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National Advisory Committee for Aeronautics, Technical Notes - Mollier Diagrams for Air Saturated with Water Vapor at Low Temperatures

Two Mollier diagrams relating the thermodynamic properties of
air saturated with water vapor in equilibrium with water and with ice
at low temperatures are presented. The development of the charts is
given and their use in the solution of problems involving thermo-e
dynamic processes of mixtures of air and water is explained. A tem-
perature range of 400° to 540° R and a pressure range of 2 to
28 pounds per square inch absolute were chosen in order that the
charts would be of greatest utility in considering problems con-
cerned with the icing of aircraft. Several examples that illustrate
the use of the diagrams are presented.

In problems involving the thermodynamic properties of a mix-
ture of air and water vapor, the enthalpy and the entropy are often
of much greater utility than other more easily determined character-
istics of the mixture. The enthalpy and the entropy of a compres-
sible fluid can be conveniently presented as a Mollier diagram that
relates these characteristics to other fundamental properties of
the fluid.

Two Mollier diagrams for air saturated with water vapor were
prepared at the NACA Cleveland laboratory and are presented. The
diagrams represent two conditions: One diagram is applicable when
vapor-liquid equilibrium exists over the entire temperature range
considered; whereas the other diagram should be used if vapor-solid
equilibrium exists for subfreezing temperatures and vapor-liquid
equilibrium for higher temperatures. These diagrams are useful in
dealing with the properties of saturated mixtures of air and water
vapor or mixtures containing water in excess of the saturation
quantity in,various types of thermodynamic process and in the solu-
tion of problems involving the icing of aircraft components.

The evaluation of the contributions of the liquid-water or ice
content to the enthalpy and the entropy of a system is considered.
These contributory terms must be evaluated when mixtures with water
in excess of the saturation quantity are considered.