Superancillary Equations for Nonpolar Pure Fluids Modeled with the PC-SAFT Equation of State

Superancillary equations are presented for the PC-SAFT equation of state of Gross and Sadowski for nonpolar pure fluids. The equations cover the range of a number of segments from 1 to 64. These equations, formed as nested sets of Chebyshev expansions, represent the densities for vapor-liquid equilibria better than can be achieved by iterative calculations in double precision arithmetic. Furthermore, the expressions are more than 16 times faster to evaluate than the iterative calculations from the fastest thermodynamic property library. By their construction, the superancillary equations are guaranteed to be reliable over the entire temperature range. For user-friendliness, the functions have been packaged into a Python package available on PYPI.

Automated summary

Superancillary equations have been developed for the PC-SAFT equation of state, which accurately represent densities for vapor-liquid equilibria of nonpolar pure fluids. These equations outperform iterative calculations in terms of accuracy and speed, and they are reliable over the entire temperature range. The functions have been made user-friendly by packaging them into a Python package available on PYPI.