Page 288 - Steam Turbines Design, Applications, and Rerating

Chapter
14

Shortcut Graphical Methods of

Turbine Selection

14.1 Mollier Chart Instructions
As will be seen, the water rate of a steam turbine can be obtained from
a Mollier Chart, Fig. 14.1 and 14.2, if steam conditions and turbine effi-
ciency are known. On the simplified Mollier Diagram, Fig. 14.3, we
observe the following:

(A) Enthalpy A thermodynamic property that serves as a measure of
heat energy in a system above some datum temperature (for water it
is 32°F or 0°C). In this case it represents the energy in one pound of
steam (Btu/lb or kJ/kg).
(B) Entropy (BTU per lb)/°R) or (kJ per kg/K) An indication of the
unavailable energy in a system.
(C) Constant pressure line (psia or bar, absolute) Represents the
absolute steam pressure at varying enthalpy values.
(D) Constant temperature line Represents the total steam tempera-
ture at varying steam pressures.
(E) Constant moisture line Represents the percent moisture content
in the steam.
(F) Vapor dome This line represents the dry and saturated state of
steam. The area above the vapor dome represents superheated
steam, and the area below the vapor dome represents wet steam.

To determine the power output of a steam turbine, the entrance and
exhaust conditions must be determined. This process is explained in
Fig. 14.4.

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