Efficient and accurate computation scheme of p-T thermodynamic properties of water and steam

IAPWS-IF97 is widely applied to computations of thermodynamic property for water and steam; however, the proposed computation algorithm is not high efficient enough to complicated applications such as heat cycles optimization and as database for computational fluid dynamics software. This paper proposed a rapid and accurate computation scheme based on double-grid, bi-quadratic spline interpolation scheme for calculating thermodynamic properties of water and stream on p-T thermodynamic surface. The computational region proposed is valid at 273.16-1073.15K and 0.001-100MPa, covering IAPWS-IF97 regions 1-4. To resolve the discontinuity problem for thermodynamic properties and their derivatives in the vicinity of the saturated line and in the critical region, the division of computational region is divided in to thirty-two sub-regions with adopted equidistant grids in each sub-region. A boundary normalization approach is proposed to convert the sub-regions with saturated line or pseudo-critical temperature curve as boundary into rectangular computational region. Then the spline functions g^SPL(p,T), ρ^SPL(p,T), s^SPL(p,T) and h^SPL(p,T) are determined based on data by IAPWS-95 formulation. All tested results revealed superior performance in both computation speed (10.8-642 times faster) and prediction consistency (1-2 orders better) for the present interpretation scheme than the IAPWS-IF97. © 2012 Taiwan Institute of Chemical Engineers.