Brookfield CAP1000 Viscometer Manual do Utilizador descarregar pdf (Página 26)

Brookeld Engineering Labs., Inc. Page 24 Manual No. M02-312A0607

APPENDIX A - Variables in Viscosity Measurements

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

ment. 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 measure-

ments. 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

The time dependency is the time they are held at a given Shear Rate (RPM). They are non-

Newtonian, and when you change the Viscometer spindle speed, you get a different viscosity.

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 Viscom-

eter 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 and 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 P values

over time, and nd that the P values decrease with time, the material is

thixotropic.

Brookeld publication,

“More Solutions to Sticky Problems” includes a more detailed discus-

sion of rheological properties and non-Newtonian behavior.

1 2 ... 21 22 23 24 25 26 27 28 29 30

Sem comentários

Brookfield CAP1000 Viscometer Manual do Utilizador Página 26