A technique for preparing thermodynamic property tables using incomplete data sets

Extended corresponding states (ECS) algorithms provide versatile predictions for the thermophysical properties of mixtures. The NIST14 computer database implements an ECS model and the resultant property calculations are remarkably accurate for a wide variety of mixtures. This model emphasizes single phase calculations for many systems and properties, and it has the usual difficulties with the phase envelope and the critical region. Thermodynamic property tables are calculated most accurately when data are available throughout the ranges of the tables. Unfortunately, data are often not available over the entire ranges or in particularly important regions. We have observed that the deviations of the NIST14 model from PVT data for several mixtures have the same basic shape for each mixture. A single, interpolative function can adjust the model to fit compression factors for several systems within ±0.1%. Utilizing this function along with NIST14 forms a technique employing available experimental data to calculate accurately (1.0–3.5%) energies, enthalpies and entropies even in regions which lack experimental data or are near the critical point. This is not a correction for NIST14, but a method using NIST14 along with data to create accurate property tables in regions which lack data or which present difficulties for models.