Thus 2 1 s2 t k 300 310 320 s t kjkg k 170203 173498

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 2 1 Cp(T) dT T s° 2 s° 1 (7–38) where s° is the value of s° at T2 and s° is the value at T1. Thus, 2 1 s2 T, K . . . 300 310 320 . . . s °(T), kJ/kg K . . . 1.70203 1.73498 1.76690 . . . (Table A-17) FIGURE 7–33 The entropy of an ideal gas depends on both T and P. The function s° represents only the temperaturedependent part of entropy. s1 s° 2 s° 1 R ln P2 P1 (kJ/kg · K) (7–39) (kJ/kmol · K) (7–40) It can also be expressed on a unit-mole basis as – s2 – s1 – s° 2 – s° 1 Ru ln P2 P1 Note that unlike internal energy and enthalpy, the entropy of an ideal gas varies with specific volume or pressure as well as the temperature. Therefore, entropy cannot be tabulated as a function of temperature alone. The s° values in the tables account for the temperature dependence of entropy (Fig. 7–33). The variation of entropy with pressure is accounted for by the last term in Eq. 7–39. Another relation for entropy change can be developed based on Eq. 7–31, but this would require the definition of another function and tabulation of its values, which is not practical. EXAMPLE 7...
View Full Document

This document was uploaded on 11/28/2012.

Ask a homework question - tutors are online