CE319F%20Elementary%20Fluid%20Mechanics

1
FLUID PROPERTIES Chapter 2
CE319F Elementary Mechanics of Fluids
2
Elasticity (Compressibility)

• If pressure acting on mass of fluid increases
  fluid contracts
• If pressure acting on mass of fluid decreases
  fluid expands
• Elasticity relates to amount of deformation for
  a given change in pressure

Ev bulk modulus of elasticity
How does second part of equation come about?
Small dV/V large modulus of elasticity
3
Example

• Based on the definition of Ev and the equation of
  state, derive an equation for the modulus of
  elasticity of an ideal gas.

4
Vapor Pressure (Pvp)

• Vapor pressure of a pure liquid equilibrium
  partial pressure of the gas molecules of that
  species above a flat surface of the pure liquid
• Concept on board
• Very strong function of temperature (Pvp up as T
  up)
• Very important property of liquids
• When Pvp exceeds total air pressure applied at
  surface, liquid will boil.
• Pressure at which a liquid will boil for a given
  temperature
• At 10 oC, vapor pressure of water 0.012 atm
  1200 Pa
• If reduce pressure to this value - get boiling of
  water
• Formation of cavitation bubbles
• Harm to pipes, pumps, turbines, propellers
• If Pvp gt 1 atm compound gas
• If Pvp lt 1 atm compound liquid or solid

5
Vapor Pressure (Pvp)
Water
Vapor pressure of water (and other liquids) is a
strong function of temperature.
6
Vapor Pressure (Pvp) - continued
Pvp,H2O Pexp(13.3185a 1.9760a2 0.6445a3
0.1299a4)
P 101,325 Pa a 1 (373.15/T)
T oK valid to /- 0.1 accuracy for
T in range of -50 to 140 oC
Equation for relative humidity of air
percentage to which air is saturated with water
vapor. How does RH affect drying of building
materials, and why? Implications? How does RH
affect dust mites? Implications?
7
Dust Mites
8
(No Transcript)
9
(No Transcript)
10
Example (HW!) Relative Humidity

• The relative humidity of air in a room is 80 at
  25 oC.
• What is the concentration of water vapor in air
  on a volume basis?
• If the air contacts a cold surface, water may
  condense (see effects on next slide). What
  temperature is required to cause water
  condensation?

11
Example Relative Humidity
Continued