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Cen54261ch07qxd 111803 957 am page 278 278

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Unformatted text preview: rreversible process. cen54261_ch07.qxd 11/18/03 9:57 AM Page 278 278 FUNDAMENTALS OF THERMAL-FLUID SCIENCES or 2 1 Q T 1 Q T 2 0 int rev The second integral in the above relation is recognized as the entropy change S1 S2. Therefore, 2 1 Q T S1 S2 0 which can be rearranged as Q T 2 S2 S1 1 (7–7) It can also be expressed in differential form as dS Q T (7–8) where the equality holds for an internally reversible process and the inequality for an irreversible process. We may conclude from these equations that the entropy change of a closed system during an irreversible process is greater than the integral of dQ/T evaluated for that process. In the limiting case of a reversible process, these two quantities become equal. We again emphasize that T in these relations is the absolute temperature at the boundary where the differential heat dQ is transferred between the system and the surroundings. The quantity S S2 S1 represents the entropy change of the system. For a reversible process, it becomes equal to 21 dQ/T, which represents the entropy transfer with heat....
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