Fluid Mechanics Units and Properties

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Questions and Answers

What defines a dimension in measurement?

  • The standard level of measurement
  • A quantity with a specific description (correct)
  • A characteristic representing a measurement unit (correct)
  • The numerical value of mass

What is the SI unit for density?

  • kg/m
  • N/m2
  • kg/m3 (correct)
  • J/m3

According to Newton's second law, what unit measures force?

  • Joule
  • Newton (correct)
  • Watt
  • Pascal

What is the formula for specific weight of a fluid?

<p>Weight of fluid / Volume of fluid (C)</p> Signup and view all the answers

What does specific gravity compare?

<p>Density of a fluid to its density of a standard fluid (C)</p> Signup and view all the answers

What is the unit of pressure defined as a Newton per square meter?

<p>Pascal (D)</p> Signup and view all the answers

Which physical quantity is measured in Watts?

<p>Work done per second (B)</p> Signup and view all the answers

What is the relationship between mass and specific volume?

<p>Volume per unit mass of fluid (C)</p> Signup and view all the answers

What phenomenon occurs when the pressure in a flowing liquid drops below its vapor pressure?

<p>Cavitation (A)</p> Signup and view all the answers

What type of pressure is measured with reference to absolute zero or complete vacuum?

<p>Absolute Pressure (C)</p> Signup and view all the answers

What is the main function of a manometer?

<p>To measure pressure at a point in a fluid (D)</p> Signup and view all the answers

When the boiling point of a liquid can occur at a temperature lower than its normal boiling point, what condition must exist?

<p>Reduced pressure above the liquid (B)</p> Signup and view all the answers

Which of the following devices is NOT a type of mechanical gauge for measuring pressure?

<p>Simple Manometer (C)</p> Signup and view all the answers

What effect does the collapse of vapor bubbles during cavitation have on adjacent surfaces?

<p>Results in surface erosion (B)</p> Signup and view all the answers

Which of the following statements regarding gauge pressure is true?

<p>It includes atmospheric pressure in its measurement. (B)</p> Signup and view all the answers

Which pressure is defined as the difference between atmospheric pressure and absolute pressure?

<p>Vacuum Pressure (A)</p> Signup and view all the answers

What causes vapor bubbles to be formed in a moving liquid?

<p>Reduced pressure in the liquid (D)</p> Signup and view all the answers

What is a common type of simple manometer used for measuring pressure?

<p>U-tube manometer (B)</p> Signup and view all the answers

What is the definition of viscosity?

<p>The resistance to the movement of one layer of fluid over another. (D)</p> Signup and view all the answers

How is kinematic viscosity defined?

<p>The ratio between dynamic viscosity and density of fluid. (A)</p> Signup and view all the answers

Which of these fluids is classified as a Newtonian fluid?

<p>Fluid with a constant viscosity and proportional shear stress. (D)</p> Signup and view all the answers

What is the expression for the pressure inside a hollow bubble?

<p>P = 8σ/d (D)</p> Signup and view all the answers

What happens during capillary rise in a glass tube?

<p>The liquid rises above the level of the surrounding liquid. (A)</p> Signup and view all the answers

In which type of fluid is shear stress not proportional to shear strain?

<p>Non-Newtonian fluid (D)</p> Signup and view all the answers

What is surface tension in liquids defined as?

<p>The tensile force acting on the surface of a liquid in contact with another liquid. (C)</p> Signup and view all the answers

The formula for capillary rise is based on which parameters?

<p>Surface tension, density of the liquid, and diameter of the tube. (B)</p> Signup and view all the answers

In terms of weight density, how is the weight density of a liquid calculated?

<p>Weight density of liquid = S × weight density of water. (A)</p> Signup and view all the answers

What denotes a perfect fluid according to its properties?

<p>Compressible and having no viscosity. (B)</p> Signup and view all the answers

What happens to the pressure intensity inside a liquid jet as per the equilibrium condition?

<p>Pressure intensity is inversely proportional to the diameter of the jet. (D)</p> Signup and view all the answers

What is the relationship between the angle of contact and capillary fall in a liquid?

