Physical Chemistry of Aqueous Systems: Meeting the Needs of Industry

ISBN Print: 978-1-56700-034-4

ISBN Online: 978-1-56700-445-8

A NEW EQUATION OF STATE FOR WATER AS A CANDIDATE FOR THE NEW SCIENTIFIC FORMULATION OF IAPWS

DOI: 10.1615/ICPWS-1994.100
pages 66-77

Abstrakt

As a candidate for the new scientific formulation for H2O a new fundamental equation in the form of the Helmholtz energy has been developed. In comparison with the current scientific formulation of IAPWS, the IAPS-84 Formulation, the new equation of state avoids its deficiencies, meets additional requirements which have arisen meanwhile and corresponds to the ITS-90 temperature scale. The new 56-coefficient fundamental equation is valid in the entire fluid region covered by the selected data set (11 different thermodynamic properties), namely from the melting line (lowest temperature 251.2 K) to 1273 K at pressures up to about 1000 MPa. Due to the incorporation of special "nonanalytic" terms, the new equation is also able to represent the caloric properties in the immediate vicinity ·of the critical point without using any switching and transformation procedure. Moreover, the equation represents all experimental data available for the metastable regions, yields a reasonable course of the derivatives in the very accurately measured low-temperature liquid region, and shows a very good extrapolation behaviour up to very high pressures and temperatures.