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Unformatted text preview: → T2a hN T2a)
T2s) or 0.92 764 K That is, the temperature will be 16 K higher at the exit of the actual nozzle as
a result of irreversibilities such as friction. It represents a loss since this rise in
temperature comes at the expense of kinetic energy (Fig. 7–56). Actual nozzle
950 K
AIR Isentropic nozzle 764 K, 639 m/s
748 K, 666 m/s (c) The actual exit velocity of air can be determined from the definition of isentropic efficiency of a nozzle, hN 7–13 I 2
2a
2
2s → 2a N 2
2s FIGURE 7–56
A substance leaves actual nozzles at a
higher temperature (thus a lower
velocity) as a result of friction. 639 m/s ENTROPY BALANCE The property entropy is a measure of molecular disorder or randomness of a
system, and the second law of thermodynamics states that entropy can be
created but it cannot be destroyed. Therefore, the entropy change of a system
during a process is greater than the entropy transfer by an amount equal to the
entropy generated during the process within the system, and the increase of
entropy principle for any system is expressed as (Fig. 7–57)
Total
entropy
entering Total
entropy
leaving Total
entropy
generated Change in...
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 Spring '09

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