An Analysis of IAPWS-IF97 Formulae-based Model for Calculating Water and Steam Thermodynamic Properties and Its Algorithm Design

By adopting an object-oriented method, implemented was the latest industrial formulae-based IAPWS-IF97 (2007.8 Revision) for calculating water and steam thermodynamic properties. The calculation models for various zones were analyzed in detail with their corresponding implementation algorithms being designed. The basic equations, derivative equations, calculation formulae in various attributes and reversely derived equations for all the zones were implemented. The supplementary equation, B23 equation and B2bc equation for the metastable steam regions in two zones were also executed. The authors have presented the regional differentiated algorithm, sub-regional differentiated algorithm in two zones and Newton iterative algorithm in three zones to determine the density ρ from pressure P and temperature T. They have also described in detail the latest IAPWS-IF97 implementation method, matters meriting attention and relevant derivative processes, and supplemented the verification values of the computer program for specific heat capacity of equicapacitance cv, thus enhancing the consistency of B23 with boundary Ts(P) as well as that of B2bc with boundary Ps(T). The application of the above in the paper-making industry indicates that the implemented method enjoys such a variety of merits as comprehensiveness, accuracy, speedy and automatic testing etc.