Researchers in the Applied Chemicals and Materials Division play a leading role in the development of international standards for the properties of water. This work is performed under the auspices of the International Association for the Properties of Water and Steam (IAPWS). Recent contributions include the development of new reference formulations for the viscosity and thermal conductivity of water, a new standard formulation for the vapor pressure of ice, and simple but highly accurate correlations for thermodynamic properties, viscosity, thermal conductivity, and static dielectric constant of liquid water at atmospheric pressure.
Water is probably the most widely used industrial fluid 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, as well as for climate studies including the hydrosphere. (Here is a summary of the history through 2001 of water and steam property measurements for the power generation industry, featuring the contributions of NIST/NBS.) 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 new formulations for the viscosity and thermal conductivity of water that incorporate new data and extend the ranges of applicability of the formulations compared to the previous correlations from the 1980s. These formulations are useful not only for applications where the viscosity and/or thermal conductivity of water and steam is needed directly (such as the steam power industry), but also for applications where these properties are used as a reference for calibrations, measurements, or correlations involving other fluids. The formulations are available through the IAPWS website, and have also been incorporated into 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. Properties from the new viscosity and thermal conductivity formulations have also been incorporated into a new Third Edition of the widely used ASME Steam Tables book.
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). Simple correlations as a function of temperature 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.
Additional IAPWS work included the development of a new standard formulation for the vapor pressure of ice, based on a comprehensive evaluation of available thermodynamic information.