Unformatted text preview: nd the system to include the regions on both sides of the wall
that experience a temperature change. Then one side of the system boundary
becomes room temperature while the other side becomes the temperature of the
outdoors. The entropy balance for this extended system (system
immediate
surroundings) will be the same as that given above, except the two boundary
temperatures will be 300 and 273 K instead of 293 and 278 K, respectively.
Then the rate of total entropy generation becomes 1035 W
300 K 1035 W
273 K ·
Sgen, total 0 ·
→ Sgen, total 0.341 W/K Discussion Note that the entropy change of this extended system is also zero
since the state of air does not change at any point during the process. The differences between the two entropy generations is 0.150 W/K, and it represents
the entropy generated in the air layers on both sides of the wall. The entropy
generation in this case is entirely due to irreversible heat transfer through a
finite temperature difference. EXAMPLE 7–18 ·
Q
27ºC 20ºC 0ºC 30 cm...
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This document was uploaded on 11/28/2012.
 Spring '09

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