An analytical formulation of thermodynamic properties of dry and metastable steam suitable for computational fluid dynamics modelling of steam turbine flows

Abstract

Application of computational fluid dynamics to real steam flows including non-equilibrium condensing flows requires an accurate and, at the same time, computationally inexpensive formulation of thermodynamic properties of steam. The present formulation enables fast computation of all thermodynamic properties, using mass density and specific internal energy as independent variables. This choice of independent variables follows the needs of time-marching computational fluid dynamics computations of dry and metastable steam flows in steam turbines. The formulation comprises an ideal-gas part and a residual part. The residual part is expressed in a form analogous to the virial equation of state but the coefficients are functions of internal energy, rather than temperature. Here we present a variant retaining only one coefficient of the density series, corresponding to the second virial coefficient. The uncertainties of properties computed from the present formulation only slightly exceed those of the fundamental formulation IAPWS-95. The formulation is valid from 253.15 K to 1073.15 K. Up to pressures given by the isentrope 7.5 kJ/(kg K), the computed properties are within the experimental uncertainties. Beyond this limit, the accuracy continuously decreases as it can be determined from presented deviation plots.