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Guideline on an Equation of State for Humid Air in Contact with Seawater and Ice, Consistent with the IAPWS Formulation 2008 for the Thermodynamic Properties of Seawater
July 2010

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This formulation is recommended for the calculation of thermodynamic properties of humid air, including equilibria with liquid water, or ice Ih, and seawater, in combination with the IAPWS Releases for fluid water, for ice Ih, and for seawater.
The formulation is for the Helmholtz energy as a function of dry-air mass fraction, temperature and density; appropriate combinations of derivatives can produce any thermodynamic property desired (pressure, sound speed, heat capacity, enthalpy, entropy, chemical potential, etc.).
The formulation is valid for relative humidity between 0 % and 100 %, for pressure up to 5 MPa, and for temperature in the range between 193 K and 473 K. It extrapolates in a physically reasonable way outside this region.
The development of the formulation is described in detail in a scientific article.

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.

Revision History

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

This page updated May 29, 2018

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