Brookfield DV1 Viscometer Instrukcja Użytkownika Pobierz pdf (Strona 39)

Brookeld Engineering Laboratories, Inc. Page 39 Manual No. M14-023

When taking viscosity measurements with the DV1 Viscometer, there are two considerations, which

pertain to the low viscosity limit of eective 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.

e rst consideration has to do with the accuracy of the instrument. All DV1 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.

e 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. is 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 2 LV Spindle: 100 cP at 200 RPM

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

4) 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. e 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 DV1 Viscometer Instrukcja Użytkownika Strona 39