Applied Fluid Mechanics Unit 2 - Viscosity of Fluids
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Questions and Answers

What is viscosity a measure of?

  • A fluid's density
  • A fluid's pressure
  • A fluid's temperature
  • A fluid's resistance to flow (correct)
  • All fluids have the same viscosity.

    False

    What are the two types of viscosity defined in fluid mechanics?

    Dynamic viscosity and kinematic viscosity

    Glycerine, castor oil, and tar are examples of fluids with _____ viscosity.

    <p>high</p> Signup and view all the answers

    Match the following fluids with their viscosity classification:

    <p>Water = Low viscosity Kerosene = Low viscosity Glycerine = High viscosity Tar = High viscosity</p> Signup and view all the answers

    According to Newton's Law of Viscosity, what must be present for viscous flow?

    <p>Shear stress</p> Signup and view all the answers

    A Newtonian fluid's viscosity changes with shear rate.

    <p>False</p> Signup and view all the answers

    Name one method used to measure viscosity.

    <p>Viscometer</p> Signup and view all the answers

    What does the coefficient of viscosity represent?

    <p>Constant of proportionality for shear stress</p> Signup and view all the answers

    Kinematic viscosity is measured in Pa.s.

    <p>False</p> Signup and view all the answers

    What is the formula relating shear stress to dynamic viscosity?

    <p>τ = μ (du/dy)</p> Signup and view all the answers

    The unit of dynamic viscosity in SI is __________.

    <p>Pa.s</p> Signup and view all the answers

    Match the types of viscosity with their descriptions:

    <p>Dynamic viscosity = Resistance to flow of a fluid under an applied force Kinematic viscosity = Ratio of dynamic viscosity to fluid density</p> Signup and view all the answers

    Which application does viscosity NOT play a role in?

    <p>Concrete strength testing</p> Signup and view all the answers

    The dynamic viscosity is expressed in kg/ms.

    <p>True</p> Signup and view all the answers

    What is the SI unit of kinematic viscosity?

    <p>m²/s</p> Signup and view all the answers

    What is the value of 1 stoke in m²/s?

    <p>0.0001 m²/s</p> Signup and view all the answers

    Viscosity of gases decreases with an increase in temperature.

    <p>False</p> Signup and view all the answers

    What type of fluids are characterized by zero viscosity?

    <p>Ideal fluids</p> Signup and view all the answers

    The viscosity of liquids _________ when heated.

    <p>decreases</p> Signup and view all the answers

    Match the type of fluid with its characteristic:

    <p>Ideal Fluid = Zero viscosity Newtonian Fluid = Viscosity is constant Non-Newtonian Fluid = Viscosity depends on shear rate Real Fluid = All actual fluids</p> Signup and view all the answers

    Which of the following is an example of a Newtonian fluid?

    <p>Water</p> Signup and view all the answers

    Cohesive forces are more significant than molecular momentum for the viscosity of gases.

    <p>False</p> Signup and view all the answers

    1 cSt is equal to ________ m²/s.

    <p>0.000001</p> Signup and view all the answers

    Which of the following describes Newtonian fluids?

    <p>They obey Newton's law of viscosity.</p> Signup and view all the answers

    Non-Newtonian fluids include substances like honey and paints.

    <p>True</p> Signup and view all the answers

    What is the significance of the Viscosity Index (VI)?

    <p>It indicates how the viscosity of a fluid changes with temperature.</p> Signup and view all the answers

    The device used to measure the viscosity of fluids is called a ______.

    <p>viscometer</p> Signup and view all the answers

    Match the type of viscometer with its description:

    <p>Rotating drum Viscometer = Measures resistance to rotation Capillary tube Viscometer = Fluid flows through a narrow tube Falling-ball Viscometer = Ball falls through fluid to measure viscosity Saybolt Universal Viscometer = Measures flow time for a specific volume of fluid</p> Signup and view all the answers

    What does the 'W' in SAE viscosity grades represent?

    <p>Winter</p> Signup and view all the answers

    SAE-15W40 refers to a monograde oil.

    <p>False</p> Signup and view all the answers

    Write one example of a non-Newtonian fluid.

    <p>Honey</p> Signup and view all the answers

    Which of the following is a characteristic of hydraulic fluids?

    <p>Non-corrosiveness</p> Signup and view all the answers

    ISO Viscosity Grades include a range of viscosities from 0 to 100.

    <p>False</p> Signup and view all the answers

    What does the 'W' in SAE viscosity grades signify?

    <p>Winter viscosity</p> Signup and view all the answers

    The viscosity grade of ISO VG 22 means its nominal kinematic viscosity is __________ cSt at 40°C.

