Brookfield DV3T Rheometer Manual de usuario descargar pdf (Pagina 85)

Brookeld Engineering Labs., Inc. Page 85 Manual No. M13-2100

VII.2 The Herschel-Bulkley Model

(τ

=shearstress, τ

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

What does it tell you?

TheHerschel-BulkleymodelissimplythePowerLawmodelwiththeadditionofτ

for yield

stress.Yieldstress,τ

,denoteshowmuchshearstressisrequiredtoinitiateow.Thismodelalso

providesaconsistencyindex,k,whichisaproduct’sviscosityat1reciprocalsecond,and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.ForHerschel-Bulkleyuids,nwillalwaysbegreaterthanorlessthan1.

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.It’sapparentviscosityincreasesasshear

rate increases.

VII-2

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Brookfield DV3T Rheometer Manual de usuario Pagina 85