Brookfield DV-III Rheometer - Manual (Page 36)

- 36 -
Helipath with T-Bar Spindles
T-A 156 - 187,460 2,000 - 2,000,000 4,000 - 4,000,000 16,000 - 16,000,000
T-B 312 - 374,920 4,000 - 4,000,000 8,000 - 8,000,000 32,000 - 32,000,000
T-C 780 - 937,300 10,000 - 10,000,000 20,000 - 20,000,000 80,000 - 80,000,000
T-D 1,560 - 1,874,600 20,000 - 20,000,000 40,000 - 40,000,000 160,000 - 160,000,000
T-E 3,900 - 4,686,500 50,000 - 50,000,000 100,000 - 100,000,000 400,000 - 400,000,000
T-F 7,800 - 9,373,000 100,000 - 100,000,000 200,000 - 200,000,000 800,000 - 800,000,000
T-Bar
Spindle
LVDV-III RVDV-III HADV-III HBDV-III
Viscosity (cP)
In taking viscosity measurements with the DV-III Rheometer 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 precision of the instrument. All DV-III Rheometers have a full
scale range precision 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 Rheometer 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 Spindle: 100 cP at 50 RPM
3) UL Adapter: 0.85 cP at around 70 RPM
4) SC4-18/13R: 1.25 cP at around 240 RPM
Turbulent conditions will exist in these situations whenever the RPM/cP ratio exceeds the values listed
above.