S const 1 2 k 1k s const p2 p1 k s const 1 2 k1

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Unformatted text preview: l use of T ds relations depends on the availability of property relations. Such relations do not exist for a general pure substance but are available for incompressible substances (solids, liquids) and ideal gases. The entropy-change and isentropic relations for a process can be summarized as follows: b. s const. υ1 υ2 (k 1)/k s const. P2 P1 k s const. υ1 υ2 k1 Variable specific heats (exact treatment): Any process: s2 – s2 s1 – s1 s° 2 – s° 2 s° 1 – s° 1 R ln P2 P1 (kJ/kg · K) Ru ln P2 P1 (kJ/kmol · K) cen54261_ch07.qxd 11/18/03 9:57 AM Page 333 333 CHAPTER 7 Isentropic process: s° 2 s° 1 R ln P2 P1 υ2 υ1 P2 P1 (kJ/kg · K) s const. Pr2 Pr1 s const. υr2 υr1 hT where Pr is the relative pressure and υr is the relative specific volume. The function s° depends on temperature only. The steady-flow work for a reversible process can be expressed in terms of the fluid properties as 2 wrev 1 υ dP ke For incompressible substances (υ wrev υ (P2 P1) pe (kJ/kg) constant) it simplifies to ke pe Polytropic: Isothermal: wcomp, in wcomp, in wcomp, in kR(T2 T1) k1 kRT1 P2 k 1 P1 nR(T2 T1) n1 nRT1 P2 n 1 P1 RT ln P2 P1 hC hN wa h1 h2a Actual turbine work Ise...
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