Brookfield DV-I Prime Instrukcja Użytkownika Pobierz pdf (Strona 33)

Brookeld Engineering Laboratories, Inc. Page 33 Manual No. M/07-022-D0613

When n > 1 the product is shear-thickening or Dilatant. It’s apparent viscosity increases as shear

rate increases.

Figure II-44

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 ow after a certain amount of shear

stress is applied. As a result, the ow curve intersects the y-axis at a point greater than 0. After

yielding, the product creates a ow curve and behaves as a Power Law uid 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 uid, 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

II-44 show that the consistency index is 8,550

cP, the ow index is 0.66, and the yield stress

is 51.0 dynes/cm

. These results indicate that

this batch of gel does not quite meet specication. While the consistency index is within

spec, the yield value is higher than normal so the uid will not begin to ow as easily. With

a ow 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

€

= 51.0 dynes/cm

k = 8550 cP

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Brookfield DV-I Prime Instrukcja Użytkownika Strona 33