Shear, effects thinning

We can solve for Q by trial and error after setting the limit in eqn. (6.199) to i. Figure 6.40 presents the value for Q as a function of power law index. As can be seen, the shear thinning effect is not very large. 

In addition to the shear thinning effect, other non-Newtonian properties bring about additional complexities in the flow pattern, as demonstrated by Unkriier (37), such as cross-machine flow superimposed on the main machine-direction flow in the inlet region. 

The physical meaning of this result is that the drag removal action of the barrel is reduced by a factor of 0.814 as a result of the temperature profile in the film on which the shear thinning effect is superimposed. 

A. J. Poslinski and D. J. Coyle, Steady Gas Penetration through Non-Newtonian Liquids in Tube and Slit Geometries Isothermal Shear-Thinning Effects, Proc. Polymer Processing Society, 10th Annu. Meet., Akron, Ohio (1994), pp. 219-220. 

Thixotropy provides a shear thinning effect that is, viscosity decreases as the shear rate increases, and vice versa. This not only allows easy pumping, dispensing, and mixing of the adhesive, but also provides sag resistance once the adhesive is applied. The thixotropic fillers work by forming a temporary structure in the mixture, which can be broken down at high rates of shear. This structure is generally the result of van der Waals forces between molecules. 

Poslinski, A. J., Ryan, M. E., Gupta, R. K., Seshadri, S. G., and Frechette, F. J. 1988. Rheological behavior of filled polymeric systems I. Yield stress and shear-thinning effects, y. Rheol. 32 703-735. 

The behavior of lyotropic crystals is usually non-Newtonian. Lamellar liquid crystals show thixotropic or negative thixotropic behavior,but shear thinning/thixotropy is more common. The shear thinning effect is ascribed to orientation of the liquid crystalline domains and some structural breakdown. Viscoelasticity has also been observed. If the concentration of the surfactant molecules is, however, low and close to the CMC, Newtonian flow will be observed. ... 

With increasing shear, Pe — the relative viscosity of suspensions — usually decreases (see Fig. 6.19). This shear thinning effect is quite moderate in colloidally stable suspensions, which actually can behave as nearly Newtonian up to... 

It is seen that the MC acts as a thickener over the whole region studied. The shear thinning effect of the polymer in the shear rate region 0.1/s to 100/s is however not sufficient for the film-coating purpose mentioned. The coating layer thickness of course increases with increasing MC content. 

This shear reversibihty is very beneficial in enhanced oil recovery field applications. It improves the well injectivity because of the shear thinning effect at the perforation and near the wellbore. Far away from the wellbore, flow velocity is reduced and viscosity is restored. For the hydrophobically associating polymers, both shear thickening and shear thinning were observed by Bock et al. (1988). It has also been reported that the viscosity after shearing was stopped was higher than that before shearing (McCormick et al., 1988). 

The effect of fluid rheology on the power consumption of helical ribbon agitators has also been evaluated [54] and power consumption as a function of generalized Reynolds number for shear thinning but inelastic fluids defined. When shear thinning effects are small, and elasticity is negligible, deviations from the Newtonian... 

The quotient (r /r o), which indicates the magnitude of shear thinning effect with increasing y, can be estimated quite well as a function of the Weissenberg number (Nwg) and the polydispersity [7], N yg is the product of a characteristic time scale for the polymer with y, and can be approximated by Equation 13.27 where p is the polymer bulk density at the temperature of calculation. (The density must be expressed in g/m3 rather than g/cc in Equation 13.27 for consistency with the units used for the other quantities entering this equation.) Since the polydispersity Mw/Mn enters Equation 13.27, r depends on the polydispersity both indirectly via the dependence of Ny/g on Mw/Mn and directly. 

Chang and Zhao23 have compared Newtonian and non-Newtonian analysis of micro-EHD contacts. Based on numerical analysis, it was concluded that the shear thinning effects of the lubricant will produce significant errors if the non-Newtonian behavior is not properly accounted for.23 Effective... 

