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Unformatted text preview: ling). Assuming all three processes are executed between the same pressure
levels (P1 and P2) in an internally reversible manner and the gas behaves as an
ideal gas (Pυ RT) with constant specific heats, we see that the compression
work is determined by performing the integration in Eq. 7–56 for each case,
with the following results: cen54261_ch07.qxd 11/18/03 9:57 AM Page 309 309
CHAPTER 7 Isentropic (Pυ k constant):
wcomp, in Polytropic (Pυ n kRT1
k1 P2
P1 (k 1)/k nRT1
n1 P2
P1 (n 1)/n 1 (7–57a) 1 (7–57b) constant): wcomp, in Isothermal (Pυ kR(T2 T1)
k1 nR(T2 T1)
n1 constant):
wcomp, in RT ln P2
P1 (7–57c) The three processes are plotted on a Pυ diagram in Fig. 7–45 for the same
inlet state and exit pressure. On a Pυ diagram, the area to the left of the
process curve is the integral of υ dP. Thus it is a measure of the steadyflow
compression work. It is interesting to observe from this diagram that of
the three internally reversible cases considered, the adiabatic compression
(Pυ k constant) requires the maximum work...
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 Spring '09

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