Interpolation of gas-liquid multicomponent fluid properties for piping fluid flow analysis

Abstract

The article proposes the use of bicubic spline interpolation to optimize hydraulic and thermal calculations while processing thermodynamic library data. Research was carried out both in single-phase gas and liquid regions, as well as in the two-phase gas-liquid region. The accuracy of bicubic spline interpolation was tested for various thermodynamic libraries on multi-component mixtures. Various coordinate systems (P, x), (P, T), (P, H), (P, S) were tested, optimal coordinates and interpolation grids were selected based on the nature of changes in various thermophysical properties. Experiments were conducted in the range of up to 80% of critical pressure, since in the near-critical region the properties behavior changes sharply. Plots of properties and interpolation absolute and relative errors were also produced for a more detailed study and determination of problem areas where property functions undergo sharp changes that make interpolation difficult. The results obtained demonstrate an acceptable level of accuracy for engineering calculations in the approximation of data from thermodynamic libraries.