Chapter 17 | 881(d) There will be no flow through the nozzle if the back
pressure equals the stagnation pressure.
(e) The fluid velocity decreases, the entropy increases, and
stagnation enthalpy remains constant during flow
through a normal shock.
17–160 Combustion gases with k1.33 enter a converging
nozzle at stagnation temperature and pressure of 400°C and
800 kPa, and are discharged into the atmospheric air at 20°C
and 100 kPa. The lowest pressure that will occur within the
nozzle is
(a) 26 kPa (b) 100 kPa (c) 321 kPa
(d) 432 kPa (e) 272 kPaDesign and Essay Problems
17–161 Find out if there is a supersonic wind tunnel on
your campus. If there is, obtain the dimensions of the wind
tunnel and the temperatures and pressures as well as the
Mach number at several locations during operation. For what
typical experiments is the wind tunnel used?
17–162 Assuming you have a thermometer and a device to
measure the speed of sound in a gas, explain how you can
determine the mole fraction of helium in a mixture of helium
gas and air.
17–163 Design a 1-m-long cylindrical wind tunnel whose
diameter is 25 cm operating at a Mach number of 1.8.
Atmospheric air enters the wind tunnel through a converging–
diverging nozzle where it is accelerated to supersonic veloci-
ties. Air leaves the tunnel through a converging–diverging
diffuser where it is decelerated to a very low velocity before
entering the fan section. Disregard any irreversibilities. Specify
the temperatures and pressures at several locations as well as
the mass flow rate of air at steady-flow conditions. Why is it
often necessary to dehumidify the air before it enters the wind
tunnel?17–154 Air is flowing in a wind tunnel at 12°C and 66 kPa
at a velocity of 230 m/s. The Mach number of the flow is
(a) 0.54 m/s (b) 0.87 m/s (c) 3.3 m/s
(d) 0.36 m/s (e) 0.68 m/s
17–155 Consider a converging nozzle with a low velocity at
the inlet and sonic velocity at the exit plane. Now the nozzle
exit diameter is reduced by half while the nozzle inlet tem-
perature and pressure are maintained the same. The nozzle
exit velocity will
(a) remain the same (b) double (c) quadruple
(d) go down by half (e) go down to one-fourth
17–156 Air is approaching a converging–diverging nozzle
with a low velocity at 20°C and 300 kPa, and it leaves the
nozzle at a supersonic velocity. The velocity of air at the
throat of the nozzle is
(a) 290 m/s (b) 98 m/s (c) 313 m/s
(d) 343 m/s (e) 412 m/s
17–157 Argon gas is approaching a converging–diverging
nozzle with a low velocity at 20°C and 120 kPa, and it leaves
the nozzle at a supersonic velocity. If the cross-sectional area
of the throat is 0.015 m^2 , the mass flow rate of argon through
the nozzle is
(a) 0.41 kg/s (b) 3.4 kg/s (c) 5.3 kg/s
(d) 17 kg/s (e) 22 kg/s
17–158 Carbon dioxide enters a converging–diverging noz-
zle at 60 m/s, 310°C, and 300 kPa, and it leaves the nozzle at
a supersonic velocity. The velocity of carbon dioxide at the
throat of the nozzle is
(a) 125 m/s (b) 225 m/s (c) 312 m/s
(d) 353 m/s (e) 377 m/s17–159 Consider gas flow through a converging–diverging
nozzle. Of the five following statements, select the one that is
incorrect:
(a) The fluid velocity at the throat can never exceed the
speed of sound.
(b) If the fluid velocity at the throat is below the speed of
sound, the diversion section will act like a diffuser.
(c) If the fluid enters the diverging section with a Mach
number greater than one, the flow at the nozzle exit will
be supersonic.P 0
T Ma 1. 8 D^ 25 cm
0FIGURE P17–163cen84959_ch17.qxd 4/21/05 11:08 AM Page 881