Main IAPWS Thermodynamic Property Formulations


In 1995, IAPWS approved a new formulation of the thermodynamic properties of water and steam for general and scientific use. This replaced the 1984 formulation of Haar, Gallagher and Kell, and now serves as the international standard for water's thermodynamic properties.
An archival paper describing this formulation has been published:
W. Wagner and A. Pruss, "The IAPWS Formulation 1995 for the Thermodynamic Properties of Ordinary Water Substance for General and Scientific Use," J. Phys. Chem. Ref. Data, 31, 387-535 (2002).
Software implementing this formulation is available from NIST (described at this website), and from Prof. Dr.-Ing. W. Wagner (described at this website).
NIST has also provided online access to properties computed from this formulation in the "Thermophysical Properties of Fluid Systems" section of the NIST Chemistry Webbook, and a printed tabulation of properties computed from the formulation.

A compilation of experimental data used to develop the IAPWS-95 formulation is available.

For the special requirements of the steam power industry, IAPWS also maintains a separate formulation for industrial use. In 1997, IAPWS approved a new formulation of the thermodynamic properties of water and steam for industrial use (referred to as IAPWS-IF97), replacing the IFC-67 formulation that is familiar to many from its use in the 1967 ASME Steam Tables. An archival paper describing this formulation has been published:
W. Wagner et al., "The IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam," ASME J. Eng. Gas Turbines and Power, 122, 150-182 (2000).
Computer code implementing this formulation is made available from IAPWS national committees (the implementation by the American Society of Mechanical Engineers is described here; the implementation of Prof. Dr.-Ing. W. Wagner, head of the group that developed IAPWS-IF97, is described here, another group in Germany has developed software described here and an online property calculator, and the Russian national committee to IAPWS has developed software along with a web interface for property calculations).
Some IAPWS-IF97 software for pocket calculators is also available, and implementations on some other platforms (mostly for student use) are described on our Education page.

Several "Steam Tables" books based on the IAPWS-IF97 formulation for industrial use have been published. The book published in Germany is described here. The ASME in the United states has published both a full-sized steam tables book and a shorter compact booklet of steam tables. A book has also been published by the JSME in Japan, and books have been published in Russia and the Czech Republic.

Documents giving a complete description of the formulation are available for both the Formulation for General and Scientific Use and the IAPWS-IF97 Industrial Formulation.

Updated February 17, 2017


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