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Viscosity

Presented By : BASHAR MD KHAIRULStudent ID:15595901

Masters StudentGraduate School of Science & Engineering

Saga University

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Outline:IntroductionTypes of ViscosityUnits of ViscosityEffects of TemperatureViscosity Index

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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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dydvx

Shear Stress

Fluid Velocity in X Direction

Fluid Viscosity

smsm

dydv

mN 1,2

The dimensions:

2/ msN

dydv&

.10)(1011 32 cppoisep

msNsPa

smPacp 11

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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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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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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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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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Effects of temperature

Fig: Viscosity-temperature characteristics of selected oils

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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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Viscosity index

Viscosity Index Classification

..35 Low35..80 Medium80..110 High110.. 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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Thank you