Route B Liquid as Starting Phase

To overcome the difficulties with cp, process simulators usually offer the option to start with a reference state Keu(T reu) in the liquid phase. The enthalpy of the liquid phase is evaluated for each component by integration of the liquid heat capacity with respect to temperature  

Analogously to Eq. (6.60), the enthalpy of a liquid mixture can be evaluated by taking the excess enthalpy into account. Again, the liquid enthalpy refers to a saturated liquid, enthalpy changes due to further compression are neglected. 

For the calculation of a vapor enthalpy, the liquid heat capacity for each component is integrated from the reference temperature to a transition temperature trans which can be chosen arbitrarily. A good choice is the normal boiling point. 

Only at this transition temperature, the correlation for the enthalpy of vaporization is applied to calculate the enthalpy of saturated vapor at the transition temperature. Then, (h-h )i is subtracted to obtain the enthalpy of the ideal gas at transition temperature  

To move to the system temperature, the ideal gas heat capacity is integrated  

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Use Route B (liquid as starting phase), cp - can be taken from Appendix A. 

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