Dilation, liquids

Dilatant liquids have rheological behavior essentially... 

With an anomalous liquid of the pseudoplastic type, ij decreases with increasing shear stress and deformation rate, while ft increases with a dilatant liquid. There is no dependence of fj on the stress and deformation rate with a Newtonian liquid. 

The proportionality constant fe depends upon the stirrer type. For propeller stirrers fe = 10 ]68], for turbine stirrers fe = 11.5 and pitched-blade stirrers fe = 13 [104]. For blade stirrers k = 2.5, for cross-beam stirrer fe = 4.1 and for helical ribbon stirrer fe = 6.0 [411]. Calderbank [66] found that when turbine stirrers were used with Bingham and pseudoplastic fluids fe = 10 and when used with dilatant liquids fe = 12.8 (d/D) 5. Lower fe values were found as the viscoelasticity of fluids increased [104]. In the case of close-clearance anchor stirrer fe depended upon the wall clearance [24]. 

If in non-Newtonian liquids the structure of the liquid is destroyed upon increasing y, hysteresis curves are observed as shown in Fig. 1.29. The behaviour of these liquids depends not only on the time of shear but also on the past shear and thermal history. Pseudoplastic liquids of this kind are named thixotropic, and dilatant liquids are referred to as rheopectic. The longer the duration of shear, the stronger is the destruction of the liquid structure, and the longer it takes to restore it. 

In dilatant liquids, increases less than proportionally with 021, while in pseudoplastic liquids increases more than proportionally (Figure 7-4). Expressed another way In pseudoplastic liquids, the apparent viscosity rjapp = as the shear stress increases (shear thinning), whereas in... 

Feed material Dilatant liquids, cohesive pastes, filter... 

Fig. 8 Principal flow behavior of Newtonian, intrinsically viscous and dilatant liquids or melts...

By contrast, it is clear that dUatant liquids should demonstrate an increased stability in the necking sections of capillary jets and a deceleration of the later stages of the capillary breakup. A relatively rapid growth of the initial axisymmetric perturbations leads to an increase of the effective viscosity in the necking sections of the jet and its transformation into a net of practically spherical droplets connected by tiny threads. The results of the numerical calculations for dilatant liquids by Yarin [29] are depicted in Fig. 1.23. 

In dilatant liquids, D increases less than proportionally with while in pseudoplastic liquids D increases more than proportionally (Figure 7-5). Expressed another way In pseudoplastic liquids, the apparent viscosity f/app = Gij falls as the shear stress increases (shear thinning), whereas in dilatant liquids it rises (shear thickening). The fluidities, on the other hand, increase with rising g in pseudoplastic liquids and fall in dilatant liquids. At D 0, both dilatant and pseudoplastic liquids show a Newtonian behavior. Shear thickening is rare in melts and macromolecular solutions, but occurs often in dispersions. 

C) Dilatant liquid (shear thickening). This type of liquid also flows under the influence of stress, but the viscosity increases with increasing stress or shear gradient. For example, several polymer solutions show dilatant properties. 

For an ideal Newtonian liquid, the viscosity is a constant, independent of the shear rate (V). A pseudoplastic liquid exhibits a decreasing viscosity with increasing shear rate, where as a dilatant liquid shows an increasing viscosity with increasing shear rate (Fig. 6.3). Most polymer melts show pseudoplasticity. Wet beach sand is an example of a dilatant fluid. 

Figure 6.3 Viscosity as a function of shear rate for Newtonian, pseudoplastic and dilatant liquids.

Thixotropic liquids are unanimously pseudoplastic, i.e. the slope coefficient in the shear stress-shear rate diagram decreases with increasing shear rate. Pseudoplastic fluids are, however, not necessarily thixotropic. Dilatant liquids show generally rheopexy, but there are also exceptions to this rule. Rheopectic liquids are, on the other hand, always dilatant. 

A much less common type of behaviour is that of the shearthickening or dilatant liquid, which has a consistency curve of the shape of curve 4 in Fig. 6.3. The apparent viscosity increases with shear rate and, at sufficiently high shear rates, the apparent viscosity may become so high that flow ceases, an effect known as shear blocking. Shear-thickening behaviour is associated with tightly-packed, lightly-wetted or unwetted disperse substances such as oil paint sediment and wheat starch in water. 

In pseudoplastic and dilatant liquids the viscosity is no longer constant. In the former it decreases and in the latter it increases with increasing shear rate that is to say, the shear stress increases with increasing shear rate less than proportionately in a pseudoplastic and more than proportionately in a dilatant. Pseudoplastics are thus described as shear-thinning and dilatants as shear-thickening fluid systems. These two flow phenotypes can be described by an Equation the power law ... 

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