Shear thinning liquid

Figure 7-13. Deviation from Newtonian power curve for shear thinning liquids. (Source Holland, F. A. and Bragg, R. Fluid Flow for Chemical Engineers, 2nd ed., Edward Arnold, 1995.)...

For a more highly shear-thinning liquid, the minimum drag ratio becomes even smaller although more air must be added to achieve the condition. 

To reduce the pressure drop, and hence the upstream pressure in a pipeline, for a given flowrate of shear-thinning liquid. 

Deviation from Newtonian power curve for shear thinning liquids... 

Figure 5.10 illustrates the use of this method to extend a Newtonian power curve in the laminar region into a non-Newtonian power curve. The full line is the Newtonian power curve obtained by Rushton, Costich and Everett for a flat blade turbine system. The dashed line is a plot of the data of Metzner and Otto for shear thinning liquids. 

Nienow and Elson (1988) have reviewed work done mainly by them and their co-workers on the mixing of non-Newtonian liquids in tanks. The above approach for inelastic, shearing thinning liquids has been largely substantiated but considerable doubt has been cast over using this method for dilatant, shear thickening materials. 

A shear thinning liquid has an apparent dynamic viscosity given by the equation... 

Experimentally, it is sometimes difficult to detect differences between a shear-thinning liquid in which the viscosity decreases with increasing shear, and a thixotropic material in which the viscosity decreases with time, because of the combined shear and time effects that occur during a series of measurements. This is especially tme if only a few data points are collected. In addition, most materials that are thixotropic are also shear thinning. In fact,... 

Perhaps the most important and striking features of high internal phase emulsions are their rheological properties. Their viscosities are high, relative to the bulk liquid phases, and they are characterised by a yield stress, which is the shear stress required to induce flow. At stress values below the yield stress, HIPEs behave as viscoelastic solids above the yield stress, they are shear-thinning liquids, i.e. the viscosity varies inversely with shear rate. In other words, HIPEs (and high gas-fraction foams) behave as non-Newtonian fluids. 

Pressure Flow Calculations Using the Equivalent Newtonian Viscosity6 Consider fully developed isothermal laminar pressure flow between parallel plates of a shear-thinning liquid with a flow curve fitted to the following polynomial relationship above the shear rate )>0 ... 

If rj is independent of the shear rate y a liquid is called Newtonian. Water and other low molecular weight liquids typically are Newtonian. If rj decreases with increasing y, a liquid is termed shear thinning. Examples for shear thinning liquids are entangled polymer solutions or surfactant solutions with long rod-like micelles. The zero shear viscosity is the value of the viscosity for small shear rates ij0 = lim,> o tj y). The inverse case is also sometimes observed rj increases with increasing shear rate. This can be found for suspensions and sometimes for surfactant solutions. In surfactant solutions the viscosity can be a function of time. In this case one speaks of shear induced structures. 

A method for predicting pressure drop and volume fraction for non-Newtonian fluids in annular flow has been proposed by Eisen-berg and Weinberger (AlChE J., 25, 240-245 [1979]). Das, Biswas, and Matra (Can. J. Chem. Eng., 70,431 37 [1993]) studied holdup in both horizontal and vertical gas/liquid flow with non-Newtonian liquids. Farooqi and Richardson (Trans Inst. Chem. Engrs., 60, 292-305, 323-333 [1982]) developed correlations for holdup and pressure drop for gas/non-Newtonian liquid horizontal flow. They used a modified Lockhart-Martinelli parameter for non-Newtonian liquid holdup. They found that two-phase pressure drop may actually be less than the single-phase liquid pressure drop with shear thinning liquids in laminar flow. 

Liquid crystals can be classified into lyotropic and thermotropic systems. The rheology of thermotropic liquid crystals is less documented, but in general, nematic liquid crystals were found to show Newtonian flow, whereas smectic and cholesteric liquid crystals demonstrated more or less pronounced plug flow. Plug flow is typical for non-Newtonian, shear thinning liquids. ... 

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