17–147 Repeat Prob. 17–146 for helium.
17–148 Air is accelerated as it is heated in a duct with neg-
ligible friction. Air enters at V 1 100 m/s,T 1 400 K, and
P 1 35 kPa and then exits at a Mach number of Ma 2 0.8.
Determine the heat transfer to the air, in kJ/kg. Also deter-
mine the maximum amount of heat transfer without reducing
the mass flow rate of air.
17–149 Air at sonic conditions and static temperature and
pressure of 500 K and 420 kPa, respectively, is to be acceler-
ated to a Mach number of 1.6 by cooling it as it flows through
a channel with constant cross-sectional area. Disregarding
frictional effects, determine the required heat transfer from the
air, in kJ/kg. Answer:69.8 kJ/kg
17–150 Saturated steam enters a converging–diverging noz-
zle at 3.0 MPa, 5 percent moisture, and negligible velocity,
and it exits at 1.2 MPa. For a nozzle exit area of 16 cm^2 ,
determine the throat area, exit velocity, mass flow rate, and
exit Mach number if the nozzle (a) is isentropic and (b) has
an efficiency of 90 percent.Fundamentals of Engineering (FE) Exam Problems
17–151 An aircraft is cruising in still air at 5°C at a velocity
of 400 m/s. The air temperature at the nose of the aircraft
where stagnation occurs is
(a) 5°C (b) 25°C (c) 55°C (d) 80°C (e) 85°C
17–152 Air is flowing in a wind tunnel at 15°C, 80 kPa,
and 200 m/s. The stagnation pressure at the probe inserted
into the flow section is
(a) 82 kPa (b) 91 kPa (c) 96 kPa
(d) 101 kPa (e) 114 kPa17–153 An aircraft is reported to be cruising in still air at
20°C and 40 kPa at a Mach number of 0.86. The velocity
of the aircraft is
(a) 91 m/s (b) 220 m/s (c) 186 m/s
(d) 280 m/s (e) 378 m/s17–135 Helium expands in a nozzle from 1 MPa, 500 K,
and negligible velocity to 0.1 MPa. Calculate the throat and
exit areas for a mass flow rate of 0.25 kg/s, assuming the
nozzle is isentropic. Why must this nozzle be converging–
diverging? Answers:3.51 cm^2 , 5.84 cm^2
17–136E Helium expands in a nozzle from 150 psia, 900
R, and negligible velocity to 15 psia. Calculate the throat and
exit areas for a mass flow rate of 0.2 lbm/s, assuming the
nozzle is isentropic. Why must this nozzle be converging–
diverging?
17–137 Using the EES software and the relations in
Table A–32, calculate the one-dimensional
compressible flow functions for an ideal gas with k1.667,
and present your results by duplicating Table A–32.
17–138 Using the EES software and the relations in
Table A–33, calculate the one-dimensional
normal shock functions for an ideal gas with k1.667, and
present your results by duplicating Table A–33.
17–139 Consider an equimolar mixture of oxygen and
nitrogen. Determine the critical temperature, pressure, and
density for stagnation temperature and pressure of 800 K
and 500 kPa.
17–140 Using EES (or other) software, determine the
shape of a converging–diverging nozzle for air
for a mass flow rate of 3 kg/s and inlet stagnation conditions
of 1400 kPa and 200°C. Assume the flow is isentropic.
Repeat the calculations for 50-kPa increments of pressure
drops to an exit pressure of 100 kPa. Plot the nozzle to scale.
Also, calculate and plot the Mach number along the nozzle.
17–141 Using EES (or other) software and the rela-
tions given in Table A–32, calculate the one-
dimensional isentropic compressible-flow functions by
varying the upstream Mach number from 1 to 10 in incre-
ments of 0.5 for air with k1.4.
17–142 Repeat Prob. 17–141 for methane with k
1.3.
17–143 Using EES (or other) software and the rela-
tions given in Table A–33, generate the one-
dimensional normal shock functions by varying the upstream
Mach number from 1 to 10 in increments of 0.5 for air with
k1.4.
17–144 Repeat Prob. 17–143 for methane with k
1.3.
17–145 Air is cooled as it flows through a 20-cm-diameter
duct. The inlet conditions are Ma 1 1.2,T 01 350 K, and P 01
240 kPa and the exit Mach number is Ma 2 2.0. Disregard-
ing frictional effects, determine the rate of cooling of air.
17–146 Air is heated as it flows subsonically through a
10 cm 10 cm square duct. The properties of air at the inlet
are maintained at Ma 1 0.4,P 1 400 kPa, and T 1 360 K
880 | Thermodynamics
at all times. Disregarding frictional losses, determine the
highest rate of heat transfer to the air in the duct without
affecting the inlet conditions. Answer:1958 kWP 1 400 kPa
T 1 360 K
Ma 1 0.4QmaxFIGURE P17–146