Thermodynamics
PROPERTY DIAGRAMS AND STEAM TABLES
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(1
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s
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(1
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In order to solve problems in Thermodynamics, information concerning the "state" of the
substance studied must be obtained. Usually, two properties (for example, v, p, T, h, s) of the
substance must be known in order to determine the other needed properties. These other
properties are usually obtained utilizing either the Mollier diagram (if the substance is steam) or
the saturated and superheated steam tables, as shown in the Figures A-1 and A-2.
The following two examples illustrate the use of the Mollier diagram and the steam tables.
Example 1: Use of Mollier Chart.
Superheated steam at 700 psia and 680°F is expanded at constant entropy to 140 psia.
What is the change in enthalpy?
Solution:
Use the Mollier Chart. Locate point 1 at the intersection of the 700 psia and the 680°F
line. Read h = 1333 Btu/lbm.
Follow the entropy line downward vertically to the 140 psia line and read h = 1178
Btu/lbm.
h = 1178 - 1333 = -155 Btu/lbm
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