Pseudo-plastics

This procedure can be repeated for different values of N. A compilation of the experimental values of ks for a variety of impellers, turbine, propeller, paddle, anchor, and so on, has been given by Skelland(16), and an examination of Table 7.1 suggesLs that for pseudo-plastic liquids, ks lies approximately in the range of 10-13 for most configurations of practical interest/22 231 SKELLAND l6) has also correlated much of the data on the agitation of purely viscous non-Newtonian fluids, and this is shown in Figure 7.8. 

Bhi KNER. J. L. and Smith, J. M- Trans. Inst. Chem. Eng. 44 (1966) T224. Anchor-agitated systems Power input with Newtonian and pseudo-plastic fluids. 

In order to understand the nature and mechanisms of foam flow in the reservoir, some investigators have examined the generation of foam in glass bead packs (12). Porous micromodels have also been used to represent actual porous rock in which the flow behavior of bubble-films or lamellae have been observed (13,14). Furthermore, since foaming agents often exhibit pseudo-plastic behavior in a flow situation, the flow of non-Newtonian fluid in porous media has been examined from a mathematical standpoint. However, representation of such flow in mathematical models has been reported to be still inadequate (15). Theoretical approaches, with the goal of computing the mobility of foam in a porous medium modelled by a bead or sand pack, have been attempted as well (16,17). 

Grenville, R. K., Blending of viscous and pseudo-plastic fluids , Ph.D. Thesis, Cranfield Institute of Technology, Cranfield (UK) (1992). 

The Newtonian viscosity of some polymers increases essentially linearly with the weight average molecular weight, and for other polymers the Newtonian viscosity increases with an exponential power of the molecular weight. The exponential power is found to be about 3.4, but this power does deviate for some polymers. These two transitions, Newtonian to pseudo-plastic and linear to 3.4 power in the Newtonian range are often related to molecular structure as demonstrated in Fig. 3.31 [22]. The polystyrene data used to develop the Adams-Campbell viscosity function showed almost no shear thinning at [18]. That is why the power law slope, s, is a function of and M. At the slope is zero and the material would be essentially Newtonian. 

The non-aqueous HIPEs showed similar properties to their water-containing counterparts. Examination by optical microscopy revealed a polyhedral, poly-disperse microstructure. Rheological experiments indicated typical shear rate vs. shear stress behaviour for a pseudo-plastic material, with a yield stress in evidence. The yield value was seen to increase sharply with increasing dispersed phase volume fraction, above about 96%. Finally, addition of water to the continuous phase was studied. This caused a decrease in the rate of decay of the emulsion yield stress over a period of time, and an increase in stability. The added water increased the strength of the interfacial film, providing a more efficient barrier to coalescence. 

Emulsion viscosities have been measured as a function of water content (10, 20 and 40S), temperature and shear rate in a thermostatted rotating viscometer. The shear rates were varied between 0.277 and 27.7 s"1 with measurements taken at temperatures between 5 and 20° C. Above 20°C, separation of water from the emulsion occurred, rendering viscosity measurements unreliable. The apparent viscosity of the emulsion below 20° C increases drastically with the watercut in the emulsion and decreases with Increasing shear rate (Fig. 5). Emulsions containing more than 20X water were found to behave as pseudo-plastic fluids. 

Leighton, A. and Kurtz, F. 1930. The pseudo-plasticity of skim milk. Agri. Eng. 11, 22-23. 

Fig. 1. Behavior of non-Newtonian substances 0) true plastic (sometimes called a Bingham body (2) pseudo plastic (3) dllatant (4) thixotropic and (5) rheopectic...

The Effect of Pseudo-plasticity in Filling of Injection Moulds with Plastisols 109... 

The effect of pseudo-plasticity was reportedly known for different plastisols, in particular, for plastisols II described in Sect. 3. The rheological behaviour of these systems with an accuracy sufficient for the purposes of engineering is given by the Bingham-Shvedov law within the extended range of shear rates (10-2 < y < 102) ... 

The melt flow under isothermal conditions, when it is described by the rheological equation for the Newtonian or power law liquid, has been studied in detail63 66). The flow of the non-Newtonian liquid in the channels of non-round cross section for the liquid obeying the Sutterby equation have also been studied 67). In particular, the flow in the channels of rectangular and trigonal cross section was studied. In the analysis of the non-isothermal flow, attention should be paid to the analysis 68) of pseudo-plastic Bingham media. 

Solyom and Ekwall (20) have studied rheology of the various pure liquid crystalline phases in the sodium caprylate-decanol-water system at 20 °C, for which a detailed phase diagram is available. Their experiments using a cone-and-plate viscometer show that, in general, apparent viscosity decreases with increasing shear rate (pseudo-plastic behavior). Values of apparent viscosity were a few poise for the lamellar phase (platelike micelles alternating with thin water layers), 10-20 poise for the reverse hexagonal phase (parallel cylindrical micelles with polar... 

FIGURE 19 Increase of process horsepower versus weight percent solids, showing discontinuity when criteria changes from solids suspension to pseudo-plastic blending. 

Blending of high-viscosity materials, which are almost always pseudo-plastic, involves a different concept. The degree of pseudo-plasticity is determined by the exponent n in the equation... 

Figure 13.3 gives the log complex viscosity values of EVA, EVA-NMM, andEVA-OMM compounds versus log co (angular) frequency. The pristine EVA shows, due to lack of matrix reinforcement, lower viscosity than the composites. The nonlinear decrease of the viscosity of EVA against increasing shear rate is characteristic for pseudo-plastic materials. 

There are two general types of constitutive equations for fluids Newtonian and non-Newtonian. For Newtonian fluids, the relation between the stress tensor, t, and the rate of deformation tensor or the shear stress is linear. For non-Newtonian fluids the relation between the stress tensor and the rate of deformation tensor is nonlinear. The various Newtonian and non-Newtonian rheologies of fluids are shown in Figure 12.2. There are four types of behavior (1) Newtonian, (2) pseudo-plastic, (3) Bingham plastic, and (4) dilatent. The reasons for these different rheological behaviors will also be discussed in subsequent sections of this chapter. But first it is necessary to relate the stress tensor to the rate of deformation tensor. 

The stress for pseudo-plastic and dilatent fluids is not a linear function of shear rate. For non-Newtonian fluids, the relation between t and A is not a simple proportionality because the viscosity is a function of A. For a Bingham plastic fluid, the following relationship holds ... 

For a power law fluid valid for dilatant and pseudo-plastic fluids, the following relationship holds ... 

For the Reiner—Philippoff model [2] for pseudo-plastic fluids. 

At h h polymer concentrations, polymer molecules entangle, producing pseudo-plastic rheological behavior. This occurs at a polymer concentration, cf = comparable to that in the polymer... 

---