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Unformatted text preview: rreversible process. cen54261_ch07.qxd 11/18/03 9:57 AM Page 278 278
FUNDAMENTALS OF THERMALFLUID 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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