This equation of state (BWRS) is a modification of the Benedict-Webb-Rubin equation of state which was first proposed in 1940. The original equation gave poor results at low temperatures and close to the critical point. Therefore the BWR equation was modified by Starling in 1973 to improve the accuracy for light hydrocarbons in cryogenic liquid, gas and dense fluid regions and also at high temperatures.
Eleven parameters are generalized as functions of component acentric factor, critical temperature and critical density. The mixing rules are analogous to those used for the original BWR equation. The single binary interaction parameter is built into the mixing rules. The equation can predict properties for light hydrocarbons very accurately when experimental data are used to tune the parameters.
The equation is generalized in terms of critical temperatures, critical densities and acentric factors and has difficulty predicting properties for heavy hydrocarbons and polar compounds. The equation does not satisfy the critical constraints and therefore is inferior to the SRK and PR equations when applied in the critical and supercritical regions.
The equation cannot be solved analytically and normally requires more computer time than the cubic equations of state.
In addition to K-values, the BWRS equation may be used to predict the enthalpies, entropies and densities for the liquid and vapor phases.
See "Benedict-Webb-Rubin-Starling" under "Equations of State" in Chapter 3, Volume 1, of the PRO/II Reference Manual for more information.
Application Guidelines
Light hydrocarbon systems at less than critical conditions.