# 3844 kjkg k b the entropy change of air during this

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Unformatted text preview: nd substituting, we find s2 s1 s° 2 s° 1 R ln [(1.79783 P2 P1 1.66802) kJ/kg · K] (0.287 kJ/kg · K) ln 600 kPa 100 kPa 0.3844 kJ/kg · K (b) The entropy change of air during this process can also be determined approximately from Eq. 7–34 by using a Cp value at the average temperature of 37°C (Table A–2b) and treating it as a constant: s2 s1 T2 T1 P2 P1 330 K (1.006 kJ/kg · K) ln 290 K 0.3842 kJ/kg · K Cp, av ln R ln 600 kPa (0.287 kJ/kg · K) ln 100 kPa Discussion The two results above are almost identical since the change in temperature during this process is relatively small (Fig. 7–35). When the temperature change is large, however, they may differ significantly. For those cases, Eq. 7–39 should be used instead of Eq. 7–34 since it accounts for the variation of specific heats with temperature. Isentropic Processes of Ideal Gases Several relations for the isentropic processes of ideal gases can be obtained by setting the entropy-change relations developed above equal to zero. Again, this is done first for the case...
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