fluid_mechanics

140 Chapter 3 ■ Elementary Fluid Dynamics—The Bernoulli Equation
Q
x = L
Air
L
x
H(x) H 0
x = 0
V 0
Open
Oil SG = 0.7
1.5 m
1.2 m
d max
d
Water
F I G U R E P3.70
1 m
2 m
*3.71 The device shown in Fig. P3.71 is used to spray an appropriate
mixture of water and insecticide. The flowrate from tank A is
to be Q A 0.02 gal/min when the water flowrate through the hose
is Q 1 gal/min. Determine the pressure needed at point (1) and
the diameter, D, of the device For the diameter determined above,
plot the ratio of insecticide flowrate to water flowrate as a function
of water flowrate, Q, for 0.1 Q 1 gal/min. Can this device be
used to provide a reasonably constant ratio of insecticide to water
regardless of the water flowrate? Explain.
F I G U R E P3.73
3.74 Air at 80 °F and 14.7 psia flows into the tank shown in Fig.
P3.74. Determine the flowrate in ft 3 s, lbs, and slugss. Assume incompressible
flow.
Q
Water
(1)
D
0.10-in. diameter
Q + Q A = Q
Q
0.6-in.
diameter
0.5 in. Hg vacuum
Pump
h = 6 in.
0.015-in.
diameter
F I G U R E P3.74
SG = 1.0
Q A
F I G U R E P3.71
A
Insecticide
3.72 If viscous effects are neglected and the tank is large, determine
the flowrate from the tank shown in Fig. P3.72.
3.75 Water flows from a large tank as shown in Fig. P3.75. Atmospheric
pressure is 14.5 psia, and the vapor pressure is 1.60 psia.
If viscous effects are neglected, at what height, h, will cavitation
begin? To avoid cavitation, should the value of D 1 be increased or
decreased? To avoid cavitation, should the value of D 2 be increased
or decreased? Explain.
2 m
Oil,
SG = 0.81
h
D 3 = 4 in.
50-mm
diameter
0.7 m
Water
F I G U R E P3.72
3.73 Water flows steadily downward in the pipe shown in Fig.
3.73 with negligible losses. Determine the flowrate.
F I G U R E P3.75
D 1 = 1 in.
D 2 = 2 in.
3.76 Water flows into the sink shown in Fig. P3.76 and Video
V5.1 at a rate of 2 galmin. If the drain is closed, the water will
eventually flow through the overflow drain holes rather than over
the edge of the sink. How many 0.4-in.-diameter drain holes are
needed to ensure that the water does not overflow the sink? Neglect
viscous effects.