Brookfield DV2+Pro Viscometer Manual do Utilizador descarregar pdf (Página 57)

Brookeld Engineering Labs., Inc. Page 57 Manual No. M03-165-F0612

V1.3.1 The Power Law (Ostwald) Model

τ = k

( τ=shearstress,k=consistencyindex, =shearrate,andn=owindex)

What does it tell you?

The Power Law model provides a consistency index, k,whichisaproduct’sviscosityatone

reciprocal second. (Reciprocal seconds are the units of measurement for shear rate.) It also

providesaowindex,n, which indicates the degree with which a material exhibits non-Newtonian

owbehavior.SinceNewtonianmaterialshavelinearshearstressvs.shearratebehaviorand

ndescribesthedegreeofnon-Newtonianow,theowindexessentiallyindicateshow“non-

linear” a material is.

Figure V1-14

When n < 1 the product is shear-thinning or Pseudoplastic. This means the apparent viscosity

decreases as shear rate increases. The closer n is to 0, the more shear thinning the material is.

When n > 1 the product is shear-thickening or Dilatant. Their apparent viscosity increases as

shear rate increases.

When should you use it?

Thismodelshouldbeusedwithnon-Newtonian,time-independentuidsthatdonothaveayield

stress.Theseuidswillbegintoowunderanyamountofshearstress.Graphsofsuchmaterial

generally intersect the y-axis at 0.

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