A power
cycle produces 2.4 x 108 Btu and rejects 7.1 x 108 Btu of heat
to the surroundings.
Calculate the thermal efficiency of the cycle. |
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Read : |
This one is a
straightforward application of the definition of the the 1st
Law and the efficiency of a power cycle. |
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Diagram : |
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Given: |
Wcycle |
2.4E+08 |
Btu |
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QC |
7.1E+08 |
Btu |
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Find: |
hcycle |
??? |
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Assumption: |
1 - |
The cycle only exchanges heat with the two thermal
reservoirs. |
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Equations
/ Data / Solve: |
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1st
Law applied to the heat
engine: |
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Eqn 1 |
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Definition of thermal efficiency : |
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Eqn 2 |
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Degree
of freedom analysis: 2
eqns in 2 unknowns: QH and h. |
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Solve Eqn 1 for QH : |
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Eqn 3 |
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QH |
9.5E+08 |
Btu |
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Next, plug numbers into Eqn 2 : |
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h |
0.2526 |
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Verify: |
The only assumption
cannot be verified. |
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Answers : |
h |
25.3 |
% |
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