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Arias, Krizza T.
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Solayao, Alexis M. Caballero, Maria Carmela
Reporter 2
Reporter 3
Viscosity is a measure of a fluid's resistance to flow.
There are two ways to measure the fluid’s viscosity as follows:
Dynamic Viscosity (Absolute Viscosity)
Kinematic Viscosity
Absolute viscosity or dynamic viscosity is a measure of internal
resistance. It is at a unit velocity while maintaining a unit distance apart
in the fluid.
Obtained by dividing the Shear stress by the rate of shear strain. The
units of dynamic viscosity are: Force / area x time
The Pascal unit (Pa) is used to describe pressure or stress = force per
area.
This unit can be combined with time (sec) to define dynamic viscosity.
Centipoise (cP) is commonly used to describe dynamic viscosity
because water at a temperature of 20°C has a viscosity of 1.002
Centipoise. This value must be converted back to 1.002 x 10^-3 Pa . s for
use in calculations.
The viscosity acts an important fluid property while analyzing the
liquid behaviour and fluid motion near solid boundaries.
UNIT
The formula for Dynamic Viscosity is
Question:
Consider a fluid with a shear rate of 0.5 s-1and a shearing stress of 0.76
N/m2. According to its dynamic viscosity, to which one of these fluids
corresponds?
a. water: 1 Pa*s
b. air: 0.018 Pa*s
c. mercury: 1.526 Pa*s
Solution:
The fluid correspond to Mercury
Kinematic viscosity is the sort of viscosity that is computed by
calculating the ratio of the fluid mass density to the dynamic fluid,
viscosity or absolute fluid viscosity.
It is the measurement of the inherent resistance of a fluid to flow when
no external force is imparted except gravity.
It is from time to time also known as momentum diffusivity.
SI unit
v = m^2/s
Other units
(St) Stokes
(cSt) Centistokes
FORMULA
Question:
If the The absolute viscosity of a flowing fuid is given as 0.67 N per square
m. If the density is known to be 10kg per cubic m., calculate its kinematic
viscosity coefficient using Kinematic viscosity formula.
Absolute Viscosity
Kinematic Viscosity
Dynamic or Absolute
viscosity of a fluid is the
measure of its resistance to
flow when an external force
is applied
Kinematic viscoity is the
ratio of the viscous force
to the inertial force or
fluid density ρ
Question:
If the viscosity of water at 80 is 0.00302 poise and its specific gravity is
0.95. Determine its:
a. absolute viscosity in Pa-s
b. kinematic viscosity in m^2/s and in stokes.
Given:
Absolute Viscosity = 0.00302 poise
Specific Gravity (sp gr) = 0.95
Density of water = 1000 kg/m^3 (constant value)
a. Absolute viscosity in Pa * sec
b. Kinematic viscosity (v) in m^2/s and in stokes
b. Kinematic viscosity (v) in m^2/s and in stokes
Question:
Calculate the density of the fluid having
an absolute viscosity of 0.89 N s per
square m and kinematic viscosity of
2m^2s^−1.
Given:
Absolute viscosity μ=0.89 N s per square m
Kinematic viscosity,v=2m^2 s^−1
The density is: v=μ/ρ
ρ=v/μ
=0.89 N s per m^2 / 2m^2s^−1.
= 0.445 kg/m^3
Therefore, the density of fluid is 0.445 kg/m^3.
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