Definition of Viscosity, Types of Viscosity, Unit of Viscosity,Effect of Temperature on Viscosity, Viscosity index

1. Viscosity
Presented By : BASHAR MD KHAIRUL
Student ID:15595901
Masters Student
Graduate School of Science & Engineering
Saga University
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2. Outline:
Introduction
Types of Viscosity
Units of Viscosity
Effects of Temperature
Viscosity Index
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3. Introduction
• Viscosity is a quantitative measure of a fluid’s resistance to
flow.
Dynamic (or Absolute) Viscosity:
• The dynamic viscosity(η) of a fluid is a measure of the
resistance it offers to relative shearing motion.
η= F/ [A×(u/h)]
η= τ /(u/h) N-s/m²
Kinematic Viscosity :
• It is defined as the ratio of absolute viscosity to the density of
fluid.
ν= η/ρ m²/s ; ρ= density of fluid
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4. dy
dvx
 
Shear Stress
Fluid Velocity
in X Direction
Fluid Viscosity














sms
m
dy
dv
m
N 1
,2

The dimensions:



 
 2
/ m
sN
dydv

&
.10)(1011 3
2
cppoisep
m
sN
sPa 


smPacp 11
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5. Laminar Flow (Streamline)
• Slow, smooth flow over a surface in which the paths
of individual particles do not cross.
• Fluid speed at the surface is approximately zero.
• Fluid moves in theoretical layers, or laminates, with
increasing speed away from the surface.
• Frictional drag is produced by the friction between
successive layers of fluid.
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6. Turbulent Flow
• Irregular flow with eddies and whorls causing fluid to move
in different directions.
• Frictional drag and pressure drag both increase as speed
increases.
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7. Effects of temperature
• The viscosity of liquids decreases with increase the temperature.
• The viscosity of gases increases with the increase the temperature.
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8. Effects of temperature
• The lubricant oil viscosity at a specific temperature can be
either calculated from the viscosity - temperature equation or
obtained from the viscosity-temperature ASTM chart.
Viscosity-Temperature Equations
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9. Effects of temperature
Fig: Viscosity-temperature characteristics of selected oils
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10. Typical values of viscosity of some fluids:
2180,2840,17100
2090,3570,3080
2000,4690,8060
1900,6562,3140
1811,0059,8620
1711,79253,000
Viscosity Air,
Micro Poise[ p]
Viscosity Water,
centiPoise[cp]
Viscosity Castor
Oil, Poise[p]
Temperature
Celsius

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11. Viscosity index
Viscosity Index Classification
..35 Low
35..80 Medium
80..110 High
110.. Very High
Viscosity index (VI) is an arbitrary measure for the change of viscosity with
variations in temperature. The lower the VI, the greater the change of viscosity of
the oil with temperature and vice versa. It is used to characterize viscosity changes
with relation to temperature in lubricating oil
The viscosity index can be calculated using the following formula
where V indicates the viscosity index, U the oil's kinematic viscosity at 40 °C
(104 °F), and L & H are values based on the oil's kinematic viscosity at 100 °C
(212 °F)
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