Formulation
Thermodynamic properties are computed with the IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam (IAPWS-IF97, revised 2007), published by the International Association for the Properties of Water and Steam. The formulation divides the pressure–temperature plane into regions, each with its own equation:
- Region 1 – compressed liquid, up to 350 °C;
- Region 2 – steam (vapour), up to 800 °C;
- Region 3 – the area around the critical point, formulated in density and temperature; this site solves the density numerically from the basic equation;
- Region 4 – the saturation curve;
- Region 5 – high-temperature steam, 800–2000 °C up to 500 bar.
Dynamic viscosity follows the IAPWS Formulation 2008 for the Viscosity of Ordinary Water Substance (without critical enhancement, as recommended for industrial use). Thermal conductivity follows the IAPWS Formulation 2011 for the Thermal Conductivity of Ordinary Water Substance, industrial variant.
Range of validity
0 °C ≤ T ≤ 800 °C for p ≤ 1000 bar (100 MPa), and 800 °C < T ≤ 2000 °C for p ≤ 500 bar (50 MPa). Outside this range no value is returned.
Validation
The calculation library is checked automatically against the computer-program verification values printed in the IAPWS-IF97 release for regions 1, 2, 3 and 5, the saturation curve and the region 2/3 boundary, and against the verification values of the IAPWS 2008 viscosity release. It was additionally compared on several hundred random states with an independent open-source implementation.
Limitations
- IAPWS-IF97 is designed for industrial calculations. For the lowest uncertainties, IAPWS recommends its scientific formulation, IAPWS-95.
- Very close to the critical point, properties such as heat capacity vary extremely fast; small input changes cause large output changes.
- Pure ordinary water only: no ice, no seawater, no dissolved gases or salts.
- The page is an information tool provided without warranty. Do not rely on it alone for safety-critical design.