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FUNDAMENTALS OF THERMAL-FLUID SCIENCES obtained directly from the tables at the specified state. In the saturated mixture
region, it is determined from
s sf xsfg (kJ/kg · K) where x is the quality and sf and sfg values are listed in the saturation tables.
In the absence of compressed liquid data, the entropy of the compressed liquid can be approximated by the entropy of the saturated liquid at the given
s @ T, P sf @ T (kJ/kg · K) The entropy change of a specified mass m (such as a closed system) during a
process is simply
S ms m(s2 s1) (kJ/K) (7–12) which is the difference between the entropy values at the final and initial
When studying the second-law aspects of processes, entropy is commonly
used as a coordinate on diagrams such as the T-s and h-s diagrams. The
general characteristics of the T-s diagram of pure substances are shown in
Fig. 7–11 using data for water. Notice from this diagram that the constantvolume lines are steeper than the constant-pressure lines and the constantpressure lines are parallel to the constant-temperature lines in the saturated
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This document was uploaded on 11/28/2012.
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