    <p>22</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Viscosity = Resistance to flow Shear Force = Force acting parallel to surface Power of the shaft = Rate of doing work Cleanliness = Absence of contaminants</p> Signup and view all the answers

    What is one of the formulas for calculating shear stress?

    <p>Shear Stress = Shear Force / Area</p> Signup and view all the answers

    The numbers in SAE viscosity grades indicate the viscosity of an oil only when hot.

    <p>False</p> Signup and view all the answers

    The formula for calculating the velocity of a shaft is __________.

    <p>πdN/60</p> Signup and view all the answers

    Study Notes

    Applied Fluid Mechanics (Unit 2) - Viscosity of Fluids

    • Viscosity is a measure of a fluid's resistance to flow (internal resistance).
    • All fluids exhibit some viscosity.
    • Viscosity is a property of fluids that resists the movement of one fluid layer over another.
    • Fluids with high viscosity flow slowly (e.g., glycerine, castor oil, tar).
    • Fluids with low viscosity flow quickly (e.g., water, kerosene, petrol).

    Newton's Law of Viscosity

    • Shear stress is directly proportional to the rate of shear strain (velocity gradient).
    • τ = μ (du/dy)
      • τ = shear stress (N/m²)
      • μ = dynamic viscosity (kg/ms or Ns/m²)
      • du/dy = velocity gradient (1/s)

    Types of Viscosity

    • Dynamic viscosity (μ): Measures the internal resistance of a fluid. Units: Pa·s, Ns/m², kg/m·s, poise.
    • Kinematic viscosity (ν): Measures the ratio of dynamic viscosity to density. Units: m²/s, stokes (St), centistokes (cSt).
      • ν = μ/ρ

    Viscosity and Temperature

    • Liquids: Viscosity decreases with increasing temperature. Cohesion forces decrease as temperature increases.
    • Gases: Viscosity increases with increasing temperature. Molecular momentum transfer increases.

    Viscosity Measurement

    • Viscometers or rheometers are used to measure fluid viscosity.
    • Various types of viscometers include rotating drum, capillary tube, falling-ball, and Saybolt Universal.

    Viscosity Measurement/ Saybolt Universal Viscometer

    • Saybolt equations calculate kinematic viscosity (v(cS)) based on time (t) it takes for 60 cm³ to flow through an orifice.
    • v(cS) = 0.226t – 195/t, if t < 100 SUS
    • v(cS) = 0.220t – 135/t, if t > 100 SUS

    SAE Viscosity Grades

    • SAE viscosity grades represent viscosity at different temperatures.
    • The first number signifies low-temperature viscosity.
    • The second number signifies high-temperature viscosity.

    ISO Viscosity Grades

    • ISO viscosity grades use ISO VG followed by a number.
    • The number represents nominal kinematic viscosity in cSt (mm²/s) at 40°C.

    Newtonian and Non-Newtonian Fluids

    • Newtonian fluids: Obey Newton's law of viscosity (e.g., water, air).
    • Non-Newtonian fluids: Do not obey Newton's law of viscosity (e.g., honey, paints).

    Viscosity Index (VI)

    • Shows how viscosity changes with temperature.
    • Important for lubricating oils and hydraulic fluids.

    Applications of Viscosity

    • Transparent and storing facilities for fluids (pipes, tanks)
    • Bitumen used for road construction
    • Sewer line/pipe flow design and analysis
    • Oil and gas drilling
    • Maintaining machine and automobile performance

    Fluid Classification

    • Ideal fluid: Imaginary fluid with zero viscosity, surface tension, and incompressibility.

    • Real fluid: Practical fluid with viscosity, surface tension, and compressibility.

    • Newtonian fluid: Viscosity is independent of shear rate (e.g., water, air).

    • Non-Newtonian fluid: Viscosity changes with shear rate (e.g., honey, paints).

    • Ideal plastic fluid: A non-Newtonian fluid in which shear stress must exceed a yield point before flow begins (e.g., drilling fluid).

    Characteristics of Hydraulic Fluids

    • Adequate viscosity
    • Lubricating ability
    • Cleanliness
    • Chemical stability
    • Non-corrosiveness
    • Resistance to bacterial growth
    • Ecologically acceptable
    • Low compressibility

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    Description

    This quiz covers the key concepts related to viscosity in fluids from the Applied Fluid Mechanics Unit 2. Understand the definitions, formulas, and types of viscosity, as well as how temperature affects fluid resistance. Test your knowledge and grasp the importance of viscosity in fluid dynamics.

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