REQUIRED ACCURACIES OF THE INVERSE EQUATIONS, T(h,P) AND T(s,P) FOR SUPERHEATED STEAM, DETERMINED BY POWER CYCLE CALCULATIONS

The accuracies required for computations of the inverse equations for steam properties in industrial use, such as T = T(h,P) and T = T(s,P) were assessed. The effects of the accuracies on the calculated plant performance were tested using the power cycle calculation program·s used by turbine and boiler manufacturers. The steam conditions of tested cycles ranged from those for conventional power plants to those for future power plants with very high pressure (41 MPa) and temperature (650 °C). The program for cycle calculations was modified to intentionally return temperature value with numerical errors. The deviations in calculated plant performance due to such errors varied linearly with the magnitude of the errors. The deviations in the turbine calculations were significantly larger than those in the boiler calculations. Sensitivity of the calculated performance to numerical errors is code dependent. Using the manufacturers' practice for performance calculations as a guide, the accuracy required for the computations of the inverse equations was estimated to be better than 11 or 18 mK, which should be considered in the development of new industrial formulations for steam properties currently being developed by IAPWS. In addition, the effects of errors of Tsat(Psat) on power cycle calculations were found to be much smaller than those of T(h,P) and T(s,P).