ENGRD 221:
Engineering Thermodynamics
Problem Set 7
Due:
March 13
th
2009, Upson Room 123
(5 Questions)
Problem 1 (6.84):
By injecting liquid water into superheated steam, the desuperheater show in
Figure 1 has a saturated vapor stream at its exit. Steadystate operating data are provided in the
accompanying table.
Stray heat transfer and all kinetic and potential energy effects are negligible.
(a)
Locate states 1, 2, and 3 on a sketch of the Ts diagram. (b) Determine the rate of entropy
production within the desuperhater, in kW/K.
State
P (MPa)
T (
o
C)
ν
x10
3
(m
3
/kg)
u (kJ/kg)
h (kJ/kg)
s (kJ/kg K)
1
2.7
40
1.0066
167.2
169.9
0.5714
2
2.7
300
91.01
2757.0
3002.8
6.6001
3
2.5
Sat. vap.
79.98
2603.1
2803.1
6.2575
Figure 1
Problem 2 (6.88):
Air at 400 kPa, 970 K enters a turbine operating at steady state and exits at
100kPa, 670 K.
Heat transfer from the turbine occurs at an average outer surface temperature of
315 K at the rate of 30 kJ per kg of air flowing.
Kinetic and potential energy effects are negligible.
For air as an ideal gas with c
p
=1.1 kJ/kg K, determine (a) the rate power is developed, in kJ per kg
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 Spring '08
 TORRANCE
 Thermodynamics, potential energy effects, Upson Room

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