fluid_mechanics

Problems 81
manometer the air pressure is 16 psia. Determine the reading on the
pressure gage for a differential reading of 4 ft on the manometer.
Express your answer in psi (gage). Assume standard atmospheric
pressure and neglect the weight of the air columns in the manometer.
2.29 A closed cylindrical tank filled with water has a hemispherical
dome and is connected to an inverted piping system as shown in Fig.
P2.29. The liquid in the top part of the piping system has a specific
gravity of 0.8, and the remaining parts of the system are filled with
water. If the pressure gage reading at A is 60 kPa, determine: (a) the
pressure in pipe B, and (b) the pressure head, in millimeters of
mercury, at the top of the dome (point C).
p A =
60 kPa
A
Hemispherical dome
C
Water
3 m
F I G U R E P2.29
4 m
3 m
2 m
Water
SG = 0.8
2.30 Two pipes are connected by a manometer as shown in Fig.
P2.30. Determine the pressure difference, p A p B , between the pipes.
Water
A
0.5 m
0.6 m
Gage fluid
(SG = 2.6)
Water
1.3 m
B
the tank is oil 1g 54.0 lbft 3 2. The pressure at point A is 2.00 psi.
Determine: (a) the depth of oil, z, and (b) the differential reading, h,
on the manometer.
2.32 For the inclined-tube manometer of Fig. P2.32 the pressure
in pipe A is 0.6 psi. The fluid in both pipes A and B is water, and
the gage fluid in the manometer has a specific gravity of 2.6. What
is the pressure in pipe B corresponding to the differential reading
shown?
3 in.
A
Water
8 in.
30°
F I G U R E P2.32
SG = 2.6
Water
2.33 A flowrate measuring device is installed in a horizontal
pipe through which water is flowing. A U-tube manometer is
connected to the pipe through pressure taps located 3 in. on either
side of the device. The gage fluid in the manometer has a specific
weight of 112 lb/ft 3 . Determine the differential reading of the
manometer corresponding to a pressure drop between the taps
of 0.5 lb/in. 2 .
2.34 Small differences in gas pressures are commonly measured
with a micromanometer of the type illustrated in Fig. P2.34. This
device consists of two large reservoirs each having a crosssectional
area A r which are filled with a liquid having a specific
weight g 1 and connected by a U-tube of cross-sectional area A t
containing a liquid of specific weight g 2 . When a differential gas
pressure, p 1 p 2 , is applied, a differential reading, h, develops.
It is desired to have this reading sufficiently large (so that it can
be easily read) for small pressure differentials. Determine the
relationship between h and p 1 p 2 when the area ratio A tA r is
small, and show that the differential reading, h, can be magnified
by making the difference in specific weights, g 2 g 1 , small.
Assume that initially (with p 1 p 2 ) the fluid levels in the two
reservoirs are equal.
B
3 in.
F I G U R E P2.30
B
2.31 A U-tube manometer is connected to a closed tank as shown in
Fig. P2.31. The air pressure in the tank is 0.50 psi and the liquid in
Air
Open
h
p 1
p 2
2
γ 1
γ 1
γ
z
Oil
A
SG = 3.05
F I G U R E P2.31
2 ft
h
F I G U R E P2.34
2.35 The cyclindrical tank with hemispherical ends shown in Fig.
P2.35 contains a volatile liquid and its vapor. The liquid density is
800 kgm 3 , and its vapor density is negligible. The pressure in the
vapor is 120 kPa (abs), and the atmospheric pressure is 101 kPa
(abs). Determine: (a) the gage pressure reading on the pressure
gage; and (b) the height, h, of the mercury manometer.