Brookfield DV-III Ultra Rheometer Manual do Utilizador descarregar pdf (Página 61)

Brookeld Engineering Laboratories, Inc. Page 61 Manual No. M98-211-E0912

An Example of the Bingham Model at Work

A manufacturer of drilling uid applies the

Bingham Model to ensure the quality of their

product. Results from a recent batch, shown

in Figure VI-50, showed that the yield stress

and plastic viscosity were both below the

pass/fail criteria, which would cause the uid

to insuciently hold-up the cuttings. The

shipment was cancelled and the root-cause

of the problem was identied.

Drilling Fluid

Plastic Viscosity (

η) = 6621 cP

Yield Stress (

€

) = 166.4 dynes/cm

IV.7.4 The Casson Model

€

t = t

+ h

(

€

= shear stress,

€

= yield stress, η = plastic viscosity, and D = shear rate)

What does it tell you?

The Casson model provides parameters similar to that of the Bingham model. However, unlike

the Bingham model, it was developed for materials that exhibit non-Newtonian ow after yielding.

The Casson model indicates the product’s yield stress (

€

) which is the amount of shear stress

required to initiate ow, and the product’s plastic viscosity,

η, which is the viscosity of the product

after it yields.

Figure IV-51

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Brookfield DV-III Ultra Rheometer Manual do Utilizador Página 61