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Brookeld Engineering Labs., Inc. Page 98 Manual No. M13-167-A0415

Appendix C - Variables in Viscosity Measurements

Aswithanyinstrumentmeasurement,therearevariablesthatcanaffectaRheometermeasurement.

Thesevariablesmayberelatedtotheinstrument(Rheometer),orthetestuid.Variablesrelatedto

thetestuiddealwiththerheologicalpropertiesoftheuid,whileinstrumentvariableswouldinclude

theRheometerdesignandthespindlegeometrysystemutilized.

Rheological Properties

FluidshavedifferentrheologicalcharacteristicsthatcanbedescribedbyRheometermeasurements.

Wecanthenworkwiththeseuidstosuitourlaborprocessconditions.

Therearetwocategoriesofuids:

Newtonian - TheseuidshavethesameviscosityatdifferentShearRates(differentRPMs)

andarecalledNewtonianovertheShearRaterangetheyaremeasured.

Non-Newtonian - These uids have different viscosities at different shear rates (different

RPMs).Theyfallintotwogroups:

1) TimeIndependentnon-Newtonian

2) TimeDependentnon-Newtonian

Time Independent

Pseudoplastic - Apseudoplasticmaterialdisplaysadecreaseinviscositywithanincrease

inshearrate,andisalsoknownas“shearthinning”.IfyoutakeRheometer

readingsfromalowtoahighRPMandthenbacktothelowRPM,andthe

readingsfalluponthemselves,thematerialistimeindependentpseudoplastic

(shearthinning).

Time Dependent

Thixotropic - Athixotropicmaterialhasdecreasingviscosityunderconstantshearrate.

IfyousetaRheometerataconstantspeedrecordingcPvaluesovertime

andndthatthecPvaluesdecreasewithtime,thematerialisthixotropic.

 - IfyoutakerheometerreadingsfromalowRPMtoahighRPMandthen

backtothelowRPM,andthereadingsarelowerforthedescendingstep,

thematerialistimedependant,thixotropic.

Brookeldpublication,“More Solutions to Sticky Problems”,includesamoredetaileddiscussionof

rheologicalpropertiesandnon-Newtonianbehavior.

Brookfield DV3T User Manual

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