fluid_mechanics

456 Chapter 8 ■ Viscous Flow in Pipes
added to the water by the pump if the pressure immediately before
the pump is to be the same as that immediately after the last filter.
The length of the pipe between these two locations is 80 ft.
Cold air register
Filters
Duct
Water
Pump
F I G U R E P8.83
8.84 Water at 40 °F flows through the coils of the heat exchanger
as shown in Fig. P8.84 at a rate of 0.9 galmin. Determine the
pressure drop between the inlet and outlet of the horizontal
device.
18 in.
Q
Threaded 180°
return bend
F I G U R E P8.88
Furnace
Filter
8.89 As shown in Fig. P8.89, a standard household water meter is
incorporated into a lawn irrigation system to measure the volume
of water applied to the lawn. Note that these meters measure volume,
not volume flowrate. (See Video V8.15.) With an upstream
pressure of p 1 50 psi the meter registered that 120 ft 3 of water
was delivered to the lawn during an “on” cycle. Estimate the upstream
pressure, p 1 , needed if it is desired to have 150 ft 3 delivered
during an “on” cycle. List any assumptions needed to arrive at
your answer.
0.5-in. copper pipe (drawn tubing)
F I G U R E P8.84
8.85 For the flow in Problem 8.84, ethylene glycol is added to the
water for freeze protection if the temperature drops below the freezing
point. The density is unchanged, and all flow conditions are
the same except that the viscosity of the mixture has changed to
0.01 Ns/m 2 at the given temperature. Recalculate the pressure drop
between inlet and outlet. Discuss how this loss will change if the
fluid temperature does drop below freezing.
8.86 Water flows through a 2-in.-diameter pipe with a velocity of
15 fts as shown in Fig. P8.86. The relative roughness of the pipe
is 0.004, and the loss coefficient for the exit is 1.0. Determine the
height, h, to which the water rises in the piezometer tube.
(1)
WATER
METER
F I G U R E P8.89
8.90 A fan is to produce a constant air speed of 40 ms throughout
the pipe loop shown in Fig. P8.90. The 3-m-diameter pipes are
smooth, and each of the four 90° elbows has a loss coefficient of
0.30. Determine the power that the fan adds to the air.
20 m
Irrigation
system:
pipes, fittings,
nozzles, etc.
Open
V = 40 m/s
15 ft/s
h
2 in.
8 ft
10 m
Fan
D = 3 m
8 ft
F I G U R E P8.86
8.87 Water is pumped through a 60-m-long, 0.3-m-diameter pipe
from a lower reservoir to a higher reservoir whose surface is 10 m
above the lower one. The sum of the minor loss coefficients for
the system is K L 14.5. When the pump adds 40 kW to the water
the flowrate is 0.20 m 3 s. Determine the pipe roughness.
† 8.88 Estimate the pressure drop associated with the air flow from
the cold air register in your room to the furnace (see Figure P8.88).
List all assumptions and show all calculations.
F I G U R E P8.90
Section 8.5.1 Single Pipes—Determine Flowrate (Also
see Lab Problems 8.128 and 8.129.)
8.91 The turbine shown in Fig. P8.91 develops 400 kW. Determine
the flowrate if (a) head losses are negligible or (b) head loss
due to friction in the pipe is considered. Assume f 0.02. Note:
There may be more than one solution or there may be no solution
to this problem.