with homogeneously distributed surfactants. Due to diffusion and Marangoni effects, insoluble surfactants alter the time required for pattern formation but do not alter the final pattern profile itself. Bifurcation analysis allows us then to predict the ranges of film parameters in which pattern formation, rupture, or total film spreading is possible.

Some practical applications of recent core analysis advances

The Eromanga Basin is Australia's main onshore oil province, consisting of a large number of thin good permeability reservoirs. This basin overlies the Cooper Basin, Australia's main onshore gas province, consisting of many thicker but low permeability gas reservoirs. Both basins often contain stacked reservoirs. In order to identify improvements in core analysis which can be applied to the basins the Operator has conducted a series of experiments using newly or recently developed procedures. Following are some highlights. (1) Reservoirs which may have leaked: Some Eromanga basin reservoirs are believed to have leaked into overlying reservoirs. For the reservoir which has leaked it is not really valid to compare the log analysis to a drainage capillary pressure curve. Neither does a traditional laboratory imbibition capillary curve exactly describe the process. A new laboratory imbibition procedure was developed which appears to match the log analysis better than drainage data. (2) Low invasion coring: This has become an established procedure in Australia. Many of our reservoirs are well suited to it. In one case we obtained saturations by four different laboratory procedures and compared them to the log analysis, obtaining a somewhat large spread in the various laboratory results. (3) Transitional reservoirs: For waterflood and some relative permeability experiments the traditional laboratory procedure of using high capillary pressure ( P c) to achieve s wc then a high flood velocity (or capillary number N) to achieve s or has been shown to produce incorrect results across the Eromanga Basin and has been replaced by a low P c/low N method, yielding better agreement with log analysis. (4) Mud testing on cores for formation damage: Comparison of a particle size distribution from the mud with a pore size distribution from the reservoir has a lot of pitfalls. It does not follow that particles much smaller than a pore automatically have the opportunity to enter the pore. (5) Spreading experiments: Two suites of experiments were conducted involving waterflooding a core followed by gasflooding it. One suite was run with a positive spreading coefficient, and the other with a negative spreading coefficient. Oil recovery was the same in both cases.

Micromodel Observation of the Role of Oil Layers in Three-Phase Flow

We have studied the flow of a non-aqueous phase liquid (NAPL, or oil), water and air at the pore scale using a micromodel. The pore space pattern from a photomicrograph of a two-dimensional section through a Berea sandstone was etched onto a silicon wafer. The sizes of the pores in the micromodel are in the range 3–30,μm and are the same as observed in the rock from which the image was taken. We conducted three-phase displacement experiments at low capillary numbers (in the order of 10-7) to observe the presence of predicted displacement mechanisms at the pore scale. We observed stable oil layers between the wetting phase (water) and the non-wetting phase (gas) for the water–decane–air system, which has a negative equilibrium spreading coefficient, as well as four different types of double displacements where one fluid displaces another that displaces a third. Double imbibition and double drainage are readily observed, but the existence of an oil layer surrounding the gas phase makes the other double displacement combinations very unlikely.

Enhancement of gas to water mass transfer rates by a dispersed organic phase

Experimental data are presented on the enhancement of oxygen mass transfer into an aqueous sulphite solution in a stirred cell, due to the presence of a dispersed liquid octene phase. The observed enhancement factors can be described with a new mass transfer theory, called the Film Variable Hold-up (FVH) model. This model is based on the film theory and explains the influence of hold-up, droplet diameter and permeability of the organic phase, on the obtained enhancement. It is assumed that the dispersed phase hold-up gradually increases from zero at x = 0 (the gas-liquid interface) towards a constant average bulk value for x ≥ αδ, according to a distribution function with parameter values α = d 43 δ and β = 0.3, where d 43 is the volumetric mean diameter of the dispersed droplets, δ is the mass transfer film thickness, and β is a geometrical factor. Surprisingly, also the experimental data of Bruining et al. (1986) for oxygen mass transfer enhancement due to hexadecane droplets and the data of Littel (1991) for carbon dioxide mass transfer enhancement due to toluene droplets can be reasonably well described, assuming the same dispersed hold-up distribution in the mass transfer film. This may indicate that this dispersed phase distribution is similar for different organic droplets dispersed in water, at least if these systems are characterized by a negative spreading coefficient. The recent observation of Wilkinson et al. (1991), that the reaction rate of the uncatalyzed sulphite oxidation increases with decreasing values of the pH, initially adjusted by adding H 2SO 4, was confirmed.

