Shear, effects thickening

Figure 3 A mineral, base oil. Significant shear thickening effect is found above 10 kPa shear stress. The spread of the measuring points may Indicate a minor change from liquid state. L/D =1, 25 C, Pressure s. 1 MPa.

Fig. 3. Brownian (solid and dash-dotted lines) and hydrodynamic (dashed and dotted lines) viscosities in terms of the shear rate for different values of the radius of the Brownian particle. The figure shows the shear thinning and shear thickening effects associated to the Brownian and hydrodynamic contributions, respectively. The values of the parameters we have used are j Santamaria Holek (2005).

Firstly, at the high flow rates prevailing near the well bore in a reservoir the resulting shear thickening effect causes the injection pressure to be built up more than proportionally. As a consequence. 

Viscoelasticity may put constraints on the application of PAAm solutions in the field. At the high flow rates around the injection well the shear thickening effect can lead to excessive pressure build-up or consequently low maximum injection rates. This emphasises the need for quantification of the effects of viscoelasticity on reservoir flow. 

Some materials will increase in viscosity as the flow rate increases, and, although this is relatively rare, it is crucial to be aware of this if processi ng is to be effective. Shear thickening occurs as a result of one or more of the following situations ... 

Shear-thickening is shown in particular, as a dilatant effect, by pastes of densely packed peptised particles in which there is only sufficient liquid to fill the voids. As the shear rate is increased, this dense packing must be broken down to permit the particles to flow past one another. The resulting expansion leaves insufficient liquid to fill the voids and is opposed by surface tension forces. This explains why wet sand apparently becomes dry and firm when walked upon. 

As the shear rate increases, the viscosity of some dispersions actually increases. This is called dilatancy, or shear-thickening. Dilatancy can be due to the dense packing of particles in very concentrated dispersions for which at low shear, the particles can just move past each other but at high shear they become wedged together such that the fluid cannot fill (lubricate) the increased void volume, and the viscosity increases. An example of this effect is the apparent drying of wet beach sand when walked on, the sand in the footprint initially appears very dry and then moistens a few seconds later. Other examples include concentrated suspensions (plastisols) of polyvinyl chloride (PVC) particles in plasticizer liquid and the commercial novelty product Silly Putty (which is a silicone material). 

Shear thickening in colloidal suspensions is governed by particle size and surface roughness, in addition to the effective volume fraction of sohds. The onset of shear thickening depends on the effective particle radius, R in the hterature two relations for this dependency are formd. The first is the Peclet nmnber ... 

If one finally considers that the Magnus force depends on the particles radius as the strong dependency of the onset of shear thickening on the particles effective radius is obvious without concern for which relation exactly holds. 

Dintzis, F. R. and Bagley, E. B. 1995. Shear-thickening and transient flow effects in starch solutions. J. Appl. Polymer Sci. 56 637-640. 

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