Brookfield DV-E Viscometer - Manual (Page 19)

Brookfield Engineering Labs., Inc. Page 19 Manual No. M98-350-J0912
In taking viscosity measurements with the DV-E Viscometer, there are two considerations which
pertain to the low viscosity limit of effective measurement.
1) Viscosity measurements should be accepted within the equivalent % Torque Range from
10% to 100% for any combination of spindle/speed rotation.
2) Viscosity measurements should be taken under laminar flow conditions, not under turbulent
flow conditions.
The first consideration has to do with the accuracy of the instrument. All DV-E Viscometers have a
full scale range accuracy of (+/-) 1% of any spindle/speed rotation. We discourage taking readings
below 10% of range because the potential viscosity error of (+/-) 1% is a relatively high number
compared to the instrument reading.
The second consideration involves the mechanics of fluid flow. All rheological measurements of
fluid flow properties should be made under laminar flow conditions. Laminar flow is flow wherein
all particle movement is in layers directed by the shearing force. For rotational systems, this means
all fluid movement must be circumferential. When the inertial forces on the fluid become too great,
the fluid can break into turbulent flow wherein the movement of fluid particles becomes random
and the flow can not be analyzed with standard math models. This turbulence creates a falsely high
viscometer reading with the degree of non-linear increase in reading being directly related to the
degree of turbulence in the fluid.
For the following geometries, we have found that an approximate transition point to turbulent flow
occurs:
1) No. 1 LV Spindle: 15 cP at 60 RPM
2) No. 1 RV (optional) Spindle: 100 cP at 50 RPM
3) UL Adapter: 0.85 cP at 60 RPM
Turbulent conditions will exist in these situations whenever the RPM/cP ratio exceeds the values listed
above. The viscosity at which turbulence starts is still at best a guess. Because it is a relationship
between viscous and inertial forces, it can vary dramatically from fluid to fluid. Turbulence starts
as a small deviation or increase in viscosity for a Newtonian fluid. Basically there is no specific
shear that it starts at, only an approximate region of shear depending on the fluid.