The low viscosity and the shear thinning effect of liquid crystalline polymers are advantageous for application. For instance, the filling of molded... 

With a lower power-law index, say, n = 0.2, the apparent viscosity would still be close to the limiting shear viscosity at A of 1.6 s and the shear rate of 0.1 s. For these conditions. Cross equation (17.7) gives 77 = T7o/1.23, and Carreau equation (17.8) gives 77 = 770/I.OI. However, at A of 16 s and the shear rate of 10 s (see above), the apparent viscosity would be much lower, that is, the shear thinning effect would be much more pronounced. Both Cross and Carreau equations give 77 = 77o/14,500, that is, 36 times lower apparent viscosity compared to that at n = 0.5. 

Just to give an idea how different are the apparent and true shear rates, we will notice that the higher the shear thinning effect, the larger the difference. For example, at the power-law index n = 0.8, the difference in shear rates and, hence, apparent and true viscosities is 6.25%. For n = 0.2, the difference is 100%. 

The Power-Law Index of Some Neat Plastics As it was explained in the section Shear-thinning Effect and the Power Law Equation, the higher the deviation of a molten plastic from Newtonian behavior, the lower its power-law index and the steeper the dependence of its viscosity on shear rate. The lower the power-law index, the more sensitive the shear viscosity to flow speed. As it will be shown in this chapter later, the lower the quality of a regrind, the lower (often) its power-law index. As can be seen from Tables 17.4 and 17.5, PVC, PS, ABS, and PMMA have particularly low power-law index compared to PET or PE, hence, that lowers the window of processability for the former plastics in terms of speed. Both the... 

Flow of multilayer viscoelastic fluids in converging channel slit die was analyzed. The neutral stability contours were altered in the channel flow. The effect of convergence on interfacial stabflity was similar to that of the elasticity. Channel convergence can be used to stabilize the interface at low depth ratios provided that shear thinning effects are more dominant in more viscous layers. 

Friction speed has a small effect on the maximum friction stress. This low dependence on speed can be explained by the very low value of the glass transition temperature PDMS networks are used at ambient temperature, on their rubbery plateau. However, for PDMS 6, a slight decrease in friction stress could be explained by a pseudoplastic behavior of the confined interfacial layer (a shear thinning effect). 

In 1996, Pal studied the effect of droplet size and found it had a dramatic influence on emulsion rheology (62). Fine emulsions have much higher viscosity and storage moduli than the corresponding coarse emulsions. The shear thinning effect is much stronger in the case of fine emulsions. Water-in-oil emulsions age much more rapidly than oil-in-water emulsions. More recently, Lee et al. (63) and Aomari et al. (64) examined model emulsions and found that a maximum shear strain existed which occurred around 100s. ... 

For such flows, the range of flow rates is such that the variations in normal stresses are inconsequential relative to the shear stresses. Even when the fluid is highly elastic, the flow geometry and confinement may be such that the fluid elasticity has only a minor influence on the streamline orientations. On the other hand, shear-thinning effects upon the flow characteristics and the pressure distribution may appear to be quite important, even for low values of the shear rate. Such flow problems can be solved by considering constitutive equations that are of analogous (although, not necessarily the same) forms as those adopted for Newtonian flows as follows ... 

Figure 9. Shear thinning effect on water fractional flow under foaming conditions.

Figure 3 illustrates the relationship between steady shear viscosity and shear rate for PBTA homopolymer solutions in NMP/4% LiCl with various concentrations. This figure clearly revels the shear-thinning effect for isotropic (C C r) solutions and anisotropic (C > Ccj-) solutions with the most shear rate region. Meanwhile, a Newtonian plateau appears in a low shear rate region for anisotropic solutions, especially for C = 6 wt% and C = 6.5 wt%. Furthermore, the experimental data could be fitted with theoretical non-Newtonian fluid model. Among which, power-law model was applied for isotropic solutions and Carreau model (22) for anisotropic solutions, as shown below ... 

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