Helmholtz function-based global phase stability test and its link to the isothermal–isochoric flash problem

The global phase stability test is formulated based on the Helmholtz function. The corresponding phase stability function is minimized and, if the system is found to be unstable, the initial estimates for the properties of the incipient phase are such that the systemʹs Helmholtz function after its incipient partition is smaller than before the partition. This ensures trivial solutions are avoided in flash problems with specifications of temperature, volume, and component mole numbers. Also, there is no need for reformulation of the thermodynamic model as in procedures proposed earlier for similar purposes. The procedure succeeded in the stability analysis of several situations previously used as test cases in the literature.