Brookfield DV3T Rheometer Manuale Utente Scaricare il pdf (Pagina 86)

Brookeld Engineering Labs., Inc. Page 86 Manual No. M13-2100

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

VII-2 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 DV3T Rheometer Manuale Utente Pagina 86