Lehrstuhl fur Thermodynamik, Ruhr-Universita¨t Bochum, D-44780 Bochum, Germany
In 1995, the International Association for the Properties of Water and Steam ~IAPWS!
adopted a new formulation called ‘‘The IAPWS Formulation 1995 for the Thermodynamic
Properties of Ordinary Water Substance for General and Scientific Use’’, which we
abbreviate to IAPWS-95 formulation or IAPWS-95 for short. This IAPWS-95 formulation
replaces the previous formulation adopted in 1984. This work provides information
on the selected experimental data of the thermodynamic properties of water used to
develop the new formulation, but information is also given on newer data. The article
presents all details of the IAPWS-95 formulation, which is in the form of a fundamental
equation explicit in the Helmholtz free energy. The function for the residual part of the
Helmholtz free energy was fitted to selected data for the following properties: ~a! thermal
properties of the single-phase region (prT) and of the vapor–liquid phase boundary
(psr 8r 9T), including the phase-equilibrium condition ~Maxwell criterion!, and ~b! the
caloric properties specific isochoric heat capacity, specific isobaric heat capacity, speed of
sound, differences in the specific enthalpy and in the specific internal energy, Joule–
Thomson coefficient, and isothermal throttling coefficient. By applying modern strategies
for optimizing the functional form of the equation of state and for the simultaneous
nonlinear fitting to the data of all mentioned properties, the resulting IAPWS-95 formulation
covers a validity range for temperatures from the melting line ~lowest temperature
251.2 K at 209.9 MPa! to 1273 K and pressures up to 1000 MPa. In this entire range of
validity, IAPWS-95 represents even the most accurate data to within their experimental
uncertainty. In the most important part of the liquid region, the estimated uncertainty of
IAPWS-95 ranges from 60.001% to 60.02% in density, 60.03% to 60.2% in speed of
sound, and 60.1% in isobaric heat capacity. In the liquid region at ambient pressure,
IAPWS-95 is extremely accurate in density ~uncertainty <60.0001%! and in speed of
sound ~60.005%!.
Полный текст работы в формате .PDF
W. Wagnera, A. Pruß
The IAPWS Formulation 1995 for the Thermodynamic Properties of Ordinary Water Substance for General and Scientific Use
