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.•Method avoids trivial solutions in isochoric flash calculations.•Method uses properties and derivatives as usually available in computer implementations.•There is excellent agreement with results available in the literature.

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 system's 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.