Brookfield DV-I Prime Instrukcja Użytkownika Pobierz pdf (Strona 34)

Brookeld Engineering Laboratories, Inc. Page 34 Manual No. M/07-022-D0613

II.12.3 The Bingham Model

€

t =

€

(

€

= shear stress,

€

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

What does it tell you?

The Bingham model indicates a product’s yield stress,

€

, which is the amount of shear stress

required to initiate ow. It also provides the plastic viscosity,

h, which is the viscosity after a

product yields.

Figure II-45

When should you use it?

This model should be used with non-Newtonian materials that have a yield stress and then behave

in a Newtonian fashion once they begin to ow. As a result, the shear stress-shear rate plot forms

a straight line after yielding. (Products that have a yield stress only begin to ow after a certain

amount of shear stress is applied. They are also called “viscoplastic”. Their shear stress vs. shear

rate graphs intersect the y-axis at a point greater than 0.)

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 II-45, 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 (

h) = 6621 cP

Yield Stress (

€

) = 166.4 dynes/cm

1 2 ... 29 30 31 32 33 34 35 36 37 38 39 ... 70 71

Brak uwag

Brookfield DV-I Prime Instrukcja Użytkownika Strona 34