<p>Smaller angle results in lower capillary rise. (C)</p> Signup and view all the answers

Which equation represents Newton's law of viscosity?

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

What characterizes a fluid's density?

<p>Mass per unit volume (A)</p> Signup and view all the answers

Which unit is used to measure pressure?

<p>Newton per square meter (B)</p> Signup and view all the answers

What is the unit for specific weight or specific density?

<p>N/m3 (A)</p> Signup and view all the answers

Which of these represents the correct formula for calculating work done?

<p>Force x Distance (B)</p> Signup and view all the answers

What is the characteristic of a specific volume?

<p>Volume of fluid per unit mass (B)</p> Signup and view all the answers

What does a Joule measure in terms of work done?

<p>Force multiplied by distance (C)</p> Signup and view all the answers

What aspect of a fluid does the term 'weight density' refer to?

<p>Weight per unit volume of a fluid (D)</p> Signup and view all the answers

What is the phenomenon where vapor bubbles form in a flowing liquid due to pressure dropping below the vapor pressure?

<p>Cavitation (D)</p> Signup and view all the answers

Which pressure is measured with reference to atmospheric pressure?

<p>Gauge pressure (D)</p> Signup and view all the answers

What type of manometer uses a U-shaped tube to measure pressure differences?

<p>Differential manometer (C)</p> Signup and view all the answers

At what condition can a liquid start boiling at a temperature lower than its normal boiling point?

<p>When the pressure is reduced to its vapor pressure (C)</p> Signup and view all the answers

What is the primary cause of pitting and erosion on metallic surfaces in cavitation?

<p>Collapse of vapor bubbles (D)</p> Signup and view all the answers

Which device is used to balance a column of fluid for pressure measurement?

<p>Manometer (C)</p> Signup and view all the answers

Which of the following statements about absolute pressure is correct?

<p>It is the pressure measured with respect to a complete vacuum. (C)</p> Signup and view all the answers

What occurs when the vapor pressure of a liquid equals the surrounding pressure in a closed vessel?

<p>Boiling of the liquid (A)</p> Signup and view all the answers

What defines vacuum pressure?

<p>Pressure below atmospheric pressure (C)</p> Signup and view all the answers

Which type of mechanical pressure gauge relies on the expansion and compression of a spring?

<p>Bourdon tube pressure gauge (B)</p> Signup and view all the answers

How is the density of a fluid calculated when its specific gravity is known?

<p>By multiplying specific gravity with the density of water. (A)</p> Signup and view all the answers

Which statement accurately describes Newtonian fluids?

<p>They have a constant viscosity at all shear rates. (D)</p> Signup and view all the answers

What is the expression for pressure inside a liquid jet derived from equilibrium conditions?

<p>p = 2σ / d (C)</p> Signup and view all the answers

What phenomenon describes the rise or fall of a liquid in a tube due to surface tension?

<p>Capillary action (D)</p> Signup and view all the answers

What is the relationship between shear stress and the rate of shear strain for Non-Newtonian fluids?

<p>Not proportional at all. (C)</p> Signup and view all the answers

In the equation for capillary rise, what does the symbol 'σ' represent?

<p>Surface tension of the liquid (B)</p> Signup and view all the answers

Which type of fluid is defined as having no viscosity?

<p>Ideal fluid (A)</p> Signup and view all the answers

What force balances the weight of liquid in the capillary rise phenomenon?

<p>Surface tension force (D)</p> Signup and view all the answers

What is the relationship between pressure intensity inside a hollow bubble and surface tension?

<p>P = 8σ / d (B)</p> Signup and view all the answers

What does kinematic viscosity measure?

<p>The ratio of dynamic viscosity to density of fluid. (B)</p> Signup and view all the answers

What equation represents the balance of forces in a capillary rise scenario?

<p>h = 4σ / ρg (A)</p> Signup and view all the answers

How does pressure intensity behave inside a liquid droplet relative to outside pressure?

<p>It is greater than the outside pressure. (B)</p> Signup and view all the answers

Which of the following is a property of a real fluid?

