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Unformatted text preview: l number of cycles. Then the preceding relation becomes cen54261_ch07.qxd 11/18/03 9:57 AM Page 275 275
CHAPTER 7 WC Q
T TR since the cyclic integral of energy (the net change in the energy, which is a
property, during a cycle) is zero. Here WC is the cyclic integral of dWC, and it
represents the net work for the combined cycle.
It appears that the combined system is exchanging heat with a single thermal energy reservoir while involving (producing or consuming) work WC during a cycle. On the basis of the Kelvin–Planck statement of the second law,
which states that no system can produce a net amount of work while operating
in a cycle and exchanging heat with a single thermal energy reservoir, we reason that WC cannot be a work output, and thus it cannot be a positive quantity.
Considering that TR is an absolute temperature and thus a positive quantity, we
must have
Q
T 0 (7–1) which is the Clausius inequality. This inequality is valid for all thermodynamic cycles, reversible or irreversible, including the refriger...
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 Spring '09

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