Effect of Wettability and Spreading on Recovery of Waterflood Residual Oil by Immiscible Gasflooding

Summary This paper investigates the mobilization and recovery of waterflood residual oil by immiscible gasflooding in 2D glass micro-models under strongly oil- and water-wet conditions. Two oil/water/gas systems, one displaying a positive and the other a negative spreading coefficient (oil over water), were used. The results clearly show the importance of fluid/solid and fluid/fluid interactions on tertiary oil recovery. Oil recovery was highest for the oil-wet displacements where the oil formed thick wetting films. Recovery was considerably lower for the positive spreading system under strongly water-wet conditions where the oil was observed to form thin but continuous spreading films. Recovery was lowest for the negative spreading system under strongly water-wet conditions where no oil films were formed.

An experimental study of the antifoam behaviour of mixtures of a hydrocarbon oil and hydrophobic particles

An experimental study of the synergistic antifoam behaviour of hydrophobic particle—hydrocarbon oil mixtures is presented here. The system for study has been selected to minimise specific effects in order to highlight the phenomenology of the antifoam process. Thus, liquid paraffin and a commercial sodium alkyl benzenesulphonate were chosen as oil and surfactant respectively, because this oil exhibited a negative spreading coefficient at the air—water surface of the solution of that surfactant under all circumstances investigated. These circumstances included situations where the air—water surface was rapidly expanded to represent the conditions prevailing during foam generation. In the main, finely divided silica, hydrophobised with trimethylsilane, was used as the particulate component. Again, this material had no tendency to spread at air—water surfaces and had no effect on the spreading behaviour of the liquid paraffin. The study was also extended to include examples of intrinsically hydrophobic organic particles such as calcium stearyl acid phosphate. Contact angles, electrophoretic mobilities, electron microscopy and observations of emulsion behaviour all suggested that these oil—particle mixtures form composite entities where the particles tend to adhere to the oil—water surface with a contact angle (measured through the aqueous phase) θ ow§>π/2. The particles also exhibited a finite contact angle θ ow at the air—water surface so that θ aq<π/2. Weak antifoam effects associated with the particles alone probably concerned dewetting and bridging in foam films to form holes in a manner analogous to that found previously with polytetrafluoroethylene particles. Preliminary observations indicated that the presence of particles adhering to the oil—water surface facilitates the emergence of oil droplets into the air—water surface by rupturing unsymmetrical oil—water—air films. The observations reported here are consistent with an antifoam mechanism where oil droplets form mechanically unstable bridging lenses in foam films. Formation of such configurations requires rupture of oil—water—air films by particles. The contact angle requirement for rupture of such films is less severe than that required for symmetrical air—water—air films. Therefore particles may promote the emergence of oil droplets into air—water surfaces to form lenses without themselves exhibiting significant antifoam effects.

Particle growth in aqueous suspensions: the influence of surface energy and polarity

The aggregation of drug particles in suspensions can cause products to be spoiled. In this paper the role of surface energetics in controlling the dispersion of powders in water is considered, by use of a spreading coefficient. The contact angles, surface energies and the polarities were determined for a series of barbiturate powders. Contact angles were measured using a Wilhelmy plate technique. Aqueous suspensions of each powder were prepared and the change in particle size was monitored over a period of hours and days. By extrapolation the limiting size of the aggregates was calculated and this was related to the original particle size of each powder. The powders were largely hydrophobic in nature, and as such were difficult to disperse in the liquid. It was determined that dispersion was possible only if the negative spreading coefficient of water over the powder did not have a significantly larger value than the dispersion component of the water. This has been explained in terms of the hydrophobic powder tending to interact with the dispersive, rather than the polar, entities in the water. For powders which spontaneously dispersed in the water a good correlation existed between the increase in particle size noted in the suspension and the spreading coefficient.

