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.

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 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.

*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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