Non-Newtonian Flow Properties

As mentioned earlier, for non-Newtonian fluids, the coefficient of viscosity is not a constant, but is itself a function of the shear rate. This leads to some very interesting flow properties. Some convenient ways to summarize the flow properties of 

Pseudoplastic As shear rate increases, Paint, polymer solutions. 

Pseudoplastic with yield Pseudoplastic or Newtonian Toothpaste, lipstick, grease, oil-well 

Thixotropic Time-dependent pseudoplastic flow. At constant applied shear rate, viscosity decreases. In a flow curve, hysteresis occurs. Paint, quicksand. In bentonite clay gels which liquefy on shaking and solidify on standing, there is a time-dependent aligning to match the induced flow. After the shear rate is reduced it takes some time for the original alignments to be restored. 

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Non-Newtonian Flow Properties 231 Table 6.7 Some descriptions appropriate to different yieid stresses. 

These non-Newtonian flow properties of the melts are designated by the term intrinsic viscosity. 

Subsequent work with a helical ribbon impeller [Carreau et al., 1992 Cheng and Carreau, 1994] suggests that the power consumption in the presence of a gas may either increase or decrease, depending upon the non-Newtonian flow properties of the liquid. For instance, Carreau et al. [1992] report reduced levels of power consumption in highly pseudoplastic liquids when gas is present (presumably due to the enhanced levels of shearing) whereas, in aerated visco-elastic liquids, the power always increases. The currently available correlations for the estimation of power imder aerated conditions are too tentative to be included here [Cheng and Carreau, 1994],... 

Ronningsen, H. P., Bjorndal, B., Hansen, A. B., Pedersen, W. B. (1991). Wax precipitation from North Sea crude oils. 1. Crystallization and dissolution temperature, and Newtonian and non-Newtonian flow properties. Energy and Fuels. 5 895-908. 

The best designed die or feedblock does not necessarily ensure a commercially acceptable product. Layered melt streams flowing through a coextrusion die can become unstable leading to layer nonuniformities and even intermixing of layers under certain conditions. The causes of these instabilities are related to non-Newtonian flow properties of pol5uners and viscoelastic interactions. 

This test method covers the determination of the viscosity of asphalt cements by means of a cone-plate viscometer. It is applicable to materials having viscosities in the range from 10 to 10 P (10 to 10 Pa s) and is therefore suitable for use at temperatures where viscosity is in the range indicated. The shear rate may vary between approximately 10 to 10 s and the method is suitable for determination on materials having either Newtonian or non-Newtonian flow properties. 

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. 

A wide variety of nonnewtonian fluids are encountered industrially. They may exhibit Bingham-plastic, pseudoplastic, or dilatant behavior and may or may not be thixotropic. For design of equipment to handle or process nonnewtonian fluids, the properties must usually be measured experimentally, since no generahzed relationships exist to pi e-dicl the properties or behavior of the fluids. Details of handling nonnewtonian fluids are described completely by Skelland (Non-Newtonian Flow and Heat Transfer, Wiley, New York, 1967). The generalized shear-stress rate-of-strain relationship for nonnewtonian fluids is given as... 

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... 

Non-Newtonian flow may result if the monolayer array consists of molecules that interact by specific Coulombic or dipole interactions to form floating islands , which in turn may interact by van der Waals forces around their peripheries (Joly, 1956). Non-Newtonian flow may also be a property of collapsed films. The resulting differences in viscosity over a range of flow rates may then reflect film-component segregation or partial monolayer collapse. 

Schremp,F. W., Ferry, J.D., Evans, W. W. Mechanical properties of substances of high molecular weight. IX. Non-Newtonian flow and stress relaxation in concentrated polyisobutylene and polystyrene solutions. J. Appl. Phys. 22,711-717 (1951). 

For convenience, this chapter has been divided into three sections in which the viscosity of dilute solutions and dispersions, non-Newtonian flow, and the viscoelastic properties of semi-solid systems are discussed. 

Inoue T, Okamoto H, Osaki K (1991) Birefringence of amorphous polymers. 1 Dynamic measurements on polystyrene. Macromolecules 24 5670—5675 Isayev AI (1973) Generalised characterisation of relaxation properties and high elasticity of polymer systems. J Polym Sci A-2 116 2123—2133 Ito Y, Shishido S (1972) Critical molecular weight for onset of non-Newtonian flow and upper Newtonian viscosity of polydimethylsiloxane. J Polym Sci Polym Phys Ed 10 2239— 2248... 

Selection of a polymerization reactor depends on production costs, simplicity, and energy efficiency, all of which depend on the viscosity and the non-Newtonian rheological properties of the reaction mixture (Oldshue et al, 1982 Middleman, 1977). Flow properties significantly influence the nature of the reactor, agitator size, power, and design (Gerrens, 1982). 

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... 

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