Brookfield DV2+Pro Viscometer - Manual (Page 59)

Brookfield Engineering Labs., Inc. Page 59 Manual No. M03-165-F0612
Figure V1-15
When should you use it?
The Herschel-Bulkley model should be used with non-Newtonian, time-dependent materials that
have a yield stress. Products with a yield stress only begin to flow after a certain amount of shear
stress is applied. As a result, the flow curve intersects the y-axis at a point greater than 0. After
yielding, the product creates a flow curve and behaves as a Power Law fluid so that n indicates
where there is a shear-thinning or shear-thickening tendency. (In this case, if n =1, the material
is behaving as a Bingham fluid, which is discussed next.)
An Example of the Herschel-Bulkley Model at Work
A company uses a gel-like substance as part of
their production process. Upon arrival they test
the material and apply the Herschel-Bulkley
model to ensure it will perform correctly during
process. The results in figure VI-2 show that
the consistency index is 8,550 cP, the flow
index is 0.66, and the yield stress is 51.0 dynes/
cm 2 . These results indicate that this batch of
gel does not quite meet specification. While the consistency index is within spec, the yield
value is higher than normal so the fluid will not begin to flow as easily. With a flow index
of 0.66, this batch is also less shear thinning than normal. Pump and mixer speeds must be
adjusted before using this material.
Gel-Like Substance
n = 0.66
τ° = 51.0 dynes/cm 2
k = 8550 cP