This formulation is recommended for industrial use (primarily the steam power industry) for the calculation of thermodynamic properties of ordinary water in its fluid phases, including vapor-liquid equilibrium.
The formulation is a close approximation to the IAPWS-95 formulation for general and scientific use, but is designed for much greater computational speed. The range of validity is divided into several regions (with close tolerances for consistency at region boundaries), each of which is represented by a different fundamental equation. Appropriate combinations of derivatives from this equation can produce any thermodynamic property desired (density or specific volume, sound speed, heat capacity, enthalpy, entropy, etc.).
The formulation is valid from 273.15 K to 1073.15 K at pressures to 100 MPa, and there is a high-temperature region extending to 2273.15 K at pressures to 50 MPa. There is also a separate equation for metastable steam at pressures up to 10 MPa.
The release also contains "backward" equations to allow calculations with certain common sets
of independent variables to be made without iteration; these equations may also be used to provide good
initial guesses for iterative solutions.
Since the release was first issued, it has been supplemented by several additional "backward" equations that are available for use if desired; these are for p(h,s) in Regions 1 and 2, T(p,h), v(p,h), T(p,s), v(p,s) in Region 3, p(h,s) in Region 3 with auxiliary equations for independent variables h and s, and v(p,T) in Region 3.
The development of the formulation is described in detail in a scientific article.
The Russian National Committee of IAPWS (through Moscow Power Engineering Institute) has provided facilities for online calculation, which may be useful in program development and verification. Note that IAPWS is not responsible for the content of these online calculation pages.
This Release is the product of the Working Groups "Thermophysical Properties of Water and Steam" (TPWS) and "Industrial Requirements and Solutions" (IRS) of the International Association for the Properties of Water and Steam (IAPWS).
This page updated May 29, 2018