CE 230-Engineering Fluid Mechanics

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CE 230-Engineering Fluid Mechanics

• Week 1
• Introduction

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Policy

• Get to know each other
• Things to know about instructor policy
• Grading

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Basic terminology

• What is fluid mechanics
• What is a fluid
• Difference between solid, liquid and gas

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Applications

• Applications of fluid mechanics in daily life

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Fluid Properties
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Units

• Basic Units versus derived units
• SI versus Traditional units
• prefixes

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What are the units of?

• Mass
• Length
• Time
• Temperature
• Weight
• Pressure
• Energy
• Power

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Intensive versus Extensive properties

• Density
• Specific weight
• Specific gravity
• Tables A.2-A.4 at the end of the text
• Gases, air, water, and some liquids

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Example

• What is the weight of a 1 cubic meter of water
  if the temperature is 5 C?
• What if the temperature was 90 C? or 0 C?

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terminology

• Incompressible fluid
• Compressible fluid
• Ideal fluid
• Perfect gas?

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Perfect gas law

• P?RT
• R is the gas constant with units of m.N/kg K
  or ft lb/slug R
• See appendix A.2 for R values

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Problem 2.6

• What is the weight of a 10 cubic feet tank
  containing oxygen if it is pressurized to 400 psi
  (absolute pressure) and at a temperature of 70 F?
• answer 22.5 lb

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Elasticity Bulk modulus

• The needed pressure change needed to reduce the
  volume of a fluid
• Ev -?p/(?V/V)
• What does it mean if Ev is very big?
• For water Ev 2.2 GN/m2

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Problem 2.46

• What pressure increase must be applied to water
  to reduce its volume by 1?

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Surface tension

• Due to unbalanced molecular forces at interface
  of two fluids. Force /length
• For water-air surface s0.073 N/m
• This accounts for capillary rise

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Estimate the capillary rise of water in a tube of
diameter d.
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Applications of surface tension

• Pressure in a droplet
• Pressure in a soap bubble
• Cylinder supported by surface tension
• Ring being pulled out of liquid
• Capillary rise between two plates

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Vapor pressure

• The pressure at which a liquid boils
• Function of T (direct proportion)
• At what pressure does water boil?
• Table A.5

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Example

• Consider two cases of water boiling in a tea
  kettle one near the sea and the other on top of a
  very high mountain.
• a) compare the value of vapor pressure for both
  cases
• b) compare the temperature for both cases
• does this make sense?

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Fluid Properties (2)
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Examine velocity distribution in pipe
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Viscosity

• Consider two plates separated be a thin film of
  fluid. The lower plate is fixed and the upper is
  moving with a constant velocity.
• Investigate what is happening in the fluid in
  terms of flow or stresses.

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Viscosity

• No slip boundary condition
• Relation between shear stress and velocity
  gradient
• Classification of fluids

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Mechanisms of fluid resistance to shear stress

• Particle cohesion
• Transfer of molecular momentum
• Influence of temperature on viscosity

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Units of viscosity

• Dynamic viscosity
• absolute viscosity
• viscosity
• Kinematic viscosity

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• Influence of temperature on viscosity

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Classification of fluids according to relation of
shear to strain rate
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Problems on viscosity

• Board sliding on an inclined surface separated by
  a thin film of oil
• Is there a shear stress in the film?
• lets calculate the terminal velocity

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Problem 34
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Problem 39

• Calculate the weight of piston given
• Terminal velocity
• µ
• Spacing between piston and cylinder
• Piston dimensions

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Problem 2.39
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Problem 2.41