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Sisolated 0 (7–10) cen54261_ch07.qxd 11/18/03 9:57 AM Page 279 279
CHAPTER 7 This equation can be expressed as the entropy of an isolated system during a
process always increases or, in the limiting case of a reversible process, remains constant. In other words, it never decreases. This is known as the increase of entropy principle. Note that in the absence of any heat transfer,
entropy change is due to irreversibilities only, and their effect is always to increase entropy.
Entropy is an extensive property, and thus the total entropy of a system is
equal to the sum of the entropies of the parts of the system. An isolated system
may consist of any number of subsystems (Fig. 7–6). A system and its surroundings, for example, constitute an isolated system since both can be enclosed by a sufficiently large arbitrary boundary across which there is no heat,
work, or mass transfer (Fig. 7–7). Therefore, a system and its surroundings
can be viewed as the two subsystems of an isolated system, and the entropy
change of this isolated system during a process is the sum of the entropy
changes of the system and its surroundings, which is equal to the entropy generation since an isolated system involves no entropy tran...
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 Spring '09

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