Brookfield DV2+Pro Viscometer Bedienungsanleitung PDF herunterladen (Seite 58)

Brookeld Engineering Labs., Inc. Page 58 Manual No. M03-165-F0612

An Example of the Power Law Model at Work

Formulators at a personal care company

would like to use a substitute ingredient to

decrease cost. They use the Power Law model

to evaluate the eect the new ingredient

will have on the behavior of their shampoo.

They need to know how it will behave during

processing and how it will behave when it is

being used be the consumer

With the new ingredient the shampoo has a ow index (n) of 0.08. This indicates that

the shampoo is shear-thinning enough to ow properly during processing and that it

will ow properly for the end-user. The consistency index, k, indicates how the shampoo

behaves when it experiences low shear rates. The power law values show that the shampoo

becomes quite thin at process shear rates and therefore it can be easily pumped into lling

equipment, hold tanks, etc. The consistency index of 91,071 cP shows that the shampoo

is very viscous at low shear rates, and as a result, it will appear to customers to be “rich

and creamy” while still being easy to apply.

Shampoo

Flow Index (n) = 0.08

Consistency Index (k) = 91071cP

V1.3.2 The Herschel-Bulkley Model

(

=shearstress,

=yieldstress,k=consistencyindex, =shearrate,andn=owindex)

What does it tell you?

The Herschel-Bulkley model is simply the Power Law model with the addition of

€

for yield

stress.Yieldstress,

,denoteshowmuchshearstressisrequiredtoinitiateow.Thismodelalso

provides a consistency index, k,whichisaproduct’sviscosityat1reciprocalsecond,andaow

index, n,whichindicatesthedegreewithwhichamaterialexhibitsnon-Newtonianowbehavior.

Since Newtonian materials have linear shear stress vs. shear rate behavior and n describes the

degreeofnon-Newtonianow,theowindexessentiallyindicateshow“non-linear”amaterial

is.ForHerschel-Bulkleyuids,n will always be greater than or less than 1.

When n < 1 the product is shear-thinning or Pseudoplastic. This means the apparent viscosity

decreases as shear rate increases. The closer n is to 0, the more shear thinning the material is.

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

rate increases.

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Brookfield DV2+Pro Viscometer Bedienungsanleitung Seite 58