Contributions to International Standards on the Properties of Water

Researchers in the Thermophysical Properties Division of CSTL played a leading role in the development of several new international standards for the properties of water. This work was performed under the auspices of the International Association for the Properties of Water and Steam (IAPWS). Contributions included the development of a new reference formulation for the viscosity of water, new “backward equations” for properties which substantially decrease the computation time for steam-turbine calculations, a new seawater standard for oceanographic and engineering applications, and simple but highly accurate correlations for thermodynamic properties, viscosity, thermal conductivity, and static dielectric constant of liquid water at atmospheric pressure.

Water is one of the most important industrial fluids and it is important to have internationally accepted standards for its properties. This information is crucial to the analysis and design of thermal power cycles. IAPWS is an international non-profit association of national organizations concerned with the properties of water and steam, particularly thermophysical properties and other aspects of high-temperature steam, water and aqueous mixtures that are relevant to thermal power cycles and other industrial applications. NIST researchers are active in the leadership and working groups of IAPWS and have led the development of several recent standards adopted by IAPWS.

Researchers developed a new formulation for the viscosity of water that incorporates new data and extends the range of applicability of the formulation compared to the previous 1985 correlation. It is expected that this formulation will be useful not only for applications where the viscosity of water and steam is needed directly (such as the steam power industry), but also for applications where the viscosity of water is used as a reference for calibrations, measurements, or correlations involving other fluids. The formulation is available through the IAPWS website, and also will be incorporated into the next release of NIST Standard Reference Database 23, (REFPROP, Reference Fluid Thermodynamic and Transport Properties) and NIST Standard Reference Database 10 (NIST/ASME Steam Properties) distributed by the Standard Reference Data Program of NIST, as well as through the NIST Chemistry Webbook (http://webbook.nist.gov). Properties from the new viscosity formulation have also been incorporated into a new Second Edition of the widely-used ASME Steam Tables book.        

NIST researchers participated in an IAPWS effort, driven by the oceanographic community, to develop a new formulation for the thermodynamic properties of seawater. The new formulation is a significant improvement in accuracy and thermodynamic consistency over the previous standard (which was approximately 30 years old), and is fully consistent with the IAPWS standard for the properties of pure water.

Additional IAPWS work includes the development of “backward” equations to greatly increase the speed of common calculations of thermodynamic properties in the steam power industry.

These calculations would otherwise have to be performed iteratively; the explicit backward equations enable the use of computer-intensive applications such as finite-element analysis and detailed turbine programs.

Another IAPWS project, co-led by a NIST researcher, was for the benefit of those in science and industry who do not need the comprehensive, wide-ranging IAPWS formulations because their interest is only for liquid water at atmospheric pressure (for example, for calibration of instruments).

One-dimensional correlations were developed for convenient calculation of thermodynamic properties, viscosity, thermal conductivity, and static dielectric constant.

In the region of applicability, the uncertainties of these correlations are no greater than those of the underlying IAPWS formulations.

• Release on the IAPWS Formulation 2008 for the Viscosity of Ordinary Water Substance
• Release on the IAPWS Formulation 2008 for the Thermodynamic Properties of Seawater
• IAPWS Supplementary Release on Properties of Liquid Water at 0.1 MPa
• ASME International Steam Tables for Industrial Use, 2nd Ed.