fluid_mechanics

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454 Chapter 8 ■ Viscous Flow in Pipes
Estimate the extra pressure drop between points (1) and (2) caused
by these straws.
C1130F
(1)
Tightly packed 0.25-in.-diameter,
12-in.-long straws
(2)
12 in.
WARNING Stand clear of
Hazard areas while engine is
running
F I G U R E P8.66
8.67 Repeat Problem 8.66 if the straws are replaced by a piece of
porous foam rubber that has a loss coefficient equal to 5.4.
F I G U R E P8.63
8.64 (See Fluids in the News article titled “New hi-tech fountains,”
Section 8.5.) The fountain shown in Fig. P8.64 is designed
to provide a stream of water that rises h 10 ft to
h 20 ft above the nozzle exit in a periodic fashion. To do this
the water from the pool enters a pump, passes through a pressure
regulator that maintains a constant pressure ahead of the
flow control valve. The valve is electronically adjusted to provide
the desired water height. With h 10 ft the loss coefficient
for the valve is K L 50. Determine the valve loss coefficient
needed for h 20 ft. All losses except for the flow control valve
are negligible. The area of the pipe is 5 times the area of the exit
nozzle.
8.68 As shown in Fig. P8.68, water flows from one tank to another
through a short pipe whose length is n times the pipe diameter.
Head losses occur in the pipe and at the entrance and exit.
(See Video V8.10.) Determine the maximum value of n if the major
loss is to be no more than 10% of the minor loss and the friction
factor is 0.02.
D
= nD
F I G U R E P8.68
h
8.69 Air flows through the fine mesh gauze shown in Fig. P8.69
with an average velocity of 1.50 m/s in the pipe. Determine the
loss coefficient for the gauze.
4 ft
Gauze over
end of pipe
V = 1.5 m/s
Pump
Flow control valve
Pressure regulator
F I G U R E P8.64
8 mm
Water
*8.65 Water flows from a large open tank through a sharp-edged
entrance and into a galvanized iron pipe of length 100 m and diameter
10 mm. The water exits the pipe as a free jet at a distance
h below the free surface of the tank. Plot a log–log graph of the
flowrate, Q, as a function of h for 0.1 h 10 m.
8.66 Air flows through the mitered bend shown in Fig. P8.66 at
a rate of 5.0 cfs. To help straighten the flow after the bend, a set
of 0.25-in.-diameter drinking straws is placed in the pipe as shown.
F I G U R E P8.69
8.70 Water flows steadily through the 0.75-in-diameter galvanized
iron pipe system shown in Video V8.14 and Fig. P8.70 at
a rate of 0.020 cfs. Your boss suggests that friction losses in the
straight pipe sections are negligible compared to losses in the
threaded elbows and fittings of the system. Do you agree or disagree
with your boss? Support your answer with appropriate calculations.