Cross-co-volume interaction¶

This report studies the PR78 cross-co-volume parameter \(l_{12}\), which changes the repulsive mixing rule and therefore is not a volume translation. Only \(l_{12}\) is fitted on the estimation isobar; the constant-temperature isotherm is disjoint validation data.

Before and after fitting¶

Co-volume density curves before and after fitting

Co-volume density parity

Dashed curves and crosses identify the zero-interaction model; solid curves and open markers identify the fitted interaction. The transfer from the estimation isobar to the held-out isotherm is visible rather than represented only by a pooled score.

Validation residuals and sensitivity¶

Co-volume validation residuals

Co-volume parameter sensitivity

The residual plot exposes pressure and composition structure on the held-out isotherm. The sensitivity plot compares the estimation objective with validation error over a wider parameter interval. It does not establish that one constant transfers to other component families or equilibrium regimes.

Sources: Privat and Jaubert (2023); Pedersen, Christensen, and Shaikh (2024); and Segovia et al. (2017).