Brookfield DV-III Ultra Rheometer Manual de usuario descargar pdf (Pagina 104)

Brookeld Engineering Laboratories, Inc. Page 104 Manual No. M98-211-E0912

In taking viscosity measurements with the DV-III Ultra 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 spindle/speed combination.

2) Viscosity measurements should be taken under laminar ow conditions, not under turbulent

ow conditions.

The rst consideration has to do with the precision of the instrument. All DV-III Ultra Rheometers

have a full scale range precision of (+/-) 1% of any spindle/speed combination. 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 uid ow. All rheological measurements of

uid ow properties should be made under laminar ow conditions. Laminar ow is ow wherein all

particle movement is in layers directed by the shearing force. For rotational systems, this means all uid

movement must be circumferential. When the inertial forces on the uid become too great, the uid can

break into turbulent ow wherein the movement of uid particles becomes random, and the ow 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 uid.

For the following geometries, we have found that an approximate transition point to turbulent ow

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. 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 uid to uid. Turbulence starts as a

small deviation or increase in viscosity for a Newtonian uid and grows quickly. Basically there is no

specic shear that it starts at, only an approximate region of shear depending on the uid.

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Brookfield DV-III Ultra Rheometer Manual de usuario Pagina 104