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Unformatted text preview: cific heats may lead to considerable errors in entropy-change
calculations. For those cases, the variation of specific heats with temperature
should be properly accounted for by utilizing accurate relations for the specific heats as a function of temperature. The entropy change during a process
is then determined by substituting these Cυ(T) or Cp(T) relations into Eq. 7–31
or 7–32 and performing the integrations.
Instead of performing these laborious integrals each time we have a new
process, it is convenient to perform these integrals once and tabulate the results. For this purpose, we choose absolute zero as the reference temperature
and define a function s° as
0 Cp(T) dT
T (7–37) According to this definition, s° is a function of temperature alone, and its
value is zero at absolute zero temperature. The values of s° are calculated
at various temperatures, and the results are tabulated in the appendix as a
function of temperature for air. Given this definition, the integral in Eq. 7–32
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This document was uploaded on 11/28/2012.
- Spring '09