Brookfield DV-E Viscometer Manual do Utilizador descarregar pdf (Página 19)

Brookeld 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 ow conditions, not under turbulent

ow conditions.

The rst 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 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

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 point to turbulent ow

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 uid to uid. Turbulence starts

as a small deviation or increase in viscosity for a Newtonian uid. Basically there is no specic

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

1 2 ... 14 15 16 17 18 19 20 21 22 23 24 ... 36 37

Sem comentários

Brookfield DV-E Viscometer Manual do Utilizador Página 19