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Unformatted text preview: is not clear where exactly the entropy generation takes place, and how. To pinpoint the location of entropy generation, we
need to be more precise about the description of the system, its surroundings,
and the system boundary.
In that example, we assumed both the system and the surrounding air to be
isothermal at 100°C and 25°C, respectively. This assumption is reasonable if
both fluids are well mixed. The inner surface of the wall must also be at 100°C cen54261_ch07.qxd 11/18/03 9:57 AM Page 331 331
CHAPTER 7 while the outer surface is at 25°C since two bodies in physical contact must
have the same temperature at the point of contact. Considering that entropy
transfer with heat transfer Q through a surface at constant temperature T is
Q/T, the entropy transfer from the water into the wall is Q/Tsys 1.61 kJ/K.
Likewise, entropy transfer from the outer surface of the wall into the sur2.01 kJ/K. Obviously, entropy in the amount of
rounding air is Q/Tsurr
2.01 1.61 0.4 kJ/K is generated in the wall, as illustrated in Fig. 7–70b.
Identifying the location of entropy generation enables us to...
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This document was uploaded on 11/28/2012.
- Spring '09