Modern Engineering Thermodynamics

442 CHAPTER 12: Mixtures of Gases and Vapors
1.00 kg/min of nitrogen at 30.0°C and 1.00 atm. The mixture
leaves the mixing chamber at 60.0°C and 0.800 atm. Find
the heat transfer rate and indicate whether it is into or out of
the mixture.
18. On planet 3M4G6 in the subsystem Zeta-12, the atmosphere
consists of a binary mixture of sewer gas (methane) and an
unknown gas, called Esh-nugim Marookee Moo by the local
mushfoot natives. An extremely accurate spectral scan reveals
that the mass fraction to mole fraction ratio for methane
is 0.9341875 and the mole fraction of methane is
0.4281378. Determine the name of the unknown gas (in
English).
19. Methane, ethane, and propane, all ideal gases, are mixed
together in equal parts by mass to create a new “super” fuel gas.
Then, it is adiabatically compressed from 40.0°F to 1.75 ft 3 at
300. psia, 80.0°F. Determine the work required.
20.* A chemical processing facility produces exhaust gases (46.0%
N 2 , 43.0% CO 2 , and 11.0% SO 2 by volume) at a total pressure
of 0.320 MPa at 1000.°C. It is proposed that energy be
recovered from this gas by expanding it through a turbine to
atmospheric pressure. Assuming ideal gas behavior, determine
the maximum possible power output per unit mass flow rate for
this system.
21.* Two parts of molecular hydrogen gas are mixed with one part of
molecular oxygen gas (on a molar basis) at 2.00 MPa, 0.00°C
and expanded through a reversible nozzle from a negligible
inlet velocity to 292 m/s at the entrance to the combustion
zone of a rocket engine. Through a preheating process in the
nozzle, the gas mixture receives 1325.5 kJ per kg of mixture
of heat at 500.°C. Determine the exit pressure of the gas
mixture. Assume ideal gas behavior.
22. A diving experiment is to be performed with a mixture of
helium and air at a total pressure of 50.0 psia. The composition
must be such that the partial pressure of oxygen in the
compressed mixture is the same as that in air at standard
pressure and temperature (14.7 psia and 70.0°F). Assuming a
closed system and ideal gas behavior, determine
a. The work required to isentropically compress 2.70 lbm of
the mixture from 14.7 psia, 70.0°F to 50.0 psia.
b. The heat transfer required to aergonically cool the
compressed mixture back to 70.0°F again.
23.* Acetylene and oxygen are drawn from pressurized storage tanks
and mixed together in an oxyacetylene torch in a ratio of 5.00
parts of oxygen per 1 part acetylene on a volume basis. This
mixture flows reversibly through the torch from 0.140 MPa,
20.0°C, to atmospheric pressure at 173°C, at which point it is
ignited by the flame. The mean surface temperature of the
torch is 30.0°C, and it uses 0.100 m 3 /s of oxygen at STP
(0.101325 MPa, 20.0°C). Assuming ideal gas behavior,
determine the work and heat transfer rates.
24.* 18.0 m 3 /s of methane are mixed with 10.0 m 3 /s of isobutane
in a test of a new furnace gas. The mixture is preheated before
being ignited by passing it through an adiabatic, isobaric heat
exchanger. The second fluid in the heat exchanger is condensing
steam at 200.°C flowing at 8.30 kg/s. The steam enters as a
saturated vapor and exits with a quality of 21.0%. The gas
mixture enters at 20.0°C and exits at 150.°C (Figure 12.13).
Determine the entropy production rate of the heat
exchanger.
Steam at 200.°C
(x in = 1.00)
Methane
(20.0°C)
Isobutane
(20.0°C)
FIGURE 12.13
Problem 24.
Q internal
Steam at 200.°C
x out = 0.210
p out = p in
Mixture at 150.°C
p out = p in
25.* Air at 0.101 MPa and 50.0°C is saturated with water vapor. It is
to be aergonically heated to 80.0°C in a steady flow, isobaric
process by putting it in contact with an isothermal reservoir at
100.°C. Determine the heat transfer and entropy production
rates per unit mass flow rate if
a. The presence of the water vapor is ignored.
b. The presence of the water vapor is considered (as an ideal
gas).
c. Determine the percent error in the answer a due to the effect
of the water vapor.
26.* The combustion of 1.00 mole of octane, C 8 H 18 , yields 8 moles
of CO 2 , 9.00 moles of H 2 O, and 47.0 moles of N 2 . The exhaust
gases at 811 K, 0.172 MPa from a spark ignition engine are to
be expanded through a turbocharger used to compress the
incoming air charge to the engine. The incoming air is at 20.0°C
and atmospheric pressure, and the turbocharger turbine exhausts
to the atmosphere (Figure 12.14). Find the compressor’s
isentropic outlet temperature T 2 and its isentropic power input
per unit mass flow rate _W C / _m s :
Dry air
1
FIGURE 12.14
Problem 26.
Compressor
Turbocharger
2 3
Engine
Turbine
4
Exhaust
27. A pneumatic motor in a highly explosive environment uses a
mixture of the ideal gases argon and helium in equal parts on a
mass basis. The motor has inlet conditions of 150. psia at 500. R
and an exit pressure of 14.7 psia. If the motor must produce
3.00 hp of output power while operating in a steady state,
steady flow, reversible, and adiabatic manner, then
a. What is the exit temperature of the gas mixture?
b. What mass flow rate of the mixture is required?
28.* An insulated gas turbine is attached to the exhaust stack of an
oil-fired boiler in a power plant. The pressure and temperature
at the inlet to the turbine are 0.500 MPa absolute, 1000.°C and
the exit pressure is atmospheric. The exhaust gas analysis by
volume is 12.0% CO 2 , 2.00% CO, 4.00% O 2 , and 82.0% N 2 .
What is the maximum possible power output from this turbine
per kg of exhaust gas flowing through it? Assume that the