Brookfield DV2+Pro Viscometer Bedienungsanleitung PDF herunterladen (Seite 74)

Brookeld Engineering Labs., Inc. Page 74 Manual No. M03-165-F0612

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 dpendant, thixotropic.

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

rheological properties and non-Newtonian behavior.

Viscometer Related Variables

Mostuidviscositiesarefoundtobenon-Newtonian.TheyaredependentonShearRate,timeoftest

andthespindlegeometryconditions.ThespecicationsoftheViscometerspindleandchambergeom-

etry will affect the viscosity readings. If one reading is taken at 2.5 rpm, and a second at 50 rpm, the

two cP values produced will be different because the readings were made at different shear rates. The

faster the spindle speed, the higher the shear rate.

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Brookfield DV2+Pro Viscometer Bedienungsanleitung Seite 74