Transcript Pressure in Fluid Systems

Pressure in Fluid Systems
1.2.2
Buoyancy and Archimedes’
Principle
• Archimedes’ Principle – an object immersed
in a fluid has an upward force exerted on it
equal to the weight of the fluid displaced by
object.
• Because Vobject = Vfluid displaced
Fbuoyant  w Vobject
• Buoyancy rules using weight of object.
• Buoyancy rules using density.
Pascal’s Principle
• A change in pressure at any point in a
confined fluid is transmitted undiminished
throughout the fluid (Fig 1.22)
• Formal expression
P1  P2
or
F1 F2

A1 A2
Example 1.10, p 38
Atmospheric Pressure
• At sea level:
• 101.3 kPa = 760 mm Hg
= 14.7 psi = 1 atm
• Measure with a
barometer (see Fig
1.24, p. 39).
Absolute and Gauge Pressure
• Absolute pressure is the formal expression of the total force per unit area.
It includes the pressure from the atmosphere (air pressure), the pressure
from any external forces applied to the fluid and the pressure resultant
from the weight of the fluid itself.
Pabsolute  Pgauge  Patmosphere
Pressure is Prime Mover
• Fluids Systems
• Liquid or gas that moves though a system of
pipes.
• Pressure differences in the system create a net
force which causes fluids to move or perform a
function.
Equilibrium in a Fluid System
• Figures 1.26 to 1.28, pp. 42-43.