Newtonian viscous behavior

Caustic Waterflooding. In caustic waterflooding, the interfacial rheologic properties of a model crude oil-water system were studied in the presence of sodium hydroxide. The interfacial viscosity, the non-Newtonian flow behavior, and the activation energy of viscous flow were determined as a function of shear rate, alkali concentration, and aging time. The interfacial viscosity drastically... 

The typical viscous behavior for many non-Newtonian fluids (e.g., polymeric fluids, flocculated suspensions, colloids, foams, gels) is illustrated by the curves labeled structural in Figs. 3-5 and 3-6. These fluids exhibit Newtonian behavior at very low and very high shear rates, with shear thinning or pseudoplastic behavior at intermediate shear rates. In some materials this can be attributed to a reversible structure or network that forms in the rest or equilibrium state. When the material is sheared, the structure breaks down, resulting in a shear-dependent (shear thinning) behavior. Some real examples of this type of behavior are shown in Fig. 3-7. These show that structural viscosity behavior is exhibited by fluids as diverse as polymer solutions, blood, latex emulsions, and mud (sediment). Equations (i.e., models) that represent this type of behavior are described below. 

The physical appearance of liquid laundry detergents remained unchanged for a long time. They were on the market as low viscous (250-300 mPa s) water-thin products with Newtonian flow behavior. This changed with the launch of deter-... 

Consistent with the Newtonian flow of concentrated PAMAM solutions, it was found that all three types of dendrimers [40, 41, 50] under steady-shear conditions, and both PAMAMs [40] and PPIs [50] under creep [16,50] showed typical viscous behavior at all applied stress levels and testing temperatures. For example, as illustrated in Figure 14.9 [40], all of the first seven generations of PAMAMs showed constant viscosities over the entire ranges of shear rates investigated, and in addition to this, there was no hysteresis between the forward and the reverse stress sweeps in steady shearing, indicating the absence of thixotropy. 

With this background of non-Newtonian behavior in hand, let us examine the viscous behavior of suspensions and slurries in ceramic systems. For dilute suspensions on noninteracting spheres in a Newtonian liquid, the viscosity of the suspension, r)s, is greater than the viscosity of the pure liquid medium, rjp. In such cases, a relative viscosity, rjr, is utilized, which is defined as rjs/rjL. For laminar flow, is given by the Einstein equation... 

II. Viscous flow through a capillary and flow processes between rotating cylinders. We shall try to calculate the viscous behavior for non-Newtonian liquids flowing... 

Thus far we have given exclusive attention to the flow of purely viscous fluids. In practice the chemical engineer often encounters non-Newtonian fluids exhibiting elastic as well as viscous behavior. Such viscoelastic fluids can be extremely complex in their rheological response. The le vel of mathematical complexity associated with these types of fluids is much more sophisticated than that presented here. Within the limits of space allocated for this article, it is not feasible to attempt a summary of this very extensive field. The reader must seek information elsewhere. Here we shall content ourselves with fluids that do not exhibit elastic behavior. 

With the help of model experiments, a wiped film heat exchanger, needed in a continuous production process to heat up a very viscous throughput, q, exhibiting Newtonian viscosity behavior, should be designed. 

Real materials are neither truly Hookean nor truly Newtonian, though some exhibit Hookean or Newtonian behavior under certain conditions (Barnes et al., 1989). Real materials may exhibit nonlinearity, which is a lack of direct proportionality between stress and strain, or between stress and strain rate. Real materials may exhibit either predominantly elastic behavior or predominantly viscous behavior, or a measurable combination of the two, depending on the stress or strain and the duration of its application (Barnes et al., 1989). Such materials are termed viscoelastic. Barnes et al. (1989) pointed out that it is better to classify rheological behavior than to classify materials, a given material can then be included in more than one rheological class depending on experimental conditions. 

