Brookfield DV2T - Appendix C - Variables in Viscosity Measurements; Rheological Properties of Fluids

Brookeld Engineering Labs., Inc. Page 67 Manual No. M13-167
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.