<p>It possesses viscosity. (B)</p> Signup and view all the answers

What causes a capillary rise to occur in a small-diameter tube?

<p>Adhesive forces between the liquid and tube walls. (D)</p> Signup and view all the answers

Flashcards

Density

Mass per unit volume of a fluid.

Unit of Density

Kilograms per cubic meter (kg/m³).

Specific Weight (Specific Density)

Weight per unit volume of a fluid.

Specific Volume

Volume per unit mass of a fluid.

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Specific Gravity

Ratio of the density of a fluid to the density of a standard fluid (usually water for liquids, air for gases).

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Newton

Unit of force, equal to the force required to accelerate 1 kg of mass by 1 m/s².

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Pascal (Pa)

Unit of pressure, equal to 1 Newton per square meter.

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Joule (J)

Unit of work or energy, equal to 1 Newton-meter.

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Vapor Pressure

The pressure exerted by vapor molecules above a liquid surface in a closed system at a given temperature.

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Cavitation

The formation of vapor bubbles in a flowing liquid when pressure drops below the liquid's vapor pressure, followed by their collapse in high-pressure regions.

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Absolute Pressure

Pressure measured with reference to a complete vacuum.

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Gauge Pressure

Pressure measured relative to atmospheric pressure.

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Vacuum Pressure

Pressure below atmospheric pressure.

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Manometer

A device for measuring pressure by balancing fluid columns.

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Simple Manometer

A manometer with one open end to the atmosphere.

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Differential Manometer

A manometer measuring the pressure difference between two points.

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Boiling Point

The temperature at which a liquid's vapor pressure equals the surrounding pressure.

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Atmospheric Pressure

The pressure exerted by the atmosphere.

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Specific Gravity (S)

The ratio of the weight density of a liquid or gas to the weight density of water (for liquids) or air (for gases).

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Weight Density

The weight of a substance per unit volume.

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Viscosity

A fluid's resistance to flow.

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Newtonian Fluid

A fluid whose shear stress is directly proportional to the rate of shear strain.

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Non-Newtonian Fluid

A fluid whose shear stress is not directly proportional to the rate of shear strain.

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Kinematic Viscosity

The ratio of dynamic viscosity to the fluid's density.

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Newton's Law of Viscosity

Shear stress is proportional to the rate of shear strain.

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Ideal Fluid

An imaginary fluid with no viscosity and is compressible

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Real Fluid

A fluid with viscosity.

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Surface Tension

The tendency of liquid surfaces to shrink into the minimum surface area possible.

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Capillarity

The ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity.

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Capillary Rise

The upward movement of a liquid in a narrow tube.

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Capillary Depression

The downward movement of a liquid in a narrow tube.

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What are the fundamental dimensions?

The fundamental dimensions are the basic measurable characteristics of an object. The four primary dimensions are mass (M), length (L), time (T), and temperature (t).

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What is the unit of density?

The unit of density is kilograms per cubic meter (kg/m³).

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What is a Newton?

A Newton is the unit of force. One Newton is the force needed to accelerate a 1 kg mass by 1 m/s². It's based on Newton's second law of motion (F = ma).

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What is a Pascal?

A Pascal is the unit of pressure. It's the pressure exerted by 1 Newton of force applied over 1 square meter.

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What is a Joule?

A Joule is the unit of work or energy. It's the work done when a force of 1 Newton moves an object 1 meter.

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What is a Watt?

A Watt is the unit of power. It represents the amount of work done per second. One Watt is equivalent to one Joule per second.

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What is specific weight?

Specific weight refers to the weight per unit volume of a fluid. It's the weight density.

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What is specific volume?

Specific volume represents the volume occupied by a unit mass of a fluid. It's the inverse of density.

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Specific Gravity (S) for Liquids

The ratio of the weight density of a liquid to the weight density of water.

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Specific Gravity (S) for Gases

The ratio of the weight density of a gas to the weight density of air.

