Flow behavior Newtonian

The mechanical properties of LDPE fall somewhere between rigid polymers such as polystyrene and limp or soft polymers such as polyvinyls. LDPE exhibits good toughness and pHabiUty over a moderately wide temperature range. It is a viscoelastic material that displays non-Newtonian flow behavior, and the polymer is ductile at temperatures well below 0°C. Table 1 fists typical properties. 

Dispersion of a soHd or Hquid in a Hquid affects the viscosity. In many cases Newtonian flow behavior is transformed into non-Newtonian flow behavior. Shear thinning results from the abiHty of the soHd particles or Hquid droplets to come together to form network stmctures when at rest or under low shear. With increasing shear the interlinked stmcture gradually breaks down, and the resistance to flow decreases. The viscosity of a dispersed system depends on hydrodynamic interactions between particles or droplets and the Hquid, particle—particle interactions (bumping), and interparticle attractions that promote the formation of aggregates, floes, and networks. 

Solutions of methylceUuloses are pseudoplastic below the gel point and approach Newtonian flow behavior at low shear rates. Above the gel point, solutions are very thixotropic because of the formation of three-dimensional gel stmcture. Solutions are stable between pH 3 and 11 pH extremes wiU cause irreversible degradation. The high substitution levels of most methylceUuloses result in relatively good resistance to enzymatic degradation (16). 

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 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-... 

The main result was that regardless of dendrimer generation (i.e. molecular weight) and concentration, all of the examined solutions exhibited characteristic Newtonian flow behavior, as shown in Figure 14.6. This was in striking contrast to the typical behavior of either chain-type polymers of comparable molecular weights [33], or suspensions of spherical particles [34-37], both of which exhibit... 

As with many polymers, polyisoprene exhibits non-Newtonian flow behavior at shear rates normally used for processing. The double bond can undergo most of the typical reactions such as carbene additions, hydrogenation, epoxidation, ozonolysis, hydrohalogena-tion, and halogenation. As with the case of the other 1,4-diene monomers, many copolymers are derived from polyisoprene or isoprene itself. 

Mixing processes involved in the manufacture of disperse systems, whether suspensions or emulsions, are far more problematic than those employed in the blending of low-viscosity miscible liquids due to the multi-phasic character of the systems and deviations from Newtonian flow behavior. It is not uncommon for both laminar and turbulent flow to occur simultaneously in different regions of the system. In some regions, the flow regime may be in transition, i.e., neither laminar nor turbulent but somewhere in between. The implications of these flow regime variations for scale-up are considerable. Nonetheless, it should be noted that the mixing process is only completed when Brownian motion occurs sufficiently to achieve uniformity on a molecular scale. 

The electroviscous effects and the other effects discussed in Sections 4.7a-c lead to what is called non-Newtonian behavior in the flow of dispersions. In the next section, we begin with a brief review of the basic concepts concerning deviations from Newtonian flow behavior and then move on to consider how high particle concentrations and electroviscous effects affect the flow and viscosity. 

Explain what a non-Newtonian fluid is, and list the different types of non-Newtonian flow behavior. 

The critical stirrer speed for solid suspension increases slightly with increasing aeration rate, sohd loading, and non-Newtonian flow behavior [14]. 

Uppuluri, S., Keinath, S. E., Tomalia, D. A., Dvornic, P. R., Rheology of dendrimers. I. Newtonian flow behavior of medium and highly concentrated solutions of polyamidoamine (PAMAM) dendrimers in ethylenediamine (EDA) solvent. Macromolecules 1998, 31, 4498-4510. 

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... 

Because the Reynolds number is much smaller than 1 and a Newtonian flow behavior is being observed in the first place, the Navier-Stokes equations convert to Stokes equations, and we obtain a system of linear equations for the flow calculations. It therefore follows that there must be a linear relationship both between the flow rate and the pressure and between the flow rate and the power. This is demonstrated in Figs. 8.10 and 8.11 in which the dimensionless conveying and power characteristic are illustrated, respectively. The red lines reflect the Newtonian cases. As expected, a linear relationship is revealed. 

The following observations also assume a Newtonian flow behavior. The pressure difference in the axial direction is 0 bar. 

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°°. 

Colloidal systems, because of their large number of dispersed particles, show non-Newtonian flow behavior. For a highly dilute dispersion of spherical particles, the following equation has been proposed by Einstein ... 

In this equation, viscosity is independent of the degree of dispersion. As soon as the ratio of disperse and continuous phases increases to the point where particles start to interact, the flow behavior becomes more complex. The effect of increasing the concentration of the disperse phase on the flow behavior of a disperse system is shown in Figure 8-41. The disperse phase, as well as the low solids dispersion (curves 1 and 2), shows Newtonian flow behavior. As the solids content increases, the flow behavior becomes non-Newtonian (curves 3 and 4). Especially with anisotropic particles, interaction between them will result in the formation of three-dimensional network structures. These network structures usually show non-Newtonian flow behavior and viscoelastic properties and often have a yield value. Network structure formation may occur in emulsions (Figure 8-42) as well as in particulate systems. The forces between particles that result in the formation of networks may be... 

From equation 3.7, as shown in Table 3-1, it can be deduced that for non-Newtonian foods the correction term to Newtonian shear rate depends on the extent to which a fluid deviates from Newtonian behavior and the size of gap between the inner and outer cylinders. To minimize errors in the calculated shear rates, it would be preferable to employ concentric cylinders with narrow gap between them. Therefore, some of the commercially available units have the ratio of the radii (n/ro) of about 0.95. However, it is not obvious that the software provided by viscometer manufecturers contains corrections for non-Newtonian flow behavior, so that, when ever possible, it is advisable to use narrow gap concentric cylinder systems for fluids that deviate considerably from Newtonian behavior. 

Double Layer Interactions and Interfacial Charge. Schulman et al (42) have proposed that the phase continuity can be controlled readily by interfacial charge. If the concentration of the counterions for the ionic surfactant is higher and the diffuse electrical double layer at the interface is compressed, water-in-oil microemulsions are formed. If the concentration of the counterions is sufficiently decreased to produce a charge at the oil-water interface, the system presumably inverts to an oil-in-water type microemulsion. It was also proposed that for the droplets of spherical shape, the resulting microemulsions are isotropic and exhibit Newtonian flow behavior with one diffused band in X-ray diffraction pattern. Moreover, for droplets of cylindrical shape, the resulting microemulsions are optically anisotropic and non-Newtonian flow behavior with two di-fused bands in X-ray diffraction (9). The concept of molecular interactions at the oil-water interface for the formation of microemulsions was further extended by Prince (49). Prince (50) also discussed the differences in solubilization in micellar and microemulsion systems. 

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