High capillary

S. E. Kistier and L. E. Scriven, "Finite Element Analysis of Dynamic Wetting for Curtain Coating at High Capillary Numbers," presented at... 

The concept of a T2 cut-off that partitions the relaxation time distribution between the pores which can be displaced and those that cannot does not always apply. An exception is when there is significant diffusional coupling between the micropores that retain water at a high capillary pressure and the macropores in close proximity to the microporous system [26, 27]. A spectral BVI model or a forward model has been suggested to interpret these systems [30, 31, 53]. 

We would anticipate from a consideration of the Gibbs equation that the addition of a solute to a solvent will cause marked changes in the composition of the surface phase if the solvent and solute possess different surface tensions. On the addition of a highly capillary active material to water the surface phase becomes rich in the solute and the surface tension of the solution will fall rapidly. 

When a foam with high capillary pressure is in contact with water or aqueous solution the pressure in which is equal to the atmospheric, the foam sucks as much liquid as it needs to... 

Fig. 2.11. Block-scheme of the apparatus for study of foam films under high capillary pressure [51] 1 -...

It is interesting to apply the method of n(h) isotherms at high capillary pressures to studying the multilayer structure of black films. The first results obtained refer to biostructures (see Chapter 11) and lamellar structures in solubilising solutions (see Section 3.4.2.5). 

The dependence of the surfactant concentration at which equilibrium asymmetric aqueous films are formed on the nature of the organic phase is presented in Table 3.18 [551]. It is seen that the stabilising ability of the surfactants strongly reduces with the increase in organic phase polarity. The experiments performed in [552] have shown that at high capillary pressures in the meniscus the stability of films on organic substrate substantially depends on the surfactant concentration. 

In the study of foams that are destoyed under high capillary pressures, it is necessary to record the lowering of pressure in the container caused by the liquid outflow from the foam. An expression for the specific surface area of the foam can be found by equalising the product of the pressure by foam volume for an arbitrary state and the final state... 

Probably, the first condition can be realised at the moment of foam formation, but then the foam becomes hydrostatically non-equilibrium and h(t) ho. For very stable foams this condition can be realised at high capillary pressures (pc 104 Pa). The second condition can be fulfilled in a foam with thin films at not very high capillary pressures. In order to have the condition r = ro = const conformed with it is necessary that... 

The visual observations of Kruglyakov, Exerowa and Khristov on a dry foam at high capillary pressure using a source of light, indicate that the relatively frequent flashes of... 

Recently a new method for formation of monodisperse emulsions that creates high capillary pressures, involving osmotic stress technique, has been introduced [73]. It proves to be most reliable for the purpose. Preliminary calculations showed that the emulsion films in such monodisperse systems rupture in a narrow range of critical disjoining pressure. For example, NaDoS emulsion films rupture in the range from 1 to 1.3-105 Pa, which is analogous to foam films from the same surfactant solution. Unfortunately, the foam film type has not been considered. 

The physical means of defoaming involve foam breakdown by thermal treatment (heating, processing with overheated vapour, freezing), by acoustic (mainly ultrasound) waves, vibrations, a-particles irradiation, creation of high capillary pressure in the foam, etc. 

For the absorption of water it is equally important the foam to possess high capillary pressure (high expansion ratio). 

However, all methods of current major interest use the ability of surfactants to disperse one (or more) fluid phase(s) in another. Oil recovery processes in which a dispersion might be used to modify flow patterns include water flooding and high-capillary number (i.e.,... 

Phase Behavior and Surfactant Design. As described above, dispersion-based mobility control requires capillary snap-off to form the "correct" type of dispersion dispersion type depends on which fluid wets the porous medium and surfactant adsorption can change wettability. This section outlines some of the reasons why this chain of dependencies leads, in turn, to the need for detailed phase studies. The importance of phase diagrams for the development of surfactant-based mobility control is suggested by the complex phase behavior of systems that have been studied for high-capillary number EOR (78-82), and this importance is confirmed by high-pressure studies reported elsewhere in this book (Chapters 4 and 5). 

Macroscopic experiments such as core flooding have been used to obtain relative permeabilities, dispersion coefficients, and other variables relevant to reservoir flow. However, they cannot reveal details of how immiscible phases interact on the pore level. Instead visual experiments have been used to elucidate microscopic flow mechanisms. The latter approach is taken here with experiments using a novel flow cell and state-of-the-art video equipment. The pore level phenomena observed provide a basis for the proper modeling of two-phase flow through porous media at high capillary numbers. 

Relative permeability theory may not apply at high capillary number flow for the nonwetting phase since it becomes discontinuous and its flow rate may thus not be proportional to the macroscopic pressure gradient. 

The capillary pressure will have an effect only at high capillary numbers when the curvatures of the front and rear ends of the Taylor bubble are not symmetrical. At low velocity and in narrow channels, the frictional pressure drop is viscosity-dominant and can be calculated using the Hagen-Poisseuille equation... 

In electrospray, corona discharge can occur, particularly in negative ion mode at very high capillary voltasges. Signal variability and instability will result. 

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