65 kjk 432 kjk lake 285 k iron casting m 50 kg t1 500

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Unformatted text preview: undary temperature of the extended system is at 285 K at all times: Sin Sout 14243 { Sgen ∆Ssystem 123 Net entropy transfer by heat and mass Entropy generation Change in entropy Sgen ∆Ssystem Qout Tb or Sgen Q out Tb ∆Ssystem 4838 kJ 285 K (12.65 kJ/K) 4.32 kJ/K LAKE 285 K IRON CASTING m = 50 kg T1 = 500 K FIGURE 7–67 Schematic for Example 7–19. cen54261_ch07.qxd 11/18/03 9:57 AM Page 328 328 FUNDAMENTALS OF THERMAL-FLUID SCIENCES Discussion The entropy generated can also be determined by taking the iron block and the entire lake as the system, which is an isolated system, and applying an entropy balance. An isolated system involves no heat or entropy transfer, and thus the entropy generation in this case becomes equal to the total entropy change, ∆Stotal Sgen ∆Ssystem ∆Slake 12.65 16.97 4.32 kJ/K which is the same result obtained above. EXAMPLE 7–20 Entropy Generation in a Mixing Chamber Water at 20 psia and 50°F enters a mixing chamber at a rate of 300 lbm/min where it is mixed steadily with steam entering at 20 psia and...
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This document was uploaded on 11/28/2012.

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