Gas holdup in a bubble column with immikible liquid mixtures

AbstractExperimental measurement of gas holdup was carried out in a medium‐size gas‐liquid‐liquid bubble column with a multiple nozzle sparger plate using air, water and organic liquids. It was found that the fractional holdup depends on gas velocity, liquid properties, phase inversion in the liquid mixture as well as spreading coefficient of the organic liquid. In the presence of a liquid with a negative spreading coefficient the holdup is a minimum at the phase inversion point. but the reverse is true for a liquid with a positive coefficient of spreading. Observed bubble characteristics have been discussed. Correlations for gas holdup have been developed for different ranges of liquid composition.

EFFECT OF ADDITIVES ON MASS TRANSFER IN AN AERATED MIXING VESSEL

The effect of additive solutes in air/water aerated mixing vessel over a wide range of operation conditions was investigated. The n-dodecane with negative spreading coefficient reduced the mass transfer capability; and the sodium dodecyl sulfate increased it; however, the ethanol exhibited no difference in KLa initially and then enhanced it linearly proportional to its volume fraction. In these air-water-additive systems, correlative equations were also proposed.

Oxygen transfer in mechanically agitated aqueous systems containing dispersed hydrocarbon

AbstractThe effect of dispersed n ‐dodecane or n ‐hexadecane on the air‐to‐aqueous phase overall volumetric oxygen transfer coefficient in a simulated (cell‐free) stirred‐tank fermentor is described. The oil volume fraction ranged from zero to 0.10; the ionic strength of the aqueous phases was varied from 0 to 0.45. The air‐to‐aqueous phase coefficients in both oil‐free (KLa) and oil‐bearing (KLa*) systems were evaluated from unsteady‐state experiments using a membrane‐covered probe to follow the aqueous phase dissolved oxygen tension.For all systems studied, KLa*/KLa was found to be independent of P/V and vs for all practical purposes. However, for a particular aqueous phase and at a given P/V and vs, the ratio KLa*KLa generally differed from unity. Depending on the combination of hydrocarbon type and volume fraction and the aqueous‐phase ionic strength employed, the dispersed hydrocarbon may, in some cases, reduce the rate of oxygen transfer and in others enhance it relative to that of the corresponding oil‐free gas–liquid dispersion. Enhancement of the air‐to‐aqueous transfer rate by such negative spreading coefficient hydrocarbons has not been reported previously.

A study of the mechanism of gas absorption into oil-water emulsions

The mechanism of oxygen and argon transfer into aqueous emulsions of n-alkans and of oleic acid was studied both theoretically and experimentally. An apparatus allowing to measure the coefficient of mass transfer from individual bubbles into the turbulent medium of either a single- or multi-phase liquid has been designed and constructed. The effect of the oil phase on the bubble-to-emulsion mass transfer coefficient was investigated. In o/w type emulsions (oil as the dispersed and water as the continuous phase) of n-alkans (the system with negative spreading coefficient) the mass transfer coefficient k L w is not affected by the content of the oil phase, and is equal to the coefficient of mass transfer into a pure aqueous phase. In the w/o type emulsion the k L w value increases proportionately to the volume fraction of n-alkans. In the oleic acid-in-water emulsion (the system with positive spreading coefficient) k L w initially decreases and then increases proportionately to the oil fraction. The initial decrease of k L w is attributed to surface activity effects of oleic acid. The data suggest that the mechanism of gas transfer to the emulsions is as follows: No direct contact between the oil and the gas phase exists in o/w type emulsions with negative spreading coefficient, and the transfer path is gas-water-oil. In w/o type emulsions (both with negative and positive spreading coefficient), however, there is a direct contact between the gas and both the continuous oil phase and the dispersed aqueous phase; there is a parallel transfer of gas to both the phases.