Cen54261ch07qxd 111803 957 am page 321 321 chapter

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Unformatted text preview: d by heat transfer, and the direction of entropy transfer is the same as the direction of heat transfer since absolute temperature T is always a positive quantity. cen54261_ch07.qxd 11/18/03 9:57 AM Page 321 321 CHAPTER 7 When the temperature T is not constant, the entropy transfer during a process 1-2 can be determined by integration (or by summation if appropriate) as 2 Sheat 1 Qk Tk Q T (7–72) where Qk is the heat transfer through the boundary at temperature Tk at location k. When two systems are in contact, the entropy transfer from the warmer system is equal to the entropy transfer into the cooler one at the point of contact. That is, no entropy can be created or destroyed at the boundary since the boundary has no thickness and occupies no volume. Note that work is entropy-free, and no entropy is transferred by work. Energy is transferred by both heat and work, whereas entropy is transferred only by heat. That is, Entropy transfer by work: Swork 0 (7–73) The first law of thermodynamics makes no distinction between heat transfer and work; it considers them as equals. The distinction between heat transfer and work is brought out by the second law: an en...
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This document was uploaded on 11/28/2012.

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