Three articles on the approximation functions for the properties of H2O have been published.
Note: the files on this page are password protected because of copyright restrictions. Individuals can contact me for further information.
Approximate Functions for the Fast Calculation of Light-Water Properties at Saturation by Wm. J. Garland and J. D. Hoskins,
International Journal of Multiphase Flow, Vol. 14, #3, pp 333-348, May-June/1988.(pdf 558kb) [password protected]
ABSTRACT: For thermalhydraulic systems analysis, linear interpolation algorithms are commonly used for the calculation of thermodynamic properties. However, these algorithms can use a substantial amount of computer time and memory. An alternative to this approach suggested in the past is the use of approximation formulas. Such formulas for the calculation of the thermodynamic properties of light water for saturation conditions are presented here, based on the 1984 NBS/NRC Steam Tables. The range of these approximations is from below 1b to just below the critical point (22.055 MPa) with a deviation from tabulated values of not more than 0.22%. The formulas were determined by the method of least squares, enabling a minimization of deviations from the line of best fit and the fitting of functions simple enough to be used with programmable calculators, as well as microcomputers. In addition to the rapid calculation of the properties, the simple curve fits are instrumental in the development of the rate form of the equation of state.
Since any given property cannot be accurately fitted over the entire pressure range with a single simple expression, the pressure range was split into subranges. Special care was taken to ensure that the slopes of the curve fits were continuous across the boundaries since discontinuities in the slopes of the property tables can cause instabilities and failure of search algorithms in typical computer codes.
Simple Functions for the Fast Approximation of Light-Water Thermodynamic Properties
by W. J. Garland and B. J. Hand,
Nuclear Engineering and Design, Vol 113, pp 21-34, 1989.
(pdf 542kb)[password protected]
ABSTRACT: Thermalhydraulic systems analysis and simulation requires the fast and accurate generation of light water thermodynamic properties. An approach suggested in the past is the use of simple, non-linear functions to give approximations to the properties. Such functions have been developed and are presented here. The range of use is from 0.085 MPa to 21.3 MPa, and is usually much less than 1%. This error is based on comparisons to the latest internationally accepted formulation for the thermophysical properties of steam and water. These simple analytic functions provide an alternative to the use of linear interpolation algorithms and complex transcendental equations to generate light water thermodynamic properties. They are well suited to be made into computer sub programs, yet they are simple enough to be used with programmable calculators.
Extensions to the Approximation Functions for the Fast Calculation of Saturated Water Properties by Wm. J. Garland, R. J. Wilson, J. Bartak, J. Cizek, M. Stastny and I. Zentrich,
Nuclear Engineering and Design, # 136, pp 381-388, 1992. (pdf 354kb)[password protected]
ABSTRACT: 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 90C. 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 18C to 450C.
The accuracy of these functions has been evaluated by calculating the deviations from the latest internationally accepted formulations fro 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.