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Viscosity

All fluids possess a definite resistance to change of form and many solids show a gradual yielding to forces tending to change their form. This property, a sort of internal friction, is called viscosity. It is expressed in dyne-seconds per cm2, or poises.

Definitions

Newtonian Fluid: Viscosity remains constant with a change in shear rate. Example: water.

Non-Newtonian Fluid: Viscosity varies with a change in shear rate. Example: catsup, batters.

Kinematic Viscosity

Kinematic viscosity is the ratio of viscosity to density. The c.g.s. unit of kinematic viscosity is the stroke.

Flow of liquids through a tube; where l is the length of the tube, r is its radius, p the difference of pressure at the ends, n the coefficient of viscosity, the volume escaping per second,

v = pi x pr4
 8ln
(Poiseuille)

The volume will be given in cm3 per second if l and r are in cm, p in dynes per cm2 and n in poises or dyne-seconds per cm2.

Viscosity Values
Centipoise* (cp) Centistokes (cSt) Saybolt Second Universal (SSU) Typical liquid
1 1 31 Water
3.2 4 40 Milk
12.6 15.7 80 No. 4 fuel oil
16.5 20.6 100 Cream
34.6 43.2 200 Vegetable oil
88 110 500 SAE 10 oil
176 220 1000 Tomato juice
352 440 2000 SAE 30 oil
880 1100 5000 Glycerine
1561 1735 8000 SAE 50 oil
1760 2200 10,000 Honey
3000 4500 20,000 Glue
5000 6250 28,000 Mayonnaise
8640 10,800 50,000 Molasses B
15,200 19,000 86,000 Sour cream
17,640 19,600 90,000 SAE 70 oil

*Centipoise = centistokes x specific gravity where specific gravity is assumed to be 0.8 (except for water). To find the exact cp of your fluid: cp = cSt x (weight per gallon x 0.120).

 

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