ETS1 Fluid Mechanics Introduction Lecture slides PDF

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These are the lecture slides for the fluid mechanics section. This section is actually the area where you can do really well....

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Faculty of Engineering and Information Technology

Engineering: Technology and Society Introduction to Fluid Mechanics Learning Objectives: • • • • •

Introduction to Design Problem Basic concepts of fluid properties Common units Introduce hydrostatic pressure Flow Instabilities

Design Project: Questions Design in Sub-Systems!!!!

WATER TOWER

Distribution Sub-System

Pump Sub-System

Water Storage Tank

Tap

Particle Filter

Tap

IIM Membrane Unit

Pump

100 m

Start with: What are the key parameters to describe water flowing in a pipe?

Questions – Section 1 What is the volume of water that is processed every day? How long should the process take? What is the flow rate in section 1? Lecture – Fluid Mechanics Introduction

Section 2 How much water does the water tower need to hold? What it the flow rate and pressure required at each tap? What pipe is the diameter? Are all diameters the same? 2

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Pressure – what is it? •

Pressure is the force over an area applied to an object in a direction perpendicular to the surface.. 1m2 surface area

Force (Newtons)

• Pascal (Pa) is the SI unit of pressure: – 1Pa = 1N / 1m2

• Consider pressure due to force from gravity: •

kg Force (Newtons = kg.m/s2)

Pa = N / m2 = kg . m/s2 / m2 = kg / (m.s2)

1m2 surface area Lecture – Fluid Mechanics Introduction

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Other units of pressure • Pressure is measured in: – N/m2 = Pascal (Pa) – pounds per square inch (psi) – millimeters of Mercury (mmHg) – atmospheres (atm)

Pressure at ambient conditions 1 atm 101325 Pa or 101.325 kPa 14.7 PSI 760 mmHg

Lecture – Fluid Mechanics Introduction

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Atmospheric pressure http://www.baywx.com.au

• Atmospheric pressure = Barometric pressure = Pressure at sea-level – 1 atm – 101325 Pa or 101.325 kPa – 14.7 psi – 760 mmHg

1hPa = 1hectopascal = 100Pa

Pressure in most airplanes

Atmosphere

8,000 ft = 564 mm Hg

Boeing 787 Dreamline – 6,000 ft = 609 mm Hg Lecture – Fluid Mechanics Introduction

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How to measure Pressure (Gauge Pressure)

• Gauge pressure is the pressure relative to the local atmospheric or ambient pressure. • Recall atmospheric pressure: – 1 atm = 101.325 kPa = 14.7 psi

Pressure Gauge on Rig

• What does a gauge pressure of 30 psi mean? – Absolute pressure in tyre is 44.7 psi (= 14.7 + 30) psi Lecture – Fluid Mechanics Introduction

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Pressure in an Open Container • In a liquid, there is additional pressure from the weight of the liquid above it.

r – liquid density, kg/m3 g – gravity = 9.8 m/s2 H – height, m •

Liquid

H

Pa = N / m2 = kg . m/s2 / m2 = kg / (m.s2) = r . m/s2 . m = r.g.H

Lecture – Fluid Mechanics Introduction

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Pressure in an Open Container • In a liquid, there is additional pressure from the weight of the liquid above it.

Liquid

∆𝑝 = 𝑝! − 𝑝"#$ = 𝜌gH H1

𝑝! = 𝑝"#$ + 𝜌g(𝐻% + 𝐻! ) H2

Lecture – Fluid Mechanics Introduction

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What characterises a fluid? • A fluid is a substance that continually deforms (flows) under an applied shear stress. – “fluid” is often used as a synonym for “liquid”

• Density - r (kg/m3) – mass per unit volume

• Viscosity - µ (Pa.s) – measure of the resistance of a fluid which is being deformed by either shear stress or tensile stress. – for fluids, viscosity can be thought of as “thickness” Lecture – Fluid Mechanics Introduction

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Density – what is it? • Density - r (kg/m3) – the density of a material is defined as its mass per unit volume • Densities of some common materials: Material

Density (kg/m3)

Density (g/ml)

Fresh Water

1000

1

Salt Water

1030

1.030

Glycerol

1261

1.261

Iron

7874

7.874

Lecture – Fluid Mechanics Introduction

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Viscosity • Dynamic Viscosities of some common fluids: Liquid (at 25 °C)

Viscosity (Pa.s)

Water

0.000894

Blood

0.003

Sulfuric acid

0.0242

Olive oil

0.081

“Blood is thicker than water...” Related to pourability

• Important aspects of viscosity: – Viscosity decreases as temperature increases. – Fluid Flow has friction, a more viscous fluid has more friction. – This friction can lead to energy dissipation and flow instabilities Lecture – Fluid Mechanics Introduction

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Faculty of Engineering and Information Technology

Engineering: Technology and Society Introduction to Fluid Mechanics: Consultation Examples Learning Objectives: • • • •

Basic concepts of fluid properties Common units Introduce hydrostatic pressure Flow Instabilities

Pressure in an Open Container

Liquid

∆𝑝 = 𝑝! − 𝑝"#$ = 𝜌gH 𝑝! = 𝑝"#$ + 𝜌gH 𝑝! =? ? ? ? ? 𝐻 = ????? H1 = 4 H5 = 12 H2 = 10

H3 = 15 H4 = 7

Lecture – Fluid Mechanics Introduction

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Viscosity • Viscosity Units • The SI unit for dynamic viscosity: – – – –

pascal second, Pa.s. 1 Pa.s = 10 Poise 100 centi-Poise = 1 poise (P) So 1 Pa.s = ? Centi-Poise

Liquid (at 25°C)

Viscosity (Pa.s)

Viscosity (mPa.s)

Water

0.000894

.894

Blood

0.003

3

Sulfuric acid

0.0242

24.2

Olive oil

0.081

81

Lecture – Fluid Mechanics Introduction

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Viscosity (Poise)

Viscosity (Centi-Poise)

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Flow Instabilities

Lecture – Fluid Mechanics Introduction

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