Viscosity infinite-shear

Non-Newtonian fluids include those for which a finite stress 1,. is reqjiired before continuous deformation occurs these are c ailed yield-stress materials. The Bingbam plastic fluid is the simplest yield-stress material its rheogram has a constant slope [L, called the infinite shear viscosity. 

L Characteristic length m R.. Infinite shear viscosity (Bingham plastics) Pa s... 

The viscosities of most real shear-thinning fluids approach constant values both at very low shear rates and at very high shear rates that is, they tend to show Newtonian properties at the extremes of shear rates. The limiting viscosity at low shear rates mq is referred to as the lower-Newtonian (or zero-shear /x0) viscosity (see lines AB in Figures 3.28 and 3.29), and that at high shear rates Mo0 is the upper-Newtonian (or infinite-shear) viscosity (see lines EF in Figures 3.28 and 3.29). 

Note 6 Extrapolation of rj and /app for non-Newtonian liquids to infinite y gives the infinite-shear viscosity, which is given the symbol qaj-... 

If some or all of this curve is present, the models used to fit the data are more complex and are of two types. The first of these is the Carreau-Yasuda model, in which the viscosity at a given point (T ) as well as the zero-shear and infinite-shear viscosities are represented. A Power Law index (mi) is also present, but is not the same value as n in the linear Power Law model. A second type of model is the Cross model, which has essentially the same parameters, but can be broken down into submodels to fit partial data. If the zero-shear region and the power law region are present, then the Williamson model can be used. If the infinite shear plateau and the power law region are present, then the Sisko model can be used. Sometimes the central power law region is all that is available, and so the Power Law model is applied (Figure H. 1.1.5). 

In most pseudoplastic liquids, Newtonian flow behavior is observed at sufficiently low and at high shear rates y, see Fig. 18. Viscosity approaching a constant value with low shear rates is called the zero-shear viscosity, p0> and its constant value at very high shear rates is called the infinite shear viscosity, p°°. 

FIGURE 12.32 Shear moduli and dynamic viscosities measured for silica spheres at = 0.46, a = 28 2nm, O + a = 76 2nm(Mellemaetal. [68]). The broken lines correspond to the infinite shear viscosities (de Kruif et al. [43]) and the solid curves to the frequency dependence predicted by the visco-elastic fluid model of Table 12.4 with the measured values of 170,171 , and Gi. Redrawn from Russel et al. [31]. Reprinted with the permission of Cambridge University Press. 

The Casson plastic viscosity can be used as the infinite shear viscosity, t]oo, (Metz et al., 1979) of dispersions by considering the limiting viscosity at infinite shear rate ... 

Figure 2-3 Plot of Shear Rate versus Apparent Viscosity for Shear Thinning Foods Identifying Three Separate Regions A Zero-Shear Viscosity at Low Shear Rates, a Power Law Region at Intermediate Shear Rates, and an Infinite-Shear Viscosity at High Shear Rates. Often, only data in the power law region are obtained.

Apparent viscosity-shear rate data of food polymer dispersions have been reviewed by Launay et al. (1986), Lopes da Silva and Rao (1992) and others. The general log versus log y curve, discussed in Chapter 2, has been used to characterize food polymer dispersions. For example, Lopes da Silva et al. (1992) found that both the modified Carreau and the Cross models, wherein the infinite shear viscosity was considered to be negligible, described the apparent viscosity-shear rate data of locustbean (LB)... 

Table 4-9 Volume Fraction (cQ), Casson Yield Stress (ooc. Pa, /n = 0.25 and m = 0.50) and Infinite Shear Viscosity (r]co, mPa s), Viscosity of Supernatant (ijs, mPa s), and Relative Viscosity ( jr) of Tapioca Starch Dispersions...

Highest magnitude of during gelatinization, infinite shear viscosity. Pa s Angular velocity, rad s ... 

Figure 1.6 Demonstration of zero shear and infinite shear viscosities for a shear-thinning polymer solution [Roger, 1977]...

Usually the limiting values of the viscosity of non-Newfonian liquids af very low and very high shear rate respectively (the so-called zero-shear and infinite-shear viscosities) are symbolised by tjo and //oa It is also worth noting that the following viscosity-related quantities are often quoted (with the appropriate symbols and imits)... 

It can be seen that as the concentration or molecular weight is increased or the temperature is decreased, both the zero and infinite shear viscosities, Tjo and Ti increases with the change in the zero shear viscosity being much greater than that for infinite shear viscosity. The... 

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