Brookfield DV-I Prime Instrukcja Użytkownika Pobierz pdf (Strona 50)

Brookeld Engineering Laboratories, Inc. Page 50 Manual No. M/07-022-D0613

When taking viscosity measurements with the DV-I PRIME Viscometer, there are two

considerations, which pertain to the low viscosity limit of effective measurement.

1. Viscosity measurements should be taken within the equivalent % Torque Range from 10%

to 100% for any combination of spindle/speed rotation.

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

ow conditions.

The rst consideration has to do with the accuracy of the instrument. All DV-I PRIME Viscometers

have a Full Scale Range allowable error of (+/-) 1% of any spindle/speed in use. 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 cannot 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 uid.

For the following geometries, we have found that an approximate transition to the onset of turbulent

ow occurs in the following situation:

1) No. 1 LV Spindle: 15 cP at 60 RPM

2) No. 1 RV Spindle: 100 cP at 50 RPM (optional spindle available from Brookeld)

3) UL Adapter: 0.85 cP at 60 RPM

Turbulent conditions may 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, and 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-I Prime Instrukcja Użytkownika Strona 50