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 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.
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.
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 September 21, 2016