IAPWS R6-95(2018)
Revised Release on the IAPWS Formulation 1995 for the Thermodynamic Properties
of Ordinary Water Substance for General and Scientific Use
September 2018
PDF of document
Description
This formulation is recommended for the calculation of thermodynamic properties
of ordinary water in its fluid phases, including vapor-liquid equilibrium.
The formulation (commonly referred to as IAPWS-95) is for the Helmholtz energy as a function of temperature and density;
appropriate combinations of derivatives can produce any thermodynamic property desired
(pressure, 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.
The development of the formulation and comparisons to
available data are described in detail in a
scientific article.
Online Calculation
The Russian National Committee of IAPWS (through Moscow Power Engineering Institute) has provided an
online calculation page,
which may be useful in program development and verification.
Note that IAPWS is not responsible for the content of these online calculation pages.
Software Implementation
The IAPWS Subcommittee on Seawater, in cooperation with the
SCOR/IAPSO Working Group 127,
developed the "Thermodynamic Equation of Seawater 2010" (TEOS-10) which was endorsed as an international standard for oceanography by
UNESCO-IOC in 2009 and by
IUGG in 2011.
The open-source code of TEOS-10
includes software implementations of this IAPWS formulation.
Note that IAPWS is not responsible for the content of these external pages.
Links to other software implementations of this formulation, sponsored by IAPWS Members, can be found on
this page.
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.
- In 2012, minor changes were made in the document to give advice regarding extrapolation of the formulation in the gas region down to 130 K.
- In 2014, minor changes were made in the document to give improved estimates of the uncertainty of the sound speed and heat capacity at some high-pressure conditions.
- In 2016, minor changes were made in the document to improve uncertainty estimates for the specific isobaric heat capacity and to update language regarding extrapolation to the metastable subcooled liquid.
- In 2018, minor changes were made in the document to add details about computing virial coefficients and to clarify uncertainty estimates at low densities.
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 December 21, 2018
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