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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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- Spring '09