Continuum thermo-mechanical model for homogeneous liquid–gas flows with internal surface tension effects

This work presents a rational thermodynamic model which consistently incorporates internal surface tension effects in homogeneous and isothermal two-component two-phase flows, without appealing to additional kinematical variables to describe its microstructure. The liquid and gaseous phases are regarded as a pseudo-fluid whose constitutive behavior is obtained from two thermodynamic potentials—the Helmholtz free energy and a pseudo-potential of dissipation. The structure of the flow is assumed to be described solely by the void fraction, which is treated as an internal variable. The constraint associated with it is regarded as a material property, being an effective part of the constitutive equations. Surface tension is taken by the model into account by adding a suitable extra term, with dependence on the void fraction, in the Helmholtz free energy. The capability of the proposed model in properly describing pertinent physical phenomenon is demonstrated by comparing the analytical predictions of sound speeds in the medium with available experimental data.