CE 230-Engineering Fluid Mechanics

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CE 230-Engineering Fluid Mechanics

• Lecture 23
• Fluid properties (1)

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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

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Example 2.6

• What is the weight of a 10 cubic feet tank
  containing oxygen if it is pressurized to 385.3
  psi 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?