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Weight Density of a Liquid

The weight of a liquid per unit volume. It can be calculated using the formula: Weight density = S * Weight density of water = S * 1000 kg/m³ * 9.81 N/m³

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Density of a Liquid

The mass of a liquid per unit volume. It can be calculated using the formula: Density = S * Density of water = S * 1000 kg/m³

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What determines the capillary rise of a liquid?

The height of the liquid rise is influenced by factors like: surface tension of the liquid, diameter of the tube, and density of the liquid.

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Study Notes

Fluid Mechanics Units and Properties

  • Dimensions and Units: Dimensions describe measurable characteristics (mass, length, temperature). Units are standard measures for dimensions. Fundamental dimensions are mass (kg), length (m), time (s), and temperature (°C or K).

  • Density: Mass per unit volume (kg/m³). Fluid density (ρ) = mass of fluid / volume of fluid. Water density is 1000 kg/m³.

  • Specific Weight/Specific Density: Weight per unit volume (N/m³). Specific weight (w) = weight of fluid / volume of fluid.

  • Specific Volume: Volume per unit mass (m³/kg). Specific volume = volume of fluid / mass of fluid.

  • Specific Gravity (Relative Density): Ratio of fluid's weight density (or density) to a standard fluid's weight density (or density). For liquids, the standard is water; for gases, it's air. Specific gravity (S) is dimensionless.

    S (liquid) = weight density of liquid / weight density of water S (gas) = weight density of gas / weight density of air

  • Viscosity: Fluid's resistance to layers moving past each other. Shear stress (τ) is proportional to the rate of velocity change (du/dy) across the layers.
    Newtonian fluids obey this relationship (τ = μ (du/dy)); Non-Newtonian fluids do not.

  • Kinematic Viscosity: Ratio of dynamic viscosity to fluid density (ν).

Fluid Types

  • Ideal Fluid: Imaginary fluid, incompressible and non-viscous.

  • Real Fluid: Possesses viscosity - all real-world fluids.

  • Newtonian Fluid: Shear stress is directly proportional to shear rate.

  • Non-Newtonian Fluid: Shear stress is not proportional to shear rate.

  • Ideal Plastic Fluid: Shear stress exceeds a yield value, and then is proportional to shear rate beyond that yield point.

Surface Tension

  • Definition: Tensile force acting at a liquid-gas interface or liquid-solid interface. Measured in N/m.

  • Liquid Droplet: Pressure inside a droplet (excess over outside pressure) = 4σ/d (σ=surface tension, d=diameter).

  • Hollow Bubble: Pressure inside a hollow bubble = 8σ/d

  • Liquid Jet: Pressure inside a liquid jet = 2σ/d.

Capillarity

  • Definition: Rise or fall of a liquid surface in a narrow tube. Capillary rise/depression determined by liquid specific weight, tube diameter, and surface tension.

  • Capillary Rise: Height (h) of liquid rise in a tube: h = 4σ cos θ/(ρgd) (σ = surface tension, θ = contact angle, ρ = density, g = acceleration due to gravity, d = tube diameter).

  • Capillary Fall: Similar formula to the capillary rise equation, showing the height below the liquid surface in a tube (e.g. mercury in a glass tube).

Vapor Pressure and Cavitation

  • Vapor Pressure: Pressure exerted by a liquid's vapor when it's in equilibrium with its liquid phase.

  • Cavitation: Formation and collapse of vapor bubbles in a flowing liquid (when pressure drops below vapor pressure). Collapse creates high pressure, damaging nearby surfaces.

Pressure Measurement

  • Absolute Pressure: Measured against a perfect vacuum.

  • Gauge Pressure: Measured relative to atmospheric pressure (atmospheric pressure is set to zero).

  • Vacuum Pressure: Measured below atmospheric pressure.

    Absolute pressure = Atmospheric pressure + Gauge pressure Vacuum pressure = Atmospheric pressure - Absolute pressure

  • Manometers: Devices balancing fluid columns to measure pressure (simple and differential types).

  • Mechanical Gauges: Devices balancing fluid column with springs or dead weights (diaphragm, Bourdon tube, dead-weight, bellows types). Simple manometers include Piezometers, and U-Tube manometers.

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