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Unformatted text preview: ion always cause the entropy of a system
to increase, and entropy generation is a measure of the entropy created by
such effects during a process.
For a reversible process (a process that involves no irreversibilities), the
entropy generation is zero and thus the entropy change of a system is equal to
the entropy transfer. Therefore, the entropy balance relation in the reversible
case becomes analogous to the energy balance relation, which states that
energy change of a system during a process is equal to the energy transfer
during that process. However, note that the energy change of a system equals
the energy transfer for any process, but the entropy change of a system equals
the entropy transfer only for a reversible process.
The entropy transfer by heat Q/T is zero for adiabatic systems, and the
entropy transfer by mass ms is zero for systems that involve no mass flow
across their boundary (i.e., closed systems).
Entropy balance for any system undergoing any process can be expressed
more explicitly as
Mass Sout Sgen ∆Ssystem System 14243 13
2 123 Mass Net entropy transfer
by heat and mass Entropy
generation Sgen ≥, 0 (kJ/K) (7–76) Change
in entropy ∆ Ssystem
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This document was uploaded on 11/28/2012.
- Spring '09