Because of the great economic significance to the world power equipment industry of accurate, reliable, and internationally accepted formulations for the calculation of the thermodynamic properties of water and steam, the Subcommittee on Industrial Formulations of the International Association for the Properties of Water and Steam (IAPWS) has recognized the need for new formulations which are faster and more accurate than existing standards.
Existing standards consist of distinct formulations for industrial and scientific use. The former consists of a number of piece-wise-valid sub-formulations, each pertaining to a specific area on the pressure-temperature state plane and to a specific pair of independent variables. These subformulations are of moderate accuracy with respect to the laboratory data base and have been designed for high speed calculation of the properties frequently required in industrial power equipment design and analysis. The standard scientific formulation, in contrast, consists of a single canonical and continuous function of one pair of independent variables (density and temperature) valid for the entire state plane and nominally representing all experimental data within the experimental uncertainty. Because it has typically 2 or 3 times as many terms as each of the industrial sub-formulations, and because its use typically requires iterative calculations to satisfy the input variable pairs of greatest industrial interest, calculations using this kind of formulation will generally require an order of magnitude greater calculation time.
This paper is addressed to the question of whether or not, while retaining high speed and accuracy, and flexibility of access, future replacements of existing standard formulations for industrial and scientific use should be, as in the past, entirely distinct. It is argued that there are substantial advantages to be gained by closely integrating the development and use of these forthcoming kinds of formulations, in what may be termed a single integrated formulation.