Thermodynamics
PROPERTY DIAGRAMS AND STEAM TABLES
where:
s
=
specific entropy of the mixture (Btu/lbm-°R)
x
=
quality of the mixture (no units)
sg
=
specific entropy of the saturated vapor (Btu/lbm-°R)
sf
=
specific entropy of the saturated liquid
(Btu/lbm-°R)
sfg
=
specific entropy change of vaporization (Btu/lbm-°R) or sfg = sg - sf
Enthalpy-Entropy (h-s) or Mollier Diagram
The Mollier diagram, shown in Figure A-1 of Appendix A, is a chart on which enthalpy (h)
versus entropy (s) is plotted. It is sometimes known as the h-s diagram and has an entirely
different shape from the T-s diagrams. The chart contains a series of constant temperature lines,
a series of constant pressure lines, a series of constant moisture or quality lines, and a series of
constant superheat lines. The Mollier diagram is used only when quality is greater than 50% and
for superheated steam.
Steam Tables
Steam tables consist of two sets of tables of the energy transfer properties of water and steam:
saturated steam tables and superheated steam tables. Portions of the tables are shown in Figure
A-2 of Appendix A. Both sets of tables are tabulations of pressure (P), temperature (T), specific
volume (n), specific enthalpy (h), and specific entropy (s). The following notation is used in
steam tables. Some tables use v for n (specific volume) because there is little possibility of
confusing it with velocity.
T
=
temperature (°F)
P
=
pressure (psi)
n
=
specific volume (ft3/lbm)
nf
=
specific volume of saturated liquid (ft3/lbm)
ng
=
specific volume of saturated vapor (ft3/lbm)
Rev. 0
Page 47
HT-01
