Viscous fingering instability

Under a Featureless Mask Nucleation and Viscous Fingering Instabilities... 

Nittmann, J., Daccord, G., and Stanley, H., Fractal growth of viscous fingers A quantitative characterization of a fluid instability phenomenon, Nature, Vol. 314, 1985, pp. 141-144. 

Figure 1 shows schematically viscous fingering, which occurs because the injection fluid is less viscous, and gravity override, which occurs because the injection fluid is less dense. Chapter 2 of this book, by Chang and Slattery, describes a linear instability analysis for gas flooding and also introduces a nonlinear treatment of the flow instabilities. 

When the mobility ratio is greater than one, viscous instability ensues during displacements in i stems of sufficient width OlO cm) to permit the formation and propagation of viscous fingers. These... 

When a viscous feed is used, an instability of the band front may be observed and viscous fingering may take place, potentially ruining the separation (see Chapter 5, Section 5.3.5). This phenomenon cannot be taken into account in a chromatographic model. 

Immiscible displacements rarely proceed as uniform fronts. The most well-documented instability is viscous fingering, which occurs due to an unfavorable mobility ratio, meaning... 

Other instabilities include gravity fingering (which is analogous to viscous fingering) and capillary fingering (which is unrelated phenomenologically but also leads to highly nonuniform displacement fronts). 

The third problem is known as the Saffinan-Taylor instability of a fluid interface for motion of a pair of fluids with different viscosities in a porous medium. It is this instability that leads to the well-known and important phenomenon of viscous fingering. In this case, we first discuss Darcy s law for motion of a single-phase fluid in a porous medium, and then we discuss the instability that occurs because of the displacement of one fluid by another when there is a discontinuity in the viscosity and permeability across an interface. The analysis presented ignores surface-tension effects and is thus valid strictly for miscible displacement. ... 

Viscous Fingering effect This phenomenon is observed when the viscosity of the injected sample is significantly larger than the eluent viscosity. A hydro-dynamic instability appears within the column, leading to a fingering elution of the viscous solution in the bed. This disturbance of the flow will strongly impact the obtained efficiency. A reduction of the injected concentration is efficient to correct this effect, which can appear during a process scale-up. 

Kawaguchi studied the problem of viscous fingering in silica suspensions in polymer solutions (44). Experiments in drop towers revealed that sedimentation of the silica particles affected slightly the tip-splitting instability. 

Although a simple extended fractional flow model, based on the Koval approach, is presented to describe laboratory viscous fingering experiments using polymer slugs, this does not imply that this can be carried over to the larger-scale simulation of fluid flow instabilities in polymer flooding in the... 

Displacement of oil by waterflooding is increasingly dominated by viscous forces as the viscosity of the oil displaced increases. When the oil mobility is less than that of the injected water, the oil-water interface is not a piston-like front." Instead, instabilities occur at the flood front in the form of viscous fingers which tend to penetrate the less mobile oil bank. The magnitude of these protrusions, or the degree of channeling, increases... 

Hydrodynamically unstable viscous fingering is a well-known phenomenon that occurs at the interface between fluids with different viscosities in the first moments of mixing and has been applied here to explain the formation of finger-like voids in ceramic membrane precursors [16]. When the suspension is in contact with the nonsolvent, a steep concentration gradient results in solvent/nonsolvent exchange, a rapid increase in local viscosity, and finally precipitation of the polymer phase. However, due to instabilities at the interface between the suspension and the precipitant. 

We review here the viscosity of the most common mobile phases, the factors that influence this viscosity, the temperature, the pressure, and the mobile phase composition, and we discuss two phenomena of practical importance in the preparative applications of chromatography (i) the dependence of the mobile phase viscosity on the concentration in feed components and the pressure excursion generated by the elution of high concentration bands of viscous feed and (ii) the occurrence of flow instabilities and fingerings due to the rapidly varying viscosity of the eluent. 

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