It is important to realize that this type of behavior is not just a simple addition of linear elastic and viscous responses. An ideal elastic solid would display an instantaneous elastic response to an applied (non-destructive) stress (top of Figure 13-74). The strain would then stay constant until the stress was removed. On the other hand, if we place a Newtonian viscous fluid between two plates and apply a shear stress, then the strain increases continuously and linearly with time (bottom of Figure 13-74). After the stress is removed the plates stay where they are, there is no elastic force to restore them to their original position, as all the energy imparted to the liquid has been dissipated in flow. 

If we have a model for linear elastic behavior, we must surely have one for Newtonian viscous flow and we do, the dashpot shown also in Figure 13-87. This is simply a piston in a cylinder that can be filled with various Newtonian fluids, each with a different value of the viscosity. Pulling (or pushing) on the piston causes it to move, as the fluid flows past the small gap between the piston and the cylinder walls, but the rate of deformation will depend on the viscosity of the fluid. (Some students who are a bit slow on the uptake or, more probably, trying to give us a hard time, ask what happens when the piston clunks to a stop at the bottom of the cylinder or pops out of the end don t be too literal minded here, this is just a picture representing a type of behavior )... 

FIGURE 11.12 Viscous behavior of complex fluids (i) shear stress vs. shear rate and (ii) viscosity vs. shear rate. The notation for the curves is (a) Newtonian, (b) shear thinning, (c) shear thickening, (d) Bingham plastic, and (e) pseudoplastic. 

Finally, the material will flow as if it were a Newtonian body (C-D in Fig. 13A). Here, the ruptured links have no time to reform, and the linearity of this part of the curve indicates fully viscous behavior. In the mechanical model, this region refers to the deformation of dashpot 2 (Fig. 13B). The Newtonian compliance can be calculated from ... 

Shear thinning of concentrated suspensions is typical for submicron particles dispersed in a low viscosity Newtonian fluid.At low shear strain rates. Brownian motion leads to a random distribution of the particles in the suspension, and particle collision will result in viscous behavior. At high shear strain rates, however, particles will arrange in layers, which can slide over each other in the direction of flow. This results in a reduced viscosity of the system in agreement with the principles of shear thinning. A pro-noimced apparent yield stress can be found for shear thinning suspensions, if the Brownian motion is suppressed by electrostatic repulsion forces, which result in three-dimensional crystal-like structures of the particles with low mobility. 

In practice, there are few materials employed in the formulation of pharmaceutical and biomedical systems that conform to either Hooke s law or Newtonian theory (16,18). Most polymeric systems exhibit behavior in which the applied stress is proportional to both the resultant strain and the rate of strain, i.e., exhibit varying degrees of both elastic and viscous behavior simultaneously. Such materials are known as viscoelastic (the term elastoviscous is sometimes used when referring to materials that exhibit predominantly viscous behavior). 

The effects of such physical properties as hquid density, viscosity and surface tension on the capillary jet breakup in the case of Newtonian viscous hquids are discussed in the previous sections of this chapter. In many applications non-Newtonian liquid jet flows are used, which demonstrate very peculiar deviations from the Newtonian behavior. This section is devoted to the discussion of the dominating effects of rheological properties on jet breakup. 

Most of the polymers are veiy viscous even at high temperatures. Moreover, they exhibit non-Newtonian flowing behavior. Considerable care is required to ensure precise measurements. We will discuss here surface tensions of polymer blends and of random copolymers especially, we will focus on its variation with composition. 

Unfortunately, the Reynolds-Nusselt dimensional analysis studies are not directly applicable to polymer melt and rubber processing for two important reasons. First, they are based on Newtonian fluid behavior, and second, they do not include viscous dissipation heating. 

Fermentation media may exhibit a highly viscous non-Newtonian flow behavior (1,2) resulting in low aeration efficiencies (3). For studying the volumetric mass transfer coefficients (kj a) under such conditions solutions of sodium carboxymethylcellulose (CMC) are often used as model media. In bubble columns such investiga-... 

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