Brookfield DV2T Viscometer Manual do Utilizador descarregar pdf (Página 66)

Brookeld Engineering Labs., Inc. Page 66 Manual No. M13-167-B0614

Appendix C - Variables in Viscosity Measurements

As with any instrument measurement, there are variables that can affect a Viscometer

measurement.Thesevariablesmayberelatedtotheinstrument(Viscometer),orthetest

uid.Variablesrelatedtothetestuiddealwiththerheologicalpropertiesoftheuid,while

instrumentvariableswouldincludetheViscometerdesignandthespindlegeometrysystem

utilized.

Rheological Properties

Fluids have different rheological characteristics that can be described by Viscometer

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Viscometer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Viscometer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 viscometer 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.

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Sachin Vaijanath Ashture 05 Mar 2025 | 15:48:33

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Brookfield DV2T Viscometer Manual do Utilizador Página 66