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Entropy transfer is recognized at the system boundary as it crosses the boundary, and it represents the entropy gained or lost by a system during a process.
The only form of entropy interaction associated with a fixed mass or closed
system is heat transfer, and thus the entropy transfer for an adiabatic closed
system is zero. Surroundings 1 Heat Transfer
Tb = 400 K
SYSTEM Q = 500 kJ
= 1.25 kJ/K Sheat = FIGURE 7–58
Heat transfer is always accompanied
by entropy transfer in the amount of
Q/T, where T is the boundary
temperature. Heat is, in essence, a form of disorganized energy, and some disorganization
(entropy) will flow with heat. Heat transfer to a system increases the entropy
of that system and thus the level of molecular disorder or randomness, and
heat transfer from a system decreases it. In fact, heat rejection is the only way
the entropy of a fixed mass can be decreased. The ratio of the heat transfer Q
at a location to the absolute temperature T at that location is called the entropy
flow or entropy transfer and is expressed as (Fig. 7–58)
Entropy transfer by heat transfer: Sheat Q
T (T constant) (7–71) The quantity Q/T represents the entropy transfer accompanie...
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- Spring '09