fluid_mechanics

258 Chapter 5 ■ Finite Control Volume Analysis
but with a well-rounded entrance (see Fig. P5.102). The room is
held at a constant pressure of 1.5 psi above atmospheric. Both vents
exhaust into the atmosphere. The loss in available energy associated
with flow through the cylindrical vent from the room to the
vent exit is 0.5V 2 2/2, where V 2 is the uniformly distributed exit velocity
of air. The loss in available energy associated with flow through
the rounded entrance vent from the room to the vent exit is
0.05V 2 2/2, where V 2 is the uniformly distributed exit velocity of air.
4 in.
Gas
Oil
Piston
Channel
1-in. diameter
p = 0
4 in.
200 lb
F I G U R E P5.107
F I G U R E P5.102
Section 5.3.2 Application of the Energy Equation–With
Shaft Work
5.108 What is the maximum possible power output of the hydroelectric
turbine shown in Fig.P5.108?
5.103 A gas expands through a nozzle from a pressure of 300 psia
to a pressure of 5 psia. The enthalpy change involved, ȟ 1 ȟ2,
is 150 Btu/lbm. If the expansion is adiabatic but with frictional effects
and the inlet gas speed is negligibly small, determine the exit
gas velocity.
5.104 For the 180° elbow and nozzle flow shown in Fig. P5.104,
determine the loss in available energy from section 112 to section 122.
How much additional available energy is lost from section 122 to
where the water comes to rest?
50 m
1 m
6 in.
6 m/s
p 1 = 15 psi
V 1 = 5 ft/s
Section (2)
12 in.
F I G U R E P5.104
Section (1)
y
x
Turbine
F I G U R E P5.108
5.109 The pumper truck shown in Fig. P5.109 is to deliver
1.5 ft 3 /s to a maximum elevation of 60 ft above the hydrant. The
pressure at the 4-in.-diameter outlet of the hydrant is 10 psi. If head
losses are negligibly small, determine the power that the pump
must add to the water.
5.105 An automobile engine will work best when the back pressure
at the interface of the exhaust manifold and the engine block is minimized.
Show how reduction of losses in the exhaust manifold, piping,
and muffler will also reduce the back pressure. How could
losses in the exhaust system be reduced? What primarily limits the
minimization of exhaust system losses?
†5.106 Explain how, in terms of the loss of available energy involved,
a home sink water faucet valve works to vary the flow
from the shutoff condition to maximum flow. Explain how you
would estimate the size of the overflow drain holes needed in the
sink of Video V5.1 (Video V3.9 may be helpful).
5.107 (See Fluids in the News article titled “Smart shocks,” Section
5.3.3.) A 200-lb force applied to the end of the piston of the shock absorber
shown in Fig. P5.107 causes the two ends of the shock absorber
to move toward each other with a speed of 5 fts. Determine the head
loss associated with the flow of the oil through the channel. Neglect
gravity and any friction force between the piston and cylinder walls.
60 ft
10 psi
4-in.
diameter
Hydrant
F I G U R E P5.109