2/1/11
Class 7 – Fluid Mechanics
Uses and restrictions of Bernoulli’s
equation
Tuesday, February 1st
Stagnation, dynamic and hydrostatic pressure
A pitot-static tube is used to measure the velocity
of helium in a pipe. The temperature are 40oF and
25 psia. A water manometer connected to the tube
indicates a reading of 2.3 in. What is the helium
velocity? Is it reasonable to consider the flow as
incompressible?
Stagnation, dynamic and hydrostatic pressure
1
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Use of the Bernoulli Equation:
a)  Free jets
b)  Confined flows
c)  Cavitation
d)  Flow measurement
2
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Where is the lowest
pressure going to
occur in the hose?
a.
b.
c.
3
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Water is siphoned from a tank. The water
barometer indicates a reading of 30.2 ft.
Determine the maximum value of h allowed
without cavitation occurring. Note that the
pressure of the vapor in the closed end of
the barometer equals the vapor pressure.
Water is siphoned from a tank. The water
barometer indicates a reading of 30.2 ft.
Determine the maximum value of h allowed
without cavitation occurring. Note that the
pressure of the vapor in the closed end of
the barometer equals the vapor pressure.
Plan:
a) Use Bernoulli between 0 and 1
and 1 and 2 to find V2
b)  Use continuity to find V3
c)  Use Bernoulli between 1 and 3
to find h
Water is siphoned from a tank. The water
barometer indicates a reading of 30.2 ft.
Determine the maximum value of h allowed
without cavitation occurring. Note that the
pressure of the vapor in the closed end of
the barometer equals the vapor pressure.
Which part of the Bernoulli expression
changes to take into account unsteady flow?
a) Use Bernoulli between 0 and 1 and 1 and
2 to find V2
b)  Use continuity to find V3
c)  Use Bernoulli between 1 and 3 to find h
A
B
C
4