Shear-thinning viscosity behavior

The Williamson equation is useful for modeling shear-thinning fluids over a wide range of shear rates (15). It makes provision for limiting low and high shear Newtonian viscosity behavior (eq. 3), where T is the absolute value of the shear stress and is the shear stress at which the viscosity is the mean of the viscosity limits TIq and, ie, at r = -H... 

As is evident from Eq. (3-20) or (3-21), the Bingham plastic exhibits a shear thinning viscosity i.e., the larger the shear stress or shear rate, the lower the viscosity. This behavior is typical of many concentrated slurries and suspensions such as muds, paints, foams, emulsions (e.g., mayonnaise), ketchup, or blood. 

The polymer melt used in this example has a density of 1000 kg/m3. The following initially assumes a Newtonian flow behavior with a viscosity of 1000 Pa-s. In later computations, a more realistic shear thinning flow behavior is assumed, which can be described using the power law equation. The flow exponent n ranges between 0.4 and 0.9 and the consistency... 

While many process fluids are Newtonian, some are non-Newtonian (as seen in Figure 9.7). For such cases, it is not sufQcient to use a single value for viscosity to determine the impeller Reynolds number. Concentrated slurries are typically non-Newtonian and particle-size dependent. They are frequently shear-thinning. Dilatant behavior seldom occurs. If the system is simply shear thinning, it is usually possible to describe its rheological behavior with a simple power-law relationship ... 

These polymer fluids are typically called non-Newtonian or nonlinear fluids, as they show a decrease of viscosity with increasing fluid velocity (shear rate). This is also known as shear thinning. This behavior results from the fact that the polymer molecules are long and have many contact points interacting with each other, or entanglements. These molecular interactions determine the viscosity of polymers. When one moves them slowly, viscosity is still relatively high. For example, it is... 

Pseudoplastic A fluid whose viscosity decreases as the applied shear rate increases. Also termed shear-thinning. Pseudoplastic behavior may occur in the absence of a yield stress and also after the yield stress in a system has been exceeded (i.e., when flow begins). 

As indicated by their name.s. shear-thinning and shear-thickening fluids exhibit a decrease or inerea.se of visco.sity under shear. Mo.si. suspensions and emulsions display a shear-thinning viscosity and this is the most common behavior of non-Newtonian fluids. 

In all of these cases, the extensive intermolecular association occurring through clustering of the hydrocarbon groups was shown to result in appreciable viscosity enhancements. This was shown to be consistent with several observations including shear thinning (pseudoplastic) behavior, on addition of substances known to compete with hydrophobic interactions such as organic solvent surfactants, etc. Nevertheless, the nature of these hydrophobic... 

Figure 3-2 presents a number of t/D and rj/D curves which summarize the various phenomenological descriptions of how dispersion viscosity depends upon shear rate or time. In many cases, one observes shear thinning (viscosity decreases with increasing shear rate) and thixotropic behavior (viscosity falls with time at a constant shear rate). For this reason, the flow curve is recorded (as shown in Fig. 3-1) by measuring the shear stress both as a function of increasing shear rate and as a function of decreasing shear rate. The hysteresis visible in Fig. 3-1 is typical of thixotropic dispersions. 

Shaving products Shaw process Shear breeding Shear energy Shearlings Shearometer Shear plane Shear rate Shear stresses Shear test Shear thinning behavior Shear viscosity Sheath-core fiber... 

In packed beds of particles possessing small pores, dilute aqueous solutions of hydroly2ed polyacrylamide will sometimes exhibit dilatant behavior iastead of the usual shear thinning behavior seen ia simple shear or Couette flow. In elongational flow, such as flow through porous sandstone, flow resistance can iacrease with flow rate due to iacreases ia elongational viscosity and normal stress differences. The iacrease ia normal stress differences with shear rate is typical of isotropic polymer solutions. Normal stress differences of anisotropic polymers, such as xanthan ia water, are shear rate iadependent (25,26). 

For a Hquid under shear the rate of deformation or shear rate is a function of the shearing stress. The original exposition of this relationship is Newton s law, which states that the ratio of the stress to the shear rate is a constant, ie, the viscosity. Under Newton s law, viscosity is independent of shear rate. This is tme for ideal or Newtonian Hquids, but the viscosities of many Hquids, particularly a number of those of interest to industry, are not independent of shear rate. These non-Newtonian Hquids may be classified according to their viscosity behavior as a function of shear rate. Many exhibit shear thinning, whereas others give shear thickening. Some Hquids at rest appear to behave like soHds until the shear stress exceeds a certain value, called the yield stress, after which they flow readily. 

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