Revised Release on the IAPWS Formulation 1995 for the Thermodynamic Properties of Ordinary Water Substance for General and Scientific Use (September 2009)

Description
This formulation is recommended for the calculation of thermodynamic properties of ordinary water in its fluid phases, including vapor-liquid equilibrium.
The formulation is for the Helmholtz energy as a function of temperature and density; appropriate combinations of derivatives can produce any thermodynamic property desired (density or specific volume, sound speed, heat capacity, enthalpy, entropy, etc.).
The formulation is valid in the entire stable fluid region from the melting curve to 1273 K at pressures to 1000 MPa. It extrapolates in a physically reasonable way outside this region.

Revision History

• This Release was adopted by IAPWS in 1995, replacing the previous Release of 1984.
• In 2009, the Release was revised in order to produce greater consistency with conventions for the arbitrary zero values for entropy and internal energy at the triple point. No calculations for measurable properties or property differences were affected by this change. A few minor editorial updates were also made.
• In 2010, minor editorial changes were made in the document to add a reference to the uncertainty of enthalpy calculations.

This Release is the product of the Working Group "Thermophysical Properties of Water and Steam" (TPWS) of the International Association for the Properties of Water and Steam (IAPWS).

This page updated July 14, 2010