Instruction Manual
- A rheopectic uid has an increasing viscosity under a constant shear rate
(rpm).
Brookeld 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 Shear Rate dependent on the measurement
conditions. The specications of the viscometer spindle and chamber geometry 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.
The shear rate of a given measurement is determined by: the rotational speed of the spindle, the size
and shape of the spindle, the size and shape of the container used, and therefore, the distance between
the container wall and the spindle surface.
A repeatable viscosity test should control or specify the following:
1) Test temperature
2) Sample container size (or spindle/chamber geometry)
3) Sample volume
4) Viscometer model
5) Spindle used (report 2-digit spindle identication code)
6) Test speed or speeds (or the shear rate)
7) Length of time or number of spindle revolutions to record viscosity.