VAPOR PRESSURE AND CAVITATION – 2
Viscosity: A property that represents the internal resistance of a fluid to
motion or the “fluidity”.
Drag force: The force a flowing fluid exerts on a body in the flow
direction. The magnitude of this force depends, in part, on viscosity
A fluid moving relative to
a body exerts a drag
force on the body, partly
because of friction
caused by viscosity.
The behavior of a fluid in
laminar flow between two
parallel plates when the
upper plate moves with a
Fluids for which the rate of deformation is
proportional to the shear stress are called
kg/m s or N s/m2 or Pa s
1 poise = 0.1 Pa s
VISCOSITY Newton’s Viscosity Relation
The rate of deformation (velocity gradient)
of a Newtonian fluid is proportional to
shear stress, and the constant of
proportionality is the viscosity.
Variation of shear stress with the
rate of deformation for
Newtonian and non-Newtonian
fluids (the slope of a curve at a
point is the apparent viscosity of
the fluid at that point).
VISCOSITY Newtonian & Non Newtonian Fluids
m2/s or stoke (1 stoke = 1 cm2/s)
The viscosity of liquids decreases and the
viscosity of gases increases with temperature.
VISCOSITY – 2
This equation can be used to calculate the viscosity of a
fluid by measuring torque at a specified angular velocity.
Therefore, two concentric cylinders can be used as a
viscometer, a device that measures viscosity.
L length of the cylinder
number of revolutions per unit time