07463 btulbm r p c on st t 2 h2o figure 713 schematic

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Unformatted text preview: R P =c on st. T 2 H2O FIGURE 7–13 Schematic and T-s diagram for Example 7–4. P1 = 20 psia 1 T1 = 70°F s1 s2 s cen54261_ch07.qxd 11/18/03 9:57 AM Page 285 285 CHAPTER 7 7–4 I ISENTROPIC PROCESSES Steam s1 We mentioned earlier that the entropy of a fixed mass can be changed by (1) heat transfer and (2) irreversibilities. Then it follows that the entropy of a fixed mass will not change during a process that is internally reversible and adiabatic (Fig. 7–14). A process during which the entropy remains constant is called an isentropic process. It is characterized by Isentropic process: s 0 or s2 s1 (kJ/kg · K) (7–13) That is, a substance will have the same entropy value at the end of the process as it does at the beginning if the process is carried out in an isentropic manner. Many engineering systems or devices such as pumps, turbines, nozzles, and diffusers are essentially adiabatic in their operation, and they perform best when the irreversibilities, such as the friction associated with the process, are minimized. Therefore, an isentropic...
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