PROBLEM 6.81
Air enters a compressor operating at steady state at 15 lbf/in.2, 80oF and exits at 400oF. Stray
heat transfer and kinetic and potential energy effects are negligible. Assuming the ideal gas model
applies for the air, determine the maximum th
PROBLEM 6.100
Refrigerant 22 in a refrigeration system enters one side of a counter-flow heat exchanger at 12
bar, 28oC. The refrigerant exits at 22 bar, 20oC. A separate stream of R-22 enters the other side
of the heat exchanger as saturated vapor at 2 b
PROBLEM 7.50
7.50 Determine the specific ow exergy, in Btu/lbmol and Btu/1b, A HA LYS! S I We and: E7 . 7. l 1- an a.
at 440F, 73.5 lbf/in.2 for (a) nitrogen (N2) 'and (b) carbon dioxide b . d 1 V3,?-
(C02), each modeled as an ideal gas, and relative to a
PROBLE M 1 2?
7.27 Two kilograms of water in a piston-cylinder assembly, initially at 2 bar and 120C, are
heated at constant pressure with no internal irreversibilities to a nal state where the water is a
saturated vapor. For the water as the system, de
Problem 7.41
A gearbox operating at steady state receives 4 hp along the input shaft and delivers 3 hp along
the output shaft. The outer surface of the gearbox is at 130F. For the gearbox, (a) determine, in
Btu/s, the rate of heat transfer and (b) perform
Problem 7.46
A thermal reservoir at 1000 K is separated from another thermal reservoir at 350 K by a 1cm by
1 cm square-cross section rod insulated on its lateral surfaces. At steady state, energy transfer by
conduction takes place through the rod. The ro
Problem 7.53
At steady state, hot gaseous products of combustion from a gas turbine cool from 3000F to
250F as they flow through a stack. Owing to negligible fluid friction, the flow occurs at nearly
constant pressure. Applying the ideal gas model with cp
(
(
)
(
)
(
)
)
Reducing an energy balance:
With Eq. 7.2:
(
)
(
)
(
)
(
)(
)
In keeping with the discussion of Fig. 7.4, the exergy decreases because the system is brought
closer to the dead state with p2 = p0 and T2 approaching T0.
Problem 7.23
As shown
PROBLEM 6.91
Air at 200 kPa, 52oC, and a velocity of 355 m/s enters an insulated duct of varying crosssectional area. The air exits at 100 kPa, 82oC. At the inlet, the cross-sectional area is 6.57 cm2.
Assuming the ideal gas model for the air, determine
(
PROBLEM 7. +8 C Cowhnued/ P. 3)
Exergy transfer accompanying work is determined from Eq. 7.6.
Ew : [W*P0(V2 ~ V0]
Volume can be determined from the ideal gas equation of state
1545 'lbf
(0.5 lb M (540R)
28 01 lb
_ mRT _ ' lbmol ft2 3
V
PROBLEM 6.78 (CONTINUED)
PROBLEM 6.79
Air enters a turbine operating at steady state at 8 bar, 1400 K and expands to 0.8 bar. The
turbine is well-insulated, and kinetic and potential energy effects can be neglected. Assuming
ideal gas behavior for the air
PROBLEM 6.94
PROBLEM 6.95
The figure below
PROBLEM 6.96
Students in a laboratory are studying air flowing at steady state through a horizontal, insulated
duct. One student group reports the measured pressure, temperature, and velocity at one location
in t
Problem 7.39
Figure P7.39 provides steady state data for the outer wall of a dwelling on a day when the indoor
temperature is maintained at 25C and the outdoor temperature is 35C. The heat transfer rate
through the wall is 1000 W. Determine, in W, the rat
PROBLEM 6.108
PROBLEM 6.109
PROBLEM 6.110
Figure P6.110 shows an air compressor and regenerative heat exchanger in a gas turbine system
operating at steady state. Air flows from the compressor through the regenerator, and a separate
stream of air passes t
PROBLEM 6.111
The figure
(e) If the goal is to increase the power developed per kg
of steam flowing, which of the components (if any)
might be eliminated? Explain.
PROBLEM 6.112
PROBLEM 6.112 (CONTINUED)
PROBLEM 6.113
PROBLEM 6.116 (CONTINUED)
and the final mass is
m2 = V/v2 = (3.5 lb)/( 0.11482 ft3/lb)= 30.48 lb
The entropy rate balance reduces to dScv/dt =
si +
m2s2 =
+
Now
m2s2 = m2si +
= m2
From Table A-10E: si sf(50oF) = 0.0585 Btu/lboR. At state 2;
s2 = sf2 + x2(
Problem 7.34
One lbmol of carbon monoxide gas is contained in a 90-ft3 rigid, insulated vessel initially at 5
atm. An electric resistor of negligible mass transfers energy to the gas at a constant rate of 10
Btu/s for 2 min. Employing the ideal gas model
PROBLEM 6.114
PROBLEM 6.115
A tank of volume 1 m3 initially contains steam at 60 bar, 320oC. Steam is withdrawn slowly from the
tank until the pressure drops to 15 bar. An electric resistor in the tank transfers energy to the steam
maintaining the tempera
PROBLEM 6.88
An open feedwater heater is a direct-contact heat exchanger used in vapor power plants. Shown
in Fig. P6.88 are operating data for an open heater with H2O as the working fluid operating at
steady state. Ignoring stray heat transfer from the o
PROBLEM 6.98
Steam at 550 lbf/in.2, 700oF enters a turbine operating at steady state and exits at 1 lbf/in.2 The
turbine produces 500 hp. For the turbine, heat transfer is negligible as are kinetic and potential
energy effects.
(a) Determine the quality o
Problem 7.56
R-134A at 100 lbf/in.2, 200F enters a valve operating at steady state and undergoes a throttling
process. (a) Determine the exit temperature, in F, and the exergy destruction rate, in Btu per lb
of R-134A flowing, for an exit pressure of 50 l
Problem 7.29
As shown in Fig. P7.29, 1 kg of H2O is contained in a rigid, insulated cylindrical vessel. The
H2O is initially saturated vapor at 120C. The vessel is fitted with a paddle wheel from which a
mass is suspended. As the mass descends a certain d
Problem 7.24
Three pounds of carbon monoxide initially at 180F and 40 lbf/in.2 undergo two processes in
series:
Process 1-2: Constant pressure to T2 = -10F
Process 2-3: Isothermal to p3 = 10 lbf/in.2
Employing the ideal gas model,
(a) represent each proce
[
(
]
)
)(
(
)
(
)|
The magnitude of the rate of exergy transfer accompanying heat is:
]| |
[
](
[
)
The rate of exergy destruction can be found from
, where is the rate of entropy
production, or by reducing the exergy rate balance at steady state to o
Exergy Destruction Rate vs. Pressure 2
6
5
4
#2
3
2
1
0
50
55
60
65
70
75
80
85
90
95
100
Pressure 2 (lbf/in.^2)
Comments:
1. As seen on the accompanying T-s diagram, the exit temperature decreases as p2 decreases
for fixed h. Thus, the plot of exit tempe
here to an energy balance for the isolated system, which does not require such
information.
Problem 7.30
A rigid insulated tank contains 0.5 kg of carbon dioxide, initially at 150 kPa, 20C. The carbon
dioxide is stirred by a paddle wheel until its pressur