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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
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.
- Spring '09