Chapter 7

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Unformatted text preview: P2 P1 (kJ/kg · K) (kJ/K) The inequality part of the Clausius inequality combined with the definition of entropy yields an inequality known as the increase of entropy principle, expressed as Or, on a unit-mole basis, Sgen 0 (kJ/K) – s2 – s2 where Sgen is the entropy generated during the process. Entropy change is caused by heat transfer, mass flow, and irreversibilities. Heat transfer to a system increases the entropy, and heat transfer from a system decreases it. The effect of irreversibilities is always to increase the entropy. Entropy is a property, and it can be expressed in terms of more familiar properties through the T ds relations, expressed as T ds du T2 – C υ, av ln T1 – s1 Ru ln υ2 υ1 (kJ/kmol · K) T2 – C p, av ln – s1 Ru ln P2 P1 (kJ/kmol · K) T1 Isentropic process: T2 T1 P dυ T2 T1 and T ds dh P2 P1 υ dP These two relations have many uses in thermodynamics and serve as the starting point in developing entropy-change relations for processes. The successfu...
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This document was uploaded on 11/28/2012.

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