Appendix C - Viscosity Range Change
C-2 P/N M/97-520
Speed of Rotation Change
If only the speed of rotation is altered, the measured viscosity range
changes to the proportion of:
By doubling the speed of rotation, the shear rate will double and the
measured viscosity range is decreased by a factor of two. If the old
measured shear rate was 67 sec
-1
, the new shear rate will be 134 sec
-1
.
Each stator has a shear rate constant, that when multiplied by the speed of
rotation, yields the measured shear rate.
Rule of thumb; with all else equal, by increasing the speed of rotation
(rpm), the measured viscosity range is more refined but at a larger shear
rate. By decreasing the speed of rotation, the viscosity range broadens and
shear rate decreases.
Stator Change
By only changing the stator, the shear rate and viscosity range will change
by the ratio of factors for shear rate and geometry (ranging).
Rule of thumb; with all else equal, by changing to a stator which decreases
gap size, the viscosity range is more refined, but the shear rate increases.
By increasing the measurement zone gap, the viscosity range broadens, but
the shear rate decreases.
OLD VISCOSITY RANGE X OLD SPEED
NEW SPEED
1000 cP x 100 RPM
200 RPM
= 500 cP
EXAMPLE:
SPEED OF
ROTATION CHANGE
=
OLD SHEAR RATE X NEW SHEAR RATE FACTOR
OLD SHEAR RATE FACTOR
NEW SHEAR RATE =
OLD RANGE X NEW GEOMETRY FACTOR
OLD GEOMETRY FACTOR
NEW RANGE =
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