Media apparent viscosity

Hirasaki, G. J. and Lawson, J. B, "Mechanisms of Foam Flow Through Porous Media — Apparent Viscosity in Smooth Capillaries", Soc. Petr. Eng. J. April 1985 pp 176-190. 

Hirasaki G., Lawson J. B., Mechanism of foam flow in porous media apparent Viscosity in smooth Capillaries, Soc. Petr. Engng., 1986, Vol. 25, p. 176-190. 

Semisolid Dosage Forms The nature of the base (vehicle) used for the fabrication of semisolid dosage forms affects their hydrolytic stability. Increased degradation of benzylpenicillin sodium in hydrogels of various natural and semisynthetic polymers has been reported [14]. Also at pH 6 in Carbopol hydrogels, the percentage of undecomposed pilocarpine at equilibrium is a function of the apparent viscosity of the medium [15]. 

Fermentation broths - that is, fermentation medium containing microorganisms - often behave as non-Newtonian liquids, and in many cases their apparent viscosities vary with time, notably during the course of fermentation. 

Apparent viscosity the viscosity of a fluid, or several fluids flowing simultaneously, measured in a porous medium (rock), and subject to both viscosity and permeability effects also called effective viscosity. 

Certain dilute lamellar liquid crystalline phases having relatively low apparent viscosities can propagate through this porous medium micromodel without plugging it. Their behavior followed the trends established with isotropic phases. 

If the foam phase is thought of as a pseudo continuous fluid with an apparent viscosity Vapp = it follows that Papp is greater than that of the aqueous liquid phase. (For the tests here, values of Uapp were on the order of 1 to 50 times that of water). Because of this, when foam and liquid move through a porous medium under an applied pressure drop, the foam, being the most viscous phase, must occupy a larger region of the pore space. Consequently, as observed, the gas saturation is increased over that of non-dispersed phase flow and the liquid permeability is correspondingly decreased. 

The viscosity (or apparent viscosity) of a suspension can be related to the viscosity of the continuous medium in terms of the relative viscosity, rjr. ... 

Because no general theories exist even for concentrated non-food suspensions of well defined spherical particles (Jeffrey and Acrivos, 1976 Metzner, 1985), approaches to studying the influence of the viscosity of the continuous medium (serum) and the pulp content of PF dispersions, just as for non-food suspensions, have been empirical. In PF dispersions, the two media can be separated by centrifugation and their characteristics studied separately (Mizrahi and Berk, 1970). One model that was proposed for relating the apparent viscosity of food suspensions is (Rao, 1987) ... 

Figure 14 shows a very interesting and an important correlation between the rate of coalescence in macroemulsions and the apparent viscosity in the flow through porous media. It was observed that a minimum in apparent viscosity for the flow of macroemulsions in porous media coincides with a minimum in phase separation time at the optimal salinity. This correlation between the phenomena occurring in the porous medium and outside the porous medium allows us to use coalescence measurements as a screening criterion for many oil recovery formulations for their possible behavior in porous media. It is. very likely that a rapidly coalescing macroemulsion may give a lower apparent viscosity for the flow in porous media (53). 

Viscosity, Fluidity, and Oxygen Supply. When plant cells grow well, they can occupy 40 to 60% of the whole culture volume, and the apparent viscosity becomes very high. Tanaka (1982) examined the relationship between apparent viscosity and concentration of solids in suspension, and concluded that when the cell density exceeds 10 g/1, the slope of the apparent viscosity increases rapidly, and when cell density reaches 30 g/1, the culture medium becomes difficult to agitate and supply with oxygen. 

In [300-302], thermohydrodynamic problems for non-Newtonian fluids were studied under the assumption that temperature varies along the walls of the tube (or channel) in this case, convective heat transfer plays an important role. It was assumed that the dependence of the apparent viscosity of the medium on temperature is exponential or power-law dissipative heat release was neglected. In one-dimensional steady-state flows of this type, the pressure gradient varies along the tube. It was shown that in some cases a situation typical of thermal explosion may arise. In this situation, heat supply due to fluid convection exceeds heat withdrawal through the walls. It was also discovered that there exists another mechanism for crisis phenomena to arise. If there is a constant heat withdrawal from the tube walls and the fluid velocity is sufficiently small, then the intensive cooling of the fluid may result in an accelerated increase of the fluid viscosity, which, in turn, results in flow choking. 

The use of surfactant-stabilized foams to counteract these kinds of problems was suggested several decades ago (7, 2) and has recently become actively pursued in laboratory and field tests (3—8). The use of foam is advantageous compared with the use of a simple fluid of the same nominal mobility because the foam, which has an apparent viscosity greater than the displacing medium, lowers the gas mobility in the swept or higher permeability parts of the formation. This lowered gas mobility diverts at least some of the displacing medium into other parts of the formation that were previously unswept or underswept. From these underswept areas, the additional oil is recovered. Because foam mobility is reduced disproportionately more in higher permeability zones, improvement in both vertical and horizontal sweep efficiency can be achieved. 

Equation 20 shows that a porous medium is permeative, that is, a shear factor exists to account for the microscopic momentum loss. Our preliminary study recently reveals that, however, a porous medium is not only permeative but dispersive as well. The dispersivity of a porous medium has been traditionally characterized through heat transfer (in a single- or multifluid flow) and mass transfer (in a multifluid flow) studies. For an isothermal single-fluid flow, the dispersivity of a porous medium is characterized by a flow strength and a porous medium property-de-pendent apparent viscosity. For simplicity, we discuss the single-fluid flow behavior in this chapter without considering the dispersivity of the porous medium. 

The emulsion behaviour in porous media is discussed in [235]. O/w emulsions with volume fractions of up to 50% show Newtonian behaviour, whereas those with more than 50% are non-Newtonian liquids, the apparent viscosity of which depends on the shear rate. The viscosities of such emulsions are more than 20 times that of water and sometimes can be even comparable with that of oil. When the emulsion is moving, a temporary permeability reduction of the reservoir may occur due to the capture of small droplets by the surface of the porous medium. In this case, stable o/w emulsions may flow not as a continuous liquid, i.e. the emulsion flow largely depends on the nature of the porous medium. Therefore, it is necessary to know about the structure and physicochemical characteristics of the oil reservoir (porous medium) porosity, the mean pore diameter, the mean pore size and pore size distribution, chemical composition of the minerals ( acidic , basic , neutral ), the nature of the pore surface, first of all wettability, for a successful application of the emulsion flooding method. 

While various methods and equipment can be used to measure viscosity, the most common uses the Brookfield viscometer (Fig. 7.1). ASTM D2196, Rheological Properties of Non-Newtonian Materials by Rotational (Brookfield) Viscometer, covers this method for Model LVF and Model RVF viscometers. Brookfield LV viscometers are used for low-viscosity materials, RV for medium-viscosity formulations, and HV for high-viscosity formulations. Test Method ASTM D2556, Apparent Viscosity of Adhesives HavingShear-Rate Dependent Flow Properties also specifies... 

As regards industrial application of the method, the phenomenon entails undesirable consequences. In an oil-wet reservoir, an identical hydrodynamical effect can be approximated only if the apparent viscosity exhibited in the water-wet medium is compensated by an increase in the laboratory viscosity of the solution employed. This actually requires the use of 3-6 times as much of polymer. 

At low polymer concentrations, simple salts caused a slight reduction in the viscosity of Statoil polymer (a medium pyruvate content xanthan), and a more noticeable change in the flow curves of Flocon 4800 (a high pyruvate content xanthan). However, at higher polymer concentration, the addition of salts increased the apparent viscosity of the high pyruvate content xanthan. 

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