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Unformatted text preview: is satisfied, the compression work at each stage becomes identical, that is, wcomp I, in wcomp II, in.
EXAMPLE 7–13 Work Input for Various Compression Processes Air is compressed steadily by a reversible compressor from an inlet state of
100 kPa and 300 K to an exit pressure of 900 kPa. Determine the compressor
work per unit mass for (a) isentropic compression with k
1.4, (b) polytropic
compression with n 1.3, (c) isothermal compression, and (d ) ideal two-stage
compression with intercooling with a polytropic exponent of 1.3. SOLUTION We take the compressor to be the system. This is a control volume
since mass crosses the boundary. A sketch of the system and the T-s diagram
for the process are given in Fig. 7–47.
Assumptions 1 Steady operating conditions exist. 2 At specified conditions, air
can be treated as an ideal gas since it is at a high temperature and low pressure cen54261_ch07.qxd 11/18/03 9:57 AM Page 311 311
Isentropic (k = 1.4)
Polytropic (n = 1.3)
P2 = 900 kPa
100 wcomp 1 P1 = 100 kPa...
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This document was uploaded on 11/28/2012.
- Spring '09