Extensions to the approximation functions for the fast calculation of saturated water properties

The knowledge of accurate physical properties of water is fundamental for the analysis of thermalhydraulic systems and the design of a broad range of equipment in many diverse fields. Whilst formulations do exist for the accurate calculation of these properties they often prove too slow for many engineering and technological applications. The rapid generation of these properties without relinquishing accuracy has been the purpose of previous work. This paper presents extensions to the range of validity of the functions developed in the earlier work.The low pressure range for the saturation properties has been extended downward from approximately 0.08 MPa and 90°C. Also some modifications were made to allow all functions to have a consistent upper pressure limit of 21.5 MPa. This now gives a useful range from 0.002 MPa to 21.5 MPa and 18°C to 450°C.The accuracy of these functions has been evaluated by calculating the deviation from the latest internationally accepted formulations for the thermophysical properties of steam and water. Namely the International Association for the Properties of Water formulation for the Thermodynamic Properties of Ordinary Water Substance for Scientific and General Use, 1984.The deviations from these formulations are very small usually much less than 0.2 percent in the valid pressure and temperature range. Only near the critical pressure do these deviations exceed this but in no case does the deviation exceed 0.6 percent.