CHEG 2313
Thermo I
HW#6
Spring 2011
Due Wednesday, March 9, 2011 by 5pm.
1. A process produces power by expanding 1.3 kg/s of steam from 500C and 3.5 MPa to
250C and 3000 kPa.
A breakdown in insulation around the process allows a heat loss of
30 kJ per kg of steam.
a)
How much power can be produced from this process? (5 pts)

system: process

start with mass balance – since steady state
M
M
M
out
in
=
=

next energy balance
.
.
1
2
.
2
2
2
W
Q
gh
H
M
gh
M
U
dt
d
k
K
k
k
+
+
+
+
=
+
+
∑
=
∧
ν
ν

steady state and no kinetic or potential energy changes

reduced energy balance
.
.
2
1
.
0
W
Q
H
H
M
+
+

=
∧
∧

determine enthalpy values from steam tables
(
29
kg
kJ
MPa
C
H
9
.
3450
5
.
3
,
500
ˆ
1
=
(
29
kg
kJ
MPa
C
H
8
.
2855
3
,
250
ˆ
2
=

solve for work
(
29
kW
s
kJ
W
s
kg
kg
kJ
kg
kJ
s
kg
Q
H
H
M
W
6
.
734
6
.
734
3
.
1
30
9
.
3450
8
.
2855
3
.
1
.
.
1
2
.
.

=

=



=


=
∧
∧
b)
If the heat is being transferred at 350°C, is this process possible? (5 pts)

entropy equation
gen
k
k
S
T
Q
S
M
dt
dS
+
+
=
∑
∧
.

steady state

reduced entropy eqn
gen
S
T
Q
S
S
M
+
+

=
∧
∧
.
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 Spring '11
 STAFF
 Thermodynamics, Entropy, 2 moles, 4.06 J, 8.314kJ

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