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Chapter 6
678
The source and sink temperatures of a power plant are given. The maximum efficiency of the plant is to be
determined.
Assumptions
The plant operates steadily.
Analysis
The maximum efficiency this plant can have is the Carnot
efficiency, which is determined from
0.75
K
1200
K
300
1
1
max
th,
H
L
T
T
684E
The claim of an inventor about the operation of a heat engine is to be evaluated.
Assumptions
The heat engine operates steadily.
Analysis
If this engine were completely reversible, the thermal efficiency would be
0.45
R
1000
R
550
1
1
max
th,
H
L
T
T
When the first law is applied to the engine above,
Btu/h
720
,
27
Btu/h
000
,
15
hp
1
Btu/h
2544.5
)
hp
5
(
net
L
H
Q
W
Q
The actual thermal efficiency of the proposed heat engine is then
459
.
0
hp
1
Btu/h
2544.5
Btu/h
27,720
hp
5
net
th
H
Q
W
Since the thermal efficiency of the proposed heat engine is greater than that of a completely reversible heat engine
which uses the same isothermal energy reservoirs,
the inventor's claim is invalid
.
695E
The claim of a thermodynamicist regarding to the thermal efficiency of a heat engine is to be evaluated.
Assumptions
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This note was uploaded on 09/05/2010 for the course MEEN 315 taught by Professor Ramussen during the Summer '07 term at Texas A&M.
 Summer '07
 RAMUSSEN

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