How do you select the appropriate thermodynamic model in a process simulator?

Selection guidelines: Light hydrocarbons/gases: use equation of state (PR, SRK). Polar/non-ideal liquids at low pressure: activity coefficient models (NRTL, UNIQUAC). High-pressure polar: combine activity coefficient with EOS (e.g., PSRK). Aqueous electrolytes: electrolyte-NRTL. Polymers: polymer-NRTL or PC-SAFT. Steam/water: specialized steam tables (NBS, IAPWS). Consider: component types, pressure range, presence of electrolytes, available data for parameter fitting. Validate against experimental data for key separations. Most simulators provide selection wizards based on system type.