3 the kinetic and potential energy changes of the

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Unformatted text preview: ore, the iron block will cool to 285 K during this process while the lake temperature remains constant at 285 K. Assumptions 1 Both the water and the iron block are incompressible substances. 2 Constant specific heats can be used for the water and the iron. 3 The kinetic and potential energy changes of the iron are negligible, ∆KE ∆PE 0 and thus ∆E ∆U. 4 There are no work interactions. Analysis (a) Approximating the iron block as an incompressible substance, its entropy change can be determined from ∆Siron m(s2 s1) mCav ln T2 T1 (50 kg)(0.45 kJ/kg · K) ln 285 K 500 K 12.65 kJ/K (b) The temperature of the lake water remains constant during this process at 285 K. Also, the amount of heat transfer from the iron block to the lake is determined from an energy balance on the iron block to be Ein Eout 14243 ∆Esystem 123 Net energy transfer by heat, work, and mass Change in internal, kinetic, potential, etc., energies ∆U Qout mCav(T2 T1) or Qout mCav(T1 T2) (50 kg)(0.45 kJ/kg · K)(500 285) K 4838 kJ Then the entropy change of the lake becomes ∆Slake Qlake Tlake 4838 kJ 285 K 16.97 kJ/K (c) The entropy generated during this process can be determined by applying an entropy balance on an extended system that includes the iron block and its immediate surroundings so that the bo...
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This document was uploaded on 11/28/2012.

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