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Unformatted text preview: The inequality sign in the preceding relations is a constant reminder that the
entropy change of a closed system during an irreversible process is always
greater than the entropy transfer. That is, some entropy is generated or created
during an irreversible process, and this generation is due entirely to the presence of irreversibilities. The entropy generated during a process is called
entropy generation and is denoted by Sgen. Noting that the difference between
the entropy change of a closed system and the entropy transfer is equal to
entropy generation, Eq. 7–7 can be rewritten as an equality as
2 Ssys S2 S1 1 Q
T Sgen (7–9) Note that the entropy generation Sgen is always a positive quantity or zero. Its
value depends on the process, and thus it is not a property of the system. Also,
in the absence of any entropy transfer, the entropy change of a system is equal
to the entropy generation.
Equation 7–7 has far-reaching implications in thermodynamics. For an isolated system (or simply an adiabatic closed system), the heat transfer is zero,
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This document was uploaded on 11/28/2012.
- Spring '09