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Unformatted text preview: system increases by ms when mass in the amount
of m enters and decreases by the same amount when the same amount of mass
at the same state leaves the system. When the properties of the mass change
during the process, the entropy transfer by mass flow can be determined by
integration from
·
Smass sr
Ac n dAc and Smass sdm where Ac is the crosssectional area of the flow and
normal to dAc. t n ·
Smass dt (7–75) is the local velocity Entropy is not
transferred
with work Entropy
generation
via friction FIGURE 7–59
No entropy accompanies work as it
crosses the system boundary. But
entropy may be generated within
the system as work is dissipated
into a less useful form of energy. hm
s Control volume
mh
ms FIGURE 7–60
Mass contains entropy as well as
energy, and thus mass flow into or out
of system is always accompanied by
energy and entropy transfer. cen54261_ch07.qxd 11/18/03 9:57 AM Page 322 322
FUNDAMENTALS OF THERMALFLUID SCIENCES Entropy Generation, Sgen Irreversibilities such as friction, mixing, chemical reactions, heat transfer
through a finite temperature difference, unrestrained expansion, nonquasiequilibrium compression, or expans...
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 Spring '09

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